Files to 'print your own' Rosetta comet

Finally, we have a more definitive description of the size of Comet 67P

Europe's space agency (Esa) has finally released a proper model for the shape of Comet 67P/Churyumov-Gerasimenko.

The organisation's Rosetta mission will try to put a small robot on the surface of this "ice mountain" on 12 November.

The model provides some further details on the comet's size, and also allows enthusiasts to print their own 3D version of the duck-shaped object.

Rosetta has been flying around 67P since August, and could get as close as 10km, if it is deemed safe to do so.

Esa Flight Director Andrea Accomazzo told the International Astronautical Congress in Toronto on Friday that a final decision on this matter would be made next week.

The comet and the Rosetta probe are currently speeding through space some 464 million km from Earth.

The rule is run

The files released by Esa mean anyone can have their own personal version of 67P

The daring landing manoeuvre is planned for the afternoon (European time) of Wednesday 12 November.

Rosetta will attempt to deploy its piggybacked Philae lander to the surface in a procedure that is likely to last roughly seven hours.

The 100kg robot will be aimed at the "head" of the "duck".

If it gets down successfully - and that is a big "if" because of the difficulties involved - it would be a historic first for space exploration.

The shape model just released provides some more definitive physical parameters for 67P.

Previously, mission scientists have used the vague phrase of "about 4km wide" to describe the object's size.

Now, we have measurements to two significant figures.

Closely guarded

The head, or smaller lobe of the comet, is 2.5km by 2.5km by 2.0km. The "body" is described as being 4.1km by 3.2km by 1.3km.

With the previously released mass of 10 billion tonnes and a density of 400kg per cubic metre, which I published last month, this makes for an object that has a volume of 25 cubic km.

Its rotation rate is also now known to at least six significant figures - at 12.4043 hours.

Mission scientists have taken almost two months to release Friday's very simple data-set.

In part, this is because they were trying to make very careful measurements of a highly irregular object. And, it should be said, not all of the comet is visible - parts are permanently in darkness.

But it also speaks to their desire to hold back information that has enormous intellectual primacy.

No-one has ever been this close to a comet before, and there are major discoveries to be made.

To follow a completely open approach to the mission could allow anyone to claim a breakthrough.

Blacker than black

To date, very few pictures have been released that have been acquired by the high-resolution Osiris cameras on the Rosetta probe.

The public has had to make do with the much lower resolution images produced by the satellite's navigation cameras.

And even the shape model released on Friday presents only a very coarse view of 67P. The mission team is currently working with far more precise data-sets.

One very interesting parameter for which we still await a report is the comet's albedo - the degree to which it reflects light

Although it may look quite bright in pictures, the object is actually very black. Quite how black it is, though, is still being kept back.

All this said, those with access to the necessary software and a 3D printer can now turn out a desktop depiction of the most famous comet in the Solar System.

The relevant files are available in .wrl and .obj formats.

Other details released:

• Spin axis: Right ascension, 69 degrees; Declination, 64 degrees

• Water vapour production rate: 300ml/sec (Jun 2014); 1-5 l/sec (Jul-Aug 2014)

• Surface temperature: minus 68C to minus 43C (Jul-Aug 2014)

• Subsurface temperatureminus 243C to minus 113C (Aug 2014)

• Gases detected:Water, carbon monoxide, carbon dioxide, ammonia, methane, methanol

• Dust grains sizes detected: A few tens of microns to a few hundreds of microns

Mission scientists will be working with much more precise models than this publicly released version

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