What's the Hottest Place In the Universe?
Astrum Extra
0:00 In 2013, scientists attempted to recreate the evolution
0:04 of the universe from shortly after the Big Bang until today.
0:09 This simulation, which took 19 million CPU hours to produce,
0:14 started with a predicted amount of matter,
0:16 dark matter, and dark energy that should
0:19 have existed shortly after the Big Bang.
0:21 The simulation was allowed to run to see if these parameters that were set
0:25 at the beginning can produce the galaxies
0:27 and the universe's structure we see today.
0:34 What you are looking at here is limited
0:36 to a 32 million lightyear cube of the simulation.
0:41 The expansion of the universe is considered
0:44 with simply gas density and temperature visible.
0:49 This is the intergalactic medium.
0:53 Even though space is a vacuum,
0:55 there are still a few particles in every cubic cm of space.
1:00 Blues are the coldest regions here.
1:02 Whites are the hottest.
1:04 As gas particles are drawn together
1:06 by their own gravity and that of dark matter,
1:09 the gas clumps and over the course of millions of years coaleses into galaxies,
1:14 which increases the gas's temperature drastically.
1:17 What you'll immediately notice is that there appear
1:20 to be explosions coming from the densest clumps.
1:23 But galaxies exploding, that can't be right.
1:26 I surely would have heard of that before.
1:29 But remember, this is the intergalactic gas temperature we are seeing.
1:33 And each second passing in the video is a few million realtime years.
1:41 Quazars or extremely active black holes
1:44 are the brightest objects in the universe,
1:46 emitting more electromagnetic radiation than entire galaxies combined.
1:52 When a quazar lights up, its rapid increase in radiation blasts into space,
1:58 ionizing the intergalactic gas as it expands out,
2:01 heating it up to extreme temperatures.
2:04 This is known as quazar mode or active galactic nuclei feedback.
2:10 Black holes don't remain as quazars for lengthy periods of time.
2:13 Rather, quaazars are the result of a large amount of mass falling into them,
2:18 lighting them up and causing them to eject huge amounts of mass and energy.
2:23 They'll remain as quaazars as long as there is matter being fed into them.
2:28 Although you may wonder, how can a black hole emit anything?
2:32 Don't they absorb it all?
2:34 And the answer is yes.
2:36 It is in fact the accretion disc around
2:39 the quazar that is so energetic and luminous.
2:42 A black holes accretion disc is the result of matter
2:44 passing by being ripped apart and sucked into orbit.
2:49 These super massive black holes often have billions of solar masses.
2:54 The gravity around them is immense.
2:56 As the material in the accretion disc orbits and falls inwards,
3:00 the friction from the material in the disc rubbing together creates energy so
3:05 intense that a quazar can be thousands of times brighter than our Milky Way.
3:11 In fact, a quazar's host galaxy is often
3:14 too dim to detect next to the bright quazar.
3:17 Although techniques with the Hubble Space Telescope have allowed
3:21 a few of these host galaxies to be seen, too.
3:25 quazars could light up from collisions of galaxies when suddenly
3:30 an abundance of matter falls into the super massive black hole.
3:33 Although this doesn't always happen.
3:51 You'll also notice these jets coming from the quazar's poles.
3:55 These extend well beyond the galactic disc and can be
3:58 seen illuminating other galaxies and dust clouds like a spotlight.
4:04 Quaazars themselves are bright, but when these jets are pointed towards us,
4:08 they are known as blazars.
4:11 The jets are believed to be powered
4:12 by the black hole's magnetic structure and they
4:15 can carry high energy plasma away from the black
4:18 hole at almost the speed of light.
4:22 The days of quaazars and blazars are thought to be over.
4:26 The closest quaazar to us is 600 million lighty years
4:29 away and thus was going on 600 million years ago.
4:34 However, you'll notice that the explosions in the simulation
4:37 don't let up in this video as time passes.
4:40 This comes from the last in the active
4:42 galactic nuclei family of black holes, radio galaxies.
4:47 Typical quaazars and blazars are so bright that they
4:50 light up in all frequencies of the electromagnetic spectrum uniformly.
4:55 Radio galaxies originate from black holes
4:58 that unsurprisingly are brighter in radio wavelengths.
5:02 These explosions now come from radio galaxies
5:05 and this is known as radio mode feedback.
5:10 The simulation stops at the present day.
5:16 Now, while impressive, the simulation isn't perfect.
5:19 For instance, it could only simulate a trillion particles compared
5:23 to the countless number of particles in the equivalent section of space.
5:28 Also, we don't have a perfect knowledge of the perimeters of the universe.
5:32 And so, there were certain mistakes evident
5:34 in the model like the overprediction of star formation.
5:38 There are plans to try this again at some point with an updated understanding.
5:43 Being able to model how the universe evolved can
5:46 give us a confirmation about how we believe it formed.
5:49 And this is of great interest to scientists.
5:52 Let's see what future results will bring.
5:56 So, can galaxies explode?
5:58 Not in the conventional sense, but if you are talking about
6:02 exploding with electromagnetic radiation, then absolutely.
6:09 In October 2022, a brilliant flash pierced the cosmos,
6:15 brighter and more intense than anything human civilization had ever seen.
6:21 And that's not an exaggeration.
6:23 The strength of the blast blinded our gammaray
6:26 detectors the world over and unleashed more energy
6:29 in a matter of seconds than our sun
6:31 will emit over its entire 9 billionyear lifespan.
6:36 Over the 18 months that followed,
6:37 it became the most widely studied gammaray burst in history.
6:42 Creatively dubbed the boat for the brightest of all time.
6:47 As researchers began to decipher its cause,
6:50 their findings unraveled one mystery after another.
6:54 Scientists have been cataloging gammaray burst for decades.
6:57 But this one was closer, brighter,
7:00 and unexplainably devoid of some key signatures you'd expect to see.
7:05 It also raises some farreaching questions about our standard model,
7:10 the possibility of a dark matter particle,
7:13 and how heavy elements like gold are made.
7:17 I'm Alex Mccoan, and you're watching Astramm.
7:20 Join me today as we dive into the mystery
7:23 of the biggest and brightest gammaray burst of all time.
7:27 What caused such a colossal explosion?
7:30 How is it different from other gammaray bursts before it?
7:34 And what can it teach us about our understanding
7:37 of the universe and the particles that constitute it?
7:42 Gammaray bursts are brief intense flashes of high
7:46 energy gamma radiation lasting from milliseconds to several minutes.
7:51 The first of its kind was detected in 1967 when American satellites designed
7:56 for detecting covert Soviet nuclear testing picked
8:00 up an unusual pattern of electromagnetic energy.
8:04 Since then, gammaray bursts have been of tremendous
8:07 interest to the cosmological community as they
8:10 allow scientists to study states of matter
8:12 and physics that are not reproducible on Earth.
8:15 Essentially, they provide researchers with a glimpse of how stars
8:20 are formed and evolve across the whole timeline of the universe.
8:25 There are two different kinds of gammaray bursts.
8:28 Short gammaray bursts last less than 2
8:30 seconds and are attributed to either the collision
8:33 of two neutron stars or the merger of a neutron star and a black hole.
8:38 They can be followed by a kilon nova, an emission of bright light resulting
8:43 from the radioactive decay of chemical elements.
8:46 This decay creates even heavier elements,
8:49 an important feature of nove which we'll discuss more later.
8:53 Anything lasting longer than 2 seconds is classed as a long gammaray burst.
8:59 These are thought to be caused by the explosive
9:01 deaths of massive stars and their subsequent supernova.
9:06 The collapsed core may form either a neutron star or a black hole.
9:11 These typically occur close to the edges
9:13 of the observable universe because they are
9:15 characteristic of low metalicity stars which formed
9:19 when there were less heavy elements around.
9:22 When we see one of these, we are witnessing events from billions of years ago.
9:27 In the case of both long and short gammaray bursts,
9:30 the newly formed black hole blasts out jets in opposing directions,
9:35 containing particles accelerated close to the speed of light.
9:39 When these particles interact with surrounding matter,
9:42 they emit the gamma rays we detect.
9:45 So, what made the boat so special?
9:49 Let's start by analyzing some of its key characteristics.
9:53 Firstly, the boat lasted 10 whole minutes
9:57 and was detectable for 10 hours after the fact.
10:00 It occurred in the Sajitta constellation only 2 billion lighty years away,
10:05 which is much closer than other gammaray bursts we've detected until now.
10:10 In fact, such a bright explosion [music] so close
10:12 to Earth is thought to be a 1 in 10,000year event.
10:17 Meaning the last time one happened, humans had barely started farming.
