Sunday, May 6, 2012

My Favourite Soil: Martian Soils

This months MFS is written by Eriita Jones from ANU. Eriita has just completed a PhD on looking for life on Mars. She is also a keen baker, crafter and gamer.

Soil on Mars is very different to soil on Earth. As there is no vegetation on Mars and little or no organics at the surface, martian soil has not formed from organic processes such as the decaying of plant matter and the action of microorganisms. The martian soil has formed simply from the erosion and weathering of rock- large crustal rocks being ground into smaller and smaller pieces- through physical and chemical processes. What we know about martian soil comes mainly from the six successful missions that have landed on the surface. The outer layers of the martian crust are primarily basalt, like the oceanic crust of Earth, and the soil is composed mainly of iron oxides, iron rich smectite clays, and salts. I am interested in the search for life on other planets, and so I am fascinated by the question of whether the martian soil could support any Earth-like life. Low availability of liquid water is the strongest challenge for any life at or near the martian surface. Let’s assume for a minute though that the martian soil is in contact with frequent liquid water. Then would it be hospitable for some forms of life?

Yes! The soil on Mars has plenty of sources of nutrients. The soil is quite salty, with chlorides, sulphates and carbonates. The image above shows a layer of bright white soil rich in sulphates (iron and probably calcium) with small amounts of water bound to the minerals. The minerals present in this bright soil formed in hydrothermal vent conditions (hot water!), analogous to the kind of vents found at Yellowstone National Park. This tells us that these conditions, under which many Earth organisms thrive, must have existed millions of years ago on Mars. Amazingly, this subsurface layer was only discovered because the Spirit rover was forced to drag its broken wheel behind it, effectively tilling the soil. Soil analysed by the Phoenix lander in the image below has plenty of nutrients (potassium, magnesium, chlorides) and with its slightly alkaline pH it would be ideal for growing vegetables like asparagus and turnips, if there was liquid water available. The concentrations of salts found at both these sites (and in fact everywhere that we have looked at the martian soil) are very important in the search for life on Mars. The main reason for this, apart from the nutrients that they provide, is their ability to draw water vapour from the atmosphere to form liquid films within the soil. Salts help to wet the soil, and they also help stabilise any liquid water so that it has a longer lifetime in the martian soil.

Curiosity Touching Down, Artist's Concept

Curiosity Touching Down, Artist's Concept via NASA Goddard Photo and Video on Flickr

There is so much still to learn about soil on Mars. We hope to learn more about the soil when the Mars Science Laboratory lands in August, but there is always more to learn from the multitude of imagery and spectra that we have of the martian surface. You can also learn about martian soil by looking at soils on Earth such as in the photo below – where I examined the salty dry soil around gullies (we see similar features on Mars) near Arkaroola. Mars is such an exciting place, and every day we draw closer to finding environments that are hospitable to life, have the potential to support microorganisms, and can help us answer the question of ‘is there life on Mars?’. The best way to learn though, would be to visit and dig up that soil ourselves!

1 comment:

  1. Awesome!

    And ten minutes after reading this post, this link popped up in my twitter feed: A geological map of Mars...