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00:00:00 --> 00:00:02 Anna: Three decades of exploding stars
00:00:02 --> 00:00:04 pulled apart and rebuilt from the ground up
00:00:04 --> 00:00:07 into a single consistent picture,
00:00:07 --> 00:00:10 2 of them.
00:00:10 --> 00:00:13 And when an Australian led team stepped back
00:00:13 --> 00:00:14 to look at what that picture was saying about
00:00:14 --> 00:00:17 dark energy, it wasn't saying what the
00:00:17 --> 00:00:18 textbook says.
00:00:18 --> 00:00:20 Avery: We've also got a study asking whether our,
00:00:20 --> 00:00:23 uh, own sun once swallowed a planet and
00:00:23 --> 00:00:25 whether the evidence for it is still sitting
00:00:25 --> 00:00:28 inside the star right now, waiting to be
00:00:28 --> 00:00:29 ready.
00:00:29 --> 00:00:31 Anna: Plus why the quietest stretch of the solar
00:00:31 --> 00:00:34 cycle is the one that matters most.
00:00:34 --> 00:00:36 If you spend your working life at
00:00:36 --> 00:00:39 Avery: 35ft, and the James Webb
00:00:39 --> 00:00:41 Space Telescope has just run the most
00:00:41 --> 00:00:43 sensitive search for a moon around another
00:00:43 --> 00:00:46 planet that anyone has ever attempted,
00:00:46 --> 00:00:49 it found nothing at all. That is the good
00:00:49 --> 00:00:49 news.
00:00:50 --> 00:00:52 Anna: This is Astronomy AstroDailyPod. I'm Anna.
00:00:52 --> 00:00:54 Avery: And I'm avery.
00:00:54 --> 00:00:56 It's Monday 14th September
00:00:56 --> 00:00:59 2026 and we're coming to you as always,
00:00:59 --> 00:01:02 from Syd. You, let's get into it.
00:01:02 --> 00:01:04 Anna: We're starting today with a result that has
00:01:04 --> 00:01:06 been quietly sitting in the open for about a
00:01:06 --> 00:01:09 week and I think it deserves a great deal
00:01:09 --> 00:01:11 more attention than it has had. An
00:01:11 --> 00:01:13 international team led out of the University
00:01:13 --> 00:01:16 of Queensland has published what is now the
00:01:16 --> 00:01:18 largest and most internally consistent
00:01:18 --> 00:01:21 catalogue of type 1A supernovae ever
00:01:21 --> 00:01:22 assembled,
00:01:22 --> 00:01:25 2 of them.
00:01:25 --> 00:01:28 And it adds fresh weight to a very awkward
00:01:28 --> 00:01:30 idea that dark energy might not be
00:01:30 --> 00:01:32 constant, which would be a
00:01:32 --> 00:01:35 Avery: problem because the word constant is doing
00:01:35 --> 00:01:36 enormous structural work.
00:01:36 --> 00:01:39 Anna: In modern cosmology, it is the load bearing
00:01:39 --> 00:01:42 wall. So let's build this up properly because
00:01:42 --> 00:01:44 the method here matters as much as the
00:01:44 --> 00:01:47 answer. A, uh, type 1A supernova is what
00:01:47 --> 00:01:50 happens when a white dwarf star, the dense,
00:01:50 --> 00:01:52 burnt out core left behind by a star like our
00:01:52 --> 00:01:55 sun, gathers too much material and detonates.
00:01:56 --> 00:01:58 The crucial thing is that these explosions
00:01:58 --> 00:02:00 are close to identical. They go off at
00:02:00 --> 00:02:03 roughly the same intrinsic brightness every
00:02:03 --> 00:02:05 time. So if you measure how bright one looks
00:02:05 --> 00:02:08 from here, you can work out how far away it
00:02:08 --> 00:02:10 is. Astronomers call them standard
00:02:10 --> 00:02:11 candles.
00:02:11 --> 00:02:14 Avery: And that's the technique that won the Nobel
00:02:14 --> 00:02:15 Prize in 2011.
00:02:15 --> 00:02:18 Anna: It is. And this is where Australia enters the
00:02:18 --> 00:02:20 storey early, because one of the three
00:02:20 --> 00:02:23 laureates, Brian Schmidt, was working at the
00:02:23 --> 00:02:25 Australian National University when that
00:02:25 --> 00:02:28 discovery was made. Two teams in
00:02:28 --> 00:02:30 1998 independently found that distant
00:02:30 --> 00:02:32 supernovae were fainter than they should have
00:02:32 --> 00:02:35 been, which meant they were further away than
00:02:35 --> 00:02:37 expected, which meant the expansion of the
00:02:37 --> 00:02:40 universe is not slowing down under gravity,
00:02:40 --> 00:02:42 as everyone assumed, it's speeding up.
00:02:43 --> 00:02:45 And the thing doing the Speeding up, got the
00:02:45 --> 00:02:48 placeholder name dark Energy, because nobody
00:02:48 --> 00:02:50 knew, and to be completely honest, nobody
00:02:50 --> 00:02:52 still knows what it actually is.
00:02:53 --> 00:02:55 Avery: So where does the new work come in?
00:02:55 --> 00:02:56 Anna: Here's the difficulty.
00:02:56 --> 00:02:59 In the 28 years since, we have collected
00:02:59 --> 00:03:02 supernovae from dozens of different surveys
00:03:02 --> 00:03:05 on dozens of different telescopes with
00:03:05 --> 00:03:07 different detectors, different filters,
00:03:08 --> 00:03:10 different calibrations observed across
00:03:10 --> 00:03:12 decades, in which our understanding of these
00:03:12 --> 00:03:15 explosions changed substantially.
00:03:15 --> 00:03:18 You cannot simply pour all of that into one
00:03:18 --> 00:03:20 bucket and start doing cosmology with it.
00:03:21 --> 00:03:23 The systematic errors will eat you alive.
00:03:24 --> 00:03:27 Avery: So somebody had to do the unglamorous work.
00:03:27 --> 00:03:30 Anna: Somebody had to do the unglamorous work. And
00:03:30 --> 00:03:32 that somebody is ryan Camilleri, a
00:03:32 --> 00:03:34 PhD candidate at the University of
00:03:34 --> 00:03:36 Queensland's School of Mathematics and
00:03:36 --> 00:03:39 Physics, working with Professor Tamara M.
