BepiColombo Lets Go: Eight Years, Nine Flybys, One Irreversible Moment

0:00 Anna: Hey, everyone. Welcome back to Astronomy daily. It's Thursday, September 3, 2026. I'm Anna and this is series five, episode 184. Avery: And I'm Avery. Anna, we've got a spacecraft doing something irreversible today. Anna: We do. As we're recording, BepiColombo, the European and Japanese mission to Mercury is throwing away the module that got it there. Avery: Throwing away sounds harsh. Anna: It's accurate, though. Eight years, nine planetary flybys, one very serious engine problem, and today the transfer module gets cut loose and the two science orbiters are on their own.

0:41 It's the start of the arrival phase. Avery: That's our lead, then. NASA has just handed Blue Origin $700 million to build the Internet connection for Anna: Mars, which is a much bigger deal than it sounds. Avery: It really is. Then Saturn has grown a new shape at its South Pole and nobody expected it. And an Australian in Broken Hill is part of how we found out. Anna: Love that storey. And then a second Chinese private company has flown a reusable rocket three weeks after the first one. Avery: Plus we'll get you sorted for the sky tonight.

1:17 Both hemispheres, as always. Anna: Let's get into it. Avery: Okay, set the scene for me. What is physically happening today? Anna: So BepiColombo has flown to Mercury as a stack, three pieces bolted together. At the bottom you've got the Mercury transfer module. That's the Ion engine bus, the thing with the enormous solar wings that's been doing the driving. On top of that sits the European Orbiter, the Mercury Planetary Orbiter. And on top of that sits the Japanese one, Mio, the Mercury Magnetospheric Orbiter Avery: M3 spacecraft in a tower.

1:53 Anna: A tower. And Today, at around 8 in the morning, US Eastern Time, which is about 10 o' clock tonight for us in Sydney, the transfer module separates. ESA is carrying it live. They start the broadcast a bit before, pause it, and come back about an hour later to confirm they've got a signal from what is now, for the first time, an independent spacecraft. Avery: And there's no putting it back together. Anna: None. That's why Today matters. Up to this point, if something went wrong, you still had the propulsion module.

2:25 From today, the Ion engines are gone. Everything after this runs on the orbiter's own chemical thrusters. Avery: Take me back. This launched in 2018, October 20, 2018, Anna: on an Ariane 5 out of Kourou. So we are three weeks shy of eight years. Avery: Eight years to reach the closest planet to the sun. Which sounds backwards. Anna: It sounds backwards and it's the single most counterintuitive thing About Mercury. If you point a rocket at Mercury and just let go, you don't gently arrive, you fall.

2:58 The Sun's gravity well is enormous and you pick up speed the whole way down. The hard part isn't getting there, the hard part is arriving slowly enough that Mercury's very weak gravity can actually catch you. Avery: So the whole mission is a braking problem. Anna: The whole mission is a breaking problem. BepiColombo has used one flyby of Earth, two of Venus and six of Mercury itself. The last of those in January 2025 plus years of continuous, very gentle thrusting from those ion engines, all of it to shed speed rather than gain it.

3:35 Avery: Nine flybys. That's more than most missions do in a lifetime. Anna: And there's a lovely bit of history in that, because the mission is named after the man who invented that technique, Giuseppe Colombo. Bepi, to everyone who knew him was an Italian mathematician who worked out in 1974 that if you shaped Mariner 10's trajectory correctly, you could get repeat visits to Mercury instead of just one. He also figured out why Mercury rotates three times for every two orbits. So the mission carries the name of the person who made this kind of flight possible at all.

4:12 Avery: Now, you said one very serious engine problem. Anna: Yes. April 2024. The team found unexpected electric currents flowing between the transfer module's solar arrays and one of its power distribution units. The practical effect was that there wasn't enough power reaching the electric thrusters, so. So they couldn't run at full thrust. Avery: How much did they lose? Anna: They clawed back most of it. Engineers got the thrusters to about 90% of original performance, but 90% wasn't enough for the trajectory they were flying.

