Cosmic Revelations: Artemis 2’s Historic Observations and the Case of Hypernovae

[00:00:00] [SPEAKER_00] Six months ago, four people swung around the far side of the moon. And for 54 minutes, the sun disappeared behind it.

[00:00:09] [SPEAKER_01] And in that darkness, three of them saw something scientists weren't sure the human eye could catch. Tiny flashes of light. Rocks no bigger than a golf ball slamming into the lunar surface, seen from 74,000 kilometers away.

[00:00:25] [SPEAKER_00] Last week, NASA published what the Artemis 2 crew saw, said, and sketched. And it is a lovely piece of science. That's our lead.

[00:00:35] [SPEAKER_01] Plus, the case for the most powerful explosions in the universe springs a leak. Jupiter's magnetic disk turns out to be crumpled, and white dwarves that may break a 90-year-old weight limit. I'm Anna. I'm Avery. This is Astronomy Daily.

[00:00:51] [SPEAKER_00] On the 6th of April this year, Orion, the Artemis 2 capsule, call sign Integrity, went behind the moon. Reid Wiseman, Victor Glover, Christina Koch, and the Canadian Space Agency's Jeremy Hansen had been flying for five days. And for about seven hours, they took turns at the windows, doing something no crew had done since Apollo 17. Lunar Science by I.

[00:01:19] [SPEAKER_01] And on the 7th of October, NASA released the results. The Artemis 2 preliminary lunar science report. A lunar science operations report. A data user's guide. And the raw material itself in NASA's planetary data system. Photographs, recorded audio, and the notes the crew drew on their tablets.

[00:01:39] [SPEAKER_00] I want to be clear up front about what kind of report this is. It is preliminary. It is a record of human observations. It is not a peer-reviewed paper with a single headline number. Its value is that a trained human eye, describing what it sees in real time, gives scientists context that no orbiting camera provides on its own.

[00:02:03] [SPEAKER_01] So, let's start with the moment that made the science team gasp. As Orion passed behind the moon, the sun went behind it too. From where the crew were, the moon looked enormous and barely moved. So the sun stayed hidden for 54 minutes. A total solar eclipse almost an hour long.

[00:02:23] [SPEAKER_00] The lunar scientists had asked the crew to use that darkness to look for impact flashes. The brief burst of light when a small rock hits the moon at thousands of kilometers an hour. The moon has no atmosphere, so nothing burns up on the way in. And they saw them.

[00:02:44] [SPEAKER_01] Five extremely faint pinpricks of light from Orion roughly 74,000 kilometers away. NASA's page has the tablet annotations, and they're wonderful. Wiseman marked his sightings in blue, Glover in green, Hansen in red. One flash, number four, has all three colors on it. Three people, independently, at the same spot. Which matters because the obvious question is, are you sure?

[00:03:13] [SPEAKER_01] A cosmic ray hitting your retina can make a flash. So can a reflection inside the spacecraft. The science team ruled both out before confirming the sightings.

[00:03:23] [SPEAKER_00] From the brightness, scientists estimate each incoming rock was no more than about five centimeters across. Apollo crews reported similar flashes from lunar orbit. But these are likely the faintest ever seen with the unaided eye.

[00:03:39] [SPEAKER_01] And this happened during a planned loss of signal, on the far side. So the crew saw it, recorded it, and then Houston heard about it later. NASA's audio of the moment includes, I'm told, a very scientific, dude, no way.

[00:03:56] [SPEAKER_00] Why does it matter? Because nobody knows precisely how often small rocks hit the moon. And if you're going to put a habitat on the surface for months, that rate is a design number. Regular listeners will remember the new crater in the Cresium region from episode 196. 220 meters wide. A once-in-a-century event. These flashes are the other end of the same distribution. Tiny, frequent, and until now poorly counted.

[00:04:27] [SPEAKER_01] There's a lovely listener tie-in, too. NASA runs a citizen science project called Impact Flash, where amateur astronomers with modest telescopes watch the dark part of the moon and record exactly these events. Earth-based observers have been counting them for years. The crew just did it from a much better seat.

[00:04:45] [SPEAKER_00] The second big theme is color. Ask most people what color the moon is, and they'll say gray. The crew reported gray, black, brown, tan, white, green, and blue.

