Confirmed exoplanet · Database record + computed analysis
HAT-P-21 b
A confirmed world orbiting HAT-P-21, 904.4 light-years away.
A gas giant
12.44 Earth radii, Jupiter-class (Jupiter is 11.2). Orbiting this close, it is a classic 'hot Jupiter', a giant that migrated inward from where it formed.
The orbit
Its year, one full orbit, takes just 4.1 Earth days.
Temperature and starlight
Its equilibrium temperature (the airless-world estimate) is about 1,094 °C. Hot enough to melt copper; any surface would glow. It receives 459.5 times the starlight Earth gets.
Its sun
Its star is Sun-like (5,588 K, G3; the Sun is 5,772 K).
How far is that, really?
At 904 light-years, tonight's light from this system left it around the year 1121. A Voyager-speed probe would need roughly 16,000,471 years to get there.
How we found it
It was found by the transit method: the planet crosses its star's face on schedule, dimming it by a tiny, repeating fraction. The dip's depth gives the planet's size. The discovery was announced in 2010 from HATNet.
Everything above is computed from the archive’s measured values for this planet. Where a quantity is missing, the statement is omitted rather than guessed.
About this record
The measured values come from the NASA Exoplanet Archive, and any missing value has not been determined yet; the Atlas never fills gaps with guesses. More standout worlds: Proxima b, TRAPPIST-1e, K2-18 b, 55 Cancri e, and the detection methods that found them all.