Under the Microscope/Prof William Reville: In our solar system, Earth is the third and Mars is the fourth planet from the sun. Mars is about one and a half times as far from the sun as Earth. The more we investigate Mars, the more interesting it becomes.
The finding by NASA's Mars exploration rovers, Spirit and Opportunity, that liquid water once flowed on Mars was the most significant scientific discovery of 2004.
To my knowledge, we have no evidence yet that liquid water is currently on Mars, but who knows what we will find tomorrow. There is a good probability that life existed on Mars in the past when copious water was present. If so, some of this life may still persist.
The mass of Mars is about one-tenth the mass of the Earth and its surface area is about the same as the land surface area of Earth. Gravity on Mars is about one-third as strong as gravity on Earth. The Martian year is about 1.9 times the Earth year and the Martian day is 24 hours, 37 mins, and 22 seconds. Average surface temperature on the planet is -55 degrees with a minimum temperature of -133 degrees and a maximum temperature of 27 degrees. The atmosphere of Mars is 100 times thinner than the Earth's and consists of carbon dioxide (95.32 per cent), nitrogen (2.7 per cent), argon (1.6 per cent), oxygen (0.13 per cent), carbon monoxide (0.07 per cent), water (0.03 per cent) and trace amounts of neon, krypton, xenon, and ozone.
Mars has two natural satellites, Phobos (fear) and Deimos (panic). These two small moons were named after the horses that pulled the chariot of the Greek war god Ares. The moons appear to have surface materials similar to asteroids in the outer asteroid belt which leads most scientists to believe that Phobos and Deimos are captured asteroids.
Mars has a highly varied and interesting surface terrain, including Olympus Mons the largest mountain in the solar system, rising 24km above the surrounding plane. Its 500km diameter base is rimmed by a cliff 6km high. The southern hemisphere of Mars is largely ancient cratered highlands and most of the northern hemisphere consists of plains that are much younger. It is likely that internally Mars contains a dense core about 1,700km in radius, a molten rocky mantle and a thin outer crust. Mars seems to have no active movement of crustal plates (plate tectonics) at the moment.
Mars was much more like the Earth in it's early history. Most of the carbon dioxide was scavenged from its early atmosphere to form carbonate rocks. Unlike the Earth, with its active plate tectonics, Mars is unable to recycle any of the carbon dioxide from the rocks back into the atmosphere and cannot build up a significant greenhouse effect. Mars therefore has a much colder surface than the Earth would have if it orbited the sun where Mars orbits now. Even though the atmosphere on Mars is very thin it is still substantial enough to carry very strong winds and dust storms that can engulf the entire planet for months.
We have known for a considerable time that Mars has polar icecaps composed of water ice and "dry ice" (frozen carbon dioxide) that grow and shrink with the changing seasons. Water ice may also exist at lower latitudes, hidden below the surface. In 2004 NASA's exploration rovers, Spirit and Opportunity, uncovered unambiguous geological and chemical evidence that liquid water once flowed on Mars. Commenting on the results sent back from one of the landing sites, Meridiani Planum, a NASA scientist said, "Liquid water was once intermittently presently at the Martian surface at Merriadiani, and at times it saturated the subsurface. Because liquid water is a key prerequisite for life, we infer conditions at Meridiani may have been inhabitable for some period of time in Martian history."
In order to confirm whether life existed on Mars we will have to examine rock samples for fossils. It is believed that the type of rocks found on Mars would be a good preserver of fossils. The earliest date for the launch of a sample return mission is 2011.
In 1976, the Viking landers carried out experiments to detect the existence of life on Mars. The results were not clear-cut but few scientists believe they show evidence for life on Mars. In 1996 is was announced that fossils of an ancient Martian micro-organism were present in the Martian meteorite ALH84001. Further consideration of this data has cast considerable doubt over the validity of the announcement and the general scientific community believes that this question is still entirely open.
In July 1976 when searching for a landing site for the Viking 2 Lander, photographs were taken of "The Face on Mars". Some people proposed that the face was artificial, not a natural feature, and proved an intelligent civilisation once lived on Mars. More detailed pictures later showed that the face is almost surely a formation of rocks that accidentally resembles a face.
Mankind has known Mars since prehistoric times, and it continues to fascinate us. I can well remember staying up all night in my digs in Ranelagh to watch the live TV transmission of Neil Armstrong's stepping onto the moon in 1969. The next major human adventure in space will be a manned-mission to Mars. I'm sure we all look forward to repeating this experience, this time with Mars, in the not too distant future.
William Reville is associate professor of biochemistry and director of microscopy at UCC