Matt Taylor: Rosetta Might Be Followed by Mission to Asteroids
"Comets are leftover material from the beginning of the Solar System, so by studying them we get an idea of what the conditions were like at the beginning. Results we've already had now from various instruments are indicating how we may have to change our view on how certain things were…”
Dr Matt Taylor, chief scientist of the European Space Agency's Rosetta mission, is worth listening to, but also looking at. A short-sleeve shirt, a beard, short trousers and tattoos on both arms and legs – he doesn't create the impression of a leading astrophysicist who is about to deliver a presentation on comets in just two hours, wrapping up the results of ESA's Herculean effort to land on a comet and study it. Not at a first glance.
But as he is vividly outlining what is so difficult about landing on a comet some 713 million kilometers away, one can't help noticing his misleadingly casual shirt is dotted with stars, planets and galaxies, and the tattoo on his right leg shows the Rosetta spacecraft and its lander Philae – they have been there since Rosetta woke up from hibernation in 2014. "I'm incredibly confident we're gonna nail this landing - confident enough to have it drawn on my body,” he told the BBC the day Philae was to touch the comet's surface for the first time.
Dr Taylor was in Bulgaria for the Sofia Science Festival, an annual event which is now a traditional way of telling there is much more to science than quiet people looking through a microscope. Just before his presentation, he spoke to Novinite about the 14-year-old space odyssey of a probe that went after a duck-shaped comet, rendezvoused with it, entered into its orbit, dropped a lander on it, and is now about to crash into it in just a few months’ time.
It all began in 2004, when Rosetta set off to the 67P/Churyumov-Gerasimenko, after it had initially targeted another comet but a failed takeoff forced a change in destination.
The initial idea about Rosetta came decades ago, in the 1980s, when a joint ESA-NASA mission was supposed to send a probe to a comet, collect samples with it and bring them back. However, the latter task was as difficult then as it still is nowadays. One of the biggest challenges is how to return the samples – material that existed back on the comet at minus 200 degrees, near absolute freezing, but now has to be brought back to the Earth through the atmosphere, not just opening up its container but also keeping it pristine later, Dr Taylor explains.
That was what led ESA to come up with Rosetta – a mission for a space probe named after a rock stele found in Egypt which provided the key to understanding Egyptian hieroglyphs. The task involved something never done before, and as the lander Philae started to make its way out of Rosetta to 67P's surface, the world took a deep breath, with some even finding creative inspiration.
The surge in public interest was not surprising even though Philae was not all Rosetta was about, Dr Taylor says. “It's funny, because it was a small part of the main mission, but I think the fact that we were doing such an extravagant job – it was something special to try to deliver something to the surface of a comet. So, it's not unusual that people get interested.”
But why is it so difficult to land on a comet?
There are a number of reasons he can set out. The first challenge was to make sure Rosetta would come out of hibernation in 2014 after having been asleep for two years – something the Rosetta team wasn’t certain would happen.
Trajectory predictions for Rosetta’s movement were then essential to calculate the right parameters of a “rendezvous” with 67P. “We knew what the comet looked like about six months before we were supposed to land.” It wasn’t until August 2014, when the rendezvous took place, that a “tougher idea of this duck-like shape” appeared, three months before landing.
Unlike with the Moon or Mars, “the key thing with a comet is it becomes active as it gets close to the sun, it started throwing material, hundreds of thousands of kilograms of material - and although it looks like this very dark rock - it has got density actually lower than snow.” A feeling apparently like cocoa, he says, which makes scientists conclude the comet was “not made of much stuff.”
Small density, combined with size (the longest side of its large lobe is 4.1 km, while at the small one it is 2.6 km) suggests there isn’t much mass and gravity. “If you compare it to jump in the air where we are here, if you jump this far, you'll come back. If you make the same thing with the same force on the comet you'll never come back again.”
Another obstacle came from the difference in speed. Spinning around, 67P rotates every 12 hours, traveling at around 40 km/s around the Sun, while Rosetta’s relative velocity was 1 m per second.
“It was a massive challenge and many things could have gone wrong, some things did go wrong, but ultimately we did do what we said we were going to… in a little bit different way,” Dr Taylor says. The way Philae hit the comets’ “ground” and bounced off prevented the deployment of a drill and any proper collection of samples, nor did ESA know where the lander was oriented.
