April 17: Astronomers today announced their discovery of the first Earth-sized planet outside the solar system lying within its star’s habitable zone where temperatures are suitable for liquid water to exist.
The planet’s host star, Kepler-186, is smaller and cooler than the Sun, about 500 light years away from the solar system in the constellation Cygnus. The planet, named Kepler-186f and which has a radius 1.1 times that of Earth, is one of five planets orbiting the star.
“What makes this finding compelling is that this Earth-sized planet resides in a region where water could exist in liquid form,” said Elisa Quintana, a scientist at the National Aeronautics and Space Administration and the Search for Extraterrestrial Intelligence Institute, in a media release issued today.
Quintana and her colleagues used the Kepler space telescope and two ground observatories to study the star system. Their findings will appear in the US journal Science tomorrow.
Several extra-solar planets in the habitable zones of distant stars have been catalogued in recent years, but most are giant gas planets or giant potentially rocky planets and, until now, Earth-sized planets in the habitable zone have remained elusive.
“I think this is one of the most significant discoveries from Kepler,” said David Charbonneau, professor of astronomy at Harvard University who was not associated with the finding, told The Telegraph.
“For me, the biggest impact is to know that there are planets the same size as the Earth in the habitable zones of small stars. This system is far from us to scrutinise in detail, but there are many, many similar small stars around us.”
Astronomers have catalogued more than 1000 extra-solar planets since the mid-1990s, including super-Earths which are many times the size of our planet. “Humans are getting greedy, and want to find planets increasingly similar to the Earth,” said Eric Ford, professor of astronomy at the Pennsylvania State University and member of the team that found Kepler-186f. “This planet may be the most similar to the Earth yet,” Ford told The Telegraph.
But researchers caution that there are still uncertainties about the planet. “We don’t know how dense its atmosphere is or what it is made up of — those uncertainties mean we can’t be certain yet about its surface temperature,” Ford said.
However, astronomers believe, based on other observations of planets of similar size, that Kepler-186f is likely to be a rocky planet. “This is only the tip of the iceberg,” Ford said.
“We can already tell that nature has endowed the universe with an abundance of small planets and plenty of planets cool enough to support liquid water on their surface.”
“In the long-run, we plan to search the atmospheres of such planets for indications of life.”