About this world
HD 153557 b is a Neptune-like planet orbiting HD 153557, an orange dwarf (type K0) 58.5 light-years from Earth. It is about 4.8 times the size of Earth (its size estimated from its mass), with at least 20 Earth masses (a minimum, measured by radial velocity). It completes an orbit every 7.3 days at 0.068 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 772 K (499 °C): far too hot for liquid water on its surface. At its size it almost certainly keeps a deep envelope of hydrogen and helium.
It was discovered in 2022 by radial velocity with Multiple Observatories. The star wobbles toward and away from us, Doppler-shifting its spectrum. HD 153557 has 3 known planets; the others are HD 153557 c and HD 153557 d.