InSight's revelation on Mars’ rotation

Sarah Al-Ahmed: Mars's rotation is speeding up, this week, on Planetary Radio. I'm Sarah Al-Ahmed of The Planetary Society with more of the human adventure across our Solar System and beyond. Data from the now retired NASA InSight mission is providing new details about how fast Mars rotates and how much it wobbles. The InSight RISE instruments principal investigator, Sebastien Le Maistre, from the Royal Observatory of Belgium joins us this week to get into the details. The Planetary Society's digital community manager, Ambre Trujillo, will share her experience observing the October 14th, 2023 annular solar eclipse and her adventure to the OSIRIS-REx sample return capsules opening at the Johnson Space Center. Then, our director of Government relations, Jack Kiraly, will share the triumphs of our most recent Planetary Society Day of Action and update all of us on the status of the Mars Sample Return mission. Hang on until the end for what's up with Bruce Betts, our chief scientist as he shares an asteroid mission themed random space fact. And for those of you looking forward to our upcoming episode about Diffraction Solar Sailing, which we announced on last week's show, don't worry, we're still going to be hearing from that team in the coming weeks. If you love Planetary Radio and want to stay informed about the latest space discoveries, make sure you hit that subscribe button on your favorite podcasting platform. By subscribing, you'll never miss an episode filled with new and awe-inspiring ways to know the cosmos and our place within it. Before we delve into today's episode, I want to take a moment to acknowledge current world events. Our hearts are with everyone impacted. In times like these, we hope that taking a moment to reflect on our tiny shared place in this vast cosmos inspires all of us to treat each other with kindness and to build a better future for everyone on this precious planet. No matter who you are or where you hail from, we're glad you're with us. On October 14th, 2023, an annular solar eclipse passed over parts of North and South America. Solar eclipses happen when the moon passes in front of the sun from our perspective here on Earth, but annular eclipses are something special. They occur only when the moon is a little farther from the Earth in its orbit. The smaller angular size of the moon in the sky means that it can't fully cover the disc of the sun as it does during total solar eclipses. This creates a beautiful phenomenon that some people call a ring of fire. Ambre Trujillo, our digital community manager, is here to share her experience on that day and her journey to Texas a few days earlier on October 11th for the unveiling of the NASA OSIRIS-REx asteroid sample return capsule's contents. Hey Ambre.

Ambre Trujillo: Hi.

Sarah Al-Ahmed: It's cool seeing you in the office, being able to record together.

Ambre Trujillo: This is amazing. I wish we could do this all the time.

Sarah Al-Ahmed: I know, right? It's our co-working week here at The Planetary Society. So for the first time since the COVID pandemic began, we have the entire crew in the office. So it's just a really magical time for all of us, but it's also been a really big moment in space history for the last few weeks, and you've been lucky enough to witness several of these events, starting with the annular solar eclipse that happened this last weekend. You were actually there in the place where you could see the full annular eclipse. How was that?

Ambre Trujillo: It was amazing. I was in the path of totality. I went with my parents and my nephews to a little place in New Mexico called Torreon. We have a ranch out there. And I had never seen an eclipse before. This was my first time ever.

Sarah Al-Ahmed: Really?

Ambre Trujillo: Yeah. So it was really special to experience that with my family, and I made sure the nephews had their super safe solar eclipse glasses that actually bill nice. So they were all set up, they were ready to go. And I couldn't decide if I was more excited to see the annular eclipse or to watch my nephews experience annular eclipse. So it was really cool to be able to see that.

Sarah Al-Ahmed: It's always one of those moments. Whenever there's a big eclipse, I always try to get all the eclipse glasses and give them all the younger members of my family because these are those events that even as an adult, when you experience them, they change the way you personally feel about space because it's altering your reality, the light changes, you see all the effects. But as a child, it's one of those moments that honestly could change the arc of your life and interest you in science in a way that you never could be before.

Ambre Trujillo: Yeah, there's very few events here on Earth that can bring space to you, and definitely the eclipse is one of them.

Sarah Al-Ahmed: Of course, this is like a precursor moment for us. An annular eclipse is very different from a total solar eclipse, and we do have a total solar eclipse coming up in the United States next April, in April 2024. So this has been a test moment for a lot of people that are looking forward to that eclipse, but annular eclipses, they're a little different. What was the experience like?

Ambre Trujillo: Yeah, I have never seen a total eclipse, and I hear from everybody that it is a completely different experience than an annular eclipse, but it was really cool, the main difference being that the annular eclipse kind of shows that ring of fire, so it's fun to watch the moon move into that little perfect disc with the little red rim around it. So that was really fun. It also got very, very cold. I can't imagine how much the temperature will drop for the total eclipse, but yeah, it definitely got a little cold. It was interesting. You actually heard the birds start to chirp less, which was really interesting. It definitely got a little gray outside. So it was a very cool event, but I will say that it makes me look forward to the total eclipse even more. I'm so excited.

Sarah Al-Ahmed: Well, this is just one of the coolest space things you've gotten to do recently. You're one of the people who actually got to go be there when they opened the OSIRIS-REx sample return capsule recently. What a week, what a few weeks for us, but I mean, how did you end up on that journey?

