<p>NASA-funded researchers have detected the first signs of an exomoon - a moon orbiting a planet that lies outside our solar system - after witnessing a chance encounter between objects in the Milky Way.<br /><br /></p>.<p>Researchers said that though it is impossible to confirm the exomoon's presence, the finding is a tantalising first step toward locating others.<br /><br />The discovery was made by watching a chance encounter of objects in our galaxy, which can be witnessed only once, researchers said.<br /><br />"We won't have a chance to observe the exomoon candidate again," said David Bennett of the University of Notre Dame, and lead author of a new paper on the findings appearing in the Astrophysical Journal.<br /><br />The international study is led by the joint Japan-New Zealand-American Microlensing Observations in Astrophysics (MOA) and the Probing Lensing Anomalies NETwork (PLANET) programmes, using telescopes in New Zealand and Tasmania.<br /><br />Their technique, called gravitational microlensing, takes advantage of chance alignments between stars.<br /><br />When a foreground star passes between us and a more distant star, the closer star can act like a magnifying glass to focus and brighten the light of the more distant one. These brightening events usually last about a month.<br /><br />If the foreground star - or what astronomers refer to as the lens - has a planet circling around it, the planet will act as a second lens to brighten or dim the light even more.<br /><br />By carefully scrutinising these brightening events, astronomers can figure out the mass of the foreground star relative to its planet.<br /><br />In some cases, however, the foreground object could be a free-floating planet, not a star.<br /><br />Researchers might then be able to measure the mass of the planet relative to its orbiting companion: a moon. While astronomers are actively looking for exomoons - for example, using data from NASA's Kepler mission - so far, they have not found any.<br /><br />In the new study, the nature of the foreground, lensing object is not clear. The ratio of the larger body to its smaller companion is 2,000 to 1.<br /><br />That means the pair could be either a small, faint star circled by a planet about 18 times the mass of Earth - or a planet more massive than Jupiter coupled with a moon weighing less than Earth.<br /><br />The problem is that astronomers have no way of telling which of these two scenarios is correct.<br /><br />The answer to the mystery lies in learning the distance to the circling duo. A lower-mass pair closer to Earth will produce the same kind of brightening event as a more massive pair located farther away.<br /><br />But once a brightening event is over, it's very difficult to take additional measurements of the lensing system and determine the distance.<br /><br />The true identity of the exomoon candidate and its companion, a system dubbed MOA-2011-BLG-262, will remain unknown, researchers said. </p>
<p>NASA-funded researchers have detected the first signs of an exomoon - a moon orbiting a planet that lies outside our solar system - after witnessing a chance encounter between objects in the Milky Way.<br /><br /></p>.<p>Researchers said that though it is impossible to confirm the exomoon's presence, the finding is a tantalising first step toward locating others.<br /><br />The discovery was made by watching a chance encounter of objects in our galaxy, which can be witnessed only once, researchers said.<br /><br />"We won't have a chance to observe the exomoon candidate again," said David Bennett of the University of Notre Dame, and lead author of a new paper on the findings appearing in the Astrophysical Journal.<br /><br />The international study is led by the joint Japan-New Zealand-American Microlensing Observations in Astrophysics (MOA) and the Probing Lensing Anomalies NETwork (PLANET) programmes, using telescopes in New Zealand and Tasmania.<br /><br />Their technique, called gravitational microlensing, takes advantage of chance alignments between stars.<br /><br />When a foreground star passes between us and a more distant star, the closer star can act like a magnifying glass to focus and brighten the light of the more distant one. These brightening events usually last about a month.<br /><br />If the foreground star - or what astronomers refer to as the lens - has a planet circling around it, the planet will act as a second lens to brighten or dim the light even more.<br /><br />By carefully scrutinising these brightening events, astronomers can figure out the mass of the foreground star relative to its planet.<br /><br />In some cases, however, the foreground object could be a free-floating planet, not a star.<br /><br />Researchers might then be able to measure the mass of the planet relative to its orbiting companion: a moon. While astronomers are actively looking for exomoons - for example, using data from NASA's Kepler mission - so far, they have not found any.<br /><br />In the new study, the nature of the foreground, lensing object is not clear. The ratio of the larger body to its smaller companion is 2,000 to 1.<br /><br />That means the pair could be either a small, faint star circled by a planet about 18 times the mass of Earth - or a planet more massive than Jupiter coupled with a moon weighing less than Earth.<br /><br />The problem is that astronomers have no way of telling which of these two scenarios is correct.<br /><br />The answer to the mystery lies in learning the distance to the circling duo. A lower-mass pair closer to Earth will produce the same kind of brightening event as a more massive pair located farther away.<br /><br />But once a brightening event is over, it's very difficult to take additional measurements of the lensing system and determine the distance.<br /><br />The true identity of the exomoon candidate and its companion, a system dubbed MOA-2011-BLG-262, will remain unknown, researchers said. </p>