Astronomers using a potent NASA space telescope to search for life say they have found planets which are the most Earth-like candidates yet. Two of the five planets orbiting a Sun-like star called Kepler-62 are squarely in the habitable zone – not too hot, not too cold, possibly bearing water – NASA scientists report in the journal Science ::::
“These are the most similar objects to Earth that we have found yet,” said Justin Crepp, assistant professor of physics at the University of Notre Dame.
The two planets are slightly larger than ours, with radiuses measuring 1.41 and 1.61 times the radius of the Earth.
Scientists do not yet know if their surfaces are rocky or watery, or if they have atmospheres that could sustain life.
But their location and size suggest they “could plausibly be composed of condensable compounds and be solid, either as a dry, rocky super-Earth or one composed of a significant amount of water,” the study said.
Other studies have indicated that planets with a radius under 1.6 “have been found to have densities indicative of a rocky composition”.
Astronomers detected the planets by observing their star dim when the planets pass in front of it, a process known as a “transit”.
Professor Crepp first saw a dot near Kepler-62 about a year ago, and has studied the movements of the system for months in order to confirm the discovery.
“What really helped is that this star has five planets,” he said.
“You can mimic one planet with another event, but when you have five of them and they’re all periodic, that helps to put the nail in the coffin.
“It’s hard to make that kind of signature with anything else that you can dream up.”
In late 2011, NASA confirmed its first-ever planet in a habitable zone outside our solar system – Kepler 22b, spinning around its star some 600 light years away.
However, the large size of that exoplanet, at 2.4 times the size of the Earth, has left some doubt over whether the planet is rocky, gaseous or liquid.
Kepler is NASA’s first mission in search of Earth-like planets orbiting suns similar to ours.
It is equipped with the largest camera ever sent into space in its search for planets as small as Earth, including those orbiting stars in a warm, habitable zone where liquid water could exist on the surface of the planet.
We’re a step closer to knowing if our galaxy is home to a multitude of planets like Earth or if we are a rarity. The three habitable zone super-Earth-size planets are in two systems containing a total of seven newly discovered planets:
Star Kepler-62 is not Sun-like: just 2/3 the size of the Sun, cooler, older, and only 1/5 as bright.
- Planet Kepler-62f, 40% larger than Earth, the smallest known habitable zone exoplanet, orbits every 267 days.
- Planet Kepler-62e, about 60% larger than Earth, orbits every 122 days in the the habitable zone’s inner edge.
- Kepler-62b, Kepler-62c and Kepler-62d, orbit every 5, 12, and 18 days, respectively, making them very hot and inhospitable for life as we know it. Two are larger than Earth and one is about the size of Mars.
- Star Kepler-69 is a sun-like star (G-type, 93% the size of the Sun, 80% as luminous, about 2,700 light-years from Earth).
- Planet Kepler-69c is 70% larger than Earth, the smallest yet found in the habitable zone of a sun-like star. It orbits in 242 days, resembling the orbit of Venus.
- Planet Kepler-69b is just over twice the size of Earth and, orbiting every 13 days, is toasty hot, not even close to the habitable zone.
“Finding a planet in the habitable zone around a star like our sun is a significant milestone toward finding truly Earth-like planets,” said Thomas Barclay, Kepler scientist at the Bay Area Environmental Research Institute in Sonoma, Calif., and lead author of the Kepler-69 system discovery published in the Astrophysical Journal.
“The Kepler spacecraft has certainly turned out to be a rock star of science,” said John Grunsfeld, associate administrator of the Science Mission Directorate at NASA Headquarters in Washington. “The discovery of these rocky planets in the habitable zone brings us a bit closer to finding a place like home. It is only a matter of time before we know if the galaxy is home to a multitude of planets like Earth, or if we are a rarity.”
CHECK! The full table of Kepler discoveries: kepler.nasa.gov
- Discovery paper in Science
- Kepler Discovery Table
- Kepler-62 Discovery Page
- Kepler-69 Discovery Page
- Index of Graphics for Kepler-62 and Kepler-69 discoveries