Ambre Trujillo: Yeah, I was able to go out to Johnson Space Center in Houston, Texas and be there when they unveiled the sample from OSIRIS-REx, and it was amazing, as usual. I mean, NASA, obviously, their productions are absolutely incredible. It was amazing to be there with the people who worked so hard to make this a reality because you see in them how excited and how moved they are by this. I had the opportunity to talk to Dr. Kimberly Allums, who is the lead engineer and having to do with the curation of the samples. She led the team for creating the glove box in the clean room and how to get the samples. And that was one fascinating to speak to her about the work that went in. Just speaking to her, she was trying not to cry because this was such a huge moment in not only her life, but in lives of so many. And I know that just from what she expressed, what it meant to the team, because they spent years putting so much time into this away from their family. And so to see it become a successful mission flawlessly pretty much, and even when they did come up with they came into any obstacle, they overcame it perfectly and she spoke to what it means when you have a team that worked really well together. So that was really nice to see, just seeing her express that. And I also got to speak to Dr. Dante Lauretta, who's the principal investigator. And I mean, he knows everything in and out, and it was just really cool to be able to chat with him about what this means for humanity and what we can look forward to when it comes to not only rewriting the textbooks for Solar System formation, but also how life got here, the origin of life, and what that could mean for if we hold the ingredients for life from an asteroid, they could have also landed on Venus and Mars and the moons of Saturn and Jupiter and what that could mean for the search for life. It's so mind-blowing that we're able to get these samples from so far away. So yeah, it was really cool to just be in that moment and to be around the people that made it happen. Yeah, it was a really wonderful experience

Sarah Al-Ahmed: And already, just the beginning science that we're getting out of this is already telling us a lot. We have samples from some other objects in space, even other asteroids, comets. But in this tiny amount of time, even before they got into the core samples, we've found water and we've found carbon compounds, both of which we know are key for life. And if this is something that happens so readily in our Solar System, it would be highly unlikely to say that that's not common across all the worlds in our galaxy and beyond.

Ambre Trujillo: Yeah. It's exciting for the search for life, for sure, and I'm really excited to see. I mean, we've seen the science that comes from samples from the moon, from the Apollo missions and how we're still getting science from that. I'm excited to see how they utilize these samples, what we can learn from it, and maybe we can grow something out of this. And so I don't know, there's so many things that the list is long, but I look forward to seeing what comes from it.

Sarah Al-Ahmed: And as our person that does social media, I'm sure you've gotten to see a lot of the reactions from people online.

Ambre Trujillo: Yeah.

Sarah Al-Ahmed: What has that been like?

Ambre Trujillo: It's really cool. I think definitely the most exciting thing for people is the search for life, to see what can come of this. And also panspermia. I have gotten so many panspermia comments. They're just like, "We knew it. It was panspermia." So it's really cool to see people ask questions. It always brings me such joy when people are like, "Oh my gosh, I love these questions. I have so many questions." Keep asking questions. I love it. So it's been very positive from the worlds of social media.

Sarah Al-Ahmed: That's always good to hear. That's what we're here for and that's really what this is all about. We're learning wonderful things about the Solar System and our place and space, but we're also giving people the opportunity to feel truly inspired about not just where we're at right now, but about the things we can do together in the future.

Ambre Trujillo: Yeah. I mean, that's what brings us together, right? Is space. We're all on this rock together.

Sarah Al-Ahmed: Well said. Well, thanks for joining me, Ambre.

Ambre Trujillo: Thank you.

Sarah Al-Ahmed: Adventures like that remind me why sharing space science and exploration and advocating for the missions that matter really makes a difference. On Monday, September 18th, we held our 2023 in-person Day of Action. The Planetary Society took to the halls of the US Congress to advocate for a balanced and robust budget for Planetary Science. It was Jack Kiraly's, our director of government relations, first time organizing the event. Hey, Jack.

Jack Kiraly: Hey, Sarah.

Sarah Al-Ahmed: Good to be here in person with you.

Jack Kiraly: It's fantastic to be here in person with you and the whole team.

Sarah Al-Ahmed: I know, right? You're usually off in Washington DC, which is where we need you. You recently were in charge of a mammoth task, which was getting hired here at The Planetary Society, then being in charge of our Day of Action. And of course, Casey Dreier is usually in charge of doing our Day of Action in Washington DC, but Casey was on paternity leave, so all the perfect reasons, but it put you in a position as a new person to have to do this organization all by yourself. How was that?

Jack Kiraly: It was exhilarating, I think is the word I'd use to describe it. Having been a past participant in the Day of Action, I wasn't totally new to the concept, neither for The Planetary Society or in general, but it was fantastic. I am just really happy with how everything turned out.

Sarah Al-Ahmed: And I'm sure not everybody is completely familiar with what our Day of Action is, especially after the last few years. We've done this event, but we've had to hold it virtually, and this was our first time doing it in person again. So what is the vibe of this event and what are you trying to accomplish?

Jack Kiraly: Well, you do really small things, like change the world and influence government policy and funding for space missions, just really small stuff like that.

Sarah Al-Ahmed: No big deal.

Jack Kiraly: The Day of Action, it's our flagship advocacy event. Like you said, we do this every year, albeit virtual the last two years in 2021 in 2022, and this was our return to in-person. And it really is. We have in this year the same, over a hundred members of The Planetary Society and our supporters descend on DC to influence legislators at critical junctures in the funding of our federal government and in the direction of US space policy.

Sarah Al-Ahmed: I think what's really cool about this is that it gives people an opportunity not just to advocate for space, but to be put face to face with their representatives and have an in-person conversation about something that they're really passionate about. So how many of these sessions did you end up setting up with all of our legislators?

