 Artist's impression of SPECULOOS-3 b and its host star, a red dwarf much cooler, dimmer than smaller than the Sun. | |
| Discovery[1] | |
|---|---|
| Discovered by | Michael Gillon et al. |
| Discovery site | SPECULOOS |
| Discovery date | May 15, 2024 |
| Transit method[2] | |
| Designations | |
Named after | SPECULOOS |
| Orbital characteristics[1] | |
| 0.00733AU | |
| 0.719 days (17 hours and 15 min.) | |
| Inclination | 89.44°±0.39° |
| Star | LSPM J2049+3336 (SPECULOOS-3) |
| Physical characteristics[1] | |
| 0.977±0.02 R🜨 0.07273 RJ | |
| Mass | 0.894 M🜨 (estimate)[3] |
| Temperature | 553±8 K (280±8 °C) |
SPECULOOS-3 b is an Earth-sizedexoplanet, orbiting the ultracoolred dwarf starSPECULOOS-3. It is relatively close to Earth, at a distance of 55light-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 istidally locked, meaning that one side of the planet always faces its host star.[5] Its discovery was made using theSPECULOOS project, and announced in May 2024 in the academic journalNature Astronomy.[6]
The host star of SPECULOOS-3 b isSPECULOOS-3 (LSPM J2049+3336, TIC 230741378), an ultra-coolred dwarf star in the constellationCygnus, with just one tenth of theSun's mass, 13% of the size and 0.09% of its luminosity.[1]
The planet's radius, as deduced from itstransit depth, is 0.98 R🜨, making it similar to Earth in size.[1] The mass of SPECULOOS-3b has been not measured,[1] but theNASA Exoplanet Catalog estimated it at0.894 M🜨.[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] Thesemi-major axis is equivalent to 0.7% of anastronomical 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 nullbond albedo, meaning that its dayside is likely made of solid rock.[1] It is alsotidally 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'sastronomic spectrum (of emission) might be measured by the MIRI/RLS instrument aboard theJames Webb Space Telescope. Such observations should reveal the presence of an atmosphere around the planet, or constrain itsmineralogical surface, if no atmosphere is detected.[1]
The discovery of SPECULOOS-3 b was made using theSPECULOOS project, led by theUniversity of Liège, inBelgium, 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 theAtacama Desert, Chile.[7]
The planet was detected using thetransit method.[2] The host star SPECULOOS-3 was observed by theSAINT-EX telescope in 2021, for five nights, producing twolight curves containingplanetary 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 anorbital period of 0.719 days.[1] SPECULOOS-3 b's discovery was announced in May 2024, in the journalNature Astronomy.[6]
LSPM J2049+3336, also known as SPECULOOS-3, is ared dwarf star (spectral type M6.5), 16.75 parsecs (54.6 ly) away[1] in the constellationCygnus.[a] It is one of thesmallest known stars, and is much cooler, dimmer and smaller than the Sun, having 0.1 times themass, 0.08% theSun's luminosity, and an effective temperature of 2,800 K (2,530 °C), which is less than half the Sun's temperature (5,772 K).[1] Its small radius of 0.12 R☉ make it the second-smallest star with atransiting planet, with onlyTRAPPIST-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 theMilky Way galaxy. They are expected to live 10 times more than the Sun, with lifespans longer than 100 billion years.[4]
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