[00:04:59] [SPEAKER_01] And those aren't artistic license. Blue tints point to titanium-rich volcanic rock. Browns track iron content. Greens signal glass made in volcanic fire fountains or melted by impacts. Christina Koch described one regis as a jaundiced cheek of the moon, which I think is the best geology description I've heard this year.

[00:05:23] [SPEAKER_00] The scientists will compare those descriptions, and the handheld photographs, with data from the Lunar Reconnaissance Orbiter. The point isn't to replace the orbiter. It's to learn how human perception of color and brightness shifts with the angle of the light. Because astronauts on the surface will be making those judgments with no orbiter to check against.

[00:05:46] [SPEAKER_01] NASA shows one worked example. The crew's photographs of the Orientale Basin, the great bullseye on the moon's western limb, matched pixel for pixel onto the orbiter's maps of elevation, roughness, rock cover, and brightness. A human snapshot pinned to years of orbiter data. Which brings us to the third theme, the Terminator, the line between lunar day and night.

[00:06:12] [SPEAKER_01] The science team asked the crew to study it, because the lighting there, sun skimming the horizon, shadows stretching for kilometers, mimics the moon's south pole, where Artemis wants to land.

[00:06:25] [SPEAKER_00] Victor Glover described islands of terrain, standing completely surrounded by darkness, peaks catching sunlight while everything around them is in shadow. NASA's image shows the crater Carno, about 130 kilometers across, right on that line.

[00:06:43] [SPEAKER_01] In Cauch, during the eclipse, as the limb lit up from behind, you can actually see mountains. That's the practical payoff. Knowing what level of detail, what cameras, what lighting future crews need to work safely near the pole.

[00:06:59] [SPEAKER_00] The crew also watched the sun's corona for nearly an hour. And Hansen sketched one streamer that appeared to pulse. That's an observation of the solar atmosphere that drives space weather. Made by someone with no instrument but his eyes.

[00:07:15] [SPEAKER_01] And then there's Hello World, the photo of the whole Earth taken on day two from about 10,000 kilometers out. It looks sunlit. It isn't. It was lit by moonlight. Scientists stayed up through the night combing it, and found weather systems, auroras at both poles, a Saharan dust plume, lightning over the Congo basin, city lights across North Africa and Iberia, and zodiacal light capped by Venus.

[00:07:43] [SPEAKER_00] Koch put it beautifully. The moon was a light sponge, and the Earth a light mirror.

[00:07:51] [SPEAKER_01] Now, the southern note. During the eclipse, the crew photographed the Milky Way, and NASA's labeled version is a southern sky chart. The Earth, Bella, Carina, Musca, Crux, the Southern Cross, Centaurus, the Carina Nebula, and the Large Magellanic Cloud. Four astronauts from North America, beyond the moon, pointing their camera at our sky.

[00:08:17] [SPEAKER_00] Hansen said the stars had a depth he'd never seen from Earth. That brighter ones seemed nearer. That's perception, not distance. And he knew it. But it's exactly the kind of honest human observation this report is full of.

[00:08:33] [SPEAKER_01] So, the caveats one more time. This is a preliminary report. The flash count is five. The sizes are estimates from brightness. And the real science happens now, as researchers match what the crew said to where they were looking and what the orbiters measured.

[00:08:51] [SPEAKER_00] There's also a quieter result in the operations report. Artemis II was the first time NASA ran a modern science backroom for a crewed lunar flight. A lunar science team and mission control in Houston. New flight controller roles. Scientists talking through what the crew should look at next.

[00:09:09] [SPEAKER_01] NASA's photo of that room, the deputy lunar science lead, Marie Henderson, and her colleagues reacting as the descriptions came in, tells you how much the moment meant to them. Learning how scientists and astronauts work together in real time is half the reason this flight carried a science plan at all.

[00:09:27] [SPEAKER_00] NASA calls it a relay race. Decades of robotic data handed to the crew and the crew's observations handed back. The next leg is Artemis III. Then a crew on the surface. And for once, the science team had people at the window. Five flashes says that was worth it.

[00:09:48] [SPEAKER_01] Next. Hypernovae. In theory, they're the most powerful stellar explosions there are. A very massive, fast-spinning star collapsing and releasing at least ten times the energy of an ordinary supernova. And one strand of evidence for them has been chemical. A handful of ancient stars whose makeup seemed only explicable if they'd formed from hypernova debris.

