A November image of Comet 67P/Churyumov-Gerasimenko shows faint jets of gas and dust. Credit European Space Agency[/caption]Photographs and data from the European Space Agency’s Rosetta spacecraft have provided an unprecedented close-up examination of a comet, but there is one thing that has not shown up yet: the small lander that bounded to the surface in November.
Scientists working on the mission described their initial observations of Comet 67P/Churyumov-Gerasimenko in seven articles published Thursday in the journal Science. “This sets the baseline for the rest of the mission,” said Matt Taylor, the project scientist.
Rosetta arrived at the comet in August after a trip of 10 years and four billion miles. For the first time, scientists are having an extended look at a comet as the spacecraft accompanies it for at least a year as it swings around the sun. As the comet heats up, it will spew greater amounts of gas and dust.
In November, a washing-machine-size lander named Philae made it to the surface, but systems designed to anchor it failed, and the lander bounced, ending far from the intended site in a position that greatly reduced the amount of sunlight hitting its solar panels. Instruments on the lander operated for two days until the batteries drained.
In mid-December, the orbiter’s high-resolution camera took pictures of the spot where the scientists think the lander ended up, but the scientists were not able to find it — a few pixels in a four-million-pixel image.
Holger Sierks, the principal investigator for Rosetta’s main camera, said that Philae, which photographed its surroundings and performed various measurements after landing, was still expected to awake in the spring when increasing sunlight recharged the batteries. Even if Philae does not wake up, Rosetta should be able to spot it after the comet has made its closest approach to the sun, in August.
The high-resolution camera has taken photographs with a resolution as fine as two and a half feet per pixel. The comet, just two and a half miles wide with a two-lobe shape that resembles a rubber duck toy, has a remarkably wide variety of terrain. That includes smooth dust-covered regions, fields of boulders, steep cliffs and large depressions that may have been blown out by underground melting of carbon dioxide. The variety is surprising because many think the comet is, by and large, made of the same material throughout. Scientists are not sure if the shape comes from two smaller comets that bumped and stuck together or one large comet that eroded in an unusual manner.
On the surface of Comet 67P, there are even what look like ripples of sand dunes like those seen on Earth and Mars. That appears befuddling, as a comet has no atmosphere — and so no wind — and only a wisp of gravity.
“You have to ask yourself, is that possible?” said Nicolas Thomas, a professor of experimental physics at the University of Bern in Switzerland and lead author of one of the papers. Dr. Thomas said that back-of-the-envelope calculations indicated that it might be plausible, with the jets of gas acting as wind and the particles held together through intermolecular attraction known as the van der Waals force instead of gravity. “You can convince yourself you can make them move,” Dr. Thomas said. “It’s plausible, at least at the moment.”
The scientists split the surface into 19 regions based on terrain, naming them after Egyptian gods. Rosetta is named after an inscribed rock, found in Egypt, that proved crucial in deciphering ancient hieroglyphics.
In another region, along the comet’s “neck,” is a cliff about 3,000 feet high with fractures hundreds of feet long. The scientists cannot agree on what they are seeing, whether the lines reflect layering in the material making up the comet or cracks caused by the heating and cooling of the material as it passes in and out of sunshine.
In the smooth regions, there are circular structures. “Which look very, very bizarre,” Dr. Thomas said. “To be frank, we don’t know how those things were created. We have no clue.”
There is also a long crack, about a yard wide and several hundred yards long, that runs around the neck. Dr. Thomas said it was unclear whether the comet was about to snap in two.
The jets of gas currently emanate from the neck area, a region named Hapi. That, too, seems counterintuitive because the neck is often in shade and cooler. But Dr. Sierks said the area was still warm enough and gravity was weaker there, allowing particles to escape more easily.
The scientists previously described some of the most significant findings reported in the Science papers — that the water on the comet does not resemble that found on Earth, probably ruling out comets as the source of the Earth’s oceans, and that a diverse stew of molecules streaming off the surface includes those found in the odors of rotten eggs and urine.