Jack Kiraly: Yeah, like I like to say, democracy is not a spectator sport. It involves showing up and over a hundred Planetary society members showed up on September 18th, and we had 164 meetings, which is phenomenal. 164 meetings, it's I think across 36 states that those members of Congress represent. That's over half of the United States, and really can have a tremendous impact on government policy. Like you said, I'm based in DC and I talk to these legislators and their staff all the time, and they're often telling me, "Oh, your Day of Action is something that we talk about constantly within our offices. And the impact that a constituent can have on their legislator is tremendous. And if you've never participated outside of, say, voting in an election, this is that next step, to actually engage with your member of Congress, engage with your representatives in Washington and air your concerns or your hopes and desires for your federal government. That's what the system is designed to do. And it was a fantastic experience. And in addition to our in-person participants, we had over 300 people participate virtually in a complimentary session writing to their members of Congress, detailing what our specific policy priorities are for this year's Day of Action.

Sarah Al-Ahmed: That's cool. I always, every year, during the Day of Action, write my Congress people about at least one thing that I care about. And thankfully, we've got a really easy website for doing this kind of thing.

Jack Kiraly: Planetary.org/action.

Sarah Al-Ahmed: Right? Of course, I've already signed all those petitions, so I had to get a little personalized this time. But it's always very meaningful to feel like you're throwing your voice behind something that you care about. Here in the United States, we have a really robust system for being able to do this. But no matter where you live, just voicing that you care about these things to either your family members or your representatives in whatever country you live in can have a huge impact on the future of space exploration. And we see it all the time through this event.

Jack Kiraly: We do. We do. And yeah, that's a great point you made there about the international component to this, because we don't live in a world, we don't live in a time where there's only one major space actor. And a lot of governments have mechanisms, although different and in different configurations than maybe here in the United States and being well-versed in the US system, there's a way that things are done, but there's ways to engage with your government at all levels, local, state, and federal, and across governments, influencing within the European Space Agency or affiliated countries that their space agency participates in that alliance. And being able to engage with your legislators, your representatives is a hallmark of democracy and something that can really influence the future of humanity's presence in the stars.

Sarah Al-Ahmed: So what were we trying to influence during this Day of Action? Because there are so many different things that we advocate for as an organization, but we must have picked some key priorities for this event.

Jack Kiraly: Well, our timing for this event could not have been better. Honestly, normally, we do this event in the spring. It's usually timed around when the president's budget request comes out, which is February, March timeframe. And it allows us to, at the start of this annular appropriations or funding process for the federal government, allows us to stake our priorities out. This year in particular, there is a big discussion happening in DC. And you turn on the news, you can see this discussion happening in real time about the role and nature of the federal government and the process by which we're going to fund the federal government. And our timing, in September of 2023 when there seemed to not be a path forward for funding the federal government in fiscal year 2024, which began just last week on October 1st, which, hey, we're sitting here, there is a federal government, we are funding it. Their discussions and negotiations are happening, which is a great thing to see. But as we're having those discussions and as Congress goes into negotiations on this full year budget, we were making sure that our priorities were staked out, and that is portfolio of Planetary Science missions. That includes our big ticket items, Mars Sample Return, which is really three flagship missions wrapped into one, returning those samples that the Perseverance rover has already collected and cashed on the surface of Mars, these scientifically robust samples that really will give us an insight into 3.7 billion years of Mars geologic history. But in addition to that, balance is not just the flagship missions, but it's also those medium and small missions. So your new Frontiers missions. Think OSIRIS-REx was a new Frontiers mission. So the next one in that series is going to be Dragonfly, which is set to launch in later this decade to the Moon Titan of Saturn. So really making sure that is supported. This is an... What's our phrasing for the nuclear-powered octocopter that's going to soar the skies of Titan that represents almost a primordial Earth. All the secrets there to this really interesting place in our Solar System and supporting that endeavor. VERITAS, which we've talked about before on this show, the first US-led orbiter to Venus since 1989. And then, on top of that, making sure that research and analysis funding gets the funding it needs. All of this comes from that decadal survey document for Planetary Science. Ours just came out last year. And so sticking to that this early in the decade is so vitally important because if you deviate from that now, it could really change the course that has already been plotted out by the scientific community. There's a consensus around what the focus should be or the foci should be for the coming decade, and making sure that is front and center for legislators to know that, hey, these decisions that you're going to be making impact not just that one mission or that one program line, but the entire balance of the Planetary Science Division and science writ large within NASA because it's not just Planetary science, it's astrophysics, and heliophysics and Earth science, and making sure that this decadal survey process that we go through, that the scientific community goes through painstakingly coming up with what the community wants to do for the next 10 years is vitally important for future policymakers at future key decision points. And this Day of Action, we are championing that, the decadal survey, championing balance and championing those missions that make up a balanced portfolio, Sample Return, Dragonfly, New Horizons, all research and analysis, VERITAS. There are so many exciting missions. And NEO Surveyor. Let's not forget, NEO Surveyor, the planet killer finder, right? Looking for those asteroids that might potentially, at some point, in Earth's future, cause us harm. We need to find those.

Sarah Al-Ahmed: Yeah, that's been a priority for us for quite a while. So it was really wonderful seeing that we got support for NEO Surveyor through these previous advocacy events. But even now, still needs our advocacy along with a lot of these other missions. I know something that I've been personally on the edge of my seat about is the Mars Sample Return mission. A lot of us didn't think that was even in any way potentially on the chopping block, but it is a possible future that Mars Sample Return could see budget cuts or even a potential cut entirely. And I know you have given me some hope on this in the past. So what's your hot take on this?

Jack Kiraly: One of the timing components of all this of our Day of Action happening on September 18th, I think it was that Thursday following it, a major report came out, the independent review board that had been convened earlier this year to take out an independent look at the Mars Sample Return program. And notice I say program and not mission because, again, it is three missions in one. It is a lander, it is a Mars ascent vehicle. How cool is that?

