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00:00:00 --> 00:00:03 Anna: Hi, everyone, and welcome back to astronomy
00:00:03 --> 00:00:05 daily. Today, 10
00:00:05 --> 00:00:08 cracks in the face of the Moon, and every one
00:00:08 --> 00:00:11 of them tells the same story. Our Moon
00:00:11 --> 00:00:13 is still shrinking, and today
00:00:13 --> 00:00:16 Avery: we know by how much. Plus, a
00:00:16 --> 00:00:18 PhD student in Sydney has drawn the first
00:00:18 --> 00:00:20 soil map of Mars.
00:00:20 --> 00:00:23 A dark energy telescope has stumbled onto a
00:00:23 --> 00:00:25 brand new comet. And two planets
00:00:25 --> 00:00:28 everyone calls twins turn out to be more
00:00:28 --> 00:00:29 like distant cousins.
00:00:30 --> 00:00:32 Anna: We'll also catch up on Japan's Phobos
00:00:32 --> 00:00:35 mission, now safely on its way, and a
00:00:35 --> 00:00:37 telescope that's turned out even sharper than
00:00:37 --> 00:00:38 its builders hoped.
00:00:39 --> 00:00:41 Avery: It's Tuesday, the 20th of October
00:00:41 --> 00:00:44 2026. This is Astronomy AstroDailyPod
00:00:44 --> 00:00:46 series five, episode 209.
00:00:47 --> 00:00:47 I'm, um, Avery.
00:00:48 --> 00:00:50 Anna: And I'm Anna. Let's get into it.
00:00:51 --> 00:00:52 Avery: Here we go then.
00:00:52 --> 00:00:54 Anna: Most of us grow up thinking of the Moon as
00:00:54 --> 00:00:56 finished, geologically dead.
00:00:57 --> 00:00:59 Everything interesting happened billions of
00:00:59 --> 00:01:02 years ago, and since then, it has just
00:01:02 --> 00:01:05 sat there collecting craters. A
00:01:05 --> 00:01:07 new study published last Wednesday in the
00:01:07 --> 00:01:09 Planetary Science Journal says that picture
00:01:09 --> 00:01:12 is wrong in a very specific, measurable way.
00:01:13 --> 00:01:16 Avery: This comes from Tom Waters, a, uh, scientist
00:01:16 --> 00:01:18 Emeritus at the Smithsonian's National Air
00:01:18 --> 00:01:20 and Space Museum with Maria Banks at NASA
00:01:20 --> 00:01:23 Goddard Corporation, Cole Knyphaver and Mark
00:01:23 --> 00:01:25 Robinson, who leads the camera on NASA's
00:01:25 --> 00:01:26 Lunar Reconnaissance Orbiter.
00:01:26 --> 00:01:29 Anna: And Robinson's name should ring a bell for
00:01:29 --> 00:01:31 regular listeners. His team's change
00:01:31 --> 00:01:34 detection work on that same camera gave us
00:01:34 --> 00:01:36 the brand new lunar crater we covered back in
00:01:36 --> 00:01:39 episode 196. So what did
00:01:39 --> 00:01:42 they find? More than 10 young
00:01:42 --> 00:01:45 faults spread right across the lunar surface.
00:01:45 --> 00:01:47 About 8 of them are what
00:01:47 --> 00:01:50 geologists call lobate scarps. And little
00:01:50 --> 00:01:53 over 2 are small ridges on the dark lunar
00:01:53 --> 00:01:54 plains.
00:01:54 --> 00:01:57 Avery: The maria paint us a picture of a lobate
00:01:57 --> 00:01:57 scarp.
00:01:58 --> 00:02:00 Anna: Imagine a cliff or a step
00:02:00 --> 00:02:03 running across the landscape. It forms when
00:02:03 --> 00:02:06 the crust is squeezed so hard it breaks and
00:02:06 --> 00:02:08 one side gets shoved up and over the other.
00:02:09 --> 00:02:11 That's a thrust fault on the Moon. They're
00:02:11 --> 00:02:14 usually tens of metres high and a few
00:02:14 --> 00:02:16 kilometres long, though the release shows one
00:02:16 --> 00:02:19 near the North Pole, inside a crater called
00:02:19 --> 00:02:22 Mouch's L, standing more than 100 metres
00:02:22 --> 00:02:22 tall.
00:02:23 --> 00:02:26 Avery: And, um, these are young. On
00:02:26 --> 00:02:28 the Moon, young is a relative word.
00:02:28 --> 00:02:31 Anna: Very relative. Young here means the last few
00:02:31 --> 00:02:34 hundred million years. The tell is that they
00:02:34 --> 00:02:36 look crisp, they cut straight through small
00:02:36 --> 00:02:38 craters, and they haven't been battered flat
00:02:38 --> 00:02:41 by later impacts over the age of the Moon.
