Goodbye, Star Traveller: 3I/ATLAS Bids Farewell at Jupiter

0:00 Speaker 1: Hello, and welcome to Astronomy Daily.

0:03 Speaker 2: I'm Anna and I'm Avery. You're listening to Season five,

0:06 Speaker 2: episode sixty four, and what a Monday we have for

0:10 Speaker 2: you we do.

0:12 Speaker 1: Right now as we record this, an interstellar comet is

0:16 Speaker 1: making its final farewell pass through our solar system. It

0:20 Speaker 1: is swinging past Jupiter today and it's never coming back.

0:24 Speaker 2: That story alone would be enough, but we've also got

0:28 Speaker 2: a brand new mineral potentially discovered on Mars, a pre

0:31 Speaker 2: don sky show you can catch this week, ghost particles

0:35 Speaker 2: that carry memories of stars that died before Earth was born,

0:39 Speaker 2: and two genuinely mind bending stories about the nature of

0:43 Speaker 2: life itself.

0:44 Speaker 1: So let's get into it, starting with our cosmic farewell

0:48 Speaker 1: right then.

0:49 Speaker 2: If you've been following the story of three I Atls

0:53 Speaker 2: since it arrived in our solar system last July, today

0:56 Speaker 2: is a significant day. The comment is making its close

1:00 Speaker 2: this approach to Jupiter right now, and after that it

1:02 Speaker 2: begins its long one way journey back out into interstellar space.

1:07 Speaker 2: It will never return.

1:10 Speaker 1: Just to recap for anyone catching up, Three I Atlas

1:13 Speaker 1: is only the third known object ever confirmed to have

1:17 Speaker 1: come from outside our Solar System, after Omuamua in twenty

1:21 Speaker 1: seventeen and Borisov in twenty nineteen. This is our third

1:25 Speaker 1: interstellar visitor, and like the others, it's been an absolute

1:30 Speaker 1: gift to science.

1:31 Speaker 2: What makes today particularly satisfying is that astronomers have had

1:35 Speaker 2: months to study this thing up close, and the picture

1:38 Speaker 2: that's emerged is remarkable. In the last few weeks alone,

1:41 Speaker 2: the it's a Comma Large millimeter Array ALMA published finding

1:45 Speaker 2: showing that three i atls is packed with methanol, not

1:50 Speaker 2: just a bit of it, far more than almost any

1:52 Speaker 2: other comment we've ever seen from our own Solar System.

1:56 Speaker 1: Researchers described the methanol to hydrogen cyanide ratios as being

2:01 Speaker 1: up to about one hundred and twenty in places, which

2:04 Speaker 1: puts it completely off the charts compared to Solar System comets.

2:08 Speaker 1: And that matters because the methanol appears to be coming

2:12 Speaker 1: from two sources, directly from the comet's core and also

2:16 Speaker 1: from tiny ice grains drifting through the coma around it.

2:20 Speaker 1: That tells us something really interesting about how this object

2:23 Speaker 1: was built.

2:24 Speaker 2: One of the lead researchers describe observing three i atls

2:28 Speaker 2: as and I love this phrase. Taking a fingerprint from

2:32 Speaker 2: another solar system, because that's literally what it is. The

2:35 Speaker 2: chemistry locked in this comment reflects the conditions in the

2:38 Speaker 2: planetary system where it was born billions of years ago,

2:42 Speaker 2: around some star we may never identify.

2:45 Speaker 1: There's also the intrigue of Auvi Lobe's recent summary. He

2:49 Speaker 1: listed twenty two anomalies observed in three iatls during its passage.

2:55 Speaker 1: Some of those are almost certainly explained by unusual but

2:58 Speaker 1: natural chemistry. But the point is that every comet born

3:02 Speaker 1: in our solar system is at least somewhat familiar. This

3:06 Speaker 1: one keeps surprising us.

3:08 Speaker 2: And now it's leaving. If you want to try to

3:10 Speaker 2: catch it one last time, it's currently in the constellation Gemini.