00:03:39 --> 00:03:42 Davis and a long list of collaborators across
00:03:42 --> 00:03:45 Australia, the United States, the United
00:03:45 --> 00:03:47 Kingdom, South Africa, Spain and
00:03:47 --> 00:03:50 France. What they've done is take Pantheon
00:03:50 --> 00:03:53 plus, which is the big historical compilation
00:03:53 --> 00:03:55 of supernovae going back roughly 30 years,
00:03:56 --> 00:03:58 and combine it with the Dark energy survey's
00:03:58 --> 00:04:01 full five year sample, which added around
00:04:01 --> 00:04:04 1500 new high redshift supernovae
00:04:04 --> 00:04:07 of its own. And rather than stapling the two
00:04:07 --> 00:04:09 together, they rebuilt both from the same
00:04:09 --> 00:04:12 starting assumptions in one framework
00:04:12 --> 00:04:14 with one set of calibrations.
00:04:14 --> 00:04:17 Avery: Camilleri's own description of it is the
00:04:17 --> 00:04:19 cleanest summary I've read. Quote,
00:04:19 --> 00:04:22 we've rebuilt three decades of astronomical
00:04:22 --> 00:04:25 observations into a single consistent
00:04:25 --> 00:04:26 framework.
00:04:26 --> 00:04:28 And he makes the point that this isn't just
00:04:28 --> 00:04:31 tidying up, it's reanalysis.
00:04:32 --> 00:04:34 Over the years, we've learned a lot more
00:04:34 --> 00:04:37 about how supernovae behave. So we've
00:04:37 --> 00:04:40 been able to go back and apply that improved
00:04:40 --> 00:04:42 understanding to older data.
00:04:42 --> 00:04:44 Anna: That improved understanding is doing real
00:04:44 --> 00:04:47 work here. Two of the biggest headaches in
00:04:47 --> 00:04:50 supernova cosmology are, uh, dust, cosmic
00:04:50 --> 00:04:53 dust between us and the explosion reddens and
00:04:53 --> 00:04:55 dims the light in ways that mimic distance
00:04:55 --> 00:04:57 and the mass of the galaxy. The supernova
00:04:57 --> 00:05:00 went off in which turns out to correlate with
00:05:00 --> 00:05:02 the supernova's brightness in a way we still
00:05:02 --> 00:05:05 don't fully understand. Both had to be
00:05:05 --> 00:05:07 handled consistently across the whole sample.
00:05:08 --> 00:05:09 The team cared about that second problem
00:05:09 --> 00:05:12 enough that they published a companion paper
00:05:12 --> 00:05:15 on host galaxy masses alongside the main
00:05:15 --> 00:05:15 one.
00:05:16 --> 00:05:18 Avery: Alright, so what does the rebuilt catalogue
00:05:18 --> 00:05:19 actually say?
00:05:20 --> 00:05:22 Anna: Two things, and the first one is reassuring.
00:05:23 --> 00:05:25 If you take the supernovae on their own and
00:05:25 --> 00:05:28 assume the standard model, a flat universe
00:05:28 --> 00:05:31 with a genuinely constant dark energy, you
00:05:31 --> 00:05:33 get a matter density of 0
00:05:34 --> 00:05:36 that is bang in line with everything else we
00:05:36 --> 00:05:39 Know, the catalogue is not broken, it's
00:05:39 --> 00:05:40 behaving.
00:05:40 --> 00:05:42 Avery: And the second thing is the interesting one.
00:05:42 --> 00:05:44 Anna: The second thing is what happens when you
00:05:44 --> 00:05:47 fold in the other two great pillars of
00:05:47 --> 00:05:49 cosmology. The cosmic microwave
00:05:49 --> 00:05:52 background, the leftover glow of the Big
00:05:52 --> 00:05:54 Bang, and baryon acoustic
00:05:54 --> 00:05:57 oscillations, which are frozen sound waves
00:05:57 --> 00:05:59 from the early universe that act as a cosmic
00:05:59 --> 00:06:02 ruler. Do that, and under the standard
00:06:02 --> 00:06:04 constant dark energy model, the three
00:06:04 --> 00:06:07 datasets start pulling against each other.
00:06:07 --> 00:06:09 There's a tension, and here's the pointed
00:06:09 --> 00:06:12 bit, that tension eases if you allow
00:06:12 --> 00:06:15 dark energy to change with time. The team
00:06:15 --> 00:06:17 find a preference for evolving dark energy
00:06:18 --> 00:06:20 over the standard model at between
00:06:20 --> 00:06:22 2.5 and 3.1-sigma,
00:06:22 --> 00:06:24 depending on exactly which combination you
00:06:24 --> 00:06:25 use.
00:06:25 --> 00:06:28 Avery: Let's be careful with sigma, because we've
00:06:28 --> 00:06:30 had this conversation before on this show.
00:06:31 --> 00:06:33 Anna: We have, and we should be careful. Back when
00:06:33 --> 00:06:36 we covered the LZ dark matter flash, we
00:06:36 --> 00:06:37 spent a while on this.
00:06:37 --> 00:06:40 Three Sigma is roughly a, uh, 1 in 700 chance
00:06:40 --> 00:06:43 of the data looking like this. If the
00:06:43 --> 00:06:45 standard model is right, that is interesting.
00:06:45 --> 00:06:48 That is worth chasing. It is emphatically
00:06:48 --> 00:06:51 not a discovery. Particle physics won't call
00:06:51 --> 00:06:54 anything discovered below five sigma. And
00:06:54 --> 00:06:56 cosmology has been burned by three sigma
00:06:56 --> 00:06:59 results before. Nobody on this paper is
00:06:59 --> 00:07:00 claiming otherwise.
00:07:00 --> 00:07:02 Avery: But it's the second independent line of
00:07:02 --> 00:07:05 evidence pointing the same way, which is a
00:07:05 --> 00:07:06 different kind of argument.
