Note: You can click on each image below to view a larger version.
| The question of
whether there is, or has ever been, life on Mars is still open. The atmosphere is less than a hundredth of the
thickness of ours, leaving the surface exposed to a high level of ultraviolet radiation from the Sun.
RIGHT: Mars, with Valles Marineris winding across the centre of the image. |
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It is also cold, and even at the equator the maximum summer temperature is only 22C. Even then, it would fall to around -110C during the night, and typical Martian temperatures are comparable to the Antarctic.
However, it is possible that some micro-organisms could survive in more sheltered spots. Mars has polar ice caps consisting of carbon dioxide ice and water ice, and there may be widespread deposits of ice beneath the surface elsewhere. Initial results from the Phoenix mission, which landed on the northern arctic plain on May 25th 2008, appear to confirm that water ice exists just under the surface of the soil there.
The surface itself is a rocky desert of red sand, beneath a pink sky. There are craters, extinct volcanoes, and a giant canyon complex called Valles Marineris, which runs for over 2800km. The craters were actually seen from Earth by the American astronomer E. E. Barnard in the 19th Century, but he didn't publicise his observation because he thought that nobody would believe him! There are even winding channels that could be dry riverbeds. This implies that the Martian atmosphere was considerably thicker in the distant past, as any open body of water on the surface nowadays would quickly boil away due to the low atmospheric pressure.
However, some recent observations from the Mars Global Surveyor spacecraft have been interpreted as evidence of water flowing down the interior wall of a crater.
The picture above was taken by NASA's Mars Pathfinder, which landed in Ares Vallis, an area thought to be an ancient flood plain, in 1997. Pathfinder carried a small rover named Sojourner, which can be seen examining the large rock near the centre of the picture. Parts of the lander can be seen at the bottom of the picture, including the deflated remains of the airbags used to cushion the impact of landing.
NASA currently has two more advanced rovers, named Spirit and Opportunity, examining the surface of Mars in unprecedented detail. They landed in January 2004, but to the surprise even of the engineers who designed them they are still going strong.
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Each rover has a mechanical arm, known as the Instrument Deployment Device, which allows it to position a set of scientific instruments next to rocks and other surface features. This includes a rock abrasion tool (RAT) which can be used to drill into a rock or brush soil away from its surface, as shown in the picture at left. |
Their most important result to date has been to provide strong geological evidence that liquid water definitely was present on Mars in the past. Opportunity's landing site in Meridiani Planum appears to have been a shallow, salty sea at one time.
A variety of further Mars missions are planned. Both NASA and the European Space Agency intend to launch sample return missions during the next decade, to return Martian rocks and soil to Earth for analysis.
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| Another close-up of the surface from the Spirit rover | |
Olympus Mons, a volcano three times the height of Mount Everest |
Mars has two moons, Phobos and Deimos, which are so small that they are thought to be asteroids which were captured by the planet's gravitational pull at some point in the past.
 Phobos as seen by the ESA's Mars Express orbiter; the largest crater is called Stickney, and is about 5km across |
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 Deimos as seen by NASA's Viking 1 orbiter; many of the craters are partially obscured by a thick layer of dust, known as "regolith" |
Mars looks like a reasonably bright reddish-orange star to the naked eye or in binoculars, but through a telescope it appears as a small disk. The polar caps and a variety of dark markings can be seen. At times there are great dust storms on Mars, which can obscure the whole surface.
The two moons can only be seen in a very large telescope.
URL: http://www.randomnotes.co.uk/Astronomy/Marsprint.htm