By the time its last catalogue of exoplanet candidates was released in February, Nasa’s Kepler space observatory, launched in March 2009, first light in April 2009, had identified 1,235 planetary candidates – and 54 candidates within the habitable zone.
The Kepler team have now identified 2,326 planet candidates – of those, 207 are approximately Earth-size, 680 are super Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter. And there are now 48 planet candidates in their star’s habitable zone
There are also 28 confirmed exoplanets. And, as the BBC reports, among those is Kepler-22b – the first confirmed near-Earth-size planet in the habitable zone of a Sun-like star. [Another ‘pale blue dot’? – Ed] Possibly…
From the BBC report
The planet, Kepler 22-b, lies about 600 light-years away and is about 2.4 times the size of Earth, and has a temperature of about 22C.
It is the closest confirmed planet yet to one like ours – an “Earth 2.0”.
However, the team does not yet know if Kepler 22-b is made mostly of rock, gas or liquid.
Kepler 22-b was one of 54 candidates reported by the Kepler team in February, and is just the first to be formally confirmed using other telescopes.
More of these “Earth 2.0” candidates are likely to be confirmed in the near future, though a redefinition of the habitable zone’s boundaries has brought that number down to 48.
Kepler 22-b lies at a distance from its sun about 15% less than the distance from the Earth to the Sun, and its year takes about 290 days. However, its sun puts out about 25% less light, keeping the planet at its balmy temperature that would support the existence of liquid water.
Here’s a comparative diagram of the Kepler-22b system [Image credit: NASA/Ames/JPL-Caltech]
This diagram compares our own solar system to Kepler-22, a star system containing the first “habitable zone” planet discovered by NASA’s Kepler mission. The habitable zone is the sweet spot around a star where temperatures are right for water to exist in its liquid form. Liquid water is essential for life on Earth.
Kepler-22’s star is a bit smaller than our sun, so its habitable zone is slightly closer in. The diagram shows an artist’s rendering of the planet comfortably orbiting within the habitable zone, similar to where Earth circles the sun. Kepler-22b has a yearly orbit of 289 days. The planet is the smallest known to orbit in the middle of the habitable zone of a sun-like star. It’s about 2.4 times the size of Earth.
From the Kepler Mission press release
Kepler discovers planets and planet candidates by measuring dips in the brightness of more than 150,000 stars to search for planets that cross in front, or “transit,” the stars. Kepler requires at least three transits to verify a signal as a planet.
“Fortune smiled upon us with the detection of this planet,” said William Borucki, Kepler principal investigator at NASA Ames Research Center at Moffett Field, Calif., who led the team that discovered Kepler-22b. “The first transit was captured just three days after we declared the spacecraft operationally ready. We witnessed the defining third transit over the 2010 holiday season.”
The Kepler science team uses ground-based telescopes and the Spitzer Space Telescope to review observations on planet candidates the spacecraft finds. The star field that Kepler observes in the constellations Cygnus and Lyra can only be seen from ground-based observatories in spring through early fall. The data from these other observations help determine which candidates can be validated as planets.
Kepler-22b is located 600 light-years away. While the planet is larger than Earth, its orbit of 290 days around a sun-like star resembles that of our world. The planet’s host star belongs to the same class as our sun, called G-type, although it is slightly smaller and cooler.
Of the 54 habitable zone planet candidates reported in February 2011, Kepler-22b is the first to be confirmed.
Here’s an overview of the Kepler mission from the scientists involved.
‘Tis not unlikely, but that there may be yet invented several other helps for the eye, as much exceeding those already found, as those do the bare eye, such as we may perhaps be able to discover living Creatures in the Moon, or other Planets, the figures of the compounding Particles of matter, and the particular Schematisms and Textures of Bodies.
Added And here’s the Kepler mission’s science team announcing its latest finding at a press conference on Monday, Dec. 5, 2011. Via NasaAmes
The problem, as many astronomers point out, is getting any more information about these planets. “Astronomers are going to have to learn to live with ignorance,” Dr. Seager said.
Some exoplanets, like the Gliese worlds, were discovered by the “wobble method” — looking at the motions they induce in their parent stars — which allows their masses and orbits to be measured. Other planets, like the ones identified by Kepler, are found by watching for the blinks when they pass in front of their stars; that also allows their sizes to be determined.
To date, none of the Goldilocks candidates have been observed to transit their stars, and thus none have been assigned both masses and sizes, which would allow astronomers to calculate their densities and compositions and find out if they are water worlds, rocks or gassy fluff balls.
Kepler fixes its gaze on a patch of stars in Cygnus that are hundreds if not thousands of light-years away — too far for any wobble detections that would assess the abundance of Earthlike planets in the galaxy or any other close scrutiny. We are liable to never know anymore about those planets than we know now, astronomers say. The brute reality, astronomers admit, is that even if there are thousands or millions of habitable planets in the galaxy, only a few hundred of them are within range of any telescope that will be built in the conceivable future.