Comet observation from Mars, comets close encounters to Mars in 2013 and 2014 Options

[James Sorenson]

M100 images from Sol-408. This image, according to Starry Night, ISON should be in there, but its not visible.


Original animated GIF
http://www.flickr.com/photos/43581439@N08/...in/photostream/

[dilo]

This early morning, looking to "just released" material, I found this image and this image and, initially, I believed that the very bright object with apparent halo was the comet!
However, looking to the time when pictures were taken (Sol393) I realized that these are "just" over-exposed Phobos pictures before the eclipse (there is also a totality image here)...

[fredk]

Yeah, it looks like the comet is faint. Here's my shot at recovering it. I've taken four distinct differences from the four longer-exposure M100 frames and averaged them all (with rotation to account for the different observation times for the two pairs). This gets the S/N way up there for the stars James highlighted (sigma, rho UMa), but I don't see anything at the comet's location on James' map:

Maybe there's some kind of threshold effect here - the S/N is so good for those stars that I'd expect to see more stars, but I can't. It looks like I've increased S/N for the obvious stars without bringing out any new ones. Obviously the original raw images would work better.

[xflare]

I think this is something that will require the original high quality RAW files to detect - if it's visible at all that is.

[Greenish]

Of the pre-dawn Sol 408 images that have come down so far, all except this one have "E" in the filename, which according to the SIS means they are JPEG 422; the one linked has "C" which means lossless compression was used. (Of course, they are all JPEG-ed [again?] for posting on the web). I don't know if the uncompressed versions are stored on board or if the "E" files were originally stored as JPEGs, but I think it means they are actually compressed in the camera instrument.

Edit: checking a few of them, it looks like the web-posted files are all JPEG quality 70, but the "C" files do have subsampling turned off. FWIW.

[fredk]

There's also this C frame:
http://mars.jpl.nasa.gov/msl-raw-images/ms...1000C0_DXXX.jpg
The C frames appear in greyscale on the jpl jpeg site.

[mcaplinger]

I don't know if the uncompressed versions are stored on board...

The camera can either take JPEG images in "immediate" mode, in which case the raw image is never stored anywhere, or in "deferred" mode, in which case the raw image is stored in camera flash and JPEGed when transmitted. In the latter case we can send it in any compression mode we want, or no compression at all, or transmit it multiple times in multiple modes.

For MAHLI, if we have the image as a JPEG, the web image is exactly the JPEG bits that we have. For Mastcam and MARDI, the web image is always a decompressed-recompressed JPEG version.
The web image is always JPEG even if we have a lossless version of the image.

I think you can rest assured that if we see the comet, we will make that fact known.

[fredk]

Incidentally, you can see that the fields in the sol 3441 Oppy pancam sequence and the 408 MSL sequence are the same if you compare my two images above. Comparing them you can also see that Oppy picks out the stars considerably better, as you'd expect for the L1 open filter setting.

By my estimation, the Oppy sequence was taken about 7 hours after the MSL sequence (someone should check this). I wonder how much ISON would've moved against the stars in that time. Perhaps someone could repeat James's rendering showing ISON at the time Oppy took her images - this is clearly our best shot at spotting ISON.

[Explorer1]

MRO got it:

http://www.uahirise.org/releases/ison.php

[Greenish]

mcaplinger, thank you for the explanation .... I was hoping you could provide some insight. The difference between the data paths for MAHLI vs the other MM cameras is interesting, too.

[fredk]

Here's a stack of the four hirise frames, with 1 pix gaussian blur and a bit of linear stretch:

A hint of some extension towards the upper left?

[James Sorenson]

Here is the Starry Night Star map overlayed ontop of Fred's image from Oppy. It corresponds very nicely with Gerald's identification of ISON in Pancam images. I'm now fairly confident that what we are seeing is ISON with Pancam.

[fredk]

Thanks a lot for rendering that, James. I don't see any sign of a trail at that location, so I'm sceptical we're seeing ISON. I suppose based on the hirise images that ISON should appear essentially pointlike to pancam?

ISON is relatively close to Mars, so it should matter if the Starry Night map shows ISON where it would appear from the centre of Mars vs Oppy's location - are you using Oppy's location?

In case the position is off somehow, it looks like all of the trails match with Starry Night stars, except possibly the trail immediately below the label "C/2012". Is there a star at that position (it may be covered up by the "C")?

[Deimos]

There are two Hipparcos stars partially overlapping that label. The one you point out is Vmag 7.6! Pancam is quite red-sensitive compared to Mastcam. Both of those stars are K-type. For hot stars, Mastcam wins, by the way. I'm skeptical of any comet ID in the Pancam or Mastcam, although the reported locations are about right. I'm still on the lookout for more MER goodies, but am not optimistic about the comet.

I don't know much about the HiRise images, but they seemed near the noise threshold, and HiRise has a bit more optics to throw at the comet than Pancam does.

[James Sorenson]

Fred that is correct, ISON shouldn't have a trail that follows the stars, but should move between long exposure frames and have its own movement or trail if the images were taken with very long exposure. In my opinion, Gerald's heavily processed images do make a good case that it's the comet based on aligning the stars in his image and what starry night spits out, ISON's position aligns very well with his candidate. I'm curious though exactly how he processed those. I did use Opportunity's current position. Hopefully the PDS images will be a help in solidly confirming it when they are released.