Confirmed exoplanet · Database record + computed analysis
HD 21520 b
A confirmed world orbiting HD 21520, 258.3 light-years away.
A sub-Neptune
2.70 Earth radii, likely a rocky core under a thick gas or steam envelope rather than a walkable surface. With 17.7 Earth masses packed into that size, its density points to rock and iron rather than gas.
The orbit
Its year, one full orbit, takes just 25.1 Earth days.
Temperature and starlight
Its equilibrium temperature (the airless-world estimate) is about 364 °C. Above water's boiling point. It receives 25.7 times the starlight Earth gets.
Its sun
Its star is Sun-like (5,871 K; the Sun is 5,772 K).
How far is that, really?
At 258 light-years, tonight's light from this system left it around the year 1767. A Voyager-speed probe would need roughly 4,570,739 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 2024 from Transiting Exoplanet Survey Satellite (TESS).
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.