One hundred thousand billion free-floating planets in the Milky Way?

An international group of scientists led by the University of Buckingham in UK has claimed that life-bearing planets may exist in vast numbers in the space between stars in the Milky Way.

An artist's concept shows a planet floating freely through the Milky Way galaxy. Credit: NASA/JPL

Their findings, published online in the journal Astrophysics and Space Science, suggest that a few hundred thousand billion free-floating life-bearing Earth-sized planets may exist in the space between stars in the Milky Way.

The researchers have proposed that these life-bearing planets originated in the early Universe within a few million years of the Big Bang, and that they make up most of the so-called missing mass of galaxies.

The group calculated that such a planetary body would cross the inner solar system every 26 million years on the average and during each transit, zodiacal dust, including a component of the solar system’s living cells, becomes implanted at its surface. The free-floating planets would then have the added property of mixing the products of local biological evolution on a galaxy-wide scale.

Since 1995, when the first extrasolar planet was reported, interest in searching for planets has reached a feverish pitch. The 750 or so detections of exoplanets are all of planets orbiting stars, and very few, if any, have been deemed potential candidates for life.

The possibility of a much larger number of planets was first suggested in previous studies where the effects of gravitational lensing of distant quasars by intervening planet-sized bodies were measured. Recently several groups of investigators have suggested that a few billion such objects could exist in the galaxy.

Prof. Chandra Wickramasinghe, a lead author and Director of the Buckingham Centre for Astrobiology at the University of Buckingham, and his colleagues increase this grand total of planets to a few hundred thousand billion – a few thousand for every Milky Way star – each one harboring the legacy of cosmic primordial life.

Here is the abstract of the paper, published on May 8th:

The space density of life-bearing primordial planets in the solar vicinity may amount to ∼8.1×10⁴ pc⁻³ giving total of ∼10¹⁴ throughout the entire galactic disk. Initially dominated by H₂ these planets are stripped of their hydrogen mantles when the ambient radiation temperature exceeds 3 K as they fall from the galactic halo to the mid-plane of the galaxy. The zodiacal cloud in our solar system encounters a primordial planet once every 26 My (on our estimate) thus intercepting an average mass of 10³ tonnes of interplanetary dust on each occasion. If the dust included microbial material that originated on Earth and was scattered via impacts or cometary sublimation into the zodiacal cloud, this process offers a way by which evolved genes from Earth life could become dispersed through the galaxy.

Sources:

• John Shanks, Free-Floating Life-Bearing Planets May Exist in Vast Numbers in Milky Way, Sci-News.com, May 10, 2012
• N. Chandra Wickramasinghe et al., Life-bearing primordial planets in the solar vicinity, Astrophysics and Space Science, May 8, 2012