Her 10-year mission - in 2 minutes
Wake up and smell the comet: Rousing the Rosetta probe
Rosetta arrives – and sends images of 'superstar comet'
The final countdown: Days from the toughest space landing ever
Comet landing live blog
Problems hit Philae after historic first comet landing
Race to get comet data before Philae dies
Philae drills comet, but may not survive the night
Philae's hop, skip and jump across comet 67P
Asleep in the dark near Jupiter, a spacecraft is almost ready to make the first ever landing on a comet – if we can wake it. Stuart Clark joins mission control
YOU know that anxious feeling the night before an exam or a job interview, when the alarm clock absolutely, positively has to work. Take that feeling and double it. Multiply it by a large factor, add the number you first thought of... you get the picture. That's how restless mission controllers at the European Space Agency are feeling right now.
For if there is one alarm clock in the whole solar system that has to work, it is the one on their Rosetta spacecraft. Set for 1000 GMT on 20 January, it will, if all goes to plan, wake Rosetta from a three-year slumber travelling through the deepest reaches of space. Bleary-eyed and disoriented, the craft will keep mission controllers on tenterhooks for a few hours more until they hear a faint beep – just enough to tell them that the €1 billion, 3-tonne spacecraft is alive and well.
Launched in 2004 (see "Rosetta blasts off at last), Rosetta's mission is to give us our first up close and personal look at a comet. By August 2014, it will have caught up with comet Churyumov-Gerasimenko and will hang on to its coat-tails all the way from the frigid outer reaches of the solar system, near Jupiter, to the cauldron of the inner solar system. Rosetta's orbit around "Chury" will take it to within a few tens of metres above the surface – a vantage point that will allow it to map the comet's exterior.
By November, scientists and engineers will have chosen a site to drop Philae, Rosetta's washing-machine-sized lander. It will drift down from the mother ship and latch on to the surface of the comet. Once settled, Philae will begin to reveal secrets about the solar system and maybe even give us clues about the origin of life (see "Secrets of the solar system").
First, though, Rosetta must wake up. For most of the past three years, it has been in hibernation mode, deep asleep except for the tick of an oscillating crystal and a dozing onboard computer with one eye on the clock. Everything else is dark: the cameras, the instruments, even the communications equipment. Nothing has been heard from the comet chaser for 32 months.
That's because to reach its rendezvous with Chury, Rosetta has travelled deeper into space than any solar-powered spacecraft before it. Near Jupiter's orbit, where sunlight levels drop to around 4 per cent of those on Earth, its giant solar panels – the largest ever flown in space – can only generate enough power to keep some internal heaters going. Almost everything else on Rosetta had to be turned off.
For spacecraft operators who are used to daily communication, the silence has been a wrench. "It is very weird to be out of contact for such a long time," says Roberto Porto who works at the European Space Operations Centre (ESOC) in Darmstadt, Germany.
I first met Porto in 2010 when Rosetta flew past asteroid Lutetia. He called me into the control room to witness a manoeuvre. He showed me four graphs on a computer screen and held up a clenched fist with his little finger and thumb extended, as if imitating a telephone. His fingers stood for the solar panels and his fist the bulk of the spacecraft, which is about the size of a small car.
As the lines snaked across the screen, he gently rolled his fist. "The spacecraft is doing this," he told me. His mental connection to the craft was extraordinary. At the time, he realised that something had happened inside him. "That fly-by was the first time I felt really attached to the spacecraft," he recalls. Turning Rosetta off a year later was far from easy. "It was like saying goodbye to a friend and knowing you weren't going to see them for almost three years. I guess it was worse for the people who had worked on the mission for longer than me."
One such person is Andrea Accomazzo. He joined the Rosetta mission in 1996 and is now the spacecraft's operation manager. He knew early on that hibernation would be a challenge. "In the development phase of the mission, I tried to convince my manager many, many times not to design a hibernation mode. We had no other choice but to create this," he says.
No one on Accomazzo's team wanted to be the one to send Rosetta to sleep, just in case it never woke up. So when the time came, they turned to Alois Eibner, who designed the hibernation mode for Astrium, the company that built the spacecraft. "We said to him, 'OK, you have created this monster, so you can be the one to send the signal'," says Accomazzo.
Eibner was unperturbed. "Everything had worked up until that point, so I didn't see anything to be worried about," he says. Preparing the spacecraft was an arduous procedure that lasted a few days. To remain stable after the thrusters were turned off, Rosetta had to be gradually shut down and then made to gently spin. Finally, when the only remaining link was a beep sounding every few seconds in the control room, Eibner sent the last command. The spacecraft's faint heartbeat stopped. Rosetta was as deeply asleep as any spacecraft could be and still be alive.
Fast-forward to now, and a team is waiting like anxious parents for Rosetta to call home. Before the spacecraft does that on 20 January, it has a lot to do on its own. When the onboard computer realises it is time to wake up, it will switch on two heaters. These will gradually warm up Rosetta's star trackers, the sensors that allow the spacecraft to determine its orientation.
After six hours of heating, thrusters will slow down its rotation to a leisurely crawl. The deceleration will take less than 1 minute. Next, the spacecraft must find Earth. It does this by turning on its star trackers, which will scan the skies for familiar patterns of stars. Once it has worked out where it is and where it is pointing, it will consult the onboard map to find Earth's position. Then the spacecraft will start moving to point its antenna towards home. Next, it will switch on the transmitter and the signal will begin its 800 million kilometre journey to Earth. At this distance, the radio waves will take about 45 minutes to reach us.
The quickest all of this can happen is in about 7½ hours, with most of that time spent waiting for the star trackers to warm up. Even if the signal does not arrive on time, panic would be premature. The timings are inherently uncertain. For example, the computer only looks at the clock every 15 minutes to see if 1000 GMT has passed, so there could be a delay of at least a quarter of an hour. If the spacecraft is in any doubt about the state of the star trackers or the rotation manoeuvre, then software is designed to stop and start the particular process again. Altogether, such shenanigans could delay the receipt of the first transmission by around 2 hours.
As nail-biting as those 8 to 10 hours will be, the spacecraft has been up and about operating independently before. Rosetta is a master at doing things for itself. In 2007, it skimmed past the night-time side of Mars, and had to rely on battery power to keep itself alive. Even then, it managed to take a stunning selfie of its solar panels above the Syrtis region of the Red Planet.
Stunning image of Rosetta above Mars taken by the Philae lander camera
(Image: CIVA / Philae / ESA Rosetta)
Three years later, the spacecraft had to turn away from Earth to concentrate on gathering data as it flew by asteroid Lutetia. It worked on its own for 40 minutes before turning around to beam its results back to Earth. Shortly afterwards, as a test, the team placed Rosetta into temporary hibernation for a week.
Busy doing nothing
The team has also learned a thing or two from Rosetta's sister spacecraft, Mars Express and Venus Express. Both of these are more-or-less identical to Rosetta. All told, the flight team now has 25 flight-years of experience operating these three probes and if there is one lesson they have learned, it is this, says Accomazzo: "Many of the problems we have met were because we were in control of the spacecraft. We either made a mistake or discovered a feature of the spacecraft that didn't work as expected. Every time we left the spacecraft alone, we didn't have a problem."
Nevertheless, they are taking Rosetta's awakening very seriously. "We haven't seen the spacecraft for nearly three years. The tension is more like you experience at a launch," he says.
With the whole mission resting on the outcome of Rosetta's wake-up call, the team has prepared for every eventuality. They have been running simulations using software models and a full-size replica of the spacecraft that is housed at ESOC. And they have been working out what to do if the signal doesn't arrive – nothing, at least initially. "The risk is that we send a command to the spacecraft but the spacecraft is already doing something, so we don't want to interfere," says Accomazzo.