4:46 Santa Martinez, the mission manager, put it plainly at the time. After months of investigation, they concluded the thrusters would stay below the minimum thrust needed for the orbit insertion they'd planned for December 2025. Avery: So they redesigned the Arrival. Anna: They redesigned the Arrival, new trajectory, a revised set of flybys, and the arrival slipped by 11 months, from December 2025 to November this year, which is why we're talking about it now rather than last Christmas. Avery: 11 months is a long slip.

5:19 Was anything gained? Anna: A bit, actually. Johannes Benkov, the project scientist, made the point that the extra time flew the instruments through parts of Mercury's environment they'd never otherwise have sampled. It's not compensation for the delay, but it isn't nothing either. Avery: Alright, so today the module goes. What's the calendar from here? Anna: It's a slow staged arrival. November 21st is gravity capture. That's when Mercury actually takes hold of both orbiters. Then in the second week of December, around the 9th and 10th, MIO is released into its own very stretched orbit.

5:58 About a week after that, the European orbiter starts working its way down. It reaches its final Science orbit on March 10th next year and routine science operations formally begin on April 6th, 2027. Avery: So today is the beginning of a seven month arrival. Anna: That's exactly the right way to think about it. Nobody's landing, nobody's braking hard. It's a long, careful settling in and Avery: the two orbiters end up in quite Anna: different places deliberately so. The European orbiter goes low and tight, roughly 480 kilometres at its closest, 1500 at its furthest.

6:37 That's the mapping orbit. Mineralogy, elemental composition, the surface at a range of wavelengths. MIO goes much higher and much more elliptical out to something like eleven and a half thousand kilometres because it's chasing the magnetic field and the particles and you need to fly through a big volume of space to sample that properly. Avery: Which brings me to the thing I actually want to know. What are the questions? Anna: Three big ones, and they're all genuinely strange. The first is the magnetic field.

7:07 Mercury is small. It should have cooled and frozen solid billions of years ago. And yet it has a global magnetic field. Of the rocky planets, only Earth and Mercury do so. Something inside it is still liquid and still moving and we don't have a settled explanation for that. Avery: And uh, Mercury's core is huge, isn't it? Anna: Enormous. Relative to the planet, the iron core takes up something like 85% of the radius. Mercury is essentially a metal ball with a thin coat of rock on it and nobody is entirely sure why.

7:40 Avery: Second question. Anna: Ice. There is water ice sitting in permanently shadowed craters at Mercury's poles on the planet closest to the sun, where the day side gets to well over 400 degrees Celsius. The floors of some polar craters never see sunlight, so they stay cold enough to hold ice. But where it came from and how much there is is open. Avery: And the third? Anna: The hollows. These are my favourite messenger. The last mission to orbit Mercury found these bright, shallow, irregular pits scattered across the surface.

8:14 No impact structure, no volcanic vent, just ground that appears to be disappearing. The best guess is some volatile material in the rock is sublimating straight to gas and leaving the hollow behind. And they look fresh. There's a real possibility Mercury's surface is actively changing right now, which is not something you expect from a dead little world. Avery: How many times have we actually been to Mercury before this? Anna: Barely. Two missions ever. Mariner 10 did three flybys in 1974 and 75.

8:46 Messenger orbited from 2011 to 2015. That's it. It is the least explored planet in the inner solar system by a very wide margin. Avery: And is there an Australian thread here? There usually is. Anna: There is, and it's a nice one. ESA tracks its deep space missions through a network that includes new Norcia in Western Australia, north of Perth. And ESA opened a brand new deep space antenna at that site in October last year, working with csiro Southern Hemisphere ground stations aren't, ah, a courtesy on missions like this.

9:21 They're how you keep a spacecraft in contact as the Earth turns. Avery: So what should people actually watch for today? Anna: Signal acquisition. That's the moment. Separation itself is a mechanical event. You can't really see the thing that tells you it worked is the ground station hearing a healthy carrier from a spacecraft that an hour earlier didn't exist as an independent object. If that comes through clean, Bepicolombo is genuinely on approach. Avery: Right, second storey. And this one is about plumbing, but the good kind.

