TRAPPIST-1 is a cool red dwarf star with seven known exoplanets. It lies in the constellation Aquarius about 40.66 light-years away from Earth, and has a surface temperature of about 2,566 K. Its radius is slightly larger than Jupiter and it has a mass of about 9% of the Sun. It is estimated to be 7.6 billion years old, making it older than the Solar System. The discovery of the star was first published in 2000.
TRAPPIST-1 is within the red circle in the constellation Aquarius.
True-colour illustration of the Sun (left) next to TRAPPIST-1 (right). TRAPPIST-1 is darker, redder, and smaller than the Sun.
Comparison of the orbits of the TRAPPIST-1 planets with the Solar System and Jupiter's moons
Relative sizes, densities, and illumination of the TRAPPIST-1 system compared to the inner planets of the Solar System
An ultra-cool dwarf is a stellar or sub-stellar object that has an effective temperature lower than 2,700 K .
This category of dwarf stars was introduced in 1997 by J. Davy Kirkpatrick, Todd J. Henry, and Michael J. Irwin. It originally included very low mass M-dwarf stars with spectral types of M7 but was later expanded to encompass stars ranging from the coldest known to brown dwarfs as cool as spectral type T6.5. Altogether, ultra-cool dwarfs represent about 15% of the astronomical objects in the stellar neighborhood of the Sun. One of the best known examples is TRAPPIST-1.
Size comparison of the Sun (at left) and TRAPPIST-1 (an ultra-cool dwarf)