00:07:07 --> 00:07:09 Anna: That's exactly the argument Professor Davis
00:07:09 --> 00:07:11 makes, and it's the heart of why this
00:07:11 --> 00:07:13 matters. Her words quote
00:07:14 --> 00:07:16 our Supernova data from DES in
00:07:16 --> 00:07:19 2024 first showed hints that dark energy
00:07:19 --> 00:07:22 may be time varying. And this new compilation
00:07:22 --> 00:07:24 also sees a deviation from the standard
00:07:24 --> 00:07:26 model. And then. So
00:07:27 --> 00:07:29 two completely independent measurements have
00:07:29 --> 00:07:32 found hints of time variation in dark energy
00:07:33 --> 00:07:35 challenging the standard model. That dark
00:07:35 --> 00:07:36 energy doesn't change.
00:07:36 --> 00:07:39 Avery: And this sits alongside what DESSI the,
00:07:39 --> 00:07:42 the Dark Energy Spectroscopic instrument
00:07:42 --> 00:07:45 has been reporting from an entirely different
00:07:45 --> 00:07:47 direction, using those baryon
00:07:47 --> 00:07:50 acoustic oscillations rather than
00:07:50 --> 00:07:51 supernovae.
00:07:51 --> 00:07:54 Anna: Right. Three separate methodologies with
00:07:54 --> 00:07:56 separate systematics, separate failure modes
00:07:56 --> 00:07:59 and separate teams. And they keep producing
00:07:59 --> 00:08:01 the same faint smell of something wrong.
00:08:02 --> 00:08:04 The other number worth flagging is precision.
00:08:05 --> 00:08:07 This compilation tightens the uncertainties
00:08:07 --> 00:08:09 on the dark energy parameters by about
00:08:09 --> 00:08:11 30% compared with what came before.
00:08:12 --> 00:08:14 Which means the next round of data won't just
00:08:14 --> 00:08:17 add noise. It'll actually be able to settle
00:08:17 --> 00:08:17 this.
00:08:17 --> 00:08:20 Avery: So spell out the stakes. What changes if
00:08:20 --> 00:08:22 dark energy really is
00:08:22 --> 00:08:25 Anna: evolving almost everything downstream?
00:08:25 --> 00:08:28 A constant dark energy is the simplest
00:08:28 --> 00:08:30 possible thing. Einstein's cosmological
00:08:30 --> 00:08:33 constant, a fixed energy density baked into
00:08:33 --> 00:08:36 empty space itself. If instead it's a field
00:08:36 --> 00:08:39 that changes strength over cosmic time, then
00:08:39 --> 00:08:41 it's not a constant. It's a dynamic thing
00:08:41 --> 00:08:43 with a history and possibly a future.
00:08:44 --> 00:08:46 It changes how the universe ends.
00:08:46 --> 00:08:48 And Professor Davis takes it further than
00:08:48 --> 00:08:51 that. Her line is that all of this quote
00:08:51 --> 00:08:53 may also hold the clue to explain how gravity
00:08:53 --> 00:08:56 and quantum physics fit together. That's the
00:08:56 --> 00:08:58 biggest unfinished problem in physics. And
00:08:58 --> 00:09:01 dark energy is one of the very few places
00:09:01 --> 00:09:03 where the two are forced into the same room.
00:09:04 --> 00:09:06 Avery: Now, I want to note where this was published
00:09:06 --> 00:09:08 because it's not incidental.
00:09:08 --> 00:09:11 Anna: No, it isn't. This is in publications of
00:09:11 --> 00:09:13 the Astronomical Society of Australia,
00:09:14 --> 00:09:17 Australia's own journal, led from the
00:09:17 --> 00:09:19 University of Queensland with the Australian
00:09:19 --> 00:09:21 National University and Swinburne on the
00:09:21 --> 00:09:24 author list and South African colleagues
00:09:24 --> 00:09:27 alongside. And the Dark energy survey data at
00:09:27 --> 00:09:29 the core of it came off the Blanco 4 metre
00:09:29 --> 00:09:32 telescope at Cerro Tololo in Chile. A
00:09:32 --> 00:09:34 southern telescope looking at a southern sky.
00:09:34 --> 00:09:37 From the Nobel winning work at Matt Stromlo
00:09:37 --> 00:09:39 through to this, the question of what dark
00:09:39 --> 00:09:42 energy is has been a southern hemisphere
00:09:42 --> 00:09:43 argument for a very long time.
00:09:44 --> 00:09:46 Avery: And there's a lovely thread back through our
00:09:46 --> 00:09:47 own recent episodes here.
00:09:48 --> 00:09:51 Anna: There really is. Back in episode 181,
00:09:51 --> 00:09:53 we covered a rebuttal from Nobel laureates,
00:09:53 --> 00:09:55 including Schmidt and Adam Reese, pushing
00:09:55 --> 00:09:57 back hard on a claim that the universe's
00:09:57 --> 00:10:00 acceleration was slowing and confirming the
00:10:00 --> 00:10:03 acceleration is real. That still stands.
00:10:03 --> 00:10:05 This is a different question, not whether
00:10:05 --> 00:10:08 dark energy exists, but whether it holds
00:10:08 --> 00:10:11 still. On Thursday of last week, we talked
00:10:11 --> 00:10:13 about fast radio bursts being used to weigh
00:10:13 --> 00:10:16 the missing gas in the cosmic web, and how
00:10:16 --> 00:10:18 that bears on the S8 tension. And on
00:10:18 --> 00:10:20 Saturday, our Skywatch feature was
00:10:20 --> 00:10:23 SN2026AAIV,
00:10:23 --> 00:10:25 uh, a type 1A going off in NGC
00:10:26 --> 00:10:29 7331. One single example
00:10:29 --> 00:10:31 of exactly the kind of explosion that fills
00:10:31 --> 00:10:33 this catalogue. Bright enough to chase with a
00:10:33 --> 00:10:34 backyard telescope.
00:10:35 --> 00:10:38 Avery: 2 more of
00:10:38 --> 00:10:40 those and you've got a cosmology
00:10:40 --> 00:10:41 that's the whole trick.