10:22 As is the case with other long gammaray bursts,
10:25 we know a collapsing and exploding star was behind it.
10:29 But this is where things start to get fuzzy.
10:33 A supernova alone isn't enough to explain
10:36 the magnitude of the gamma rays emitted.
10:39 The boat was a whopping 70 times
10:42 stronger than any other gammaray burst detected.
10:46 Initially, the theory was that this must be the supernova
10:49 of a ginormous star the likes of which we rarely see.
10:53 However, upon closer inspection of the afterglow,
10:56 scientists found that the supernova behind the boat was shockingly ordinary.
11:01 To get a clearer picture,
11:03 astronomers pointed the James Web Space Telescope in the boat's direction.
11:07 Web's near infrared spectrograph revealed that the supernova
11:11 behind the boat was actually pretty average.
11:14 It wasn't nearly as bright as you'd
11:16 expect given the gammaray burst that accompanied it.
11:20 So what could have caused such a flash?
11:24 One idea [music] is that we simply perceive the flash is
11:27 bigger and brighter because of Earth's relative position to the blast.
11:32 Imagine a flashlight shining in the dark, diffused and soft.
11:37 It lights the path 1 to 2 m ahead of you.
11:39 Now imagine [music] capturing all that light
11:42 and focusing it into a singular laser beam.
11:46 It wouldn't illuminate the path as widely,
11:48 but it would reach hundreds of meters into the distance.
11:51 And if Earth was in the direct path of that laser,
11:55 it would register a super bright reading.
11:58 That doesn't mean the laser released more energy than the flashlight.
12:01 It just means the way it was concentrated
12:04 and then detected resulted in a higher reading.
12:08 The same concept can be applied to these gamma ray bursts.
12:11 If a massive star is spinning super fast when it collapses,
12:15 then the shape and structure of the near lighteed jets
12:18 it emits will be more narrow and focused and therefore brighter.
12:23 In fact, the jets seen from the boat are some of the narrowest we've ever seen.
12:29 But not only were these particle jets brighter than expected,
12:33 scientists also detected way more of them going faster than expected,
12:39 they traveled with such fervor that after 2 billion years traversing the cosmos,
12:44 they arrived here and momentarily disrupted the Earth's atmosphere.
12:49 Sitting just 50 to 1,000 km above the surface of our planet,
12:54 Earth's ionosphere is rich in electrically charged particles.
12:58 When the boat struck, it left a mark comparable to that of a major solar flare,
13:04 pushing the ionosphere down into lower altitudes.
13:08 If photons from an explosion 2 billion light-years away
13:11 can have this kind of effect on our planet,
13:14 I don't really want to think about what
13:16 happens if something like that in our neighborhood explodes.
13:20 The large high alitude air shower observatory in Dawen County,
13:24 China managed to capture data on tens of thousands of photons
13:29 over the course of the initial blast and into the afterglow.
13:33 This is a quantity unlike anything seen before in gammaray astronomy.
13:37 In fact, it's so far out of pocket that some astrophysicists
13:41 think that they might be pointing towards something missing from our models.
13:46 According to our current understanding,
13:49 it's very unlikely these super high energy
13:51 photons are traveling for 2 billion years.
13:54 Cosmic microwave background radiation, interactions with intergalactic dust,
13:59 or red shifting caused by the expansion of the universe
14:02 are all factors that can interfere with a photon's trajectory.
14:06 One hypothesis put forward is that photons
14:09 convert themselves into a hypothetical particle called
14:13 an axion and then convert back into gamma
14:16 rays upon reaching our galaxy's magnetic field.
14:20 Axons are thought to be an ultra light particle responsible for dark matter.
14:25 Their existence is currently purely hypothetical.
14:29 We have no evidence for them.
14:31 And even if we did, they would
14:32 lie outside the standard model of particle physics.
14:36 We don't have time to delve into detail in today's video,
14:39 but let me know if you'd enjoy a separate video on this in the comments.
14:43 Okay, so far we've established that boat was caused
14:47 by a massive star collapsing and turning into a black hole,
14:51 which incidentally is known as a collapsar.
14:55 Aside from generating a long gammaray burst,
14:58 collapsars are also known for generating something else.
15:02 Gold.
15:04 Wait, wait.
15:05 How is gold connected to gamma rays?
15:08 Good question.
15:09 To understand that, let's take a minute to discuss how elements are made.
15:15 [music] The core of a star is a super high pressure environment,
15:19 some 200 billion times higher than the atmospheric pressure on Earth.
15:24 In these conditions,
15:25 nuclear fusion reactions create heavier elements out of lighter ones.
15:30 For example, one helium atom comes from fusing four hydrogen atoms together.
15:35 Elements 2 through 26 on the periodic table, that's helium to iron,
15:41 are made this way, process known as stellar nucleioynthesis.
15:46 However, once you get to iron, it isn't energetically favorable to continue
15:51 making bigger and bigger elements this way.
15:54 So, how do we account for the rest of the periodic table?
15:58 Where do these heavier elements like gold come from?
16:01 At the moment, we know two different ways these elements are formed.
16:06 The first was recently confirmed by the James Webb Space Telescope.
16:10 When two ultra dense neutron stars collide,
16:13 they emit an immense amount of neutron particles.
16:16 Surrounding material captures these neutrons,
16:19 making their atoms temporarily unstable.
16:22 In order to stabilize, the neutrons undergo radioactive decay into protons,
16:27 creating new, heavier elements.
16:30 This process is known as rapid neutron capture or R processed nucleiosynthesis.
16:36 Some calculations suggest one neutron star collision can produce
16:40 up to three Earth masses worth of heavy elements.
16:44 However, this explanation alone isn't sufficient to account
16:48 for all the heavy elements in the universe.
16:50 Neutron star collisions are rare and take a long
16:54 time to happen in the order of billions of years.
16:57 On top of that, observations of very old
17:00 stars show that heavy elements were already present
17:03 in parts of the universe well before most binary
17:06 neutron stars would have had a chance to collide.
17:10 So, how do you explain that?
17:12 There must be another source of heavy elements in the cosmos.
17:17 Which brings us back to our boat.
17:21 There's another theory that collaps like the boat
17:24 could be another source of our process nucleiosynthesis.
17:29 In their dying stages, massive stars like the one that caused
17:32 the boat are surrounded by layers of exploding gas.
17:36 These explosions leave discs of matter
17:38 swirling around the resulting infant black hole.
17:41 As the black hole begins devouring the surrounding material,
17:45 it can only ingest so much at a time.
17:48 What it cannot manage is swept away in a neutron dense wind.
17:53 Here the same R process nucleiosynthesis
17:56 occurs forming heavier elements like gold, silver and platinum.
18:01 This seems promising but unfortunately even
18:05 factoring in these kinds of supernova
18:08 isn't enough to account for the abundance of gold in the universe.
18:12 To make matters worse,
18:14 analysis of the boat spectrum didn't show any traces of heavy elements,
18:19 raising questions about the validity of this collapsar gold making theory.
18:24 Some scientists suggest the boat's host galaxy might have something
18:28 to do with the lack of heavy elements in the explosion.
18:31 Upon modeling the host galaxy spectrum,
18:34 researchers discovered it has the lowest metallicity of all
18:39 previous host galaxies where gammaray bursts were detected.
18:42 In other words, maybe the environment didn't have
18:45 the right building blocks to make heavier elements.
18:49 How do we know how much gold should be out there in the first place?
18:53 How does scientists predict something like
18:54 the relative abundance of elements in the universe?
18:59 There are two main methods of calculating this.
19:01 The spectroscopy of stellar photospheres and meteorite analysis.
19:06 By analyzing the absorption lines in the spectra of stars,
19:10 astronomers can determine the relative abundances
19:12 of elements in the photosphere of those stars.
19:16 The composition of meteorites, remnants of an early solar system,
19:20 are analyzed in parallel to determine the relative abundances of elements.
19:24 Meteorites are especially useful for measuring
19:27 the abundances of volatile elements like hydrogen,
19:30 helium, and noble gases that are unrepresented in stellar photospheres.
19:36 The results of both of these methods are usually congruent,
19:39 indicating we're probably doing something right.
19:42 But this is physics, so of course nothing is so cut and dry.
19:47 One famous exception to this rule is lithium.
19:50 According to the standard big bang nucleiosynthesis theory,
19:54 the early universe should have produced about three
19:56 times more lithium 7 than is currently observed.
20:00 The plot thickens when we consider its isotope, lithium 6,
20:04 where we observe 1,000 times more than our predictions can account for.
20:10 This discrepancy is known as the lithium problem and remains unsolved,
20:15 presenting a significant challenge to the standard cosmological model.
