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00:00:00 --> 00:00:03 Anna: Six months ago, four people swung around
00:00:03 --> 00:00:06 the far side of the moon and for
00:00:06 --> 00:00:08 54 minutes the sun disappeared
00:00:08 --> 00:00:09 behind it.
00:00:10 --> 00:00:13 Avery: And in that darkness, three of them saw
00:00:13 --> 00:00:15 something scientists weren't sure the human
00:00:15 --> 00:00:18 eye could catch. Tiny flashes of light.
00:00:18 --> 00:00:21 Rocks no bigger than a golf ball slamming
00:00:21 --> 00:00:23 into the lunar surface seen from
00:00:23 --> 00:00:25 74 kilometres away.
00:00:26 --> 00:00:28 Anna: Last week NASA published what the Artemis 2
00:00:28 --> 00:00:31 crew saw, said and sketched. And
00:00:31 --> 00:00:34 it is a lovely piece of science. That's our
00:00:34 --> 00:00:34 lead.
00:00:35 --> 00:00:37 Avery: Plus the case for the most powerful
00:00:37 --> 00:00:40 explosions in the universe springs a leak.
00:00:40 --> 00:00:42 Jupiter's magnetic disc turns out to be
00:00:42 --> 00:00:45 crumpled and white dwarfs that may break a
00:00:45 --> 00:00:47 90 year old weight limit. I'm M
00:00:47 --> 00:00:50 Anna, I'm Avery, this
00:00:50 --> 00:00:51 is astronomy daily.
00:00:52 --> 00:00:54 Anna: On the 6th of April this year, Orion, uh,
00:00:55 --> 00:00:57 the Artemis II capsule, callsign
00:00:57 --> 00:01:00 integrity went behind the moon.
00:01:01 --> 00:01:03 Reid Wiseman, Victor Glover, Christina
00:01:03 --> 00:01:06 Koch and the Canadian Space Agency's Jeremy
00:01:06 --> 00:01:09 Hansen had been flying for five days.
00:01:09 --> 00:01:12 And for about seven hours they took turns at
00:01:12 --> 00:01:15 the windows doing something no crew had done
00:01:15 --> 00:01:18 since Apollo 17, lunar
00:01:18 --> 00:01:19 science by eye.
00:01:19 --> 00:01:22 Avery: And on 7 October, NASA released a
00:01:23 --> 00:01:26 the Artemis II Preliminary Lunar Science
00:01:26 --> 00:01:28 Report, a Lunar Science Operations Report,
00:01:29 --> 00:01:32 a data user's guide and the raw
00:01:32 --> 00:01:34 material itself in NASA's Planetary Data
00:01:34 --> 00:01:37 System. Photographs, recorded audio
00:01:37 --> 00:01:40 and the notes the crew drew on their tablets.
00:01:40 --> 00:01:43 Anna: I want to be clear up front about what kind
00:01:43 --> 00:01:46 of report this is. It is preliminary.
00:01:46 --> 00:01:48 It is a record of human observations.
00:01:49 --> 00:01:52 It is not a peer reviewed paper with a single
00:01:52 --> 00:01:54 headline number. Its value is
00:01:54 --> 00:01:57 that a trained human eye describing what it
00:01:57 --> 00:02:00 sees in real time gives scientists
00:02:00 --> 00:02:03 context that no orbiting camera provides
00:02:03 --> 00:02:04 on its own.
00:02:04 --> 00:02:07 Avery: So let's start with the moment that made the
00:02:07 --> 00:02:10 science team gasp. As Orion passed
00:02:10 --> 00:02:12 behind the Moon, the sun went behind it too.
00:02:13 --> 00:02:15 From where the crew were, the Moon looked
00:02:15 --> 00:02:18 enormous and barely moved. So the sun
00:02:18 --> 00:02:20 stayed hidden for 54 minutes. A total
00:02:21 --> 00:02:23 solar eclipse almost an hour long.
00:02:24 --> 00:02:26 Anna: The lunar scientists had asked the crew
00:02:26 --> 00:02:29 to use that darkness to look for impact
00:02:29 --> 00:02:32 flashes, the brief burst of light when
00:02:32 --> 00:02:35 a small rock hits the Moon at thousands of
00:02:35 --> 00:02:38 kilometres an hour. The Moon has
00:02:38 --> 00:02:41 no atmosphere, so nothing burns up on the
00:02:41 --> 00:02:42 way in.
00:02:42 --> 00:02:44 Avery: And they saw them. Five
00:02:44 --> 00:02:47 extremely faint pinpricks of light
00:02:47 --> 00:02:50 from Orion, roughly 74
00:02:50 --> 00:02:53 kilometres away. NASA's page has
00:02:53 --> 00:02:56 the tablet annotations and they're wonderful.