00:10:42 --> 00:10:44 Anna: And what happens next is that the sample size
00:10:44 --> 00:10:47 goes up by an order of magnitude. The Vera
00:10:47 --> 00:10:49 Rubin Observatory in Chile is about to start
00:10:49 --> 00:10:51 finding these things in industrial
00:10:51 --> 00:10:54 quantities. And the Nancy Grace Roman Space
00:10:54 --> 00:10:56 Telescope, which we watched launch a
00:10:56 --> 00:10:58 fortnight ago and which powered up its
00:10:58 --> 00:11:01 coronagraph earlier this month, was designed
00:11:01 --> 00:11:03 in large part to nail exactly this
00:11:03 --> 00:11:05 measurement. If dark energy is changing,
00:11:06 --> 00:11:08 we are going to know within a few years. If
00:11:08 --> 00:11:11 it isn't, we'll know that too. And this will
00:11:11 --> 00:11:13 go down as A very well built catalogue that
00:11:13 --> 00:11:14 briefly made everybody nervous.
00:11:15 --> 00:11:18 Avery: Either way, somebody had to do 30 years
00:11:18 --> 00:11:19 of homework first.
00:11:20 --> 00:11:23 Anna: Somebody did. His name's on the paper.
00:11:23 --> 00:11:25 Avery: Here's a question you don't often hear asked
00:11:25 --> 00:11:27 of our own star.
00:11:27 --> 00:11:29 Did the sun eat a planet?
00:11:29 --> 00:11:31 Anna: We ask that about other stars all the time,
00:11:32 --> 00:11:33 Constantly.
00:11:33 --> 00:11:36 Avery: It's one of the standard results in exoplanet
00:11:36 --> 00:11:39 science. You find a star with an oddly high
00:11:39 --> 00:11:42 abundance of the heavy rock forming elements.
00:11:42 --> 00:11:44 And the neat explanation is that it swallowed
00:11:44 --> 00:11:47 one of its own planets and and the debris is
00:11:47 --> 00:11:50 still floating in its outer layers. New
00:11:50 --> 00:11:52 work published in Monthly Notices of the
00:11:52 --> 00:11:55 Royal Astronomical Society turns that
00:11:55 --> 00:11:58 telescope around and points it at us. It's
00:11:58 --> 00:12:01 by Professor Mutlu Yildiz at Egg University
00:12:01 --> 00:12:04 in Turkey. And the Royal Astronomical
00:12:04 --> 00:12:06 Society put it out on the 10th of September.
00:12:07 --> 00:12:10 Anna: And the argument is that the sun has form.
00:12:10 --> 00:12:13 Avery: The argument is that the sun has two long
00:12:13 --> 00:12:15 standing unexplained quirks.
00:12:15 --> 00:12:15 Anna: And.
00:12:15 --> 00:12:18 Avery: And one event could account for both. Quirk
00:12:18 --> 00:12:21 1 is a genuine embarrassment in solar
00:12:21 --> 00:12:24 physics. We can measure the inside of the
00:12:24 --> 00:12:27 sun, not model it. Measure it using
00:12:27 --> 00:12:29 helioseismology. Sound waves
00:12:29 --> 00:12:32 ring through the solar interior. We watch the
00:12:32 --> 00:12:35 surface vibrate and from that we can
00:12:35 --> 00:12:37 reconstruct the speed of sound at different
00:12:37 --> 00:12:40 depths with real precision. And the
00:12:40 --> 00:12:42 standard solar models don't quite match what
00:12:42 --> 00:12:45 we measure. They've never quite matched.
00:12:45 --> 00:12:47 Anna: That's been an open soar for a couple of
00:12:47 --> 00:12:48 decades.
00:12:48 --> 00:12:51 Avery: It has. Quirk two is lithium.
00:12:52 --> 00:12:54 The sun has far less lithium than it ought
00:12:54 --> 00:12:57 to. It's depleted by a factor of well over
00:12:57 --> 00:12:59 a hundred compared with the material it
00:12:59 --> 00:13:02 formed from. And Yildiz's proposal is that
00:13:02 --> 00:13:05 if the young sun swallowed a super Earth,
00:13:05 --> 00:13:08 something in the range of 5 to 10 times the
00:13:08 --> 00:13:10 mass of our planet, the chemical
00:13:10 --> 00:13:12 rearrangement that follows can push the
00:13:12 --> 00:13:14 models toward the measurements and take the
00:13:14 --> 00:13:16 lithium down at the same time.
00:13:17 --> 00:13:19 Anna: How does eating a planet lower your lithium?
00:13:20 --> 00:13:22 Avery: Broadly by changing the structure and the
00:13:22 --> 00:13:25 mixing near the base of the convective zone,
00:13:25 --> 00:13:28 the boundary where the churning outer layers
00:13:28 --> 00:13:31 meet the still interior. That boundary is
00:13:31 --> 00:13:33 where lithium gets dragged down deep enough
00:13:33 --> 00:13:35 to be destroyed by nuclear reactions.
00:13:36 --> 00:13:38 Adjust the composition and the temperature
00:13:38 --> 00:13:41 gradient there and you change how efficiently
00:13:41 --> 00:13:43 the sun burns its own lithium away.
00:13:44 --> 00:13:46 Yildiz's framing is careful.
00:13:47 --> 00:13:50 A planet several times more massive than
00:13:50 --> 00:13:52 Earth may have fallen into the young sun and
00:13:52 --> 00:13:55 left a uh, lasting chemical imprint deep
00:13:55 --> 00:13:58 inside it. And the
00:13:58 --> 00:14:00 ingestion of a super Earth could help explain
00:14:00 --> 00:14:03 long standing differences between standard
00:14:03 --> 00:14:05 solar models and observations.
00:14:05 --> 00:14:08 Anna: May could. Those are Load bearing
00:14:08 --> 00:14:10 words they are,
00:14:10 --> 00:14:13 Avery: and I want to keep them. This is a
00:14:13 --> 00:14:15 modelling result offering a candidate
00:14:15 --> 00:14:18 solution to a modelling discrepancy. It
00:14:18 --> 00:14:21 is not a fossil. Nobody has dug up the
00:14:21 --> 00:14:23 planet. And there are other live
00:14:23 --> 00:14:26 explanations for the solar abundance problem.
00:14:26 --> 00:14:29 Revisions to the measured composition of the
00:14:29 --> 00:14:32 solar photosphere. For one that don't
00:14:32 --> 00:14:34 require eating anything. What makes this
00:14:34 --> 00:14:37 one attractive is economy. One event,
00:14:38 --> 00:14:39 two problems.
