Up to 100 million exoplanets could support life

(The Milky Way – Photo Credit: Serge Brunier)

The number of planets in the Milky Way which could host complex life could be as high as 100 million. 

A recent study by Louis Irwin from the University of Texas at El Paso, and a team of colleagues, are behind the claim.

Based on objective data, the group of scientists believe they have the first measurable estimate on the number of worlds that could harbour life in our galaxy.

The team surveyed more than 1,000 exoplanets using a formula that examined each planet’s density, temperature, composition (whether it consists of liquid, solid, or gas), chemistry, distance from its star, and age. From this data, they created a “Biological Complexity Index (BCI)”.

This produced a rating for each planet on a scale of 0 to 1.0 according to the number of characteristics they fulfilled which could support microbial life.

The BCI calculation revealed that 1 – 2% of known exoplanets had a BCI rating higher than Jupiter’s moon Europa, which has a global ocean under its icy surface which is thought to contain traces of life.

Based on an estimate that there are 10 billion stars in the Milky Way and assuming each star has an average of one planet, the team calculated there are 100 million possible life-hosting planets.

Some scientists believe the number could be 10 times higher.

The estimation is based on ‘life’ in the microbial sense. It simply means organisms which are larger and more complex than microbes, not evolved human beings. Nevertheless, this is a breakthrough study as it is the first that relies on observable data from actual planetary bodies instead of educated guesses based on hypothetical assumptions.

Despite the large number of planets that could harbour complex life, planets with high BCI values are very far apart due to the vast nature of the Milky Way.

One of the closest and most promising extrasolar systems is Gliese 581. This hosts two planets with the capacity for complex biospheres, however Gliese 581 is still about 20 light years from Earth.

This new study has produced valuable information that supports that humans are not alone in the universe, however the challenge is that these worlds are too far away from us to do much yet.

Louis Irwin, lead author announced: “On the one hand, it seems highly unlikely that we are alone…on the other hand, we are likely so far away from life at our level of complexity, that a meeting with such alien forms is extremely improbable for the foreseeable future.”