For a long time, the only moon human beings knew of was our own. In the early 17th century, the invention of the telescope extended our vision into the cosmos and allowed Galileo to discover four new moons, in orbit around Jupiter. Five moons around Saturn were found in that century, and two more in the next. By the 19th century, astronomers had detected moons around Mars, Neptune, and Uranus. Today, we know the solar system is flush with them. There are nearly 200 known moons, dutifully circling their planets and dwarf planets.
Now, after more than 400 years of studying these planetary companions, the search has reached beyond our home in the cosmos, to a different sun thousands of light-years away.
A pair of astronomers announced Wednesday that they have detected a distant object they believe to be a moon. If confirmed, the finding would mark the first discovery of a moon orbiting a planet outside of our solar system, known as an exomoon.
The potential exomoon orbits a planet about 8,000 light years away from Earth. It’s unlike any moon astronomers have ever observed: It is not rocky or icy like the moons we know, but gaseous. And it’s about the size of Neptune, which makes it 10 times bigger than the largest moon in our solar system.
“The closest analog would be picking up Neptune and putting it around Jupiter,” says David Kipping, the astronomer who co-discovered the object with Alex Teachey, his colleague at Columbia University. Their findings were published Wednesday in Science Advances.
Kipping and Teachey first came across the object in data from the Kepler Space Telescope, a NASA mission that has discovered more than 5,000 exoplanets and confirmed about half of them since it launched in 2003. The telescope detects planets through a technique called the transit method. When a planet passes, or transits, across the face of its star, it blocks a tiny fraction of the star’s light. Kepler stares at stars for years and watches for this dimming in action.
Kepler recently surveyed 284 exoplanets in its repertoire that astronomers suspected would make good hosts for moons. They’re large, and “the bigger the planet, the more leftover material there is to form moons,” Kipping explained. (The biggest planet in our solar system, Jupiter, also has the most moons and may add more; just this summer, astronomers discovered …read more
Source:: The Atlantic – Science