Mistakes also helped gain some benefits, though. After the landing, which ended with Philae rebounding from the ground several times for technical reasons the team was then unable to explain, the dishwasher-size lander was able to send signals for nearly two-and-a-half days before losing contact. ESA later announced that
by landing the wrong way, Philae had actually given scientists the benefit of exploring additional sites.
Dr Taylor nods. “By the point that Philae bounced to cross the surface we got measurements at three different spots which we didn’t think we were going to make. If we had landed where we planned it wouldn’t have been as exciting and there would have been certain measurements we couldn’t have done.”
The bounces helped nail down a measurement of 67P’s possible magnetic field – it was discovered it has none at all. Gas and dust measurements were also conducted across Philae’s trajectory.
“The original land site was in a dusty area but we landed in an area that is much less dusty so we got to see some very interesting features of the comet. We couldn’t have targeted that [area] either. It’s in a region we wouldn't have selected because it's very undulated and bumpy.”
And yet Philae could be still covered in dust – or could be somewhere else as ESA hopes, he explains. As we are talking, the Rosetta spacecraft has approached the center of a comet at just 10 km distance, searching for the lander. A step to entering a lower orbit, 7 km from the center, will be made next week and as Rosetta approaches, high-resolution images are supposed to show where Philae is located. The irregularly shaped body and resultant weird local gravity has always meant Rosetta has been wary of nearing 67P.
“We have a rough idea where the lander is. We’re going to search that area and if it isn't there, that will be a problem. But maybe it also adds some mystique and magic to the mission.”
ESA already warned in February that, after so many months of no contact with the lander, it was time to say “a slow farewell”. And yet,
the question of whether there is even a slim chance that Philae ever wakes up one day remains tempting.
“No,” Dr Taylor is quick to reply. “In principle there is a very, very slim chance, but by that point we won't be able to communicate anyway.” As the comet is moving away from the Sun and will only come back in six years (it takes it more than 2300 days to make a complete orbit), it is likely to fail to start as it isn’t fully functioning now either, even though it will have the same amount of energy when it returns as it did upon approaching the sun in 2014. “It’s not in a situation it can function from all information we have; but Rosetta can.”
With Philae and Rosetta working together, scientific knowledge brought by the mission to the ESA laboratories helped gain insight into 67P – and possibly into other comets – that hadn’t been available before. 67P, or at least its head part, turned out to be more homogeneous than expected, with few differences in its texture. Scientists’ assumption that it had been comets that returned water to Earth after much of it evaporated sometime during the evolution of the solar system proved wrong to a certain extent: it had been mostly asteroids that fulfilled the task; but what comets most possibly delivered to earth are organic materials, amino acids and other things that grabbed ESA’s attention.
“We found organic material that we had never detected before on a comet - it's POM [polyoxymethylene], which goes into making plastic plectrums for guitars.”
Nothing close to life, is it?
The answer is “no” – but quite a cautious “no”: “There is stuff on there that could go on to being life. But there's nothing that is life. That's very important to highlight.”
“The comets are these windows into the past and they contain material that was there at the beginning, but they do not contain life and there is no organism there or something that used to be alive from what we can say.”
As we are talking, the Rosetta mission is just several months away from its end in September, and little time is left for Rosetta to be active as the spacecraft will have to follow Philae in landing on the comet. Any further activities of the probe are nearing the impossible with 67P moving way from the sun, Rosetta running out of fuel and unable to use power from sun rays, and sending data back to Earth becoming the more difficult the further it gets. Its instruments are increasingly old and shaky, functioning beyond their designed lifetime, and low temperatures in deeper space where the comet is going make it unlikely to survive yet another hibernation as the one it went through in 2012-2014.
However, while the lander was programmed to work on the surface, the orbiter “doesn’t know what to do when it’s on the ground,” Dr Taylor notes.
From an engineering perspective, the easiest thing would be to turn Rosetta off – but that would prevent ESA from getting as close as possible to the surface and getting the highest-resolution measurement – an arduous task because of the material coming out of the surface, throwing all of this gas and dust. “When you get closer, it's a weak gravity, it's a funny shape, so it's weird how the gravity is close to the comet. We have always stayed reasonably far away from the comet, even when we can get close, we try to keep safe.“ For the first and only time now, precaution will be unnecessary.
After all, the Rosetta mission “is designed to end on a particular day,” Dr Taylor points out, and it will not be long before the spacecraft stops operating after touching the surface, losing communication and power. “We’ll try to get data as much as possible to the end, maybe it will be like way back when you had dial-up Internet and you were trying to download a picture or a document and it would come down in lines.”
