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Lander in awkward spot on comet, but sends pictures

Nov. 13, 2014
World Science staff

A probe sent to land on a com­et yes­ter­day is sitting askew in a dark spot on that ob­ject—not quite where it was aimed, and it’s not ex­actly clear where, mis­sion sci­en­tists said Thurs­day.

And that is cre­at­ing some prob­lems.

None­the­less, the sci­en­tists said the Eu­ro­pe­an Space Agen­cy’s Phi­lae lan­der is work­ing, gath­er­ing da­ta. Pho­tos—the first ev­er tak­en up­on a com­et—showed what looked like dark, rocky sur­round­ings. Sci­en­tists added that they’re stu­dy­ing what to do next, and ex­actly where it is; they have a rough idea.

The blue dia­mond on this graph­ic shows the area where sci­ent­ists be­lieve Phi­lae is sit­ting, almost on its side. The red spot shows where the land­er was aimed, and origin­ally struck be­fore bounc­ing. At right, Ste­phan Ula­mec, Phi­lae proj­ect man­ag­er, pre­sent­ed the re­sults at a news con­fer­ence Thursday in Darm­stadt, Ger­ma­ny. Ula­mec said the lan­der might be on the crater rim within the blue area. (Courtesy ESA)


About the pho­tos, “I can­not tell you much more than you can in­ter­pret your­self” for now, Stephan Ulamec, Phi­lae proj­ect man­ag­er at DLR, Ger­many’s na­t­ional aer­o­naut­ics and space re­search cen­ter, told jour­nal­ists at a con­fer­ence Thurs­day.

The prob­lems arose af­ter the lan­der bounced twice away from its planned im­pact spot due to a fail­ure of har­poons that were sup­posed to tie it down. 

“We still have the pos­si­bil­ity to ma­neu­ver” the lan­der, and a pri­or­ity is get­ting in­to a better-lit ar­ea, said Jean-Pierre Bib­ring, lead sci­ent­ist for the probe, speak­ing at the con­fer­ence in Darm­stadt, Ger­ma­ny.

The probe is al­most on its side, with one of its three feet stick­ing out in­to open space, he ex­plained. A cliff seems to be near­by, per­haps a few me­ters or yards away. The lan­der’s “some­what bi­zarre ori­enta­t­ion” might be ex­plained by the pos­si­bil­ity that it’s on the rim of a large crat­er, Ula­mec said. 

The in­side of that crat­er—on the head of the roughly 5-km (3-mile) long com­et, 67P/Chur­yu­mov-Ge­ras­i­men­ko—happened to be among the al­ter­na­tive land­ing spots orig­i­nally un­der con­sid­era­t­ion. Mis­sion sci­en­tists even­tu­ally opted to in­stead tar­get an­oth­er site clos­er to the com­et’s tip.

An image of the lan­der's sur­round­ings shot by the land­er imag­ing sys­tem Çi­va/Ro­lis. (Cour­tesy ESA)


Phi­lae hit that spot cor­rectly but then “made quite the leap,” end­ing up per­haps about a thou­sand me­ters or yards away, ac­cord­ing to Ula­mec.

Phi­lae Opera­t­ions Man­ag­er Koen Geurts, speak­ing from the Lan­der Con­trol Cen­ter in Co­logne, Ger­ma­ny, told the con­fer­ence that about two hours passed from the first bounce to the fi­nal land­ing, based on sig­nals that showed when the lan­der started and stopped mov­ing.

Ulamec said sci­en­tists have a rough idea of its cur­rent loca­t­ion thanks to an in­stru­ment on­board known as Con­sert (Com­et Nu­cle­us Sound­ing Ex­pe­ri­ment), which probes the com­et’s in­ter­nal struc­ture with ra­di­o waves.

The lan­der is al­so not screwed in­to the com­et sur­face, as was in­tend­ed, al­though this may be fix­a­ble, sci­en­tists said. Just “the weight of the lan­der” is keep­ing it down on the com­et, Ula­mec not­ed. That’s not much force: since a comet is much smaller than a plan­et, a per­son stand­ing where Phi­lae is would weigh around as much as a tic-tac. Philae’s Earth-weight is 46 pounds (21 kg).