The comet chaser
The ESA's Rosetta mission launched in 2004 and its journey to meet the comet Churyumov-Gerasimenko has taken in fly-bys of planets and asteroids
Once awake, some niggles may appear. Like many of us on waking up, Rosetta will take a while to really get going. Only by May will all the subsystems and instruments have been switched on and checked. By this time, the spacecraft should be back close enough to the sun to generate juice to power all its systems.
In particular, Porto is waiting to see what happens with the reaction wheels that help point the spacecraft in the right direction. The failure of reaction wheels is what crippled NASA's planet-hunting Kepler spacecraft and Porto has found that two of Rosetta's four wheels experience unexpected friction when turning at high speed. During the hibernation, the team has used the replica of Rosetta in the lab to understand the behaviour and design workarounds.
They are also prepared for some damage to the solar panels caused by micrometeoroid strikes during the hibernation. While this will inevitably degrade Rosetta's ability to generate electricity, it is an accepted part of spacecraft ageing. Armelle Hubault, who joined the team in 2004, is sanguine about what they will find. You can hear her shrug as she says, "there will be ageing of the spacecraft to take into account but we know this spacecraft very well now".
Accomazzo also sounds philosophical: "I spent many years being really scared of this hibernation mode, but after years of flight my confidence has grown dramatically."
Hubault sums the team's feeling up, simply and directly. "We are ready," she says.
Wake up Rosetta, it's time to go to work.
Stuart Clark is a New Scientist consultant and the author of The Day Without Yesterday (Polygon). His website is stuartclark.com.
"Rosetta is the sexiest space mission that has ever been," said European Space Agency mission scientist Matt Taylor. He was speaking as the Rosetta probe finally arrived at comet 67P/Churyumov-Gerasimenko after a ten-year mission.
Others were scarcely more reserved. "It is the most crazy bonkers superstar comet in the solar system," said ESA senior scientific adviser Mark McCaughrean. "We have won the gold medal with this comet – it is an astonishing object."
Rosetta has travelled 400 million kilometres to reach 67P, and now begins a 16-month mission to study it in detail. Cameras on board the probe have already revealed 67P to be a comet of two halves, with a shape some have compared to a rubber duck, and there is much more to learn. Comets are the frozen leftovers from the formation of the solar system, so they can teach us about the origin of water and other molecules necessary for life on Earth.
Image: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
The probe executed its final manoeuvre at around 9am GMT today, firing its thrusters to match 67P's speed. Roughly 23 minutes later, ESA technicians at the European Space Operations Centre in Darmstadt, Germany, received confirmation that everything had gone smoothly. "We have never seen the temperature of the thruster going as cleanly as today. It is a fantastic result," said Rosetta flight director Andrea Accomazzo.
Since the comet is only around 4 kilometres wide its gravity is very low, meaning Rosetta will initially have to travel in an unusual triangle-shaped orbit. It will start at a distance of 100 kilometres in order to learn more about 67P's weird shape, before moving in for a closer look. "It's like entering a chaotic town with a lot of traffic where the signs are confusing," said Accomazzo.
Mission: to survey a comet
The ESA's Rosetta spacecraft will carry out tough manoeuvres once it arrives at comet 67P/Churumov-Gerasimenko
"What a wonderful moment. We're there, we've arrived, 10 years we've been in the car waiting to arrive at scientific Disneyland," said McCaughrean. Now the ESA team must identify a landing site for Philae, a smaller probe that has ridden with Rosetta and will touch down on the comet's surface later this year and drill 23 centimetres into its surface. "The big roller coaster awaits us in November – that's the scary ride to go on."
Image: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
ESA has already performed a preliminary analysis of landing sites, which lie mostly on the "head and shoulders" of the duck, said Philae manager Stephan Ulamec. The comet's density and the roughness of its surface will be a factor in the choice of landing site, as is the changing illumination from the sun. "We want to have a clear day-night cycle for scientific reasons." ESA can't control Philae once it is released from Rosetta, so it will land somewhere in a 1-square-kilometre chosen area.