00:02:56 --> 00:02:59 Wiseman marked his sightings in blue, Glover
00:02:59 --> 00:03:01 in green, Hansen in red. One
00:03:01 --> 00:03:04 flash number four has all three colours on
00:03:04 --> 00:03:07 it. Three people independently at the
00:03:07 --> 00:03:10 same spot. Which matters because the
00:03:10 --> 00:03:12 obvious question is, are you sure
00:03:13 --> 00:03:15 a cosmic ray hitting your retina, uh, can
00:03:15 --> 00:03:18 make a Flash. So can a reflection inside the
00:03:18 --> 00:03:21 spacecraft. The science team ruled both
00:03:21 --> 00:03:23 out before confirming the sightings.
00:03:23 --> 00:03:26 Anna: From the brightness, scientists estimate
00:03:26 --> 00:03:29 each incoming rock was no more than about
00:03:29 --> 00:03:31 five centimetres across. Apollo
00:03:31 --> 00:03:34 crews reported similar flashes from lunar
00:03:34 --> 00:03:37 orbit, but these are likely the faintest ever
00:03:37 --> 00:03:38 seen with the unaided eye.
00:03:39 --> 00:03:42 Avery: And this happened during a planned loss of
00:03:42 --> 00:03:45 signal on the far side. So the crew
00:03:45 --> 00:03:48 saw it, recorded it and then Houston
00:03:48 --> 00:03:51 heard about it later. NASA's audio of
00:03:51 --> 00:03:54 the moment includes, I'm told a, uh, very
00:03:54 --> 00:03:56 scientific dude. No way.
00:03:56 --> 00:03:59 Anna: Why does it matter? Because
00:03:59 --> 00:04:02 nobody knows precisely how often small
00:04:02 --> 00:04:04 rocks hit the moon. And if you're going to
00:04:04 --> 00:04:07 put a habitat on the surface for months, that
00:04:07 --> 00:04:10 rate is a design number Regular listeners
00:04:10 --> 00:04:12 will remember the new crater in the Chrysium
00:04:12 --> 00:04:14 region from episode 196.
00:04:14 --> 00:04:17 220 metres wide. A ah, once
00:04:17 --> 00:04:20 in a century event. These flashes are
00:04:20 --> 00:04:23 the other end of the same distribution. Tiny,
00:04:23 --> 00:04:26 frequent and until now, poorly
00:04:26 --> 00:04:26 counted.
00:04:27 --> 00:04:29 Avery: There's a lovely listener tie in too.
00:04:30 --> 00:04:32 NASA runs a citizen science project called
00:04:32 --> 00:04:35 Impact Flash, where amateur astronomers with
00:04:35 --> 00:04:37 modest telescopes watch the dark part of the
00:04:37 --> 00:04:40 moon and record exactly these events. Earth
00:04:40 --> 00:04:42 based observers have been counting them for
00:04:42 --> 00:04:44 years. The crew just did it from a much
00:04:44 --> 00:04:45 better seat.
00:04:46 --> 00:04:48 Anna: The second big theme is colour.
00:04:49 --> 00:04:51 Ask most people what colour the Moon is and
00:04:51 --> 00:04:54 they'll say grey. The crew reported
00:04:54 --> 00:04:57 grey, black, brown, tan,
00:04:57 --> 00:04:59 white, white, green and blue.
00:05:00 --> 00:05:02 Avery: And those aren't artistic licence. Blue
00:05:02 --> 00:05:05 tints point to titanium rich volcanic
00:05:05 --> 00:05:08 rock. Browns track iron content,
00:05:08 --> 00:05:11 greens signal glass made in volcanic
00:05:11 --> 00:05:14 fire fountains or melted by impacts.
00:05:14 --> 00:05:17 Christina Koch described one Regis as a
00:05:17 --> 00:05:20 jaundiced cheek of the moon, which
00:05:20 --> 00:05:22 I think is the best geology description I've
00:05:22 --> 00:05:23 heard this year.
00:05:23 --> 00:05:25 Anna: The scientists will compare those
00:05:25 --> 00:05:28 descriptions and the handheld photographs
00:05:28 --> 00:05:30 with data from the Lunar Reconnaissance
00:05:30 --> 00:05:33 Orbiter. The point isn't to replace
00:05:33 --> 00:05:35 the orbiter, it's to learn how human
00:05:36 --> 00:05:39 perception of colour and brightness shifts
00:05:39 --> 00:05:41 with the angle of the light. Because
00:05:41 --> 00:05:43 astronauts on the surface will be making
00:05:43 --> 00:05:46 those judgments with no orbiter to check
00:05:46 --> 00:05:46 against.
00:05:47 --> 00:05:50 Avery: NASA shows one worked example, the
00:05:50 --> 00:05:52 crew's photographs of the Orientale Basin.
00:05:53 --> 00:05:55 The great bullseye on the moon's western limb
00:05:56 --> 00:05:58 matched pixel for pixel onto the orbiter's
00:05:58 --> 00:06:01 maps of elevation, roughness, rock cover
00:06:01 --> 00:06:04 and brightness. A human snapshot
00:06:04 --> 00:06:06 pinned to years of orbiter data.
00:06:06 --> 00:06:09 Which brings us to the third theme, the
00:06:09 --> 00:06:12 terminator, the line between lunar day and
00:06:12 --> 00:06:15 night. The science team asked the crew to
00:06:15 --> 00:06:17 study it because the lighting there, sun
00:06:17 --> 00:06:20 skimming the horizon, shadows stretching for
00:06:20 --> 00:06:22 kilometres, mimics the Moon's south pole,
00:06:22 --> 00:06:24 where Artemis wants to land.