The lan­der is col­lect­ing per­haps a fourth as much sun­light as it would have in the planned land­ing spot, ac­cord­ing to es­ti­mates pro­vided by Geurts. The short­age of sun­light pre­s­ents dif­fi­cul­ties for the lan­der’s so­lar pan­els though its main bat­tery can go ahead.

Be­cause of the lan­der’s del­i­cate po­si­tion the mis­sion needs to be care­ful about which in­stru­ments it will ac­ti­vate next, to avoid desta­bi­liz­ing the lan­der more, Ula­mec said. 

But he said mis­sion sci­en­tists are some­what in­clined to­ward ac­ti­vat­ing an in­stru­ment called Mu­pus (Mul­ti­-Purpose Sen­sor for Sur­face and Subsur­face Sci­ence) which uses sen­sors to meas­ure the hard­ness, dens­ity and oth­er prop­er­ties of the sur­face. Anoth­er pos­si­bility is to de­ploy APXS (Al­pha Pro­ton X-ray Spec­trom­e­ter) which de­tects par­t­i­cles and X-rays near the ground to un­der­stand the sur­face make­up.


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A probe sent to land on a comet yesterday sits askew in a dark spot on the comet—not quite where it was aimed, and it’s not exactly clear where, mission scientists said Thursday. And that is creating some problems. Nonetheless, the scientists said the European Space Agency’s Philae lander is working, gathering data. Photos—the first ever taken upon a comet—showed what looked like dark, rocky surroundings. Scientists added that they’re studying what to do next, and exactly where it is; they have a rough idea. As far as the photos, “I cannot tell you much more than you can interpret yourself” for now, Stephan Ulamec, Philae project manager at DLR, Germany’s national aeronautics and space research center, told journalists at a conference Thursday. The problems arose after the lander bounced twice away from its planned impact spot due to a failure of harpoons that were supposed to tie it down. “We still have the possibility to maneuver” the lander, and a priority is getting into a better-lit area, said Jean-Pierre Bibring, lead scientist for the probe, speaking at the conference in Darmstadt, Germany. The probe is almost on its side, with one of its three feet sticking out into open space, he explained. A cliff seems to be nearby, perhaps a few meters or yards away. The lander’s “somewhat bizarre orientation” might be explained by the possibility that it’s on the rim of a large crater, said Stephan Ulamec, Philae project manager at DLR, Germany’s national aeronautics and space research center, at the conference. The inside of that crater—on the head of the roughly 5-km (3-mile) long comet, 67P/Churyumov-Gerasimenko—happened to be among the alternative landing spots originally under consideration. Mission scientists eventually opted to instead target another spot closer to the comet’s tip. Philae hit that spot correctly but then “made quite the leap,” ending up perhaps about a thousand meters or yards away, according to Ulamec. Philae Operations Manager Koen Geurts, speaking from the Lander Control Center in Cologne, Germany, told the conference that about two hours passed from the first bounce to the final landing, based on signals that showed when the lander started and stopped moving. Ulamec said scientists have a rough idea of its current location thanks to an instrument onboard known as CONSERT (Comet Nucleus Sounding Experiment ), which probes the internal structure of the comet using radio waves. The lander is also not screwed into the comet surface, as was intended, although this may be fixable, scientists said. Just “the weight of the lander” is keeping it down on the comet, Ulamec noted. That’s not much force: since a comet is much smaller than a planet, its weak gravity leaves the lander—whose Earth-weight is 21 kg (46 pounds)—weighing less than a tic-tac. The lander is collecting perhaps a fourth as much sunlight as it would have in the planned landing spot, according to estimates by Geurts. The shortage of sunlight presents difficulties for the lander’s solar panels though its batteries can go ahead. Because of the lander’s delicate position the mission needs to be careful about which instruments it will activate next, to avoid destabilizing the lander more, Ulamec said. But he said mission scientists are somewhat inclined toward activating an instrument called Mupus (Multi-Purpose Sensor for Surface and Subsurface Science) which uses sensors to measure the hardness, density and other properties of the surface. Another possibilitty is to deploy APXS (Alpha Proton X-ray Spectrometer) which is to detect particles and X-rays near the ground to understand its makeup.