Posted to sci.astro:

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From: rgregoryclark@yahoo.com (Robert Clark)
Newsgroups: sci.astro,alt.sci.planetary,sci.space.history,sci.astro.amateur,rec.arts.sf.science
Subject: Mars, the "Greenish" Planet?

Below I discussed the fact that Mars frequently presents a greenish
tint to Earth bound observers. This had been attributed to an optical
illusion but the best Hubble image taken of Mars also showed areas
with a greenish hue:

Hubble Captures Best View of Mars Ever Obtained From Earth
http://oposite.stsci.edu/pubinfo/pr/2001/24/

Now the THEMIS camera on Mars Odyssey also shows an area on Mars with
greenish patches:

PIA03738: Candor Chasma on Mars, in Color
http://photojournal.jpl.nasa.gov/catalog/PIA03738

Bob Clark

______________________________________________________
From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Re: First color images from 2001 Mars Odyssey?
Newsgroups: alt.sci.planetary, sci.space.history, sci.astro,
sci.astro.amateur
Date: 2002-04-06 08:35:28 PST

You wouldn't get the impression that Mars is a colorless world from
this Hubble image either:

Hubble Captures Best View of Mars Ever Obtained From Earth
http://oposite.stsci.edu/pubinfo/pr/2001/24/

Impossible not to notice that the darker areas have greenish tinge to
them.
I found this web site that says this is common from telescope views
from Earth but attributes it to an optical illusion:

Mars
"When Mars is viewed through a telescope, it looks like a red and
orange disk. An observer can easily see white ice caps at the north
and south poles of Mars. These caps grow and shrink throughout the
Martian year, just as the polar caps of Earth do. The darker areas of
Mars's surface may look greenish to the observer, but this is an
optical illusion caused by the contrast in color between the dark
patches and brighter areas. Scientists believe that the dark areas are
regions of relatively unweathered bare rock, while the bright areas
are regions with deposits of weathered material, especially fine
dust."
http://www.cosmiverse.com/reflib/marspage1.htm

Whether this seasonal change is an optical illusion or not is
something color light imaging from THEMIS could also address.
I imagine examination of the spectra of this Hubble image also could
address the question of whether these dark areas really are reflecting
most strongly in the green part of the spectrum.

rgregoryclark@yahoo.com (Robert Clark) wrote in message news:<832ea96d.0204021257.6ee68b47@posting.google.com>...
> henry@spsystems.net (Henry Spencer) wrote in message news:<Gtwpt6.58@spsystems.net>...
> > In article <1017689746.286824@server.gh.wh.uni-dortmund.de>,
> > Holger Isenberg <H.Isenberg@ping.de> wrote:
> > >> http://mars.jpl.nasa.gov/odyssey/ Pretty color pictures are probably
> > >> not a high priority...
> > >
> > >Can you explain further? We send the first real color camera to Mars orbit
> > >and its pictures are low priority in relation to 20 m/pixel b&w pictures,
> > >which already had been taken back in 1972 by Mariner 9?
> >
> > They're (probably) low priority because they don't *tell* you anything
> > new. It was established early that Mars is not a colorful place -- that
> > is, its color doesn't *vary* much -- and that (conventional) color imaging
> > thus doesn't add much information compared to B&W images. So tripling the
> > data volume to bring back color isn't very attractive.
> >
> > Note that THEMIS is primarily an IR instrument. The visual part is mostly
> > just a supplement to the IR imaging.
>
> I agree with you that the IR images should have higher priority but I
> don't agree that color images wouldn't tell you very much. I copied
> below a post discussing some questions that color imaging could
> answer. Other questions that would be interesting to answer is what
> are the colors of the dark streaks seen forming in current times? In
> the MGS images they look just look black to varying shades of grey.
> What about the color of the "dalmation spots" that some have claimed
> to be indicative of life?
> A region I'm especially interested in is Solis Lacus. This has long
> been known to be a variable feature on Mars both seasonally and long
> term. This is interesting because there are several lines of evidence
> suggesting there could be near surface liquid water in Solis. Are the
> known albedo changes in Solis accompanied by color changes?
> This web page by the Association of Lunar & Planetary Observers lists
> several variable features on Mars that very likely would also be
> accompanied by color changes:
>
> 1998-1999 Aphelic Apparition of Mars: Part 3
> http://www.astroleague.org/marswatch/Newsletr/imv03i06.html
>
> Bob Clark
>
> **************************************************************
> From: Robert Clark (rgregoryclark@yahoo.com)
> Subject: On the colors of Mars and the mystery of the "Sinton bands".
> Newsgroups: sci.astro, alt.sci.planetary, sci.astro.seti, sci.bio.misc
> Date: 2002-02-02 15:19:44 PST
>
> The color imager on Mars Odyssey should have about the same resolution
> as the Viking orbiter, about 20 meters/pixel.
>
> A question about some features on Mars is whether some color
> differences are real or are only apparent in comparison to surrounding
> terrain.
>
> White Rock for example has been claimed to not really be white but
> only lighter than the surrounding area. Will the color imager be able
> to determine if it really is white?
>
> Another area where the interpretation of its color has been
> controversial is the Syrtis Major region. It has long been known to
> present an apparent bluish tint that appears to change seasonally.
> William Sinton made some spectrographic observations of the area in
> the 50's that appeared to show it's spectrum matched that of complex
> organic molecules. This and the seasonal changes led Sinton to
> originally propose the spectra were due to life. Will Mars Odyssey be
> able to determine if Syrtis Major really does become blue seasonally?
> Some of the bands Sinton observed have been explained as actualy due
> to HDO in Earth's atmosphere. However, the bands at 3.4 microns which
> are frequently seen in complex hydrocarbons have not been definitively
> explained. Will the THEMIS infrared imager on Mars Odyssey finally be
> able to resolve the mystery of the "Sinton bands"?
>
> The history of the Sinton bands is told in the second chapter of
> Barry DiGregorio's book, _Mars: the Living Planet_,
> http://www.amazon.com/exec/obidos/ASIN/1883319587/marsbugstheelect
>
> References on the Sinton bands:
>
> Home Page for IRTF Mars Image Gallery
> Sinton bands in February 1995 IRTF images
> http://marswatch.astro.cornell.edu/irtf.html
>
> 3-4m mm IMAGING SPECTROSCOPY OF MARS.
> http://www.lpi.usra.edu/meetings/LPSC98/pdf/1658.pdf
>
> It's also discussed in the dissertation of David Klassen:
>
> Infrared Imaging Spectroscopy of Martian Volatiles
> by David R. Klassen
> http://elvis.rowan.edu/~klassen/papers/dissertation/chapter1.htm
>
> Bell et.al. have also proposed the aluminum mineral diaspore
> for the origin of the "Sinton bands":
>
> SPECTROSCOPIC EVIDENCE FOR DIASPORE (a-AlOOH) ON MARS.
> http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1227.pdf
>
>
> Bob Clark
> ****************************************************
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