Exoplanets are old news, we have found more than 1,000 of them beyond the solar system. But there’s also another search… For exomoons — moons orbiting alien planets — which are much smaller and harder to find also due to their lack of brightness. .
Now astronomers led by David Bennett of the University of Notre Dame, say they may have found an odd system of a planet and a moon (which they designate MOA-2011-BLG-262) floating free in the galaxy and not orbiting a star. The explanation that best fits the data is a giant planet, about four times the mass of Jupiter, orbited by a moon weighing less than Earth. If that interpretation is correct, the planet and its moon would be relatively nearby, between 1,000 and 2,000 light-years from Earth.
Another possibility is that the researchers have detected a more distant system comprising a small star, around one tenth the mass of the sun, and a planet roughly 18 times as massive as Earth. This system would need to be much farther away to explain the micro lensing pattern.
The system showed up in a study using micro lensing, which looks for the bending of starlight due to the gravitational pull of an unseen object between a star and Earth. But the signal is not very clear, the researchers acknowledge, and could instead represent a dim star and a lightweight planet.
According to Einstein’s general theory of relativity, massive objects warp the spacetime in their vicinity, so that anything, even light, will take a curved path around them. When light from a background star travels past a massive object on its way to our telescopes, it manifests in bright circles of warped light called Einstein rings. If the massive object consists of two bodies, such as a planet and its moon, the circle will appear broken and bulgy in places. Sometimes the ring is too small to resolve the details, but the overall micro lensing effect can be calculated by the way the star’s overall brightness varies in time.
Micro lensing is promising because it can detect moons beyond the close-in satellites that transit searches are best equipped to find. According to scientists, the results indicate the potential of micro lensing to detect exomoons.
We’ll see what news micro lensing will bring and which mysteries it will help solve…