00:02:41 --> 00:02:43 That's yesterday afternoon.
00:02:43 --> 00:02:46 Avery: So why is the Moon being squeezed at
00:02:46 --> 00:02:49 all? There's no plate tectonics up there.
00:02:49 --> 00:02:52 Anna: Exactly. And that's the key. The Moon's
00:02:52 --> 00:02:55 interior is still warm and it's slowly
00:02:55 --> 00:02:58 cooling. As rock cools, it contracts.
00:02:58 --> 00:03:00 The inside of the moon gets a little smaller
00:03:00 --> 00:03:02 and the rigid outer shell has to fit around
00:03:02 --> 00:03:05 it. Think of a grape drying into a raisin.
00:03:05 --> 00:03:08 Except the Moon's skin is brittle rock,
00:03:08 --> 00:03:11 so instead of wrinkling, it cracks and breaks
00:03:11 --> 00:03:12 along these thrust faults.
00:03:12 --> 00:03:15 Avery: And Earth tides add to it, don't they?
00:03:15 --> 00:03:18 Anna: They do. Earlier work by the same group
00:03:18 --> 00:03:21 showed the orientation of the faults.
00:03:21 --> 00:03:23 Only makes sense if you add tidal stresses
00:03:23 --> 00:03:26 from Earth on top of the global shrinking.
00:03:26 --> 00:03:28 But the shrinking is the engine.
00:03:28 --> 00:03:30 Avery: Here's the headline, then. Um, how much
00:03:30 --> 00:03:32 smaller has it gotten?
00:03:32 --> 00:03:34 Anna: The team added up how much the surface has
00:03:34 --> 00:03:36 been compressed across all of those faults,
00:03:36 --> 00:03:39 highlands and Maria together, and converted
00:03:39 --> 00:03:42 that into a change in radius. The answer is
00:03:42 --> 00:03:45 about 42 to 46 metres. The
00:03:45 --> 00:03:47 Smithsonian rounds it to 45. That's over
00:03:47 --> 00:03:50 roughly the last 400 to 800 million
00:03:50 --> 00:03:51 years.
00:03:52 --> 00:03:54 Avery: 45 metres off a radius of more
00:03:54 --> 00:03:57 than 1700 kilometres.
00:03:57 --> 00:03:58 That's tiny.
00:03:59 --> 00:04:01 Anna: It is. If the pace were steady,
00:04:02 --> 00:04:05 it works out to at most about 11 centimetres
00:04:05 --> 00:04:07 every million years. A tenth of a
00:04:07 --> 00:04:10 micrometre a year. Earth's tectonic plates
00:04:10 --> 00:04:12 move about a centimetre and a half a year,
00:04:12 --> 00:04:15 roughly the rate your fingernails grow. So
00:04:15 --> 00:04:18 the Moon is shrinking more than 100 times
00:04:18 --> 00:04:20 more slowly than Earth's plates move.
00:04:20 --> 00:04:22 Avery: And, um, this updates an older figure,
00:04:22 --> 00:04:22 doesn't it?
00:04:22 --> 00:04:25 Anna: It does. Waters team first raised
00:04:25 --> 00:04:28 this in 2010, when the orbiter's camera had
00:04:28 --> 00:04:31 turned up 14 new scarps. Back then,
00:04:31 --> 00:04:34 they offered a rough estimate of about 100
00:04:34 --> 00:04:37 metres. By 2015, the count was
00:04:37 --> 00:04:39 over 3. Now, with more than
00:04:39 --> 00:04:42 10 mapped, the number has firmed up
00:04:42 --> 00:04:45 and it's come in at less than half that early
00:04:45 --> 00:04:46 rough guess.
00:04:46 --> 00:04:48 Avery: So what's the surprise here? The Moon
00:04:48 --> 00:04:49 shrinking isn't new.
00:04:50 --> 00:04:53 Anna: The surprise is how little. Models of
00:04:53 --> 00:04:55 how the Moon should have cooled predict much
00:04:55 --> 00:04:57 more contraction than these faults record.
00:04:58 --> 00:05:01 And the team didn't find old, worn down
00:05:01 --> 00:05:03 scarps from earlier in lunar history. So
00:05:03 --> 00:05:05 it looks as if the widespread faulting
00:05:05 --> 00:05:07 started relatively late.
00:05:07 --> 00:05:10 Avery: Which means something held the heat in.
