In this episode Starship Flight 13 ● Window opens 6:45pm EDT / 2245 GMT Thursday 23 July — 8:45am AEST and 10:45am NZST Friday 24 July. ● Schedule is not locked: Starbase road and beach closure notices point to further Pad 2 testing. ● The 16 July attempt aborted at T-0 when four of 33 Raptors missed start parameters; the limit is three. ● Two Raptors were removed and replaced before this attempt. ● First-ever Starship deployment of V3 Starlink satellites — 20 of them. ● Super Heavy splashes down in the Gulf at ~7 minutes; Ship targets the Indian Ocean off Western Australia at ~65 minutes. No catch attempts. Chang'e-6 and the solar wind ● Published in Nature Geoscience by a team at the Chinese Academy of Sciences' Institute of Geology and Geophysics. ● Based on 1,935 grams of regolith returned from the South Pole–Aitken basin on the lunar far side. ● First direct laboratory comparison of solar wind implantation between the near and far sides. ● Far-side soil records faster, deeper-penetrating particles; the neon isotope ratio sits below every near-side sample measured. ● About a quarter of the solar wind exposure at the Chang'e-5 near-side site involved wind decelerated by Earth's magnetosphere. The far-side site shows none. ● Opens the possibility of using lunar noble gases as a fossil record of Earth's magnetic field over deep time. The far side debate — NAM 2026 ● Held Tuesday 21 July at the RAS National Astronomy Meeting, University of Birmingham. Convened by Prof Martin Ward. ● For the motion: Prof Joe Silk (Johns Hopkins) and Dr Jonathan McDowell (Durham Space Research Centre). ● Against: Dr Nikita Chiu (Durham) and Dr Manuel Salvoldi (aerospace engineer and educator). ● For: the far side is the only radio-quiet site near Earth — critical for detecting the cosmic dark ages, and an exceptional platform for gravitational wave detection. ● Against: commercial investment is what makes lunar exploration sustainable, and governance can let science and industry coexist. ● Audience support for the motion rose from 68% to 76% across the debate. V445 Puppis ● Presented at NAM 2026 by John Mills, University of Warwick. ● The only confirmed helium nova in the Milky Way. Erupted in late 2000, then vanished behind its own dust for over twenty years. ● Now confirmed as a white dwarf accreting from a rare stripped helium star — only a few thousand such stars are thought to exist in the entire galaxy. ● Orbital period of 3.7 days, roughly double previous estimates. Mass transfer has resumed. ● Unexplained high-speed "bullets" of possibly oxygen-rich gas travelling up to 20 million mph (~9,000 km/s) — never seen in any other nova. ● Data from ESO's Very Large Telescope, Hubble, the Southern African Large Telescope and TESS. ● Helium novae may be one pathway to Type Ia supernovae, the standard candles used to measure cosmic expansion. The Milky Way disc flip ● Presented at NAM 2026 by Kirill Batrakov, Durham University. ● Based on 25 Milky Way-like galaxies in the Auriga simulation suite, followed across roughly 11 billion years. ● Galaxies with the most slowly rotating stellar haloes shared a major head-on merger and a disc reorientation greater than 90 degrees. ● Our stellar halo rotates at only 10–20 km/s; the disc moves at around 220 km/s. ● The Gaia-Sausage-Enceladus collision roughly 10 billion years ago is the candidate trigger. ● Batrakov describes a disc flip as likely rather than confirmed, and is looking for independent signatures. ● Separate 2026 work led by Ling Zhu, using 600,000+ giant stars from Gaia and LAMOST, found the outer dark matter halo oriented almost vertically to the stellar disc — consistent with the disc having tilted. Skywatch ● Southern Delta Aquariids are active now, running into late August, with maximum around 30 July. ● Full Moon on 29 July means peak night is close to 98% illuminated — the worst conditions of the run. ● Best window: the pre-dawn mornings from now until roughly 27 July, after moonset. ● Radiant near Skat in Aquarius. Use Fomalhaut and the Great Square of Pegasus to locate it. ● Australia and New Zealand: radiant climbs near overhead. Best from around 2am to first light. ● North America: radiant sits low in the south — fewer meteors, but a better chance of long-trailed earthgrazers. Same 2am-to-dawn window, local time. ● Sunspot region AR4493 has grown rapidly to beta-gamma-delta complexity — the highest classification — and has already fired three M-class flares in a day. Worth watching aurora alerts. Sources ● SpaceX / Space.com — Starship Flight 13 mission details and timing ● Nature Geoscience — noble gas analysis of Chang'e-6 regolith (Chinese Academy of Sciences, Institute of Geology and Geophysics) ● Royal Astronomical Society — NAM 2026 far side governance debate ● Royal Astronomical Society — NAM 2026, V445 Puppis (John Mills, University of Warwick) ● Royal Astronomical Society — NAM 2026, Milky Way disc flip (Kirill Batrakov, Durham University) ● EarthSky and the American Meteor Society — Delta Aquariid observing guidance ● NOAA Space Weather Prediction Center / EarthSky Sun News — AR4493 activity
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00:00:00 --> 00:00:02 Anna: The side of the Moon we never see has been
00:00:02 --> 00:00:04 quietly keeping a secret about our own
00:00:04 --> 00:00:06 planet. And this week, two very different
00:00:06 --> 00:00:09 groups of scientists arrived at the same
00:00:09 --> 00:00:10 place from opposite directions.
00:00:11 --> 00:00:13 Avery: One group read it out of the dirt. The other
00:00:13 --> 00:00:15 argued about who gets to own it.
00:00:15 --> 00:00:17 Anna: Meanwhile, a rocket sits on a pad in South
00:00:17 --> 00:00:19 Texas waiting for a second chance.
00:00:20 --> 00:00:22 Avery: And a star that vanished behind its own
00:00:22 --> 00:00:24 wreckage 25 years ago has finally
00:00:24 --> 00:00:26 stepped back into the light.
00:00:26 --> 00:00:29 Anna: Welcome to Astronomy Daily. I'm Ana.
00:00:29 --> 00:00:31 Avery: And I'm, um. Avery. It's Thursday 23rd
00:00:31 --> 00:00:34 July 2026, and this is episode
00:00:34 --> 00:00:35 148.
