Millions of celestial objects could carry life
– News of October 15, 2018 –
The origin of life is usually a question studied by biology. But this is also of interest to astronomers, with a hypothesis involving celestial objets. This hypothesis is called panspermia. The idea is that life could have been transported to Earth by asteroids or comets. This hypothesis dates from several centuries ago, but the discovery of extremophilic organisms accredit this hypothesis. Some species can survive and reproduce at temperatures and levels of radiation previously thought to be incompatible with life. Since then, numerous orbital experiments have been conducted to observe the survival capacities of certain microorganisms in space. Spores of the bacterium Bacillus subtilis have survived nearly six years in orbit, protected by materials simulating a meteor. The panspermia hypothesis does not solve the origin of life but rather proposes to move the question. If we admit that life did not appear on Earth, then it may come from another planet, the main asteroid belt, the Oort cloud or some other system.
A team from Harvard University wondered whether life would be able to spread through a whole galaxy or even between galaxies. The idea of the study comes from the discovery of Oumuamua, the first interstellar object detected in the solar system a year ago. It is still impossible to give definitive answers to this question, but we can study several variables, that is to say the quantity of objects exchanged between the different planetary systems, the velocity of these objects and the maximum life expectancy of a life form aboard an object rushing into space. Their calculations estimate that the various systems of the galaxy have already exchanged billions of objects. Of these, nearly 100 million objects could carry life. These are enough numbers to allow life to spread throughout the galaxy, or even from one galaxy to another on board stars.
These are for the moment only speculations because it remains impossible to accredit or discredit this hypothesis before having found life on another celestial object than the Earth. If it were to happen one day on the planet Mars, on Titan or on Europe for example, then we would have some tracks to explore. For example, the presence or absence of DNA and genetic similarities could indicate that life has a common origin. In the meantime, life remains a terrestrial miracle that we still have difficulty understanding.
Image by Silver Spoon Sokpop [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons
