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July 3, 2014

How big is Rosetta's comet?

Diagram of Comet 67P/C-G compared to terrestrial landmarks. Credit: ESA
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Diagram of Comet 67P/C-G compared to terrestrial landmarks. Credit: ESA

Pretty darn big, I'd say.

The illustration above shows the relative scale of the that ESA's Rosetta and Philae will explore "up-close and personal" later this year. And while it's one thing to say that the nucleus of Comet 67P/Churyumov-Gerasimenko is about three by five kilometers in diameter, it's quite another to see it in context with more familiar objects. Think about it鈥攁 comet as tall as Mt Fuji!

At the time of this writing Rosetta is 35 days out on approach to Comet 67P/C-G, at a distance of about 51,000 km (31,700 miles) and closing. Three聽"big burn" maneuvers have already been performed between May 7 and June 4 to adjust the spacecraft's course toward the incoming comet, and after smaller ones on June 18 and July 2 there are a total of five聽more to go. See details of Rosetta's聽burn maneuvers here.

As incredibly sensitive as they are, Rosetta's instruments鈥攚hich were聽able to detect the water vapor coming from Comet 67P/C-G from a distance of over 360,000 km鈥攈ave even sniffed the hydrazine exhaust from its own thruster burns.

Luckily the remaining burns are relatively small compared to the first three, with the final being very brief, so any聽data聽contamination by Rosetta's own exhaust shouldn't become an issue once the spacecraft has established orbit in August.

Artist鈥檚 impression (not to scale) of the Rosetta orbiter deploying the Philae lander to comet 67P/Churyumov鈥揋erasimenko. Credit: ESA鈥揅. Carreau/ATG medialab.
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Artist鈥檚 impression (not to scale) of the Rosetta orbiter deploying the Philae lander to comet 67P/Churyumov鈥揋erasimenko. Credit: ESA鈥揅. Carreau/ATG medialab.

Launched in March 2004, ESA's Rosetta mission will be the first to orbit and land a probe on a comet, observing its composition and behavior as it makes its close approach to the Sun in 2015. Click here to see聽where Rosetta is right now.

Note: While 3-5 km seems pretty big聽(especially when stood on end) comet nuclei can be聽much larger, 10 to 20 km in diameter up to the enormous 40+ km size of Hale-Bopp. As comets go, 67P/C-G is fairly聽average. (Except that, come August, it will be the only comet with an Earthly spacecraft in tow!)

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