Extrasolar panspermia: are we the aliens?

Tuesday 21st November, 2017

Our speaker was James Blake who is studying for his doctorate at Warwick University. He introduced himself by saying he is in the first year of his post-graduate studies and was a co-founder of the astronomical society at the University. One of his undergraduate projects was studying the subject of panspermia in planets in other solar systems, and so he chose to talk to us about "Extrasolar Panspermia: Are We The Aliens?".

He began by explaining that the term "panspermia" comes from the ancient Greek words meaning "all" and "seed". It is the theory that life can originate somewhere and then be transported to other worlds. He then said that this theory can be split into different models and the earliest one is known as "radiopanspermia" by the chemist Svante Arrhenius in 1903 whereby microscopic lifeforms less than 1.5 micrometres in size could be pushed through space by the Sun's radiation. Unfortunately, we now know from various experiments actually carried out in space that the Sun's radiation will kill any unprotected organism.

Another idea is "directed panspermia", put forward by the biologist Francis Crick and chemist Leslie Orgel in 1973. This needs an advanced alien civilization to actually transport life from one place to another. At present, none of the searches for extraterrestrial intelligent life have yielded results so the jury is still out, so to speak.

A further idea proposed by the astronomers Fred Hoyle and Chandra Wickramasinghe is called "pseudo-panspermia" where some of the building blocks of life, organic molecules, are formed in space. Evidence for this theory has come from laboratory experiments in 2015 that managed to form complex DNA and RNA compounds in conditions that imitated those of outer space. Also in 2016 the Rosetta spacecraft recorded the presence of organic molecules in the dust ejected from a comet.

Mr Blake continued by saying that his preferred theory was known as "lithopanspermia" where life could form on a planet and then be carried to other worlds inside asteroids or comets. The advantage with this method is that lifeforms are protected from space radiation, although they would need to survive ejection from their home world and re-entry onto their new home as well as the conditions in space.

One of the recently discovered system of seven planets outside our own Solar System, i.e. exoplanets, is called the TRAPPIST-1 system after the telescope that discovered it. Mr Blake was hopeful that this system, in theory, was stable enough for life to evolve on one of the planets and then transfer to other planets as they were so close to each other. However, with further scrutiny, it turns out that the central star is rather turbulent and emits lethal blasts of radiation that encompasses these planets.