00:00:35 --> 00:00:38 Anna: Coming up, Starship gets another go with
00:00:38 --> 00:00:41 a caveat. What the far side of the Moon knows
00:00:41 --> 00:00:43 about Earth's magnetic field, whether that
00:00:43 --> 00:00:46 far side should be off limits to industry. A
00:00:46 --> 00:00:48 one of a kind stellar explosion finally
00:00:48 --> 00:00:51 identified. And the possibility that our
00:00:51 --> 00:00:53 entire galaxy once turned over.
00:00:54 --> 00:00:56 Avery: Uh, plus a skywatch closer with some
00:00:56 --> 00:00:58 genuinely useful advice about the Delta
00:00:58 --> 00:01:01 Aquarids, which is to not wait for the peak.
00:01:01 --> 00:01:02 Anna: Let's get into it.
00:01:02 --> 00:01:05 Avery: We start at Starbase, because today is meant
00:01:05 --> 00:01:05 to be the day.
00:01:06 --> 00:01:08 Anna: SpaceX is targeting Flight 13 of
00:01:08 --> 00:01:11 Starship with a 90 minute launch window that
00:01:11 --> 00:01:14 opens at 6:45 in the evening Eastern
00:01:14 --> 00:01:16 Time. That's 5:45 Central and
00:01:16 --> 00:01:19 3:45 in the afternoon on the Pacific coast.
00:01:20 --> 00:01:22 For those of us on this side of the world,
00:01:22 --> 00:01:24 that lands at a quarter to nine on Friday
00:01:24 --> 00:01:27 morning Australian Eastern Time and a quarter
00:01:27 --> 00:01:29 to 11 Friday morning in New Zealand.
00:01:30 --> 00:01:32 Avery: So North America gets it over dinner and we
00:01:32 --> 00:01:35 get it over breakfast for once, nobody has to
00:01:35 --> 00:01:37 set an alarm for three in the morning for
00:01:37 --> 00:01:37 once.
00:01:37 --> 00:01:40 Anna: Although, and this is the part I want to be
00:01:40 --> 00:01:43 upfront about, that schedule is not locked.
00:01:43 --> 00:01:45 Meaning? Meaning the public schedule says
00:01:45 --> 00:01:48 today, but the road and beach closure
00:01:48 --> 00:01:50 notifications around Starbase suggest
00:01:50 --> 00:01:52 additional testing is happening happening on
00:01:52 --> 00:01:54 Pad 2. Those closure notices are one of the
00:01:54 --> 00:01:57 more reliable tells in this business because
00:01:57 --> 00:01:59 they have to be filed in advance and they
00:01:59 --> 00:02:01 tend to reflect what's actually planned
00:02:01 --> 00:02:03 rather than what's been announced. So there
00:02:03 --> 00:02:05 is a realistic chance this
00:02:05 --> 00:02:07 Avery: slides again, which would make it the third
00:02:07 --> 00:02:08 date for Flight 13.
00:02:09 --> 00:02:11 Anna: It would. Let's recap how we got here because
00:02:11 --> 00:02:14 the arc matters. Flight 13 was first set
00:02:14 --> 00:02:17 for Thursday 16th July. The countdown went
00:02:17 --> 00:02:20 all the way to zero and then stopped. The
00:02:20 --> 00:02:22 flight software triggered an automatic abort
00:02:22 --> 00:02:25 right at T0 because four of the 33
00:02:25 --> 00:02:27 Raptor engines on the Super Heavy booster
00:02:28 --> 00:02:29 failed to reach acceptable starting
00:02:29 --> 00:02:30 parameters.
00:02:30 --> 00:02:32 Avery: And um, the threshold is 3, so
00:02:32 --> 00:02:35 Anna: it missed by exactly one engine. That's the
00:02:35 --> 00:02:38 system working as designed and it protected
00:02:38 --> 00:02:41 both the vehicle and the pad. Elon Musk said
00:02:41 --> 00:02:43 afterwards that two Raptors would be pulled
00:02:43 --> 00:02:45 and replaced before the next attempt.
00:02:45 --> 00:02:47 Avery: That's a remarkably narrow margin between a
00:02:47 --> 00:02:48 scrub and a launch.
00:02:49 --> 00:02:51 Anna: It is, and it's deliberate. The vehicle was
00:02:51 --> 00:02:53 cleared to fly in the first place because the
00:02:53 --> 00:02:56 SAA closed out its mishap investigation into
00:02:56 --> 00:02:59 Flight 12 on 13 July. And the
00:02:59 --> 00:03:02 booster had already completed a full duration
00:03:02 --> 00:03:04 static fire of all 33 engines back on the
00:03:04 --> 00:03:05 10th.
00:03:05 --> 00:03:07 Avery: So the hardware had been through its paces.
00:03:07 --> 00:03:08 It just didn't like the moment.
00:03:09 --> 00:03:11 Anna: That's about the size of it. Here's what
00:03:11 --> 00:03:13 makes this flight worth paying attention to.
00:03:13 --> 00:03:16 Beyond the launch itself, Blight 13 is
00:03:16 --> 00:03:19 carrying 20 V3 Starlink satellites,
00:03:19 --> 00:03:21 the next generation of the Constellation, and
00:03:21 --> 00:03:23 the first time Starship has ever deployed
00:03:23 --> 00:03:23 them.
00:03:24 --> 00:03:25 Avery: That's the whole point of the vehicle
00:03:25 --> 00:03:28 eventually. Not the spectacle, the payload.
00:03:28 --> 00:03:30 Anna: Right up to now, these have been test flights
00:03:30 --> 00:03:33 carrying simulators and mass models. This is
00:03:33 --> 00:03:35 the first time the thing does the job it was
00:03:35 --> 00:03:38 built for. Even on a suborbital trajectory
00:03:38 --> 00:03:41 and the flight profile. Oster and ship
00:03:41 --> 00:03:43 separate as usual. Super Heavy steers
00:03:43 --> 00:03:46 itself to a controlled splashdown in the Gulf
00:03:46 --> 00:03:49 about seven minutes after liftoff. No
00:03:49 --> 00:03:51 catch attempt with the chopstick arms on this
00:03:51 --> 00:03:53 one. The ship continues on,
00:03:54 --> 00:03:56 deploys the satellites and then comes down
00:03:56 --> 00:03:59 for its own splashdown in the Indian Ocean
00:03:59 --> 00:04:01 off the coast of Western Australia at around
00:04:01 --> 00:04:02
00:04:02 --> 00:04:04 Avery: minutes, which is worth flagging for our, uh,
00:04:04 --> 00:04:07 listeners in Perth and along that coast. You
00:04:07 --> 00:04:09 are not going to see it from the beach. It's
00:04:09 --> 00:04:11 a long way offshore, but it is your patch of
00:04:11 --> 00:04:12 ocean.
00:04:12 --> 00:04:15 Anna: It is. And for anyone in North America
00:04:15 --> 00:04:17 hoping to catch the launch itself, it's a
00:04:17 --> 00:04:20 star based departure. So the viewing sites
00:04:20 --> 00:04:23 around Boca Chica and South Padre island are
00:04:23 --> 00:04:24 the ones that matter.
00:04:24 --> 00:04:26 Avery: So assuming it goes.
00:04:26 --> 00:04:29 Anna: Assuming it goes. If you're listening to this
00:04:29 --> 00:04:32 on Thursday, check before you commit your
00:04:32 --> 00:04:34 evening. If you're listening later, you
00:04:34 --> 00:04:36 already know how it turned out and we'll pick
00:04:36 --> 00:04:38 up the result in the next episode. Either
00:04:38 --> 00:04:41 way, this ark has taught us not to get ahead
00:04:41 --> 00:04:41 of ourselves.
00:04:42 --> 00:04:44 Avery: Now, to the moon and to something I find
00:04:44 --> 00:04:46 genuinely lovely about this next result,
00:04:47 --> 00:04:49 which is that it turns lunar soil into a
00:04:49 --> 00:04:50 record of Earth.
00:04:51 --> 00:04:51 Anna: Go on.
00:04:52 --> 00:04:54 Avery: The sun blows a continuous stream of charged
00:04:55 --> 00:04:57 particles out across a solar system. The
00:04:57 --> 00:05:00 solar wind. The moon has no atmosphere and
00:05:00 --> 00:05:03 no global magnetic field to speak of. So
00:05:03 --> 00:05:05 those particles hit the surface directly and
00:05:05 --> 00:05:08 bury themselves in the soil over billions of
00:05:08 --> 00:05:11 years. The regolith becomes an archive of
00:05:11 --> 00:05:12 everything that struck it.
00:05:12 --> 00:05:15 Anna: And noble gases are the good bookkeepers.
00:05:15 --> 00:05:18 Avery: Exactly. Helium, neon, argon,
00:05:18 --> 00:05:21 krypton, xenon. They don't react with
00:05:21 --> 00:05:23 anything. So whatever went in stays in.
00:05:24 --> 00:05:26 And how deep it went tells you how fast it
00:05:26 --> 00:05:28 was traveling when it arrived.
00:05:28 --> 00:05:29 Anna: So what did they find?
00:05:30 --> 00:05:32 Avery: A team at the Chinese Academy of Sciences,
00:05:32 --> 00:05:35 Institute of Geology and Physics analyzed
00:05:35 --> 00:05:38 samples from Chang' E6. The mission that
00:05:38 --> 00:05:41 returned material from the far side from the
00:05:41 --> 00:05:43 south pole aitken Basin. That's
00:05:43 --> 00:05:46 1 grams of soil,
00:05:46 --> 00:05:48 just under 2 kilograms.
00:05:48 --> 00:05:51 Anna: And that's the first far side material anyone
00:05:51 --> 00:05:53 has ever had in a laboratory.
00:05:53 --> 00:05:56 Avery: Every previous return sample, Apollo, Luna,
00:05:56 --> 00:05:59 Chang' e5 came from the near side. So this
00:05:59 --> 00:06:01 is the first time anyone could directly
00:06:01 --> 00:06:03 compare the two hemispheres. They worked
00:06:03 --> 00:06:06 through seven portions using stepwise heating
00:06:06 --> 00:06:09 and laser extraction, measuring the isotopes
00:06:09 --> 00:06:12 of all five noble gases. And the far side
00:06:12 --> 00:06:15 soil is measurably different. The solar
00:06:15 --> 00:06:17 wind went in faster and went in deeper.
00:06:17 --> 00:06:19 Anna: Deeper, meaning higher energy.
00:06:19 --> 00:06:22 Avery: Higher energy, yes. The clearest signal was
00:06:22 --> 00:06:25 in neon. The ratio of Neon 20 to
00:06:25 --> 00:06:28 Neon 22 in the Cheng' E6 material
00:06:28 --> 00:06:30 sits below anything recorded in any near
00:06:30 --> 00:06:33 sight sample, which points to stronger
00:06:33 --> 00:06:35 processing on the way in. And the heavier
00:06:35 --> 00:06:38 gases krypton and xenon come out of the
00:06:38 --> 00:06:40 sample at different temperatures than they do
00:06:40 --> 00:06:43 from Chang' E5 material, which is another way
00:06:43 --> 00:06:44 of reading implantation depth.
00:06:45 --> 00:06:48 Anna: So why would the far side get hit harder?
00:06:48 --> 00:06:50 Avery: Because we're in the way. M
00:06:50 --> 00:06:53 Earth magnetosphere. As the moon
00:06:53 --> 00:06:56 travels around its orbit, it spends part of
00:06:56 --> 00:06:58 each month downstream of Earth, inside the
00:06:58 --> 00:07:01 long magnetic tail our planet trails behind
00:07:01 --> 00:07:04 it. And in that region, the solar wind
00:07:04 --> 00:07:06 gets slowed down before it reaches the lunar
00:07:06 --> 00:07:09 surface. But it's the near side that's facing
00:07:09 --> 00:07:11 us. So the near side is the one that catches
00:07:11 --> 00:07:14 at the celerated wind. The far side is
00:07:14 --> 00:07:16 permanently turned away and takes the full
00:07:16 --> 00:07:17 unmoderated stream.
00:07:18 --> 00:07:20 Anna: Earth has been sheltering the side of the
00:07:20 --> 00:07:22 moon that looks at us for 4 billion
00:07:22 --> 00:07:23 years.
