A cloud of debris around a nearby planet may soon yield the first detection of an exomoon. While the planet itself won’t be crossing between Earth and its sun anytime soon, scientists realized that any moons or rings would interrupt the light coming from the star. If the planet has a large enough satellite, it could be spotted by the end of 2017.
Located about 63 light-years from Earth, Beta Pictoris is a young star with a warped debris disk orbiting nearly edge-on to Earth. In 2009, scientists photographed a massive planet about 10 times as large as Jupiter orbiting the star about as far away as Saturn lies from our sun. Every 20 years, the planet, known as Beta Pictoris b (Beta Pic b), reaches its closest distance to the star, making it easier to detect any potential rings or satellites.
Instruments like NASA’s Kepler spacecraft find exoplanets by relying on transits, or worlds passing between the sun and Earth. The passage dims the light of the star, and requires multiple observations to confirm the world. These observations can help scientists determine how long it takes a planet to circle the star, and thus how wide its orbit is, but can only spot planets that move between the star and our sun. Beta Pic b was spotted using direct imaging, which essentially photographs the planet as it orbits its star. While this allows for a wider range of paths around the star, it can make it more challenging to trace the planet’s path.
Using the Gemini Planet Imager (GPI), a team of astronomers lead by Jason Wang, a graduate student at the University of California, Berkeley, refined the orbit of Beta Pic b. While the planet comes tantalizingly close to passing between its star and the Earth, they found it doesn’t quite transit.
But while the planet won’t yield up its secrets through transiting, Wang and his colleagues found that any material gravitationally bound in a region known as the Hill sphere could be visible.
“Interestingly, the planet is not by itself. Generally planets have a cocoon of material around it if it’s very young, like this one,” says team member Franck Marchis, a researcher at the SETI Institute in California. Marchis presented the research last month at the Division of Planetary Sciences meeting in Pasadena, California. “Maybe in this cocoon, we have rings, information of natural satellites, the equivalent of the moons of the Jovian system.” If the moons are as large enough as Io or Ganymede, the largest of Jupiter’s satellites, they could be visible.
“This may be the first time we have the detection of an exomoon,” Marchis says.