The Great Water Mystery: Jezero Crater and the Hunt for Mars' Hidden History

0:00 Anna: They went looking for the bottom of a lake. They found the inside of a volcano Avery: and then they found that water had been through it three separate times. Anna: Perseverance at the Edge of Jezero Crater published Monday, and it rewrites what that shoreline actually is. Avery: Also today, Europe's Jupiter probe comes home on Monday night and for 15 minutes it flies straight over Australia in a dark sky. Anna: Two teams, two completely different techniques, both pointing at a fifth planet hiding inside the most famous planetary system we have ever photograph.

0:32 Avery: And water in an interstellar comet and what its heavy hydrogen says about the star that made it. Anna: I'm Anna. Avery: I'm, um, Avery. Anna: This is Astronomy AstroDailyPod. And this is series five, episode 200. In September of 2023, NASA's perseverance rover drove up onto a strip of ground called the Margin Unit. It hugs the inner edge of Jezero Crater's rim and it runs along what was once the shoreline of a lake. If you had asked the science team what they expected to find there, the answer would have been straightforward.

1:02 Sediment, clay and silt laid down in layers the way sand piles up on a lakebed over thousands of years. There was a good reason to expect it. Orbiters had been picking up strong signals of carbonate murals from that spot for years. On Earth, carbonates very often form in shallow lakes and shallow seas. Exactly the kind of warm, wet, shallow environment where life can get a foothold. And exactly the kind of rock that is good at preserving the evidence afterwards. That is a large part of why Jezero was chosen as a landing site in the first place.

1:36 Avery: So they drove up expecting a beach. Anna: And what the rover found was igneous rock. Rock that forms from magma either deep underground or from volcanic activity at the surface. The work was published on Monday in the journal Communications Earth and Environment, published by Candace Bedford, a research scientist at Purdue University in Indiana. It went straight to the Journal. There is no preprint sitting behind it. So what we are describing is the peer reviewed version, not an early draught.

2:04 The instrument doing the heavy lifting is Supercam. It sits up on the rover's mast and it works by firing a laser at a rock from as far as six and a half metres away. The laser vaporises a tiny patch of the surface into a glowing plasma. And the spectrum of light coming off that plasma tells you what the rock is made of. Perseverance has done this on more than 185 bedrock targets across the Margin unit. And the rover did not just sample one spot. It worked its way across about 265 metres of elevation from high on the unit down to the old lakebed.

2:39 That vertical range turns out to be the whole storey. Avery: What changes as you go down? Anna: High up, the rock is coarse, greened and crystalline, and it's dominated by olivine, a mineral made of magnesium and iron. Coarse crystals mean slow cooling. This rock formed in a body of magma well underground, cooled slowly enough for its grains to grow large, and only reached the surface much later after everything above it had eroded. And up there, it's almost pristine. Almost no sign that water ever touched it.

3:11 And lower down, lower down on the lake bed itself, the same rock looks transformed. The olivine grains are fractured and there's silica sitting between them. Same starting material, completely different history. That's what makes igneous rock so useful here. And it's slightly counterintuitive. We tend to think of sedimentary rock as the record keeper. But mineral crystals in igneous rock preserve the precise conditions of the moment they formed. And when water comes through later and alters them, it leaves a signature too.

3:41 So instead of a beach, the team got something arguably better. A rock that had been written on more than once and kept every draught three separate episodes. Here is the sequence the team reads out of the chemistry. And I want to be precise about this because it is the finding. First, carbon dioxide, rich groundwater came up through the rock and reacted with the olivine. That reaction produced carbonate and it filled the fractures running through the bedrock at the low elevations. Today, those carbonate filled fractures are left standing proud like ridges, because the softer rock around them has worn away faster.

4:20 Second, an episode that may well be the lake itself. Turning olivine into carbonate leaves silica behind. And Eleni Ravanis at the University of Hawaii at Manoa, a, uh, co author, puts it that they see more of that silica in the rocks that sat below the waterline. And third, in one location, in the eastern part of the margin unit, there are mineral veins about 25 centimetres thick, and they contain calcium sulphate and fluorite. Fluorite is the tell. On Earth, fluorite typically forms when hot water circulates through volcanic rock.

