Rosetta prepares for risky comet landing

Rosetta prepares for risky comet landing
By Jeremy Wilks
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This week sees the most risky moment in ESA’s Rosetta mission, as it tries to place the first ever probe on the surface of a comet. The eyes of the space world will be on the little lander, called Philae, as it pushes off from the mothership and drifts down towards comet 67/P Churyumov-Gerasimenko, it’s destiny unknown. Confirmation of its landing will come around 5-6pm Central European Time on Wednesday evening.

The stakes are high for the European Space Agency, as around 300 members of the media converge on the European Space Operations Centre in Darmstadt, Germany to witness the event. It is an unprecedented moment in space exploration, a daring attempt to land a man-made object on an alien world.

Many things could go wrong. That’s because the comet remains a deeply mysterious place. The scientists don’t even know what the surface of 67/P will be like. “We know that it’s porous, not icy,” Rosetta Project Scientist Matt Taylor told euronews. “But we don’t know what it will feel like. It could be firm but not dense, like cork or Styrofoam, or it could be very dusty. There may be a 30cm thick layer of dust with hard material below, or it could be much deeper than that.”

The area where Philae will land, known as Agilkia, is on the smaller lobe, or ‘head’ of the rubber duck shaped comet. It was chosen by the science team this summer as the best location to offer Philae an interesting spot to study and a half-decent chance of landing. The team expect what Taylor describes as ‘a bit of sinkage’ when it lands – that’s to say at least some dust to cushion the landing, which will happen at walking pace. Then they hope that Philae will be able to fix itself to the comet with a harpoon and screws, than activate its 11 instruments, drill down into some of the harder primordial material below, take panoramic photos of the surface and analyse the materials that it finds there.

Pictures of the comet, courtesy of ESA

(function(d, s, id) {var js,ijs=d.getElementsByTagName(s)[0];if(d.getElementById(id))return;js=d.createElement(s);;js.src="//";ijs.parentNode.insertBefore(js, ijs);}(document, 'script', 'scrbbl-js'));But before that can happen a lot else has to go right. Rosetta only arrived at the comet this August, and the lander has to be deployed before the comet becomes too active as it nears the Sun early next year, so the spacecraft operations team have been in a race against time to map and measure the comet in order to calculate the right orbit, approach and trajectory for the spacecraft and its lander.

Once Philae separates from Rosetta, around 09.30 CET on Wednesday, the team will be eagerly looking to see if the communications link between Rosetta and Philae has been established. The lander can’t send signals directly to Earth, so that line between lander and mothership is vital for the scientists. Philae will begin sending back images and data to Rosetta early into its seven hour drift down to the comet.

Philae can’t be steered or guided in any way once it has left Rosetta, so the success of the landing will be down to clever flight dynamics, top quality flight controllers and a big dose of luck. There is a reasonably high chance that Philae could sink deep into dust and be covered with powder, be knocked sideways by a hard boulder or even fall sideways into a cleft in the comet surface. If everything goes well and it lands more or less upright then it should be able to generate power from its solar panels to fuel it beyond its 60 hour battery life, and it could even keep on working an hour or so per day for the next few months.

Why all this interest in comets?

Rosetta spent 10 years spinning around the solar system in order to gather the speed and trajectory needed to catch up with 67/P and fly alongside for a year of comet observation. The reason for such an ambitious mission is that comets are seen as holding the keys to understanding our origins.

Previous missions, which have flown through comet tails, brought back comet dust to Earth, and smashed impactors into comet nuclei, have all helped fuel the argument that comets hitting our early planet may have brought much of the water that surrounds us, and they could also have brought some of the complex molecules like amino acids that are building blocks of life on Earth.

So the Rosetta mission aims to take huge leaps in our understanding of comets, the origins of life, and the formation of our solar system. Already instruments have measured water and carbon dioxide coming off the comet, both key components of this 4km wide ball of icy dust. They have also found sodium and magnesium, and a variety of compounds that would smell rather bad on planet Earth, such as hydrogen sulphide, like rotten eggs, and ammonia, like horse manure. There’s also a whiff of almond, hydrogen cyanide, and alcohol, in the form of methanol.

The science findings from Rosetta itself will begin to ramp up next year, as the comet becomes more active and begins to eject gases and dust as it gets nearer the Sun. At its closest approach in August next year, comet 67/P will be about 186 billion kilometres from the Sun, around halfway between the orbits of Earth and Mars.

A media-friendly mission

Rosetta has been a darling of the media throughout 2014. Hundreds of media outlets have covered the mission, and Euronews has featured the team each month in its original Comet Hunters series. The success of this particular space probe stems not just from the audacious nature of its decade-long flight and rendezvous with a comet, but also the efforts by ESA to go beyond its conservative image and to invent cartoon characters, Twitter personalities and public-engagement competitions that have continuously spurred interest in the science and technology of Rosetta.

This ambitious programme of outreach found its ultimate expression in a sci-fi short film, called appropriately enough Ambition, funded by ESA. Starring actor Aiden Gillen and young actress Aisling Franciosi, shot on location in Iceland and directed by the Oscar-nominated Tomek Bagiński, it features two post-human beings creating planets on a rocky landscape, and discussing the fabled Rosetta mission of the past. The stunning visual effects and striking cinematography took science outreach filmmaking to another, unexpected level of style and panache.

Find more about the Rosetta mission on euronews’ Comet Hunters page

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