00:06:25 --> 00:06:28 Anna: Victor Glover described Islands
00:06:28 --> 00:06:31 of terrain standing completely surrounded by
00:06:31 --> 00:06:33 darkness. Peaks catching sunlight while
00:06:34 --> 00:06:35 everything around them is in shadow.
00:06:36 --> 00:06:39 NASA's image shows the crater Carnot,
00:06:39 --> 00:06:41 about 130 kilometres across,
00:06:42 --> 00:06:43 right on that line
00:06:44 --> 00:06:47 Avery: in Kock during the eclipse, as the limb
00:06:47 --> 00:06:49 lit up from behind, you can actually see
00:06:49 --> 00:06:52 mountains. That's the practical payoff,
00:06:53 --> 00:06:55 knowing what level of detail, what cameras,
00:06:55 --> 00:06:58 what lighting future crews need to work
00:06:58 --> 00:06:59 safely near the pole.
00:06:59 --> 00:07:02 Anna: The crew also watched the sun's corona for
00:07:02 --> 00:07:05 nearly an hour. And Hansen sketched
00:07:05 --> 00:07:07 one streamer that appeared to pulse.
00:07:08 --> 00:07:10 That's an observation of the solar atmosphere
00:07:10 --> 00:07:13 that drives space weather, made by someone
00:07:13 --> 00:07:15 with no instrument but his eyes.
00:07:16 --> 00:07:19 Avery: And then there's hello world. The photo of
00:07:19 --> 00:07:21 the whole Earth taken on day two from about
00:07:21 --> 00:07:24 10 kilometres out. It looks sunlit.
00:07:24 --> 00:07:27 It isn't. It was lit by moonlight.
00:07:27 --> 00:07:29 Scientists stayed up through the night
00:07:29 --> 00:07:31 combing it and found weather systems,
00:07:31 --> 00:07:34 auroras at both poles. A Saharan dust
00:07:34 --> 00:07:37 plume, lightning over the Congo Basin,
00:07:37 --> 00:07:40 city lights across North Africa and Iberia
00:07:40 --> 00:07:43 and and zodiacal light capped by Venus.
00:07:43 --> 00:07:46 Anna: Koch put it beautifully. The Moon
00:07:46 --> 00:07:48 was a light sponge and the Earth
00:07:49 --> 00:07:50 a light mirror.
00:07:51 --> 00:07:54 Avery: Now the southern note. During the eclipse,
00:07:54 --> 00:07:57 the crew photographed the milky Way. And
00:07:57 --> 00:07:59 NASA's labelled version is a southern sky
00:07:59 --> 00:08:01 chart. Bella Carina,
00:08:02 --> 00:08:05 Musca Crux, the Southern
00:08:05 --> 00:08:07 Cross, Centaurus, the Carina
00:08:07 --> 00:08:10 Nebula and the Large Magellanic Cloud.
00:08:11 --> 00:08:13 Four astronauts from North America
00:08:13 --> 00:08:16 beyond the Moon, pointing their camera at our
00:08:16 --> 00:08:17 sky.
00:08:17 --> 00:08:20 Anna: Hansen said the stars had a depth he'd
00:08:20 --> 00:08:23 never seen from Earth, that brighter ones
00:08:23 --> 00:08:25 seemed nearer. That's perception, not
00:08:25 --> 00:08:28 distance, and he knew it. But it's exactly
00:08:28 --> 00:08:31 the kind of honest human observation this
00:08:31 --> 00:08:32 report is full of.
00:08:34 --> 00:08:37 Avery: So the caveats one more time. This is
00:08:37 --> 00:08:39 a preliminary report. The flash count is
00:08:39 --> 00:08:42 five. The sizes are estimates from
00:08:42 --> 00:08:45 brightness. And the real science happens now
00:08:45 --> 00:08:48 as researchers match what the crew said to
00:08:48 --> 00:08:50 where they were looking and what the orbiters
00:08:50 --> 00:08:50 measured.
00:08:51 --> 00:08:53 Anna: There's also a quieter result in the
00:08:53 --> 00:08:56 operations report. Artemis 2 was the
00:08:56 --> 00:08:59 first time NASA ran a modern science backroom
00:08:59 --> 00:09:01 for a crewed lunar flight. A lunar
00:09:01 --> 00:09:04 science team in Mission Control in Houston,
00:09:04 --> 00:09:06 new flight controller roles, Scientists
00:09:06 --> 00:09:08 talking through what the crew should look at
00:09:08 --> 00:09:08 next.
00:09:09 --> 00:09:12 Avery: NASA's photo of that room. The deputy Lunar
00:09:12 --> 00:09:14 science lead, Marie Henderson and her
00:09:14 --> 00:09:16 colleagues reacting as the descriptions came
00:09:16 --> 00:09:19 in, tells you how much the moment meant to
00:09:19 --> 00:09:22 them. Learning how scientists and astronauts
00:09:22 --> 00:09:24 work together in real time is half the reason
00:09:24 --> 00:09:26 this flight carried a science plan at all.
