Kepler’s Transit Trio
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. Image credit: NASA/Ames/JPL-Caltech
NASA has announced the discovery of two Saturn-size planets, as well as one likely Earth-size planet, all transiting a star called Kepler 9. This is the first confirmed planetary system with more than one planet transiting the same star.
The measurements were made using NASA’s Kepler spacecraft and were confirmed by the W. M. Keck Observatory in Hawaii. The observations are published in the journal Science.
“This system of planets is a thrilling example of the Kepler mission’s power,” said co-author Tim Brown, scientific director of the Las Cumbres Observatory Global Network.
“It is astounding that Kepler can show us, circling one star, a pair of planets that pull each other’s orbits around, and also an object that is likely a planet not much bigger than the Earth,” he said. “Rich systems like this one will be the best laboratories for understanding how planets form, and how planetary systems evolve.”
The Kepler mission looks for the data signatures of planets by measuring tiny decreases in the brightness of stars when planets transit or cross in front of them. In June of this year, mission scientists announced that the mission has identified more than 700 planet candidates, including five candidate systems that appear to have more than one transiting planet.
NASA’s Kepler spacecraft was launched from NASA’s Kennedy Space Center on March 6.
The more massive planets were named Kepler-9b and 9c. The observations show Kepler-9b is the larger of the two planets, and both have masses similar to but less than Saturn. Kepler-9b lies closest to the star with an orbit of about 19 days, while Kepler-9c has an orbit of about 38 days. By observing several transits by each planet over the seven months of data, the time between successive transits could be analyzed.
The data suggest the transits of a super-Earth-sized planet about 1.5 times the radius of Earth in a scorching, near-Sun 1.6 day-orbit. Additional observations are required to determine whether this signal is indeed a planet or an astronomical phenomenon that mimics the appearance of a transit.
Launched in 2009, the Kepler space-borne telescope is designed to search the nearby region of our galaxy for planets the size of Earth, orbiting in the habitable zone of stars similar to our Sun. Scientists describe the habitable zone as the region around a star where temperatures permit water to be liquid on a planet’s surface.
Liquid water is considered essential for the existence of life as we know it. Therefore, the challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting Sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy.