Their star is probably a lot like our Sun but several billion years older, and the planets are much closer to it, said the study in Science Express, the online edition of the journal Science.
The rocky planet, Kepler-36b, is about 1.5 times the size of Earth and orbits about every two weeks at an average distance of less than 11 million miles (18 million kilometers) from its star.
The Earth's average distance from the Sun is about 93 million miles (150 million kilometers).
The bigger, outer planet nicknamed Kepler-36c is almost four times as big as Earth and is known as a "hot Neptune" because its atmosphere is mainly made up of hydrogen and helium and it may have a rocky core.
Kepler-36c orbits once each 16 days at a distance of 12 million miles (19 million kilometers).
They share nearly the same orbital plane and never collide, skimming one another at a distance of 1.2 million miles (1.9 million kilometers) on their closest approach, or five times the distance of the Earth to the Moon.
"These are the closest two planets to one another that have ever been found," said Eric Agol, a University of Washington associate professor of astronomy and co-lead author of the paper.
"The bigger planet is pushing the smaller planet around more, so the smaller planet is harder to find."
People would not be able to stand on the rocky planet -- it is so close to the hot star that its surface might be like molten lava.
But if they could, they would likely see the giant gas planet about three times the size of the Moon looming in the skies.
"These two worlds are having close encounters," said Josh Carter, a Hubble fellow at the Harvard-Smithsonian Center for Astrophysics.
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The rocky planet, Kepler-36b, is about 1.5 times the size of Earth and orbits about every two weeks at an average distance of less than 11 million miles (18 million kilometers) from its star.
The Earth's average distance from the Sun is about 93 million miles (150 million kilometers).
The bigger, outer planet nicknamed Kepler-36c is almost four times as big as Earth and is known as a "hot Neptune" because its atmosphere is mainly made up of hydrogen and helium and it may have a rocky core.
Kepler-36c orbits once each 16 days at a distance of 12 million miles (19 million kilometers).
They share nearly the same orbital plane and never collide, skimming one another at a distance of 1.2 million miles (1.9 million kilometers) on their closest approach, or five times the distance of the Earth to the Moon.
"These are the closest two planets to one another that have ever been found," said Eric Agol, a University of Washington associate professor of astronomy and co-lead author of the paper.
"The bigger planet is pushing the smaller planet around more, so the smaller planet is harder to find."
People would not be able to stand on the rocky planet -- it is so close to the hot star that its surface might be like molten lava.
But if they could, they would likely see the giant gas planet about three times the size of the Moon looming in the skies.
"These two worlds are having close encounters," said Josh Carter, a Hubble fellow at the Harvard-Smithsonian Center for Astrophysics.
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