An artist's illustration of PH1, a planet discovered by volunteers from the Planet Hunters citizen science project. PH1, shown in the foreground, is a circumbinary planet and orbits two suns. // illustration by Haven Giguere/Yale
The 44th annual meeting of the
Division for Planetary Sciences of the American Astronomical Society started with a bang October 15. Planetary scientists from around the world are gathering at the Grand Sierra Resort and Casino in Reno, Nevada, this week. No doubt many of the non-scientists here hope to strike it rich at the slot machines or poker tables. But the researchers at the conference feel like they’ve already hit the scientific jackpot.
Perhaps the two most exciting discoveries announced Monday involve planets orbiting other stars. Both systems appear to be unique, at least at this moment in the rapidly burgeoning field of exoplanet detections.
One goes by the name PH1 because it is the first planet detected by volunteers working with the citizen-science project known as “Planet Hunters.” Kian Jek of San Francisco, California, and Robert Gagliano of Cottonwood, Arizona, spotted the object in data returned by the orbiting Kepler spacecraft. They found the periodic small dips in starlight that signaled the presence of an orbiting planet. A team of astronomers led by Meg Schwamb of Yale University in New Haven, Connecticut, confirmed the discovery with observations from the Keck telescopes on Hawaii’s Mauna Kea.
PH1 orbits an eclipsing binary system located some 5,000 light-years from Earth. This makes it one of six known circumbinary planets. PH1 is a gas giant with a diameter 6.2 times that of Earth that revolves around the binary every 138 days. The two stars possess 1.5 and 0.4 times the Sun’s mass and orbit each other every 20 days.
What sets this system apart, however, is that it travels through space with a second set of suns in tow. This stellar pair lies approximately 1,000 astronomical units (roughly 30 times the distance between the Sun and Neptune) from the planet-bearing stars. The dynamics inherent in a quadruple star system gives PH1 a noteworthy survival story, one that will take scientists some time to unravel.
Darin Ragozzine of the University of Florida described the second new system, in which five planets are crammed together like passengers on a Tokyo subway train during rush hour. KOI-500 — the 500th “Kepler Object of Interest” discovered by the telescope — holds five planets in a region less than one-twelfth the size of Earth’s orbit around the Sun. The planets orbit their host star in periods of just 1.0, 3.1, 4.6, 7.1, and 9.5 days. And these aren’t small objects either, ranging from 1.3 to 2.6 times Earth’s size.
To add to the system’s complexity, four of the planets follow synchronized orbits known as resonances. In the KOI-500 system, two interlocking systems of three-body resonances exist. Ragozzine and his team think that the planets formed farther from their star and later migrated into their current ultra-compact configuration.
All in all, it was a great start to the conference. Continue to check back this week for more updates in the world of planetary science.