Life on Mars and elsewhere
Well, it appears that interesting science stories are like buses, you wait ages for one and then two come along together. Although in this case the two stories are related. For it appears that extraterrestrial life may be further away than we hoped, but closer than we feared. That’s if two recent scientific studies are to be believed.
The first one appeared in this week’s Science and speculates that although Mars may well have played host to liquid water in the past, this water was probably too salty to harbour life. The second was presented yesterday at the American Astronomical Society meeting in St. Louis, Missouri, and reports the discovery of the smallest extra-solar planet yet detected orbiting a star.
With exquisite timing, seeing as Nasa’s Phoenix spacecraft has just landed on Mars to search for signs of life, US researchers led by geochemist Nicholas Tosca have suggested that there may be no signs to find. They deduced this by analysing data on salt deposits detected by Nasa’s Mars rovers.
Initially, the detection of these salt deposits raised hopes that life may once have existed on Mars, because on Earth they only form in the presence of water. But by taking fluid chemistry and saline mineralogy into account, Tosca and his team have concluded that these deposits formed in water that was much saltier than any found on Earth. And far too salty for life to have developed within it.
This is the latest in a long line of scientific speculations on the likelihood of life on Mars, with every positive finding seemingly counteracted by a negative one. For instance, just after the Mars rovers found the salt deposits, US researchers announced that Mars has probably always been too cold for liquid water. This was based on their analysis of argon levels in Martian meteorites that had landed on Earth.
Overall, though, it does increasingly seem like the odds are lengthening on Mars ever having been able to support life, especially as the negative findings now seem to be supporting each other. For if the water that used to flow over the surface of Mars was very salty that could explain how it was able to exist at sub-zero temperatures, because salty water freezes at lower temperatures than pure water.
But if extraterrestrial life is looking increasingly unlikely on Mars, it might still not be too far away. This possibility stems from the detection of a planet only three times more massive than Earth by an international team of astronomers led by David Bennett from the University of Notre Dame, US.
This is the smallest extra-solar planet ever discovered and was a detected using a gravitational microlensing technique, which involves monitoring the deflection of light emitted from a background star by the gravity of a nearer planet. The astronomers also found that the planet orbits around a very small star, only around 6–8% the size of the Sun.
According to Bennett, this finding implies that Earth-size planets are probably quite common, especially around small stars. Furthermore, if some of these planets orbit at the just right distance away from the star, then life could well have developed on them.
There are quite a few low mass stars close to the Sun, some of which may possess habitable Earth-like planets. They may even be close enough for the James Webb Space Telescope, which is a new infrared space telescope due for launch in 2013, to search for signs of life on them.
So although extraterrestrial life may not be next door, it could be just down the street.
