Rosetta spacecraft arrives at comet destination

Aug 9, 2014

By Science Daily

After a decade-long journey chasing its target, ESA’s Rosetta has today become the first spacecraft to rendezvous with a comet, opening a new chapter in Solar System exploration.

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

The comet is in an elliptical 6.5-year orbit that takes it from beyond Jupiter at its furthest point, to between the orbits of Mars and Earth at its closest to the Sun. Rosetta will 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. But many fundamental questions about these enigmatic objects remain, and through a comprehensive, in situ study of the comet, Rosetta aims to unlock the secrets within.

The journey to the comet was not straightforward, however. 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 scientific data on these two objects.

“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’,” says Jean-Jacques Dordain, ESA’s Director General.

“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.”

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

“Today’s achievement is a result of a huge international endeavour spanning several decades,” says Alvaro Giménez, ESA’s Director of Science and Robotic Exploration.

“We have come an extraordinarily long way since the mission concept was first discussed in the late 1970s and approved in 1993, and now we are ready to open a treasure chest of scientific discovery that is destined to rewrite the textbooks on comets for even more decades to come.”

The comet began to reveal its personality while Rosetta was on its approach. Images taken by the OSIRIS camera between late April and early June showed that its activity was variable. The comet’s ‘coma’ — an extended envelope of gas and dust — became rapidly brighter and then died down again over the course of those six weeks.

In the same period, first measurements from the Microwave Instrument for the Rosetta Orbiter, MIRO, suggested that the comet was emitting water vapour into space at about 300 millilitres per second.

17 comments on “Rosetta spacecraft arrives at comet destination

  • Excellent. Someone here will be able to answer this question. When they say the spacecraft has gone into orbit around the comet do they really mean a gravitational orbit ? Is the gravitational force between the comet and the spacecraft sufficient for this ?

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  • I can’t answer your question Michael, but it never entered my mind that it was other than a matter of gravitation.

    But that aside, what a wonderful achievement; this could lead to new horizons indeed.

    Another bite out of religion’s lunch?

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  • As I understand it Rosetta will initially enter a “triangular” powered orbit using small amounts of propellant to maintain the orbit.
    Eventually it will enter a circular, and then an elliptical, orbit which will be maintained by their mutual gravitational attraction.

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  • Ah that’s clever. I was thinking of them using propellant to maintain a circular orbit which of course would use it up pretty quickly. But a triangular one makes more sense. I’m still puzzled at the gravitational one. Thanks.

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  • Thanks EricTheRed.

    The initial calculations a decade ago regarding fuel consumption with the vessel maintaining and gathering velocity looping around the Sun five times were of course accurate to the minutest degree, so that now self propulsion doesn’t present a problem.

    But, what if it did run out of gas!

    No, it’s simply amazing.

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  • Thanks for the link. That’s amazing.

    At last some news which makes one proud to be part of the human race, rather than the opposite.

    Indeed. Not been a good few weeks.


    (Thanks to the mods for getting my username back to mmurray!)

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  • 9
    aroundtown says:

    No knee jerk theory or conjecture, no over exuberant platitudes or speculation, just sure and steady science looking for truth that is going to pay an absolute and verifiable dividend. Been following this mission for quite awhile and I’ll love the point where it actually touches down on the comet, a first. No prayer needed, just the culmination of the abilities of a evolving human mind that wondered, what if we tried this.

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  • Hi,

    Rosetta isn’t in his final orbit – it’s still 100 km from the comet and his flying some sort of triangle around the comet. In different phases it will approach the comet to ca. 10km distance in September, where he will stay and that will be also a gravitational orbit. ESA had made a nice video of the final phase: Roseatta Orbit final phase

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  • Oh I think there will be a lot of Prayers to calm the almighty Murphy Law for the landing phase. Especially that harpoon and screws are able to anchor well in the comet.

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  • mmurray Aug 9, 2014 at 6:10 am

    Is the gravitational force between the comet and the spacecraft sufficient for this ?

    The viability of a gravitational orbit, depends on the proximity of the objects to a star or large planet.

    Hence a remote dwarf planet like Pluto can retain several moons, while the Planet Mercury is incapable of retaining any, because of its proximity to the Sun’s gravity.

    This comet appears to be a “rubble-pile comet” (see also rubble-pile asteroids), with parts held loosely together by gravity. Not only can small bodies orbit each other, but they can land on each other and merge if they spiral down from the orbits.
    They can also separate again if disturbed by the strong gravity of a large planet – as was illustrated by comet Shoemaker-Levy-9.
    (a) Disrupted comet Shoemaker-Levy-9 (SL9) was pulled into more than 20 similar-sized fragments during its penultimate encounter with Jupiter in 1992 when it passed within 1.6 Jovian radii of the planet’s center (Asphaug and Benz 1996). How did this disruption occur, and why did it create a train of equal-sized fragments much like a “string of pearls”?

    Also the previous notion of a clear distinction between asteroids and comets as different categories, has become blurred!

    Astronomers and scientists like to put celestial objects into categories, or boxes, by their common physical and orbital characteristics. Three decades ago, the known stony asteroids moved about the sun in roughly the same plane and in the same direction as the planets. We put the asteroids into one box. Into another box went the icy comets whose orbits had very diverse orbital inclinations with many of them in orbits called retrograde orbits that carried them about the sun in a direction opposite to that of the planets.

    Recently, Mother Nature has kicked over these boxes and demonstrated that the line between comets and asteroids is no longer clearly drawn.

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  • Rosetta is now getting down to the business of investigation!

    The Rosetta spacecraft has sent a hauntingly beautiful picture of itself from deep space.

    It was taken with the CIVA camera situated on Rosetta’s landing craft known as Philae.

    The image was taken on 7 September from a distance of about 50km from the comet seen at the top of the picture.

    It shows the edge of the spacecraft and one of its 14m-long solar wings glistening in sunlight against the blackness of space.

    Faint details of the spacecraft’s protective blanket, the ridges of one of the solar wing’s supports can be seen clearly as can the wiring and hinges on the wing itself.

    At the top of the picture is Comet 67P also known as Churyumov-Gerasimenko with each of its distinct lobes visible.

    The 10-billion-tonne target: No space mission has ever made a soft landing on a comet

    J” marks the spot for Rosetta’s robot landing craft Philae

    Scientists and engineers have spent weeks studying the 4km-wide “ice mountain” known as 67P, looking for a location they can place a small robot.

    They have chosen what they hope is a relatively smooth region on the smaller of the comet’s two lobes.

    But the team is under no illusions as to how difficult the task will be.

    Comet 67P/Churyumov-Gerasimenko, currently sweeping through space some 440 million km from Earth, is highly irregular in shape.

    Its surface terrain is marked by deep depressions and towering cliffs.

    Even the apparently flat surfaces contain potentially hazardous boulders and fractures.

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  • Latest!

    The date has been fixed for Europe’s daring attempt to land on a comet: Wednesday 12 November.

    It will see the Rosetta satellite, which is currently orbiting the huge “ice mountain” known as 67P, drop a small robot from a height of 20km.

    If all goes well, the lander will free-fall towards the comet, making contact with the surface somewhere in a 1km-wide zone at roughly 15:35 GMT.

    The European Space Agency (Esa) says the challenges ahead are immense.

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