100 Million Planets in Milky Way May Support Complex Life Say Astronomers

Posted on June 10, 2014

Image showing DNA on exoplanets

Astronomers report in a new study that 100 million planets in the Milky Way may support complex life. The astronomers used a new computation method to examine data from planets orbiting other stars in the universe. The study provides the first quantitative estimate of the number of worlds in our galaxy that could harbor life above the microbial level.

The researchers surveyed over 1,000 planets and devised a formula that takes in planet density, temperature, substrate, age and distance from its parent star. The data is used to calculate the planet's Biological Complexity Index (BCI). Planets are rated from 0 to 1.0 on the BCI scale. The researchers say 1 to 2% of the planets analyzed have a BCI rating higher than that of Europa. Jupiter's moon Europa is thought to have a subsurface ocean that may harbor life.

The findings were published here in the journal Challenges by authors Alberto Fairen, Cornell research associate; Louis Irwin, University of Texas at El Paso (lead author); Abel Mendez, University of Puerto Rico at Arecibo; and Dirk Schulze-Makuch, Washington State University. The authors say in a statement, "This study does not indicate that complex life exists on that many planets. We're saying that there are planetary conditions that could support it. Origin of life questions are not addressed - only the conditions to support life."

The authors also say, "Complex life doesn't mean intelligent life - though it doesn't rule it out or even animal life - but simply that organisms larger and more complex than microbes could exist in a number of different forms. For example, organisms that form stable food webs like those found in ecosystems on Earth."

The chart below compares BCI values of planets and moons with their ESI values. The Earth Similarity Index (ESI) rates exoplanets also on a scale of 0 to 1.0 according to how similar they are to Earth.

Chart showing BSI and ESI for exoplanets and moons


Photo: PHL @ UPR Arecibo, NASA, Richard Wheeler @Zephyris
Image: Planetary Habitability Laboratory @ UPR Arecib