According to NASA, more than 1,000 extrasolar planets have been confirmed in recent years. There are also thousands more potential planets beyond our solar system that are waiting to be discovered.
Now, an international group of astronomers think they may have found the first exomoon, or moon circling an exoplanet, some 1,800 light years away from Earth. This possible planet/moon system has been dubbed MOA-2011-BLG-262.
Then again, what the astronomers saw just might be some other kind of object, since they said it’s impossible to confirm its presence. Nonetheless the scientists call their finding a “tantalizing first step” in the search for other exomoons.
The researchers said that they made their discovery by watching a chance encounter of objects in our galaxy, something that can only be observed once.
“We won’t have a chance to observe the exomoon candidate again,” said David Bennett of the University Of Notre Dame, lead author of a new paper published in the Astrophysical Journal that outlines the discovery. “But we can expect more unexpected finds like this,” he adds.
Using telescopes located in New Zealand and Tasmania, the research team took advantage of an astronomical phenomenon that’s known as gravitational microlensing.
For example, whenever a nearby star passes directly between Earth and a more distant star, the gravitational field of the closer star will bend and focus the light of that distant star much like a lens in an optical telescope.
If the star closest to Earth should happen to have a planet orbiting it, the scientists said that the planet would serve as a secondary lens that would further brighten or dim the distant object’s light even more.
Through careful analysis of these brightening/dimming events, the astronomers then can determine the mass of the closer star relative to its orbiting planet.
But the astronomers point out that sometimes the object closest to earth may not be a star, but a free-floating planet with a moon circling it. In this case researchers might then be able to measure the mass of the planet relative to its orbiting moon.
While they haven’t been successful so far, astronomers have been trying to locate exomoons orbiting distant planets by using other means, such as data provided by NASA’s Kepler mission.
For the research that led to this new discovery, the nature of the objects that were closest to Earth weren’t really clear to the astronomers.
They said that the ratio of the larger object to its smaller companion is 2,000 to 1 which could mean that the two objects could either be a small, dim star that’s orbited by a planet about 18 times the mass of Earth, or the pair could be a planet that is more massive than Jupiter circled by a moon with a mass that’s less than Earth.
The research team said that they have no way of telling which of the two circumstances is correct.
“One possibility is for the lensing system to be a planet and its moon, which if true, would be a spectacular discovery of a totally new type of system,” said Wes Traub, chief scientist for NASA’s Exoplanet Exploration Program office at the Jet Propulsion Laboratory in Pasadena, California. Traub, who wasn’t involved with the international team’s studies, also said that “The researchers’ models point to the moon solution, but if you simply look at what scenario is more likely in nature, the star solution wins.”
The astronomers said to get a true answer in determining whether or not they observed an exomoon and not another star system they would need to figure out the actual distance to the circling twosome.
A pair of objects closer to Earth that are low in mass, according to the astronomers, will produce the same kind of brightening event as one that would be produced by two more massive objects located farther away. But unfortunately once the observed brightening/dimming event is over; it’s very difficult for the scientists to take the needed additional measurements to calculate the distance. That means the actual identity of what may or may not be an exomoon will remain a mystery.
The astronomers said that perhaps sometime in the future, it just may be possible to acquire these distance measurements during lensing events by using, for example, NASA’s Spitzer and Kepler space telescopes.
If it turns out that this sighting is actually a real exomoon that’s orbiting a free-floating planet, the astronomers think that the planet may have been kicked out of a young planetary system, bringing its orbiting moon along for the ride as a travel companion.