Rosetta and Philae are equipped with a total of 21 scientific instruments set to analyse the comet as it approaches the sun, heating up and releasing gas to form a lengthy tail, right up until August next year when it reaches the closest distance to the sun. "It's going to be an awesome ride. Stay tuned," says Taylor.
By Jacob Aron - 6 August 2014
Ten years after leaving Earth, one of humanity's most ambitious space missions is ready for its climax – a nail-biting drop onto the surface of a comet
MATT TAYLOR will soon experience the most agonising 28 minutes and 20 seconds of his life. That's how long it takes a signal to travel the 500 million kilometres from the surface of comet 67P Churyumov-Gerasimenko to the European Space Agency's mission control in Darmstadt, Germany. So that's how long Taylor must wait to find out if his team has made history by landing a spacecraft on a comet for the very first time.
The European Space Agency (ESA) craft, Rosetta, has been orbiting comet 67P since August. But the most daring part of the mission begins on 12 November. At 0835 GMT, Rosetta will cast adrift a washing-machine-sized lander called Philae. For the next 7 hours or so, Philae will be pulled down by the comet's puny gravity, dropping 23 kilometres. Touchdown is scheduled for around 1530 GMT, when the nail-biting wait to hear a signal from Philae will begin.
Plenty could go wrong. Philae could overshoot its target. It could bounce off the comet. Or crash land. It could even be blasted to pieces by jets of gas erupting from the comet. "This is the most challenging mission ESA has ever attempted," says Taylor. By 1600 GMT, we will know if Philae has earned a place in the space hall of fame and started its pioneering scientific investigations, or become an extremely expensive piece of space junk.
There is a great deal we want to find out about 67P. "Many of us are now convinced that life was possible on Earth only because water and certain organics were brought by the comets," says Philae's lead scientist Jean-Pierre Bibring of the Space Astrophysics Institute in Orsay, France.
Comets are often called dirty snowballs. They appeared early in the solar system's history and formed anywhere water can freeze. Back then, dust and rocks merged into ever larger proto-worlds that went on to merge and make planets. Comets were also part of this process and brought their supply of water to the forming planets.
The comets that remain today are the astronomical leftovers – the getaways. They were slingshotted to the farthest reaches of the solar system by the gravity of Jupiter and Saturn. Now they wander in darkness, bound to the sun by only the weakest of gravitational threads. Occasionally, one falls back towards the sun and we catch a window back in time to when they filled the solar system.
Ground-based observations of about 150 comets have revealed that most have an abundance of organic compounds. There is little doubt that they helped to supply our planet with the molecular building blocks of life. "A fundamental question to answer is what are all the complex molecules that are on the comet?" says Mike A'Hearn at the University of Maryland in College Park.
Identifying these molecules from Earth is difficult because it relies on the comet throwing them into space to form its tail. The molecules seldom survive intact and so astronomers see only fragments, usually just pairs and triplets of carbon atoms. The unbroken molecules on a comet's surface can sometimes be seen using infrared equipment, but rarely do comets become bright enough at these wavelengths to produce adequate signals.
A better way is to visit a comet. In 2005, A'Hearn headed a NASA mission called Deep Impact that fired a copper cannonball into comet Tempel 1 and observed the cloud of dust and gas the collision threw up. The trouble was that the impact also broke up many of the organic molecules in which they were interested.
From a distance, Rosetta has already caught a passing whiff of rotten eggs, cat urine and bitter almonds (see "Comet stinks of rotten eggs and cat wee, finds Rosetta").
Having tried a slap, it's time for a tickle. Philae will put its mechanical hands into the undamaged carbon compounds and analyse them with its many instruments. "Philae should sort this all out," says A'Hearn.
