The scientists 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 scientists calculate that such a planetary body would cross the inner solar system every 25 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.
Astrophysics and Space Science - Life-bearing primordial planets in the solar vicinity
The space density of life-bearing primordial planets in the solar vicinity may amount to ∼8.1×10^4 pc−3 (81000 per cubic parsec) giving total of ∼10^14 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.
Two months ago we covered work from Stanford which indicated that there were 100,000 nomad planets per star.
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