00:05:10 --> 00:05:13 Anna: That's their leading explanation. The ancient
00:05:13 --> 00:05:16 lunar crust was pulverised by billions of
00:05:16 --> 00:05:18 years of impacts into a thick, porous,
00:05:18 --> 00:05:21 heavily fractured layer called the mega
00:05:21 --> 00:05:24 regolith. Porous broken rock is a poor
00:05:24 --> 00:05:26 conductor of heat, so it may have acted like
00:05:26 --> 00:05:29 a blanket, keeping the interior warm and
00:05:29 --> 00:05:31 delaying the cooling and so delaying the
00:05:31 --> 00:05:34 shrinking. The paper also offers an
00:05:34 --> 00:05:37 alternative a strong, rigid outer
00:05:37 --> 00:05:39 shell that simply resisted breaking until the
00:05:39 --> 00:05:41 stress built past a threshold.
00:05:42 --> 00:05:44 Avery: And, um, they see a hint of that in where the
00:05:44 --> 00:05:46 faults are right.
00:05:46 --> 00:05:49 Anna: The thickest crust has the fewest faults,
00:05:49 --> 00:05:52 which also suggests those areas are the most
00:05:52 --> 00:05:53 stable.
00:05:53 --> 00:05:56 Avery: Regular listeners might feel a sense of
00:05:56 --> 00:05:57 deja vu here.
00:05:58 --> 00:06:00 Anna: Back in episode 192, we covered Mercury,
00:06:00 --> 00:06:03 where scarps were hiding under rough terrain
00:06:03 --> 00:06:05 and the planet had shrunk more than anyone
00:06:05 --> 00:06:08 counted. Here, it's the reverse. A, uh,
00:06:09 --> 00:06:11 careful count of nearly every fault finds the
00:06:11 --> 00:06:13 Moon shrank less than the theory expected.
00:06:14 --> 00:06:17 Same physics, opposite surprise. And
00:06:17 --> 00:06:19 it's a reminder we keep coming back to on
00:06:19 --> 00:06:22 this show. What you can count depends on how
00:06:22 --> 00:06:23 hard you looked.
00:06:23 --> 00:06:25 Avery: So we all need to look harder.
00:06:26 --> 00:06:28 Anna: It does. And this matters for anyone planning
00:06:28 --> 00:06:31 to live there. Waters calculates the
00:06:31 --> 00:06:33 compressional stress from this much shrinking
00:06:33 --> 00:06:36 at about 4 MPa. That lines
00:06:36 --> 00:06:38 up with the stress released in the shallow
00:06:38 --> 00:06:40 moonquakes that Apollo's seismometers
00:06:40 --> 00:06:43 recorded in the 1970s. On
00:06:43 --> 00:06:45 Earth, about 90% of seismic activity is
00:06:45 --> 00:06:48 concentrated along plate boundaries. The Moon
00:06:48 --> 00:06:51 is a single plate, so its faults are spread
00:06:51 --> 00:06:53 everywhere. Waters says the growth of
00:06:53 --> 00:06:55 existing faults and the formation of new ones
00:06:55 --> 00:06:57 is expected to continue today.
00:06:57 --> 00:07:00 Avery: So a, uh, moonquake could happen anywhere.
00:07:00 --> 00:07:03 Anna: That's the point. And we want to be careful
00:07:03 --> 00:07:05 with it. This isn't a warning that something
00:07:05 --> 00:07:08 is about to happen. It's about where
00:07:08 --> 00:07:11 you choose to put a permanent base. Waters
00:07:11 --> 00:07:13 earlier work crowned young faults near some
00:07:13 --> 00:07:15 of the candidate Artemis landing regions at
00:07:15 --> 00:07:18 the South Pole. If the thickest crust is the
00:07:18 --> 00:07:21 most stable, that's useful information for
00:07:21 --> 00:07:21 planners.
00:07:22 --> 00:07:23 Avery: What should we keep in mind?
00:07:24 --> 00:07:24 Anna: Three things.
00:07:25 --> 00:07:27 First, the rate assumes the shrinking
00:07:27 --> 00:07:30 happened at a steady pace, which it may not
00:07:30 --> 00:07:32 have. Second, the ages of these
00:07:32 --> 00:07:35 faults are relative. They come from how crisp
00:07:35 --> 00:07:38 they look and what they cut across, not from
00:07:38 --> 00:07:40 dated samples. And third, the
00:07:40 --> 00:07:42 moonquake point is about sighting and
00:07:42 --> 00:07:44 engineering, not prediction.
00:07:44 --> 00:07:46 Avery: And there's no Australian team on this one?
00:07:47 --> 00:07:49 Anna: No, and we won't pretend otherwise.
00:07:50 --> 00:07:52 But the Moon is the one world every listener
00:07:52 --> 00:07:55 can step outside and see north or south.
00:07:56 --> 00:07:58 Tonight's waxing gibbous will be up in the
00:07:58 --> 00:08:00 evening sky from Sydney to London.
00:08:01 --> 00:08:03 And somewhere on that face too small to
00:08:03 --> 00:08:05 see, a, uh, fault might be
00:08:05 --> 00:08:08 Avery: growing, staying in the solar system.
