- weight
- 2.43 g
- sun
- 6.0× wider
- sky
- warm white
Illustration computed from this world’s measured and derived values, not a photograph.
HD 21520 b
HD 21520 b is a confirmed sub-Neptune exoplanet 258 ly from Earth in the constellation Eridanus, discovered in 2024 by Transiting Exoplanet Survey Satellite (TESS).
Transit: spotted by the tiny, repeating dip in its star’s light each time the planet crosses in front of it.
Standing on HD 21520 b, you would weigh about 143% more than you do on Earth. Its yellow, Sun-like star looks 6.0× wider than ours, bathing the surface in warm white light. It is likely tidally locked, so that sun never moves in the sky: one hemisphere in endless day, the other in permanent night. A year passes in just 25 days, and at an estimated 364°C (687°F) it is blistering.
How closely this world matches Earth in size and warmth, from 0 to 1 (Earth = 1.0). Computed by gravityfinder. See every world ranked →
What these mean: surface gravity · tidal locking · equilibrium temperature · Earth similarity
If your children grew up herea playful thought experiment
Heavier than home, at 2.4 times Earth's gravity. A child would end up markedly shorter and powerfully built, about 0.84x as tall as on Earth: a 5 ft 10 in adult could stand nearer 4 ft 11 in. