TIC 172900988 Exoplanet System

Warm circumbinary gas giant around a pair of Sun-like stars // TIC 172900988 (TIC 1729), also known as BEBOP-2, is a real exoplanet system located 803 light-years away in the constellation Cancer, consisting of two stars and one planet. The stars form an eclipsing binary with a fairly eccentric 19. 7-day orbit. TIC 1729 A, the primary component, is of an F9 spectral type with 1. 24 solar masses and 1. 38 solar radii. TIC 1729 B is a slightly smaller G0 yellow dwarf with 1. 20 solar masses and 1. 31 solar radii. The stars are younger than the Sun at 3. 1 billion years old, and hotter with surface temperatures of 6050 K (5777 °C) and 5983 K (5710 °C), respectively. Identified in 2021, TIC 1729 (AB) b is a planet on a nearly circular orbit around both stars of the binary pair, hence the use of “(AB)” in its designation. It is a gas giant with a size virtually identical to that of Jupiter. Still, its mass and orbital period could not be uniquely determined at the time of its discovery. This is because the planet was detected via transits across stars that are themselves in motion, so the observed signal reflects a combination of moving components rather than a simple orbit. In such systems, a degeneracy arises—different combinations of orbital period and mass can reproduce the same transit signal—leaving several possible solutions. Thus, the original discoverers could only constrain its mass in the range of 2. 65–3. 09 Jupiter masses, with an orbital period between 188 and 204 days. A 2024 follow-up study revisited the system using improved spectroscopic techniques to disentangle the spectral contributions of both stars. This enabled precise measurements of radial velocity—tiny shifts in the stars’ motion caused by the gravitational pull of the planet—substantially reducing the degeneracy inherent to transit data alone. With these additional constraints, the data are best fit by a planet with a mass of approximately 2 Jupiter masses on a shorter orbit of around 150 days, replac