But first it has to get there. Usually, space flight is a comparative piece of cake. With no air pressure or friction to disturb spacecraft, they follow precise orbits that can be predicted using Newton's law of gravity. Around a comet, things are different. First, comets boast hardly any gravity. Rosetta had to get within 30 kilometres to experience 67P's gravitational pull. Before then thrusters had to be fired now and again to manoeuvre the spacecraft around its target.
But that's not the worst of it. Heat from the sun boils away the ice on the comet to create an atmosphere, known as the coma, that streams away to become the characteristic tails. This is not a gradual or a uniform process. The activity comes from specific sites on the comet, and is highly variable in the amount of gas that is driven away.
Peril at every turn
Rosetta's giant solar panels, which measure 70 square metres, act like sails and mean the spacecraft is constantly buffeted, unpredictably changing its course and its orientation. The ground crew have had to become used to the navigation-camera images showing empty space when they should be showing the comet. "With Rosetta, you're never where you think you are," says ESA's Nicolas Altobelli, who works on the mission.
Although mission controllers are now adept at correcting these meanderings, there is no way to predict them in advance. And as the comet warms up as it gets closer to the sun, the activity increases and the problem gets worse.
The upshot is that the team cannot know exactly where Rosetta will be when the lander is released. Neither can they know exactly how Philae will drop to the surface. Taking all the uncertainty into account, the lander could touchdown anywhere within half a kilometre of its designated target spot – and that's a big problem.
At the beginning of the mission, the design team had assumed that the comet was a potato-shaped object with large, smooth areas on its surface. They pegged their chances of a successful landing at 70 to 75 per cent. Now, all bets are off. Read more on this odd-ball comet
The reason is the comet's dramatic and unexpected shape. When new images from Rosetta arrived at Bibring's laboratory on 14 July, they showed that 67P looks more like a rubber duck than a potato. Even now, the smaller lobe is still referred to as the head and the larger lobe as the body.
Worse, they showed that 67P was rotating every 12 hours around an axis that passed at an angle through the duck's neck rather than from head to toe. "It was juggling around in all different directions," says Bibring, "When we saw that, we feared this is just not going to happen. There will be nowhere that we can land safely. We were excited, but desperate."
But you only live once, so the flight-dynamics team began to look for ways to make it happen. To everyone's surprise, landings were possible in a number of locations, albeit at the highest touchdown speed that the lander was designed to survive. Spirits lifted.
Then more detailed pictures arrived. "Our fears returned when we saw a large variety of surface features we hadn't envisioned. Instead of being flat, the surface looks terribly odd," says Bibring.
Of five candidate sites, the most promising was labelled B. It was the only one that looked more or less flat across the whole landing area. But there was more bad news just around the corner. Higher-resolution images showed that the landing field was strewn with boulders 2 to 10 metres in size. Tens of thousands of smaller boulders might be there too. Each rock could upturn or wreck Philae if the lander happened to come down on top of one.
So mission controllers finally plumped for landing site J on their shortlist. J is located on the top of the duck's head. It's not the flattest area but there are fewer slopes steeper than 30 degrees, the maximum Philae is designed to cope with. "It is not necessarily the best site for science, but it offers the best chance of success," says Bibring.
If Philae makes it, its science investigations will start as soon as possible
Philae's first science
Bibring is keeping an open mind but points out that a comet's activity is driven by its shape. Sunlight entering a crack in the surface, for example, drives off volatile ice underneath and widens the crack. This enhances the activity and sets up a feedback loop. Where you once had a crack, now you have a crevasse. This chimes with what might have happened at 67P. Most of the activity observed so far is coming from the neck, meaning that it is inexorably becoming narrower and weaker. "If we are lucky, it will fall to pieces the day after we land," he says, only half-jokingly.
Rosetta's instruments have already started sizing up 67P. They show that the comet is 4 kilometres across at its widest point and isn't very dense at all – in fact, its density is much lower than water ice. This means that 67P must be more than 60 per cent empty space. Perhaps that means there are large caverns inside – cathedral-sized spaces that could burst open as the comet becomes more active. "We just don't know yet," says Martin Pätzold at the University of Cologne in Germany. It could be that the dust and gas is instead in a fluffy, loosely bound aggregate. "Whatever it is, it will help tell us how comets are formed. We really don't know that yet either," he says.
