The earliest writers dreamt of life on the planets in our solar system; the Aborigines have stories dating thousands of years about the Dreamtime and how we came from the stars. The satirist Lucian (120 – c185 AD) claims in “A True Story” to have visited the moon after his ship was caught in a whirlwind which sends them to the Moon: a place inhabited by beings at war with the people of the Sun over the colonisation of the Morning Star, Venus. The title of first science fiction writer is most likely his!
Lucian. H.G. Wells.
In more recent times we had HG Wells’ ‘War of the Worlds’ (1897) followed a few years later by the astronomer Percival Lowell’s canals on Mars (1906) – where he believed he saw artificial canals, going so far as to draw them – to the idea that Venus might contain dinosaurs we have always been desperate to find life “out there”.
Looking for life beyond Earth is one of the most fascinating, exciting and difficult things to do. Every time we think we might have found a clue a discovery comes along to challenge us.
Modern research looks for ‘bio-markers’; these are chemicals that could only be present as a result of life. Nothing has been found (so far!!) in the solar system so the search has broadened into he universe to the exo-planets, the worlds around distant stars.
How do you find which gasses are present in a world in another solar system? It seems that the size (diameter) of the planet plays a role in whether we can detect atmospheres; a recent report in the Astrophysical Journal (https://arxiv.org/abs/1704.05413) goes into more detail. According to Angelos Tsiaras, the lead author, “More than 3,000 exoplanets have been discovered but, so far, we’ve studied their atmospheres largely on an individual, case-by-case basis.”
Using the Hubble Space telescope researchers looked at the spectral profiles of 30 exoplanets and analysed them for the characteristic fingerprints of gases that might be present. About half had strongly detectable atmospheres. Most of the atmospheres detected show evidence for clouds. The two hottest planets, where temperatures exceed 1,700 degrees Celsius, appear to have clear skies, at least at high altitudes. Results for these two planets indicate that titanium oxide and vanadium oxide are present in addition to the water vapour features found in all 16 of the atmospheres analysed successfully.
It is not only ‘Hot Jupiters’ that have had their atmospheres analysed: in April 2017 it was announced that Gliese 1132b, a super-earth, (that is a planet with a diameter upto 40% greater than the Earth’s) atmosphere had been detected. This is a major step in detecting signs of life in more earth like planets. (https://arxiv.org/abs/1612.02425)
How do astronomers detect the atmospheres? Well as a planet passes in front (transits) its host star the light from the star dims slightly; the planet blocks some of the light and the atmosphere absorbs some of the star light. If the composition of the star’s atmosphere is already known, when the planet transits the star, the planet’s atmosphere absorbs some of the starlight and changes what chemicals we can see from the starlight. It Is then possible to work out the composition of the planet’s atmosphere by the effect it had on the starlight.
The chemicals that astronomers look for when seeking life are called ‘bio-markers.’ They include Oxygen and Methane, which tend to be the product of organic processes and a chemical known as Freon-40. This latter was hoped to be a good indicator but, like Lucian’s moon people or Lowell’s canals things are not what they seem.
Organohalogen methyl chloride (Freon-40) discovered by ALMA around the infant stars in IRAS 16293-2422
Freon-40 (CH3Cl), also known as methyl chloride. is known as an organohalogen; these are compounds which on Earth are formed by organic processes. Organohalogens consist of halogens (the inert gasses of the periodic table), such as chlorine and fluorine, bonded with carbon and sometimes other elements. On Earth, these compounds are created by some biological processes — in organisms ranging from humans to fungi — as well as by industrial processes such as the production of dyes and medical drugs.
The idea was if Freon-40 is formed naturally on or earth or through artificial means then its detection in an exo-planet’s atmosphere would be a very good indicator of life, however that hoped has been dashed as Observations made with the Atacama Large Millimeter/submillimeter Array (ALMA) and ESA’s Rosetta mission, have revealed the presence of Freon-40 in gas around both an infant star and a comet. The star lies 400 light years way, the comet is the famous 61/P Churyamov-Gerasimenko; this is the comet that saw the European Rosetta probe orbit it and send the little lander Philae to its surface.
This is the first ever detection of them in interstellar space.
This chart shows the location of the Rho Ophiuchi star formation region in the constellation of Ophiuchus. The star Rho Ophiuchi, which gives the region its name, is marked with the Greek letter rho (ρ). The position of IRAS 16293-2422, a young binary star with similar mass to the Sun, is marked in red.
This may mean that astronomers have understood things the wrong way round; rather than being a marker for life perhaps it is a necessary constituent of the ‘primordial soup’ from which life arises:
“ALMA’s discovery of organohalogens in the interstellar medium also tells us something about the starting conditions for organic chemistry on planets. Such chemistry is an important step toward the origins of life,” adds Karin Öberg, a co-author on the study.
This isn’t the only chemical that ALMA has detected, other molecules of astrobiological interest found around young stars on scales where planets may be forming have precursors to sugars and amino acids.
The discovery of Freon-40 around Comet 67P strengthens the idea that what we see in the pre-biological chemistry of distant protostars may have been what we would have seen in our own Solar System. It would seem that young solar systems inherit some of their chemical characteristics from their parent star forming cloud and then from cometary impacts.
ALMA the Atacama Large Millimeter/submillimetrer Array.
It just shows, that when you think you may be onto a clue the Universe has different ideas!