The Search for Life

Artist's impression of Beagle 2 on Martian surface

Life on other planets is always going to be an exciting subject for debate. But how do we find out if life really exists elsewhere in the Universe?

One way is to travel to the planets, either with remotely operated probes or with manned spacecraft.
Mars is currently the only planet in our Solar System on which there is a strong possibility of finding life, either past or present. ESA’s Mars Express is Europe’s first mission to the Red Planet, and its Beagle 2 lander will perform on-the-spot experiments to search for signs of this life.

In 2004, ESA's Huygens probe to Titan, a moon of Saturn, could provide vital information towards the great mystery of how life began on Earth. Later, Rosetta will be the first spacecraft to land on a comet, analysing its surface for organic compounds that could be the building blocks of life. This will help us to understand if life on Earth began with the help of 'comet seeding'.

First, find the stars with planets...

However, these missions are only looking for life within our own Solar System. But how do we find life on planets around other stars? ESA has a plan for searching for this life in other solar systems.

First you have to find the stars that have planets. There are too many stars to analyse them all, so you have to choose a small part of the sky as your starting point. Next you have to decide what kind of planets you are looking for.

Constellation of Lacerta

With Earth-based telescopes, the only planets we have detected around other stars have been giant gaseous worlds, like Jupiter, over 10 times the diameter of the Earth. Scientists believe we should be looking for rocky, Earth-like planets, because a solid surface is needed on which organic molecules can form and develop into life.

then decide what kind of planets...

The joint CNES/European mission Corot will be the first spacecraft capable of detecting large rocky planets in short-period orbits around nearby stars.

It will use its 30-centimetre telescope to look at few thousand stars, monitoring changes in their brightness caused by planets crossing in front of them.


...then identify signs of life

Artist's impression of Corot

When we have found some suitable planets, then we can look for signs of life. ESA will continue the search into the second decade of the century with the Darwin mission. Darwin's main objective is to find the most likely places for life to develop - at least as we know it!

Darwin will make observations in the infrared since life on Earth leaves its mark in our atmosphere at these wavelengths. On Earth, biological activity produces gases that mingle with our atmosphere.

For example, plants give out oxygen and animals expel carbon dioxide and methane. This flotilla of eight spacecraft will survey 1000 of the closest stars, looking for rocky planets and analysing their atmospheres for this evidence of possible life.

Artist's impression of Darwin

Signatures of Life

Mars may have lost much of its atmosphere during asteroid impacts early in its history

Where there's water, there could be life. "Meteorites from Mars that have landed on Earth show clear evidence that conditions appropriate to life did exist on the planet, including in the recent past," said Colin Pillinger, Consortium Leader for the Beagle 2 lander at the Open University, Milton Keynes, UK. "However, features in the meteorites which have been described as nanofossils are highly controversial. Unfortunately, we cannot be sure that organic matter found in the meteorites is the remnant of organisms that lived on Mars and not due to contamination on Earth. We need to repeat the experiments on rocks that never left the Red Planet."

The Beagle 2 lander would have looked for signatures of life on Mars, whether long-dead or still-living, by measuring the ratio of two different types of carbon in the rock. Biological processes on Earth favour the lighter isotope of carbon, carbon-12, over the heavier carbon-13. Hence, a high carbon-12 to carbon-13 ratio is taken as evidence of life and has been found in rocks up to 4000 million years old, even where geological processing has occurred.


On Earth, some life that is still active produces another signature - methane. The simplest biological sources, such as those associated with peat bogs, rice fields and ruminant animals, continuously supply fresh gas to replace that destroyed by oxidation.
Methane also has a very short lifetime on Mars because of the oxidising nature of the atmosphere, so its presence would indicate a replenishing source, which may be life, even if it is buried beneath the surface. If this methane exists, the Mars Express orbiter's PFS intrument will be able to detect this gas in the atmosphere.

The only previous landers to look directly for evidence of life on Mars were NASA's Vikings in 1976. However, Mars's harsh, oxidising atmosphere would almost certainly have destroyed any such evidence on the surface.

The Highest Volcano in the Solar System

Olympus Mons, 25 kilometres high, is the highest volcano in the Solar System
It has the highest volcano in the solar system, Olympus Mons which stands at 26 kilometres above the surrounding plain: Mount Everest is only one third as high.

Olympus Mons lies at the western edge of another gargantuan feature, the Tharsis dome which is a 10 kilometre-high, 4000 kilometre-wide bulge in the Martian surface.

Size comparison between Earth and Mars

Then there is the Hellas Basin in the southern hemisphere, which is an enormous impact crater 2300 kilometres in diameter and more than nine kilometres deep.

But perhaps most striking of all is the general difference in height and surface roughness between the northern and southern hemispheres. The northern hemisphere is smooth and flat and on average six kilometres lower than the rugged highlands of the south.

Geography of Mars

Although Mars is a small planet – its radius is just a little over half of Earth's – we now know that it boasts scenery on a scale that makes Mount Everest and the Grand Canyon seem unimpressive by comparison.

Running from the eastern flanks of the rise, roughly along the equator, is Valles Marineris.
This is a split in the Martian crust 4000 kilometres long (about a fifth of the distance around the whole of Mars), up to 600 kilometres wide and seven kilometres deep. The Grand Canyon is a mere 450 kilometres long, up to 29 kilometres wide and 1.6 kilometres deep.

The Valles Marineris hemisphere of Mars

Was There Water On Early Mars?