[00:10:14] [SPEAKER_00] This is stellar archaeology, isn't it? You can't watch a star explode 13 billion years ago, but you can read the debris in the stars that formed from it.

[00:10:23] [SPEAKER_01] Exactly. The oldest, most metal-poor stars carry the chemical signature of the generation before them. So a weird abundance pattern becomes evidence for a weird explosion.

[00:10:34] [SPEAKER_00] And a pair of papers from University College London says that strand doesn't hold.

[00:10:40] [SPEAKER_01] Anmol Agarwal, a PhD student at UCL's Mullard Space Science Laboratory, and Ralph Schonrich. Two papers in monthly notices of the Royal Astronomical Society. Quick disclosure, the first was accepted back in March. The second is newer. UCL announced both on the 5th of October.

[00:10:59] [SPEAKER_01] So what's the argument? The old models treated a supernova as a well-stirred pot. The dying star's elements mixed evenly, and the next generation of stars inherits that average. But real supernova remnants aren't like that. Oxygen can fly off one way, sulfur another. A star that forms downstream might be built from a few pieces of the explosion, not the whole recipe.

[00:11:28] [SPEAKER_00] So an odd chemical fingerprint doesn't need an exotic explosion. It might be an ordinary explosion sampled unevenly.

[00:11:37] [SPEAKER_01] Exactly. They looked at four stars, previously attributed to hypernovae. In three, an ordinary lopsided supernova was statistically favored. The fourth is a red giant in the Milky Way's halo, rich in heavy elements like silver and uranium. It had been argued that a neutron star merger couldn't explain it, because the stars seemed to form too early for one. But?

[00:12:03] [SPEAKER_01] But it's moving fast and orbiting backwards relative to most of the galaxy, which suggests it was born in a small dwarf galaxy, where metal-poor stars can form much later, and was swallowed afterwards. Their verdict? One neutron star merger plus one ordinary supernova.

[00:12:23] [SPEAKER_00] Now, the caveat. And it's important. We have directly observed some extraordinarily energetic explosions. Broad-lined supernovae tied to gamma-ray bursts, like the one we covered in episode 160. This work doesn't say those didn't happen. It says the chemical fingerprints in these old stars no longer require hypernovae.

[00:12:44] [SPEAKER_01] And the southern footnote, hunting the oldest stars, is something Australia does well. In 2014, the ANU's SkyMapper Telescope at Siding Spring found one of the most iron-poor stars known. And its chemistry was also explained by a low-energy supernova. Same lesson. Be careful what you build on one strange star.

[00:13:05] [SPEAKER_00] Next story today. Jupiter's magnetic field is the biggest structure in the planetary solar system. And wrapped around the planet's equator is something called the magnetodisc. A vast sheet of electric current, fed by sulfur and oxygen spewed out by the volcanic moon Io, and flung outward by Jupiter's 10-hour spin.

[00:13:27] [SPEAKER_01] And Juno is the right spacecraft to test it. Since 2016, it has looped over Jupiter's poles on long, elongated orbits, slicing through the magnetosphere at different distances and local times, with instruments sampling the field and the particles directly.

[00:13:44] [SPEAKER_00] Which matters for what comes next.

[00:13:47] [SPEAKER_01] And the textbook picture of that sheet is fairly simple. Jupiter's magnetic axis is tilted. So as the planet turns, the sheet rocks up and down like a warped record. A spacecraft sitting in it should cross the sheet about twice per rotation.

[00:14:04] [SPEAKER_00] A team led by Roilong Guo at Shandong University, with co-authors including Dennis Grodent and Bertrand Bonfant from Liege, went through Juno's magnetic field and energetic particle data. Published in Science China Earth Sciences.

[00:14:29] [SPEAKER_01] And what did they find?

[00:14:32] [SPEAKER_00] During active periods, Juno didn't cross the sheet twice. It crossed it again and again. In one case, four times in ten minutes. And almost every crossing carried the signature of magnetic reconnection. Where field lines snap and reconnect and release energy. Along with bursts of energized electrons and ions.

[00:14:55] [SPEAKER_01] So it's not just flapping.

[00:14:57] [SPEAKER_00] No. The orientation analysis shows a kink-like surface wave. Ripples lasting from minutes to over an hour. The authors argue that many small reconnection sites, scattered across about 100 degrees of longitude, keep breaking the field and shoving the sheet off balance. And because Jupiter spins so fast, the whole crumpled sheet is carried around with the planet.

[00:15:25] [SPEAKER_00] Their image is a crumpled tablecloth on a spinning turntable.

[00:15:29] [SPEAKER_01] That's different from Earth, isn't it?

[00:15:32] [SPEAKER_00] Very. In Earth's magnetic tail, a kink wave travels away from a reconnection site. At Jupiter, there's no fixed period and reconnection everywhere. Which points to a rotating, rippled structure instead. It matters because that structure helps decide how Io's material is accelerated, how it's pushed inward, and how energy reaches Jupiter's auroras. A quiet sheet is a simpler machine. A crumpled one is messier.

[00:16:02] [SPEAKER_00] And probably more honest.

[00:16:04] [SPEAKER_01] For about 90 years, white dwarfs have had a weight limit. Subramanian Chandrasekhar showed that a white dwarf supported by electron pressure can't exceed about 1.4 solar masses. Push it past that, and a carbon-oxygen white dwarf ignites and explodes as a Type Ia supernova.

[00:16:22] [SPEAKER_00] Which is why Type Ia supernovae are such good standard candles. Same trigger, similar brightness.

[00:16:30] [SPEAKER_01] It's how cosmic acceleration was discovered. And why we leaned on them for the dark energy story back in Episodes 193 and 195. So, a paper saying the limit can bend gets attention.

[00:16:44] [SPEAKER_00] Who's saying it?

[00:16:45] [SPEAKER_01] Zenia Zu-Reich, a PhD student, and Bani Brata Mukhopadhyay at the Indian Institute of Science, with collaborators including Christopher Tout, whose Cambridge group's Stellar Evolution Code stars they modified. Astrophysical Journal letters, release on the 9th of October. And what did they do? They added magnetic fields and white dwarf cooling to stars, and followed stars from the main sequence all the way to white dwarfs feeding off a companion.

[00:17:15] [SPEAKER_01] In their example, a 1.02 solar mass white dwarf, born from an 8th solar mass star, accretes slowly. The field starts too weak to matter. But as mass piles on, the star contracts, the field is squeezed and strengthens, and magnetic pressure starts carrying some of the load.

[00:17:35] [SPEAKER_00] So, the field is doing work, the electrons can't?

[00:17:39] [SPEAKER_01] In effect, yes. Magnetic pressure adds support, so the usual relationship between a white dwarf's mass and its radius changes. The team even suggests it might explain why some well-studied white dwarfs look larger than their masses predict.

[00:17:55] [SPEAKER_00] And it keeps growing?

[00:17:58] [SPEAKER_01] To about 2.4 solar masses in their magnetized model, against 1.4 without the field. And observers have seen a few over-luminous type 1a supernovae that hint at progenitors up to around 2.8 solar masses. So there's something to explain. Caveats? Several. That's one model, not a survey of outcomes. Super Chandra Sheikhar white dwarfs have been argued over for more than a decade. And the cosmology doesn't hinge on it directly.

[00:18:29] [SPEAKER_01] Astronomers calibrate type 1a supernovae empirically from their light curves. The real question is whether a hidden subpopulation is quietly mixed in. That's worth knowing either way.

[00:18:40] [SPEAKER_00] Two missions in countdown mode. First, Issa's Hera. A week ago, on its second birthday in space, it caught its first glimpse of Didymus. A single pixel from about 236,000 kilometers. And early on Thursday the 15th, European time, it fires three thrusters for 93 minutes to break towards the asteroid dart hit in 2022.

[00:19:08] [SPEAKER_01] That's BRM1. A second, shorter burn follows on the 22nd, then three small transition burns later this month. And close-in characterization from 25 to 30 kilometers in November and December. And the Australian thread. ESA's flight dynamics team will check the burn using signals through its 35-meter antenna at New Norcia in Western Australia.

[00:19:31] [SPEAKER_00] And JAXA's Martian Moon's exploration mission launches on an H3 from Tanegashima at 641 Tuesday morning, Sydney time, Monday afternoon in the Americas. It will land on Phobos, deploy a French-German rover, and its samples are deemed to land in South Australia in 2031. Full curtain-raiser on Monday. Skywatch. And tonight starts with the Moon.

[00:19:56] [SPEAKER_00] It's a slim crescent, around a sixth lit, and it's sliding past Antares, the red heart of Scorpius. And how close depends very much on where you are.