20:19 It highlights the importance of understanding the processes
20:22 that shape the relative abundances of elements
20:24 in the universe and suggests that our current
20:27 understanding of nucleiosynthesis might be incomplete.
20:32 Just because boat didn't yield gold as expected doesn't mean we should discard
20:37 these kinds of extreme gammaray bursts
20:39 as places where heavy elements could be made.
20:42 Observations of nearby stars have provided strong evidence for an early
20:46 R process that enriched the universe with heavy elements.
20:50 But the boat findings cannot be ignored as they suggest there may
20:54 be alternative currently unknown processes responsible
20:58 for this elemental enrichment of our cosmos.
21:01 The results may call into question our entire model of understanding
21:05 regarding collab stars and their role in creating heavy elements.
21:09 This discovery is much bigger than just the boat or gamma rays.
21:14 It's about the literal building blocks of our universe as we know it.
21:19 Where do our different atoms come from?
21:22 And why do they exist in the proportions they do?
21:25 How much of our model is accurate?
21:27 And how much is missing?
21:30 What role does dark matter play in all of this?
21:33 We need more time and research before we know for sure.
21:37 But the boat is a great example of how
21:39 new findings keep our understanding of physics ever evolving,
21:44 just like the universe itself.
21:47 Imagine standing on a quiet hill watching the sky burst
21:51 into a symphony of colors as the sun peaks above the horizon.
21:55 [music] It's a daily spectacle that many of us take for granted.
21:59 The warm hues of orange, red, and pink splashing across the sky.
22:05 Yet, this beautiful sunrise is only
22:08 the final chapter in the light's long journey.
22:11 If we trace the path of these photons from their end point
22:15 in the retina at the back of your eye through the Earth's
22:18 atmosphere across the 150 million km void separating our planet from its
22:24 host star and finally through the varied and tumultuous layers of that star.
22:30 We discover the source of the warmth
22:32 on your face and the colors painted across the sky.
22:36 The sun's core, a nuclear engine that has
22:39 been raging for 4 and a half billion years.
22:43 Born in a cosmic nursery from the remnants of ancient stars,
22:47 the glowing sphere of searing plasma that dominates our sky is
22:51 the product of complex forces that have played out over millennia.
22:56 So, [music] let's take a journey back in time, tracing the origins of the sun,
23:02 exploring its intricate layers,
23:04 and mapping the elements that make up its very structure.
23:08 I'm Alex Mccoan, and you're watching Astramm.
23:11 Join me as we dive into the [music] depths of our sun
23:15 and learn what secrets lie behind the blinding curtain of light and time.
23:20 [music] To understand how the sun formed, we must go back to before our solar
23:28 system even existed about 4.6 billion years ago.
23:34 At that time, in a relatively quiet region of the Milky Way galaxy,
23:38 a massive cloud of gas and dust known
23:41 as a giant molecular cloud drifted silently through space.
23:46 This was no ordinary cloud.
23:49 It was immense, possibly spanning hundreds of light years
23:53 across with a mass equivalent to millions of suns.
23:57 Within this cloud lay the scattered remnants of ancient stars
24:01 that had long since exhausted their nuclear fuel and exploded as supernova,
24:06 casting their enriched contents into the cosmos.
24:10 This stellar debris included a mix of elements such as hydrogen and helium,
24:15 the building blocks of stars along with heavier elements like carbon,
24:19 oxygen, nitrogen, and iron.
24:23 The presence of these elements made this molecular cloud
24:26 fertile ground for forming new stars and planetary systems.
24:31 However, such a massive cloud requires a trigger
24:34 to initiate the cascading collapse that results in stellar birth.
24:38 Scientists believe that this trigger could have been a shock wave
24:41 from a nearby supernova explosion that compressed parts of the cloud,
24:45 causing it to fragment and collapse into regions of higher density.
24:49 This collapse marked the beginning of the pre-olar nebula,
24:53 the dense region within the molecular cloud
24:55 that would eventually give birth to our solar system.
24:59 Some scientists have even proposed a name
25:01 for this hypothetical exploding star Kati Quay.
25:06 Named after the Aztec goddess of Earth and fertility,
25:10 Kati Quay symbolizes the death and rebirth cycle where in this case
25:15 the death of one star conceded the formation of new ones.
25:20 As the gravitational collapse of the giant molecular cloud progressed,
25:24 it did not result in a single massive object,
25:27 but rather fragmented into multiple dense clumps.
25:31 This fragmentation occurs due to a phenomenon known as genes instability,
25:35 named after the British physicist Sir James Jeans.
25:39 The genes length is a critical distance within a cloud at which the forces
25:43 of gravity are balanced with the natural internal
25:46 gas pressure that keeps the cloud propped up.
25:49 When a defined section of the cloud exceeds the gene's length,
25:52 it will collapse in [music] on itself.
25:55 Different regions within the molecular cloud exceed this gene's length
25:58 at different times due to variations in density and temperature.
26:02 As these regions become gravitationally unstable,
26:06 they collapse independently to form multiple protostellar
26:10 cores as opposed to one single massive body.
26:14 The protostellar core was the earliest phase
26:17 in our sun's life that was recognizably star-like,
26:20 crunching itself into a tighter and tighter sphere
26:24 by the ever clenching fist of its own gravity.
26:27 The core is surrounded by infalling gas and dust.
26:30 As more material accumulates, the core becomes denser and hotter,
26:35 setting the stage for the next phase of star formation, the protoar.
26:40 [music] Once a protostellar core becomes sufficiently dense and hot,
26:45 it evolves into a protoar.
26:47 The central region has heated up to the point that it begins
26:50 to emit light and heat from the energy released by gravitational contraction.
26:55 But its core has yet to reach the temperatures
26:58 required to ignite nuclear fusion in the core.
27:00 As the protoar continues to accumulate material and grow in mass,
27:04 the pressure and temperature in its core increase dramatically.
27:08 Our sun developed through this embryionic state of contraction and heating
27:12 for millions of years before eventually building up its core temperature
27:17 to about 10 million° C at which point hydrogen nuclei began
27:22 to fuse into helium and with that the sun was born.
27:28 At this stage the innate angular momentum of the surrounding
27:32 material that shrouds the infant star generates rotation.
27:36 A cloud of this size will always have some slight rotation.
27:39 Nothing in the universe is still.
27:42 And conservation of angular momentum dictates that the cloud must
27:46 spin faster and faster as it crunches down into tighter space,
27:51 similar to how a spinning figure skater speeds up as they tuck in their arms.
27:55 [music] Around the equator of rotation,
28:01 some of the material is moving fast enough to stay in orbit.
28:05 But higher up and lower down,
28:07 the momentum is insufficient to resist [music] the protostar's
28:10 ravenous pull and falls helplessly into its jaws.
28:14 And so the cloud flattens [music] out into a disc, a protolanetary disc.
28:20 This disc is a cosmic lottery.
28:23 As it cools and coaleses, planets, moons, asteroids,
28:28 and comets will be relentlessly created and destroyed.
28:32 Some material will be robbed of its momentum and tumble into the sun,
28:36 while neighboring matter will go on to become part
28:39 of the many bodies that make up our solar system today.
28:44 With its new ability to fuse hydrogen atoms into helium,
28:48 the sun could finally generate energy to push back against
28:51 the forces of gravity that sought to squeeze it further.
28:55 The energy streaming out of the fusion reactions created an outward
28:59 radiation pressure that balanced the inward gravitational pull of the gas,
29:03 allowing the young star to achieve
29:05 a stable state known as hydrostatic equilibrium.
29:09 In this state, the star no longer contracts under its own gravity
29:13 and it enters a stable phase of its life known as the main sequence.
29:18 This balancing act between internal pressure
29:21 pushing outward and gravity crushing in is
29:24 the axis that defines every stage of the sun and all stars lives.
29:30 We saw it during the initial collapse and here as it settles into a stable
29:35 main sequence star and it will be
29:37 the pendulum that eventually swings towards its dramatic death.
29:41 For now, let's unpick the process of nuclear
29:44 fusion and how it's capable of keeping
29:46 an object as massive as the sun stable and steady for billions of years.
29:53 To understand how nuclear fusion occurs in the sun,
29:56 we need to examine extreme conditions present within its core.
30:00 Today, temperatures reach around 15 million° and pressures more
30:06 than 250 billion times that of the Earth's atmosphere.
30:11 In this blazing cauldron, hydrogen atoms are stripped of their electrons,
30:16 forming a plasma composed of free protons and electrons.
30:21 Under such intense conditions, these protons,
30:24 normally repelled by their shared positive electric charges,
30:28 are forced into extremely close proximity.