00:09:27 --> 00:09:29 Anna: NASA calls it a relay race.
00:09:30 --> 00:09:33 Decades of robotic data handed to the crew
00:09:33 --> 00:09:36 and the crew's observations handed back.
00:09:36 --> 00:09:38 The next leg is Artemis 3.
00:09:39 --> 00:09:42 Then a Ah, crew on the surface and for
00:09:42 --> 00:09:44 once the science team had people at the
00:09:44 --> 00:09:47 window. Five flashes says that was
00:09:47 --> 00:09:48 worth it.
00:09:48 --> 00:09:51 Avery: Next, hypernovae.
00:09:51 --> 00:09:54 In theory they're the most powerful stellar
00:09:54 --> 00:09:57 explosions. There are a very massive,
00:09:57 --> 00:10:00 fast spinning star collapsing and releasing
00:10:00 --> 00:10:02 at least 10 times the energy of an ordinary
00:10:02 --> 00:10:05 supernova. And one strand of evidence
00:10:05 --> 00:10:08 for them has been chemical. A handful
00:10:08 --> 00:10:10 of ancient stars whose makeup seemed only
00:10:10 --> 00:10:13 explicable if they'd formed from hypernova
00:10:13 --> 00:10:14 debris.
00:10:14 --> 00:10:17 Anna: This is stellar archaeology, isn't it? You
00:10:17 --> 00:10:19 can't watch a star explode 13 billion years
00:10:19 --> 00:10:22 ago, but you can read the debris in the stars
00:10:22 --> 00:10:23 that form formed from it.
00:10:23 --> 00:10:26 Avery: Exactly. The oldest, most metal poor
00:10:26 --> 00:10:28 stars carry the chemical signature of the
00:10:28 --> 00:10:31 generation before them. So a ah, weird
00:10:31 --> 00:10:33 abundance pattern becomes evidence for a
00:10:33 --> 00:10:34 weird explosion.
00:10:35 --> 00:10:37 Anna: And a pair of papers from University College
00:10:37 --> 00:10:40 London says that Strand doesn't hold.
00:10:40 --> 00:10:43 Avery: Anmol Aggarwal, a PhD student at
00:10:43 --> 00:10:46 UH, UCL's Muller Space Science Laboratory,
00:10:46 --> 00:10:49 and Ralph Schoenrick, two papers
00:10:49 --> 00:10:51 in monthly Notices of the Royal Astronomical
00:10:51 --> 00:10:54 Society. Quick disclosure. The first
00:10:54 --> 00:10:57 was accepted back in March, the second is
00:10:57 --> 00:10:59 newer. UCL announced both on the 5th of
00:10:59 --> 00:11:00 October.
00:11:00 --> 00:11:02 Anna: So what's the argument?
00:11:02 --> 00:11:05 Avery: The old models treated a supernova
00:11:05 --> 00:11:08 as a well stirred pot. The dying
00:11:08 --> 00:11:11 star's elements mixed evenly and the next
00:11:11 --> 00:11:13 generation of stars inherits that average.
00:11:14 --> 00:11:17 But real supernova remnants aren't like that.
00:11:18 --> 00:11:20 Oxygen can fly off one way,
00:11:20 --> 00:11:23 sulphur another. A star that forms
00:11:23 --> 00:11:25 downstream might be built from a few pieces
00:11:25 --> 00:11:28 of the explosion, not the whole recipe.
00:11:29 --> 00:11:31 Anna: So an odd chemical fingerprint doesn't need
00:11:31 --> 00:11:34 an exotic explosion. It might be an ordinary
00:11:34 --> 00:11:36 explosion, sampled unevenly.
00:11:37 --> 00:11:40 Avery: Exactly. They looked at four stars
00:11:40 --> 00:11:43 previously attributed to hypernovae. In
00:11:43 --> 00:11:45 three, an ordinary lopsided
00:11:45 --> 00:11:47 supernova was statistically favoured.
00:11:48 --> 00:11:51 The fourth is a red giant in the Milky Way's
00:11:51 --> 00:11:54 halo, rich in heavy elements like silver
00:11:54 --> 00:11:57 and uranium. It had been argued that
00:11:57 --> 00:11:59 a neutron star merger couldn't explain it
00:11:59 --> 00:12:01 because the star seemed to form too early for
00:12:01 --> 00:12:02 one.
00:12:02 --> 00:12:03 Anna: But.
00:12:03 --> 00:12:06 Avery: But it's moving fast and orbiting
00:12:06 --> 00:12:08 backwards relative to most of the galaxy.
00:12:09 --> 00:12:11 Which suggests it was born in a small
00:12:11 --> 00:12:14 dwarf galaxy where metal pore stars can
00:12:14 --> 00:12:16 form much later. And was swallowed
00:12:16 --> 00:12:19 afterwards. Their verdict, one neutron
00:12:19 --> 00:12:22 star merger plus one ordinary supernova.