4:57 That points to a later heated underground water event, something quite different from the first two. Avery: So why does any of this bear on the question people actually care about? Anna: When water interacts with olivine on Earth, the reaction can release hydrogen. Hydrogen is a food source for certain microbes, and the same reaction leaves behind carbonate and silica to two minerals that happened to be very good at locking in traces of whatever was living there. So what the Margin unit is describing is not a single wet moment.

5:30 It is a place where the right chemistry was available repeatedly over a long stretch of the planet's history. Bedford's own framing is that this location became, quote, a sort of crossroads for aqueous systems. And she makes the point that reaches past Jezero. This crater sits inside one of the largest exposures of carbonate anywhere on Mars. If the carbonate here did not form the way everyone assumed from orbit, that is a question mark hanging over a lot of other carbonate on that planet, Avery: which is a slightly uncomfortable finding for orbital geology.

6:05 Anna: It is, and Bedford says so almost cheerfully. Her line is that after 10 years working with Mars rovers, what she has learned is that Mars constantly throws surprises at you and that it's very rare for things to be as we expect them to be from orbital data. Now, three things to hold onto and none of them are optional. One, the team can establish the order of these water events. They cannot date them. We know first, second, third, we do not know when and we do not know how far apart. Two, and this is the important one, this is a habitability result.

6:41 It is not a detection of life and it is not a biosignature. Nobody on this team is claiming one. We are saying the ingredients and the conditions were there more than once, which is a genuinely different statement and a weaker one. Three, the origin of the margin unit is still argued over. Earlier this year, a separate team used the rover's ground penetrating radar, rimfax, to look underneath this same ground and reported layered beds dipping down towards the basin, the sort of structure you would associate with a delta front.

7:15 That's not obviously the same picture as slowly cooled magma from deep underground. Both results are real measurements. Reconciling them is unfinished business and we'll tell you when it's finished. Avery: And, um, is there an Australian connection to the storey? Anna: There's no Australian science team on this paper and we're not going to pretend otherwise, but there is an Australian link in the chain and it's a real one. Every bit of this data came, uh, to Earth through NASA's Deep Space Network.

7:44 And one of the network's three complexes is at Tidbinbilla outside Canberra. The Canberra Deep Space Communication Complex, managed for NASA by the csiro. When Mars is on the sky over the Southern hemisphere, Canberra is the ear listening the laser fires on Mars. The answer comes home through the act. Supercam itself is co led by Purdue, Los Alamos National Laboratory and IRAP and CENS in Toulouse. It's a genuinely international instrument. Avery: Well, here's one for our Australian listeners to mark in their calendars next Monday night.

8:21 If you are anywhere in Australia with a clear sky, there is a spacecraft passing overhead that is on its way to Jupiter. The European Space Agency confirmed the details on Monday. Juice, the Jupiter icy moons explorer, returns to Earth on 28 September for its third gravity assist. Closest approach is over the Indian Ocean at 11:45 UTC. The flyby bends the spacecraft's path by about 20 degrees and adds roughly 3.5 kilometres per second to its speed. No fuel spent, just geometry and the Australian part.

9:00 Between 15 and 30 minutes before that closest approach, JUICE crosses Australia, travelling from the northeast of the country to the northwest. We ran the clock on that and it works out beautifully. That crossing falls between about 9:15 and 9:30 in the evening, Eastern Standard Time, in Central Time roughly quarter to 9 to 9 o', clock, and in Western Australia between about 7:15 and 7:30 in the evening. Now here is why that is worth clearing your Monday night for. The sun sets in Brisbane at 10 to 6, in Darwin at about 20 to 7 and in Perth at a quarter to 6 with which means that when Juice comes over, it is properly dark everywhere.

9:44 The entire continent is in night and the spacecraft is tracking straight across the top of it. Make it I no, and let's be honest about that, ESA's own wording is that amateur astronomers with the right telescope or binocular equipment may be able to track it. This is a small spacecraft, a long way off, moving fast. It is a target for someone who knows what they are doing with a scope and a set of coordinates. Not something you will catch by looking up. But for that crowd, it is a genuine opportunity and there will be very few chances left.