00:08:08 --> 00:08:11 And a story from right here in Sydney. If
00:08:11 --> 00:08:13 people are ever going to grow food on Mars,
00:08:13 --> 00:08:15 they'll need to know what they're growing it
00:08:15 --> 00:08:17 in. The University of Sydney has just
00:08:17 --> 00:08:19 produced the first comprehensive
00:08:19 --> 00:08:21 classification and map of Martian soils.
00:08:21 --> 00:08:22 Anna: Who's behind it?
00:08:23 --> 00:08:25 Avery: PhD student Daniel Irving from the Sydney
00:08:25 --> 00:08:27 Institute of Agriculture, working with
00:08:27 --> 00:08:30 Professor Alex McBratney, one of the world's
00:08:30 --> 00:08:33 leading soil scientists. The
00:08:33 --> 00:08:36 paper is in the soil science journal Ktena,
00:08:36 --> 00:08:38 went online at the start of this month, and
00:08:38 --> 00:08:39 the university announced it on Friday.
00:08:40 --> 00:08:42 Anna: And they've had to invent a word
00:08:43 --> 00:08:44 they have.
00:08:44 --> 00:08:46 Avery: On Earth, we talk about soils, but, uh,
00:08:46 --> 00:08:49 they've proposed calling Martian soil classes
00:08:49 --> 00:08:51 Areths, from Ares, the Greek name for
00:08:51 --> 00:08:54 Mars. The System groups almost 800
00:08:54 --> 00:08:57 million locations into a hierarchy. Ten
00:08:57 --> 00:08:59 broad realms, 100 assemblages
00:09:00 --> 00:09:03 and 2 detailed forms. The
00:09:03 --> 00:09:05 map covers 92% of the planet, based
00:09:05 --> 00:09:08 on what? Orbital observations
00:09:08 --> 00:09:11 and models of properties like texture,
00:09:11 --> 00:09:14 mineralogy, ph, and how deep the soil
00:09:14 --> 00:09:17 goes. As a test, they scored all
00:09:17 --> 00:09:20 2000 forms on how well they might support
00:09:20 --> 00:09:23 plants. One called Nohi
00:09:23 --> 00:09:24 Barreth, came out on top at
00:09:24 --> 00:09:26 0.93 out of 1.
00:09:27 --> 00:09:30 Its mottled profile is about 72%
00:09:30 --> 00:09:33 clay, with a pH of 6.8, which
00:09:33 --> 00:09:36 is close to neutral. It turns up in
00:09:36 --> 00:09:39 the mid latitudes around Tharsis
00:09:39 --> 00:09:42 Arabia Terra and Elysium Planitia,
00:09:42 --> 00:09:45 but on only 0.14% of the
00:09:45 --> 00:09:45 surface.
00:09:46 --> 00:09:49 Anna: So the Martian potato patch.
00:09:50 --> 00:09:53 Avery: Not quite. And the team is clear about that.
00:09:53 --> 00:09:56 These are candidate areas for closer study,
00:09:56 --> 00:09:59 not greenhouse sites. Nobody's going to plant
00:09:59 --> 00:10:01 crops straight into Martian dirt. Any habitat
00:10:01 --> 00:10:03 will need controlled environments, water,
00:10:04 --> 00:10:06 nutrients and treatment for harmful
00:10:06 --> 00:10:08 chemicals. In fact, the map doesn't yet
00:10:08 --> 00:10:11 include perchlorate, the toxic salt found
00:10:11 --> 00:10:14 across Mars, or nitrogen. And many of
00:10:14 --> 00:10:16 the Sol properties are inferred from orbit,
00:10:16 --> 00:10:19 so the classification will change as rovers
00:10:19 --> 00:10:20 measure more.
00:10:20 --> 00:10:23 Anna: What's the limiting factor for plants?
00:10:23 --> 00:10:25 Avery: Water holding capacity in
00:10:25 --> 00:10:28 73% of the forms they assessed.
00:10:28 --> 00:10:31 The next up is back on Earth, mixing Mars
00:10:31 --> 00:10:34 like substrates for the promising classes and
00:10:34 --> 00:10:35 growing crops in them under controlled
00:10:35 --> 00:10:36 conditions.
00:10:36 --> 00:10:39 Anna: And there's a payoff for Australia, too,
00:10:39 --> 00:10:40 there is.
00:10:40 --> 00:10:43 Avery: Martian soils have no organic matter,
00:10:43 --> 00:10:46 and McBratney points out that some of Earth's
00:10:46 --> 00:10:48 toughest arid soils have very little either.
00:10:49 --> 00:10:51 The work may help scientists think about
00:10:51 --> 00:10:53 places like the Pilbara and the Atacama
00:10:53 --> 00:10:56 differently. Mars as a lens on our own red
00:10:56 --> 00:10:57 dirt.
