Hydrated Mars

ESA's Mars Express has just published a new global map of Mars, showing the location of hydrated minerals, in the journal Science (press release). This follows the publication in Nature last November of the initial findings (press release) suggesting that Mars may have had liquid water in the dim, distant past.

OMEGA instrument
The OMEGA spectrometer onboard ESA's Mars Express CREDIT: Institut d'Astrophysique Spatiale/ESA
The results come from the Observatoire pour la Mineralogie, l’Eau, les Glaces et l’Activité (OMEGA) instrument onboard Mars Express. This little spectrometer observes Mars in the visible to infra-red part of the electromagnetic spectrum (350 to 5,200 nanometres) and can study both the ground and the atmosphere. So far it has mapped over 90% of the Martian surface with a spatial resolution between about 0.5 to 5 kilometres. The team have released a global map showing the location of various hydrated minerals superimposed on a MOLA elevation map.

Hydrated Mars
The global distribution of hydrated minerals. Click for the full-sized version. CREDIT: IAS/OMEGA/ESA
Hydrated minerals come in two forms: phyllosilicates (the red areas on the map) and hydrated sulphates (yellow). The phyllosilicates - an example of which is clay - are composed of thin layers and can form when igneous rocks get altered by contact with water or carbonic acid (H2CO3). The result is that water (H2O) molecules end up within the crystal structure of the mineral. On the other hand a hydrated sulphate forms as deposits from acidic water, but does not need a long-term presence of liquid water to produce it. The authors have put the sites where these two types of hydrated minerals are found into a geological (should that be areological?) context and along with crater counting techniques they have estimated their ages. The results suggest that the two types come from two different periods in Martian history.

In fact, the authors suggest that Mars has had three geological periods. The first, the "phyllosian", occurred just after the planet formed - 4.5–4.2 billion years ago - and may have been warm and moist. The second, the "theiikian", lasted until about 3.8 billion years ago and is characterised by lots of volcanic activity pumping sulphur into the atmosphere and thus producing acid rain. The last period, the "siderikian", has lasted until the present day and seems to have been dry with slow weathering by the atmosphere. Obviously, going from a moist Mars to a dry one means that the water has either gone underground or was lost into space from Mars's rather thin atmosphere.

Posted in astro blog by Stuart on Friday 21st Apr 2006 (16:37 UTC) | Permalink
[an error occurred while processing this directive]
[an error occurred while processing this directive]