What will comet 67P/Churyumov-Gerasimenko look like?Comet_Artist_Impression_node_full_image

The short answer is that we simply don’t know… but that wouldn’t make for a very interesting blog post, would it?!

The “Here be dragons” title of this post refers to the medieval practice of drawing dragons or serpents on uncharted areas of maps. Exploring uncharted territory is what humankind has been doing for centuries of course, be it mapping the outline of undiscovered continents on our own planet, to mapping entirely new worlds in the far reaches of the Solar System.

Just as I’m sure that ancient explorers had plenty of discussion about what they might find on the other side of an ocean, so we – in fact you on our social media channels, the Rosetta mission team, and us, here in ESA’s science communication team – are speculating what Rosetta will discover at comet 67P/CG after an epic ten year voyage through the Solar System. And we started our discussions with one of the most basic questions: what will the comet look like?

Will it be covered in treacherous mountains and canyons, or will it be smooth? Will it have impact craters? Will it send geysers of ice and dust jetting into space? Maybe it will have a bit of everything!

Here are some interpretations from our graphics artists from over ten years ago, compared with our latest offerings from 2013/2014:


Rosetta_s_Philae_lander_on_comet_nucleus_node_full_image Rosetta_orbiting_Comet_67P_Churyumov-Gerasimenko_node_full_image
Rosetta_orbits_comet_with_lander_on_its_surface_node_full_image Rosetta_s_Philae_lander_descending_onto_comet_nucleus_node_full_image


Philae_on_the_comet_Front_view_node_full_imageOf course, with some knowledge of the comets that we do already know about one could argue that some of the older graphics are verging more on science fiction than science fact, but really, everyone is entitled to have a different idea, because we haven’t yet seen 67P/CG close up.

What we are equipped with now that we weren’t ten years ago, however, are the wonderful insights gained by NASA’s Deep Impact mission to comet Tempel-1 (2005) and Hartley-2 (2010), and the Stardust mission to Wild-2 (2004), and Tempel-1 (2011). Previously, we’d only seen Comet Halley up close (ESA’s Giotto got the closest view, at around 600 km, in 1986), and Comet Borrelly, with NASA’s Deep Space 1 in 2001.

So here is what we do know about how five different comets look:

Comet Halley, by ESA's Giotto, from a distance of about 2000 km

Comet Halley, by ESA’s Giotto in 1986, from a distance of about 2000 km. Halley’s nucleus is about 16 x 8 x 8 km.

Comet Borrelly, by NASA's Deep Space 1, from a distance of 3417 km. The nucleus is about 8 km long.

Comet Borrelly, by NASA’s Deep Space 1 in 2001, from a distance of 3417 km. The nucleus is about 8 km long. The resolution in this image is about 45 metres/pixel.

Comet Wild-2 by NASA's Stardust mission in 2004, from a distance of 500 km. Wild-2's nucleus is about 5 km across.

Comet Wild-2 by NASA’s Stardust mission in 2004, from a distance of 500 km. Wild-2’s nucleus is about 5 km across.

Comet Tempel-1, by NASA's Deep Impact, in 2005

Comet Tempel-1, by NASA’s Deep Impact in 2005. The image is a composite built from scaling images to 5 metres/pixel. The nucleus is 7.6 x 5 km.

Comet Hartley-2 by NASA's EPOXI in 2010, from a distance of about 700 km. The nucleus is 2.2 km long.

Comet Hartley-2 by NASA’s EPOXI in 2010, from a distance of about 700 km. The nucleus is 2.2 km long.

As you can see, these comets all have quite different appearances; it’s not simply the case of “one size fits all”. But the detailed views of Tempel-1, Wild-2 and Hartley-2 in particular, enable us to make some educated guesses as to the types of terrain we could possibly encounter at comet 67P/CG.

comet shape

We are also in the lucky position of already having observed comet 67P/CG from the ground, and with the Hubble Space Telescope, which has enabled some estimates of the comet’s shape and size.

Et voilà, after some lengthy discussions between our comet experts, graphics artists and science communicators, we came up with this, essentially a hybrid of the comet textures we’ve already seen in space:


Comet 67P/CG artist impression, 2013

Comet 67P/CG artist impression, 2013

But it could be completely wrong. Personally, I think it makes it all the more exciting that we don’t know what it looks like (but there’s only a few months to go until we do!).

Not knowing is also a little unnerving. After all, Philae has to land there, so one of the first things we’ll be doing when we get to the comet is mapping it in great detail.

Although I favour the latest set of artist impressions over the earlier suggestions, I know that comet 67P/CG will have plenty of surprises – but likely no dragons!