Sarah Al-Ahmed: So cool.

Jack Kiraly: And an Earth Return Orbiter to bring those samples back. And that report details, or really, they were given sort of carte blanche to review and analyze the Mars Sample Return program, their plans for the future and see if it's feasible, right? This is a massive undertaken. We have never, ever sent something to another planetary body and returned it. We've never launched off the surface of Mars. We've done this on the moon, sample return. We've done this from asteroids with something like OSIRIS-REx just a few weeks ago. And Mars Sample Return is that next big step in Mars exploration, and it's the next big step in just planetary exploration writ large. The IRB was given carte blanche, meaning they could have gone in and said, "This program is unsustainable. We need to cut it or gut it or cancel it entirely," but they didn't. The IRB definitively came out and said that although there is cost overruns on the current architecture and that they instructed NASA JPL to go back to the drawing board on some of the components to make sure that it's robust and resilient to future changes in whether it's the infrastructure available at Mars, we have the Perseverance rover on the surface that has a shelf life. We have our orbital assets that have shelf lives. The conditions on Mars vary from year to year, from Martian year to Martian year. And making sure that whatever we send as a part of Mars Sample Return is resilient to delays, resilient to the conditions on the surface, resilient to the infrastructure available to support the mission. So long as we do all that, this is still the top priority of the planetary science community, and it has been for the past two decades. I mentioned the decadal surveys. The previous decadal survey from 2012, Visions and Voyages, and the current decadal survey, Origin, Worlds, and Life, OWL. That's how you remember it. Origin, Worlds, and Life both list Mars Sample Return is the top priority. And the IRB is yet another document in that corner saying, "Yeah, it's going to be difficult. This is the first time we're ever going to try and do something like this. It's going to cost money and we don't know how much it's going to cost right on the outset, and budgets are going to change and our expectations for budgets will change. And NASA is keeping a tab on that, and the IRB was keeping a tab on that. There's some great charts in their report. But at the end of the day, these are scientifically significant samples that we have painstakingly taken the time to use the Perseverance rover, our assets on the surface to find samples that are going to unlock secrets of Mars geologic history, 3.7 billion years. It blows my mind what we are going to be able to even thinking about what we might be able to uncover with these samples.

Sarah Al-Ahmed: And they're going to surprise us. You know they're going to surprise us.

Jack Kiraly: They will. And they're going to rewrite textbooks based on these samples. And this is the greatest undertaking that the US has ever endeavored to do. And it's not just the US. This is an international mission. Let's not forget that. The European Space Agency's providing a lot of support, not just in the form of the Earth Return Orbiter, but is also a part of the Sample Retrieval Lander and the Mars Ascent Vehicle. There's components that are international in every aspect of this program. And it does a disservice to our international allies. At a time of great geopolitical tension right now, the US needs to show a strong face and continue our sample return. Yes, it's going to be a costly endeavor, but doing it in a smart, fiscally smart and sustainable way is a recommendation of this IRB. And it probably, according to the IRB, not going to happen in 2028, but we're looking at 2030 launch dates into the mid to late 2030s. There are a number of opportunities. And the sooner we can do it, obviously the better. But doing it in a way that is fiscally smart is also of importance to the IRB.

Sarah Al-Ahmed: And I think it's always important in these cases where we're talking about budget and numbers for NASA, just to point out that NASA's budget is a very small part of the federal budget. It's something like 0.5%. So a lot of people think that we spend a bunch of money on these space missions. And if you look at the numbers on paper, it can seem that way in the context of our everyday lives, but in the context of the federal budget, this is not a huge amount of money that they're asking for to accomplish something that could literally change the entire way we think of ourselves and our Solar System and the history of our Solar System.

Jack Kiraly: And on top of that, it's a precursor mission to future human exploration. And the IRB says it as much, that the ultimate goal of the Artemis program, the ultimate goal of NASA's human space flight program is to send humans to Mars. And this isn't just something that's written down on the back of a napkin right now, "I should send humans to Mars." This is federal policy that NASA needs to lay out a plan for getting humans to Mars, and this is part of it, sample return. If you can send a rocket there, launch it back into orbit autonomously, mind you, there's a 46-minute delay for the time it takes for signals to travel between Earth and Mars, you need to be able to do that autonomously with a robot. And that's going to be really important technology to sending future human missions. So Mars Sample Return is in the same way with the Apollo program. We did sample return as a part of our lead up to Apollo 11. Mars Sample Return is that precursor mission to future human missions. Maybe at this juncture, don't know what those missions will be called, Aries or whatever name we eventually give them.

Sarah Al-Ahmed: That's a good name.

Jack Kiraly: They might be the missions and the martians. So I don't know if...

Sarah Al-Ahmed: You're right. This is why it sounds so familiar.

Jack Kiraly: It's a good name. It's very interesting name. And yeah, Mars Sample Return is that precursor mission. And there's an international... Obviously, the international partnership component, but there's some international competition too, right? The IRB points out that this is of not just scientific importance, but of national importance, right? Strategic importance to the US. And that's because the Chinese National Space Agency has also identified Mars Sample Return as a goal for their space program. And they've very impressively been able to get to land and operate a rover on the surface of Mars on their first try.

Sarah Al-Ahmed: Nailed it.

Jack Kiraly: I love seeing this race to Mars. And now it's a race to get to Mars and back. And that's just going to lay the groundwork for future human exploration, future robotic exploration. If we're able to do that, imagine all the things we're going to be able to do, all the technology breakthroughs that we're going to have between now and bringing those samples back that are going to enable further exploration of other places in the Solar System.