30:32 The force that usually keeps them apart is the coolum force,
30:35 an electrostatic repulsion between positively charged particles.
30:39 It's exactly the same force that resists as you try
30:42 to push the same ends of a bar magnet together.
30:45 Overcoming this force is the primary challenge for nuclear fusion to occur.
30:51 Despite the extreme kinetic energy of protons in the sun's core,
30:55 most collisions are still not energetic enough to overcome the coolum barrier.
31:00 Under normal conditions, protons need immense energy to get close enough
31:04 for the strong nuclear force to bind them together.
31:07 This barrier is so significant that physicists around the early
31:11 1920s using a classical understanding of how particles interact
31:15 with each other determined that fusion should not occur
31:18 at the temperatures and pressures found in the sun's core.
31:22 To solve the puzzle, we needed a scientific model that has come to explain
31:26 many of the seemingly impossible phenomena we observe in the universe.
31:30 Quantum mechanics.
31:35 The quantum mechanics revolution of the 1920s introduced the concept
31:39 of particles behaving both as particles and as waves.
31:44 One of these phenomena is quantum tunneling
31:47 where particles have a certain probability of tunneling
31:50 through a barrier even when they lack
31:53 the classical energy needed to overcome it.
31:56 In the sun's core, quantum tunneling allows
31:58 a small fraction of protons to effectively
32:01 bypass the coolum barrier without having
32:04 to climb over it in the classical sense.
32:07 Even though these protons do not have enough
32:09 kinetic energy to overcome the electrostatic repulsion directly,
32:13 quantum mechanics gives them a chance to appear
32:16 on the other side of the barrier.
32:19 To visualize this process, consider a diagram of the coolum barrier.
32:23 In the diagram, you will see a high energy barrier representing
32:28 the repulsive electrostatic force [music]
32:30 between two protons at varying distances.
32:33 The energy needed to climb over this barrier is represented as a peak.
32:37 The calculations of a classical physicist would require the sun
32:41 to have temperatures high in the billions of degrees C,
32:45 thousands and thousands of times higher than
32:47 the sun's core to hurdle this barrier.
32:50 But quantum mechanics allows for the probability wave
32:53 of a proton to tunnel through this barrier,
32:56 appearing on the other side without ever going over the peak.
33:01 This tunneling effect is what enables fusion
33:03 to [music] occur in stars like the sun,
33:06 despite the seemingly insurmountable coolum barrier.
33:10 Once a proton has tunnneled through the coolum barrier,
33:13 it gets close enough to another proton
33:15 for the strong nuclear force to take over.
33:19 The strong nuclear force which is far more powerful
33:22 than the kulum force operates only at very short ranges
33:27 on the order of phentometers where one phento is equal
33:31 to 10^ -15 m roughly the size of a single proton.
33:38 The strong nuclear force binds the protons together.
33:42 But this is only the first step in a series
33:45 of nuclear events known as the proton proton chain.
33:50 The proton proton chain reaction is the dominant fusion pathway in the sun
33:55 and other stars of similar size accounting
33:58 for roughly 99% of the sun's energy production.
34:04 It starts with two free roaming protons combining to form dutyium,
34:09 a heavy isotope of hydrogen along
34:11 with the emission of a posetron and a neutrino.
34:15 This step is rare but essential as it allows the fusion process to continue.
34:22 The dutarium then rapidly fuses with another proton to form helium 3,
34:27 releasing a higher energy photon, a gamma ray.
34:31 In the final step, two helium 3 nuclei collide and fuse to form helium 4,
34:38 releasing two protons and a significant amount
34:42 of energy in the form of radiation.
34:45 While the proton proton chain is the dominant fusion process in the sun,
34:50 there is another pathway at play particularly
34:53 in stars hotter and more massive than our sun.
34:57 This pathway is known as the CN O cycle, short for carbon, nitrogen, oxygen.
35:04 In this cycle, carbon, nitrogen,
35:06 and oxygen nuclei act as catalysts to fuse protons into helium.
35:11 The CNO cycle is more efficient at higher temperatures
35:15 and only contributes a small percentage of our sun's energy output.
35:19 The energy produced in these fusion reactions comes from a small amount
35:23 of mass being converted into energy
35:25 as described by Einstein's famous equation E= MC².
35:30 In the fusion process, the mass of the resulting helium 4 nucleus is slightly
35:35 less than the combined mass of the original four protons.
35:39 This missing mass is not lost,
35:42 but rather converted into energy that radiates outward from the sun.
35:47 Every second, the sun converts about 4.3 million tons of its mass into energy.
35:55 That's right.
35:55 The sun is losing mass all the time.
35:59 To put this into perspective, this is the equivalent of the mass of about
36:03 3 million cars being turned into pure energy every second.
36:09 This is the energy that ultimately powers the sun
36:11 and provides the light and heat that reaches Earth.
36:16 But before these photons pouring out of these reactions can reach
36:20 the Earth and everything else in the solar system and beyond,
36:23 they must first escape the 700,000 km
36:28 of chaotic solar interior that lies above them.
36:32 To truly grasp the complexity of the sun and its stratified layers,
36:36 let's follow a single photon, a particle of light,
36:40 from its creation within a proton proton reaction all the way to the surface.
36:46 This journey is anything but straightforward.
36:49 In fact, it will take thousands, if not hundreds of thousands of years,
36:53 for this photon to complete its journey,
36:56 passing through several distinct layers of the sun,
36:59 each with their own unique [music] properties and behaviors.
37:04 As we've already found out, our photon's journey starts in the core,
37:09 a region that spans about 25% of the sun's radius,
37:12 but holds nearly half of its total mass.
37:16 And as we've also heard,
37:18 the core is incredibly dense at around 160 g per cubic cm.
37:24 It's over 20 times denser than iron.
37:27 To put that into perspective, if your phone was made of material that dense,
37:32 it would weigh as much as a heavyduty sledgehammer for our photon.
37:38 This means that the environment is so tightly packed with [music] particles,
37:43 it cannot travel far before being absorbed by a neighboring particle.
37:47 Of course, not long later,
37:50 that particle will pack the photons's bags and send it out into the mele
37:54 of the core for another particle to catch
37:56 and release in some other random direction.
38:00 It's a bit like trying to navigate through a dense crowd where
38:04 every few steps you bump into someone and have to change direction.
38:08 This constant interaction of absorption and remission
38:13 is what gives the core its chaotic nature,
38:16 resulting in a journey for a photon that is
38:18 more of a random walk than a direct path outward.
38:21 This random movement of photons is
38:24 reminiscent of Brownian motion where particles suspended
38:27 [music] in a fluid move erratically
38:30 due to collisions with smaller fastoving molecules.
38:34 And there is no preference for the direction that a photon
38:37 could fly back out of a particle that had just absorbed it.
38:41 In theory, a photon could make it all the way to the surface
38:44 of the sun before random chance directs it back towards the core.
38:49 To add to the complexity, as photons are continuously absorbed and remitted,
38:55 the energy gradually decreases from gamma rays to x-rays and eventually
39:00 to visible light as they move towards the sun's outer layers.
39:07 Understanding the processes occurring within the sun's
39:10 core has been a challenging endeavor for astronomers.
39:14 The core is completely obscured by the outer layers of the sun,
39:18 meaning we cannot directly observe it through any form of light.
39:22 Instead, scientists have developed ingenious methods to infer
39:25 the dynamics of the roaring inferno below.
39:28 One of the key techniques is the study of heliosismology,
39:33 the observation of waves rippling across the sun's surface.
39:38 Just like seismologists study earthquakes to understand Earth's interior,
39:42 helioismologists measure the vibrations of the sun's surface
39:46 caused by sound waves that travel through its interior.
39:50 These sound waves are influenced by the temperature,
39:52 density, and composition of the sun's layers,
39:56 allowing scientists to construct models of what is happening deep within.
40:01 Solar nutrinos, elusive subatomic particles that I've
40:05 talked about in a previous video,
40:07 are also released during the fusion reactions in the sun's core.
40:11 Nutrinos interact so weakly with matter that they can
40:14 travel straight out of the sun in just 2 seconds,
40:18 hardly aware of the tangle their photon counterparts are caught up in.
40:23 For decades, solar neutrino detectors on Earth
40:26 measured fewer nutrinos than predicted by theoretical models,
40:30 leading to what was known as the solar nutrino problem.
40:35 It wasn't until scientists discovered that nutrinos change their properties
40:39 or flavors on their journey to Earth that the mystery was resolved,
40:44 confirming both our understanding of particle physics
40:47 and the nuclear processes in the sun's core.