00:07:23 --> 00:07:26 Avery: For 4 billion years. And the team put
00:07:26 --> 00:07:29 a number on it. Roughly a quarter of the
00:07:29 --> 00:07:31 total solar wind exposure at the Chang' e 5
00:07:31 --> 00:07:34 landing site involved that slowed down flow.
00:07:34 --> 00:07:36 At the Chang' e 6 site on the far side,
00:07:37 --> 00:07:38 there's no sign of it at all.
00:07:39 --> 00:07:42 Anna: That's a beautiful result. And I assume it
00:07:42 --> 00:07:43 cuts the other way as well.
00:07:43 --> 00:07:45 Avery: That's the part that excites me most. If the
00:07:45 --> 00:07:48 near site soil records how much shielding
00:07:48 --> 00:07:51 Earth was providing, then heavy noble gases
00:07:51 --> 00:07:54 in lunar Regolith become a fossil record of
00:07:54 --> 00:07:57 our own magnetosphere. Combine that with the
00:07:57 --> 00:07:59 rock magnetism record on Earth, and you have
00:07:59 --> 00:08:02 a completely new way of reconstructing how
00:08:02 --> 00:08:04 our magnetic field has changed over deep
00:08:04 --> 00:08:05 time.
00:08:05 --> 00:08:07 Anna: Which is not a small thing, given the
00:08:07 --> 00:08:09 magnetosphere is the reason we still have an
00:08:09 --> 00:08:09 atmosphere.
00:08:10 --> 00:08:12 Avery: Not a small thing at all. The Moon has been
00:08:12 --> 00:08:14 keeping notes on us, and it turns out the far
00:08:14 --> 00:08:17 side has the cleaner copy. Which, as
00:08:17 --> 00:08:20 it happens, is exactly why a room full of
00:08:20 --> 00:08:22 astronomers spent Tuesday evening arguing
00:08:22 --> 00:08:24 about what we're allowed to do out there.
00:08:24 --> 00:08:26 Anna: So this was at the Royal Astronomical
00:08:26 --> 00:08:28 Society's National Astronomy Meeting, which
00:08:28 --> 00:08:30 is running this week at the University of
00:08:30 --> 00:08:32 Birmingham. On Tuesday evening, they staged a
00:08:32 --> 00:08:35 formal debate on a single proposition, that
00:08:35 --> 00:08:37 the far side of the Moon should be preserved
00:08:37 --> 00:08:38 solely for scientific endeavors.
00:08:38 --> 00:08:41 Avery: And the answer is presumably not obvious or
00:08:41 --> 00:08:42 there'd be no debate.
00:08:42 --> 00:08:45 Anna: It's genuinely not. Arguing in favor were
00:08:45 --> 00:08:47 Joe Silk of Johns Hopkins and Jonathan
00:08:47 --> 00:08:49 McDowell, who most of our listeners will know
00:08:49 --> 00:08:52 from Jonathan's space report and who is now
00:08:52 --> 00:08:54 an honorary professor at Durham Space
00:08:54 --> 00:08:56 Research Center. After decades at the Harvard
00:08:56 --> 00:08:58 Smithsonian center for Astrophysica, um, and
00:08:58 --> 00:09:01 against M. Nikita Chu, also at Durham, who
00:09:01 --> 00:09:03 works on space technology governance, and
00:09:03 --> 00:09:06 manuel Salvoldi, an Aram space engineer with
00:09:06 --> 00:09:08 25 years across industry and academia.
00:09:09 --> 00:09:11 Barton Ward convened it. The case for
00:09:11 --> 00:09:14 protection rests on one physical fact. The
00:09:14 --> 00:09:17 far side is the only radio quiet real
00:09:17 --> 00:09:18 estate anywhere near Earth.
00:09:18 --> 00:09:21 Avery: The Moon is tidally locked, so the same
00:09:21 --> 00:09:24 hemisphere always faces us, which means the
00:09:24 --> 00:09:26 far side is permanently shielded from every
00:09:26 --> 00:09:29 transmitter, every radar, every broadcast on
00:09:29 --> 00:09:31 this planet. And that matters because.
00:09:32 --> 00:09:34 Anna: Because there are signals we want to detect
00:09:34 --> 00:09:36 that are drowned out everywhere else. The
00:09:36 --> 00:09:39 cosmic dark ages, the stretch of time after
00:09:39 --> 00:09:41 the Big Bang before the first star switched
00:09:41 --> 00:09:44 on. The radio emission from that era is faint
00:09:44 --> 00:09:47 and it's low frequency. And Earth is far too
00:09:47 --> 00:09:49 noisy a place to hear it. A far side radio
00:09:49 --> 00:09:52 telescope is arguably the only way we ever
00:09:52 --> 00:09:52 will.
00:09:52 --> 00:09:54 Avery: That's a fairly specific and, um,
00:09:54 --> 00:09:56 irreplaceable thing to be arguing about.
00:09:56 --> 00:09:58 Anna: It is, and Cilk's framing was essentially
00:09:58 --> 00:10:01 generational, that we should protect these
00:10:01 --> 00:10:03 conditions for science. That won't be done
00:10:03 --> 00:10:05 for decades, because the questions at stake
00:10:05 --> 00:10:08 are whether we're alone and how the universe
00:10:08 --> 00:10:08 began.
00:10:09 --> 00:10:10 Avery: And, um, the physical case doesn't stop at
00:10:10 --> 00:10:11 radio.
00:10:11 --> 00:10:13 Anna: No. They also argued the far side would be an
00:10:13 --> 00:10:16 exceptional site for gravitational wave
00:10:16 --> 00:10:19 detection. No atmosphere, no weather, very
00:10:19 --> 00:10:21 little seismic activity compared with Earth,
00:10:21 --> 00:10:23 and no artificial light, which is becoming a
00:10:23 --> 00:10:25 real problem for optical astronomy down here.
00:10:25 --> 00:10:28 Avery: So what's the counterargument, because leave
00:10:28 --> 00:10:30 it alone is easy to say.
