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From the Earth, Mars is easily seen in the night sky as a red star-like object that moves through the sky with a period of just over two years.
Mars as seen by the Hubble Space Telescope
As the orbit of Mars is an eccentric ellipse its distance from the Earth at opposition (closest approach to the Earth) varies between 1.38 and 1.67 Astronomical Units (the mean distance of the Earth from the Sun is one Astronomical Unit).
Seen through a telescope Mars appears as a small reddish disk on whose surface dark markings can (with difficulty) be seen. Also visible is one or other of its polar caps.
Even at its closest to the Earth Mars is seen as a disk with a diameter of only 25 arcseconds and so with a small telescope very little can be seen. Even with large telescopes it is very difficult to see detail and many experienced observers were deceived into thinking that they had glimpsed features, such as the infamous canals, that in fact were not there.
Almost all that we know about the surface of Mars and its atmosphere were discovered by the various space probes that have orbited the planet and landed on its surface.
What we know
We know that the atmosphere of Mars has a pressure less than one hundredth of the Earth's and that it is composed mainly of carbon dioxide with a little nitrogen and argon; there is almost no oxygen. There is a small amount of water vapour which condenses in some places to give thin clouds and fog. There are polar caps at each pole which grow in the Martian winters, with the addition of deposits of solid carbon dioxide, and decrease in the Martian summers to leave what is thought to be a small residue of ordinary water ice.
Image credit: Mars Orbitting Laser Altimeter Science Team, Mars Global Surveyor.
The surface of Mars shows impact craters, like the Moon, mountains, rift valleys, ridges, hills plains and extinct volcanoes. There are signs that water existed on the surface at some earlier stage of the planet. Winds can be very severe and are responsible for extensive weathering of the rocks on the surface. Sometimes the winds blow up enormous sandstorms that obscure the view of the planet's surface. The surface temperatures on Mars can rise to about 0°C in the summer but fall to near -100°C before sunrise.
Mars rotates in 24 hours and 37 minutes about an axis tilted by 24° to its orbital plane. Although it is only 6794 km in diameter it is probably the most Earthlike of all the planets. There are some suggestions that it might be possible to alter the planet's atmosphere sufficiently to enable a permanent base to be set up there. Until that is done Mars will represent a very hostile environment for any human visitor.
Mars has two moons, Phobos and Deimos. They are both very small, both being less than 30 km across. It is likely that they were both asteroids that have been captured by Mars. Phobos is very close to Mars and its orbital period is less than the rotational period of Mars. It thus would be seen to rise in the west and set in the east! Deimos is further away from Mars and would be seen to behave more conventionally.
Is there life on Mars?
The early months of 2004 proved a testing time for the European Beagle and American Mars Exploration Rover Mission. Unfortunately Beagle 2 was lost in transmission. However, Nasa celebrated the result of life from their Mars Rover.
More information and images are available on the NASA website.
On 15 of July 2004, ammonia was detected in the Martian atmosphere using a Planetary Fourier Spectrometer on Mars Express and was detected by looking at the spectral signature detected on the European Space Agency’s orbiting Mars Express craft.
The components of ammonia are Hydrogen and Nitrogen. Nitrogen is an element which is rare and is usually only produced by two methods:
We also have to take into consideration the presence of Methane in the atmosphere, which is another component that could be the indicators of simple life on the planet.
Update: recent Mars missions
In the last few years results from the Mars Global Surveyor (MGS) and Pathfinder probes have enhanced our knowledge of the Red Planet.
The Pathfinder lander arrived in July 1997 and was the first mission to operate a robotic rover (Sojourner) on the Martian surface. The landing site was an ancient flood plain strewn with rocks carried a great distance. This allowed Sojourner to sample many different types of rock and send back closeup images. In addition, Pathfinder obtained a detailed photomosaic of the view from its location. After landing, Pathfinder was renamed the Sagan Memorial Station in honour of the late Carl Sagan.
MGS entered Martian orbit in September 1997 and used drag from the planet’s atmosphere to reduce its altitude (a process known as 'aerobraking’) so that it could obtain higher resolution images. It entered its final mapping orbit around Mars in February 1999. The images MGS has transmitted to Earth have much higher resolution than those obtained by the Viking orbiters in the 1970s.
The Martian 'Face' unmasked
In the 1970s the Viking orbiters imaged a feature in the Cydonia region on Mars which resembled a human face. A small number of people suggested that this was an artificial construction, similar to the pyramids on Earth and a relic of an ancient Martian civilisation.
On 5 April 1998 MGS's Mars Orbiter Camera took a higher resolution image of this feature. It is located at 40.8°N and 96°W and the spacecraft was at a distance of 275 miles (444km). The morning sun was 25°above the horizon. The resolution was 4.3 metres/pixel, 10 times greater than in the previous image of the same feature taken by the Viking missions in the 1970’s. The full picture covers an area of 2.7 miles (4.4km) wide and 25.7 miles (41.5km) long.
With this new image, the resemblance to a human face vanishes. It is apparent that 'The Face' is merely a hill on the Martian surface and that illumination from the Sun at a low angle and the lower resolution of the Viking cameras were responsible for this illusion.
Liquid water on the Martian surface
On June 22 2000 NASA announced that MGS had observed features suggesting the current presence of liquid water on or near the surface of the planet.
The features resemble those left by terrestrial flash floods such as gullies and deposits of soil rocks. Previous images from the Mariner and Viking programmes in the 1960s and 70s had indicated channels and valleys eroded by water over 3 billion years ago. The new features appear to be extremely young, giving a strong possibility that they formed within the past few million years and that some are forming to this day.
Water appears to flow out from cliffs in crater or valley walls. The very low atmospheric pressure on Mars would make liquid water boil violently when it reached the surface. The water must flow in large quantities - flash floods - so it can move a short distance before it evaporates completely.
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