If Philae lands successfully, its instruments will give us answers. While the first science sequence is taking place, the confirmation signal of landing will arrive at Earth. This will contain information on Philae's position, orientation and condition. As the lander team analyse this, Philae will begin drilling into the comet to begin its chemistry experiments.
These will continue for as long as Philae's initial battery power lasts. Once that runs out – anytime between 40 and 50 hours after landing – it will switch to rechargeable batteries powered from solar panels. All being well, Philae will then enter the long-term science phase in which the experiments on the surface will continue with increasing refinement.
So long as the rechargeable batteries hold out, and there is no untoward comet activity that damages the lander, the mission's natural end will come in March 2015. By then, the comet will be closer to the sun, and the temperature will begin to affect the lander's electronics.
If Philae survives that far, it will be a major triumph. Its measurements will keep cometary scientists busy for years. For Bibring, it is the organic chemistry and its role in the origin of life on Earth – and potentially elsewhere too – that holds the greatest promise. "The question 'are we alone in the universe?' is directly connected to what we are investigating with this mission," he says.
After all, exoplanet hunters have catalogued more than 1800 planets orbiting more than 1100 stars. They may not look much like our solar system, but does that mean they are all barren? Not necessarily. Excitingly, researchers have spotted comets in 11 other solar systems. So understanding the complex organic chemistry that takes place in comets and young solar systems may be the clue we need to unlock how life gains its foothold and turns a young planet into a potential habitat.
So perhaps it is no wonder that when Taylor stood in front of hundreds of planetary scientists to give a status report in September, he elicited a round of spontaneous applause with his first sentence: "This is the sexiest mission that's ever been flown in space."
But make no mistake; sexy comes with risks. The chances of failure are high. While the main orbiter mission will continue regardless of whether or not Philae makes it, the world will be watching on 12 November.
"If we fail because of something that we could not predict, then ok," says Bibring. "Worse would be if we have underestimated something we should not have underestimated." That's why he and every other Rosetta team member is working overtime to think through every eventuality and prepare as best as possible. "I look this old because it's such hard work," quips 41-year-old Taylor.
Rosetta itself was first discussed 25 years ago, and Bibring was there. "You put a lot of yourself into a mission over that length of time," he says. "As someone once said: failure is not an option. So we won't fail. This is it. What else can I say?"
Stuart Clark is a consultant to New Scientist and author of Is There Life on Mars? (Quercus Books)
The Philae lander makes its descent to comet 67P/Churyumov–Gerasimenko (Image: ESA)
Update 12 November 2015 20:31: In a press briefing, landing manager Stephan Ulamec confirmed that Philae's anchoring harpoons did not fire. Some data indicates that the lander may have bounced and rotated before touching down again. "Maybe today we didn't just land once, we landed twice," Ulamec says. A press briefing is scheduled for 1300 GMT tomorrow.
Original article, published 12 November 2015 18:13
Cheers, hugs and an explosion of joy marked the announcement that the European Space Agency's Philae lander had safely touched down on a comet – a world first.
"We are there and Philae is talking to us," said landing manager Stephan Ulamec, from the European Space Operations Centre in Darmstadt, Germany. "We are on the comet!"
The landing was not perfect, though: an issue with a gas thruster and harpoons intended to help Philae grapple with the surface means that the craft may not be firmly anchored to the comet.
Paolo Ferri, head of mission operations, says that Philae might be moving around on the comet's surface, perhaps even sliding – but it is unlikely to bounce off. "Frankly, given it has been on the surface for a few hours now, I would be very surprised," he says.
Watch our live blog for further updates.