9:57 NASA announced on Tuesday, September 1, that it has awarded Blue Origin a firm fixed price contract worth about $700 million to build Mars telecommunications network, which is Anna: not a science mission, deliberately not. Avery: This is a, ah, dedicated communications orbiter. Its entire job is relaying science data, imagery, navigation information and mission commands for anything operating on or around Mars. No instruments of its own, competing for power and pointing time. Anna: And that's the change, isn't it?

10:34 Because right now that job is done by science orbiters moonlighting. Avery: Exactly right. Every picture you have ever seen from Curiosity or perseverance came home through Mars Odyssey or the Mars Reconnaissance Orbiter. Uh, Odyssey, launched in 2001, MRO launched in 2005. Odyssey is 25 years old and it's carrying the data return for a whole planet as a side hustle. Anna: And people have been sounding the alarm about that for years. Avery: For years. The worry has always been the same if one of those two fails.

11:10 Surface missions don't go quiet exactly, but their data rates fall off a cliff. You'd be choosing which images come home. Anna: So what's Blue Origin actually building? Avery: It's based on their Blue Ring platform, a hybrid spacecraft that uses both solar electric and chemical propulsion. It launches on New Glenn. Delivery deadline is December 31, 2028 and NASA expects it operational at Mars by 2030. Anna: And the contract is design, develop, launch and operate all four. Avery: All four. That's the interesting bit, structurally.

11:49 NASA isn't buying a spacecraft, it's buying A service the same way it now buys communications around the Earth and the moon. It sits under the Space Communications and Navigation programme and it follows a request for proposals NASA put out back in May. Anna: Who else was in the running? Avery: Rocket Lab was the other finalist. So this was a real competition, not a sole source award. Anna: And Blue Origin does have Mars form now, which they didn't have two years ago. Avery: That's the part I'd flag.

12:21 New Glenn's second flight in November last year carried NASA's twin escapade probes to Mars and landed its booster for the first time on the same mission. So the pitch here isn't theoretical and Anna: the longer game is crewed missions. Avery: That's stated fairly openly in the announcement. If you're serious about people at Mars in the late2030s or2040s, you cannot run that on two orbiters built in the Clinton and Bush administrations. You need infrastructure that's designed to be infrastructure.

12:54 Anna: It's the least glamorous. $700 million NASA will spend this decade and probably one of the more important. Avery: Nobody's ever made a poster of a relay satellite but nothing else works without it. Anna: Now this one is just lovely. Saturn's south pole has a ten sided shape around it and it wasn't there before. Avery: Ten sided. A uh. Decagon. Anna: A decagon published in Science Advances yesterday September 2nd. Led by Augustin Sanchez Lavega at the University of the Basque country in Spain with Amy Simon at NASA Goddard and Michael Wong at UC Berkeley among the co authors.

13:34 Avery: And we already knew Saturn does this at the other pole. Anna: That's the famous one, the northern hexagon. The six sided been known since Voyager in the 1980s and it is rock solid. Amy Simon's line is that it has been there every single time anyone has looked for more than 40 years. Avery: So why has nobody seen a southern one before? Anna: Because we couldn't look. Saturn is tilted like Earth and It takes about 30 years to go around the sun. Between roughly 2012 and 2023. The the south pole was simply turned away from us.

14:10 It has only recently come back into view. Avery: And who spotted it? Anna: This is the part I love. Amateur astronomers. The first hint turned up in ground based images in 2024. A subtle undulating band around the pole in pictures submitted to something called the Planetary Virtual Observatory Laboratory, which is a database professionals use to mine amateur planetary imagery. Two observers are credited. Jean Paul Auger and Trevor Berry. Avery: Trevor Berry as in. Anna: As in Broken Hill, New South Wales, far western Outback, New South Wales.

