This image from Opportunity just showed up from the 19th of October:

Are all of these cosmic ray impacts? Or could some be meteors?
Also, a new observation of Siding Spring is avaiable:

Sequence of cleaned and 4x-brightened MSL Sol 783 MastcamLeft images:

A dot is jumping around. Might be the comet, but I'm not yet quite sure.

Edit: It's probably the star Izar (Epsilon Boötis).

Edit: Here the corrected order:

Trying my hand at identifying stars in the noise (hats off to those who do this routinely), I think I identified Epsilon Boötis (aka Izar) in 0783MR0033840030204197C00_DXXX and find a potential candidate for Siding Spring:



Izar is at RA/dec 14:44:59/27.07 and SS per the August SPICE file was at 14:45:47/25.19. The candidate for SS isn't quite at that location, but the report from HiRISE was that SS wasn't in the predicted position exactly.

I'd say these are good candidates for the comet

Checking it forth and back, I think the streaks (and smaller spots in low-exposure images) are all Izar (Epsilon Boo).
Izar has been well visible in earlier images. All kinds of cleaning, enhancement, registering, stacking I've been trying thus far revealed nothing else than noise, hot pixels and other camera artifacts, and the likely Izar. Things seem to be even more subtle; accurate stacking of the comet position, including rotation - once it's known - may help.

Edit: Identified at least 34 W Boo in this Sol 783 MR image:

Playing with the HiRISE images a bit. I was disappointed not to get more pixels across the nucleus (i.e. I hoped they had previously underestimated its size rather than overestimated it) but reality intervenes once more (darn it). Still... I expect a rough shape will be determined from this, and maybe one or more specific active regions will be identified.

Phil

I asked Alfred what the phase angle was, and he said 110 degrees. So there's significant unilluminated comet nucleus in the photo, and coma is bright from forward scattering.

Any body has more information about this picture showing on spaceflightnow?
http://www.spaceflightnow.com/news/n1410/2...pring_large.jpg

It's the same HiRISE imagery we've been talking about here since yesterday
http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA18618

Tau is certainly high these days, making for a less transparent sky than usual.

Almost certainly cosmic rays. That 3817 Oppy sequence was taken a couple of hours before closest approach, so it's very unlikely any debris would be striking Mars at that time.

Here's a quick-and-dirty (done while traveling) average of four of the best 50 second pancam exposures. As before, bandpass filtered followed by stretches, before registering on the comet and averaging:

Note the four short vertical dashes extending to the lower left of the comet - that's a star, showing its large relative motion to the comet (or comet to star).

I would now pretty confidently say a faint extension of the coma is visible upwards, which corresponds roughly to the antisun direction.

S/N could be improved a bit by incorporating more frames.

Q for the better minds here: Was the trajectory of the comet's orbit greatly affected by the Mars encounter?

Like the sunrise sequence that was acquired on Sol-782, this one is another that I'm looking forward to when the full's come down. Here is a thumbnail preview of it just after sunset on Sol-783 during the comet imaging campaign.

Better or worse, I'll take it!

At the comet's closest-pass distance of about 140 000 km, the Mars orbital velocity would be about 0.55 km/s. In other words, the trajectory of any object at that distance from Mars and moving at that speed would be substantially affected by Mars (it would be in orbit, if the velocity was in the right direction). Ie, affected at something like the 100% level.

But SS whizzed by at around 56 km/s, which is around 100 times faster than the orbital velocity. So I would estimate that the path of SS was altered at very roughly the 1% level by its encounter with Mars, in other words hardly at all.

Good question!

Edit: Gerald adds a good point: a small (1%) change can have a huge effect over the full orbit of the comet. Orbits can be chaotic, with extreme sensitivity to small changes over long enough timescales.

In the long run:

For an Oort object like C/2013 A1 even a small delta-v as provided by the rudimentary gravity assist makes a difference. In the current case it seems to slow down the comet a little bit, enough to reduce the orbital period down to a fraction (from "several millions years" to about 1 million years, according to Wikipedia, which refers to JPL's HORIZON Web-Interface). I'd think, Jupiter will also play some role, but I don't know the respective numbers.

The Sol-783 Sunset mosaic .

Starry Night shows that comet siding spring should be at the very top of the mosaic. I have identified two candidates. There is one faint dot at the very top-left edge of the mosaic which could also be the comet or could also be an artifact or something else...?



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