Rosetta: 'Spuds in space'

Comet 67P on Fri 4 July Comet 67P seen on Friday 4 July at a separation of 37,000km

With the Rosetta probe closing in on Comet 67P/Churyumov-Gerasimenko, we're beginning to get a sense of the ice mountain's shape.

The latest picture release from the European Space Agency (Esa) may only cover an area of about 30 pixels, but it's clear that 67P is no sphere. In some views, the object appears quite elongated.

"Whether it's potato-, or peanut-shaped, or whatever - we're going to have to wait a bit longer," says Trevor Morley, who's part of the mission's flight dynamics team - the navigators who've been driving Rosetta to its quarry.

And Matt Taylor, Esa's project scientist, added: "There appears to be some indication of lobes, or large lumpy sticky-out bits, but I still feel it's not that dissimilar to the 'flying potato' we got from the Lamy shape or Lowry shape." Lamy and Lowry are scientists who used Earth telescopes to try to discern 67P's form.

The three pictures on this page were acquired by Rosetta's Osiris Narrow Angle Camera on Friday last week, when the separation was about 37,000km, not the hundreds of millions of km that the Earth telescopes had to grapple with.

Each image is taken four hours apart. Given that the comet completes a full rotation every 12.4 hours, we therefore get an impression of its overall outline.


Model of 67-P
  • Named after its 1969 discoverers Klim Churyumov and Svetlana Gerasimenko
  • Referred to as a "Jupiter class" comet that takes 6.45 years to orbit the Sun
  • Orbit takes it as close as 180 million km from the Sun, and as far as 840 million km
  • The icy core, or nucleus, is about 4km (2.5 mi) across and rotates every 12.4 hours
  • Scientists had a rough idea of its shape (above); now they'll get the definitive view

The sticky-out bit, or small lobe, seen at bottom-left in the first image is on the right in the second picture, and at the top in the third image.

Early estimates of 67P's dimensions were for an object roughly 3km by 4km by 5km. Those dimensions will be pinned down more precisely in the coming weeks.

The approach to the comet has gone flawlessly so far. Six out of 10 manoeuvres to refine Rosetta's trajectory have been completed, slowing the probe's speed with respect to 67P. The relative velocity is now about 19m/s.

The navigators plot each manoeuvre after studying a series of pictures acquired by another of the probe's camera systems - the NavCam system.

"One thing you should appreciate about how we do this - we don't move directly towards the comet," explained Morley.

"If we did move directly towards the comet then 67P wouldn't move against the star background. And if it doesn't move, you don't get any distance information from the images. So we purposely aim slightly away from the comet. We're coming in in small spirals, if you like."

The plan still is to begin orbiting the comet on 6 August, using a pyramid-like fly-around. This will be done from a distance of about 70km.

The single most important job for the mission team when it arrives is to work out the gravitational field. 67P won't have much of a tug, but, however small, it will still have an influence on the behaviour of the close-in manoeuvres.

These will likely start in September, when Rosetta will cut the separation distance to about 30km to make a detailed map of the comet's surface. It is this information that will drive the choice of landing zone for Philae - Rosetta's little contact platform. Its historic attempt to make the first soft touch-down on a comet is scheduled for 11 November.

Jonathan Amos Article written by Jonathan Amos Jonathan Amos Science correspondent

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  • rate this

    Comment number 62.

    @28 "Science is not delivering. 1 billion will try to rest tonight hungry, without adequate shelter & in need of medical attention."

    The combined wealth of the worlds top richest 200 people is $1tn
    The world spends approximately $450 bn a year on cosmetics.

    The comparatively small amount spent on science is a paltry amount of money.

    As always, you are barking up the wrong tree.

  • rate this

    Comment number 61.

    #59 Denisias
    " .... Wormood ..."

    I know what that reference means, the BBC moderators would remove my post if I explained what it implies about you. No one with a sane bone in their body can make an adequate or sensible reply. All I can say is that the universe follows scientific principles not religious ones, and will still be here in billions of years whether we are or not.

  • rate this

    Comment number 60.

    49. JonSocks
    18. Fishermans_Enemy

    But you ignore my question. I will ask again.

    What is your solution to the over-population problem?

    Simple: there is no over-population problem. The world can cope with however many people live on it so the over-population problem is nothing but an ignorant myth.

    The world could cope if the population was 100 times greater than it is now.

  • rate this

    Comment number 59.

    Costs set against relative outcome, this is the most offensive project ever when so many people on earth are dying every day through malnutrion. It is a scandalous and criminal waste of money.

    If they are so desperate, all they have to do is hang on for another few decades and Wormood will be so close to the earth, the average jet liner will be able to reach it.

  • rate this

    Comment number 58.

    All in due time


Comments 5 of 62


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