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Spacecraft reaches comet for first up-close study

Aug. 6, 2014
Courtesy of ESA
and World Science staff

A Eu­ro­pe­an Space Agen­cy space­craft has be­come the first to reach a com­et for a close-up view, com­ing with­in 100 km (60 miles) on Aug. 6 and pre­par­ing for an even clos­er ap­proach, sci­en­tists re­port.

The event fol­lows a decade-long jour­ney. “After ten years, five months and four days trav­el­ling to­wards our des­tina­t­ion, loop­ing around the Sun five times and clock­ing up 6.4 bil­lion kilo­me­tres, we are de­light­ed to an­nounce fi­nally ‘we are here,’” said Jean-Jacques Dor­dain, the agen­cy’s di­rec­tor gen­er­al, on Aug. 6.

The comet on Aug. 3. (Courtesy of ESA)


“Ro­set­ta is now the first space­craft in his­to­ry to ren­dez­vous with a com­et, a ma­jor high­light in ex­plor­ing our ori­gins. Dis­cov­er­ies can start.” Mis­sion sci­en­tists plan to di­rect the craft clos­er over the next six weeks, put­ting it with­in half its cur­rent dis­tance. Lat­er plans in­clude hav­ing it de­pos­it a lan­der di­rectly on the com­et.

Com­et 67P/Chur­yu­mov-Ge­ra­si­men­ko and Ro­set­ta now lie 405 mil­lion km (250 mil­lion miles) from Earth, about half way be­tween the or­bits of Ju­pi­ter and Mars, rush­ing to­wards the in­ner So­lar Sys­tem at nearly 55,000 km (34,000 miles) per hour.

The com­et or­bits the sun once eve­ry 6.5 years. The path takes it from be­yond Ju­pi­ter at its fur­thest point, to be­tween the or­bits of Mars and Earth at its clos­est to the Sun. Ro­set­ta is planned to ac­com­pa­ny it for over a year as they swing around the Sun and back out to­wards Ju­pi­ter again.

Com­ets are con­sid­ered to be prim­i­tive build­ing blocks of the So­lar Sys­tem and may have helped to ‘seed’ Earth with wa­ter, pe­rhaps even the in­gre­di­ents for life, ac­cord­ing to sci­en­tists. But many fun­da­men­tal ques­tions about these en­ig­mat­ic ob­jects re­main, and Ro­set­ta is aimed at an­swer­ing some of these. 

Its jour­ney to the com­et was­n’t straight­for­ward. Since its launch in 2004, Ro­set­ta had to make three gra­vity-assist fly­bys of Earth and one of Mars to help it on course to its ren­dez­vous with the com­et. This com­plex course al­so al­lowed Ro­set­ta to pass by as­ter­oids Šteins and Lu­te­tia, ob­tain­ing un­prec­e­dent­ed views and in­forma­t­ion on these two ob­jects.

Aug. 6 saw the last of a se­ries of ten ma­neu­vers that be­gan in May to ad­just Ro­set­ta’s speed and tra­jec­to­ry grad­u­ally to match those of the com­et. Had any of these failed, the mis­sion would have been lost, and the space­craft would simply have flown by the com­et.

The com­et be­gan to re­veal its pe­rsonal­ity while Ro­set­ta was on its way. Im­ages tak­en be­tween late April and early June showed that its ac­ti­vity was var­i­a­ble. The com­et’s “co­ma” – a sur­round­ing area of gas and dust – be­came quickly brighter and then died down again over those six weeks. Mea­sure­ments sug­gested that the com­et was los­ing wa­ter va­por to space at about 300 milliliters (1.3 U.S. cups) per sec­ond, and that its av­er­age tempe­rature was about mi­nus 70 de­grees C (mi­nus 94 de­grees F), point­ing to a “dark and dusty” sur­face, as­tro­no­mers said.

Then, im­ages tak­en from about 12,000 km (7,000 miles) away be­gan to re­veal that the nu­cle­us, or co­re of the ob­ject com­prises two dis­tinct seg­ments joined by a ‘neck’, giv­ing it a duck-like ap­pear­ance. Sub­se­quent im­ages showed more and more de­tail.

“Our first clear views of the com­et have giv­en us plen­ty to think about,” said Matt Tay­lor, the Eu­ro­pe­an Space Agen­cy’s Ro­set­ta proj­ect sci­ent­ist. “Is this double-lobed struc­ture built from two sep­a­rate com­ets that came to­geth­er in the So­lar Sys­tem’s his­to­ry, or is it one com­et that has erod­ed dra­mat­ic­ally and asym­met­ric­ally over time? Ro­set­ta, by de­sign, is in the best place to study one of these un­ique ob­jects.”

Even­tu­al­ly, Ro­set­ta is to at­tempt a close, near-circular or­bit at 30 km (19 miles)  and, de­pend­ing on the com­et’s ac­ti­vity, pe­rhaps come even clos­er.

