The Rosetta mission’s journey to comet Churyumov–Gerasimenko 67P spanned some 10 years, nearly all of that spent idling through space as it performed the numerous gravity assists required to get up the required speed. By comparison the mere 60 hours that the Philae Lander, the near cubic meter sized daughter craft of the parent Rosetta satellite, seemed almost insignificant by comparison but thankfully it was able to return some data before it went dead. There was some speculation that, maybe, once the comet got close enough to the sun the lander would have enough power to come back online and resume its activities. Chances were slim though as it had landed in a high walled crater that blocked much of the sun from hitting.
However, just under 12 hours ago, Philae made contact with Rosetta.
To say that the chances of Philae waking up were slim was putting it lightly given the trials and tribulations it went through during its landing attempt. In the extremely weak gravity field of its parent comet the 100KG lander weighs a mere 1g meaning the slightest push could send it tumbling across the surface or, even worse, out into space. This wouldn’t have been an issue if Philae’s landing hooks had fired but they unfortunately failed meaning it had no way with which to hang onto the surface. Thankfully it seems that an outgassing event hasn’t blown our little lander away and, after the Rosetta craft turned on its receiver to listen for it, we’ve finally made contact with Philae.
Reestablishing contact with Philae is a boon to the Rosetta mission as the lander contains a wealth of data that we could not retrieve when it was last active, due to time constraints. After the initial burst of 300 that the ESA was able to retrieve during this first contact after it went dark there are still some 8000 packets left to collect. These will provide some great insight into what happened to the lander during the dark period and what it’s been up to since it finally woke up. Early indications are that Philae has actually been awake before it was just unable to make contact with the Rosetta probe for whatever reason. We’ll likely know a lot more as the ESA team gets more time to analyze the data.
This also doesn’t appear to simply be a spurious occurrence either as the telemetry data indicates that Philae is operating at a balmy -35°C and is generating some 24 watts of power off its solar panels. Considering that its panels were rated for 32 watts at 3AUs from the sun (it is currently 1.4AUs as of writing) that’s not bad considering that it’s in something of a crater which would limit its sun exposure dramatically. This figure can only be expected to increase as time goes on meaning that Philae will likely be able to keep transmitting data and continue the experiments that it was unable to do previously. One such example is drilling into the surface of its parent comet, something which was attempted previously but didn’t prove successful.
Spacecraft coming back from the dead like this are a rare occurrence and it’s an absolute joy to hear that Philae has awoken from its 7 month slumber. It’s brief 60 hour mission will hopefully now be extended several times over, allowing us to conduct the full array of experiments and gather valuable data. What insights it will dredge up is anyone’s guess but suffice to say that Philae’s reawakening is a boon to both the ESA and the greater science community at large.
The origin of Earth’s water is still something of an open debate. The popular theory at the moment is that the primordial Earth was far too hot to contain any form of liquid water, its molten surface still reeling from the cataclysmic events that led to its creation. However others postulate that the water was trapped deep below the surface, only to arise later on as the Earth cooled and an atmosphere developed. It’s an interesting question not only because of how fundamental water is to life but also because we seem to have a lot more of it than any other planet in the solar system. Thus the question of where it came from, and why it’s managed to stick around for so long, is one of continuous scientific enquiry, including such missions as the recently celebrated Rosetta probe.
If we run with the theory that Earth’s water came from some extraplanetary source then the question turns to what the original source might be. Comets seem like a good candidate as they’re primarily water ice by composition and were far more common during the early stages of Earth’s life than they are now. However measurements of isotopes within water of several comets, including Halley, Hyakutake and Hale-Bopp has shown that they are not likely the primary source of water that’s currently on Earth’s surface. The composition of water found on asteroids and other water formed minerals on the Moon seem to indicate that a source closer to home is far more likely which Rosetta’s latest data appears to confirm.