00:10:30 --> 00:10:32 Anna: The counterargument is about sustainability,
00:10:32 --> 00:10:34 and I thought it was stronger than people
00:10:34 --> 00:10:36 might expect. Few's position was that this
00:10:36 --> 00:10:38 isn't a challenge to the value of the
00:10:38 --> 00:10:40 science, it's a question of how you keep
00:10:40 --> 00:10:43 going back at all. Lunar exploration that
00:10:43 --> 00:10:46 depends entirely on government funding is
00:10:46 --> 00:10:48 fragile. Commercial investment is what makes
00:10:48 --> 00:10:50 it resilient. And her argument was that you
00:10:50 --> 00:10:53 can have both under proper governance, that
00:10:53 --> 00:10:55 an inclusive CIS lunar economy on the far
00:10:55 --> 00:10:57 side doesn't have to turn into a free for
00:10:57 --> 00:10:58 all.
00:10:58 --> 00:11:01 Avery: Which is a fair point. A protected region
00:11:01 --> 00:11:04 nobody can afford to reach is protected in a
00:11:04 --> 00:11:05 fairly useless way.
00:11:05 --> 00:11:08 Anna: That's the tension. Exactly. And McDowell's
00:11:08 --> 00:11:09 put the stakes in the broadest possible
00:11:09 --> 00:11:12 terms. His line was is the whole solar system
00:11:12 --> 00:11:15 up for grabs or do we set aside reserves?
00:11:15 --> 00:11:18 Avery: That's the real question, isn't it? Not the
00:11:18 --> 00:11:18 Moon specifically.
00:11:19 --> 00:11:21 Anna: Not the Moon specifically. His argument was
00:11:21 --> 00:11:23 that whatever we decide in the next few years
00:11:23 --> 00:11:25 becomes the precedent for everything after
00:11:26 --> 00:11:28 Mars, the asteroids, all of it.
00:11:28 --> 00:11:29 Avery: Did they take a vote?
00:11:29 --> 00:11:31 Anna: They did. Before and after. By QR code.
00:11:32 --> 00:11:34 Support for the motion went from 68%
00:11:34 --> 00:11:37 to 76%, though the room moved
00:11:37 --> 00:11:39 towards protection, which, given the
00:11:39 --> 00:11:41 audience, isn't a shock. But an eight point
00:11:41 --> 00:11:43 swing after hearing both sides is a real
00:11:43 --> 00:11:46 result rather than a formality. And it fed
00:11:46 --> 00:11:49 into a full session the next day on lunar
00:11:49 --> 00:11:49 governance and regulation.
00:11:50 --> 00:11:52 Avery: And in the meantime, Chang' E6 has just
00:11:52 --> 00:11:54 demonstrated that the far side is
00:11:54 --> 00:11:57 scientifically valuable in ways nobody had
00:11:57 --> 00:11:58 directly measured measured until this month,
00:11:58 --> 00:11:59 which rather
00:11:59 --> 00:12:02 Anna: sharpens the argument staying at the National
00:12:02 --> 00:12:04 Avery: Astronomy Meeting because there is a
00:12:04 --> 00:12:06 genuinely extraordinary object I want to talk
00:12:06 --> 00:12:08 about, and it lives in our skies.
00:12:08 --> 00:12:11 Southern skies Puppis, which for our
00:12:11 --> 00:12:13 Australian and New Zealand listeners is well
00:12:13 --> 00:12:16 placed for a good chunk of the year, and for
00:12:16 --> 00:12:18 northern listeners sits low on the south. The
00:12:18 --> 00:12:21 object is V445 Puppis,
00:12:21 --> 00:12:24 and it is the only confirmed helium nova in
00:12:24 --> 00:12:24 the Milky Way.
00:12:24 --> 00:12:26 Anna: Define helium nova.
00:12:27 --> 00:12:29 Avery: So a nova, an ordinary nova,
00:12:30 --> 00:12:32 is a white dwarf in a binary system stealing
00:12:32 --> 00:12:35 gas off its companion. That gas piles
00:12:35 --> 00:12:37 up on the surface, pressure and temperature
00:12:37 --> 00:12:40 climb, and eventually you get a runaway
00:12:40 --> 00:12:42 thermonuclear explosion. It doesn't
00:12:42 --> 00:12:44 destroy the star, it just blows the
00:12:44 --> 00:12:47 accumulated layer off. And in virtually
00:12:47 --> 00:12:50 every case, that stolen material is
00:12:50 --> 00:12:53 hydrogen rich, because hydrogen is what stars
00:12:53 --> 00:12:54 are mostly made of.
00:12:54 --> 00:12:55 Anna: And this one isn't.
00:12:55 --> 00:12:58 Avery: This one has essentially no hydrogen at all,
00:12:58 --> 00:13:01 which is a very strange thing for a stellar
00:13:01 --> 00:13:03 explosion to be missing, given hydrogen is
00:13:03 --> 00:13:06 the most abundant element in the universe. So
00:13:06 --> 00:13:08 the obvious question is what is it stealing
00:13:08 --> 00:13:09 from?
00:13:09 --> 00:13:10 Anna: And nobody could see.
00:13:10 --> 00:13:13 Avery: Nobody could see. V445
00:13:13 --> 00:13:16 puppys erupted in late 2000, and it
00:13:16 --> 00:13:19 threw out an enormous bipolar outflow. Two
00:13:19 --> 00:13:21 lobes of material streaming in opposite
00:13:21 --> 00:13:23 directions, more than a trillion miles
00:13:23 --> 00:13:26 across. But the eruption also created a thick
00:13:26 --> 00:13:29 disk of dust that completely swallowed the
00:13:29 --> 00:13:32 system. For more than 20 years, astronomers
00:13:32 --> 00:13:34 could watch the debris expanding, but they
00:13:34 --> 00:13:36 could not see what was inside it. The dust
00:13:36 --> 00:13:39 has now thinned enough. John Mills, a
00:13:39 --> 00:13:41 researcher and PhD student at the University
00:13:41 --> 00:13:44 of Warwick, put together observations
00:13:44 --> 00:13:47 spanning two decades to finally see through
00:13:47 --> 00:13:49 using what a stack of instruments.