Sarah Al-Ahmed: So cool. Well, thanks for joining me and for helping to do this ginormous thing. You should be so proud of what you accomplished during your first time doing this Day of Action. And I'm hoping next time I'm there with you. And I know Casey will be with us there on the hill next time. It's going to be an even bigger party than it was this time.

Jack Kiraly: Absolutely. So mark calendars for early 2024. We are going to be coming back. Keep an eye on your inbox. We'll be announcing the next Day of Action very soon.

Sarah Al-Ahmed: And if you want to know more about what actually happened during the Day of Action, you can check out Jack's article. It came out on September 21st. It's called The Day of Action Returns to Capitol Hill. I'll put that in the links for this episode of Planetary Radio. Thanks, Jack. NASA's InSight spacecraft, which is short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport, launched to Mars in May 2018 and landed later that year in November. The lander's mission was to learn more about the interior structure of Mars so scientists could compare the red planet to all of the other worlds in our Solar System. The mission ended in December 2022, and scientists worldwide have been combing through the data, including the findings from the spacecrafts rotation and interior structure experiment, or RISE. The RISE instruments principal investigator, Sebastien Le Maistre, from the Royal Observatory of Belgium and the Catholic University of Leuven, recently spoke with our senior communications advisor, Mat Kaplan. His team's research suggests that Mars's rotation is speeding up. Their new paper called Spin State and Deep Interior Structure of Mars from InSight Radio Tracking was published earlier this year in the journal Nature.

Mat Kaplan: Sebastien, welcome and thank you for joining us, and congratulations on the release of this paper published in the journal Nature that tells us much more about Mars, especially the deep interior of Mars. Again, thank you for joining us.

Sebastien Le Maistre: Thanks for inviting me.

Mat Kaplan: It seems that what RISE has told us about the accelerating rotation of Mars, that might be the somewhat sexier result. In fact, it was the headline in the press release that I saw. But really, if you'll pardon the pun, the core of your work seems to be what you've been able to tell us, what RISE and your team has been able to tell us about what's happening down inside Mars. So tell us what have we learned about Mars' core?

Sebastien Le Maistre: We have learned a lot, not only thanks to RISE, but also thanks to other instruments that was on board the InSight mission, like the seismometer SEIS. But mostly, what RISE brought specifically to the picture is the shape and the size of the core that was very not expected, I would say. First of all, the RISE experiments had as a main objective to constrain the very deep interior that we didn't think we could infer from seismic data. And the role of RISE was to basically monitor the rotational dynamic of the planet with high accuracy, and with that accuracy, try to identify if we were seeing some signature of the very deep of the planet. And that's what we did. We needed a lot of time to accumulate a lot of data because we want to see arising from the noise, the signature of the deep interior. So that was a very exciting work. Also very, let's say, challenging because the signature we were looking for, so the signature of the liquid core of Mars is extremely small. So we are talking here about something that corresponds to a motion of the surface of Mars of about 40 centimeters over a Martian year. So it's extremely small, and we wanted to detect that from Earth with a radio link between the Mars surface, so between the RISE instruments and the ground station on the Earth, the DSN station that are well known and that corresponds to gigantic antennas that are used to track the space props. So we had to accumulate those data over time. And from that, at some point, we identified what we call a rotational normal mode. So something that only exists if there is a liquid layer beneath the solid mantle of Mars. And we detected that after hundreds of days. And then we tried to interpret that. So with colleagues more expert in the geophysics of Mars, we identified that the shape of the core was not what we expected. The size was, let's say, quite close to what had been observed using, let's say, other method like the seismic data or the tidal measurements. But the shape was quite different. So it puzzled us at the beginning and we came up with some explanation of why the core looks really much like the core of a liquid planet, if you wish, a planet that would be liquid rotating on itself, what we call the hydrostatic shape of the core. So RISE had this specificity of characterizing the core itself, its size, its shape, its composition, its moment of inertia as we call that, which is basically the distribution of mass inside the core, the density jumps, so basically, the density of the core with respect to the density of the external part of the planet. Those are the specific thing that RISE brought to the picture of Mars interior.

Mat Kaplan: Whenever I talk to someone like you who conducts what we know as radio science, I am blown away by the exquisite sensitivity. I mean, we're talking here about using the Doppler effect, right?

Sebastien Le Maistre: Correct.

Mat Kaplan: But to do this at the level of being able to detect a 40 centimeter change over the course of a year, could this have been done, I mean, years ago, let's say by the Viking Landers in the 1970s, or maybe even in the years after that?

Sebastien Le Maistre: Yeah, no, actually not. And the idea of looking for that specificity of the planet rotation was already in the minds decades ago, but we couldn't reach that because of the accuracy of the previous data. So Viking had stayed on Mars and operated on Mars for a long period, which is necessary, as I said, to accumulate the signal and to have a chance to see it. But actually, the Viking data was using other frequencies, lower frequencies in the signal that were more sensitive to propagation noises. So these data were not precise enough to see this signal, and so we had to wait. And also, I mean, orbiters are also sensitive to the rotation of a planet through the rotation of the gravity film. But here, again, the precision was not good enough. And so we had to wait for a new mission stick to the surface, and that would be providing data for a long time span and with very high accuracy. And actually, even that, RISE provided us, even if we spend years to prepare the mission, to prepare the models, to implement the softwares, to get ready of what kind of observable we expect, what kind of ranges we expect, et cetera. And in the end, everything was not what we expected. And also, in terms of accuracy, we didn't expect the spacecraft to provide such a good set of data. So we had to improve the models of all kinds, the models regarding the calibration of the data. We had now to introduce, for instance, models to calibrate the Martian troposphere data noise. And also, the dynamical model of Mars rotation had also to be improved to match and to be representative of the data.

