TRAPPIST-1 is a red dwarf star about 40.7 light-years away from Earth.

It is of particular interest because it has seven earth-like planets orbiting around it. The star was discovered using the Transiting Planets and Planetesimals Small Telescope (TRAPPIST), hence the rather strange name.

The planets were found by carefully monitoring the brightness of the star. If the planets have orbits taking them between the star and us, we will detect a tiny dimming of the star.

Amazingly, just from observing these transits, we can infer a lot about the planet in question. How long the planet takes to transit across the star's disc and the interval between these transits gives us a good idea of the planet's diameter and how long it takes to orbit its star.

That, in turn, gives us its distance from the star. Because we know how bright the star is, we can calculate how much energy is falling on the planet. From that, we can make a pretty good estimate of the planet's surface temperature.

In some cases, we........

© Castanet