Touch­down: Rosetta probe lands on comet 67P

Malta Independent - - SCIENCE -

The Euro­pean Space Agency’s most am­bi­tious mis­sion yet has come to an end as the Rosetta space­craft col­lided with the comet’s sur­face yes­ter­day.

Some space mis­sions go out with a bang, oth­ers with a vic­to­ri­ous re­turn to Earth, but Rosetta’s fi­nal mo­ment was marked sim­ply by ra­dio si­lence.

Af­ter twelve-and-a-half years in space, the Euro­pean Space Agency space­craft fi­nally met the sur­face of the duck-shaped mass of dust, ice and rock, switched off its trans­mit­ters and hung up the phone to its con­trollers on Earth.

Pa­trick Martin, Rosetta’s mis­sion man­ager, said: “This is the cul­mi­na­tion of tremen­dous sci­en­tific and tech­ni­cal suc­cess for this mis­sion. It was his­toric, it was pi­o­neer­ing and it is rev­o­lu­tion­is­ing how we see comets. Farewell Rosetta, you’ve done the job, that was space science at its best.”

Sci­en­tists faced a nail-bit­ing 40 minute wait for con­fir­ma­tion that it had touched down and to see the last im­ages cap­tured by Rosetta, taken around 15 me­tres from the comet’s sur­face.

The space­craft touched down on the “head” of the comet at a speed of about 90 cen­time­tres per sec­ond - around a walk­ing pace. Mis­sion sci­en­tists de­scribed this as a “con­trolled de­scent” rather than a crash.

Al­though the sur­face is soft some­thing akin to the tex­ture of a soft snow-drift - the lan­der is likely to get dam­aged in the col­li­sion and could even bounce off the sur­face, as the Phi­lae lan­der did. Even if its so­lar pan­els and other hard­ware re­main in­tact, the craft has been pre-pro­grammed to shut down its sys­tems on con­tact, mark­ing the end of a mis­sion that has gripped the world.

Its pre­cise fate will never be known, be­cause Rosetta is now switched off for good and there are no tele­scopes on Earth pow­er­ful enough to see it.

“We won’t know, be­cause we turn off when we touch the sur­face,” said Pro­fes­sor Mark McCaugh­rean, a se­nior science ad­vi­sor at ESA. “This is space, any­thing can hap­pen out there ... It’s a bit like does a tree make a sound in the for­est if no one is there to hear it?”

Ahead of the land­ing, the flight team es­ti­mated that the craft would im­pact just 40 me­tres away from their orig­i­nal tar­get on the Ma’at re­gion of the head, which marked by large pits and “goose bump” struc­tures.

The last im­ages sent back may look like dust-cov­ered rocks, but mea­sure­ments sent back from Rosetta show that the comet is ex­tremely por­ous - about 70% of its in­te­rior is empty space.

“When you see these beau­ti­ful im­ages of the comet you should not think of it as rock,” said Björn Davids­son, a Rosetta sci­en­tist based at Nasa’s jet propul­sion lab­o­ra­tory. “It’s some­thing like spun sugar or cot­ton candy – some­thing very, very fluffy.”

Rosetta ar­rived at 67P/Churyu­mov-Gerasi­menko in Au­gust 2014, af­ter spending a decade chas­ing down the comet.

In the two years since, it has sent back spec­tac­u­lar pho­to­graphs of the comet’s dra­matic land­scapes as well as reams of sci­en­tific data mea­sur­ing its com­po­si­tion, den­sity and mag­netic field.

In terms of sheer drama, the mis­sion’s cli­max came when a small ro­botic probe, Phi­lae, was dis­patched onto the comet’s sur­face in Novem­ber 2014 to gather sur­face sam­ples.

Comet 67P is now head­ing out to­wards the or­bit of Jupiter, and as it speeds away from the sun, Rosetta’s so­lar power sup­ply was set to run out.

Matt Tay­lor, ESA Rosetta project sci­en­tist, said that rather than hob­bling on in a sub-op­ti­mal state, the team de­cided to com­mit to some fi­nal close-up ob­ser­va­tions. “I’ve seen cer­tain rock bands with cer­tain singers that can’t sing any­more. They should have stopped when they were fully func­tion­ing,” he said, ahead of the mis­sion’s end. “And that is what we are do­ing here with Rosetta. It is max­imis­ing what we can do with the space­craft at this time. This plunge is the only way to get this science.”

These are thought to be the orig­i­nal icy boul­ders that formed in the so­lar sys­tem more than four bil­lion years ago and then came to­gether to form this comet. In short, the goose bumps are some of the most an­cient un­al­tered ob­jects from the be­gin­ning of the so­lar sys­tem. They con­tain all the in­gre­di­ents that were avail­able to form life on Earth.

McCaugh­rean told BBC Ra­dio 4 it was a sad day as he re­flected on what the Rosetta mis­sion had achieved

“It’s giv­ing us a real in­sight into the build­ing blocks of the so­lar sys­tem and the ma­te­rial which could have formed life on the earth, not life it­self but the raw build­ing blocks,” he said.

“But more im­por­tantly for me, it’s en­gaged the pub­lic in a way which is just un­par­al­leled for a ro­bot­ics space mis­sion. The en­thu­si­asm I see on the faces of kids around the world when I give talks and the pub­lic fol­low­ing on­line it’s go­ing to be very sad day but a very proud day for every­one that’s been in­volved.”

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