00:10:57 --> 00:11:00 Anna: Next, here's a discovery made almost
00:11:00 --> 00:11:02 by accident. The European Space
00:11:02 --> 00:11:05 Agency's Euclid telescope is built to map
00:11:05 --> 00:11:08 billions of galaxies so astronomers can study
00:11:08 --> 00:11:10 dark matter and dark energy. It is
00:11:10 --> 00:11:13 emphatically not a comet hunter. Yet
00:11:13 --> 00:11:15 ESA announced yesterday that Euclid has
00:11:15 --> 00:11:18 discovered its first previously unknown
00:11:18 --> 00:11:18 comet.
00:11:19 --> 00:11:22 Avery: How does a galaxy telescope trip over a
00:11:22 --> 00:11:22 comet?
00:11:23 --> 00:11:25 Anna: Through a, uh, PhD student and some clever
00:11:25 --> 00:11:28 software? Miko Poynton at the University
00:11:28 --> 00:11:31 of Helsinki wrote a programme to spot
00:11:31 --> 00:11:33 moving solar system objects in Euclid's
00:11:33 --> 00:11:36 images, mainly so they can be cleaned out of
00:11:36 --> 00:11:39 the galaxy data. In images taken between the
00:11:39 --> 00:11:42 16th and 24th of September, his software
00:11:42 --> 00:11:44 flagged a streak smeared across several
00:11:44 --> 00:11:47 frames. He tracked it into five image
00:11:47 --> 00:11:50 sets, 16 exposures in all, and found a
00:11:50 --> 00:11:52 fuzzy cloud around it. That's a, uh, coma.
00:11:52 --> 00:11:55 The sign of an active comet shedding dust and
00:11:55 --> 00:11:55 gas.
00:11:56 --> 00:11:57 Avery: And it checked out?
00:11:57 --> 00:12:00 Anna: No, no match in any catalogue. It was
00:12:00 --> 00:12:02 reported to the International Astronomical
00:12:02 --> 00:12:05 Union's Minor Planet Centre. Global ground
00:12:05 --> 00:12:07 based observers followed up and it was
00:12:07 --> 00:12:09 confirmed as a comet on 8th October.
00:12:09 --> 00:12:11 It's now officially C
00:12:12 --> 00:12:14 2026 S1 Euclid.
00:12:15 --> 00:12:15 Avery: Where is it?
00:12:16 --> 00:12:19 Anna: About 1.3 billion kilometres from Earth,
00:12:19 --> 00:12:21 roughly between the orbits of Jupiter and
00:12:21 --> 00:12:24 Saturn. But it isn't in the plane of
00:12:24 --> 00:12:26 the planets. From the sun's point of view,
00:12:26 --> 00:12:29 it's almost straight up on a steep orbit
00:12:29 --> 00:12:31 that takes thousands of years to complete.
00:12:32 --> 00:12:33 Avery: Why is that a lucky catch?
00:12:34 --> 00:12:36 Anna: Because Euclid deliberately avoids the band
00:12:36 --> 00:12:38 of sky along the plane of the solar system,
00:12:38 --> 00:12:40 where comets and asteroids are most common,
00:12:41 --> 00:12:43 since the dust there adds glare and it
00:12:43 --> 00:12:45 usually photographs each patch of sky only
00:12:45 --> 00:12:48 once. So a comet has to wander through the
00:12:48 --> 00:12:51 right field at the right time. Euclid archive
00:12:51 --> 00:12:54 scientist Bruno Altieri called it a happy
00:12:54 --> 00:12:54 coincidence.
00:12:55 --> 00:12:57 Avery: Any bigger significance?
00:12:57 --> 00:13:00 Anna: Two things. It was a real world test of how
00:13:00 --> 00:13:02 Euclid could alert ESA's future Comet
00:13:02 --> 00:13:04 Interceptor mission to a fresh target.
00:13:04 --> 00:13:06 Although this particular comet isn't a
00:13:06 --> 00:13:09 candidate and it's a nice reminder of
00:13:09 --> 00:13:12 something we often say on this catalogues are
00:13:12 --> 00:13:15 detection limits, not censuses. One honest
00:13:15 --> 00:13:17 note for southern listeners, it was found in
00:13:17 --> 00:13:19 Euclid's DEET field north, and it's far too
00:13:19 --> 00:13:21 faint to see without a big telescope.
00:13:21 --> 00:13:24 Avery: Uranus and Neptune are usually described
00:13:24 --> 00:13:27 as twins. Similar size, similar
00:13:27 --> 00:13:30 mass, both blue green ice giants.