00:13:49 --> 00:13:51 Infrared from the Very Large Telescope in
00:13:51 --> 00:13:54 Chile, Optical imaging from Hubble,
00:13:54 --> 00:13:56 Long term spectroscopy from the Southern
00:13:56 --> 00:13:59 African Large Telescope and photometry from
00:13:59 --> 00:14:02 tess. And the answer is a white dwarf
00:14:02 --> 00:14:04 feeding off a helium star.
00:14:04 --> 00:14:07 Anna: And a helium star is a star
00:14:07 --> 00:14:09 Avery: that has been stripped of its outer hydrogen
00:14:09 --> 00:14:11 envelope, most likely by the companion it's
00:14:11 --> 00:14:14 now feeding. They are genuinely rare.
00:14:14 --> 00:14:16 The estimate is a few thousand stripped
00:14:16 --> 00:14:18 helium stars among the hundreds of billions
00:14:18 --> 00:14:20 of stars in the entire galaxy.
00:14:21 --> 00:14:23 Anna: So one of the rarest kinds of stars in the
00:14:23 --> 00:14:26 only known example of one of the rarest kinds
00:14:26 --> 00:14:26 of explosions.
00:14:27 --> 00:14:29 Avery: And it's already loading the gun again. The
00:14:29 --> 00:14:32 system is actively transferring material once
00:14:32 --> 00:14:35 more. The two stars orbit each other every
00:14:35 --> 00:14:38 3.7 days, which is around twice as
00:14:38 --> 00:14:39 long as anyone previously thought.
00:14:39 --> 00:14:41 Anna: You said there was a mystery.
00:14:41 --> 00:14:43 Avery: The bullets. The bullets embedded in the
00:14:43 --> 00:14:46 outflowing debris are discrete clumps of gas,
00:14:46 --> 00:14:49 possibly oxygen rich, though the composition
00:14:49 --> 00:14:51 isn't nailed down. Moving at up to 20
00:14:51 --> 00:14:54 million miles an hour, that's roughly
00:14:54 --> 00:14:57 9 kilometers per second, around
00:14:57 --> 00:14:58 3% of the speed of light.
00:14:59 --> 00:15:00 Anna: And nothing like that has been seen
00:15:00 --> 00:15:01 elsewhere.
00:15:01 --> 00:15:04 Avery: Nothing like it in any other nova anywhere.
00:15:04 --> 00:15:06 Mills suspects they formed after the outburst
00:15:06 --> 00:15:09 rather than during it. But as he put it,
00:15:09 --> 00:15:10 their origin is a mystery.
00:15:10 --> 00:15:12 Anna: Which is the honest answer. And I appreciate
00:15:12 --> 00:15:13 that he said it.
00:15:13 --> 00:15:16 Avery: So do I. Now, the reason this matters. Beyond
00:15:16 --> 00:15:19 its own strangeness, Astronomers suspect that
00:15:19 --> 00:15:21 repeated helium rich eruptions on a white
00:15:21 --> 00:15:23 dwarf might be one of the pathways that
00:15:23 --> 00:15:26 eventually produces a type 1A supernova.
00:15:26 --> 00:15:29 Anna: And type IAs are the standard candles.
00:15:29 --> 00:15:31 Avery: They are. They explode with remarkably
00:15:31 --> 00:15:33 consistent brightness, which is what makes
00:15:33 --> 00:15:35 them useful as distance markers across the
00:15:35 --> 00:15:38 universe. They're how we measured cosmic
00:15:38 --> 00:15:40 expansion. The work that won the Nobel Prize
00:15:40 --> 00:15:42 for the discovery that the expansion is
00:15:42 --> 00:15:42 accelerating.
00:15:43 --> 00:15:45 Anna: So the ruler we use to measure the universe
00:15:45 --> 00:15:48 depends on understanding how these things
00:15:48 --> 00:15:48 detonate.
00:15:49 --> 00:15:51 Avery: It does. And whether helium novae actually
00:15:51 --> 00:15:54 get there is still an open question. But
00:15:54 --> 00:15:56 V445 Puppis is now the clearest
00:15:56 --> 00:15:59 laboratory anyone has for testing it. And it
00:15:59 --> 00:16:02 took 25 years of dust clearing to get the
00:16:02 --> 00:16:02 door open.
00:16:03 --> 00:16:05 Anna: Last story before we look up. And it's the
00:16:05 --> 00:16:08 biggest one in terms of sheer scale. There's
00:16:08 --> 00:16:10 a case being made that the entire Milky Way
00:16:10 --> 00:16:11 once flipped over.
00:16:12 --> 00:16:14 Avery: Flipped over how exactly? Because a galaxy
00:16:14 --> 00:16:15 doesn't have a right way up.
00:16:16 --> 00:16:18 Anna: It doesn't. And that's the right instinct.
00:16:18 --> 00:16:20 What's being proposed is a change of
00:16:20 --> 00:16:23 orientation. That the disk of our galaxy
00:16:23 --> 00:16:25 reoriented itself by more than 90 degrees
00:16:26 --> 00:16:28 relative to the halo of old stars around it.
00:16:28 --> 00:16:30 Avery: And what put that idea on the table?
00:16:30 --> 00:16:32 Anna: A puzzle that's been sitting there since
00:16:32 --> 00:16:35 Gaia. Our galaxy has a flat disk where
00:16:35 --> 00:16:37 most of the stars live. And around that a
00:16:37 --> 00:16:40 much larger, much sparser stellar halo.
00:16:41 --> 00:16:43 Mostly stars that formed in smaller galaxies
00:16:43 --> 00:16:45 and got absorbed when those galaxies were
00:16:45 --> 00:16:47 Avery: pulled in debris from past meals.
00:16:47 --> 00:16:50 Anna: Essentially. And Gaia showed that the halo
00:16:50 --> 00:16:53 barely rotates. It creeps around at something
00:16:53 --> 00:16:56 like 10 to 20 kilometers per second. The
00:16:56 --> 00:16:58 disk by comparison is moving at about
00:16:58 --> 00:16:59 220.
00:17:00 --> 00:17:02 Avery: That is a very large discrepancy.
00:17:02 --> 00:17:04 Anna: It is. And nobody had a satisfying
00:17:04 --> 00:17:07 explanation. So Kirill Botrikov at
00:17:07 --> 00:17:10 Durham went looking for one in simulations.