40:51 Next, the photon enters the radiative zone,
40:54 which extends from the edge of the core to about 70% of the sun's radius.
40:59 Here, temperatures gradually drop from 15 million° to around 2 million°.
41:06 The density of matter also drops,
41:08 going from around the density of gold in the zone's
41:10 depths to less than water near the top.
41:14 The dominant energy transportation method is still
41:17 this frenetic process of photons skittering through the layer,
41:21 carrying their energy on average towards the surface.
41:25 And as the density of the plasma continues to decrease as we move outward,
41:29 our photon has slightly more wiggle
41:31 room capable of bigger leaps between interactions.
41:35 But even here, outside of the core,
41:38 the sun's material is still so opaque that even a few centimeters
41:42 could block out as much light as hundreds of meters of water.
41:47 We are able to envision such precise models of the sun's
41:50 interior because of models like the standard solar model or SSM.
41:54 [music] It is a mathematical framework
41:57 based on the principles of hydrostatic equilibrium,
42:00 energy conservation, and radiative transfer.
42:04 Essentially using our understanding of how materials
42:07 and fluids behave here in our laboratories
42:09 on Earth to infer the properties of a place out of our reach.
42:14 The SSM models how energy is passed between particles in its complex equations,
42:19 describing how photons are transported through the dense plasma.
42:24 This allows us to calculate how transparent the solar
42:27 material is to radiation at different temperatures and densities.
42:31 And from there we can work out where
42:33 the radiative zone ends and the next layer begins.
42:38 This is one of my favorite things about mathematics.
42:41 It allows us to explore environments that we can never visit.
42:45 Almost like how quantum tunneling allows protons to jump over
42:49 the coolum barrier and produce the photons we are now following.
42:54 As our photon approaches the upper boundary of the radiative zone,
42:58 it enters the tacoline,
43:01 a thin transitional layer where the radiative zone meets the next layer,
43:05 the convective zone.
43:07 The tacoline is an environment of extreme contrast where the relative
43:12 uniformity of the radiative zone meets the boiling bubbling convective zone.
43:18 The strange conditions in this extremely thin layer likely plays a key
43:23 role in the solar dynamo that generates the sun's magnetic field.
43:27 The tacoline is thought to twist [music] and amplify the magnetic field,
43:31 shaping the sunspots and solar flares that define the star surface.
43:36 Zipping through the thin taco, our photon arrives at the convective zone,
43:42 stretching out from about 70% of the sun's
43:44 radius to just beneath the visible surface, the photosphere.
43:49 The temperatures have dropped to below 2 million° C.
43:53 Now, the sun's plasma is no longer
43:56 dense enough to effectively transfer energy by radiation.
44:00 Instead, the plasma becomes unstable [music] and begins to move
44:04 in massive convection currents much like boiling water in a pot.
44:09 Hot plasma rises towards the surface in large cells called granules.
44:14 These granules with diameters of thousands of kilometers surge upward
44:20 under their power of buoyancy at speeds of hundreds of meters/s
44:24 like a beach ball that you force below the water
44:27 rushing to the surface as it squirms from under you.
44:31 The force required to move this volume
44:33 of matter against the sun's gravity is astonishing.
44:37 Imagine the force of 10 billion hurricanes and you'd
44:42 be just starting to get close to the energy necessary.
44:46 This convective process moves energy much
44:49 more efficiently than the radiative zone,
44:51 creating turbulent rolling waves of plasma that churn vigorously.
44:57 I have explained these convection cells
44:59 and the beautiful hypnotic patterns they create
45:01 on the sun's surface in a lot of detail in this previous video.
45:05 This is a significant change in how energy is transported.
45:10 While photons still interact with particles,
45:12 the primary mechanism of energy transfer in the convective zone
45:16 is no longer the random absorption and remission between particles,
45:20 known as radiative diffusion,
45:22 but rather the movement of hot plasma rising and cooler plasma sinking.
45:28 This convection motion carries the energy outward
45:31 more efficiently than in the radiative zone.
45:34 Upon reaching the top of the convective zone,
45:38 the photon is carried to the photosphere, the sun's visible surface.
45:43 Temperatures have now cooled to about 5,500°, and the plasma has thinned enough
45:49 for photons to escape without being constantly reabsorbed.
45:54 It is from this thin,
45:56 roughly 500 km deep layer that the light we see from the sun is emitted.
46:02 Above them lies only the sun's corona which
46:05 is itself a fascinating environment but only around
46:09 a billionth of the density of the photosphere
46:11 and therefore not much of an obstacle to our photon.
46:14 It is incredible that an object like the sun that many refer
46:18 to as a ball of gas can have such a sharp boundary.
46:24 But the photosphere is where our photon finally breaks free,
46:28 traveling at the speed of light and beginning
46:31 its journey across the vastness of space.
46:35 Our nutrino friend that was created at the same time,
46:38 it's long out of the Milky Way by now.
46:44 Since settling into its stable main sequence phase,
46:48 nuclear fusion has altered the strength of the sun's layers,
46:51 gradually increasing its brightness over billions of years.
46:55 This is because the fusion process inevitably
46:58 leads to changes in the composition, density, and temperature of the sun's core,
47:03 which in turn affects the overall behavior and the future of our star.
47:08 As hydrogen fuses into helium,
47:10 hydrogen gradually depletes in the core and helium ash begins to build up.
47:16 Unlike hydrogen, which readily undergoes fusion
47:19 at the sun's current core temperatures,
47:22 helium requires much higher temperatures to fuse.
47:25 As the abundance of helium increases, the core becomes denser.
47:29 Helium nuclei are more massive than hydrogen nuclei.
47:33 And as more helium collects in the core, the overall density increases.
47:38 At the same time, because helium is not fusing and creating energy,
47:43 [music] it does not contribute to the outward
47:45 radiation pressure that counterbalances the sun's immense gravitational pull.
47:50 The result is that gravity will begin to dominate,
47:54 causing the core to contract further.
47:58 To prevent collapse under its own gravity,
48:00 the sun must increase its core temperature.
48:03 As helium builds up, the hotter core turns up the dial on hydrogen fusion
48:08 because nuclear fusion rates are extremely sensitive to changes in temperature.
48:13 This increase in fusion releases more energy,
48:16 which results in a brighter star and temporarily
48:20 restores the balance between gravity and radiation pressure.
48:23 Through this process,
48:24 the sun's energy output has increased by about 30% over its lifetime.
48:30 And this trend will continue for billions of years
48:33 as long as hydrogen fusion dominates in the core.
48:37 In the radiative zone, the layers have grown hotter and more opaque.
48:43 The rising temperature of the core means more energetic photons are produced,
48:47 which are more prone to interacting
48:49 with the surrounding plasma and pinballing around.
48:52 As a result, this zone has become less efficient at radiating energy outward,
48:57 trapping photons for longer before they can continue their escape.
49:01 The convective zone has also expanded slightly
49:04 over time due to the increased energy production.
49:10 As the sun continues to burn through its
49:12 hydrogen fuel over the next 5 billion years,
49:15 its core will eventually be left overburdened with inert helium
49:19 that can no longer sustain fusion under its own pressure.
49:23 When this happens, the sun will evolve into a red giant,
49:27 dramatically expanding and engulfing its inner planets,
49:31 including Mercury and Venus and possibly the Earth.
49:35 In this phase, the core will contract and heat
49:38 up until it ignites in a helium flash,
49:42 starting the fusion of helium into heavier elements like carbon and oxygen.
49:47 Yet again, swinging the pendulum between the relentless gravitational
49:51 hammering and the resisting forces of energy from the core.
49:55 This process will create new layers and cause the sun to swell
49:59 even further before shedding its outer layers to form a ghostly remnant.
50:05 [music] a planetary nebula.
50:07 The core that remains will cool and fade, becoming a white dwarf,
50:12 a dense earth-sized ember of a once raging fire.
50:20 This transformation from a stable star to a red
50:24 giant and eventually a white dwarf is a remarkable
50:28 and complex process with many fascinating details which
50:32 we will no doubt explore in a future video.
50:36 But ending our journey from the depths
50:39 of the sun's ancient past to its modern interior,
50:42 let's return to that quiet hill where we began, watching the colors of sunrise.
50:48 I hope the next sunrise you see becomes that little bit more special.
50:53 I hope the pink and orange photons scattered
50:56 for one final time on the molecules of Earth's
50:59 atmosphere before streaming through your pupils will make
51:03 you think of the incredible voyage they have endured.
51:07 Beginning with a collapse of a colossal
51:10 cosmic cloud [music] into an elementb building furnace,
51:14 struggling for hundreds of thousands of years through a melting
51:18 pot of plasma to gift you with this beautiful scene.