The comet that Rosetta was investigating, the romantically named 67P/Churyumov–Gerasimenko, has a ratio of isotopes that is completely different to anything that’s seen on Earth. The reason that this is important is due to it’s orbit as 67P is what we call a Jupiter class comet, a collection of various comets that have orbits that don’t extend far past Jupiter. It was thought that these kinds of comets would have been more likely to have been involved in the creation of Earth’s oceans than comets from further out, due to their proximity. However 67P, with its wildly different composition to Earth (and even other bodies in the same vicinity), lends credence to the idea that comets aren’t the likely source of Earth’s oceans. Indeed it’s far more likely that water and minerals trapped in asteroids are the likely source, based on how similar their composition is.
Now this doesn’t rule out comets completely as there’s potential for further out Kuiper belt class comets to have the composition we’re looking for but it’s looking far more likely that objects from within the asteroid belt are responsible for the oceans we have today. What the mechanism was for them making their way to Earth, whether it was early on in the cataclysmic forming of our solar system or later on when things calmed down, is something that’s still an open question. It’s one we might also have answers to very soon as Dawn is scheduled to arrive at Ceres early next year, the biggest object in the asteroid belt. What Dawn finds there might be the key to unlocking the secrets of our Earth’s oceans and, potentially, the asteroid belt itself.
Comets are relics of an era that has long since passed. They formed in the same accretion disk that gave birth to our Earth, Sun and the rest of the solar system but managed to avoid being subsumed into a larger celestial body. This, along with the amazing show they put on whenever they come close to the Sun, makes them objects of particular interest to star gazers and scientists alike. However few craft have studied them as their highly elliptical orbits make it incredibly difficult to do anything more than a flyby. That is, of course, unless you’re the ESA’s Rosetta spacecraft which just made history by deploying its Philae lander to the surface of the Churyumov–Gerasimenko 67P comet.
Many would have heard about the Rosetta craft recently as it was the first craft to ever enter an orbit around a comet which was achieved back in August. However few would know that it’s been on that journey for over 10 years as the Rosetta craft was launched in March of 2004. Since then it’s been slowly making it’s way to rendezvous with 67P, using multiple gravity assists to give it the velocity it needed to match the comet’s speed. Once it arrived at the comet it began imaging its surface in incredible detail, searching for a landing site for it’s attached Philae lander. In the early hours of this morning the Philae lander detacted from its parent craft and began its descent down to the surface and shortly after we received confirmation that it had touched down successfully.
It’s not all good news unfortunately as whilst the telemetry indicates that the lander did make it to the surface the anchoring harpoons that are on it’s feet did not fire. This causes two problems, the first (and most troubling) of these is that the lander is not securely fixed to the comet’s surface. In the minuscule gravity of the comet the lander weighs about 1 gram, meaning any out gassing from the comet could flip the craft over, or worse, send it tumbling out into space. Additionally those harpoons also contained instruments for measuring surface density, a lesser issue but still a blow to the project all the same. The ESA is currently investigating the reasons behind this and might refire them to ensure that the lander doesn’t get blow away.
Firing the harpoons again is risky but the people behind the Rosetta program have never been one to shy away from potentially mission ending decisions. Back in 2007 they scheduled an incredibly low altitude pass by Mars, a mere 250KM above its surface, in order to correct its trajectory to be closer to 67P. The trouble with this though was Rosetta couldn’t use its solar panels during this manoeuvre due to it being in the shadow of Mars, forcing it to power down for the duration. The batteries on the craft were not designed with this purpose in mind however and so this trajectory correction was dubbed The Billion Euro Gamble which, thankfully, paid off.
Rosetta and Philae both carry with them a host of tools designed to analyse the make up of the 67P comet including spectrometers, thermal imagers and radio/microwave based devices. The original spacecraft design was far more ambitious, including such things a sample return mission ala Hayabusa, however whilst it might not be as lofty a mission as it once was it’s still highly capable of giving us a detailed picture of what makes up this comet. This will then give us incredible insight into the early stages of our solar system and how it evolved into what it is today.
Hopefully the harpoon issues will get sorted out in short order and the Philae lander can continue its work without the possibility of it getting blown out into the depths of space. Rosetta’s mission is slated to continue through to the end of next year, just after 67P buzzes passed us on its journey back out to the edges of our solar system. Like all good space missions there’s potential for it to go even longer and here’s hoping that Rosetta and Philae will continue to deliver long past their used by date.