00:17:10 --> 00:17:13 The Auriga Suite, which models Milky Way like
00:17:13 --> 00:17:15 galaxies in detail. He took 25 of them
00:17:15 --> 00:17:18 and followed their evolution across roughly
00:17:18 --> 00:17:21 11 billion years. And the
00:17:21 --> 00:17:23 galaxies that ended up with the most slowly
00:17:23 --> 00:17:26 rotating halos had two things in common.
00:17:26 --> 00:17:29 They'd experienced a major head on merger
00:17:29 --> 00:17:32 and their disks had reoriented by more than
00:17:32 --> 00:17:33 90 degrees.
00:17:33 --> 00:17:35 Avery: And we know we had a major head on merger.
00:17:35 --> 00:17:38 Anna: We do. Gaia Sausage, Enceladus. The
00:17:38 --> 00:17:41 collision roughly 10 billion years ago that
00:17:41 --> 00:17:43 dumped an enormous quantity of stars into our
00:17:43 --> 00:17:46 halo and is the reason the halo looks the way
00:17:46 --> 00:17:46 it does.
00:17:47 --> 00:17:49 Avery: So the proposal is that the same collision
00:17:49 --> 00:17:51 exerted a gravitational torque on our disk
00:17:51 --> 00:17:54 and slowly turned it over inside the
00:17:54 --> 00:17:55 surrounding dark matter halo.
00:17:56 --> 00:17:58 Anna: Slowly meaning over hundreds of
00:17:58 --> 00:18:00 millions of years. Nothing about this was
00:18:00 --> 00:18:03 sudden, but the end state is that the plane
00:18:03 --> 00:18:05 the sun orbits in today may bear no
00:18:05 --> 00:18:07 relationship to the plane stars were orbiting
00:18:07 --> 00:18:09 in before the collision.
00:18:09 --> 00:18:11 Avery: That does something odd to my sense of place.
00:18:11 --> 00:18:14 Anna: It does mine too. And I want to be careful
00:18:14 --> 00:18:16 here because Botcherkov himself is careful.
00:18:16 --> 00:18:19 His position is that a disk flip is a likely
00:18:19 --> 00:18:22 explanation given how slowly the halo turns,
00:18:22 --> 00:18:24 but that it's too early to claim it with full
00:18:24 --> 00:18:27 confidence. What he wants is independent
00:18:27 --> 00:18:30 signatures, other scars that a reorientation
00:18:30 --> 00:18:31 on that Scale should have left behind.
00:18:32 --> 00:18:34 Avery: Is there anything pointing the same way
00:18:34 --> 00:18:34 already?
00:18:34 --> 00:18:37 Anna: There is, and it's suggestive rather than
00:18:37 --> 00:18:39 conclusive. Separate work this year led by
00:18:39 --> 00:18:42 Ling Xu used the motions of more than
00:18:42 --> 00:18:45 600 giant stars from Gaia and the
00:18:45 --> 00:18:47 LAMOST survey to reconstruct the shape of our
00:18:47 --> 00:18:50 dark matter halo. And the outer halo appears
00:18:50 --> 00:18:52 to be oriented almost vertically relative,
00:18:52 --> 00:18:53 uh, to the
00:18:53 --> 00:18:56 Avery: stellar disk, which is what you'd expect if
00:18:56 --> 00:18:58 the inner part tilted and the outer part
00:18:58 --> 00:18:58 didn't.
00:18:58 --> 00:19:01 Anna: That's the reading. The outer halo kept the
00:19:01 --> 00:19:04 old orientation. The disk and inner halo
00:19:04 --> 00:19:06 swung round. Two independent lines of
00:19:06 --> 00:19:09 evidence converging on the same story from
00:19:09 --> 00:19:12 completely different data. Not proof,
00:19:12 --> 00:19:14 but it's the kind of thing that turns a
00:19:14 --> 00:19:17 curiosity into a research program. And
00:19:17 --> 00:19:19 I rather like that. The biggest structural
00:19:19 --> 00:19:22 question about our own galaxy is one we can
00:19:22 --> 00:19:25 only answer by looking at it from the inside.
00:19:25 --> 00:19:27 Avery: Right, Time to look up.
00:19:27 --> 00:19:29 And Anna, uh, we have actual advice today
00:19:29 --> 00:19:30 rather than a countdown.
00:19:30 --> 00:19:33 Anna: We do. And the advice is don't wait for the
00:19:33 --> 00:19:34 peak.
00:19:34 --> 00:19:35 Avery: Explain.
00:19:35 --> 00:19:38 Anna: The southern Delta Aquarids are running now.
00:19:38 --> 00:19:41 The shower is already active and it stays
00:19:41 --> 00:19:43 active into late August. The American Meteor
00:19:43 --> 00:19:46 Society puts maximum activity around the
00:19:46 --> 00:19:47 30th of July.
00:19:48 --> 00:19:50 Avery: And the problem with the 30th is the moon.
00:19:50 --> 00:19:53 Anna: The moon is the problem. Full moon falls on
00:19:53 --> 00:19:56 the 29th of July. So on peak night, you're
00:19:56 --> 00:19:59 looking at a sky that is something like 98%
00:19:59 --> 00:20:01 illuminated. That will wash out most of the
00:20:01 --> 00:20:04 shower. Because Delta Aquariad meteors tend
00:20:04 --> 00:20:07 towards long, graceful trails rather than
00:20:07 --> 00:20:09 bright fireballs. They're exactly the kind
00:20:09 --> 00:20:11 that moonlight erases.
00:20:11 --> 00:20:13 Avery: So the peak is the worst night of the run.
00:20:14 --> 00:20:16 Anna: Close to it. But here's the good news. This
00:20:16 --> 00:20:19 shower has no sharp maximum. It
00:20:19 --> 00:20:21 rambles. Rates build slowly and stay
00:20:21 --> 00:20:24 roughly level for well over a week. Which
00:20:24 --> 00:20:27 means the mornings between now and about the
00:20:27 --> 00:20:29 27th are better than peak night because the
00:20:29 --> 00:20:32 waxing gibbous moon still sets before the
00:20:32 --> 00:20:33 radiant gets high.
