Image: Small object spotted orbiting 67P/Churyumov-Gerasimenko

Image: Small object spotted orbiting 67P/Churyumov-Gerasimenko
Credit: ESA/Rosetta/MPS/OSIRIS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA/J. Roger (CC BY-SA 4.0)

Last week marked five years since ESA's Rosetta probe arrived at its target, a comet named 67P/Churyumov-Gerasimenko (or 67P/C-G). Tomorrow, 13 August, it will be four years since the comet, escorted by Rosetta, reached its perihelion—the closest point to the sun along its orbit. This image, gathered by Rosetta a couple of months after perihelion, when the comet activity was still very intense, depicts the nucleus of the comet with an unusual companion: a chunk of orbiting debris (circled).

Comet 67P/C-G is a dusty object. As it neared its to the sun in late July and August 2015, instruments on Rosetta recorded a huge amount of dust enshrouding the comet. This is tied to the comet's proximity to our parent star, its heat causing the comet's nucleus to release gases into space, lifting the dust along. Spectacular jets were also observed, blasting more dust away from the comet. This disturbed, ejected material forms the "coma," the gaseous envelope encasing the comet's nucleus, and can create a beautiful and distinctive tail.

A from Rosetta's OSIRIS instrument can contain hundreds of dust particles and grains surrounding the 4 km-wide comet nucleus. Sometimes, even larger chunks of material left the surface of 67P/C-G—as shown here.

The sizable chunk in this view was spotted a few months ago by astrophotographer Jacint Roger from Spain, who mined the Rosetta archive, processed some of the data, and posted the finished images on Twitter as an animated GIF. He spotted the orbiting object in a sequence of images taken by Rosetta's OSIRIS narrow-angle camera on 21 October 2015. At that time, the spacecraft was at over 400 km away from 67P/C-G's center. The animated sequence is available for download here.

Scientists at ESA and in the OSIRIS instrument team are now looking into this large piece of cometary debris in greater detail. Dubbed a "Churymoon' by researcher Julia Marín-Yaseli de la Parra, the chunk appears to span just under 4 m in diameter.

Modelling of the Rosetta images indicates that this object spent the first 12 hours after its ejection in an orbital path around 67P/C-G at a distance of between 2.4 and 3.9 km from the comet's center. Afterwards, the chunk crossed a portion of the coma, which appears very bright in the images, making it difficult to follow its path precisely; however, later observations on the opposite side of the coma confirm a detection consistent with the orbit of the chunk, providing an indication of its motion around the comet until 23 October 2015.

Scientists have been studying and tracking debris around 67P/C-G since Rosetta's arrival in 2014. The object pictured in this view is likely the largest chunk detected around the , and will be subject to further investigations.

Comet 67P/C-G is currently in the outer solar system, between the orbits of Mars and Jupiter, and will have its next perihelion in late 2021.


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Citation: Image: Small object spotted orbiting 67P/Churyumov-Gerasimenko (2019, August 13) retrieved 23 August 2019 from https://phys.org/news/2019-08-image-small-orbiting-67pchuryumov-gerasimenko.html
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Aug 13, 2019
If anybody else wants to do their own research on the shed load of images from 67P, here is a good place to start;

https://imagearch...esa.int/

Some of them are truly spectacular.

Aug 13, 2019
Of course, if anybody wants to examine the data from all Rosetta instruments, the PSA is the place to go;

https://archives....=mission

Pick your instrument, date, and see what was detected. For instance, if you wanted to confirm the complete lack of electric discharge machining (EDM; lol) as predicted by a certain Velikovskian cult, then the magnetometer data is where you want to look in order to not be able to find it! :)

Aug 13, 2019
with some of the pebbles & gtavel slowly getting stripped off the comethead by our Sun's gravity as the comet gets flung away?

might it be advantageous to send a retrieval probe to collect the debris?

sounds like a more conservative strategy to me
than going to all the expensive effort & risk to a very expensive probe
sending it to scrape off a similar quantity of rock samples by drilling or explosives?
those will just be picking at a few inches of asteroid surface anyway

Aug 14, 2019
with some of the pebbles & gtavel slowly getting stripped off the comethead by our Sun's gravity as the comet gets flung away?

might it be advantageous to send a retrieval probe to collect the debris?

sounds like a more conservative strategy to me
than going to all the expensive effort & risk to a very expensive probe
sending it to scrape off a similar quantity of rock samples by drilling or explosives?
those will just be picking at a few inches of asteroid surface anyway


Debris is easy enough to collect, and this has already been done at a comet by Stardust, at Wild 2. The problem with that is that the ejected material is already devolitilised, and the capture process in aerogel leaves it even more so. They want pristine samples from depths that have not yet been affected by exposure to sunlight. The other option, as tried at Tempel 1, is to whack it with an impactor, and look spectroscopically at what is released. Again, this is not a detailed enough view.

Aug 14, 2019
ahh, i see your point, Castro

whelp, back to the drawing board!


Aug 14, 2019
Of course, this is not necessarily a problem at asteroids, as they are rock anyway. There may well be some small amount of volatiles present, but these are mostly going to be contained within the rock as hydrated minerals. What the Rosetta mission wanted to do was for Philae to drill down into the comet and deliver a sample into its wee oven. Problem was, the surface was harder than expected, and the spacecraft was at a rather peculiar angle, due to the failure of certain systems that were meant to keep it anchored to the surface. However, from such disappointments we live and learn. Next time they'll nail it. Or drill it!

Aug 15, 2019
the chunk appears to span just under 4 m in diameter.
A little too big to be Philae -- what are the chances the thruster and harpoon finally fired with the lander on its side and launched it back into orbit?

Aug 15, 2019
the chunk appears to span just under 4 m in diameter.
A little too big to be Philae -- what are the chances the thruster and harpoon finally fired with the lander on its side and launched it back into orbit?


No, these pics were taken at a time when we know Philae to have been on the surface. It was finally imaged in September 2016, almost a year after these images were taken.

https://www.esa.i...ae_found


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