Notă: A version of this article appears in print on January 23, 2015, on page A6 of the New York edition with the headline: Close-Up of Comet Fails to Pinpoint Stray Lander. Order Reprints| Today’s Paper|Subscribe
Ciuriumov-Gherasimenko, oficial denumită 67P/Ciuriumov-Gherasimenko, este o cometă cu o perioadă orbitală curentă de 6,45 ani și o perioadă de rotație de aprox. 12,7 ore[2]. Cometa va ajunge la periheliu (cea mai scurtă distanță de Soare) la 13 august 2015. Cometa este numită după descoperitorii ei, Klim Ciuriumov și Svetlana Gherasimenko, primii care au observat-o pe plăci fotografice în 1969.
Această cometă a fost descoperită de astronomul Klim Ivanovici Ciuriumov în timp ce examina o placă fotografică a cometei 32P/Comas Solà / 32P/Comas Solá, luată la 11 septembrie 1969 de astronoma Svetlana Ivanovna Gherasimenko la Institutul de Astrofizică de la Alma-Ata, acum Almatî, fostă capitală a Kazahstanului.
El a găsit imaginea unui obiect pe marginea plăcii fotografice și a presupus că era vorba de cometa 32P/Comas Solà.
La Kiev, plăcile au fost minuțios inspectate și, la 22 octombrie, s-a descoperit că obiectul nu putea fi cometa Comas Solà, întrucât poziția sa diferea cu mai mult de 1,8° de poziția așteptată.
O examinare mai atentă a scos în evidență o slabă imagine a cometei Comas Solà în poziția corectă, ceea ce a dovedit că obiectul identificat de Ciuriumov era o cometă care nu fusese încă descoperită.
Orbita cometei 67P/Ciuriumov-Gherasimenko are o istorie destul de interesantă.
Când cometa se apropie de unul din giganții gazoși, Jupiter sau Saturn, orbita sa este deseori modificată.
S-a putut calcula, pentru această cometă, că, înainte de 1840, ar fi fost aproape imposibil să fie observată, distanța sa la periheliu fiind de circa 4 ua. Din cauza gravitației exercitate de Jupiter, orbita cometei s-a modificat, iar distanța la periheliu s-a redus la 3 ua.
Mai târziu, în 1959, o altă apropiere de Jupiter a modificat, din nou, orbita cometei, distanța la periheliu ajungând la valoarea actuală, 1,28 ua.
Misiunea Rosetta
Ciuriumov-Gerasimenko este destinația misiunii Rosetta a Agenției Spațiale Europene, lansată la 2 martie 2004. Rosetta a intrat pe orbită în jurul cometei pe 6 august 2014[3], după care o va studia și va identifica un loc de coborâre și de așezare pe solul nucleului cometei potrivit pentru sonda (engleză lander) Philae, programate pentru data de 10 noiembrie 2014.
Potrivit Agenției Spațiale Europene, s-a hotărât ca așezarea sondei Philae pe solul cometei să aibă loc miercuri, 12 noiembrie 2014, în jurul orelor 17:35 (ora României), într-o regiune cu diametrul de circa 1 kilometru.[4]
La 12 noiembrie 2014, minilaboratorul „Philae” s-a desprins de pe „Rosetta” și s-a așezat pe cometa 67P/Ciuriumov-Gherasimenko, exact în locul stabilit.[5] La asolizare au apărut probleme. Unele din experimentele planificate nu vor mai putea avea loc.[6]
Caracteristici fizice
Clișeele luate de Telescopul Spațial Hubble în martie 2003[7] au permis să se estimeze diametrul obiectului la circa 4 kilometri. În iulie 2014, noi imagini luate de Rosetta au scos în evidență faptul că nucleul lui „Ciuri” este un binar de contact, cu o talie globală de 4 km pe 3,5 km. [8]
Cometa se rotește în jurul ei însăși în 12,4 ore.[9]
Temperatura solului nucleului cometei este de -90°C.
Multiversuri! 