10:19 Juice only comes back Once more in January 2029. Anna: There's one more detail worth having because it's the part that makes flight controllers nervous in the way in. Juice passes through Earth's shadow for about eight and a half hours, ending in the early hours of Monday morning, European time. No sunlight at all. The spacecraft runs on battery power alone and then comes out the other side and performs the most precise manoeuvre of its year. Avery: Remind everyone where it's been launched. Anna: On an Ariane 5 from Kourou in April 2023.

10:52 Eight year cruise in August 2024. It did something nobody had done before. A gravity assist off the moon. And then Earth, 336 hours apart. Venus in August 2025. This is Earth number two. Earth number three is January 2029. And then Jupiter in July 2031 where it makes 35 flybys of the big moons before settling into orbit around Ganymede. Avery: And one small coincidence for the diary, Starship's Flight 14 is currently targeted to 12:15 UTC that same Monday. Juice's closest approach is 11:45, half an hour apart on opposite sides of the planet in opposite directions.

11:35 Anna: Alright, moving on to our next storey. HR 8799 is the system that made direct imaging of exoplanets real.4 giant planets photographed as actual points of light orbiting a uh, young star between a warm inner belt of debris and a cold outer ring. It's the benchmark. And for years there's been a hole in it, a region a few astronomical units out, too close in for conventional high contrast imaging to resolve. And very hard for the radial velocity method because the star itself pulsates and smears the signal.

12:10 People have long suspected something is in there. The inner edge of that warm belt sits at about five to six astronomical units, well inside the orbit of the innermost known planet. Something appears to be sweeping it. Avery: And this month two groups went at it from opposite directions. Anna: They did. And the honest headline is both of them see something and they do not obviously agree about what it is. The first posted on 9th September is led by Jake Nguyen with a large team. They went back to archival JWST data taken with the aperture masking interometer and reprocessed it with a new pipeline.

12:50 They find a source sitting just above their 3 sigma contrast curve at a projected separation of about 150 milliarcseconds which works out to roughly 7 astronomical units and a few to several Jupiter masses. And its position sits near a stable orbital solution for a fifth planet in a three to one resonance with the innermost known planet. Avery: And um, this is where it becomes an Australian storey in a way that I did not expect. Anna: The aperture masking interometer is the only piece of Australian designed hardware on the James Webb Space Telescope.

13:25 It was created by Professor Peter Toothhill at the University of Sydney. It works by masking the telescope's mirror down to a handful of patches and combining their light which buys you resolution right in close to a bright star, exactly where this planet would be. And the pipeline that made this detection possible came out of that same group. Sydney PhD students built a software only calibration system to correct a detector effect that had been quietly blurring AMI's images and recovered the instrument's full sensitivity without anyone leaving the ground.

14:02 The paper says in plain terms that the Detection was enabled by a pipeline accounting for the systematics that limited earlier analyses. That is the Sydney Fix doing the job it was built for. The second paper landed on Monday led by Anne Marie Lagrange, and it's submitted to Nature Astronomy. Completely different approach. Gaia's absolute astronomy combined with proper motion anomalies between Hipparcos and Gaia, plus radial velocities and imaging. They're not photographing anything, they're watching the star get tugged.

14:37 Their allowed solutions span roughly a third of an astronomical unit out to 6, with the probability peaking at 2 to 3 and masses of about 10 to 14 jupiters. They also show that an object like that on a low eccentricity orbit can coexist with the long lived resonant chain of the four known planets and sculpt that inner belt edge. Avery: Next, the honest reading. Anna: So 7 astronomical units and a few Jupiter masses versus 2 to 3 and 10 to 14. Those are not the same object as stated. They may be the same object with wide error bars or two different detections, or one of them may not survive.

15:19 Both are preprints. Neither has been through peer review. This is a candidate and we've been here before. You'll remember from last week how contested the history of directly imaged protoplanets is. And for the observers, HR 8799 is at declination 21. It transits nearly 77 degrees up from Los Angeles and about 71 from New York. From here in Sydney it barely clears 35. This one belongs to the north. Avery: We've been holding this one for a couple of weeks, waiting for the right slot. So here it is at last.

