# Rosetta’s Closing In

This close up image focused on a smooth region on the “base” of the “body” section of comet 67P/Churyumov-Gerasimenko was taken by Rosetta’s Onboard Scientific Imaging System (OSIRIS) on 6 August, 2014. The picture shows a range of features, including boulders, craters and steep cliffs. It was taken from a distance of 130 km. The resolution is about 2.5 m/pixel.

Image Credit: ESA

## 5 thoughts on “Rosetta’s Closing In”

1. In the last discussion about the Rosetta mission, there was a discussion about the velocity of cometary dust hitting Rosetta. According to http://blogs.esa.int/rosetta/2014/08/08/cosima-reaches-for-dust/ , the instrument designed for capturing the dust “should decelerate and capture cometary dust particles impacting with velocities of ~100 m/s” – which gives you an idea what the experiment designers thought the maximum dust speeds would be like. This is more in the neighborhood of F1 racecar top speeds than highway driving, but I believe most dust particles would be much slower than that. By comparison, the minimum speed of meteors impacting earth’s atmosphere is about 10,000 m/s and for meteor showers due to periodic comets it’s typically around 4 times that high. So, totally different from what Rosetta will be exposed to.

2. This is fascinating stuff…and the mathematics and science that allow the human race to intercept a comet with a ship is mind-boggling.

I do have a question related to scale. My background includes an education o geology, and I was wondering if the comet had the size, mass, and gravity to justify those features being called “boulders,” implying they rest on the surface…or should they be called “accretions,” attached to the surface by some form of adhesion?

Simply asked, I guess, if the gravity exerted by the comet is only one ten-thousandth of earth’s, is that enough to hold everything together without something else “sticking” it all together?

• re: “Simply asked, I guess, if the gravity exerted by the comet is only one ten-thousandth of earth’s, is that enough to hold everything together without something else “sticking” it all together?” VI

Check out Meta Research and the book “Dark Matter, Missing Planets and New Comets — 2nd Edition (1999)
by the late Dr. Tom Van Flandern ” and the site itself. or
http://metaresearch.org/publications/books/books.asp or
http://metaresearch[DOT]org/publications/books/books{DOT]asp

Dan Kurt

• There’s a chance of “boulder” features looking much different up close. But in typical experience, that is what a boulder looks like. The reverse may also happen, where something that first looks odd is probably nothing more than a boulder (see http://en.wikipedia.org/wiki/Phobos_monolith )

At low enough temperatures, the volatile materials of a comet can freeze together, so that is something besides gravity that helps keep it together. As for the surface, gravity, it probably varies hugely at different points on the surface, but is high enough to (eventually) overcome any force weak enough. If you were standing on the surface of this comet, you could use your arm power to launch a baseball faster than escape velocity. You could probably push a bowling ball hard enough for it to escape the comet’s gravity. Your human strength would be too low to throw any of those boulders off the comet; they’re fairly well stuck there now. In fact, I’d estimate you could not throw your own weight out of the comet’s gravitational influence using only your arms, and perhaps leg strength wouldn’t be enough either.

3. We truly live in an age of wonders.