Using data from the NASA Kepler space telescope, scientists have confirmed the first near-Earth-size planet orbiting in the habitable zone of a sun-like star, 1400 light-years away.
A star's habitable zone is an orbital region where temperatures are just right for water to exist on planetary surfaces. Earth-sized exoplanets (or exomoons) within the habitable zone (sometimes referred to as the "Goldilocks zone"), with liquid water on their surfaces, are good candidates for hosting life.
Kepler-452b is about 60% larger than Earth, and more massive - this type of exoplanet is typically referred to as a "Super-Earth;" a human standing on its surface would weigh almost twice as much as they would on Earth.
Both Earth and Kepler-452b orbit a G2-type star, each about the same temperature. Kepler-452b's star is 1.5 billion years older than our sun (about 6 billion years old), and is hotter and brighter than our Sun.
Kepler-452b is receiving ten percent more energy from its parent star than Earth is currently receiving from the Sun; if Kepler-452b is a rocky world, it may not possess a habitable environment - it could be suffering from a runaway greenhouse effect similar to Venus.
Some media agencies are headlining that "Earth 2.0" has been found; I have to give that kind of sensationalism the squinty-eye of disdain - it's a bit too early to be making claims like that. This extensive NASA briefing refers to Kepler-452b as "Earth's Bigger, Older Cousin" - I like that much better.
The briefing also states: "The first exoplanet orbiting another star like our sun was discovered in 1995. Exoplanets, especially small Earth-size worlds, belonged within the realm of science fiction just 21 years ago." I was struck by two thoughts: Carl Sagan would have just LOVED this, and how frequently in recent years some aspect of science fiction has become reality.
The Kepler space telescope has scanned only a tiny portion of the northern sky - in the constellations of Cygnus, Lyra and Draco; it has discovered hundreds of exoplanets, with thousands more candidates awaiting confirmation. A study from the PLANET (Probing Lensing Anomalies NETwork) collaboration estimates there are more than 10 billion terrestrial planets across our galaxy.
(mission and community)
|Candidates and Confirmed in Habitable Zone
(180 K < Equilibrium (T) < 310 K) or
(0.25 < Insolation (Earth flux) < 2.2)
|Kepler Project Candidates||4696|
|Kepler Project Unconfirmed Candidates||3704|
|Total Candidates and Confirmed Planets||4737|
Exoplanet Archive: http://exoplanetarchive.ipac.caltech.edu/