“Ar­riv­ing at the com­et is really only just the be­gin­ning of an even big­ger ad­ven­ture, with great­er chal­lenges still to come as we learn how to ope­rate in this un­char­tered en­vi­ron­ment, start to or­bit and, eventually, land,” said Syl­vain Lo­diot, the agen­cy’s Ro­set­ta space­craft ope­ra­t­ions man­ag­er.

As many as five pos­si­ble land­ing sites are to be iden­ti­fied by late Au­gust. “In ad­di­tion to char­ac­ter­iz­ing the com­et nu­cle­us and set­ting the bar for the rest of the mis­sion, we will beg­in fi­nal prepara­t­ions for an­oth­er space his­to­ry first: land­ing on a com­et,” said Tay­lor.

“After land­ing, Ro­set­ta will con­tin­ue to ac­com­pa­ny the com­et un­til its clos­est ap­proach to the Sun in Au­gust 2015 and be­yond, watch­ing its be­hav­ior from close quar­ters to give us a un­ique in­sight and real-time expe­rience of how a com­et works as it hur­tles around the Sun.”


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A European Space Agency spacecraft has become the first to reach a comet for a close-up view, coming within 100 km (60 miles) on Aug. 6 and preparing for an even closer approach, scientists report. The event follows a decade-long journey. “After ten years, five months and four days travelling towards our destination, looping around the Sun five times and clocking up 6.4 billion kilometres, we are delighted to announce finally ‘we are here,’” said Jean-Jacques Dordain, the agency’s Director General on Aug. 6. “Europe’s Rosetta is now the first spacecraft in history to rendezvous with a comet, a major highlight in exploring our origins. Discoveries can start.” Mission scientists plan to direct the craft closer over the next six weeks, putting it within half its current distance. Later plans include having it deposit a lander directly on the comet. Comet 67P/Churyumov-Gerasimenko and Rosetta now lie 405 million km (250 million miles) from Earth, about half way between the orbits of Jupiter and Mars, rushing towards the inner Solar System at nearly 55,000 km (34,000 miles) per hour. The comet orbits the sun once every 6.5 years. The path takes it from beyond Jupiter at its furthest point, to between the orbits of Mars and Earth at its closest to the Sun. Rosetta is planned to accompany it for over a year as they swing around the Sun and back out towards Jupiter again. Comets are considered to be primitive building blocks of the Solar System and may have helped to ‘seed’ Earth with water, perhaps even the ingredients for life, according to scientists. But many fundamental questions about these enigmatic objects remain, and Rosetta is aimed at answering some of these. Its journey to the comet wasn’t straightforward. Since its launch in 2004, Rosetta had to make three gravity-assist flybys of Earth and one of Mars to help it on course to its rendezvous with the comet. This complex course also allowed Rosetta to pass by asteroids Šteins and Lutetia, obtaining unprecedented views and information on these two objects. Aug. 6 saw the last of a series of ten maneuvers that began in May to adjust Rosetta’s speed and trajectory gradually to match those of the comet. Had any of these failed, the mission would have been lost, and the spacecraft would simply have flown by the comet. The comet began to reveal its personality while Rosetta was on its way. Images taken between late April and early June showed that its activity was variable. The comet’s ‘coma’ – an envelope of gas and dust – became quickly brighter and then died down again over those six weeks. Measurements suggested that the comet was losing water vapor to space at about 300 milliliters (1.3 U.S. cups) per second, and that its average temperature was about minus 70 degrees C (minus 94 degrees F), pointing to a “dark and dusty” surface, astronomers said. Then, images taken from about 12,000 km (7,000 miles) away began to reveal that the nucleus, or core of the object comprises two distinct segments joined by a ‘neck’, giving it a duck-like appearance. Subsequent images showed more and more detail. “Our first clear views of the comet have given us plenty to think about,” said Matt Taylor, the European Space Agency’s Rosetta project scientist. “Is this double-lobed structure built from two separate comets that came together in the Solar System’s history, or is it one comet that has eroded dramatically and asymmetrically over time? Rosetta, by design, is in the best place to study one of these unique objects.” Eventually, Rosetta is to attempt a close, near-circular orbit at 30 km and, depending on the activity of the comet, perhaps come even closer. “Arriving at the comet is really only just the beginning of an even bigger adventure, with greater challenges still to come as we learn how to operate in this unchartered environment, start to orbit and, eventually, land,” said Sylvain Lodiot, the agency’s Rosetta spacecraft operations manager. As many as five possible landing sites will be identified by late August. “In addition to characterizing the comet nucleus and setting the bar for the rest of the mission, we will begin final preparations for another space history first: landing on a comet,” said Taylor. “After landing, Rosetta will continue to accompany the comet until its closest approach to the Sun in August 2015 and beyond, watching its behavior from close quarters to give us a unique insight and real-time experience of how a comet works as it hurtles around the Sun.”