3:14 Speaker 2: A small telescope will do it. Though it's fading southern hemisphere,

3:18 Speaker 2: observers still have a reasonable view.

3:20 Speaker 1: Safe travels. Three I als. You were a good guest.

3:25 Speaker 2: Now let's bring it a bit closer to home, literally

3:27 Speaker 2: your own backyard. If you're willing to get up early.

3:30 Speaker 1: This week, and I know it's a Monday, so maybe

3:33 Speaker 1: set that alarm a little earlier than usual, because this

3:37 Speaker 1: is worth it. Tonight and tomorrow morning. Mercury and Mars

3:41 Speaker 1: are gathering close to the crescent Moon in the pre

3:44 Speaker 1: dawn sky.

3:45 Speaker 2: On March sixteenth, that's tonight. The spacing between the moon

3:49 Speaker 2: and the two planets is roughly the width of a

3:51 Speaker 2: clenched tiff held at arm's length, and the arrangement of

3:55 Speaker 2: the three objects creates a sort of sad face shape

3:58 Speaker 2: which is charming and slightly melancholy for reasons I can't

4:02 Speaker 2: quite articulate.

4:03 Speaker 1: By tomorrow, March seventeenth, the thin crescent moon will first

4:08 Speaker 1: pass Mercury and then move close to Mars, which tightens

4:11 Speaker 1: the grouping. All three objects rise shortly before sunrise, though,

4:16 Speaker 1: so the sky is already brightening when they appear. You

4:19 Speaker 1: do need to be quick.

4:20 Speaker 2: And here's the thing. Southern hemisphere observers genuinely have the

4:24 Speaker 2: better view here for our listeners in Australia, New Zealand,

4:27 Speaker 2: South Africa, South America. The group sits a bit higher

4:31 Speaker 2: above the horizon, which makes a real difference. In those conditions.

4:35 Speaker 1: Look east before sunrise, give yourself at least twenty minutes

4:39 Speaker 1: before the sun comes up. Mercury is the tricky one.

4:42 Speaker 1: It never strays far from the horizon because it orbits

4:45 Speaker 1: so close to the sun, though binoculars can really help, and.

4:49 Speaker 2: We're in a geomagnetically active period of the year right now.

4:53 Speaker 2: The equinox is this Friday, March twentieth, and the weeks

4:56 Speaker 2: around the March and September equinoxes are statistically the most

5:00 Speaker 2: active for auroras, so if you're in the higher latitudes,

5:03 Speaker 2: it's worth checking aurora forecasts this week too.

5:06 Speaker 1: Pre dawn planetary grouping possible auroras equinox on Friday. It's

5:12 Speaker 1: actually a really rich week for skywatching even without the comment.

5:16 Speaker 2: All right, let's head to Mars and a story that

5:18 Speaker 2: on the surface sounds almost mundanely technical, but is actually

5:22 Speaker 2: quite exciting when you dig into it.

5:24 Speaker 1: Scientists studying Mars may have uncovered a brand new mineral

5:28 Speaker 1: hidden in the planet's ancient sulfate deposits. And the reason

5:32 Speaker 1: this is interesting isn't just because new minerals are cool,

5:35 Speaker 1: though they are. It's because of what it might tell

5:37 Speaker 1: us about Mars's geological and chemical history.

5:41 Speaker 2: The way this was found is a nice example of

5:43 Speaker 2: how planetary science works these days. The team combined laboratory

5:47 Speaker 2: experiments with orbital data, so they were essentially testing chemical

5:51 Speaker 2: reactions in the lab that might have occurred on ancient Mars,

5:55 Speaker 2: and then looking for matching signatures from orbit, and they

5:58 Speaker 2: found something that doesn't quite match anything already in the catalog.

6:02 Speaker 1: Soul fit minerals on Mars are enormously important scientifically because

6:06 Speaker 1: they tend to form in the presence of water. Mars

6:09 Speaker 1: went through periods of significant liquid water activity billions of

6:13 Speaker 1: years ago, and sulfates are one of the chemical fingerprints

6:17 Speaker 1: left behind.

