TOI-172 b
TOI-172 b is a hot Jupiter orbiting TOI-172 in the constellation Capricornus. It lies about 1,118 light-years from Earth and was discovered in 2019 using the transit method.
How Big Is TOI-172 b?
TOI-172 b has a radius of 10.82 times that of Earth, or 0.97 times the radius of Jupiter. Its mass is 1,723 times that of Earth, giving it a density of 7.53 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is TOI-172 b in the Habitable Zone?
TOI-172 b orbits inside the inner edge of the habitable zone of TOI-172. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of TOI-172: 1.286–3.041 AU (conservative: 1.629–2.883 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-172 b
The equilibrium temperature of TOI-172 b is about 1,198 K (925 °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 299 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on TOI-172 b — one full orbit around TOI-172 — lasts 9.48 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.091 AU — closer to its star than Mercury is to the Sun. Its orbit is highly elliptical (eccentricity 0.38), swinging dramatically closer to and farther from its star.
How Was TOI-172 b Discovered?
TOI-172 b was discovered in 2019 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-172 b?
TOI-172 b is 1,118.2 light-years (342.8 parsecs) from Earth. Light arriving here tonight left the planet about 1,118 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 19,680,320 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-172 b scores 0.08, ranking #4,600 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: TOI-172
TOI-172
- Surface temperature
- 5,645 K (Sun: 5,772 K)
- Mass
- 1.13 M☉
- Radius
- 1.78 R☉
- Luminosity
- 2.8900 L☉
- Age
- 7.4 billion years (Sun: 4.6)
Planetary System
TOI-172 b is the only planet known to orbit TOI-172 so far.
TOI-172 b — Complete Data
| Radius | 10.817 Earth radii (0.965 Jupiter radii) |
|---|---|
| Mass | 1,722.64 Earth masses (5.420 Jupiter masses) |
| Density | 7.53 g/cm³ (Earth: 5.51) |
| Orbital period | 9.48 days |
| Orbital distance | 0.091 AU |
| Eccentricity | 0.381 |
| Equilibrium temperature | 1,198 K (925 °C) |
| Stellar irradiation | 299.00× Earth |
| Earth Similarity Index | 0.08 |
| Distance from Earth | 1,118.2 light-years (342.8 parsecs) |
| Constellation | Capricornus |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2019 |
Data: NASA Exoplanet Archive, last updated 2019-03-29. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-172 b
Is TOI-172 b habitable?
No — TOI-172 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is TOI-172 b?
TOI-172 b is about 1,118 light-years from Earth in the constellation Capricornus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 19,680,320 years to get there.
How big is TOI-172 b compared to Earth?
TOI-172 b has 10.82 times the radius of Earth and about 1,723 times its mass.
How long is a year on TOI-172 b?
One orbit around TOI-172 takes 9.5 Earth days — short enough that 39 of its years would fit into one Earth year.
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