TRAPPIST-1 System: Seven Alien Planets Discovered

By Sujan Dahal

NASA announced the discovery of seven alien planets in TRAPPIST system on 22 Feb,2017. TRAPPIST-1, is an ultra-cool dwarf star, located in the constellation Aquarius around 39.5 light-year (369 trillion kilometers) away from the sun. It is barely the size of the Jupiter (about 48 times massive than it) and 11% smaller than the size of the sun. Seven earth like temperate terrestrial planets are around the star, out of which three are in habitable zone, where liquid water and, possibly, life might exist.

In 2015, a team led by Michaël Gillon at University of Liège in Belgium detected three Earth sized planets orbiting dwarf star using transit photometry with the Transisting Planets and Planetesimals Small Telescope(TRAPPIST) at La Silla Observatory in Chile and published the findings in the May 2016 issue of journal Nature. NASA Spitzer Space Telescope and the Very Large Telescope at Paranal, found additional four planets on the same dwarf star in 2017.

TRAPPIST-1 star was initially discovered in 1999 during the Two Micron All-Sky Survey(2MASS) and designated by “2MASS J23032928-0502285”, where “J” refers to Julian Epoch and numbers to right ascension and declination. Its temperature is about 2550 K and approximately 500 million years old. Three planets around TRAPPIST-1 designated b, c and d, whereas remaining four designated e, f, g, h. Among them, planets e, f, g falls on habitable zones. Planets b, c, e, f, g are similar to the size of the earth but planets d and h are similar to the size of the half of the diameter of earth. The system is almost flat and the orbit of all planets are much closer to its star, as compared to the orbit of mercury and the star. Even the distance between the planet b and planet c is only 1.6 times the distance between the earth and the moon, results sometimes the appearance of neighboring planets several times larger than the moon to the earth. The total mass of six inner planets is approximately 0.02% of the system. Hubble Space Telescope shows the cloud free hydrogen dominate atmosphere and presence of ice. One side of all planets are permanently face the star (called tidally locked), causes the very large difference in temperature between day and night sides of planet, resulting very strong winds circling the planets. Terminating lines (mild twilight regions between the two sides) is the best places for life.

As the distance is 39 light-years, it would take 39 years to reach there with the speed of light, but no spacecraft ever built to attend such high speed. Even New Horizon (the fastest spacecraft which is currently travelling with the speed of 14.31 km per sec) would take 817,000 years (time taken is distance divided by velocity). The other fastest spacecrafts we build i.e. Juno (265,000 km/hr.), Voyage 1 (38200 mph), Space Shuttle (28,160 km/hr.) would take 159,000 years, 685,000 years and 1.5 million (respectively) years to reach TRAPPIST-1 system. Therefore, the distance has been a challenge to today’s astronomers to build such a spacecraft which would reach the system within the human’s survival.

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