Exoplanet · gas giant
HAT-P-21 b
HAT-P-21 b is a gas giant orbiting the star Mazaalai. Its year lasts 4.12 Earth days. It was discovered in 2010 by the Transit method.
| Host star | Mazaalai |
|---|---|
| Distance | 904.4 light-years (277.3 pc) |
| Orbital period | 4.12 days |
| Orbital radius | 0.0504 AU |
| Eccentricity | 0.230 |
| Radius | 12.4 R⊕ · 1.11 R♃ |
| Mass | 1,550 M⊕ · 4.87 M♃ |
| Density | 3.63 g/cm³ |
| Surface gravity | 10 × Earth |
| Equilibrium temperature | 1,367 K (1,094 °C) |
| Stellar flux received | 460 × Earth |
| Discovery method | Transit |
| Discovery year | 2010 |
| Discovered by | HATNet |
Habitable zone
Inside the inner edge of the habitable zone: it receives 460 times the light the Earth does, too hot to keep liquid water on its surface.
Its star in the sky
In the planet's sky its star is a disc 13° across: 24 times the Sun as we see it from Earth.
In the sky
A telescope is needed to see it: its apparent magnitude is 11.58. Visible from the whole Northern Hemisphere and south to latitude 49° S. North of latitude 49° N it never sets. It stands highest at midnight in March, the best time to observe it.
Light's journey
The light you see tonight set out around the year 1122. At the speed of Voyager 1, the fastest craft leaving the Solar System (16.9 km per second), the trip would take 16 million years.
Data: NASA Exoplanet Archive, PSCompPars. Its look in the simulation is a rendering based on the measured radius, mass and temperature.