Speaker 6: We'll be right back after the short break.

Bill Nye: Greetings, Bill Nye here, CEO of The Planetary Society. Thanks to you, our LightSail program is our greatest chair to accomplishment. Our LightSail 2 spacecraft was in space for more than three years, from June 2019 to November 2022, and successfully used sunlight to change its orbit around Earth. Because of your support, our members demonstrated that highly maneuverable solar sailing is possible. Now it's time for the next chapter in the LightSail's continuing mission. We need to educate the world about the possibilities of solar sailing by sharing the remarkable story of LightSail with scientists, engineers, and space enthusiasts around the world. We're going to publish a commemorative book for your mission. It will be filled with all the best images captured by LightSail from space, as well as chapters describing the development of the mission, stories from the launch, and its technical results to help ensure that this key technology is adopted by future missions. Along with the book, we will be doing one of the most important tasks of any project. We'll be disseminating our findings in scientific journals, at conferences and other events, and we'll build a master archive of all the mission data. So every bit of information we've collected will be available to engineers, scientists, and future missions anywhere. In short, there's still a lot to do with LightSail, and that's where you come in. As a member of the LightSail Mission team, we need your support to secure LightSails legacy with all of these projects. Visit planetary.org/legacy to make your gift today. LightSail is your story, your success, your legacy, and it's making a valuable contribution to the future of solar sailing and space exploration. Your donation will help us continue to share the successful story of LightSail. Thank you.

Mat Kaplan: I always love it when a scientist or engineer tells me that, one, they're instrument performed even better than they expected after a lot of work, and two, that they got unexpected results because, isn't that the most exciting thing in science? Back to the core, wasn't there thinking at one time that Mars might be so geologically dead that perhaps it doesn't even have a liquid core, which now, your data, other data, including the data from that also exquisitely sensitive seismometer, we know that it does. And in fact, it's kind of sloshing around a little bit, causing these perturbations.

Sebastien Le Maistre: Yeah, that's true. That's true, that for a while, we didn't know. We expected it from planetary formation scenarios, but we didn't know. And the first clue about the liquid core existence was obtained from orbiters that measured the tidal signal in the gravity field, and that was already almost 20 years ago. And so here we come with a totally different measurements, something that has nothing to do with tides, that has nothing to do with seismometry, and that confirms this state. Now, RISE brings something else that is still under study, which is a piece of answer to the question of the inner core, what we call the inner core, which is the solid part inside the liquid core. We have that on the Earth, and that is a weakness, let's say, or a consequence of the magnetic field that we can see on Earth, and that doesn't exist on Mars. And so there is this big question of the inner core, is there an inner core on Mars? Yes or no? Because there is no global magnetic field. And we think that there were one, billion years ago, but we don't see anything anymore. And here, we dig into the RISE data to also detect, if any, the signature of such an inner core, and we didn't detect any. So basically, our RISE... I mean, it's always very complicated to prove the absence of something, right? It's easy to prove that there is something. It is very complicated to prove that there is nothing.

Mat Kaplan: Hard to prove negative. Yeah.

Sebastien Le Maistre: Yes. I'm not saying that there is none. I'm just saying that in the RISE data, at least the analysis we've done on it, we didn't detect the signature of the inner core.

Mat Kaplan: Obviously, still more to learn. Let me turn now to that other headline making finding by RISE, which is that Mars, its rotation, it's actually spinning faster and faster. It's accelerating, which is pretty fascinating. I mean, we would expect from physics, a planet to slow down, if anything thing, right? What is going on here? Why is it speeding up, and by how much?

Sebastien Le Maistre: By how much? Is by very little, actually. It's almost, let's say, one microsecond per year. So it's very, very, very little. But if you consider that at the geological timescales, then it can be significant.

Mat Kaplan: Yeah. And the mass of a planet speeding up, I mean, there's a lot of energy there.

Sebastien Le Maistre: Yes, yes, clear. Actually, if you do the math, you can have many different... First of all, we don't have any clear explanation for that yet, so we are working on it. But if you do the math, you can really identify a dozen or it's a half a dozen of explanations that would be just a slight change in the shape of Mars, a slight change in the thickness of the polar caps. You can imagine a lot of [inaudible 00:43:53], few explanations that can really be physically sounded, and that can explain what we see. We could also imagine that there is, let's say, a glitch in the data that we consider to be associated with an acceleration, and that wouldn't be. I mean, there is a big chance that this signal actually exists because, first, once we saw that for the first time, we were really puzzled. And so what we did is we used different softwares. We also looked at it in the Orbiter data. So this is not in the publication, for instance, and we actually see the same signals. So there is a real belief that it's there, but we still need to identify the source.

Mat Kaplan: I want to come back to the possible explanations for this acceleration because there's a wonderful analogy. I don't know if it's yours or was added by whoever wrote the press release, but it was compared to an ice skater. And let's think of an Olympic ice skater spinning in one position on the ice with her arms extended, and when she brings her arm in, conservation of motion, angular momentum, she speeds up. So if Mars becomes a little bit taller, with more ice on the pole, you would expect it to speed up a little bit. Do I have that right?