00:20:34 --> 00:20:36 Avery: So the window is after moonset, before
00:20:36 --> 00:20:39 Anna: dawn, after moonset, before dawn. That's
00:20:39 --> 00:20:41 your window. And it applies wherever you are.
00:20:41 --> 00:20:44 Where do we look? The radiant sits near the
00:20:44 --> 00:20:47 star Skat in Aquarius. The easiest way
00:20:47 --> 00:20:50 in is to find Fomalhaut bright and
00:20:50 --> 00:20:52 noticeably alone in a fairly empty patch of
00:20:52 --> 00:20:55 sky. And work from there. The Great Square of
00:20:55 --> 00:20:57 Pegasus helps as well.
00:20:57 --> 00:20:59 Avery: And, um, that's a very different experience
00:20:59 --> 00:21:01 depending on which hemisphere you're in.
00:21:01 --> 00:21:04 Anna: Completely different from Australia and New
00:21:04 --> 00:21:06 Zealand. The radiant climbs close to overhead
00:21:06 --> 00:21:09 in the pre dawn hours. This is genuinely
00:21:09 --> 00:21:11 our Shower. The southern part of the world
00:21:11 --> 00:21:14 gets the best of it every year from Sydney or
00:21:14 --> 00:21:17 Auckland, anywhere from about 2 in the
00:21:17 --> 00:21:18 morning until first light.
00:21:18 --> 00:21:21 Avery: And for our North American listeners, who are
00:21:21 --> 00:21:22 the largest part of this audience,
00:21:22 --> 00:21:25 Anna: you still get a good showing, but the
00:21:25 --> 00:21:27 radiance stays lower in the southern sky, so
00:21:27 --> 00:21:29 you'll see fewer of them and they'll come in
00:21:29 --> 00:21:32 at shallower angles. And the upside of a low
00:21:32 --> 00:21:35 radiant is Earth grazers, meteors that
00:21:35 --> 00:21:37 skim along the atmosphere and leave much
00:21:37 --> 00:21:40 longer trails than usual. The best hours are
00:21:40 --> 00:21:43 the same from around 2 in the morning local
00:21:43 --> 00:21:46 time, uh, until dawn. So 2 to 5am, um,
00:21:46 --> 00:21:48 eastern and the equivalent across Central
00:21:48 --> 00:21:49 Mountain and Pacific.
00:21:50 --> 00:21:52 Avery: And get south facing and dark.
00:21:52 --> 00:21:55 Anna: Get south facing, get away from lights and
00:21:55 --> 00:21:57 give your eyes 20 minutes to adapt before you
00:21:57 --> 00:21:58 judge whether it's working.
00:21:59 --> 00:22:01 Avery: One more thing. And, um, this one is a watch
00:22:01 --> 00:22:03 this space rather than a forecast.
00:22:04 --> 00:22:05 Anna: The sun has woken up.
00:22:06 --> 00:22:07 Avery: Sunspot 4493.
00:22:08 --> 00:22:10 Anna: That one. It appeared essentially from
00:22:10 --> 00:22:12 nothing over the space of a couple of days
00:22:12 --> 00:22:15 and grew fast. And it now has what's called
00:22:15 --> 00:22:17 a beta gamma delta magnetic
00:22:17 --> 00:22:20 classification, which is the most complex
00:22:20 --> 00:22:22 classification there is. Regions like that
00:22:22 --> 00:22:24 are, uh, where the big flares come from.
00:22:25 --> 00:22:27 Avery: And it's already produced some 3M M
00:22:27 --> 00:22:30 Anna: class flares inside a single day. The
00:22:30 --> 00:22:33 Strongest an M M3.4, each of
00:22:33 --> 00:22:35 them causing brief minor radio blackouts
00:22:35 --> 00:22:37 across different parts of the world.
00:22:37 --> 00:22:39 Forecasters have been putting the odds of
00:22:39 --> 00:22:42 further M M class activity at better than
00:22:42 --> 00:22:44 even with a smaller chance of an X class
00:22:44 --> 00:22:44 event.
00:22:45 --> 00:22:47 Avery: So it's worth keeping an eye on the aurora
00:22:47 --> 00:22:48 alerts it is.
00:22:48 --> 00:22:51 Anna: Earlier this week, a fast solar wind stream
00:22:51 --> 00:22:53 from a coronal hole pushed conditions to
00:22:53 --> 00:22:56 minor storm level, with aurora possible as
00:22:56 --> 00:22:59 far equatorward as Hobart in the south and
00:22:59 --> 00:23:02 Seattle and Edinburgh in the north. That
00:23:02 --> 00:23:04 particular stream is easing now. But with a
00:23:04 --> 00:23:07 region that complex facing us, the situation
00:23:07 --> 00:23:08 can change quickly.
00:23:09 --> 00:23:11 Avery: And Southern hemisphere observers have the
00:23:11 --> 00:23:13 advantage of long winter nights right now,
00:23:13 --> 00:23:15 while northern observers are fighting short
00:23:15 --> 00:23:18 summer ones. Swings and
00:23:18 --> 00:23:19 roundabouts.
00:23:19 --> 00:23:22 Anna: That's episode 148, Starship waiting
00:23:22 --> 00:23:25 on a window that may or may not hold, a far
00:23:25 --> 00:23:27 side that's been quietly recording our
00:23:27 --> 00:23:29 magnetic field and an argument about whether
00:23:29 --> 00:23:30 we should leave it alone.
00:23:30 --> 00:23:33 Avery: Plus a star that spent 25 years behind a
00:23:33 --> 00:23:36 curtain and the galaxy that may have rolled
00:23:36 --> 00:23:37 over in its sleep.
00:23:37 --> 00:23:39 Anna: Show notes, sources and everything else are
00:23:39 --> 00:23:41 at astronomydaily, IO or
00:23:41 --> 00:23:44 astrodaily Pod, wherever you like to find us.
00:23:44 --> 00:23:46 Avery: If you're up before dawn this week chasing
00:23:46 --> 00:23:49 Delta Aquariids, we'd love to see what you
00:23:49 --> 00:23:49 catch.
00:23:49 --> 00:23:50 Anna: We'll be back tomorrow.
00:23:50 --> 00:23:52 Avery: Until then, clear skies.