TOI-1728 b
TOI-1728 b is a Neptune-like planet orbiting the M0 star TOI-1728 in the constellation Camelopardalis. It lies about 198 light-years from Earth and was discovered in 2020 using the transit method.
How Big Is TOI-1728 b?
TOI-1728 b has a radius of 5.05 times that of Earth. Its mass is 26.8 times that of Earth, giving it a density of 1.14 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is TOI-1728 b in the Habitable Zone?
TOI-1728 b orbits inside the inner edge of the habitable zone of TOI-1728. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of TOI-1728: 0.241–0.610 AU (conservative: 0.305–0.578 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-1728 b
The equilibrium temperature of TOI-1728 b is about 767 K (494 °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 57.78 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on TOI-1728 b — one full orbit around TOI-1728 — lasts 3.49 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.039 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.06).
How Was TOI-1728 b Discovered?
TOI-1728 b was discovered in 2020 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-1728 b?
TOI-1728 b is 198.3 light-years (60.8 parsecs) from Earth. Light arriving here tonight left the planet around the year 1828. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 3,490,080 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-1728 b scores 0.17, ranking #4,096 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: TOI-1728
TOI-1728
- Spectral type
- M0
- Surface temperature
- 3,980 K (Sun: 5,772 K)
- Mass
- 0.65 M☉
- Radius
- 0.62 R☉
- Luminosity
- 0.0880 L☉
- Age
- 7.1 billion years (Sun: 4.6)
Planetary System
TOI-1728 b is the only planet known to orbit TOI-1728 so far.
TOI-1728 b — Complete Data
| Radius | 5.050 Earth radii (0.451 Jupiter radii) |
|---|---|
| Mass | 26.78 Earth masses (0.084 Jupiter masses) |
| Density | 1.14 g/cm³ (Earth: 5.51) |
| Orbital period | 3.49 days |
| Orbital distance | 0.039 AU |
| Eccentricity | 0.057 |
| Equilibrium temperature | 767 K (494 °C) |
| Stellar irradiation | 57.78× Earth |
| Earth Similarity Index | 0.17 |
| Distance from Earth | 198.3 light-years (60.8 parsecs) |
| Constellation | Camelopardalis |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2020 |
Data: NASA Exoplanet Archive, last updated 2020-07-02. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-1728 b
Is TOI-1728 b habitable?
No — TOI-1728 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is TOI-1728 b?
TOI-1728 b is about 198 light-years from Earth in the constellation Camelopardalis. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 3,490,080 years to get there.
How big is TOI-1728 b compared to Earth?
TOI-1728 b has 5.05 times the radius of Earth and about 26.8 times its mass.
How long is a year on TOI-1728 b?
One orbit around TOI-1728 takes 3.5 Earth days — short enough that 105 of its years would fit into one Earth year.
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