Philae and its companion spacecraft Rosetta have spent the last 10 years travelling to comet 67P/Churyumov-Gerasimenko, some 500 million kilometres from Earth, and that distance means it takes 28 minutes and 20 seconds for signals from the spacecraft to reach us.
At 0835 GMT on 12 November, the Philae lander separated from Rosetta and began a 7-hour descent to the surface of the comet. It took so long because Philae moved at a slow walking speed of 1 metre per second. The craft had no way of manoeuvring once it was released, so gravity alone determined whether it reached the surface.
"It's all down to Isaac Newton now," said ESA senior science adviser Mark McCaughrean shortly after release.
After a long, tense wait, punctuated by the first images from the lander as it fell, the signal that Philae was on the surface finally arrived at 1603 GMT.
"We see the lander angled, sitting on the rocks," said Rosetta flight director Andrea Accomazzo. "We can't be happier than we are now."
Scratch the surface
But not everything went as planned. The comet's gravity is 10,000 times weaker than Earth's – not enough to hold a lander down – so Philae was supposed to grapple on to the comet with harpoons. It also has a gas thruster designed to push it into the surface as it lands, but the night before landing, ESA discovered it had a problem, leaving the harpoons as the only way to tether to the surface.
About half an hour after landing, it became clear that Philae had only penetrated 4 centimetres into the surface of the comet, much less than ESA was expecting. That probably means that the anchors did not fire correctly.
Possibly worse, the telemetry link with Philae, which uploads the all-important science data, was unstable shortly after landing. Ferri says the unstable telemetry is not concerning, but it does need addressing.
At some point tonight, ESA will need to move Rosetta, which will break the link with Philae in any case. This was always planned, but with the link currently unstable, it could cause problems.
Still, "this is a big step for human civilisation", said ESA director Jean-Jacques Dordain. The science pay off from even a few images could be huge.
Comets are the building blocks left over from the formation of our solar system. That means they contain pristine samples of the material that went to make up Earth. Landing on a comet and drilling into its surface will let us touch and taste that material, giving us a glimpse at our origins.
Instruments on Philae will examine the comet's water and other molecules important for life, to see how they compare to those found on Earth. If they match, Philae will essentially be scooping up handfuls of frozen primordial soup.
Barely 24 hours have passed since the European Space Agency's Philae spacecraft made history as the first probe to touch down on a comet. Now ESA researchers are racing to gather the maximum amount of scientific data from comet 67P/Churyumov-Gerasimenko before Philae shuts down and they lose contact for good.
This morning we learned that Philae bounced twice before settling down in an unknown location on the comet, perhaps a kilometre away from its original landing spot. Two of its legs are on the ground, but the third is up in the air, putting Philae at an angle. It is also sitting in the shadow of a rocky wall, limiting the sunlight that can reach its solar panels to just 90 minutes every 12 hours.
Philae's batteries will run out in less than two days unless recharged, and it is unlikely the solar power it is receiving will keep it alive. "We are calculating now what this means for the near future," said lander manager Koen Geurts during a press conference this afternoon. "This is not a situation we were hoping for."
Eight of the ten instruments aboard Philae have already sent back scientific data, and ESA already considers the mission a huge success. Senior mission staff were moved to tears of joy during today's press conference.
(Image: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)
But efforts to squeeze as much data as possible from the mission are still under way here at the European Space Operations Centre in Darmstadt, Germany. Holger Sierks, who is charge of the OSIRIS camera on Rosetta, has two teams desperately scanning images by eye for Philae's final landing spot. The lander occupies just a 3 by 3 grid of pixels in the OSIRIS images, so this really is searching for a needle in a comet.
"We're working our eyes off," Sierks told New Scientist. It's an entirely manual process, because the complex and bizarre landscape of comet 67P defies any kind of automated search. "We don't have an algorithm for this," he says.
Finding the lander in a picture will help the Philae team determine its surroundings, figure out what kind of illumination it is getting and thus how much power they can expect to receive from the solar panels.
