Gliese 777
Binary star in the constellation Cygnus
From Wikipedia, the free encyclopedia
Gliese 777, also known as HD 190360, is a binary star system approximately 52 light-years (15.9 parsecs) away in the constellation of Cygnus. The system is made up of two stars and possibly a third. Three exoplanets are known to orbit the primary star.
Stellar components
The primary star of the system (catalogued as Gliese 777 A) is a yellow subgiant, a Sun-like star that is ceasing fusing hydrogen in its core. The star is older than the Sun, about 4.79 billion years old. It is 4% less massive than the Sun. It is also rather metal-rich, having about 70% more "metals" (elements heavier than helium) than the Sun, which is typical for stars with extrasolar planets.
The secondary star (Gliese 777 B) is a distant, dim red dwarf star orbiting the primary at a distance of 3,000 astronomical units (0.047 light years). A faint companion has been reported, but not confirmed.[15]
Planetary system
In 2002, a discovery of a long-period, wide-orbiting, planet (Gliese 777 Ab) was announced by the Geneva extrasolar planet search team.[16] The planet was estimated to orbit in a circular path with low orbital eccentricity, but that estimate was increased with later measurements (e=0.36).[17] Initially therefore, the planet was believed to be a true "Jupiter-twin" but was later redefined as being more like an "eccentric Jupiter", with a mass of at least 1.5 times Jupiter and about the same size. In 2021, the true mass of Gliese 777 Ab was measured via astrometry.[18]
In 2005, further observation of the star showed another amplitude with a period of 17.1 days.[17] The mass of this second planet (Gliese 777 Ac) was only 18 times more than Earth, or about the same as Neptune, indicating it was one of the smallest planets discovered at the time. Initially thought to be on a circular orbital path (e = 0.01),[17] Gliese 777 c was revealed to have a more eccentric orbit with later measurements.[9]
Evidence for a third candidate planet with an orbital period around 89 days was presented in 2025.[9] It was confirmed in the same year.[19]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (years) |
Eccentricity | Inclination (°) |
Radius |
|---|---|---|---|---|---|---|
| c | 26.1+25.7 −4.1 M🜨 |
0.1296+0.0017 −0.0018 |
0.0468627(11) (17.12 d) |
0.163+0.020 −0.019 |
95+46 −51 |
— |
| d | ≥10.23+0.81 −0.80 M🜨 |
0.3886±0.0046 | 0.2430±0.0001 | 0.058+0.062 −0.040 |
— | — |
| b | 1.68+0.26 −0.16[9] MJ |
3.965±0.047 | 7.906±0.010 | 0.3342+0.0061 −0.0062 |
69+42 −17[9] |
— |
There was a METI message sent to Gliese 777. It was transmitted from Eurasia's largest radar, 70-meter Eupatoria Planetary Radar. The message was named Cosmic Call 1; it was sent on July 1, 1999, and it will arrive at Gliese 777 in April 2051.[20]