A
newly discovered exoplanet, Kepler-452b, comes the closest of any found so far
to matching our Earth-sun system. This artist’s conception of a planetary
lineup shows habitable-zone planets with similarities to Earth: from left,
Kepler-22b, Kepler-69c, the just announced Kepler-452b, Kepler-62f and
Kepler-186f. Last in line is Earth itself.
Credits: NASA/Ames/JPL-Caltech
The discovery of a super-Earth-sized planet orbiting a
sun-like star brings us closer than ever to finding a twin of our own watery
world. But NASA’s Kepler space telescope has captured evidence of other
potentially habitable planets amid the sea of stars in the Milky Way galaxy.
To take a brief tour of the more prominent contenders,
it helps to zero in on the “habitable zone” around their stars. This is the
band of congenial temperatures for planetary orbits -- not too close and not
too far. Too close and the planet is fried (we’re looking at you, Venus). Too
far and it’s in deep freeze. But settle comfortably into the habitable zone,
and your planet could have liquid water on its surface -- just right.
Goldilocks has never been more relevant. Scientists have, in fact, taken to
calling this water-friendly region the “Goldilocks zone.”
The zone can be a wide band or a narrow one, and
nearer the star or farther, depending on the star’s size and energy output. For
small, red-dwarf stars, habitable zone planets might gather close, like
marshmallow-roasting campers around the fire. For gigantic, hot stars, the band
must retreat to a safer distance.
About a dozen habitable zone planets in the Earth-size
ballpark have been discovered so far -- that is, 10 to 15 planets between
one-half and twice the diameter of Earth, depending on how the habitable zone
is defined and allowing for uncertainties about some of the planetary sizes.
The new discovery, Kepler-452b, fires the planet
hunter’s imagination because it is the most similar to the Earth-sun system
found yet: a planet at the right temperature within the habitable zone, and
only about one-and-a-half times the diameter of Earth, circling a star very
much like our own sun. The planet also has a good chance of being rocky, like
Earth, its discoverers say.
Kepler-452b is more similar to Earth than any system
previously discovered. And the timing is especially fitting: 2015 marks the 20th
anniversary of the first exoplanet confirmed to be in orbit around a typical
star.
But several other exoplanet discoveries came nearly as
close in their similarity to Earth.
Before this, the planet Kepler-186f held the “most
similar” distinction (they get the common moniker, “Kepler,” because they were
discovered with the Kepler space telescope). About 500 light-years from Earth,
Kepler-186f is no more than 10 percent larger than Earth, and sails through its
star’s habitable zone, making its surface potentially watery.
But its 130-day orbit carries it around a red-dwarf
star that is much cooler than our sun and only half its size. Thus, the planet
is really more like an “Earth cousin,” says Thomas Barclay of the Bay Area
Environmental Research Institute at NASA’s Ames Research Center, Moffett Field,
California, a co-author of the paper announcing the discovery in April 2014.
Kepler-452b: Earth's Bigger, Older Cousin -- Briefing
Materials
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. Today, and
thousands of discoveries later, astronomers are on the cusp of finding
something people have dreamed about for thousands of years -- another Earth.
The briefing participants are:
·
John Grunsfeld,
associate administrator for NASA's Science Mission Directorate in Washington
·
Jon Jenkins,
Kepler data analysis lead at NASA's Ames Research Center in Moffett Field,
California
·
Jeff Coughlin,
Kepler research scientist at SETI Institute in Mountain View, California
·
Didier Queloz,
professor of astrophysics at Cambridge University, United Kingdom
Source: NASA
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