6:18 Speaker 2: So if there's a previously uncataloged mineral hiding in those deposits,

6:22 Speaker 2: it's potentially a new clue to Mars's wet past, the

6:26 Speaker 2: conditions under which water was present, for how long and

6:29 Speaker 2: what temperatures. That feeds directly into the big question of

6:33 Speaker 2: whether Mars was ever habitable.

6:35 Speaker 1: This is still early stage science. A potential new mineral

6:39 Speaker 1: needs to be confirmed through further analysis and ideally through

6:42 Speaker 1: surface samples, which is one of the reasons the sample

6:45 Speaker 1: return missions being planned are so important. You can only

6:49 Speaker 1: go so far with orbital spectroscopy. At some point you

6:53 Speaker 1: need the rock in your hand.

6:55 Speaker 2: Or at least in a laboratory on Earth. But either way,

6:57 Speaker 2: another reason to keep looking at Mars. The planet still

7:01 Speaker 2: has things to teach us.

7:02 Speaker 1: Now this next story. I genuinely love this one because

7:06 Speaker 1: it involves particles that have been traveling through space for

7:09 Speaker 1: longer than Earth has existed, passing through absolutely everything in

7:14 Speaker 1: their path, and a telescope buried deep underground in Japan

7:17 Speaker 1: that might be able to catch them for the first time.

7:21 Speaker 2: We're talking about neutrinos, specifically what scientists call the diffuse

7:25 Speaker 2: supernova neutrino background. The idea is this, every time a

7:30 Speaker 2: massive star explodes in a supernova, the vast majority of

7:34 Speaker 2: the energy we're talking over ninety nine percent isn't in

7:37 Speaker 2: the light. It's in a flood of neutrinos that shoot

7:40 Speaker 2: outward at nearly the speed of light.

7:42 Speaker 1: And neutrinos are extraordinary particles. They have almost no mass,

7:46 Speaker 1: they carry no electric charge, and they interact with almost nothing.

7:51 Speaker 1: Billions of them are passing through your body right now,

7:54 Speaker 1: this very second, and you don't feel a thing. Some

7:57 Speaker 1: of them have been traveling for more than ten billion

8:00 Speaker 1: in years.

8:01 Speaker 2: So the idea is that all those supernovae across all

8:04 Speaker 2: of cosmic history have rough behind a kind of faint

8:07 Speaker 2: background glow of neutrinos, a cumulative whisper of every star

8:11 Speaker 2: that ever exploded, and Japan's Supercomyo Gunda detector, which has

8:16 Speaker 2: just received a major upgrade, may be able to detect

8:19 Speaker 2: that background glow for the first time in twenty twenty six.

8:23 Speaker 1: The upgrade is significant. Super Commoconde is buried under a

8:27 Speaker 1: mountain about a kilometer of rock overhead to filter out

8:31 Speaker 1: cosmic ray interference. It's essentially a tank containing fifty thousand

8:36 Speaker 1: tons of ultrapure water lined with photo multiplier tubes that

8:41 Speaker 1: flash when a neutrino very occasionally interacts with the water.

8:45 Speaker 1: The upgrade has made it roughly twice as sensitive.

8:49 Speaker 2: What makes this detection so remarkable if it happens, is

8:53 Speaker 2: that these neutrinos would include particles produced by stars that

8:57 Speaker 2: died before Earth even formed. Would be detecting the ghost

9:01 Speaker 2: signals of stars that died ten billion years ago, the

9:05 Speaker 2: universe's oldest obituaries.

9:07 Speaker 1: If you like the researcher quoted in the original article

9:10 Speaker 1: put it beautifully, this would mean seeing particles produced before

9:15 Speaker 1: the Earth itself existed. For a particle astrophysicist, they said,

9:20 Speaker 1: it would probably be one of the most exciting scientific

9:23 Speaker 1: achievements of their lifetime.

9:25 Speaker 2: We're not there yet. This is a might happen in

9:28 Speaker 2: twenty twenty six story, not a confirmed detection, but the

9:32 Speaker 2: fact that we're even within reach of this extraordinary.