15:54 Back in March, a team led by Martin Cordiner published a measurement of the water in 3I ATLAS, the third interstellar object ever found passing through our solar system. Specifically, they measured its deuterium to hydrogen ratio. Deuterium is heavy hydrogen, an ordinary hydrogen atom with a neutron added. And the ratio of heavy water to ordinary water in a comet is one of the most useful fingerprints we have because it's set by how cold it was and what was around when that ice first formed. Anna: And three I ATLAS came back high.

16:29 Avery: And the paper we are covering Today, posted on 14th September by a team including Kenji Furuya, Cordiner himself and Dominique Bocole Morven, is the attempt to explain why. I want to be very clear about what this is because the framing matters. This is not a new measurement. Nobody pointed a telescope at anything. This is a modelling paper working out what conditions could produce the ratio that Was already measured in March and there is no institutional press release behind it. It is a preprint eight days old.

17:01 Anna: So what does the model say? Avery: Their conclusion is that the high ratio is consistent with three I ATLs forming around a star with low met metallicity. Meaning a star poor in elements heavier than hydrogen and helium. Which in practise tends to mean an old star. An object assembled in a different chemical environment from the one that built our own comets. And it slots neatly against the result. We covered a couple of weeks back the first ion inventory of an interstellar object's tail out of Northumbria and Edinburgh, which found enough molecular nitrogen relative to carbon monoxide to imply this thing formed below about 3030 Kelvin.

17:41 Very cold and a long way from its star. Anna: Two independent lines pointing the same direction. Avery: Two independent lines, and they are genuinely independent. One is ions in a plasma tail, the other is heavy water. But the caveat is the same caveat as always with D2H. It is a tracer, not a direct reading. Converting a ratio into a birthplace runs through a chain of assumptions about chemistry and temperature. And this paper is exploring that chain rather than closing it. The Southern Note, as ever with this object, three I ATLS was discovered by the ATLAS Survey telescope at ah Rio Urtado in Chile.

18:19 Whatever we end up learning about the star that made it, the first person to see it was looking up from the southern hemisphere. Anna: Now, three quick ones. All dates. Starship Flight 14 is still targeted for Monday 28 September 1215 UTC. That's 10:15 on Monday evening, Eastern Standard Time here. The booster has been rolled out to the pad and the ship has been test fired. You will remember we had to correct ourselves on this flight once already when it moved off the 22nd. So we're saying targeted, not scheduled.

18:52 And we'll believe it when the clock runs. Avery: NASA's own mission page still reads no earlier than early October. Not a date, a window. The crew went to quarantine on the 17th, which is the normal run up. And the oxidizer valve that caused the original stand down was replaced weeks ago. There are specific dates circulating on unofficial trackers. We are not going to read you a date that NASA has not published. Anna: And Albania has signed the Artemis Accords. That happened on Monday at NASA headquarters.

19:22 Foreign Minister Fareed Hoxha signing for Albania. Deputy Administrator Matt Anderson for NASA Albania becomes the 73rd signatory. Avery: 73. It was 50 something not that long ago it was. Anna: And whatever you make of the Accords as an instrument, and there's a real Debate there about whether they substitute for treaty making. The sheer rate of accession is now the storey in itself. Avery: Moving on to Skywatch, let's start with the moment this episode goes out, because it's a moment, not a day.

19:52 The September equinox falls at five minutes past midnight utc. That's five past ten in the morning on Wednesday for us in Sydney. So it happens while you're listening to this. In London, it's just after one in the morning on the 23rd, but in New York, it's five past eight on the evening of the 22nd, and in Los Angeles, five past five that same afternoon. Anna: So half our audience had their equinox yesterday. Avery: Exactly. And that is not a quirk, it is the point. An, um, equinox is an instant, not a date.

20:24 It is one specific moment when the sun crosses the celestial equator. And what calendar date that lands on depends entirely on where you are standing. We have said the 22nd in past episodes and for North America, that was right. For Australia, it is the 23rd. The thing to actually plan for is Monday. As we said earlier, Juice crosses Australia between about 9:15 and 9:30 in the evening Eastern time. Northeast to northwest in a fully dark sky from coast to coast. Telescope or good binoculars and current coordinates cheque ESA's own pages on the day, because the ephemeris will be refined right up to the flyby.

