Whoa! Milky Way May Harbor 300 Million Potentially Habitable Planets

This illustration represents the legacy of NASA's Kepler space telescope which discovered more than 2,800 confirmed exoplanets of the known 4,374. It spent nine years collecting data from orbit before it ran out of fuel in 2018. NASA / Ames Research Center / W. Stenzel / D. Rutter

And I thought there were a lot of beetles! But with "only" 350,000 species, beetles are far outnumbered by the estimated 300 million potentially habitable planets now thought to exist in the Milky Way Galaxy. According to new research using data from NASA's former Kepler space telescope, about half of the stars similar in temperature to our sun could have a rocky planet capable of supporting liquid water on its surface. Although it's not the only ingredient required for life, liquid water is the golden key that unlocks life's potential as we know it. 

300 million is a conservative estimate according to the study released this week by a team of scientists who worked on the Kepler mission. The number is a minimum based on a conservative estimate that 7 percent of the sun-like stars could host such worlds. The authors believe the true number is closer to 50 percent. To make their calculations they looked at exoplanets (planets orbiting other stars) with diameters between one-half to 1 1/2 times that of Earth, which narrowed the search to those that are most likely made of rock. Large planets like Jupiter or Neptune possess thick, gaseous atmospheres that overlay their rocky interiors and may not be as conducive to life as smaller worlds.

This illustration depicts one possible appearance of the planet Kepler 452-b, the first near-Earth-size world to be found in the habitable zone of a star similar to the sun. The planet is 1,402 light years away in the constellation Cygnus. NASA Ames / JPL-Caltech / T. Pyle

They also looked at stars similar to our sun in age and temperature, plus or minus 1,500° Fahrenheit. Combining Kepler exoplanet data with data from the European Space Agency's Gaia mission, which determined each host star's energy output, helped the team to better understand the interplay between star and planet. Habitability is not just about a planet being close or far from its sun but also depends on the star's flux, the total amount of energy it beams toward the planet over time.

 

This is a conservative sample of currently known exoplanets that are likely to have a rocky composition and possible surface water. The images shown at left are illustrations, not actual photos. PHL@UPR Arecibo (phl.upr.edu) Oct. 5, 2020

How much of that energy arrives on the surface also depends on the atmosphere. Taking these factors into account the team determined that about half of sun-like stars have rocky planets capable of hosting liquid water on their surfaces. Four sun-like stars with Earth-like planets are thought to lie within 30 light years of the sun. 

Things worked out pretty good for our planet. The sun provides the Earth with a sustained and nearly constant amount of energy. The atmosphere allows that solar juice to reach the surface, and we're at the right distance from our host star for liquid water to slap and splash. I can walk down the road and see Lake Superior sparkling in the distance and picture another lake under a different sun a thousand light years away reflected in the light receptors of a species I'll never know. 

Hmm ... wonder if they have any beetles there?