Will we find life on Mars?

Agustin Chicarro, project scientist for Europe's first solo mission to Mars, talks to BBC News Online's Helen Briggs about the search for water and life on the planet.

HB: What one mystery would you like to solve?

AC: We know that Mars was a totally different place when life started evolving on Earth about 3.8 billion years ago.

Mars was very similar - with water and warm - and it suddenly changed and it became the hostile and cold place it is today, losing much of its water. We just don't know why.

HB: What will the mission tell us about Mars?

AC: All of the instruments on the orbiter and on the lander will be looking for water and life, the two questions being very much related.

The imaging instruments on the orbiter will be looking for traces of water in terms of dry river beds, and we will be mapping the mineralogical content of the surface which will indicate water bearing minerals for example.

Mars water facts Ice crystals less than one metre (three feet) below Mars surface Located south of 60 degrees latitude Melted, would create planet-wide ocean

We will have a radar on the orbiter looking for sub-surface water or ice down to a depth of a few kilometres and we will be measuring the amount of water in the atmosphere and how that interferes with the surface and with the oxidation processes on the surface itself.

From the lander we will be measuring in great detail the chemical composition of rocks and soil and indeed the content of water and organic components. So overall we will be able to go towards saying, 'yes there is a possibility that life may have evolved on Mars' or not.

In either case the answer to this question is very interesting because it will point in the direction of life being a very common occurrence at least in our Solar System in the Universe or being very unique.

HB: How do you compare Mars Express with the two Nasa rovers?

AC: The two missions are complementary. We are focussing on water and life as I have mentioned; the American rovers are looking more at the geochemical composition of the surface.

There is also a Japanese mission arriving at Mars about the same time that will be observing the planet in a complementary orbit to Mars Express - we will be in a polar orbit while the Japanese will be on an equatorial one.

We will be observing the planet simultaneously from two different points of view. This will help our understanding of, for example, dust storms, atmospheric circulation, the interaction with the solar wind and so on.

HB: If there is water under the surface, can Mars Express find it?

AC: With the radar on board the orbiter, we hope to reach frozen or liquid interfaces of water down to a few km.

We would like to make an inventory of the whole water of the planet. We have known there is water on Mars for a long time however we don't know how much and in what form.

We know there is water in the poles, we know there is some small amounts of water in the atmosphere but from geological evidence of past history we could infer there has been a lot more water on Mars during its history so the question is 'where is that water?' Has it disappeared or is it still there below the surface? We hope to find that out.

HB: If you were a betting man, what odds would you put on finding life on Mars?

AC: I don't bet so that is a difficult proposition! It is a logical expectation, given the conditions of both planets being very similar to one another throughout their geological history, to expect that they have had similar evolutions.

So it is entirely possible that there are traces of biological activity - we are not looking for little animals running around but rather for traces of bacterial activity during its distant past or that may have even survived until today. Even a negative answer would also be interesting.