NASA’s Kepler space telescope, which has been retired after running out of fuel (The Indian Express, November 1), is being widely described as the most prolific planet-hunting machine in history. Indeed, by June 2017, it had discovered more than 4,000 planet candidates and 2,300 confirmed planets. Kepler also showed that the galaxy is teeming with — in NASA’s words — “other surprises”. From its legacy, here are 10 landmark findings:
DOUBLE SUNSET: The Star Wars franchise showed the planet Tatooine as part of a double-star system, hence two sunsets. Kepler showed that double sunsets do exist; it discovered Kepler-16b, the first known planet (mostly likely a gas giant) around a double-star system.
EARTH-LIKE PLANETS: Kepler found planets near in size to Earth and orbiting at a distance where liquid water could pool on the surface. Kepler-62f, for example, is about 40% bigger than Earth and is likely rocky.
PLANET CANDIDATES: Many of the planet candidates are likely to have small rocky cores enveloped by a thick atmosphere of hydrogen and helium, and some are thought to be ocean worlds. That doesn’t necessarily mean the oceans are full of water.
LIFE CANDIDATES: Kepler’s survey has made it possible to measure the number of Earth-size habitable zone planets in the galaxy. Scientists hope to determine how many planets like Earth exist.
SIZE CLASSIFICATION: Kepler’s discoveries showed that a lot of planets are either approximately 1.5 times the size of Earth or just smaller than Neptune. They are, therefore, called Super Earths and mini-Neptunes.
‘LAVA WORLD:’ Kepler-10b has a year that lasts less than an Earth day, and density so high that it is probably made of iron and rock. One of Kepler’s early discoveries, the first solid evidence of a rocky planet outside the Solar System.
LIGHT & ‘ALIENS’: Kepler detected fluctuating light from “Tabby’s Star”, triggering mass speculation of an alien megastructure. Astronomers, however, have since concluded that it is probably an orbiting dust cloud.
‘CANNIBAL’ STAR: What happens when a solar system dies? Kepler discovered a white dwarf, the compact corpse of a star in the process of vaporising a planet.
EXPLODING SUPERNOVA: Kepler recorded a sped-up version of a supernova called a “fast-evolving luminescent transit” that reached its peak brightness at breakneck speed. It was caused by a star spewing out a dense shell of gas that lit up when hit with the shockwave from the blast.
SOLAR SYSTEM COUSIN: In 2014, scientists using data from Kepler discovered seven planets orbiting Kepler-90, a Sun-like star located 2,500 light-years away. Later, an eighth planet was identified in this planetary system, tying it with our own Solar System in having the highest number of known planets.