NASA's Kepler space telescope, seen here from the International Space Station in June 2011, measures miniscule changes in the brightness of more than 150,000 stars to search for planets that pass in front of or 'transit' their host star.
The stars and planets discovered by the Kepler space observatory are so distant and faint that artists' renderings of what they might look like is the best information we have to go on.
"We imagine the worlds we discover by putting all that we’ve learned from our observations and analyses into the fingers of artists," according to NASA.
Planets orbiting Kepler-9
This artist’s concept illustrates the two Saturn-sized planets discovered by NASA’s Kepler mission. The star system is oriented edge-on, as seen by Kepler, such that both planets cross in front, or transit, their star, named Kepler-9. This is the first star system found to have multiple transiting planets.
The planet Kepler-10b orbits one of the 150,000 stars that the Kepler spacecraft is monitoring, a star that is very similar to our own Sun in temperature, mass and size, but older with an age of over 8 billion years, compared to the 4-and-1/2 billion years of our own Sun.
It is one of the brighter stars that Kepler is monitoring and about 560 light years from our solar system, which means when the light from this star began its journey toward Earth, European navigators were crossing the Atlantic Ocean for the first time in search of new horizons.
Kepler-10b must be a scorched world, orbiting at a distance that’s more than 20 times closer to its star than Mercury is to our own Sun, with a daytime temperature expected to be more than 2,500 degrees Fahrenheit.
The Kepler team has determined that Kepler-10b is a rocky planet, with a surface you could stand on, a mass 4.6 times that of Earth, and a diameter 1.4 times that of Earth.
This artist's concept depicts a very small planetary system -- so compact, in fact, that it's more like Jupiter and its moons than a star and its planets.
Astronomers using data from NASA's Kepler mission and ground-based telescopes recently confirmed that the system, called KOI-961, hosts the three smallest exoplanets known so far to orbit a star other than our sun.
The star, which is located about 130 light-years away in the Cygnus constellation, is what's called a red dwarf. It's one-sixth the size of the sun, or just 70 percent bigger than Jupiter. The star is also cooler than our sun, and gives off more red light than yellow.
The smallest of the three planets, called KOI-961.03, is actually located the farthest from the star, and is pictured in the foreground. This planet is about the same size as Mars, with a radius only 0.57 times that of Earth. The next planet to the upper right is KOI-961.01, which is 0.78 times the radius of Earth. The planet closest to the star is KOI-961.02, with a radius 0.73 times the Earth's.
All three planets whip around the star in less than two days, with the closest planet taking less than half a day. Their close proximity to the star also means they are scorching hot, with temperatures ranging from 350 to 836 degrees Fahrenheit (176 to 447 degrees Celsius). The star's habitable zone, or the region where liquid water could exist, is located far beyond the planets.
The ground-based observations contributing to these discoveries were made with the Palomar Observatory, near San Diego, Calif., and the W.M. Keck Observatory atop Mauna Kea in Hawaii.
An artist's concept oshows what the planet Kepler-16b with its two stars could look like. The cold planet, with its gaseous surface, is not thought to be habitable.
The largest of the two stars, a K dwarf, is about 69 percent the mass of our sun, and the smallest, a red dwarf, is about 20 percent the sun's mass. These star pairs are called eclipsing binaries.
An artist's concept of the circumbinary planet Kepler-16b - the first planet known to definitively orbit two stars-could look like.
The cold planet, with its gaseous surface, is not thought to be habitable. The largest of the two stars, a K dwarf, is about 69 percent the mass of our sun, and the smallest, a red dwarf, is about 20 percent the sun's mass. These star pairs are called eclipsing binaries.
An artist's rendering shows a planet called Kepler-20e in this handout released December 20, 2011.
NASA's Kepler mission has discovered the first Earth-size planets orbiting a sun-like star outside our solar system, a milestone in the search for planets like the earth, the space agency said on Tuesday.
NASA's artist's illustration compares the planets in the Kepler-37 system to the moon and planets in the solar system.
NASA's Kepler mission has discovered a new planetary system that is home to the smallest planet yet found around a star like our sun, approximately 210 light-years away in the constellation Lyra.
The smallest planet, Kepler-37b, is slightly larger than our moon, measuring about one-third the size of Earth. Kepler-37c, the second planet, is slightly smaller than Venus, measuring almost three-quarters the size of Earth. Kepler-37d, the third planet, is twice the size of Earth.
A "year" on these planets is very short. Kepler-37b orbits its host star every 13 days at less than one-third the distance Mercury is to the sun. The other two planets, Kepler-37c and Kepler-37d, orbit their star every 21 and 40 days. All three planets have orbits lying less than the distance Mercury is to the sun, suggesting that they are very hot, inhospitable worlds.
Kepler-186f, the first validated Earth-size planet to orbit a distant star in the habitable zone, a range of distance from a star where liquid water might pool, on the planet's surface, is seen in a NASA artist's concept released April 17, 2014.
The star, known as Kepler-186 and located about 500 light years away in the constellation Cygnus, is smaller and redder than the sun.
An artist's concept is shown in this NASA handout illustrates Kepler-47, the first transiting circumbinary system -- multiple planets orbiting two suns, 4,900 light-years from Earth, in the constellation Cygnus.
The system was detected by NASA's Kepler space telescope, which measures minisucule changes in the brightness of more than 150,000 stars to search for planets that pass in front of or 'transit' their host star.
In a dazzling and previously undetected display of orbital dynamics, two planets beyond the solar system have been found circling a pair of stars, scientists using NASA's Kepler space telescope have said.
Kepler-11 is a sun-like star around which six planets orbit. At times, two or more planets pass in front of the star at once, as shown in a simultaneous transit of three planets observed by NASA's Kepler spacecraft on August 26, 2010.