Life on Mars is one of the most well known subjects concerning our star system to everyday people. Whether it be from science fiction movies, television series or books, or from the various missions to the planet in recent years, speculation on the issue has been thought about by my most people to some extent. Not too long ago, before the age of space exploration, it was still thought possible that Mars was inhabited by a current civilization, which we now know to be untrue. However, this does not rule out the possibility that life once did exist on the red planet, to whatever degree it did and for however long.
Observers from Earth prior to the age of space exploration noticed that the polar ice caps of the planet had a cycle of growth and shrinkage over the years, and that Mars had somewhat similar conditions to the Earth, in that its length of day was very close to that of the Earth, and that it experienced seasons in a similar fashion to Earth due to its axial tilt, although its year was longer than that of Earth.
Formations known as canals were sighted by astronomers and the darker features of the planet, like with the Moon, were thought to possibly be areas of water, whereas the lighter features were thought to possibly constitute land similar to Earths continents. In the late 1800s the notion of life on Mars rapidly became more popular as these canals were studied by telescope. However they were found to be mere illusions. American astronomer Percival Lowell theorized that the canals were the work of a civilization, like the canals on Earth. In 1897 these theories prompted science fiction writer H G Wells to write The War of the Worlds, about an invasion from Mars.
However scepticism on the issue was raised when in 1894 American astronomer William Wallace Campbell did spectroscopic tests of the planets atmosphere, showing that there was no oxygen present. The canal theory was ended in the early 1900s with improvements to telescopic technology.
In 1965, Mariner 4, a satellite, did a fly by of the planet, revealing its surface to be lifeless and barren. It showed that due to various factors, such as the low atmospheric pressure and lack of a magnetic field, no life could presently live there. At this point we enter the modern era of search for life on Mars, the search for microscopic organisms which could perhaps survive such extreme conditions as they have been shown to on Earth.
The Viking missions tried to find bacterial life on Mars in the 1970s. Much data was collected. However it was shown that since Mars lost its magnetic field 4 billion years ago (when Earth was still forming) , solar wind reaches the surface uninterrupted, which would make life on the planet impossible. Liquid water could not exist on the planet’s surface due to its low atmospheric pressure.
However several meteorites from Mars have been studied, and some show traces of bacteria like formations. Despite this there is no direct evidence for nanobacterial life forms.
