One of two newly discovered planets is a rocky planet that is 1.5 times the size of Earth. The second is a gas planet almost four times Earth’s size. Together they are part of a “bizarre” star system in which the planets orbit closer to each other than any other planets yet discovered.
“We’ve never known of planets like this,” said Yale University astronomer Sarbani Basu, a member of the research team that analyzed the system. “If you were on the smaller planet looking up, the larger planet would seem more than twice the size of Earth’s full moon. It would be jaw-dropping.”
“These two worlds are having close encounters,” said Josh Carter, lead author of the paper and a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics.
Nearly 1200 light years from the Earth, the two-planet system called Kepler-36 orbits a star similar to Earth’s sun, but older and larger.
The planet slightly further from the star, Kepler-36c, is a hot, Neptune-like, gas planet. The somewhat smaller inner planet is named Kepler-36b, and is a rocky Earth-like planet that very likely experiences large earthquakes and volcanic eruptions caused by the tidal influences of the other planet.
Kepler-36 pulsates regularly, like our sun. This data enabled the research team to accurately determine the size, weight, and age of the star. Data on the star’s radius and mass enabled the researchers to calculate the sizes and masses of the two planets. Using this information, the astronomers could then determine the densities and characteristics of the planets. “The smaller planet is denser than Earth and hence must be rocky; the larger planet is much less dense, in fact less dense than water, suggesting it is gaseous.”
“The precise determination of the planets’ properties was possible because the star around which they revolve could be characterized precisely,” said Basu.
The closeness of the planets to each other is unprecedented. “The rocky inner planet orbits its star every 14 days, at an average distance of 11 million miles. The outer gaseous planet orbits every 16 days, at an average distance of 12 million miles. Every 97 days they move into perfect alignment, a position known as conjunction. At that point they are separated by a mere 1.2 million miles — less than five times the distance between Earth and its moon. By contrast, Venus, Earth’s nearest neighbor, never comes closer than 26 million miles.”
The planets were identified by analyzing data from NASA’s Kepler satellite. The Kepler spacecraft finds planets by looking for variations in the brightness of stars, the dimming of a star’s brightness indicates the possibility that a planet might be is passing in front of the star.
The discovery of these two planets “poses new challenges to the theories of planet formation.” How planets of such different compositions and densities can come to orbit so closely to each other is a new question for researchers.
The research was done by a 46-member-strong international team, led by astronomers from Harvard and the University of Washington. Their discovery was published June 21 in Science Express. The researchers received support from NASA, the National Science Foundation, and the national research councils of the United Kingdom, Denmark and the Netherlands.
Source: Yale University
Image Credits: David Aguilar, Harvard-Smithsonian Center for Astrophysics; NASA