TOI-858 B b
TOI-858 B b is a hot Jupiter orbiting the G0 star TOI-858 B in the constellation Reticulum. It lies about 817 light-years from Earth and was discovered in 2023 using the transit method.
How Big Is TOI-858 B b?
TOI-858 B b has a radius of 14.07 times that of Earth, or 1.25 times the radius of Jupiter. Its mass is 350 times that of Earth, giving it a density of 0.69 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is TOI-858 B b in the Habitable Zone?
TOI-858 B b orbits inside the inner edge of the habitable zone of TOI-858 B. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of TOI-858 B: 1.000–2.352 AU (conservative: 1.267–2.230 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 ›
Temperature on TOI-858 B b
The equilibrium temperature of TOI-858 B b is about 1,529 K (1,256 °C) — hot enough to melt many metals. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C. It receives 909 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on TOI-858 B b — one full orbit around TOI-858 B — lasts 3.28 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.044 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.15).
How Was TOI-858 B b Discovered?
TOI-858 B 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 TOI-858 B b?
TOI-858 B b is 817.0 light-years (250.5 parsecs) from Earth. Light arriving here tonight left the planet around the year 1209. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 14,379,200 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. TOI-858 B b scores 0.07, ranking #5,053 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: TOI-858 B
TOI-858 B b belongs to a system of 2 stars; it orbits TOI-858 B.
TOI-858 B
- Spectral type
- G0
- Surface temperature
- 5,842 K (Sun: 5,772 K)
- Mass
- 1.08 M☉
- Radius
- 1.31 R☉
- Luminosity
- 1.7900 L☉
- Age
- 6.8 billion years (Sun: 4.6)
Planetary System
TOI-858 B b is the only planet known to orbit TOI-858 B so far.
TOI-858 B b — Complete Data
| Radius | 14.067 Earth radii (1.255 Jupiter radii) |
|---|---|
| Mass | 349.61 Earth masses (1.100 Jupiter masses) |
| Density | 0.69 g/cm³ (Earth: 5.51) |
| Orbital period | 3.28 days |
| Orbital distance | 0.044 AU |
| Eccentricity | 0.150 |
| Equilibrium temperature | 1,529 K (1,256 °C) |
| Stellar irradiation | 908.90× Earth |
| Earth Similarity Index | 0.07 |
| Distance from Earth | 817.0 light-years (250.5 parsecs) |
| Constellation | Reticulum |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2023 |
Data: NASA Exoplanet Archive, last updated 2025-04-07. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-858 B b
Is TOI-858 B b habitable?
No — TOI-858 B b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is TOI-858 B b?
TOI-858 B b is about 817 light-years from Earth in the constellation Reticulum. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 14,379,200 years to get there.
How big is TOI-858 B b compared to Earth?
TOI-858 B b has 14.07 times the radius of Earth and about 350 times its mass.
How long is a year on TOI-858 B b?
One orbit around TOI-858 B takes 3.3 Earth days — short enough that 111 of its years would fit into one Earth year.
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