00:12:23 --> 00:12:25 Anna: Now the caveat, and it's important
00:12:26 --> 00:12:28 we have directly observed some
00:12:28 --> 00:12:30 extraordinarily energetic explosions.
00:12:31 --> 00:12:33 Broad lined supernovae tied to gamma ray
00:12:33 --> 00:12:35 bursts like the one we covered in episode
00:12:35 --> 00:12:38 160. This work doesn't say those
00:12:38 --> 00:12:40 didn't happen. It says the chemical
00:12:40 --> 00:12:43 fingerprints in these old stars no longer
00:12:43 --> 00:12:44 require hypernovae.
00:12:45 --> 00:12:47 Avery: And the southern footnote. Hunting the oldest
00:12:47 --> 00:12:50 stars is something Australia does well. In
00:12:50 --> 00:12:52 2014, the ANU's SkyMapper
00:12:52 --> 00:12:55 telescope at Siding Spring found one of the
00:12:55 --> 00:12:58 most iron poor stars known. And its
00:12:58 --> 00:13:00 chemistry was also explained by a low energy
00:13:00 --> 00:13:01 supernova.
00:13:01 --> 00:13:04 Same lesson. Be careful what you build on one
00:13:04 --> 00:13:05 strange star.
00:13:06 --> 00:13:09 Anna: Next story. Today, Jupiter's magnetic
00:13:09 --> 00:13:11 field is the biggest structure in the
00:13:11 --> 00:13:13 planetary solar system. And wrapped around
00:13:13 --> 00:13:16 the planet's equator is something called the
00:13:16 --> 00:13:18 magneto disc, a vast sheet of
00:13:18 --> 00:13:21 electric current fed by sulphur and
00:13:21 --> 00:13:23 oxygen, spewed out by the volcanic moon
00:13:23 --> 00:13:26 IO and flung outward by Jupiter's 10 hour
00:13:26 --> 00:13:27 spin.
00:13:27 --> 00:13:30 Avery: And Juno is the right spacecraft to test it.
00:13:30 --> 00:13:33 Since 2016, it has looped over Jupiter's
00:13:33 --> 00:13:35 poles on long elongated orbits,
00:13:36 --> 00:13:38 slicing through the magnetosphere at
00:13:38 --> 00:13:40 different distances and local times, with
00:13:40 --> 00:13:43 instruments sampling the field and the
00:13:43 --> 00:13:44 particles directly.
00:13:44 --> 00:13:46 Anna: Which matters for what comes next.
00:13:47 --> 00:13:50 Avery: And the textbook picture of that sheet is
00:13:50 --> 00:13:52 fairly simple. Jupiter's magnetic
00:13:52 --> 00:13:55 axis is tilted, so as the planet
00:13:55 --> 00:13:58 turns, the sheet rocks up and down like a
00:13:58 --> 00:14:01 warped record. A spacecraft sitting in
00:14:01 --> 00:14:04 it should cross the sheet about twice per
00:14:04 --> 00:14:04 rotation.
00:14:05 --> 00:14:07 Anna: A team led by Roylong Guo at
00:14:07 --> 00:14:10 Shandong University with co
00:14:10 --> 00:14:13 authors including Dennis Grodent and
00:14:13 --> 00:14:15 Bertrand Bonfont from Liege, went through
00:14:15 --> 00:14:18 Juno's magnetic field and energetic particle
00:14:18 --> 00:14:21 data published in Science China
00:14:21 --> 00:14:24 Earth sciences release on the 6th
00:14:24 --> 00:14:27 of October. The
00:14:27 --> 00:14:29 manuscript itself dates back to 2025.
00:14:30 --> 00:14:31 Avery: And what did they find?
00:14:32 --> 00:14:34 Anna: During active periods, Juno didn't
00:14:34 --> 00:14:37 cross the sheet twice. It crossed it
00:14:37 --> 00:14:40 again and again. In one case, four
00:14:40 --> 00:14:43 times in 10 minutes. And almost every
00:14:43 --> 00:14:46 crossing carried the signature of magnetic
00:14:46 --> 00:14:49 reconnection, where field lines snap and
00:14:49 --> 00:14:51 reconnect and release energy along
00:14:51 --> 00:14:54 with bursts of energised electrons and
00:14:54 --> 00:14:55 ions.
00:14:56 --> 00:14:57 Avery: So it's not just flapping?
00:14:58 --> 00:15:01 Anna: No, um. The orientation analysis
00:15:01 --> 00:15:03 shows a kink like surface wave
00:15:04 --> 00:15:06 ripples lasting from minutes to over an
00:15:06 --> 00:15:09 hour. The authors argue that many
00:15:09 --> 00:15:12 small reconnection sites scattered across
00:15:12 --> 00:15:15 about 100 degrees of longitude keep
00:15:15 --> 00:15:18 breaking the field and shoving the sheet off
00:15:18 --> 00:15:21 balance. And because Jupiter spins
00:15:21 --> 00:15:23 so fast, the whole crumpled sheet is carried
00:15:23 --> 00:15:26 around with the planet. Their image is a
00:15:26 --> 00:15:29 crumpled tablecloth on a spinning turntable.