14:47 He's a former miner who built his own observatory. He's been imaging Saturn for the better part of two decades. He's won an Astronomical Society of Australia award for it and he has a long history of contributing to exactly this kind of professional work. Avery: So a uh, bloke in Broken Hill helps find a new feature on Saturn Anna: and then Hubble goes and confirms it. Once they knew what to look for, the team went into Hubble's Opal programme. That's the long running survey that photographs the outer planets every year and found the Decagon sitting there in data going back to 2023 with observations running through late August last year.

15:24 Avery: How big is it in Earth terms? Anna: I'm going to be careful here because some of the coverage yesterday quoted a width that's larger than Saturn. Its which obviously can't be right. The official releases don't put a hard number on it. What we can say confidently is that it's the same class of feature as the a planet scale wave locked inside a polar jet stream tens of thousands of kilometres across. I'd rather wait for the paper's own figures than repeat one that doesn't survive a sanity cheque fair.

15:57 Avery: And why 10 sides rather than six? Anna: The mechanism is thought to be the same in both cases. A meandering wave trapped inside a fast polar jet. The number of sides falls out of how fast and how wide that jet is. Different jet, different number. Avery: And the really interesting difference is the age. Anna: That's the headline for scientists. The hexagon is old and stable. This thing looks new and Simon's assessment is that it appears to be strengthening. Which means for the first time we get to watch one of these form rather than inheriting a finished one.

16:31 The plan is to keep tracking it with Hubble and JWST as sunlight builds toward the southern summer over the next few years and see whether it settles or falls apart. Avery: A planet sized geometry experiment running in real time. Anna: And we're on the right side of the planet to appreciate it. Which we'll come back to in a few minutes. Avery: Last news storey. And it's another one for the Chinese commercial launch column. Galactic Energy flew its Palace 1 rocket for the first time. That was late on August 31st US Eastern Time.

17:05 So morning of September 1st in China out of the Jiuquan Launch Centre. Anna: And it worked. Avery: Clean debut. The company says it reached its planned orbit about 30 minutes after liftoff. First flight of a brand new vehicle straight to orbit, which is not a given. Anna: Give me the numbers. Avery: 52 metres tall. So a bit over a hundred and seventy feet, about seven tonnes to low Earth orbit. And crucially, the first stage is built to be reusable hypersonic grid fins, deployable landing legs rated for up to 25 flights.

17:42 If that specification sounds familiar, it's because it's essentially the Falcon 9 playbook. Anna: Did they try to land it? Avery: No hardware was fitted, but no recovery attempt on a maiden flight. They're targeting the second half of 2027 for the first landing try. Anna: Now, the reason this matters isn't really the rocket on its own. Avery: No, it's the pattern. Look at the last eight weeks in China. July 10th a, uh, long March 10th b, that's the state programme launches and catches its first stage in a net strung across a ship at sea, making China only the second country ever to recover an orbital class booster.

18:24 Mid August land space lands Juke 3 on legs. The first Chinese private company to do it, though, as we covered at the time, it caught fire and toppled over after touchdown. And now, three weeks later, a second private company debuts a vehicle with recovery hardware already on it. Anna: Three different programmes, three different approaches in under two months. Avery: And there's a clear commercial driver. China is building out very large satellite constellations. Gul Wang Qian Fan and you cannot deploy tens of thousands of satellites on expendable rockets at any sensible price.

19:05 Galactic Energy is quite openly positioning Palace One as a constellation workhorse. Anna: And this isn't a startup with no track record, not at all. Avery: They already Fly Series 1, a small satellite launcher with more than 20 flights behind it. So Palace 1 is a step up, not a first attempt. Anna: The thing I'd watch is 2027. Landing is the hard part and everyone's landing attempt is still ahead of them. Right, let's get you outside. And we have to start with Saturn tonight. For obvious reasons after that segment, it Avery: would be rude not to.