51:22 I hope this exploration has deepened your appreciation
51:25 for that daily miracle we often take for granted.
51:29 And there's still so much more to uncover about our closest star,
51:33 from the formations it will undergo to the profound
51:36 impacts it will have on our solar systems future.
51:40 Thank you for joining me on this journey through space and time.
51:43 If you found this journey as enlightening as our host are,
51:47 please give the video a like and fuse it
51:49 with your own thoughts down in [music] the comments below.
51:52 Thanks for watching.
52:00 Beneath its swirling clouds, Venus is a world of relentless heat,
52:06 crushing pressure, and volcanic planes stretching for hundreds of kilome.
52:12 A planet reshaped by cataclysmic eruptions and alien geology.
52:17 Aside from a few haunting, grainy photos from the surface,
52:22 Venus kept its secrets hidden for centuries.
52:25 No one had truly seen what lay beneath the veil until Mellin.
52:32 On the 4th of May 1989,
52:35 Space Shuttle Atlantis launched its third flight from the Kennedy Space Center.
52:40 On board, it carried a very special payload.
52:44 The first deep space probe launched [music] by a space shuttle.
52:48 A probe bound for Venus that was about to make history.
52:52 For 4 years, the Mellan spacecraft ambitiously studied our nearest neighbor,
52:58 mapping 98% of its surface to a resolution of up to 100 m.
53:03 The images it sent back shattered our assumptions of Venus forever.
53:08 And that's what I'm going to show you today.
53:13 I'm Alex Mccoan and you're watching Astramm.
53:16 Join me today as we explore the stunning images of Venus.
53:20 NASA's Mellan mission sent back.
53:22 The surprises they revealed about Venus's violent past
53:26 and the mysteries that still linger unanswered to this day.
53:35 Mariner 10 snapped some of the first pictures of Venus in 1974,
53:40 capturing Venus's dense cloud formations on its way to Mercury.
53:45 A year later, the Soviet Union's Veneer
53:47 program landed a spacecraft on the rocky planet,
53:51 sending back the first and only images from Venus's surface.
53:56 They show a desolate, eerie landscape,
54:00 but these images only captured data from tiny portions of the planet's surface.
54:05 The lander's cameras could only see a few meters in any
54:08 direction and were destroyed within hours by Venus's crushing pressures.
54:14 In the 1970s, the Pioneer Venus Orbiter,
54:18 also known as Pioneer Venus 1 or Pioneer 12, provided some radar mapping data,
54:25 but its resolution was low and its images incomplete.
54:30 Imagine trying to map the Earth,
54:32 but Google Maps didn't let you zoom in further than 75 km.
54:37 New York City would just be one pixel, so pretty hard to make an accurate map.
54:43 Additionally, Pioneer 12 didn't map
54:46 the northern and southernmost parts of Venus.
54:49 That's like a map of Earth with most
54:51 of the Arctic and Antarctic circles missing.
54:55 NASA decided they could do better.
54:58 They wanted to see it all.
55:00 Landforms, tectonics, impact, and chemical processes, erosion,
55:07 and even get to know Venus's interior.
55:10 So they mounted an ambitious mission to capture
55:14 the entire surface of the planet in ultra
55:17 high detail along with a gravitational map
55:20 that would give insights into what lies beneath.
55:24 That mission was Mellin.
55:29 Now before I show you Mellin's photos,
55:32 you need to understand three key engineering
55:34 innovations that made me Mellin's mission so groundbreaking.
55:39 First, to penetrate Venus's dense atmosphere,
55:42 Mellin improved on Pioneer's basic radar ultimatry.
55:48 Engineers used a 3.7 m high gain
55:51 Voyager antenna and components from other past missions
55:55 to create a synthetic aperture radar that collected
55:59 multiple readings of each area from different orbital positions.
56:03 These combined readings simulated observations from a much larger antenna,
56:08 revealing unprecedented surface details.
56:12 Second, Mellin followed a polar orbital path,
56:16 scanning Venus in north south strips during each of its 3-hour 15-minute orbits.
56:22 In total, it completed six 243-day mapping cycles.
56:27 Cycles 1 to three mapped the planet surface
56:31 and cycles four to six captured gravitational field data.
56:35 By the end of its first cycle on the 15th of May 1991,
56:39 Mellin exceeded its 70% mapping goal, covering 83.7%.
56:46 By the end of cycle 3, it had mapped 98% of Venus at 100 to 250 m resolution.
56:55 The probe ended up sending home more data than all
56:59 of NASA's previous planetary missions combined, a total of 150 GB.
57:06 By today's standard, it admittedly isn't that impressive.
57:09 Your phone probably has more storage capacity,
57:13 but for the early9s, it was quite something.
57:17 Finally, [music] after its third mapping cycle in September 1992,
57:22 Mellin transmitted a continuous radio signal to NASA's deep space network
57:28 based on how the probe's acceleration changed as it orbited the planet.
57:33 This would produce a change to the radio signal via the Doppler effect,
57:37 allowing scientists to decipher Venus's gravity field.
57:41 This revealed information about the planet's
57:44 interior structure and density distribution.
57:48 The images I'm about to show you are
57:51 10 times sharper than any previous radar images taken
57:55 from Earth or orbiting spacecraft at the time
57:58 and 250 times sharper than Pioneer [snorts] 12's data.
58:02 For the first time, we actually got to see
58:05 what was lurking under those thick, noxious clouds.
58:10 Let's take a look.
58:15 Where previous missions had only shown vague outlines,
58:19 Mellin revealed a world in exquisite detail,
58:23 revealing for the first time the surface
58:25 characteristics of our next door neighbor.
58:28 This mosaic took a decade to put together,
58:31 with the bulk of the radar data coming from Mellin's readings.
58:35 Let's zoom in even further and take a little tour.
58:40 When you approach Venus, you immediately notice the lack of craters.
58:45 Compared with the moon or Mars,
58:47 it's pretty untouched with Mellin only identifying
58:51 940 impact craters across the entire planet.
58:56 Many small impact craters are missing because
58:58 their meteors burn up in Venus's atmosphere.
59:02 And the other craters we did find didn't look as expected.
59:07 Take these three craters for example.
59:10 How danalova and agleones.
59:14 On impact, debris from the surface is ejected
59:17 and forms the pale yellow blanket-like formations around each crater.
59:22 Crater ejector leave behind distinctive marks
59:25 and shapes that help scientists determine
59:27 the angle and energy of impact and how long ago it happened,
59:31 the composition of surface and subsurface materials, and much more.
59:36 What's interesting about these crater ejector is they
59:40 all show sineuous flows in a flower-shaped pattern, not unlike lava flows.
59:46 They are made of molten rock and remain this way
59:49 for way longer than expected due to Venus's high surface temperatures.
59:55 The Adivar Crater is another great example of Venus's unique ejector patterns.
1:00:01 On airless worlds like the moon,
1:00:03 ejected material from the impact follows an arked ballistic path.
1:00:08 But on Venus, the ejected debris interacts with the planet's dense atmosphere,
1:00:14 creating powerful winds that sweep the material outward in groundhugging flows.
1:00:21 This creates unusual streaks like the horseshoe-shaped one we see here,
1:00:26 which are only found on Venus.
1:00:29 Finally, the 90 km wide Adams crater has a 600
1:00:35 km outflow tail likely made of impact melt or magma
1:00:40 which can remain in its liquid form for much
1:00:42 longer due to the high temperature and pressure on Venus.
1:00:46 The scarcity of these craters suggests Venus's surface is actually quite young.
1:00:52 Indeed, gravity data collected by Mellin supports the hypothesis that Venus
1:00:57 underwent a global resurfacing event approximately 300 to 500 million years ago.
1:01:04 So, what could have caused such a dramatic event?
1:01:10 Volcanoes.
1:01:11 Lots and lots of volcanoes.
1:01:15 We knew Venus had volcanic features before Mellin,
1:01:18 but we had no idea that a staggering 85% of the planet is covered in volcanic
1:01:25 flows like these pancake domes 65 km wide
1:01:30 with broad flat tops less than 1 km tall.
1:01:34 They likely formed from highly viscous lava which later cooled and withdrew
1:01:40 leading to the cracks and pits you can see in the image.
1:01:44 or these sprawling lava flows stretching for hundreds of kilometers
1:01:49 over the fractured plains beneath two large shield volcanoes,
1:01:54 Sapasmons and Martmons.
1:01:57 By studying the varying shapes and patterns of these volcanic planes,
1:02:01 scientists can identify different volcanic formation processes from localized
1:02:06 shield volcano eruptions to massive regional lava flooding events.