00:15:29 --> 00:15:31 Avery: That's different from Earth, isn't it?
00:15:31 --> 00:15:34 Anna: Very. In Earth's magnetic tail,
00:15:35 --> 00:15:37 a kink wave travels away from a reconnection
00:15:37 --> 00:15:40 site. At Jupiter, there's no fixed
00:15:40 --> 00:15:43 period and reconnection everywhere,
00:15:43 --> 00:15:46 which points to a rotating rippled structure
00:15:46 --> 00:15:48 instead of. It matters, because that
00:15:48 --> 00:15:51 structure helps decide how IO's material
00:15:51 --> 00:15:54 is accelerated, how it's pushed inward,
00:15:54 --> 00:15:57 and how energy reaches Jupiter's auroras.
00:15:57 --> 00:15:59 A quiet sheet is a simpler machine.
00:16:00 --> 00:16:02 A crumpled one is messier and
00:16:02 --> 00:16:04 probably more honest.
00:16:04 --> 00:16:07 Avery: For about 90 years, white dwarfs have had a
00:16:07 --> 00:16:10 weight limit. Subramani and Chandrasekhar
00:16:10 --> 00:16:11 showed that a white dwarf supported by
00:16:11 --> 00:16:14 electron pressure can, can't exceed about
00:16:14 --> 00:16:16 1.4 solar masses. Push it past
00:16:16 --> 00:16:19 that and a, uh, carbon oxygen white dwarf
00:16:19 --> 00:16:21 ignites and explodes as a type 1A
00:16:21 --> 00:16:22 supernova.
00:16:22 --> 00:16:25 Anna: Which is why type 1A supernovae
00:16:25 --> 00:16:28 are such good standard candles. Same
00:16:28 --> 00:16:30 trigger, similar brightness.
00:16:30 --> 00:16:33 Avery: It's how cosmic acceleration was discovered
00:16:34 --> 00:16:36 and why we leaned on them for the dark energy
00:16:36 --> 00:16:38 story back in episodes 193 and
00:16:38 --> 00:16:41 195. So a, uh, paper saying the
00:16:41 --> 00:16:43 limit can bend gets attention.
00:16:44 --> 00:16:45 Anna: Who's saying that?
00:16:45 --> 00:16:48 Avery: Zenya zoo Reich, a PhD student,
00:16:48 --> 00:16:51 and Bani Brata Mukopadier at the Indian
00:16:51 --> 00:16:53 Institute of Science with collaborators
00:16:53 --> 00:16:56 including Christopher Tout, whose Cambridge
00:16:56 --> 00:16:58 group's Stellar Evolution Code Stars they
00:16:58 --> 00:17:01 modified Astrophysical Journal letters
00:17:01 --> 00:17:03 release on the 9th of October.
00:17:03 --> 00:17:05 Anna: And what did they do?
00:17:05 --> 00:17:08 Avery: They added magnetic fields and white dwarf
00:17:08 --> 00:17:11 cooling to stars and followed stars
00:17:11 --> 00:17:13 from the main sequence all the way to white
00:17:13 --> 00:17:16 dwarfs feeding off a companion. In their
00:17:16 --> 00:17:19 example, a, uh, 1.02 solar mass
00:17:19 --> 00:17:22 white dwarf born from an 8 solar mass star
00:17:22 --> 00:17:25 accretes. Uh, slowly the field starts. Too
00:17:25 --> 00:17:28 weak to matter. But as mass piles on, the
00:17:28 --> 00:17:30 star contracts, the field is squeezed and
00:17:30 --> 00:17:33 strengthens and magnetic pressure starts
00:17:33 --> 00:17:34 carrying some of the load.
00:17:35 --> 00:17:38 Anna: So the field is doing work the
00:17:38 --> 00:17:39 electrons can't?
00:17:40 --> 00:17:42 Avery: In effect, yes, magnetic pressure adds
00:17:42 --> 00:17:45 support. So the usual relationship between
00:17:45 --> 00:17:48 a white dwarf's mass and its radius
00:17:48 --> 00:17:51 changes. The team even suggests it might
00:17:51 --> 00:17:53 explain why some well studied white dwarfs
00:17:53 --> 00:17:55 look larger than their masses predict.
00:17:56 --> 00:17:58 And it keeps growing
00:17:59 --> 00:18:02 to about 2.4 solar masses in their
00:18:02 --> 00:18:05 magnetised model against 1.4 without the
00:18:05 --> 00:18:07 field. And observers have seen a few
00:18:07 --> 00:18:10 overluminous type Ia supernovae that hint at
00:18:10 --> 00:18:13 progenitors up to around 2.8 solar masses.
00:18:13 --> 00:18:16 So there's something to explain caveats?
00:18:17 --> 00:18:20 Several. That's one model, not a survey of
00:18:20 --> 00:18:22 outcomes. Super Chandrasekar white
00:18:22 --> 00:18:25 dwarfs have been argued over for more than a
00:18:25 --> 00:18:27 decade and the cosmology doesn't hinge on it
00:18:27 --> 00:18:30 directly. Astronomers calibrate type
00:18:30 --> 00:18:33 Ia supernovae empirically from their light
00:18:33 --> 00:18:36 curves. The real question is whether a hidden
00:18:36 --> 00:18:39 subpopulation is quietly mixed in. That's
00:18:39 --> 00:18:40 worth knowing either way.