There was – and still is (with new data taking years to process) – much fascination among scientists caused by the findings.
“Rosetta has something about it - it has big questions it is trying to answer, connecting comets to the overall evolution of the solar system. There were surprises about some of the molecules, the gases and the ices that were on the comet. Which we didn't expect to be there, we actually found molecular oxygen, which is very weird because oxygen reacts to everything it touches. The fact it’s there means the comet must have formed in a particular place. It must have been very cold.” He later adds he is referring to a place possibly outside the Solar System.
Using remote sensing to observe through a camera all the spectrum and radiation coming from the surface of a comet, scientists could explore how the surface is constructed and how its blocks of material ("they are not boulders or rocks," he explains) are put together. But what Philae gave ESA was the ability to go and touch the surface.
"At the very least it gave us the idea of what ht surface was like to actually land on. A dusty surface area, and then there is a really hard subsurface layer that we think it is a kind of processed ice, a hard ice... We wouldn't have known that unless we landed on a comet."
Even though he doesn't cast light on details about the findings, Dr Taylor makes clear they will prompt scientists to “rethink some of the theoretical predictions or the extrapolations about how the Solar System evolved.”
Whether ESA will embark on a follow-up to Rosetta is yet to be seen –
science missions are presented by the science community, based on calls that include proposals from all kinds of science ranging from X-Rays to gravity or magnetospheric physics. Out of those the next subject of studies will be selected.
“There may be a cometary mission among them, there may be not. Maybe they will go for asteroids instead. They are a bit easier to get to because they are colder, and they haven’t got these significant orbits that comets have.” He adds importance of these space objects could increase due to their commercial aspect: “Comets and asteroids are also full of cool stuff – carbon, deuterium, rare metals.”
An asteroid mission would also provide evidence for or against the theory that precisely these cosmic objects could have brought water to Earth, the same way Philae gave material from 67P that scientists will need years and years to explore.
Whatever the final mission proposal is, the knowledge obtained through Rosetta could be applied. “The big question is - once we get a better view of how the things have got to where they are today, we can use these observations to look beyond our Solar System. So, now that we got a better idea of where we are, could we use that to help us look for another Earth?“
Ending his thoughts about next missions, Dr Taylor names what has to be Rosetta's natural continuation – a successful sample and return.
“That's the thing Rosetta was supposed to do in the beginning. That is the next step. And when we do that it will take a lot of people from many different countries collaborating."
Assistance from NASA was actually essential to Rosetta's success:
“Yes, this is one of the key things to state – Rosetta was only possible through collaboration.” While it was predominantly an ESA mission, NASA provided several instruments for the spacecraft and granted use to its ground station for the mission’s purposes. On the other hand, one of the reasons for the “original Rosetta” not to be pursued was that joint missions take much more effort. “It's difficult enough to organize a big mission like this in ESA, let alone have another agency involved.” BepiColombo, ESA's first-ever mission to Mercury with a probe set to enter orbit in 2024, involves collaboration with Japan, and is taking many years to get lots of people together.
Mr Taylor doesn’t rule out that more active collaboration with NASA “could come out of the next call” for a medium-class mission proposed by the scientific community. Synergies between teams and missions are sometimes essential, he makes clear: “There’s some science you can do on a small budget and for other things you need a really big one – and that requires more than one agency.”
As Dr Taylor has to be left to have a break before telling the story of Rosetta, a last detail is worth mentioning. Apart from the Philae lander,
the Rosetta spacecraft took off from Earth carrying out a small disk - an archive of thousands of pages translated into more than 1000 human languages.
A successor (albeit incomparable in terms of the volume of information stored) to projects such as the Voyager records, the Rosetta disk is aimed at conservation of languages and cultural material that are believed to be facing extinction in a matter of decades.
“What happens to it now? Do you expect someone to find it?,“ I ask Dr Taylor
“Who knows?,” he grins. “Somebody was joking that in 1500 years, when we have cracked space travel so we are all jaunting around the Solar System, somebody might come up with this: It might be funny, we should try and see if we can start Philae up again. So we will have our kids or the kids of their kids will be the astronauts that will be there trying to kickstart Philae and putting Rosetta back together. That's what is going to happen in the future - there will be people doing astro archaeology of ESA and NASA or the other space agency missions.”
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