In search of signs of extraterrestrial life, astronomers have observed the transit of a potentially habitable Earth-like extrasolar planet located 150 light-years away. A transit is a phenomenon in which a planet passes in front of its parent star, blocking a small amount of light from the star, like a shadow of the planet. Researchers, including those from the National Astronomical Observatory of Japan (NAOJ) and the University of Tokyo, observed the transit of K2-3d using the MuSCAT instrument on the Okayama Astrophysical Observatory 188-cm telescope. Using the next generation of telescopes, such as TMT, scientists expect to be able to search the atmosphere of the planet for molecules related to life, such as oxygen. With previous space telescope observations, researchers could not calculate the orbital period of the planet precisely, which makes predicting the exact times of future transits more difficult. This research group has succeeded in measuring the orbital period of the planet with a high precision of about 18 seconds. This greatly improved the forecast accuracy for future transit times. Researchers will mow know exactly when to watch for the transits using the next generation of telescopes.
This research result is an important step towards the search for extraterrestrial life in the future. K2-3d is an extrasolar planet about 150 light-years away that was discovered by the NASA K2 mission. It is 1.5 times the size of the Earth. The planet orbits its host star, which is half the size of the Sun, with a period of about 45 days. Compared to the Earth, the planet orbits close to its host star (about 1/5 of the Earth-Sun distance). However, because the temperature of the host star is lower than that of the Sun, calculations show that this is the right distance for the planet to have a relatively warm climate like the Earth's. There is a possibility that liquid water could exist on the surface of the planet, raising the tantalising possibility of extraterrestrial life. K2-3d's orbit is aligned so that as seen from Earth, it transits (passes in front of) its host star. This causes, short, periodic decreases in the star's brightness, as the planet blocks some of the star's light. This alignment enables researchers to probe the atmospheric composition of these planets by precise measurement of the amount of blocked starlight at different wavelengths. About 30 potentially habitable planets that also have transiting orbits were discovered by the NASA Kepler mission, but most of these planets orbit fainter, more distant stars. Since it is closer to Earth and its host star is brighter, K2-3d is a more interesting candidate for detailed follow-up studies.
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