00:13:31 --> 00:13:33 But a study in Astronomy and Astrophysics,
00:13:34 --> 00:13:36 published in its final form yesterday, argues
00:13:36 --> 00:13:39 their chemistry tells a different story.
00:13:39 --> 00:13:40 Anna: Who's behind it?
00:13:41 --> 00:13:44 Avery: Tom Briand at Aix Marseille University with
00:13:44 --> 00:13:46 Vincent Hu, Olivier Moussi of the Southwest
00:13:46 --> 00:13:49 Research Institute, Thibaut Cavalier and
00:13:49 --> 00:13:51 colleagues.1 Disclosure. The
00:13:51 --> 00:13:54 accepted version of the paper has been online
00:13:54 --> 00:13:56 since late August, so this is the journal
00:13:56 --> 00:13:57 publication rather than a
00:13:57 --> 00:14:00 Anna: brand new result, though, how do you
00:14:00 --> 00:14:03 measure what's deep inside a planet with no
00:14:03 --> 00:14:03 surface?
00:14:04 --> 00:14:06 Avery: Indirectly using carbon monoxide.
00:14:07 --> 00:14:09 Deep down, where it's hot. Carbon monoxide is
00:14:09 --> 00:14:12 created from methane and water. Strong
00:14:12 --> 00:14:15 vertical mixing carries it up to the upper
00:14:15 --> 00:14:17 atmosphere faster than it can be destroyed.
00:14:17 --> 00:14:20 So the amount we see up top acts as a
00:14:20 --> 00:14:23 tracer for the oxygen hidden far below.
00:14:23 --> 00:14:25 The team used measurements of that carbon
00:14:25 --> 00:14:28 monoxide, including from the ALMA array in
00:14:28 --> 00:14:30 Chile's Atacama Desert, and fed them into
00:14:30 --> 00:14:33 chemical models that now account for how
00:14:33 --> 00:14:35 conditions change with latitude.
00:14:35 --> 00:14:36 Anna: And the answer?
00:14:36 --> 00:14:39 Avery: Neptune's deep atmosphere looks much richer
00:14:39 --> 00:14:42 in oxygen. They estimate uranus at roughly
00:14:42 --> 00:14:44 50 to 180 times the sun's original
00:14:44 --> 00:14:47 proportion of oxygen, and neptune at about
00:14:47 --> 00:14:50 180 to 340. 40 times.
00:14:50 --> 00:14:52 That gives the two planets quite different
00:14:53 --> 00:14:54 carbon to oxygen ratios.
00:14:55 --> 00:14:57 Anna: And that points to where they formed.
00:14:57 --> 00:15:00 Avery: That's the argument in the disc that formed
00:15:00 --> 00:15:02 the planets. Different ices froze out at
00:15:02 --> 00:15:04 different distances from the young Sun.
00:15:04 --> 00:15:07 Compared against models of that disc,
00:15:07 --> 00:15:09 Neptune's chemistry suggests its building
00:15:09 --> 00:15:12 blocks came from closer in before it
00:15:12 --> 00:15:15 migrated outward. Muses line is that
00:15:15 --> 00:15:17 they're more like cousins with very different
00:15:17 --> 00:15:18 histories.
00:15:18 --> 00:15:19 Anna: How firm is it?
00:15:20 --> 00:15:23 Avery: It's a modelling result built on indirect
00:15:23 --> 00:15:23 measurements.
00:15:23 --> 00:15:26 And the ranges are wide. Especially for
00:15:26 --> 00:15:29 Uranus, the biggest uncertainty is how
00:15:29 --> 00:15:31 strongly each atmosphere mixes vertically.
00:15:32 --> 00:15:34 The team says plainly that without going into
00:15:34 --> 00:15:37 those atmospheres, our understanding is
00:15:37 --> 00:15:38 fundamentally limited.
00:15:39 --> 00:15:41 Anna: Which is a case for a probe.
00:15:42 --> 00:15:44 Avery: Exactly. The paper offers a framework for
00:15:44 --> 00:15:47 choosing the latitude where a future Uranus
00:15:47 --> 00:15:50 orbiter and probe should dive in. And since
00:15:50 --> 00:15:52 planets this size are common around other
00:15:52 --> 00:15:55 stars, getting our own two right matters well
00:15:55 --> 00:15:56 beyond the solar system.
00:15:57 --> 00:15:59 Anna: Time now for some quick hits, starting with
00:15:59 --> 00:16:02 an update to yesterday's episode. Japan's
00:16:02 --> 00:16:05 MMX mission to Mars moon Phobos is on
00:16:05 --> 00:16:07 its way. The H3 rocket lifted off from
00:16:07 --> 00:16:10 Tanegashima at 4:41 this morning. Japan time.
