Frozen sea on Mars

Can anyone suggest why the (probable) frozen sea on Mars recently reported
by ESA's Mars Express orbiter wasn't spotted earlier by Mars Global
Surveyor? Also would it have appeared oddly flat in laser altimetry data?

On 2005-02-25, Andrew Wright wrote:
Can anyone suggest why the (probable) frozen sea on Mars recently reported
by ESA's Mars Express orbiter wasn't spotted earlier by Mars Global
Surveyor? Also would it have appeared oddly flat in laser altimetry data?

Note that the Mars Express pictures were taken in January 2004; it's
quite possible no-one's got around to analysing any MGS images of the
area yet.

In addition, they resemble already-known formations thought to be lava
flows; it's quite possible that any photographs of the area with
sufficient resolution to pick out the plates were looked at, noted as
being another example of a known phenomenon, and thus not something that
leaped out as important. Here, the key seems to have been someone
noticing that they a) looked like pack-ice and b) were too large for
basalt rafts.

The area was definitely imaged by MGS; the abstract that's floating
around contains at least one photo from the MOC, and there's reference
to crater-counting using these images as well. It also notes the use of
MOLA data, so presumably either no-one noticed or it was just written
off as an anomalously flat area. Note that whilst it's very horizontal
it's not very flat - it still has craters and irregular surfaces - so
this wouldn't have been quite as much of a red flag as it may seem.

--
-Andrew Gray

Originally Posted by Andrew Gray

On 2005-02-25, Andrew Wright wrote:
Can anyone suggest why the (probable) frozen sea on Mars recently reported
by ESA's Mars Express orbiter wasn't spotted earlier by Mars Global
Surveyor? Also would it have appeared oddly flat in laser altimetry data?

Note that the Mars Express pictures were taken in January 2004; it's
quite possible no-one's got around to analysing any MGS images of the
area yet.

In addition, they resemble already-known formations thought to be lava
flows; it's quite possible that any photographs of the area with
sufficient resolution to pick out the plates were looked at, noted as
being another example of a known phenomenon, and thus not something that
leaped out as important. Here, the key seems to have been someone
noticing that they a) looked like pack-ice and b) were too large for
basalt rafts.

The area was definitely imaged by MGS; the abstract that's floating
around contains at least one photo from the MOC, and there's reference
to crater-counting using these images as well. It also notes the use of
MOLA data, so presumably either no-one noticed or it was just written
off as an anomalously flat area. Note that whilst it's very horizontal
it's not very flat - it still has craters and irregular surfaces - so
this wouldn't have been quite as much of a red flag as it may seem.

--
-Andrew Gray

Actually, a number of us noticed the similarities between those features and "pack ice" several years ago. There are striking similarities, but notable differences as well. Also, some problems with the age relationships to the Medusae Fossae Formation (overlies the 'platy flows' in places). Then, there's the "problem" that they are near the equator, and ice isn't stable at the surface. It might be possible to retain the morphology as "pseudomorphs", if the ice was dirty, but this still doesn't fit with the observation that it's being exhumed from beneath the MFF.

And, as was pointed out above, they also do resemble rafts on very low viscosity lava flows - though scale is a problem with that interpretation.

Bottom line is that I and my colleagues who noticed this years ago didn't feel that the subject was quite "ready for prime time." The jury is still very much out on the nature of that material.

-Tim.