1:02:13 Speaking of Martmons, let's take a closer look.
1:02:17 Towering at a dizzying 8,000 m tall, it's almost as large as Mount Everest.
1:02:24 It's also a shield volcano characterized by its broad, gently sloping sides.
1:02:30 They are typically formed by fluid lava flows like the Mount Aloa in Hawaii.
1:02:37 If you think Matt Mons looks as awesome as I do and you
1:02:40 want to carry around a bit of Venus's fire to spice up your day,
1:02:44 then you should check out the wallpapers we've made
1:02:46 over on Patreon for your phone, desktop, or tablet.
1:02:50 Shield volcanoes are not the only kind of volcano you'll see on Venus.
1:02:55 Small volcanic domes like these are also
1:02:58 very common features on the planet's surface.
1:03:01 Unlike shield volcanoes, volcanic domes are formed by small,
1:03:06 bulbous masses of lava too thick to flow very far.
1:03:10 As it slowly exits the vent, the lava piles up and cools on the sides.
1:03:15 This cluster of volcanoes sits between rough lava flows
1:03:19 in the east and smooth lava flows in the west,
1:03:22 [music] indicating two different types of lava overlapping,
1:03:26 though the exact process remains unknown.
1:03:29 The abundance of lava flows and volcanic features on Venus
1:03:32 confirmed that volcanism played a dominant role in shaping
1:03:36 Venus's surface and gave [music] rise to the theory
1:03:39 that the planet might still be volcanically active to this day.
1:03:44 In 2024, researchers who were revisiting Mellan's archival data found that two
1:03:50 volcanoes actually erupted during the probe's watch in the early 1990s.
1:03:56 This supported a historic finding from the previous
1:03:59 year that Martmon's had also erupted in 1991.
1:04:04 So what's going on beneath the surface?
1:04:08 What is Venus's mantle like?
1:04:12 A hint to those answers lies in the surface corona.
1:04:17 Like this 500 km wide Yaveen corona.
1:04:22 When hot upwelling magma from the depths of a planet's
1:04:25 mantle reaches the surface or the lithosphere, it leaves its mark.
1:04:31 On Earth, our tectonic plates shift over this magma hot spot,
1:04:35 creating volcanic chains like Hawaii or flood bassults.
1:04:40 But Venus only has one single tectonic plate.
1:04:44 So mantle plume activity pushes the surface
1:04:46 upward before collapsing as the magma cools.
1:04:50 The result, these corona.
1:04:54 Despite being hundreds of millions of years old,
1:04:58 many corona appear well preserved.
1:05:01 There are around 500 of them widely distributed across
1:05:05 the planet in [music] patterns inconsistent with plate boundaries
1:05:09 and their characteristics suggest a lithosphere that is too
1:05:13 thick or strong to break into mobile plates like Earth's.
1:05:18 All this evidence suggests a unique style of lithospheric deformation
1:05:23 where the crust stays largely in place but is pushed,
1:05:27 pulled, and deformed by forces below.
1:05:30 This stagnant lid planet model might also
1:05:33 play a role in Venus's runaway greenhouse effect.
1:05:38 On Earth, our tectonic plates carry
1:05:40 out vital processes like burying oceanic carbon.
1:05:45 When it rains, atmospheric carbon interacts
1:05:47 with mountain rocks to create new minerals,
1:05:50 which slowly make their way to the oceans
1:05:52 and eventually find themselves stored in seabed sediment.
1:05:56 This sediment is then subducted when an oceanic
1:05:59 plate sinks the seabed back into Earth's magma layer,
1:06:04 a process that regulates Earth's temperatures
1:06:06 and the concentration of carbon dioxide in our atmosphere.
1:06:11 Since Venus's crust is stagnant and devoid of tectonic activity,
1:06:15 this regulatory process can't take place.
1:06:19 Instead, heat builds up beneath the surface and greenhouse
1:06:23 gases are not effectively removed from the atmosphere.
1:06:27 The hotter the interior becomes,
1:06:29 the more unstable the system until the whole lithosphere overturns
1:06:34 in a global resurfacing event and the cycle begins again.
1:06:42 We aren't exactly sure when the last resurfacing event occurred on Venus,
1:06:46 but NASA's technical report following Mellin suggests
1:06:50 it happened about 300 million years ago.
1:06:56 Another curious symptom of Venus's unique tectonics and mantle activity are
1:07:01 the tesseray that we can see in the highland regions of the planet.
1:07:06 They are distinct geological features characterized
1:07:09 by highly deformed terrain with a tilelike appearance.
1:07:14 They cover about 8% [music] of Venus's surface
1:07:17 and are primarily found in the highland regions.
1:07:21 As some of the oldest visible surface features on Venus,
1:07:24 they date back about 750 million years.
1:07:29 The USSR's Venera 15 and 16 missions
1:07:32 first identified these formations in the 80s,
1:07:35 but Mellin brought them to life in spectacular detail,
1:07:39 like this photo of Alpha Regio, one of the most prominent tesser on Venus.
1:07:46 Scientists still aren't sure exactly how tesseray form,
1:07:50 but the two leading theories indicate they are likely made
1:07:53 of volcanic rocks or they are part of Venus's continental crust,
1:07:58 deformed through compression or expansion.
1:08:02 If so, they'd be gateways into Venus's geological past and possibly
1:08:07 even show us what the climate was like billions of years ago.
1:08:12 Fascinatingly, Mellin actually managed to capture
1:08:15 the first evidence of active tectonics
1:08:18 occurring on another planet in the solar system in Venus's Aphroditi Terror,
1:08:24 a continental area roughly the size of Africa.
1:08:28 The image on the left was taken in late
1:08:30 November of 1990 during Mellin's first trip around Venus.
1:08:34 The image on the right was taken 8 months later
1:08:38 as the spacecraft flew over the region for the second time.
1:08:42 See the bright flow-like area that appeared.
1:08:46 It's likely the result of a landslide
1:08:48 which was possibly triggered by a Venus quake.
1:08:55 On the 13th of October 1994,
1:08:58 after completing one of the most successful deep space missions ever,
1:09:02 the probe made its final descent into the atmosphere of the planet
1:09:06 it had studied so devoutly over the last 4 years.
1:09:10 As it plunged towards the surface,
1:09:12 it continued to transmit data about Venus's upper atmosphere
1:09:16 until it was consumed by the intense heat and pressure.
1:09:21 Over 30 years later, Mellin is still our primary source of information on Venus.
1:09:28 And as any good mission, it raised as many questions as it answered.
1:09:33 Was there ever water on Venus?
1:09:36 If there was, would Venus have been habitable?
1:09:40 How has the planet evolved through time?
1:09:44 Is Venus still volcanically active today?
1:09:47 Together, NASA's upcoming Veritas and [music] Da Vinci missions
1:09:52 will set out to answer them and many more.
1:09:55 Set to launch in 2028 to 2030,
1:09:58 they will revolutionize our understanding of Venus once again.
1:10:03 Da Vinci Plus will study Venus's clouds during two gravitas flybys and also send
1:10:09 a descent probe deep into Venus's atmosphere
1:10:11 to get a better understanding of its gases, chemistry, and water history.
1:10:17 Even though it isn't expected to survive the landing,
1:10:20 the probe will collect valuable data and images
1:10:23 on its hour-long descent to the planet's scorched surface.
1:10:27 Meanwhile, the Veritas spacecraft will be a Venus orbiter,
1:10:31 similar to Maven, currently orbiting Mars.
1:10:35 Over the three Earth years it spends circling our neighbor,
1:10:38 its job will be to search
1:10:40 for evidence of ongoing volcanism and tectonic activity
1:10:44 by measuring heat coming from the surface
1:10:46 and analyzing the composition of Venus's tesseray.
1:10:51 These findings will help us understand just
1:10:53 how different or similar Venus and Earth are.
1:10:58 Could our neighbor really be a window into our future?
1:11:02 Or is it more like our hot evil twin?
1:11:09 Mercury, the solar system's closest planet to the sun.
1:11:16 Everything I'll show you today will be an actual
1:11:18 picture or video image of Mercury from the Messenger probe.
1:11:22 We'll discuss Mercury's orbit and rotation, its physical characteristics,
1:11:28 its surface conditions,
1:11:30 and the magnetic field and magneettosphere of the planet.
1:11:36 I'm Alex Mcolen, and you're watching Astramm.
1:11:39 Stick with me on this video and you will learn almost
1:11:42 everything you could want to know about this tiny yet fascinating planet.
1:11:48 Now, when you think about the physical characteristics of Mercury,
1:11:52 I'm sure you imagine it being the closest planet to the sun,
1:11:56 but also that it's this giant rock floating in space.
