Green Mars

January 23, 2004 5:36 PM

More Mars Express images. The German space agency (DLR) has the biggest and fastest loading set of Mars Express images I've seen so far. Among them is one which apparently was not part of the press kit (it hasn't been in any MEX-related report), and is not on the official ESA site: This one. It shows the Spirit rover landing site in Gusev crater -- and the area is covered with a green substance. Olivine or salt, perhaps. It should be highly interesting to get spectral readings. [Note: These images are, to my knowledge, near true color like all other MEX/HRSC photos.]
posted by Eloquence (14 comments total)

I'll be fascinated to know what the blue stuff is in the bottom of Reull Vallis.
posted by raygirvan at 6:00 PM on January 23, 2004

Neukum said at the press conference that he was certain that these were sediments carried by once flowing water. Note that many rocks on Mars have a blue-ish color -- could be some chemical process, perhaps related to UV radiation.

At this point it seems fairly certain that a lot of the water is now underground (ESA artist's impression), and occasionally makes its way to the surface, sometimes carrying salt along the way (forming some of the more interesting surface structures on Mars, evaporites). But this can only be verified by the radar onboard of MEX, which will start operating in a couple of months.

The only frustrating thing is the slow rate at which the images come out -- Neukum already has over 100 GB, and only about a dozen images are online. ESA has also failed to communicate that MEX, not Beagle2, is the main part of the mission (B2 was later tacked on a as a cheap add-on by the British). Hopefully the brilliant HRSC images will change that impression. Neukum said that not even Earth has been mapped completely in stereo and color -- he plans to do it for Mars first.
posted by Eloquence at 6:24 PM on January 23, 2004

... could be some chemical process, perhaps related to UV radiation.

Ah: I'm forgetting my mineralogy. Irradiated halite (i.e. rock salt) is blue, and halite is pretty likely if we're talking evaporites.
posted by raygirvan at 6:37 PM on January 23, 2004

Periodite has been suggested as the most likely option since it's been documented on Mars before.
posted by moonbird at 9:28 PM on January 23, 2004

Eloquence, are you also involved with the project?

So far, apart from the loss of Beagle2, MEX has been a stunning success. Let's hope the other instruments work as well as OMEGA and HRSC.
posted by salmacis at 1:33 AM on January 24, 2004

Eloquence: These images are, to my knowledge, near true color like all other MEX/HRSC photos.

I had always assumed that virtually all transmitted images were B&W and approximated later by computer. Evidently things have progressed since my Astro101 days ... Wouldn't that take a monstrous amount of memory (read: transmission time)? How do they do most imaging these days? The color photos from the recent surface probes real or augmented?
posted by RavinDave at 3:06 AM on January 24, 2004

RavinDave: See the HowStuffWorks article on digital cameras, specifically the section on capturing color. A CCD cannot detect color, only brightness, so digital cameras use filters to limit the incoming spectrum and then create a composite from this data. This also applies to MEX' HRSC camera, which has 10 different channels - one high resolution channel, four color channels, and five additional channels to get the image from different angles to produce stereo pictures. It can take photos in all 10 channels almost simultaneously. (You can view these using shutter glasses, or you can generate the oblique 3D views which you find at the DLR site.)

This makes it different from Malin's camera onboard NASA's Global Surveyor. MGS only has red and blue channels, and only for the wide angle mode (source). There are therefore very few color MGS pictures at relatively low resolution, with the green channel synthesized -- listing here .

Many of the color images you see from MGS have been hand colored by Malin based on how he believes Mars should look and were originally B/W.

MGS can also only take stereo pictures by orbiting the same region twice -- which is very difficult and doesn't get you good images if you're trying to show changes in the landscape or atmosphere.

HRSC will map all of Mars in full color and in stereo. Bandwidth is not a problem thanks to ESTRACK and DSN. Neukum said at the MEX press conference that they already have over 100 GB of images, and will move into the terabytes soon. The pictures shown so far were only selections -- at the end of the conference a group of children walked in and unveiled a huge color poster, several meters long, that also was only a selection of the images taken so far. This bugs me a little, because I see no reason not to already put these pictures online.

The green patches in Gusev crater might be only the first of many surprises to come.
posted by Eloquence at 4:16 AM on January 24, 2004

Periodite

Peridotite? That'd explain the green. But I was thinking particularly of Reull Valis, where the location would fit with the evaporites Eloquence mentioned.

Ravindave: there's a technical description of the HRSC here.
posted by raygirvan at 4:20 AM on January 24, 2004

You guys!
posted by y2karl at 7:00 AM on January 24, 2004

Mars Global Surveyor's Thermal Emission Spectrometer identified a fairly large amount of near-surface or surface olivine. They found it particularly in volcanic regions, including exposures on the rims of craters hundreds of miles across, and with different amounts of iron, giving lighter green and darker green rocks. All of that is a bad sign in the search for water, because olivine is particularly sensitive to the chemical weathering. If liquid water had ever been present in significant quantities, the olivine would be gone by now. The presence of water and chemical weathering would also produce clay minerals, which were not seen by the TES. Although the presence of olivine is consistent with ice under the surface, as the latest evidence seems to indicate, it is unlikely that Mars has had a period of warm, wet climate in the past.
posted by monju_bosatsu at 9:10 AM on January 24, 2004

Thanx to Eloquence for the very thoughtful reply and raygirvan for the link. Muchly appreciated.
posted by RavinDave at 9:45 AM on January 24, 2004

Thanks for this post--this stuff is truly amazing. Is it coincidence or necessity that US and European probes are reaching Mars at the same time? It seems a bad PR move.

Also, why are jpg and tiff images of greatly different file sizes both labeled "hi-res"?
posted by ParisParamus at 10:10 AM on January 24, 2004

The images are the same resolution, but the JPEG data is compressed resulting in a slight loss of image quality.
posted by Pretty_Generic at 11:09 AM on January 24, 2004

Is it coincidence or necessity that US and European probes are reaching Mars at the same time?

To hazard a guess, around now is when stuff launched around the optimum for a low-energy transfer would land. In other words, probably an orbital necessity.

Also, why are jpg and tiff images of greatly different file sizes both labeled "hi-res"?

tiffs are uncompressed or losslessly compressed, jpgs use lossy compression. So a jpg and a tiff of the same picture will have different file sizes.
posted by ROU_Xenophobe at 11:30 AM on January 24, 2004