[00:20:08] [SPEAKER_01] It does. From New York, at the end of civil twilight, about 645, the Moon is only 1.3 degrees from Antares, under three moon widths. But just 11 degrees up in the southwest. Los Angeles gets 2.3 degrees, with the Moon 16 degrees up. London, 2.3 degrees, but the Moon is barely 2 degrees above the horizon. So you'll need a clear southwestern view.

[00:20:35] [SPEAKER_00] And Sydney?

[00:20:37] [SPEAKER_01] From Sydney, the pair are 7 degrees apart. But the Moon is 36 degrees up at 730. High and easy. And in some parts of the world, the Moon actually covers Antares tonight, though none of our four cities see that in a dark sky.

[00:20:52] [SPEAKER_00] Next, the inner planets. And this week favors the south.

[00:20:57] [SPEAKER_01] Mercury is still well placed after last week's greatest elongation. From Sydney, it's 24 degrees up at sunset, and sets about two hours after the Sun. From Los Angeles, it's 10 degrees up. New York, 7. London, barely 3. And Venus is diving towards the Sun, passing closest around the 24th. From Sydney, it's still 15 degrees up at sunset, a brilliant magnitude minus 4. From the northern cities, it's already gone.

[00:21:26] [SPEAKER_00] Why the lopsided view?

[00:21:29] [SPEAKER_01] Our regular spring story. Around now, the evening ecliptic stands almost straight up from the western horizon in the southern hemisphere, and lies flat in the northern. A planet at the same angle from the Sun ends up far higher above a southern horizon. In March, it flips, and the north gets the good evening apparitions.

[00:21:47] [SPEAKER_00] Which brings the eye safety reminder.

[00:21:50] [SPEAKER_01] It does, and it's non-negotiable. With Mercury and Venus so close to the Sun, wait until the Sun has fully set before you sweep with binoculars or a telescope. Never look at the Sun through any optical instrument. And only ever look at the Sun directly with eclipse glasses or solar filter certified to the ISO 112 312-2 standard.

[00:22:14] [SPEAKER_00] Now the north gets its turn. Before dawn. Mars has just drifted through the beehive cluster in Cancer. Closest on the 11th. And it's still only about 2 degrees away. A lovely binocular field. At nautical dawn, Mars is 50 to 60 degrees up from the northern cities. Jupiter about 45 degrees up and brighter. From Sydney, they're lower. Mars 23 degrees.

[00:22:43] [SPEAKER_00] They're 12.5 degrees apart today and closing. Down to about 1.2 degrees on the 16th of November. And through the night?

[00:22:53] [SPEAKER_01] Saturn, 10 days past opposition. Rising in the east at dusk. Magnitude 0.4. Its rings opened only about 7 degrees. The southern torrids, debris from comet Enki, reach an early peak around now. Just a few meteors an hour. But they're slow and the occasional one is a fireball. And the radiant is well up from both hemispheres by 11 p.m. The moon sets early this week. So the sky's dark.

[00:23:21] [SPEAKER_00] And a binocular challenge.

[00:23:23] [SPEAKER_01] The asteroid Vesta at opposition yesterday. Magnitude 6.5. In northern Cetus, about 5 degrees north of theta Cetai. And this one leans south. At 11 p.m., it's 49 degrees up from Sydney. Around 40 to 45 from the U.S. cities. 30 from London. Sketch the field. Come back the next night and see which dot moved. First quarter moon is on the 19th. Sydney time.

[00:23:51] [SPEAKER_00] That's the show. Today, five faint flashes on the far side of the moon. A crack in the case for hypernovae. Jupiter's crumpled magneted disk. And white dwarfs that might be heavier than the rulebook allows.

[00:24:05] [SPEAKER_01] Tomorrow, we'll have the result of Hera's big breaking burn. And on Monday, a full curtain raiser for MMX ahead of Tuesday's launch.

[00:24:14] [SPEAKER_00] If you've got a question or you've ever caught an impact flash on the moon yourself, tell us through the contact form at astronomydaily.io. We read every one.

[00:24:25] [SPEAKER_01] Show notes and links are there too. And if you can, catch Mercury low in the west after sunset this week.

[00:24:33] [SPEAKER_00] I'm Anna.

[00:24:34] [SPEAKER_01] I'm Avery. Clear skies.