1:12:00 You wouldn't be too far wrong with that, but it
1:12:03 is much more interesting than what you may first think.
1:12:07 For example, when I look at Mercury, I do think of our moon,
1:12:11 but Mercury actually is visually more appealing than our moon.
1:12:15 Look at it in its true color.
1:12:17 The first thing that I notice is that it actually does have a color.
1:12:21 It's not just different shades of gray.
1:12:24 And what else?
1:12:26 Well, did you know, for example,
1:12:27 that Mercury consists of approximately 70% metallic and 30% silicut materials.
1:12:34 So, it's actually more metallic than rocky.
1:12:37 Because of this, Mercury's density is the second highest
1:12:40 in the solar system at 5.427 427 g per cime cubed,
1:12:45 only slightly less than the planet with the greatest density,
1:12:48 that of Earth at 5.515 g per cime cubed.
1:12:54 If Mercury happened to be the same size as Earth,
1:12:57 that would mean it would pretty much
1:12:58 have the same gravitational pull at its surface.
1:13:02 But being the size that it is, its surface gravity is only 3.7 m/s squared.
1:13:08 If you were to compare its gravity to Earth, it would look something like this.
1:13:13 This means the surface gravity of Mercury is
1:13:16 only slightly less than what it is on Mars.
1:13:19 And considering that Mars is a much bigger planet,
1:13:22 that just says something about the density of Mercury.
1:13:26 But before we leave the subject of Mercury's size,
1:13:29 I want to show you one last comparison.
1:13:32 That of Ganymede and Titan against Mercury.
1:13:35 Now, Ganymede is the solar system's biggest
1:13:38 moon and also the biggest moon of Jupiter.
1:13:41 While Titan is Saturn's biggest moon
1:13:43 and the second biggest moon in the solar system.
1:13:46 These two giant moons are bigger than Mercury,
1:13:49 as you can see here, but their masses are far less.
1:13:54 If you look closely at Mercury's surface,
1:13:57 [music] you'll see its appearance is similar to that of our moon.
1:14:00 It shows extensive marike planes and heavy cratering indicating
1:14:06 that it has been geologically inactive for billions of years.
1:14:10 But it obviously was geologically active at [music]
1:14:12 one point because one of the distinctive features
1:14:15 of Mercury's surface is the presence of many narrow
1:14:18 ridges extending up to several hundred km in length.
1:14:22 It's believed that these were formed as Mercury's core and mantle
1:14:26 cooled and contracted over time when the crust had already solidified.
1:14:30 And one of the most distinctive things you'll notice about Mercury is this huge
1:14:34 crater on its surface called Calaris Basin with a diameter of 1,550 km.
1:14:42 The impact that created Calleris Basin was so powerful it caused lava eruptions
1:14:47 and left [music] a concentric ring over 2 km tall surrounding the impact crater.
1:14:53 At the antipode of Caleris basin is a large
1:14:56 region of unusually hilly terrain known as the weird terrain.
1:15:01 If you compare this region to the rest of Mercury,
1:15:04 you can see why it would have this name.
1:15:07 So what's it like on the surface of Mercury?
1:15:12 Well, to start with, the surface temperature is hugely different all over.
1:15:17 It can range from -73° to over 400°.
1:15:24 It never rises above- 93° at the poles
1:15:27 though because there's no atmosphere retaining the heat.
1:15:31 This means that there's quite a big
1:15:32 difference between the equator and the poles.
1:15:35 But this variation is also due to its orbit and rotation,
1:15:38 which we will get back to later.
1:15:41 The subsolar point reaches about 400° while on the dark
1:15:46 side of the planet the temperatures are on average -63°.
1:15:52 Because Mercury is too small and hot for its gravity
1:15:56 to retain any significant atmosphere over long periods of time,
1:16:00 it's not able to retain any of the heat it gets from being so close to the sun,
1:16:04 which is why the dark side of the planet
1:16:06 is so much colder than the side facing the sun.
1:16:09 Mercury however does have an exosphere which is like
1:16:13 an extremely thin atmospheric-l like volume surrounding the planet.
1:16:18 Molecules in an exosphere are gravitationally bound
1:16:21 to a planet but the density is so low that it can't behave like a gas
1:16:26 because the molecules don't collide with each other.
1:16:29 In this picture you can see the Messenger probe's view of Mercury's exosphere.
1:16:34 When solar wind hits the planet, it rips off certain atoms out of the exosphere.
1:16:40 And what's left is this trail of atoms going into space.
1:16:44 We call this the planet's tail.
1:16:46 And every planet has this to a certain extent.
1:16:49 Earth even does have an exosphere, but it starts at 600 km above the surface.
1:16:55 It's really the point where space and the atmosphere meet.
1:16:59 Now, [music] in the case of Mercury, this exosphere is not at all stable.
1:17:04 Atoms are continuously lost and replenished from a variety of sources.
1:17:11 NASA has been able to confirm that craters
1:17:13 at the north pole of Mercury contain water ice.
1:17:17 Mercury also has something which Mars lacks,
1:17:20 an actual magnetosphere or a magnetic field all around the planet.
1:17:26 It is only about 1.1% as strong as Earth's,
1:17:29 but it's still strong enough to deflect
1:17:31 a lot of the solar wind around the planet.
1:17:37 Now, we're going to get to one
1:17:38 of the things I find the most interesting about Mercury,
1:17:42 its orbit and its rotation.
1:17:45 Mercury has the most eccentric orbit of all the planets with a distance
1:17:49 from the sun ranging from 46 million km to 70 million km.
1:17:55 Now, this is something a bit hard to imagine, but bear with me.
1:18:00 Mercury takes about 88 Earth days to complete an orbit around the sun.
1:18:06 It also has a 32 spin orbit resonance of the planet's rotation around its axis.
1:18:12 This means it spins three times around its axis
1:18:16 for every two times that it orbits around the sun.
1:18:19 So although it takes about 59 Earth days for Mercury to rotate on its axis once,
1:18:25 which is what we call a cidurial day,
1:18:28 this 32 orbital resonance means that if you were actually standing on Mercury,
1:18:33 it would appear that one day [music] from sunrise to sunrise
1:18:37 or what is called a solar day is two Mercuran years.
1:18:42 Standing on Mercury, that would look something like this.
1:18:46 you would see the sun rise relatively fast and then as it approaches midday
1:18:51 it slows down and even starts going
1:18:54 backwards before continuing on again to sunset.
1:18:58 As you can see that took a whole year
1:19:01 which means a nighttime on Mercury also takes a year.
1:19:05 The sun starts going backwards in the sky
1:19:08 because approximately four Earth days before perihelion,
1:19:12 the speed in which Mercury travels along its
1:19:14 orbit equals the speed in which it's rotating.
1:19:18 At this point, the sun's apparent motion stays stationary.
1:19:22 A perihelion itself, Mercury's orbital speed exceeds its rotational speed.
1:19:28 So to a person actually standing on Mercury, the sun appears to move backwards.
1:19:34 4 days after perihelion, the sun's normal motion resumes.
1:19:39 You can see this even clearer from a top- down perspective of Mercury.
1:19:44 Twice a day on one of its poles,
1:19:46 the sun seems to pause and then continue on again.
1:19:51 Something else to notice about Mercury's orbit is that it's
1:19:54 inclined by 7° to the plane of Earth's orbit.
1:19:58 As a result of this, we can only see Mercury transit in front
1:20:01 of the sun when it's directly between us on Earth and the Sun itself.
1:20:06 And because its orbit is inclined by 7°,
1:20:09 this only happens about once every seven Earth years.
1:20:13 The last thing we'll discuss about the rotation of Mercury is that its
1:20:16 axle tilt is almost zero with the best measured value as low as 0.027°.
1:20:24 This is even smaller than that of Jupiter, which has been measured at 3.1°.
1:20:30 And finally, do you want to see Earth from Mercury?
1:20:34 Well, here we are just a couple of pixels across.
1:20:38 This photo was taken from the Messenger probe several years ago,
1:20:41 and barring the newborns, every single one of us was in this picture.
1:20:50 A massive thank you to our astronauts on Patreon.
1:20:53 This video had no sponsors,
1:20:55 but it was still made possible thanks to the hundreds of members we have there.
1:21:00 Link is in the description to join our growing community.
1:21:04 Patreon is where Astramm truly takes shape.
1:21:06 A place for people who love space,
1:21:08 who want to see these videos keep improving and reaching more curious minds.
1:21:14 Every new member keeps the channel focused on what really matters,
1:21:17 making the complexity of space available to everyone.
1:21:21 If you enjoy what we do, come join the Astramm community today.