Mars: More data, more mysteries.

Posted to the Habitablezone.com

__________________________________________________ __________________________
Space Sciences
More data, more mysteries.
Posted by Robert Clark on 3/3/2004 7:25:49 AM

In Reply to: Yes! Yes! Yes!...But to be serious, we have to start
making a 'time-scale' distinction. posted by Jacob Samorodin on
3/2/2004 1:05:59 PM

Frankly, I'm disappointed that the deposit turned out not to be a
carbonate, but a sulfate.
On Earth of course there are both carbonate and sulfate deposits. So
perhaps there are still extensive carbonate deposits on Mars.
In a prior post I said if there are no carbonates found here then the
widely distributed white areas seen on Mars are probably due to
sulfate, not carbonate. It MIGHT be that the white deposits seen at
the Pathfinder site could still be carbonate. I was interested to see
that at Meridiani, the wheels of the rover were able to grind up the
white material located in the dug trenches. At Pathfinder, the
Sojourner rover was unable to scratch the surface of the white
material even with one of the spiked wheels meant to dig into the
surface materials. It occurred to me that perhaps the Pathfinder white
material was the harder caliche carbonate, while the Meridiani white
material was the softer sulfate gypsum. Tony also raised the
legitimate possibility the white material at Pathfinder is quartz.
However, it maybe the difference in the two sites is simply that the
MER rover is much heavier than the Sojourner rover and that is the
reason it was able to grind up the white material.
But if the white areas seen on Mars really are all sulfate, we have a
mystery. The (apparent) wide scale sulfate deposits suggest large
scale water deposition. But if this is so and Mars once had a thicker
CO2 atmosphere, there should also be large scale carbonate deposits.
One possible explanation: some scientists argue that *large scale*
carbonate deposits such as limestone require life to develop. Then
perhaps the reason they are not seen on Mars is because life did not
develop there.
Another possibility: perhaps when Mars had a thicker atmosphere
(presumably it did to allow the large scale water deposition), that
atmosphere did not consist of CO2. In addition to the lack of
carbonate deposits seen on Mars we also have the mystery of the lack
of CO2 in the Mars polar ice caps. Apparently, CO2 over the southern
cap is only a thin covering:

Researchers Find Mars' South Pole Cap is Mostly Water Ice.
http://www.planetary.org/html/news/a...water-ice.html

Perhaps that thicker atmosphere did not consist of CO2. Or perhaps as
this article suggests the water cut channels seen on Mars occurred
under an ice cover.
Or perhaps there are still carbonate deposits on Mars. One thing I
would like to find out: are there some distinguishing factors
surrounding sulfate deposits on Earth as compared to carbonate
deposits? For instance do sulfate deposits occur most frequently near
recent volcanic activity?


Bob Clark
__________________________________________________ __________________________
http://habitablezone.com/space/messages/316769.html


cf.:

Space Sciences
Huge Moomaw article on the current views of mars
Posted by Robert Clark on 12/18/2003 5:00:27 PM
http://habitablezone.com/space/messages/305743.html

"Robert Clark" skrev i en meddelelse
om...

snip

Frankly, I'm disappointed that the deposit turned out not to be a
carbonate, but a sulfate.
On Earth of course there are both carbonate and sulfate deposits. So
perhaps there are still extensive carbonate deposits on Mars.
In a prior post I said if there are no carbonates found here then the
widely distributed white areas seen on Mars are probably due to
sulfate, not carbonate. It MIGHT be that the white deposits seen at
the Pathfinder site could still be carbonate. I was interested to see
that at Meridiani, the wheels of the rover were able to grind up the
white material located in the dug trenches. At Pathfinder, the
Sojourner rover was unable to scratch the surface of the white
material even with one of the spiked wheels meant to dig into the
surface materials. It occurred to me that perhaps the Pathfinder white
material was the harder caliche carbonate, while the Meridiani white
material was the softer sulfate gypsum.

In the announcement MgSO4 was mentioned at Meridiano planum.

Tony also raised the
legitimate possibility the white material at Pathfinder is quartz.
However, it maybe the difference in the two sites is simply that the
MER rover is much heavier than the Sojourner rover and that is the
reason it was able to grind up the white material.
But if the white areas seen on Mars really are all sulfate, we have a
mystery. The (apparent) wide scale sulfate deposits suggest large
scale water deposition.

In Earth evaporites CaCO3 precipitates out first, followed by gypsum. This
suggests to me, that CaCO3 may be present underneath MgCO4

But if this is so and Mars once had a thicker
CO2 atmosphere, there should also be large scale carbonate deposits.
One possible explanation: some scientists argue that *large scale*
carbonate deposits such as limestone require life to develop. Then
perhaps the reason they are not seen on Mars is because life did not
develop there.

I find that reasonable. Most Earth surficial deposits of CaCO3 is
bio-mediated.

Another possibility: perhaps when Mars had a thicker atmosphere
(presumably it did to allow the large scale water deposition), that
atmosphere did not consist of CO2. In addition to the lack of
carbonate deposits seen on Mars we also have the mystery of the lack
of CO2 in the Mars polar ice caps. Apparently, CO2 over the southern
cap is only a thin covering:

Researchers Find Mars' South Pole Cap is Mostly Water Ice.

http://www.planetary.org/html/news/a...03/mars_s-pole
_water-ice.html

Perhaps that thicker atmosphere did not consist of CO2. Or perhaps as
this article suggests the water cut channels seen on Mars occurred
under an ice cover.
Or perhaps there are still carbonate deposits on Mars. One thing I
would like to find out: are there some distinguishing factors
surrounding sulfate deposits on Earth as compared to carbonate
deposits?

Se above or google "evaporites".

For instance do sulfate deposits occur most frequently near
recent volcanic activity?

I don't think so, but there may be free sulfur or ores of sulfur combined
with metals.

Carsten