THE DWARF STAR AND ITS SEVEN PLANETS - WHAT WE KNOW
THE STAR
* Trappist-1 is an ultra-cool dwarf star that is 39 light years away in the constellation Aquarius (about 44 million years away at the average cruising speed of a passenger jet).
* It was discovered using TRAPPIST (Transiting Planets and Planetesimals Small Telescope) in Chile.
* Trappist-1 is barely the size of Jupiter and about 500 million years old but has an estimated lifespan of 10 trillion years, compared with the sun, which is about halfway through its 10 billion-year life.
* Researchers believe it is about 200 times dimmer than the sun and glows red or salmon-coloured.
THE PLANETS
* Seven Earth-size planets have been discovered orbiting Trappist-1, named Trappist-1b to h.
* They were detected using NASA's Spitzer Space Telescope as well as TRAPPIST and other ground-based telescopes.
* All seven are closer to their host star than Mercury is to the sun. The furthest is only about 8.98 million kilometres from Trappist-1.
* The planets' orbits are very close. If people were standing on one planet's surface, they "could potentially see geological features or clouds of neighbouring worlds, which would sometimes appear larger than the moon in Earth's sky", NASA says.
* The planets are similar in size to Earth and Venus or slightly smaller.
* The most massive planet, Trappist-1c, is 1.38 times the mass of Earth, while the least massive, d, is only 0.41 (the mass of h is unknown).
* A year on the innermost planet lasts only about 1.5 days, while the furthest orbits about once every 20 days.
* Based on their densities, the planets are likely to be rocky.
* The six inner planets are in a zone where temperatures range from 0C to 100C, while scientists believe the seventh, 1h, could be an ice world.
* At least three of the inner planets are thought to be capable of hosting liquid water, and possibly life.
* The innermost three are likely too hot but 1e,f and g are in the star's habitable zone.
Source: NASA/Reuters/AP
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