WHAT IS THE TRAPPIST-1 SYSTEM?

TRAPPIST-1 is a planetary system consisting of seven planets orbiting an ultra-cool dwarf star, called TRAPPIST-1, about 40 light-years away in the Aquarius constellation. 

TRAPPIST-1 is named after the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, which discovered two of the seven planets we know of today - announced in 2016. 

NASA's Spitzer Space Telescope, in collaboration with ground-based telescopes, confirmed these planets and uncovered the other five in the system.

The TRAPPIST-1 planets huddle so close to one another that a person standing on the surface of one of these worlds would have a spectacular view of the neighbouring planets in the sky, which would sometimes appear larger than the Moon looks to an observer on Earth. 

TRAPPIST-1 is a planetary system consisting of seven planets orbiting an ultra-cool dwarf star, called TRAPPIST-1, about 40 light-years away in the Aquarius constellation. TRAPPIST-1 is named after the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, which discovered two of the seven planets we know of today - announced in 2016

The researchers found that the seven planets are considered temperate, meaning that under certain geological and atmospheric conditions, all could have conditions that allow water to remain in liquid form

They may also be tidally locked, meaning the same side of the planet is always facing the star, and each side is in perpetual day or night. Although the planets are all closer to their star than Mercury is to the Sun, TRAPPIST-1 is such a cool star that its planets are temperate.

Based on available data, here are scientists' best guesses about the appearance of the planets: 

• TRAPPIST-1b: The system's innermost planet is likely to have a rocky core, surrounded by an atmosphere much thicker than Earth's.
• TRAPPIST-1c: Also likely has a rocky interior, but with a thinner atmosphere than planet b. 
• TRAPPIST-1d: The lightest of the planets - about 30 per cent the mass of Earth. Researchers are not certain whether it has a large atmosphere, an ocean or an ice layer. All three of these would provide the planet an 'envelope' of volatile substances. 
• TRAPPIST-1e: Researchers suspect that this planet is most like Earth. It is slightly denser than Earth, suggesting it might have a denser core than our planet. Like TRAPPIST-1c, it doesn't necessarily have a thick atmosphere, ocean or ice layer - making these two planets distinct in the system. In addition, the planet is a lot rockier than the rest of the planets. In terms of size, density and the amount of radiation it receives from its star, this is the most similar to planet Earth.
• TRAPPIST-1f, g and h: Far enough from the host star that water could be frozen as ice across these surfaces. If they have thin atmospheres, they would be unlikely to contain the heavy molecules of Earth such as carbon dioxide.