ESA is also considering attempting to move Philae to a more favourable spot, but with no propulsion system on board this is a risky and untested plan. Philae has four instruments and systems that involve motion, and each has the potential to move the probe, so its solar panels get more light. "If we can move a few degrees it might be sufficient," Philae scientist Jean-Pierre Bibring toldNew Scientist.
They are planning to deploy the instruments in order of increasing risk, starting with a probe called MUPUS this evening. MUPUS has a small hammer, and the up and down motion could give Philae the jolt it needs. The craft's harpoon, drill and cold gas thruster could also be repurposed into a makeshift crutch to drag, push or boost Philae into the light.
Senior ESA staff have already worked through the night to determine Philae's status, and they continue to meet every 2 hours to decide the best course of action.
Whatever happens, the instruments on board the spacecraft will give us the first ever up-close look at a comet, perhaps revealing mysteries about the origin of Earth and the water and other molecules that gave it life.
But hopes that Philae will survive until March next year, when it would finally succumb to increasing heat from the sun, are fading fast, meaning ESA may not get a chance to touch and taste the comet as it heats up. "The long-term science is most at risk," says Bibring.
Even if Philae survives to report back, its drill might fail. Data received before the cut-off suggests the drill had reached 25 centimetres below the spacecraft, but with Philae standing in a precarious position, with one leg in the air, the drill may not make it to the surface to take a sample.
Since there will probably only be one chance to dig into the surface, the team had to decide which instrument on board Philae would get the sample. The pristine cometary material will be heated in an oven and passed to Philae's Cometary Sampling and Composition Experiment (COSAC), which can analyse organic molecules and identify whether they are left or right-handed.Life on Earth contains only left-handed molecules, so the results could tell us more about our origins. Another instrument called Ptolemy, which was designed to sniff the gases trapped in the comet, will miss out on a sample, because it uses more energy and Rosetta can conduct similar experiments from orbit.
If ESA does make contact with Philae again and it has some juice left, the agency might make a last-ditch attempt to move the craft to a better location, perhaps by rotating its body, re-triggering its landing gear or spinning up an internal fly wheel. They still don't know exactly where the probe is on the comet's surface, but Holger Sierks, who is in charge of the OSIRIS camera on Rosetta, said they should have a picture of Philae's 1 kilometre-high bounce after landing, which will help pinpoint its final resting spot.
There is also a small chance Philae could wake up as comet 67P nears the sun, but the spacecraft needs energy to heat up its batteries before they can start charging, so that may not be possible. Even if we never hear from Philae again, the team are very happy with the mission and say they have achieved 80 per cent of their initial science goals. "Let's stop looking at things we could have done if everything had worked properly," said Rosetta flight director Andrea Accomazzo. "This is unique and will be unique forever."
The European Space Agency's comet-hopper Philae was caught in action as it travelled above the surface of comet 67P/Churyumov–Gerasimenko last week. ESA has just released this composite image showing Philae's journey as seen by the orbiting Rosetta spacecraft.
Philae first touched down at 1535 GMT on 12 November before bouncing away from 67P, perhaps as high as 1 kilometre. The first three inset images, from left to right, show Philae as it descended towards the surface. The fourth image, taken shortly after the bounce, show the impression in the surface left by Philae – one that wasn't there in a picture taken at 1518 GMT.
The picture on the far right shows Philae ominously flying over a shadowed region. The spacecraft came to rest again at 1725 GMT, bounced a second time, and reached its final resting point at 1732 GMT. ESA has still not established the location of this last landing, but it is working hard to compare images taken by Philae on the ground with images and triangulation data from Rosetta.
The lander is now in hibernation mode. Whether or not it wakes up again will depend on getting enough sunlight on its solar panels to recharge its batteries.
(Image: ESA Rosetta Navcam)
Another image, released yesterday, shows a low-resolution view of Philae's first bounce. You can see the dust cloud thrown up from the surface, along with the lander and its shadow – taking up just a few pixels.