00:16:11 --> 00:16:14 About 71 minutes later, JAXA confirmed the
00:16:14 --> 00:16:16 spacecraft had separated and been placed on
00:16:16 --> 00:16:19 its planet path. JAXA then received signals
00:16:19 --> 00:16:21 from the spacecraft showing it's working
00:16:21 --> 00:16:24 normally. Next stop, Mars orbit next
00:16:24 --> 00:16:27 August and if all goes well, a capsule
00:16:27 --> 00:16:29 of Phobos landing in South Australia in
00:16:29 --> 00:16:30 2031.
00:16:32 --> 00:16:35 Avery: Next, the Roman Space Telescope, which keeps
00:16:35 --> 00:16:37 beating expectations. Last Wednesday, NASA
00:16:37 --> 00:16:39 reported the team has finished focusing it.
00:16:40 --> 00:16:42 They moved the secondary mirror by about 1/16
00:16:42 --> 00:16:45 of the width of a human hair. The wide field
00:16:45 --> 00:16:48 instrument's optics now show an error of just
00:16:48 --> 00:16:50 63 nanometers against a requirement of
00:16:50 --> 00:16:53 about 90. That's nearly 30% better than
00:16:53 --> 00:16:56 predicted. The coronagraph is in focus too.
00:16:56 --> 00:16:59 First Science images are still expected early
00:16:59 --> 00:17:00 next year.
00:17:00 --> 00:17:03 Anna: NASA has also published its detailed
00:17:03 --> 00:17:05 analysis of the Artemis II heat shield.
00:17:05 --> 00:17:08 After Artemis I, engineers found 103
00:17:08 --> 00:17:10 spots where charred material had broken away.
00:17:11 --> 00:17:14 Artemis II flying a shorter reentry Path
00:17:14 --> 00:17:16 had just nine. That's about a tenfold
00:17:16 --> 00:17:17 reduction.
00:17:17 --> 00:17:20 Artemis III will carry a reworked heat
00:17:20 --> 00:17:23 Avery: shield and keep an eye on ESA's Hera Mission.
00:17:23 --> 00:17:25 Its second braking burn, BRM2, is
00:17:25 --> 00:17:28 scheduled for this Thursday as it closes in
00:17:28 --> 00:17:30 on the Didymos asteroid pair. We'll bring you
00:17:30 --> 00:17:30 the result.
00:17:31 --> 00:17:34 Anna: Next up, let's go and take a look outside.
00:17:35 --> 00:17:37 Avery: Time for Skywatch. And this week the
00:17:37 --> 00:17:40 meteors win. The Orionid meteor shower
00:17:40 --> 00:17:43 peaks over the nights of the 21st and 22nd.
00:17:44 --> 00:17:46 These are crumbs of Hallie's Comet and they
00:17:46 --> 00:17:49 hit our atmosphere fast at about 66
00:17:49 --> 00:17:50 kilometres per second.
00:17:50 --> 00:17:52 Anna: But there's a waxing gibbous moon in
00:17:52 --> 00:17:55 Avery: the way there is, so timing
00:17:55 --> 00:17:57 matters. On Wednesday night into Thursday,
00:17:58 --> 00:18:00 the moon sets at about 3:38 in the morning in
00:18:00 --> 00:18:03 Sydney, 3:22 in Los Angeles,
00:18:03 --> 00:18:06 3:12 in New York and 2:49 in
00:18:06 --> 00:18:08 London. That leaves a dark window before
00:18:08 --> 00:18:11 dawn. From Sydney, astronomical dawn comes at
00:18:11 --> 00:18:13 about 4:37, so we get about an hour.
00:18:14 --> 00:18:16 Northern observers get longer. Two to three
00:18:16 --> 00:18:16 hours.
00:18:17 --> 00:18:19 Anna: And the radiant favours the north.
00:18:19 --> 00:18:22 Avery: It does. The radiant near
00:18:22 --> 00:18:25 Orion's raised club is about 440 degrees
00:18:25 --> 00:18:27 up from Sydney just before dawn, but
00:18:27 --> 00:18:30 54 degrees from London, 64 from New York
00:18:30 --> 00:18:33 and 71 from Los Angeles. A
00:18:33 --> 00:18:35 higher radiant means more meteors.
00:18:36 --> 00:18:38 Southern watchers look northeast before dawn
00:18:38 --> 00:18:40 and expect fewer, but they're still worth a
00:18:40 --> 00:18:43 look on Thursday night. The moon sets half an
00:18:43 --> 00:18:46 hour to an hour later, so the dark window
00:18:46 --> 00:18:46 shrinks.
00:18:47 --> 00:18:48 Anna: What else is up, huh?
