SPECULOOS-3 b is an Earth-sized exoplanet, orbiting the ultracool red dwarf star SPECULOOS-3. It is relatively close to Earth, at a distance of 55 light-years.[4] SPECULOOS-3 b takes only about 17 hours to complete an orbit around SPECULOOS-3, and, because of that proximity, it receives very high levels of radiation and is tidally locked, meaning that one side of the planet always faces its host star.[5] Its discovery was made using the SPECULOOS project, and announced in May 2024 in the academic journal Nature Astronomy.[6]
The host star of SPECULOOS-3 b is SPECULOOS-3 (LSPM J2049+3336, TIC 230741378), an ultra-cool red dwarf star in the constellation Cygnus, with just one tenth of the Sun's mass, 13% of the size and 0.09% of its luminosity.[1]
Characteristics
The planet's radius, as deduced from its transit depth, is 0.98 R🜨, making it similar to Earth in size.[1] The mass of SPECULOOS-3b has been not measured,[1] but the NASA Exoplanet Catalog estimated it at 0.894 ME.[3] Measuring the planet's mass is essential to determining if it is rocky and to further contrain its composition.[1]
It orbits relatively close to its host star: one year on SPECULOOS-3 b is equivalent to about 17 hours in Earth.[4] The semi-major axis is equivalent to 0.7% of an astronomical unit.[1] As a consequence, the planet receives high levels of radiation from its host star,[5] and its planetary equilibrium temperature is estimated at 280°C assuming a null bond albedo, meaning that its dayside is likely made of solid rock.[1] It is also tidally locked to SPECULOOS-3, meaning that one side of the planet is always facing the star, while the other side is always facing away.[4][5][6]
Due to the planet's high temperature and its host star's infrared brightness, its dayside's astronomic spectrum (of emission) might be measured by the MIRI/RLS instrument aboard the James Webb Space Telescope. Such observations should reveal the presence of an atmosphere around the planet, or constrain its mineralogical surface, if no gases are detected.[1]
Discovery
The discovery of SPECULOOS-3 b was made using the SPECULOOS project, led by the University of Liège, in Belgium, in collaboration with other universities across different countries.[6] SPECULOOS consists of a network of telescopes in search of faint stars and exoplanets around them.[5] The planet was discovered using the observatory in the Atacama Desert, Chile.[7]
Transit method
The planet was detected using the transit method.[2] The host star SPECULOOS-3 was observed by the SAINT-EX telescope in 2021, for five nights, producing two light curves containing planetary transits. The star was later reviewed by the SPECULOOS-North observatory's Artemis telescope, revealing a clear transit-like signature on its light curve. Subsequent observations with the SAINT-EX and SPECULOOS-South telescopes revealed more planetary transits, which were associated with an Earth-like exoplanet transiting the star with an orbital period of 0.719 days.[1] SPECULOOS-3 b's discovery was announced in May 2024, in the journal Nature Astronomy.[6]
LSPM J2049+3336, also known as SPECULOOS-3, is a red dwarf star (spectral type M6.5), 16.75 parsecs (54.6 ly) away[1] in the constellation Cygnus.[a] It is one of the smallest known stars, and is much cooler, dimmer and smaller than the Sun, having 0.1 times the mass, 0.08% the Sun's luminosity, and an effective temperature of 2,800 K (2,530 °C), which is less than half the Sun's temperature (5,772K).[1] Its small radius of 0.12 R☉ make it the second-smallest star with a transiting planet, with only TRAPPIST-1 being smaller.[1]
Red dwarf stars such as SPECULOOS-3 are the most numerous type of stars, making up 70% of all stars in the Milky Way galaxy. They are expected to live 10 times more than the Sun, with lifespans longer than 100 billion years.[4]
Notes
^Obtained with right ascension and declination placed on this website.
