TRAPPIST-1

TRAPPIST-1 is an ultracool dwarf star about 40 light-years from Earth, orbited by seven known planets roughly comparable to Earth in size.

Ultracool dwarf: A very low-mass, cool star or substellar object with a spectral type of M7 or later. TRAPPIST-1 is an unusually nearby example of this faint stellar class.
Transit timing variation: A change in an exoplanet’s transit time caused by gravitational perturbations from other bodies. Interactions among the planets shift their transits and help determine their masses.
TRAPPIST-1b: The innermost known planet orbiting TRAPPIST-1, with a radius close to Earth’s. Its short orbit makes it a key case for studying intense irradiation in the system.
TRAPPIST-1h: The outermost known planet orbiting TRAPPIST-1, with a radius smaller than Earth’s. Its cold orbit extends the system’s comparison beyond the planets often called temperate.
Michaël Gillon: A Belgian astronomer whose exoplanet research includes leading the discovery of the TRAPPIST-1 planetary system. Gillon led the team that announced seven planets orbiting the star.
TRAPPIST photometric system: A set of astronomical filters used to measure light from stars and other celestial objects. The star’s name comes from the telescope system that first detected its transits.
Transit depth: The fractional decrease in a star’s observed brightness during a planetary transit. Transit depth, combined with the star’s radius, gives estimates of the planets’ radii.
TRAPPIST-1c: The second known planet orbiting TRAPPIST-1, with a radius close to Earth’s. Its measured properties help test whether inner planets retain substantial atmospheres.
Stellar flare: A sudden, intense increase in a star’s brightness caused by magnetic energy release. TRAPPIST-1’s flares may affect atmospheric retention and surface radiation on its planets.
TRAPPIST telescope: A robotic telescope at La Silla Observatory in Chile, used to monitor stars for planetary transits. Observations with this telescope first identified transits from the system’s planets.

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