Sebastien Le Maistre: Yes, exactly. That's exactly that. Indeed, yes. That's why I was talking about ice accumulation at the pole because it means that the matter would go closer to the spin axis and would, as you say, make Mars taller. You could also imagine, like on the Earth, that at some point you would have ice, what we call the post glacial rebound on Earth. So basically, after the ice remove from the cap, the solid Mars would relax to reshape, and so would in the same way than what you just said, would elongate, if you wish, along the spin axis. So all these are possibilities.And one also is, for instance, the tidal torque from the moons of Mars. Phobos, for instance, is one of the two moons of Mars, which is the biggest one, is falling down to Mars. And so it accelerates Mars, we know that, but in fact, Phobos is responsible for an acceleration, which is three order of magnitude smaller than what we observe, so it cannot be that. We could also imagine that you have an impactor that would've brought some angular momentum to the planet just by impact. As the planet, basically, when they formed, they got their rotation speed, just certainly thanks to those impacts. But also, the first calculation about that show that it's unlikely because it would require a very big impactor or very many of them, which is very unlikely.

Mat Kaplan: It seems obvious that, and it's no surprise, we have much more to learn, you had four years of data from RISE over the course of insights lifetime on Mars. Brilliant work by the entire spacecraft team. But are we done? Is there more to learn from not just the data from RISE, but from the other instrument on this mission, the seismometer?

Sebastien Le Maistre: Clearly, no, we are not done. There is a bunch of data that are still under the eyes of the scientist of the team and of the scientists of the entire scientific community worldwide because now the data are available, so everybody can use and process the data. For the case of RISE, the specific case of RISE, as I said, because it's radio science, you often need to wait. It's not an event that you want to interpret. It's not a picture of the surface. It's really some dynamical effects that you want to see. So you really have to look at it once the entire set is there, which is the case now. So we have many other stuff that we can do, that we will do.

Mat Kaplan: That's great to hear. I'll leave you with this. I'm just curious about how you got into this business of sending exquisitely sensitive radio receivers and transmitters to other worlds because you have worked on so many missions. It just seems like a fascinating line of work, but one that takes a good deal of patience.

Sebastien Le Maistre: Yeah. Yeah, indeed. Yeah. I am an aerospace system engineer, and so, at some point, I was hired to work on Mars Express, which is a European mission, and on the radio sense of Mars Express. So I came to the team in Belgium. I'm French. And that's how I started, just because I had the opportunity. I was not expecting that from my childhood. I mean, even if I was super interested by space and [inaudible 00:49:27], but that's just a matter of chance, I would say. And then, from that point, I mean, I got in love with the field, of course.

Mat Kaplan: Sebastien, stay in love, and I look forward to hearing more results from this data, from InSight, and the other work that you are doing from missions all around our Solar System, including missions to come, like MMX, that sample return mission that the Japanese and an international consortium plan to send to Mars. Thank you, again, very much for joining us.

Sebastien Le Maistre: Thanks a lot for your invitation.

Mat Kaplan: My guest has been Sebastien Le Maistre, the principal investigator for the RISE instrument on InSight. RISE, the rotation and interior structure experiment. He's also the lead author of the paper in Nature with the results that we've been talking about, and we will put up a link to that paper on the episode page for this week that you can find at planetary.org/radio.

Sarah Al-Ahmed: Now, let's check in with Bruce Betts, the chief scientist of The Planetary Society for WhatsApp. Hey, Bruce.

Bruce Betts: Hi, Sarah. How are you doing this fine and glorious day?

Sarah Al-Ahmed: I mean, it's been super fun seeing everyone around the office. It was good hanging out with you yesterday. It's a weird thing to see everyone in the real world.

Bruce Betts: They're so three-dimensional.

Sarah Al-Ahmed: I know. That's a trip. Maybe more dimensional, who knows?

Bruce Betts: Whoa.

Sarah Al-Ahmed: Did you get to see the annular eclipse Bruce?

Bruce Betts: I did. It was super, super-duper cool. I took pictures. I watched it. I hung out with my old family and sons and stuff, and we looked and it did what it was supposed to do. And I pondered. I pondered. I thought, Ooh, look, orbs moving relative to one another in the sky that we don't usually appreciate their movement relative to each other. And then I thought, that was almost profound. And then I moved on.

Sarah Al-Ahmed: It was a moment for me, though. I felt like a superhero. All of my neighbors were outside staring up at the eclipse without eclipse glasses, and I just happened to be one of those nerds with a full bag full of eclipse glasses.

Bruce Betts: Awesome.

Sarah Al-Ahmed: So I went out there just like, and you get eclipse glasses, and you get eclipse glasses. But it was a good time, and I'm glad people got a chance to see that. And now we're all mentally prepared for the next big eclipse coming up on April 8th, 2024.

Bruce Betts: Yes. Yes.

Sarah Al-Ahmed: Sneaking up on us.

Bruce Betts: Well, I mean, time.

Sarah Al-Ahmed: Keeps slipping.

Bruce Betts: Slipping, slipping

Sarah Al-Ahmed: Into the future. And speaking of time, this weekend, International Observe the Moon Night is coming up on Saturday, October 21st.

Bruce Betts: Time is on our side.

Sarah Al-Ahmed: Are you going to go outside and check out the moon?

Bruce Betts: Sure. It's always good to check out the moon. It's a underappreciated thing to stare at, whether it's just with your eyes or with binoculars or with a telescope. Yeah, moon, it hangs out up in the sky. You going to check it out?

Sarah Al-Ahmed: I'm considering setting up my telescope and showing my neighbors that kind of thing since I had such a great time earlier this week. But maybe I'll check out one of the local events. If anybody's interested in finding an Observe the Moon Night event near them, I'll put a link to the website for it on our page for this Planetary Radio episode because there's nothing cooler than just hanging out with strangers and having a moment to ponder the universe.