00:14:40 --> 00:14:41 Anna: And there's something faintly unsettling
00:14:41 --> 00:14:44 about it, given what it implies about the
00:14:44 --> 00:14:45 early inner solar system.
00:14:46 --> 00:14:48 Avery: That's the part that stays with me.
00:14:48 --> 00:14:51 Super Earths are the single most common class
00:14:51 --> 00:14:54 of planet we find around other stars.
00:14:54 --> 00:14:57 And our solar system conspicuously lacks
00:14:57 --> 00:14:59 one. If the answer is that we had one
00:14:59 --> 00:15:02 and the sun ate it, that makes us a lot
00:15:02 --> 00:15:05 less unusual and makes the ground under
00:15:05 --> 00:15:08 Mercury's orbit feel a good deal less stable
00:15:08 --> 00:15:10 than it looks now.
00:15:11 --> 00:15:12 Anna: A storey about the sun from the opposite
00:15:12 --> 00:15:15 direction and one with a very practical
00:15:15 --> 00:15:18 edge, particularly for anyone listening from
00:15:18 --> 00:15:21 a crew rest seat. New research in the Journal
00:15:21 --> 00:15:23 of Geophysical Research Atmospheres
00:15:24 --> 00:15:26 finds that cosmic radiation at cruising
00:15:26 --> 00:15:29 altitude gets worse when the sun goes
00:15:29 --> 00:15:29 quiet.
00:15:29 --> 00:15:32 Avery: Which is backwards from how most people would
00:15:32 --> 00:15:32 guess it.
00:15:33 --> 00:15:35 Anna: Completely backwards. And the logic is worth
00:15:35 --> 00:15:38 a minute. The work is by Dr. Roy Yaniv
00:15:38 --> 00:15:41 with Professor Yoav Yair and Professor
00:15:41 --> 00:15:44 Colin Price across the Hebrew University of
00:15:44 --> 00:15:47 Jerusalem, Reichman University and Tel
00:15:47 --> 00:15:49 Aviv University. They flew six
00:15:49 --> 00:15:51 instrumented balloons from southern Israel,
00:15:52 --> 00:15:55 each climbing to around 35 kilometres and
00:15:55 --> 00:15:57 measured the radiation environment the whole
00:15:57 --> 00:15:57 way up.
00:15:58 --> 00:16:00 Avery: So what's the profile look like?
00:16:00 --> 00:16:03 Anna: It peaks higher than you fly. The maximum
00:16:03 --> 00:16:06 sits between 17 and 20 kilometres.
00:16:06 --> 00:16:08 That's a known feature called the Regener
00:16:08 --> 00:16:11 Fotzer maximum, where incoming cosmic rays
00:16:11 --> 00:16:13 have smashed into enough atmosphere to
00:16:13 --> 00:16:16 produce a full shower of secondary particles.
00:16:16 --> 00:16:18 But the shower hasn't yet been absorbed.
00:16:19 --> 00:16:22 Below that, it tails off at a typical
00:16:22 --> 00:16:24 airliner cruising altitude of around 10
00:16:24 --> 00:16:27 kilometres. They measure roughly 0.9
00:16:27 --> 00:16:29 to 1.3 microsieverts per hour.
00:16:30 --> 00:16:32 Avery: And um, the solar connection, the sun's
00:16:32 --> 00:16:35 Anna: magnetic field carried out on the solar wind,
00:16:35 --> 00:16:38 acts as a shield for the entire solar system.
00:16:38 --> 00:16:41 It deflects galactic cosmic rays, the
00:16:41 --> 00:16:43 high energy particles arriving from
00:16:43 --> 00:16:45 supernovae and other violence out in the
00:16:45 --> 00:16:46 galaxy.
00:16:46 --> 00:16:49 When the sun is active, that shield is strong
00:16:49 --> 00:16:51 and fewer of those particles get through.
00:16:51 --> 00:16:54 When the sun goes quiet, the shield weakens
00:16:54 --> 00:16:57 and more of them arrive. The team measure
00:16:57 --> 00:16:59 that anti correlation directly at minus
00:16:59 --> 00:17:02 0.71 and the size of the swing is the
00:17:02 --> 00:17:05 headline. At solar minimum, the dose rate
00:17:05 --> 00:17:08 runs something like 40 to 60% higher
00:17:08 --> 00:17:09 than
00:17:09 --> 00:17:12 Avery: at solar maximum 40 to 60%
00:17:12 --> 00:17:14 is not a rounding error. It isn't.
00:17:14 --> 00:17:16 Anna: They also break down what's actually hitting
00:17:16 --> 00:17:19 you. Neutrons are about 40 to
00:17:19 --> 00:17:22 45% of the dose. With electromagnetic
00:17:22 --> 00:17:24 radiation, another 35 to 40
00:17:25 --> 00:17:27 neutrons matter because they're difficult to
00:17:27 --> 00:17:29 shield against and they're weighted heavily
00:17:29 --> 00:17:30 for biological damage.
00:17:31 --> 00:17:34 Avery: Now, proportion before anyone cancels a
00:17:34 --> 00:17:34 holiday.
00:17:35 --> 00:17:37 Anna: Yes, proportion. A, uh, micro sievert
00:17:37 --> 00:17:40 is a millionth of a sievert. A a long haul
00:17:40 --> 00:17:43 flight puts a few tens of micro sieverts on
00:17:43 --> 00:17:45 you, which is in the same broad territory as
00:17:45 --> 00:17:48 a chest X ray for a passenger. This is not
00:17:48 --> 00:17:51 something to lose sleep over for aircrew who
00:17:51 --> 00:17:53 are occupationally exposed and monitored as
00:17:53 --> 00:17:56 radiation workers in many jurisdictions and
00:17:56 --> 00:17:59 for frequent flyers on the very long, very
00:17:59 --> 00:18:01 high, high latitude routes. And
00:18:01 --> 00:18:03 Australia runs some of the longest sectors on
00:18:03 --> 00:18:06 the planet. A, uh, 40 to 60%
00:18:06 --> 00:18:09 seasonal swing driven by where we sit in the
00:18:09 --> 00:18:12 solar cycle is a real input into how you
00:18:12 --> 00:18:13 calculate annual dose.