9:36 Speaker 1: Okay, we need to talk about how we look for

9:39 Speaker 1: life on other worlds, because there's a paper published today,

9:43 Speaker 1: literally today that I think is going to become quite important.

9:47 Speaker 2: The standard approach to finding life on exoplanets is essentially

9:51 Speaker 2: to look at their atmospheres for the same gases we

9:54 Speaker 2: associate with life on Earth oxygen, methane, ozone, the logic

9:59 Speaker 2: being that the are hard to explain without biology. But

10:02 Speaker 2: there's always been a problem lurking in that approach.

10:06 Speaker 1: The problem is that we wrote that shopping list. By

10:09 Speaker 1: studying Earth, we are essentially looking for life that looks

10:13 Speaker 1: like us, and increasingly researchers have been finding false positive

10:18 Speaker 1: scenarios purely chemical processes that can mimic those biosignature gases

10:23 Speaker 1: without any life being involved.

10:25 Speaker 2: So Sarah Walker, professor of astrobiology at Arizona State University,

10:30 Speaker 2: and her colleagues have been developing a different framework entirely.

10:35 Speaker 2: It's called assembly theory, and instead of asking what molecules

10:39 Speaker 2: are present in this atmosphere, it asks how hard were

10:42 Speaker 2: those molecules to make.

10:44 Speaker 1: Every molecule can be given an assembly index, a minimum

10:48 Speaker 1: number of construction steps required to build it from the

10:52 Speaker 1: most basic chemical building blocks. Simple molecules like water or

10:57 Speaker 1: carbon dioxide are easy to assassemble by random chemistry, but

11:02 Speaker 1: truly complex molecules, the kind requiring many sequential, specific steps,

11:08 Speaker 1: essentially don't arise by accident.

11:11 Speaker 2: When you find the planetary atmosphere rich in molecules with

11:15 Speaker 2: very high assembly indices, and where the chemistry shows signs

11:18 Speaker 2: of deep interconnection, molecules sharing and reusing chemical fragments, exploring

11:24 Speaker 2: the full range of possible bonds, something beyond ordinary physics

11:29 Speaker 2: has been at work, and that's something the theory argues

11:32 Speaker 2: is almost certainly life.

11:35 Speaker 1: What's really powerful about this is that it makes no

11:38 Speaker 1: assumptions about what kind of life, no specific biochemistry, no

11:43 Speaker 1: specific metabolism, no DNA required. It would detect life that

11:47 Speaker 1: is genuinely alien in its chemistry, life not as we

11:51 Speaker 1: know it.

11:52 Speaker 2: When they compared Earth's atmosphere to Venus, Mars, and various

11:56 Speaker 2: exoplanet types, Earth stood out clearly as having the most

12:00 Speaker 2: complex molecular chemistry by this measure, even though Earth and

12:04 Speaker 2: Venus have similar chemical raw materials available to them, Earth's

12:08 Speaker 2: atmosphere shows far greater molecular diversity. That's the signature of

12:13 Speaker 2: a biosphere actively exploring chemical possibility space.

12:17 Speaker 1: And here's the practical part. This framework is being designed

12:21 Speaker 1: specifically for the Habitable World's Observatory, NASA's next flagship telescope.

12:26 Speaker 1: Assembly values can be calculated from infrared spectroscopy, which is

12:31 Speaker 1: exactly what space telescopes use to read distant atmospheres. Rather

12:35 Speaker 1: than a binary a live or dead result, you'd get

12:39 Speaker 1: a continuous complexity score, a spectrum from purely chemical to

12:43 Speaker 1: richly biological.

12:45 Speaker 2: The universe has had nearly fourteen billion years to experiment

12:48 Speaker 2: with chemistry. Assuming it only arrived at one solution for life,

12:52 Speaker 2: our solution does seem, when you think about it, a

12:56 Speaker 2: little over confident.

12:57 Speaker 1: Agreed, this one has legs.

12:59 Speaker 2: Watch and finally, let's end today with something that genuinely

13:03 Speaker 2: ships where you look when you're searching for life in

13:06 Speaker 2: the universe.

