HD 1397 b
HD 1397 b is a hot Jupiter orbiting HD 1397 in the constellation Tucana. It lies about 260 light-years from Earth and was discovered in 2018 using the transit method.
How Big Is HD 1397 b?
HD 1397 b has a radius of 11.50 times that of Earth, or 1.03 times the radius of Jupiter. Its mass is 132 times that of Earth, giving it a density of 0.48 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is HD 1397 b in the Habitable Zone?
HD 1397 b orbits inside the inner edge of the habitable zone of HD 1397. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of HD 1397: 1.629–3.866 AU (conservative: 2.063–3.665 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on HD 1397 b
The equilibrium temperature of HD 1397 b is about 1,228 K (955 °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 356 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on HD 1397 b — one full orbit around HD 1397 — lasts 11.5 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.110 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.25).
How Was HD 1397 b Discovered?
HD 1397 b was discovered in 2018 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 1397 b?
HD 1397 b is 259.5 light-years (79.6 parsecs) from Earth. Light arriving here tonight left the planet around the year 1767. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 4,567,200 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. HD 1397 b scores 0.08, ranking #4,681 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 1397
HD 1397
- Surface temperature
- 5,521 K (Sun: 5,772 K)
- Mass
- 1.32 M☉
- Radius
- 2.34 R☉
- Luminosity
- 4.5700 L☉
- Age
- 4.5 billion years (Sun: 4.6)
Planetary System
HD 1397 b is the only planet known to orbit HD 1397 so far.
HD 1397 b — Complete Data
| Radius | 11.500 Earth radii (1.026 Jupiter radii) |
|---|---|
| Mass | 131.90 Earth masses (0.415 Jupiter masses) |
| Density | 0.48 g/cm³ (Earth: 5.51) |
| Orbital period | 11.54 days |
| Orbital distance | 0.110 AU |
| Eccentricity | 0.251 |
| Equilibrium temperature | 1,228 K (955 °C) |
| Stellar irradiation | 356.00× Earth |
| Earth Similarity Index | 0.08 |
| Distance from Earth | 259.5 light-years (79.6 parsecs) |
| Constellation | Tucana |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2018 |
Data: NASA Exoplanet Archive, last updated 2019-07-19. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 1397 b
Is HD 1397 b habitable?
No — HD 1397 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is HD 1397 b?
HD 1397 b is about 260 light-years from Earth in the constellation Tucana. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 4,567,200 years to get there.
How big is HD 1397 b compared to Earth?
HD 1397 b has 11.50 times the radius of Earth and about 132 times its mass.
How long is a year on HD 1397 b?
One orbit around HD 1397 takes 11.5 Earth days — short enough that 32 of its years would fit into one Earth year.
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