Valley Networks

Not only does Mars have the largest volcanoes and deepest canyons in the Solar System, it also shows evidence for the most catastrophic floods. Large channels carved by these floods drain into the northern plains, lending support for the existence of an ancient ocean over most of the northern hemisphere. Valley networks that criss-cross the southern highlands were also probably formed by water. And many craters, especially at high latitudes, are surrounded by fluidise ejecta resembling the ring of splattered debris around a stone dropped in soft mud. This suggests that there was underground water or ice in early times, and possibly more recently.

Water sees

If water was largely responsible for these features, however, it has long since disappeared: most of the evidence is more than 3800 million years old. When Mars was a mere infant (like Earth, the planet is 4500 million years old) much of its atmosphere and all of any surface water vanished. Today, atmospheric pressure at ground level is only about one hundredth that on Earth. So where did the atmospheric gases and water go and why? Each of the seven instruments on board the Mars Express orbiter will contribute towards the answer.


Artist’s impression of water under the martian surface.

The water could have been lost to space, trapped underground, or both. Four of the instruments on Mars Express (ASPERA, SPICAM, PFS and MaRS) will observe the atmosphere and reveal processes by which water vapour and other atmospheric gases could have escaped into space. Two instruments (HRSC, OMEGA) will examine the surface and in the process add to knowledge about where water may once have existed and where it could still lie underground. One (MARSIS) will actually look for underground water and ice.


Perceptions have changed about how much water may have existed on early Mars

Behind The Lens

The High Resolution Stereo Camera (HRSC)

This is the camera behind the stunning European imagery from Mars. The High Resolution Stereo Camera on ESA’s Mars Express is now mapping most of the Martian surface with unprecedented detail.

The HRSC was originally designed for the Russian Mars ’96 space mission. After an unsuccessful launch in November 1996, the back-up model of the camera was modified for use on the European Mars Express mission. Another version, the HRSC-AX, has been built for airborne high-resolution 3D Earth reconnaissance and has already been used in a large number of projects.

The main part of the HRSC, the Camera Head, has a resolution of 10 metres per pixel at an altitude of 250 kilometres, the point of closest approach to Mars. The Super Resolution Channel (SRC) part is the high resolving channel with a resolution of down to 2.3 metres per pixel. The whole unit measures only 515 mm by 300 mm. SRC images will provide the most detailed information about areas of special interest, for example the examination of future landing sites.
The imaging electronics of the HRSC are based on the principle of a ‘linescan’ camera. This means only a line is exposed to the light, and not an area (like on ordinary 35 mm film). One CCD line of the HRSC consists of 5184 light-sensitive cells (pixels). The HRSC has nine of these lines, one for each imaging channel. The CCD exposure time is adjusted to match the ground velocity of the spacecraft.


Three channels are sensitive to the spectral ranges of red, green and blue. Another one obtains data in near-infrared. Then there are three stereo channels which are used to the digital terrain models – these take angled views to get a downward, backward and a forward-view of the surface.

From these different views, you can derive three-dimensional images. The last two channels are two photometric channels, giving data for the physical analysis of the Martian surface.

The SRC is the second part of the HRSC camera system and uses an area sensor. This means the light intensity is measured by a matrix of 1024 by 1032 elements. This produces a picture of 1024 x 1032 pixels and, from an altitude of 250 kilometres, this corresponds to a square on the Martian surface with sides of length 2.35 kilometres, each pixel representing 2.3 metres.

Normally, the main camera and the SRC work simultaneously, because of the difficulty in locating the SRC images on the Martian surface. The high-resolution SRC images are nested in the HRSC strips, giving very detailed information about areas of special interest.

The Visual Impact of Space

ESA participates in a certain number of exhibitions throughout its Member States, including the major international air shows in Europe and conferences and congresses within the space community.

Different levels of information are required for a varied audience – from the specialist to the uninitiated - and a range of material is produced and regularly updated that is geared towards the general public.

This material can be downloaded from this site free of charge for use in exhibitions for the public. We hope that you will find it interesting and useful.

Below are some images of ESA exhibits.

Ariane 5 upper stage at ILA 2006


A preliminary design concept of ExoMars at ILA 2006


The Columbus Laboratory model at ILA 2006


Galileo at Farnborough International 2006


The ESA pavilion at the 45th International Air and Space Show

Searching for life in the Solar System

New exhibition material

3 February 2010 ESA has updated an interactive demo and visuals on its space missions that are studying the origins and evolution of life in the Universe.

How did life appear on Earth?


For life to appear on Earth, the presence of water was certainly necessary. Scientists are currently studying three possible sources of life:

-Deep-sea vents: In an environment where light and oxygen do not exist, methane is often a key element for life to form, such as in underwater hot springs in the oceans.

- Icy oceans: Simple life forms capable of photosynthesis could have evolved in the oceans, protected from the deadly effects of ultraviolet radiation by icy crusts in the colder regions.

- Space: Bacteria almost certainly travelled on comets and meteorites between planets, and thus could also have been brought to Earth in this way.



Description
The HRSC on ESA's Mars Express obtained this perspective view on 2 February 2005 during orbit 1343 with a ground resolution of approximately 15 metres per pixel.
It shows an unnamed impact crater located on Vastitas Borealis, a broad plain that covers much of Mars's far northern latitudes, at approximately 70.5° North and 103° East.

The crater is 35 kilometres wide and has a maximum depth of approximately 2 kilometres beneath the crater rim. The circular patch of bright material located at the centre of the crater is residual water ice.

The colours are very close to natural, but the vertical relief is exaggerated three times. The view is looking east.