00:18:14 --> 00:18:16 Avery: And it dovetails with what we talked about on
00:18:16 --> 00:18:18 Saturday from the other end.
00:18:18 --> 00:18:21 Anna: It's the same dial on the weekend we covered
00:18:21 --> 00:18:24 the Max Planck work on the sun's capacity for
00:18:24 --> 00:18:27 a superflare. The danger of the sun at its
00:18:27 --> 00:18:29 loudest, this is the danger of the sun at
00:18:29 --> 00:18:32 its quietest. An active sun can fire
00:18:32 --> 00:18:35 a particle storm at you. A quiet sun simply
00:18:35 --> 00:18:37 stops holding the galaxy's particles at the
00:18:37 --> 00:18:40 door. Two different risks, opposite ends
00:18:40 --> 00:18:43 of the same cycle. And both of them show up
00:18:43 --> 00:18:44 at altitude first.
00:18:44 --> 00:18:47 Avery: Our last storey before we look up is a, uh,
00:18:47 --> 00:18:49 null result. And I want to argue that it's
00:18:49 --> 00:18:51 one of the better pieces of news this week.
00:18:52 --> 00:18:54 The James Webb Space Telescope has just
00:18:54 --> 00:18:56 carried out the most sensitive search for a
00:18:56 --> 00:18:59 moon around another planet ever attempted.
00:18:59 --> 00:19:02 It didn't find one. What matters is how
00:19:02 --> 00:19:04 thoroughly it didn't find one.
00:19:04 --> 00:19:06 Anna: Exomoons have been the great near miss
00:19:06 --> 00:19:09 Avery: of the field for 15 years.
00:19:09 --> 00:19:12 We have close to 6 confirmed planets
00:19:12 --> 00:19:15 around other stars and not one confirmed
00:19:15 --> 00:19:18 moon, which is faintly ridiculous given that
00:19:18 --> 00:19:21 our own solar system has hundreds. The new
00:19:21 --> 00:19:23 work is by David Kipping, who has effectively
00:19:23 --> 00:19:26 made exomoon hunting his life's work. And
00:19:26 --> 00:19:29 it went up on the preprint server on 4
00:19:29 --> 00:19:29 September.
00:19:30 --> 00:19:31 Anna: Which planet did he point it at?
00:19:32 --> 00:19:35 Avery: LP899C,
00:19:35 --> 00:19:37 a rocky planet in the temperate zone of a
00:19:37 --> 00:19:39 very cool, very faint star.
00:19:40 --> 00:19:43 Kipping used 12 separate JWST
00:19:43 --> 00:19:46 transits, 12 passes of the planet in front
00:19:46 --> 00:19:48 of its star and stacked them. And the
00:19:48 --> 00:19:51 sensitivity he gets out of that is the storey
00:19:51 --> 00:19:54 he can exclude Moons down to one tenth of
00:19:54 --> 00:19:57 Earth's radius and at 95%
00:19:57 --> 00:19:59 confidence across the planet's entire hill
00:19:59 --> 00:20:02 sphere. That's the whole region where a moon
00:20:02 --> 00:20:04 could gravitationally hang on.
00:20:05 --> 00:20:07 Anna: One tenth of Earth's Radius is about 650
00:20:07 --> 00:20:10 kilometres which rules out the entire
00:20:10 --> 00:20:13 Avery: mid tier of our own solar system's moons.
00:20:14 --> 00:20:16 Europa's gone. Rhea's gone.
00:20:16 --> 00:20:18 Umbriel's gone. If
00:20:18 --> 00:20:21 LP899C
00:20:21 --> 00:20:23 had anything like those or Webb would have
00:20:23 --> 00:20:24 seen it.
00:20:24 --> 00:20:26 Anna: So why is the absence good news?
00:20:27 --> 00:20:30 Avery: Two reasons. First, because it was always
00:20:30 --> 00:20:32 possible that we'd found no exomoons,
00:20:32 --> 00:20:35 simply because we can't see them. That the
00:20:35 --> 00:20:38 whole search was hopeless and we were wasting
00:20:38 --> 00:20:40 our time. This demonstrates the
00:20:40 --> 00:20:43 opposite. Webb can find astonishingly
00:20:43 --> 00:20:46 small moons and stacking transits buys
00:20:46 --> 00:20:49 you far more sensitivity than a single one.
00:20:49 --> 00:20:52 That's a capability result and it applies to
00:20:52 --> 00:20:55 every other target. Second, this
00:20:55 --> 00:20:58 particular non detection is physically
00:20:58 --> 00:21:00 expected. The planet orbits at Ah, just
00:21:00 --> 00:21:03 0.04 astronomical units,
00:21:04 --> 00:21:07 extremely close in and at that distance
00:21:07 --> 00:21:09 tidal forces would strip a large moon away
00:21:09 --> 00:21:12 over time anyway. So the theory
00:21:12 --> 00:21:15 predicted an empty hill sphere and the
00:21:15 --> 00:21:16 observation delivered an empty
00:21:16 --> 00:21:19 Anna: hill sphere Theory and observation
00:21:19 --> 00:21:22 agreeing is not the most thrilling headline
00:21:22 --> 00:21:24 but it's how you know the instrument is
00:21:24 --> 00:21:25 honest.
00:21:25 --> 00:21:28 Avery: Exactly right. And a small Southern
00:21:28 --> 00:21:29 footnote. The
00:21:29 --> 00:21:32 LP899 system was
00:21:32 --> 00:21:35 found by Speculus, a survey hunting
00:21:35 --> 00:21:37 planets around the coolest stars whose
00:21:37 --> 00:21:40 southern station sits at Paranal in Chile
00:21:40 --> 00:21:43 under the same skies as the telescopes that
00:21:43 --> 00:21:44 keep turning up in this programme.
00:21:45 --> 00:21:47 Anna: Quick update before the skywatch on a storey
00:21:47 --> 00:21:49 we left open a couple of weeks back.
00:21:50 --> 00:21:52 NASA's Crew 13 mission to the International
00:21:52 --> 00:21:55 Space Station is now targeting no earlier
00:21:55 --> 00:21:57 than late September.
00:21:57 --> 00:21:59 Avery: That's the flight that was supposed to go on
00:21:59 --> 00:22:00 the 12th.
00:22:00 --> 00:22:02 Anna: It was on the 29th of August.
