Cosmos & Outer Space

More Than 100 Exoplanets Discovered By Astronomers In 3 Months

Within few years, space has not been out of reach of our planet’s people who consistently tries to explore many things in this vast universe. Talking about planets other than earth, leave our solar system because astronomers keep their eye on outer systems as well.

An international team of astronomers using a combination of ground and space based telescopes have reported more than 100 extra-solar planets (here after, exoplanets) in only three months. These planets are quite diverse and expected to play a large role in developing the research field of exoplanets and life in the Universe.

Exoplanets, planets that revolve around stars other than the Sun, have been actively researched in recent years. One of the reasons is the success of the Kepler Space Telescope, which launched in 2009 to search for exoplanets. If a planet crosses (transits) in front of its parent star, then the observed brightness of the star drops by a small amount. The Kepler Space Telescope detected many exoplanets using this method.

However, such dimming phenomena could be caused by other reasons. Therefore, confirmation that the phenomena are really caused by exoplanets is very important. The Kepler space telescope experienced mechanical trouble in 2013, which led to a successor mission called K2. Astronomers around the world are competing to confirm exoplanets suggested by the K2 data.

An international research team involving researchers at the University of Tokyo and Astrobiology Center of the National Institutes of Natural Sciences investigated 227 K2 exoplanet candidates using other space telescopes and ground-based telescopes. They confirmed that 104 of them are really exoplanets. Seven of the confirmed exoplanets have ultra-short orbital periods less than 24 hours.

Extra-solar planet

Extrasolar planet, also called exoplanet, any planetary body that is outside the solar system and that usually orbits a star other than the Sun. The first extrasolar planets were discovered in 1992. More than 3,000 are known, and more than 1,000 await further confirmation.

Detection Of Extrasolar Planets

Because planets are much fainter than the stars they orbit, extrasolar planets are extremely difficult to detect directly. By far the most successful technique for finding and studying extrasolar planets has been the radial velocity method, which measures the motion of host stars in response to gravitational tugs by their planets. The first planet discovered with this technique was 51 Pegasi b in 1995. Radial velocity measurements determine the sizes and shapes of the orbits of extrasolar planets as well as the lower limits of the masses of these planets. (They provide only lower limits on planetary mass because they measure just the portion of the star’s motion toward and away from Earth.)

Three other techniques that have detected extrasolar planets are pulsation timing, microlensing, and direct imaging. Pulsation timing measures the change in distance between the signal source and the telescope by using the arrival times of signals that are emitted periodically by the source.

When the source is a pulsar (a rotating, magnetized neutron star), current technology can detect motions in response to a planet whose mass is as small as that of Earth’s Moon, whereas only giant planets can be detected around pulsating normal stars. The first extrasolar planets were discovered in 1992 around the pulsar PSR 1257+12 by using this method. Microlensing relies upon measurements of the gravitational bending of light (predicted by Albert Einstein’s general theory of relativity) from a more distant source by an intervening star and its planets.

This technique is most sensitive to massive planets orbiting hundreds of millions of kilometres from their star and has also been used to discover a population of free-floating giant planets that do not orbit any star. Direct imaging can be done by using starlight reflected off the planet or thermal infrared radiation emitted by the planet. Imaging works best for planets orbiting those stars that are nearest to the Sun, with infrared imaging being especially sensitive to young massive planets that orbit far from their star.



The formation process of exoplanets with such short orbital periods is still unclear. Further study of these ultra-short period planets will help to advance research into the processes behind their formation. They also confirmed many low-mass rocky exoplanets with masses less than twice that of the Earth as well as some planetary systems with multiple exoplanets.

Mr. John Livingston, a Ph.D. student at the University of Tokyo and lead author of the papers reporting the exoplanets, explains, “Although the Kepler Space Telescope has been officially retired by NASA, its successor space telescope, called TESS, has already started collecting data. In just the first month of operations, TESS has already found many new exoplanets, and it will continue to discover many more. We can look forward to many new exciting discoveries in the coming years.”

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