HD 235088 b
HD 235088 b is a mini-Neptune orbiting the K V star HD 235088 in the constellation Cygnus. It lies about 134 light-years from Earth and was discovered in 2023 using the transit method.
How Big Is HD 235088 b?
HD 235088 b has a radius of 1.98 times that of Earth. Its mass is 4.2 times that of Earth, giving it a density of 2.92 g/cm³ — between that of rocky and gaseous planets.
Is HD 235088 b in the Habitable Zone?
HD 235088 b orbits inside the inner edge of the habitable zone of HD 235088. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of HD 235088: 0.468–1.129 AU (conservative: 0.593–1.070 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Orbit and Year Length
A year on HD 235088 b — one full orbit around HD 235088 — lasts 7.43 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.071 AU — closer to its star than Mercury is to the Sun.
How Was HD 235088 b Discovered?
HD 235088 b was discovered in 2023 using the transit method, with observations from Transiting Exoplanet Survey Satellite (TESS).
The transit method watches a star for the tiny, regular dip in brightness that occurs when a planet crosses in front of it. The depth and timing of these dips reveal the planet's size and orbital period.
How Far Away Is HD 235088 b?
HD 235088 b is 134.3 light-years (41.2 parsecs) from Earth. Light arriving here tonight left the planet around the year 1892. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 2,363,680 years to make the journey.
Earth Similarity Index
The Earth Similarity Index (ESI) scores how physically similar a planet is to Earth, from 0 to 1, based on radius, density, escape velocity and surface temperature. HD 235088 b scores 0.27, ranking #2,571 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 235088
HD 235088
- Spectral type
- K V
- Surface temperature
- 5,075 K (Sun: 5,772 K)
- Mass
- 0.85 M☉
- Radius
- 0.77 R☉
- Luminosity
- 0.3600 L☉
- Age
- 0.7 billion years (Sun: 4.6)
Planetary System
HD 235088 b is the only planet known to orbit HD 235088 so far.
HD 235088 b — Complete Data
| Radius | 1.982 Earth radii (0.177 Jupiter radii) |
|---|---|
| Mass | 4.15 Earth masses (0.013 Jupiter masses) |
| Density | 2.92 g/cm³ (Earth: 5.51) |
| Orbital period | 7.43 days |
| Orbital distance | 0.071 AU |
| Earth Similarity Index | 0.27 |
| Distance from Earth | 134.3 light-years (41.2 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2023 |
Data: NASA Exoplanet Archive, last updated 2025-08-07. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 235088 b
Is HD 235088 b habitable?
No — HD 235088 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is HD 235088 b?
HD 235088 b is about 134 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 2,363,680 years to get there.
How big is HD 235088 b compared to Earth?
HD 235088 b has 1.98 times the radius of Earth and about 4.2 times its mass.
How long is a year on HD 235088 b?
One orbit around HD 235088 takes 7.4 Earth days — short enough that 49 of its years would fit into one Earth year.
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