19:43 Anna: Saturn is rising around sunset now and it's up for most of the night over in Aquarius. Sitting at about magnitude 0.4. It's building toward opposition on October 4, so it gets a little better every night for the next month. Avery: And the rings are doing something unusual. Anna: They're tilted only about 8 degrees from edge on close to the narrowest they've been in a dozen years, which some people find disappointing and I think is the opposite. When the rings are nearly closed, the moons line up in a much tighter row and the globe of the planet is easier to see detail on.

20:19 Avery: It's a different Saturn Southern hemisphere advantage Anna: tonight, a real one from Sydney. Saturn climbs high overhead, so so you're looking through much less atmosphere than northern observers who get it lower in the southern sky. If you've got a telescope and you've been meaning to use it, this is the month. And to be clear, the decagon we just talked about is far beyond a backyard scope that's a Hubble class detection. What you can see is the ring tilt and the moons. Avery: For North American listeners specifically, the big one is tonight's Moon.

20:54 Anna: Yes, the Moon passes very close to the Pleiades tonight, and it's an actual occultation from North America, from East Asia and from Arctic latitudes. The cluster's stars wink out behind the lunar limb. If that's you, that's your event, and binoculars are plenty. And from here, from Australia, New Zealand. The Moon and the Pleiades rise together in the small hours as a close. Pretty pairing, but no occultation worth setting an alarm for if you're up. Anyway, moon phase waning gibbous and it hits last quarter tomorrow, September 4th.

21:32 Practically that means it rises late, so the early evening is dark, which is good news for the next one, Venus. Venus is the unmissable one, low in the west to west southwest, roughly 14 degrees up an hour after sunset from Sydney. Sunset here is about 5:35 in the afternoon at the moment. It's just pulled away from Spica after their conjunction on Monday night, and it's building toward greatest brilliancy on September 18th. There's a beautiful thin crescent moon alongside it on the 14th, so mark that one.

22:06 Avery: Pre dawn. Anna: Jupiter is back and it's worth the early start. Rising East Northeast around 10 to 4 in the morning. Mars is also there, low and slowly fading. And tonight it makes a triangle with Betelgeuse and Elnath. If you want a target to find Avery: and there's a Jupiter event coming for Anna: North America, there is. On September 8, the moon occults, uh, Jupiter, visible from Canada, the United States, Mexico, Greenland, the Caribbean and eastern Russia. The catch is that for most of that footprint, it happens in daylight with the sun above the horizon.

22:41 Avery: Which brings us to the standing reminder Anna: it does, and it applies to that occultation directly. If you are observing anywhere near the sun, take it seriously. Any filter you use for direct solar viewing must be certified to the ISO 123122 standard. Not sunglasses, not smoked glass, not a stack of exposed film, ISO 123122 and cheque. The certification is genuine. Sweeping a telescope or binoculars around a daylight sky looking for Jupiter, it is exactly the situation where people get hurt.

23:17 Avery: Anything else on the calendar three to Anna: pencil in International Observe the Moon night on the 19th, the equinox on the 22nd, spring for us, autumn for our northern listeners, and the harvest Moon rising near Saturn on the 26th, which, after tonight's conversation, feels like a nice bookend. Avery: And that's episode 184. BepiColombo has cut loose the module that carried it for eight years and is officially on approach to Mercury. Anna: Blue Origin is building Mars a proper phone line.

23:49 Saturn has grown a ten sided crown at its south pole with a hand from an amateur astronomer in Outback New South Wales, and a second Chinese private company has put a reusable rocket into orbit. Avery: Full show notes, links to every primary source and the whole back catalogue are at astronomydaily IO. Anna: You can find us on X Instagram and TikTok@astrodaily podcast. And if you've got a question or a correction, we genuinely want it, there's a contact form on the website. You'll find us at astronomydaily IO.

24:22 Avery: If today's episode was useful, the single most helpful thing you can do is send it to one person who'd enjoy it. Anna: We'll be back tomorrow. Until then, clear skies, Clear skies, um,

24:38 Avery: Are told the world.