00:18:40 --> 00:18:42 Anna: Two missions in countdown mode.
00:18:43 --> 00:18:46 First, ESA's Hera. A
00:18:46 --> 00:18:48 week ago, on its second birthday in space,
00:18:49 --> 00:18:51 it caught its first glimpse of Didymus,
00:18:52 --> 00:18:54 a single pixel from about
00:18:54 --> 00:18:57 236 kilometres.
00:18:57 --> 00:19:00 And early on Thursday the 15th European
00:19:00 --> 00:19:03 time, it fires three thrusters for
00:19:03 --> 00:19:06 93 minutes to break towards the asteroid DART
00:19:06 --> 00:19:07 hit in 2022.
00:19:08 --> 00:19:11 Avery: That's BRM1. A second
00:19:11 --> 00:19:14 shorter burn follows on the 22nd. Then
00:19:14 --> 00:19:16 three small transition burns later this month
00:19:17 --> 00:19:20 and close in characterization from 25 to
00:19:20 --> 00:19:22 30 kilometres in November and December.
00:19:23 --> 00:19:25 And the Australian thread. ESA's Flight
00:19:25 --> 00:19:27 Dynamics Tim will check the burn using
00:19:27 --> 00:19:30 signals through its 35 metre antenna at uh,
00:19:30 --> 00:19:31 New Norcia in Western Australia.
00:19:32 --> 00:19:35 Anna: And Jax's Martian moons exploration mission
00:19:35 --> 00:19:38 launches on an H3 from Tanegashima
00:19:38 --> 00:19:40 at 6:41 Tuesday morning, Sydney time.
00:19:41 --> 00:19:42 Monday afternoon in the Americas.
00:19:43 --> 00:19:45 It will land on Phobos, deploy a French
00:19:45 --> 00:19:48 German rover and its samples are deemed to
00:19:48 --> 00:19:50 land in South Australia in 2031.
00:19:51 --> 00:19:54 Full curtain raiser on Monday. Skywatch
00:19:54 --> 00:19:57 and tonight starts with the Moon. It's a slim
00:19:57 --> 00:20:00 crescent around a uh, sixth lit and
00:20:00 --> 00:20:02 it's sliding past Antares, the red heart of
00:20:02 --> 00:20:05 Scorpius. And how close
00:20:05 --> 00:20:08 depends very much on where you are.
00:20:08 --> 00:20:11 Avery: It does. From New York at the end of
00:20:11 --> 00:20:14 civil twilight about 6:45. The moon
00:20:14 --> 00:20:17 is only 1.3 degrees from Antares
00:20:17 --> 00:20:20 under three moon widths but just 11
00:20:20 --> 00:20:23 degrees up. In the southwest, Los Angeles
00:20:23 --> 00:20:26 gets 2.3 degrees with the moon 16
00:20:26 --> 00:20:29 degrees up London 2.3
00:20:29 --> 00:20:31 degrees. But the moon is barely 2 degrees
00:20:31 --> 00:20:34 above the horizon, so you'll need a clear
00:20:34 --> 00:20:35 southwestern view.
00:20:35 --> 00:20:36 Anna: And Sydney.
00:20:37 --> 00:20:40 Avery: From Sydney the pair are 7 degrees
00:20:40 --> 00:20:43 apart. But the moon is 36 degrees up
00:20:43 --> 00:20:46 at 7:30, high and easy. And
00:20:46 --> 00:20:48 in some parts of the world the Moon actually
00:20:48 --> 00:20:50 covers Antares tonight, though none of our
00:20:50 --> 00:20:52 four cities see that in a dark sky.
00:20:53 --> 00:20:55 Anna: Next, the inner planets. And this
00:20:55 --> 00:20:57 week favours the south.
00:20:57 --> 00:21:00 Avery: Mercury is still well placed after last
00:21:00 --> 00:21:03 week's greatest elongation. From Sydney
00:21:03 --> 00:21:05 it's 24 degrees up at sunset and sets about
00:21:05 --> 00:21:08 two hours after the sun. From Los Angeles
00:21:08 --> 00:21:11 it's 10 degrees up New York 7,
00:21:11 --> 00:21:14 London barely 3. And Venus
00:21:14 --> 00:21:17 is diving towards the sun, passing closest
00:21:17 --> 00:21:19 around the 24th. From Sydney it's still
00:21:19 --> 00:21:22 15 degrees up at sunset. A brilliant
00:21:22 --> 00:21:25 magnitude minus 4. From the northern
00:21:25 --> 00:21:26 cities it's already gone.
00:21:27 --> 00:21:28 Anna: Why the lopsided view?