00:18:48 --> 00:18:51 Avery: Southern skies get Mercury this week. On
00:18:51 --> 00:18:53 Wednesday at the end of civil Twilight, it's
00:18:53 --> 00:18:56 about 16 and a half degrees above the western
00:18:56 --> 00:18:58 horizon from Sydney, but uh, only four
00:18:58 --> 00:19:00 degrees from Los Angeles, two from New York
00:19:00 --> 00:19:03 and already set from London. It's fading.
00:19:03 --> 00:19:05 Anna: So catch it early this week and
00:19:06 --> 00:19:08 Venus disappears.
00:19:08 --> 00:19:10 Avery: It does. Venus reaches inferior
00:19:10 --> 00:19:13 conjunction around the 24th, passing between
00:19:13 --> 00:19:16 Earth and the sun. It'll be only about
00:19:16 --> 00:19:19 six and a half degrees from the sun, about 40
00:19:19 --> 00:19:22 million kilometres from us. So lost in the
00:19:22 --> 00:19:24 glare it'll come back as a morning object.
00:19:25 --> 00:19:27 Please don't hunt for it with binoculars or a
00:19:27 --> 00:19:30 telescope near the sun. Never point any
00:19:30 --> 00:19:32 optical instrument at or near the sun without
00:19:32 --> 00:19:35 a proper solar filter certified to ISO
00:19:35 --> 00:19:37 123122.
00:19:37 --> 00:19:39 Anna: Anything for the evening crowd?
00:19:39 --> 00:19:41 Avery: Saturn nicely placed around
00:19:42 --> 00:19:45 30 to 40 degrees up at 9pm in all four
00:19:45 --> 00:19:45 cities.
00:19:45 --> 00:19:48 On the 24th, the nearly full moon passes
00:19:48 --> 00:19:50 about 6 degrees from it.
00:19:50 --> 00:19:52 Anna: And the uh, pre dawn planets?
00:19:53 --> 00:19:55 Avery: That one belongs to the north. At nautical
00:19:55 --> 00:19:58 dawn on Thursday, Mars and Jupiter are about
00:19:58 --> 00:20:00 50 to 60 degrees up from the northern cities,
00:20:01 --> 00:20:04 but only about 21 to 24 from Sydney.
00:20:04 --> 00:20:06 They're 10 degrees apart now and closing to
00:20:06 --> 00:20:09 just over 1 degree by the 16th of November.
00:20:10 --> 00:20:11 Anna: And a clock warning.
00:20:12 --> 00:20:15 Avery: Yes, the UK goes back an hour this
00:20:15 --> 00:20:17 Sunday the 25th, but the US doesn't
00:20:17 --> 00:20:20 until the 1st of November. So for one
00:20:20 --> 00:20:23 week, London is only four hours ahead of New
00:20:23 --> 00:20:26 York and our London Times shift.
00:20:26 --> 00:20:27 Anna: And the full moon.
00:20:28 --> 00:20:31 Avery: The full moon arrives at 4:11 Universal Time
00:20:31 --> 00:20:32 on Monday the 26th.
00:20:32 --> 00:20:35 That's 3:11 in the afternoon in Sydney,
00:20:35 --> 00:20:37 4:11 in the morning in London after the clock
00:20:37 --> 00:20:40 change a few minutes past midnight in New
00:20:40 --> 00:20:43 York and 911 on Sunday evening in Los
00:20:43 --> 00:20:46 Angeles. So your calendar date depends on
00:20:46 --> 00:20:48 where you stand from either hemisphere. It'll
00:20:48 --> 00:20:50 look full on both nights.
00:20:51 --> 00:20:53 Anna: That's our show. A shrinking moon,
00:20:54 --> 00:20:57 a soil map for Mars, Euclid's
00:20:57 --> 00:20:59 accidental comet, and two ice giants
00:20:59 --> 00:21:01 that turn out to be cousins.
00:21:01 --> 00:21:04 Avery: Show notes and every source are at
00:21:04 --> 00:21:07 astronomydaily IO and if there's
00:21:07 --> 00:21:09 a story you'd like us to follow up, use the
00:21:09 --> 00:21:11 contact form there. Some of our favourite
00:21:11 --> 00:21:13 segments started that way.
00:21:13 --> 00:21:16 Anna: You can find us as astrodaily pod
00:21:16 --> 00:21:18 on social media. And if you enjoyed the show,
00:21:19 --> 00:21:21 a, uh, rating or review really helps new
00:21:21 --> 00:21:22 listeners find us.
00:21:22 --> 00:21:25 Avery: Tomorrow. We'll keep watch on the Orionids
00:21:25 --> 00:21:28 and on Hera's next breaking burn. I'm
00:21:28 --> 00:21:28 Avery.
00:21:29 --> 00:21:32 Anna: And I'm Anna. Clear skies. A
00:21:32 --> 00:21:32 star.
00:21:38 --> 00:21:38 Avery: Love.
00:21:43 --> 00:21:44 Story. Soul.