13:07 Speaker 1: In our standard mental model of a habitable world, you

13:10 Speaker 1: need a star, you need sunlight. Without a star, there's

13:14 Speaker 1: no energy, no warmth, no liquid water, no life. That's

13:18 Speaker 1: the assumption we've been working.

13:20 Speaker 2: With a new study from Ludwig Maximilian University of Munich

13:23 Speaker 2: and the max Plank Institute for Extraterrestrial Physics is quietly

13:27 Speaker 2: dismantling that assumption. Their research focuses on free floating planets,

13:32 Speaker 2: worlds that were ejected from their home Solar systems early

13:35 Speaker 2: in the chaos of planetary formation and have been drifting

13:38 Speaker 2: through the galaxy ever since, starless and alone.

13:41 Speaker 1: The question they asked is could moons orbiting those free

13:45 Speaker 1: floating planets maintain liquid water? And the answer is yes

13:50 Speaker 1: for a surprisingly long time.

13:52 Speaker 2: Two things make it possible. First, tidal heating. When a

13:56 Speaker 2: moon orbits a planet on an elliptical orbit, which is

13:59 Speaker 2: likely after the chaos ejection event, the planet's gravity compresses

14:03 Speaker 2: and releases the moon's interior as it passes close and

14:06 Speaker 2: then swings away. That friction generates heat. We see this

14:10 Speaker 2: in our own solar system. Io, Jupiter's innermost large moon

14:14 Speaker 2: is the most volcanically active body we know of. Because

14:17 Speaker 2: of tidal heating, Europa likely has a subsurface ocean for

14:21 Speaker 2: the same reason.

14:22 Speaker 1: The second piece is atmosphere. Earlier models looked at carbon

14:26 Speaker 1: dioxide as the insulating layer, but at the temperatures around

14:30 Speaker 1: a free floating planet, carbon dioxide freezes and drops out

14:34 Speaker 1: of the atmosphere the insulation collapses, so the team turned

14:38 Speaker 1: to hydrogen instead.

14:39 Speaker 2: Hydrogen has an unusual property under pressure, molecules temporarily link

14:44 Speaker 2: together and can absorb infrared radiation the kind that otherwise

14:48 Speaker 2: would carry heat away from the surface. It's called collision

14:52 Speaker 2: induced absorption. And crucially, hydrogen doesn't freeze, the atmosphere stays intact.

14:58 Speaker 1: The modeling found at a hundred bars of surface pressure,

15:01 Speaker 1: a moon could maintain habitable liquid water conditions for up

15:05 Speaker 1: to four point three billion years. That's not a coincidence.

15:09 Speaker 1: That's roughly the age of complex life on Earth. So

15:13 Speaker 1: in principle, there are moons drifting through the dark between

15:16 Speaker 1: the stars right now that could be hosting biology that

15:19 Speaker 1: started when ours did.

15:21 Speaker 2: The lead author put it simply and beautifully, the cradle

15:24 Speaker 2: of life does not necessarily require a sun.

15:27 Speaker 1: That is a sentence that I think will age very well.

15:30 Speaker 2: And that is Astronomy Daily for Monday, the sixteenth of

15:33 Speaker 2: March twenty twenty six. Interstellar farewells, new minerals on Mars,

15:38 Speaker 2: ghost particles, life without a star honestly, not a bad

15:42 Speaker 2: way to start the week.

15:43 Speaker 1: If you're heading outside before sunrise tomorrow, let us know

15:46 Speaker 1: what you see.

15:47 Speaker 2: Tag us.

15:48 Speaker 1: We are at Astro daily pod everywhere and if you're.

15:51 Speaker 2: Enjoying the show, please do leave us a review, share

15:54 Speaker 2: an episode with someone, or just tell a friend. It

15:57 Speaker 2: genuinely makes a difference.

15:58 Speaker 1: Until tomorrow, keep looking up.

16:00 Speaker 2: We are skies everyone. Sunny Day Star is the toll.

16:12 Speaker 1: Star is.

16:13 Speaker 2: The story is