TOI-157

TOI-157 is a G-type subgiant star located about 1160 light years from Earth. It has a mass of about 0.92 solar masses, a radius of about 1.1 solar radii and a temperature of about. It is approximately 12.0 to 12.8 billion years old.

Planetary system

It has one discovered exoplanet orbiting it named TOI-157b. It is a gas giant classed as a hot Jupiter with a mass of 1.18 Jupiter masses and a radius of 1.286 Jupiter radii. It orbits very close to the star taking only 2 days to complete an orbit. This places the temperature of TOI-157b to be around 1588 Kelvin. Using TESS data discrepant transit parameters as well as empirical limb-darkening coefficients could be determined. Further analysis revealed that the radius ratio of planet to star is 7.8 ± 0.4 % higher than previously determined, caused by blending with the light from background stars, at a new value of 0.1229 ± 0.0005.

It is a typical hot Jupiter. However, at an age of billion years the planet is currently the oldest discovered and only about 1 billion years younger than the age of the universe at about 13.8 billion years and part of the list of exoplanet extremes. Only PSR B1620-26 b with 11.2–12.7 Gyr remains as alternatively oldest exoplanet.