21:04 Anna: For, uh, our northern listeners, this one is not yours. Closest to approaches over the Indian Ocean in the middle of your day. Sorry. Avery: Turning to the evening sky, Venus is still the standout after sunset and the gap between hemispheres is as wide as it's been all year. From Sydney, Venus sits 36 degrees above the horizon at sunset and stays up for three hours and one minute after the sun goes down. From Los Angeles, 12 degrees and gone in an hour and nine minutes. New York, 8 degrees, 54 minutes.

21:36 London, um, 2 degrees and 20 minutes, which in practise means a clear, flat western horizon or nothing at all. Anna: And that is the ecliptic angle again. Avery: Same geometry we've talked about all spring. Around the equinox, the ecliptic stands up almost vertically from the western horizon in the southern hemisphere and lies down almost flat in the north. Same planet, same evening, completely different experience. Mercury is doing the same thing. Eighteen and a half degrees up from Sydney at sunset, three and a half from London, southern object.

22:13 Anna: The Moon is a waxing gibbous, about 86% lit on Wednesday evening, and it's heading for full at 4:48 in the afternoon UTC on the 26th. Note the calendar split on that one. That instant is 10 to 3 in the morning of the 27th in Sydney. So Australian calendars will say Sunday and northern ones will say Saturday. It looks full both nights either way. Avery: Saturn rises at about 20 to 7 in the evening from Sydney and is 54 degree up, uh six hours later. It's heading for opposition in the first week of October.

22:44 And as we worked out last week, the two standard definitions put it on the 4th and the 5th. Both are legitimate. It doesn't matter. The brightness holds at magnitude 0.32 and the disc at 19.6 arc seconds right across that week. So there's no wrong night. And now the counterweight because today's storeys have leaned north and the pre dawn sky does too. Mars at nautical dawn, 50 degrees up from Los Angeles, 48 from New York, 42 from London and 21 from Sydney. Jupiter 30 degrees from Los Angeles and 10 and a half from here.

23:22 The two of them are 20 and a half degrees apart and closing through Anna: spring, which is the tie back to the lead. Avery: It is if you want to look at the planet. We spent eight minutes on this morning and you are in the northern hemisphere. It's 50 degrees up before sunrise and easy. Jezero crater is at 18 degrees north on Mars. So even the geology is northern today. Some weeks it runs the other way. Last Monday we gave the south the better geometry and the north the deep sky. Today the north has the science, the planets and the October occultation.

23:55 And the south has Venus, Mercury and a uh, spacecraft going overhead on Monday night. Anna: And the standing reminder because we say it every single episode and we are not going to stop. If you are observing the sun at any point, for any reason, at any stage, you need filters certified to ISO 123122. That is the international standard for safe solar viewing. Sunglasses are not adequate. Stacked sunglasses are not adequate. Exposed film, smoked glass, a welding filter below shade 14, none of those are adequate.

24:33 And never ever look at the sun through a telescope, binoculars or a camera lens that does not have a purpose made solar filter fitted over the front. A filter that screws into the eyepiece can crack under the heat front of the optic. Certified every time. Avery: That's Astronomy AstroDailyPod for today. Anna: Three floods at the edge of Jezero Crater. Groundwater, then a lake, then hot water from below. Red out of rock that was not supposed to be there at all. Avery: Juice coming home on Monday nights and 15 minutes of uh, it belonging to Anna: Australia, a candidate fifth planet at HR 8799.

25:12 Found two different ways by two teams who do not quite agree with an Australian instrument and an Australian software fix in the middle of one of them Avery: and heavy water in an interstellar comet pointing at an old metopore star we will never see. And one small thing before we go this is episode 200 for the year. Anna: 200 episodes this year alone. Not many shows can say that and fewer still can say it without the quality going out the window somewhere around episode 60. Avery: That is not an accident and it is not one person.

25:48 That is a team turning this around day after day and holding the standard while they do it. Thank you to everyone who makes it happen and thank you for listening to all 200 of them. Anna: Astronomy AstroDailyPod is produced in Sydney. You'll find every episode, the show notes and the newsletter at astronomydaily IO and we're AstroDaily Pod on the socials. Avery: We're back tomorrow. Anna: Until then, Clear Skies.

26:23 Avery: Mhm. Anna: The storey.