Bruce Betts: Wow.

Sarah Al-Ahmed: Yeah.

Bruce Betts: You had me at hanging out with Strangers. Wow.

Sarah Al-Ahmed: It's been a good couple of weeks for space nerds, I feel. Between OSIRIS-REx Sample Return and Psyche Mission launching, it's just a good time.

Bruce Betts: It is. And actually, things are working really well, so it is exciting. And looking forward to Psyche getting out there and seeing some metal.

Sarah Al-Ahmed: Metal. Those pictures are going to be bonkers. At least I hope so. I hope it's really cool. I hope we get all these weird jagged pits where craters formed on this metallic asteroid instead of it being really boring on the outside and then we'll have to send a mission to excavate down to find the cool metal.

Bruce Betts: Jagged pics, band name. I call it.

Sarah Al-Ahmed: That's fair. You can have it as long as I get to be your drummer.

Bruce Betts: Sure. Do you know how to drum?

Sarah Al-Ahmed: A little bit?

Bruce Betts: That'll do. All right. Shall we dive into some random space fact? I'm going to dig into the mystery of the fact that if you look at things more broadly, the Lucy Mission, which we'll encounter an asteroid, its first asteroid, this weekend from when we're recording November 1st, 2023, why Lucy is named after Lucy O'Donnell Vodden.

Sarah Al-Ahmed: Why?

Bruce Betts: Exactly. That's the cryptic look on your face I was looking for. Well, I mean, I've extrapolated. Lucy is named after the Lucy hominin fossils from Africa that were found because the study of the Trojan asteroids could reveal "fossils of planet formation." See, there's a fossil tie.

Sarah Al-Ahmed: Clever.

Bruce Betts: So it's named after the strangely famous old hominid skeleton. And that was named after Lucy in the Sky with Diamonds by the Beatles.

Sarah Al-Ahmed: I was going to say. That's a great connection.

Bruce Betts: Yeah. They were playing it in camp, apparently, the day they found it. So they named it Lucy. And Lucy in the Sky with Diamonds was named after a classmate of four-year-old at the time, Julian Lennon, who he did a drawing, which he called Lucy in the Sky with Diamonds about Lucy O'Donnell, later, Lucy O'Donnell Vodden, who has since passed away. But that is why I view the Lucy mission as indirectly named after a British woman named Lucy.

Sarah Al-Ahmed: That's so cool. I remember learning when I was younger that Lucy, the hominid, was named for that Beatles song, but just because I was a huge Beatles fan as a kid. But that makes it even more special.

Bruce Betts: And then, they'll be encountering Dinkinesh, the asteroid which they named for the Lucy fossil. That will be their first asteroid encounter coming up. And that's based upon the Ethiopian name for the Lucy fossil, which means you are marvelous in the Amharic language. There you go.

Sarah Al-Ahmed: Every time there's a name for one of these missions, it's like you go down the rabbit hole of how it got named, and it just gets cooler and cooler. The more interesting little factoids you get about these, the more I feel connected to everyone who did it. That's a fun story.

Bruce Betts: It's fun stuff. And so I'm looking forward to seeing another asteroid. It's a 700 meter, I believe, main belt asteroid. Have you got anything from anyone out there?

Sarah Al-Ahmed: Yeah, we had a lot of great comments in our member community this week, and in previous weeks as well. But I got a message from Keith Abels, one of our members that said, "That's so cool. We'll be mining asteroids before we know it." It was in a reference to the OSIRIS-REx sample return. But I think whenever I think about the Psyche mission, I always in my brain tie it to asteroid mining. I think I've told this story in a previous show, but a little kid came up to me and said that he was going to be a rich scientist someday.

Bruce Betts: A what?

Sarah Al-Ahmed: And I asked this kid, I'm like, "How are you going to do that?" And this kid's like, "Asteroid mining. Have you heard of the asteroid Psyche?" This kid was like 10. So I think going someplace, that kid

Bruce Betts: Apparently Psyche.

Sarah Al-Ahmed: Oh, I also wanted to say, a few weeks ago we made a portal reference on the show. You close out the show by saying that, think of Sarah playing Portal 2, which I've definitely done. But we had a member, Devin O'Rourke, write into the community and say, "Oh my goodness. Portal references on this week's Plan Rad," and then sent an emoji of a piece of cake. It's beautiful.

Bruce Betts: What reference will we make today?

Sarah Al-Ahmed: Who knows?

Bruce Betts: Maybe none. We're pretty boring.

Sarah Al-Ahmed: We're pretty boring today. All right, let's take it out.

Bruce Betts: All right, everybody, go up there. Look up the night sky, and think about what fossil you would name your child after. Thank you, and goodnight.

Sarah Al-Ahmed: We've reached the end of this week's episode of Planetary Radio, but we'll be back next week with even more inspiring space adventures. You can help others discover the passion, beauty, and joy of space science and exploration by leaving a review and a rating on platforms like Apple Podcasts. Your feedback not only brightens our day, but helps other curious minds find their place in space through Planetary Radio. You can also send us your space thoughts, questions, and poetry at our email at [email protected]. Or if you're a Planetary Society member, leave a comment in the Planetary Radio space in our member community app. Planetary Radio is produced by The Planetary Society in Pasadena, California, and is made possible by our kind Pale Blue Dot loving members. You can join us as we work together to build a collaborative and inspiring future for everyone on Earth at planetary.org/join. Mark Hilverda and Rae Paoletta are our associate producers. Andrew Lucas is our audio editor. Josh Doyle composed our theme, which is arranged and performed by Pieter Schloser. And until next week, ad astra.