A fundamental question in astrobiology is: whether life can be transported between extrasolar planets, planetary systems? A team of U.S. astrophysicists proposes a new strategy to answer this question based on the principle that alien life which arose via spreading – in a process called panspermia – will exhibit more clustering than life which arose spontaneously.
In this theoretical artist’s conception of our Milky Way Galaxy, green ‘bubbles’ mark areas where alien life has spread beyond its home system to create cosmic oases, a process called panspermia. Image credit: NASA / JPL / R. Hurt.
There are two basic ways for life to spread beyond its host star.
The first would be via natural processes such as gravitational slingshotting of asteroids or comets. The second would be for intelligent life to deliberately travel outward.
A new paper, accepted for publication in the Astrophysical Journal Letters (arXiv.org preprint), does not deal with how panspermia occurs. It simply asks: if it does occur, could we detect it? In principle, the answer is yes.
The model developed by the team at the Harvard-Smithsonian Center for Astrophysics assumes that seeds from one living planet spread outward in all directions.
If a seed reaches a neighboring planet with the conditions just right for potential life, it can take root. Over time, the result of this process would be a series of life-bearing oases dotting the galactic landscape.
“In our theory clusters of life form, grow, and overlap like bubbles in a pot of boiling water,” said Dr Henry Lin, lead author on the study.
If we detect signs of life in the atmospheres of alien worlds, the next step will be to look for a pattern.
For example, in an ideal case where the Earth is on the edge of a ‘bubble’ of life, all the nearby life-hosting worlds we find will be in one half of the sky, while the other half will be barren.
The astrophysicists caution that a pattern will only be discernible if life spreads somewhat rapidly.
Since stars in our Galaxy drift relative to each other, stars that are neighbors now won’t be neighbors in a few million years. In other words, stellar drift would smear out the bubbles.
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Henry W. Lin & Abraham Loeb. 2015. Statistical Signatures of Panspermia in Exoplanet Surveys. ApJL, accepted for publication; arXiv: 1507.05614