00:22:02 --> 00:22:05 NASA and SpaceX stood the mission down after
00:22:05 --> 00:22:07 teams found an oxidizer leak in the Dragon
00:22:07 --> 00:22:10 spacecraft's propulsion system during
00:22:10 --> 00:22:13 standard pre launch processing. At the time
00:22:13 --> 00:22:14 the statement was simply that a new target
00:22:14 --> 00:22:17 date would be announced once available and
00:22:17 --> 00:22:19 that joint teams would complete any necessary
00:22:19 --> 00:22:22 rework before flight. The Canadian Space
00:22:22 --> 00:22:24 Agency has now confirmed the mission is
00:22:24 --> 00:22:26 aiming for no earlier than late September.
00:22:26 --> 00:22:29 Though as we record, NASA hasn't published
00:22:29 --> 00:22:31 Avery: a specific date and the crew is an
00:22:31 --> 00:22:32 interesting one.
00:22:32 --> 00:22:35 Anna: It is Commander Jessica Watkins and
00:22:35 --> 00:22:38 pilot Luke Delaney for NASA with mission
00:22:38 --> 00:22:40 specialist Joshua Kutryk of the Canadian
00:22:40 --> 00:22:42 Space Agency and and Sergey
00:22:42 --> 00:22:45 Teteryatnikov of Roscosmos. They'll
00:22:45 --> 00:22:48 fly on a Falcon 9 from Space Launch Complex
00:22:48 --> 00:22:51 40 at Cape Canaveral. The same pad that
00:22:51 --> 00:22:53 quietly notched its 400th orbital flight
00:22:53 --> 00:22:54 yesterday.
00:22:54 --> 00:22:56 We'll bring you the date the moment it's
00:22:56 --> 00:22:56 firm.
00:22:56 --> 00:22:59 Avery: Right, let's get you outside. And there's
00:22:59 --> 00:23:02 something live happening tonight. A large
00:23:02 --> 00:23:05 coronal hole on the sun has rotated around
00:23:05 --> 00:23:07 into a geo effective position and
00:23:07 --> 00:23:10 forecasters expect the fast solar wind
00:23:10 --> 00:23:12 streaming out of it to to reach Earth today.
00:23:13 --> 00:23:16 That means active geomagnetic conditions,
00:23:16 --> 00:23:17 which means
00:23:17 --> 00:23:19 Anna: aurora watching is on at both ends of the
00:23:19 --> 00:23:20 planet.
00:23:20 --> 00:23:22 Avery: It does for our southern hemisphere
00:23:22 --> 00:23:25 listeners. That's Aurora australis
00:23:25 --> 00:23:28 territory Tasmania first and best,
00:23:28 --> 00:23:31 with a genuine chance from southern Victoria
00:23:31 --> 00:23:33 and the far south of New Zealand. If it holds
00:23:33 --> 00:23:36 up, look south, get away from town
00:23:36 --> 00:23:39 lights and be patient. Keep cameras will pick
00:23:39 --> 00:23:42 up colour your eyes won't. For, uh, our
00:23:42 --> 00:23:44 North American listeners, you're looking
00:23:44 --> 00:23:47 north and the northern tier states and
00:23:47 --> 00:23:50 Canada are in play. This is a
00:23:50 --> 00:23:52 coronal hole stream rather than a big flare
00:23:52 --> 00:23:55 event. So think a steady moderate
00:23:55 --> 00:23:58 glow rather than a spectacular overhead
00:23:58 --> 00:24:01 display. But it's free and it's
00:24:01 --> 00:24:02 tonight and
00:24:02 --> 00:24:04 Anna: the moon is out of the way for it.
00:24:05 --> 00:24:08 Avery: Beautifully out of the way. New Moon was last
00:24:08 --> 00:24:10 Friday, so we're in a young crescent evening
00:24:10 --> 00:24:13 sky and the deep sky is still yours.
00:24:14 --> 00:24:16 Over the next week, the Moon climbs back into
00:24:16 --> 00:24:19 the evening and walks past two landmarks
00:24:19 --> 00:24:22 worth Antares, the Red
00:24:22 --> 00:24:25 Heart of Scorpius and the Teapot of
00:24:25 --> 00:24:28 Sagittarius. Use the Moon to find
00:24:28 --> 00:24:31 them between now and the 20th. And from
00:24:31 --> 00:24:34 Sydney, the centre of the Milky Way is still
00:24:34 --> 00:24:36 riding high overhead after dark.
00:24:36 --> 00:24:39 That dense textured band through the
00:24:39 --> 00:24:42 teapot is the galactic core and
00:24:42 --> 00:24:44 it is one of the genuine privileges of
00:24:44 --> 00:24:47 southern observing. From mid northern
00:24:47 --> 00:24:50 latitudes, it's much lower in the south, so
00:24:50 --> 00:24:52 northern listeners should hunt for a clear
00:24:52 --> 00:24:55 southern horizon while the season lasts.
00:24:56 --> 00:24:58 Anna: Planets. Venus is the headline.
00:24:59 --> 00:25:02 Avery: Venus is the headline and Thursday is the
00:25:02 --> 00:25:02 date.
00:25:03 --> 00:25:06 On the 18th of September, Venus reaches
00:25:06 --> 00:25:07 greatest brilliancy for this evening
00:25:07 --> 00:25:10 apparition. At magnitude
00:25:10 --> 00:25:12 -4.8. That is
00:25:12 --> 00:25:15 spectacularly bright. Bright enough to cast
00:25:15 --> 00:25:18 a shadow from a dark sight. Bright enough
00:25:18 --> 00:25:21 that you'll field phone calls about it. Look
00:25:21 --> 00:25:24 west shortly after sunset. You'll notice
00:25:24 --> 00:25:26 some listings give a different date for this.
00:25:26 --> 00:25:29 We're going with the 18th, which is the
00:25:29 --> 00:25:32 correct one for the standard definition. And
00:25:32 --> 00:25:35 this apparition favours the south. From
00:25:35 --> 00:25:38 Sydney, Venus sits higher and lingers
00:25:38 --> 00:25:40 longer in a darker sky than it does from most
00:25:40 --> 00:25:43 of the United States, where it's a lower,
00:25:43 --> 00:25:45 briefer object in the twilight.
00:25:45 --> 00:25:48 Anna: Take the win m. Anything else worth chasing?
00:25:49 --> 00:25:52 Avery: Three things Mercury is low in the
00:25:52 --> 00:25:55 western twilight, tricky but doable with
00:25:55 --> 00:25:58 a clear horizon. Mars is in the
00:25:58 --> 00:26:00 morning sky and passes about 6 degrees
00:26:00 --> 00:26:03 south of Pollux, the brighter of the Gemini
00:26:03 --> 00:26:06 twins, also on the 18th.
00:26:06 --> 00:26:09 That one's a northern favourite view. And
00:26:09 --> 00:26:12 Saturn is building towards opposition on the
00:26:12 --> 00:26:15 4th of October, with the rings about 7
00:26:15 --> 00:26:17 degree open. So it is well placed
00:26:17 --> 00:26:20 all night and getting better. The Harvest
00:26:20 --> 00:26:23 Moon rides past it on the 26th with
00:26:23 --> 00:26:25 Neptune nearby. For anyone with
00:26:25 --> 00:26:27 binoculars or a scope,
00:26:28 --> 00:26:30 Anna: there's also a date for the diary. Next
00:26:30 --> 00:26:31 Saturday there is.
00:26:32 --> 00:26:34 Avery: 19th September is international
00:26:34 --> 00:26:37 observe the Moon night, which is one of the
00:26:37 --> 00:26:39 few global astronomy events that works
00:26:39 --> 00:26:42 equally well from either hemisphere. With no
00:26:42 --> 00:26:45 equipment at all, the Moon will be a fat
00:26:45 --> 00:26:47 crescent in the evening sky, which is
00:26:47 --> 00:26:50 genuinely the best phase for it because the
00:26:50 --> 00:26:52 shadows along the terminator throw the
00:26:52 --> 00:26:55 craters and mountains into relief. If you've
00:26:55 --> 00:26:57 got a pair of binoculars, that's all you
00:26:57 --> 00:26:59 need. If you've got a telescope and a
00:26:59 --> 00:27:01 neighbour, that's even better.
00:27:02 --> 00:27:04 Anna: And the equinox is coming, the
00:27:04 --> 00:27:05 22nd
00:27:05 --> 00:27:08 Avery: spring here, autumn for our northern
00:27:08 --> 00:27:10 listeners. And it brings the zodiacal light
00:27:10 --> 00:27:13 with it. That's sunlight scattering off
00:27:13 --> 00:27:15 dust in the plane of the solar system and
00:27:15 --> 00:27:18 around the equinox. It's an evening object
00:27:18 --> 00:27:21 low in the west from the southern hemisphere,
00:27:21 --> 00:27:24 a false dusk and a pre dawn object
00:27:24 --> 00:27:27 in the east from the northern hemisphere. A
00:27:27 --> 00:27:30 faint tapering cone of light, dark
00:27:30 --> 00:27:32 skies, no moon and patience.
00:27:33 --> 00:27:35 Anna: And the safety note, which is not optional on
00:27:35 --> 00:27:36 this programme.
00:27:36 --> 00:27:39 Avery: Never optional. With Venus at its most
00:27:39 --> 00:27:41 brilliant, some of you will be tempted to
00:27:41 --> 00:27:44 hunt it in daylight and it is genuinely
00:27:44 --> 00:27:47 findable. But that means aiming optics
00:27:47 --> 00:27:49 near the sun and that is how people
00:27:49 --> 00:27:52 permanently damage their eyes. If you are
00:27:52 --> 00:27:55 going to look anywhere near the sun, use a
00:27:55 --> 00:27:57 filter Certified to the ISO
00:27:57 --> 00:28:00 123122 standard
00:28:00 --> 00:28:02 fitted over the front of the instrument,
00:28:03 --> 00:28:04 never at the eyepiece.
00:28:04 --> 00:28:06 Cheque it for scratches and pinholes before
00:28:06 --> 00:28:09 every use. Sunglasses,
00:28:09 --> 00:28:11 exposed film, smoked glass and
00:28:11 --> 00:28:14 welding glass below shade 14 are
00:28:14 --> 00:28:17 not safe and never were. And
00:28:17 --> 00:28:19 supervise children the entire time.
00:28:20 --> 00:28:22 Anna: And that's Astronomy daily for Monday
00:28:22 --> 00:28:24 14th September
00:28:25 --> 00:28:27 2884. Supernovae
00:28:27 --> 00:28:30 rebuilt from three decades of observations by
00:28:30 --> 00:28:33 an Australian led team quietly making the
00:28:33 --> 00:28:35 case that dark energy might not hold still.
00:28:35 --> 00:28:38 Avery: A sun that may have eaten a super earth and
00:28:38 --> 00:28:41 still carries the receipt. A reminder that
00:28:41 --> 00:28:44 the sun's quiet years are the ones that let
00:28:44 --> 00:28:46 the galaxy's particles through. And the most
00:28:46 --> 00:28:49 sensitive exomoon search ever attempted,
00:28:49 --> 00:28:52 finding precisely nothing in the most
00:28:52 --> 00:28:53 useful possible way.
00:28:54 --> 00:28:56 Anna: All of Today's storeys with links to the
00:28:56 --> 00:28:58 papers and the press releases are are at
00:28:58 --> 00:29:01 astronomydaily IO you'll find the
00:29:01 --> 00:29:04 full back catalogue there too, along with our
00:29:04 --> 00:29:06 news feed and the newsletter. If you'd like
00:29:06 --> 00:29:07 this in your inbox
00:29:07 --> 00:29:09 Avery: and we do read the contact form.
00:29:10 --> 00:29:12 Questions, corrections and storey tips all
00:29:12 --> 00:29:15 land with us, and they have shaped more than
00:29:15 --> 00:29:18 one segment lately. You can also find us
00:29:18 --> 00:29:19 on socials.
00:29:19 --> 00:29:22 Anna: Astrodaily pod astronomy daily
00:29:22 --> 00:29:24 is part of the bytes.com podcast network.
00:29:24 --> 00:29:25 I'm Anna.
00:29:25 --> 00:29:28 Avery: And I'm Avery. Clear skies
00:29:28 --> 00:29:29 wherever you're standing.