00:21:29 --> 00:21:32 Avery: Our regular spring story around now the
00:21:32 --> 00:21:34 evening ecliptic stands almost straight up
00:21:34 --> 00:21:36 from the western horizon in the southern
00:21:36 --> 00:21:39 hemisphere and lies flat in the northern. A
00:21:39 --> 00:21:41 planet the same angle from the sun ends uh up
00:21:41 --> 00:21:44 far higher above a southern horizon. In March
00:21:44 --> 00:21:46 it flips and the north gets the good evening
00:21:46 --> 00:21:48 apparitions, which brings
00:21:48 --> 00:21:50 Anna: the eye safety reminder.
00:21:51 --> 00:21:54 Avery: It does and it's non negotiable with
00:21:54 --> 00:21:57 Mercury and Venus so close to The Sun. Wait
00:21:57 --> 00:21:59 until the sun has fully set before you sweep
00:21:59 --> 00:22:01 with binoculars or a telescope.
00:22:02 --> 00:22:04 Never look at the sun through any optical
00:22:04 --> 00:22:06 instrument and only ever look at the sun
00:22:06 --> 00:22:09 directly with eclipse glasses or solar
00:22:09 --> 00:22:11 filter certified to the ISO
00:22:11 --> 00:22:14 1123122 standard.
00:22:14 --> 00:22:17 Anna: Now the north gets its turn before
00:22:17 --> 00:22:20 dawn. Mars has just drifted
00:22:20 --> 00:22:22 through the Beehive cluster in Cancer
00:22:23 --> 00:22:25 closest on the 11th and it's still
00:22:25 --> 00:22:28 only about 2 degrees away. A lovely
00:22:28 --> 00:22:31 binocular field at nautical
00:22:31 --> 00:22:33 dawn. Mars is 50 to 60
00:22:33 --> 00:22:36 degrees up from the northern cities. Jupiter
00:22:36 --> 00:22:39 about 45 degrees up and brighter
00:22:39 --> 00:22:42 hm from Sydney. They're lower. Mars
00:22:42 --> 00:22:45 23 degrees. They're 12 and a half
00:22:45 --> 00:22:48 degrees apart today and closing down
00:22:48 --> 00:22:50 to about 1.2 degrees on the 16th of
00:22:50 --> 00:22:53 November. And through the night.
00:22:53 --> 00:22:56 Avery: Saturn, 10 days past opposition,
00:22:56 --> 00:22:59 rising in the east at dusk. Magnitude
00:22:59 --> 00:23:02 0.4. Its rings opened only about
00:23:02 --> 00:23:05 7 degrees. The southern taurids
00:23:05 --> 00:23:08 Debris from Comet Encke reach an early peak
00:23:08 --> 00:23:10 around now just a few meteors an hour,
00:23:10 --> 00:23:13 but they're slow and the occasional one is a
00:23:13 --> 00:23:16 fireball. And the radiant is well up from
00:23:16 --> 00:23:19 both hemispheres by 11pm the moon sets
00:23:19 --> 00:23:21 early this week, so the sky's dark
00:23:21 --> 00:23:23 Anna: and a, uh, binocular challenge.
00:23:24 --> 00:23:26 Avery: The asteroid Vesta at opposition
00:23:26 --> 00:23:29 yesterday. Magnitude 6.5
00:23:29 --> 00:23:32 in northern Cetus, about 5 degrees north
00:23:32 --> 00:23:35 of Theta Cetae. And this one leans
00:23:35 --> 00:23:38 south at 11pm It's 49 degrees up from
00:23:38 --> 00:23:40 Sydney, around 40 to 45 from the US
00:23:40 --> 00:23:43 cities, 30 from London. Sketch
00:23:43 --> 00:23:46 the field, come back the next night and see
00:23:46 --> 00:23:47 which dot moved.
00:23:47 --> 00:23:50 First quarter Moon is on the 19th Sydney
00:23:50 --> 00:23:50 time.
00:23:50 --> 00:23:53 Anna: That's the show today. Five
00:23:53 --> 00:23:56 faint flashes on the far side of the Moon,
00:23:56 --> 00:23:58 a crack in the case for hypernovae,
00:23:59 --> 00:24:02 Jupiter's crumpled magneta disc and white
00:24:02 --> 00:24:04 dwarfs that might be heavier than the
00:24:04 --> 00:24:05 rulebook allows.
00:24:06 --> 00:24:08 Avery: Tomorrow we'll have the result of Hera's big
00:24:08 --> 00:24:11 breaking burn. And on Monday, a full
00:24:11 --> 00:24:14 curtain raiser for MMX ahead of Tuesday's
00:24:14 --> 00:24:14 launch.
00:24:15 --> 00:24:17 Anna: If you've got a question or you've ever
00:24:17 --> 00:24:19 caught an impact flash on the Moon yourself,
00:24:20 --> 00:24:21 tell us through the contact
00:24:21 --> 00:24:23 form@astronomydaily.IO we
00:24:23 --> 00:24:24 read everyone.
00:24:25 --> 00:24:28 Avery: Show notes and links are there too. And if
00:24:28 --> 00:24:31 you can catch Mercury low in the west
00:24:31 --> 00:24:33 after sunset this week, I'm
00:24:33 --> 00:24:36 Anna. I'm Avery. Clear Skies.
00:24:50 --> 00:24:51 Anna: Sa.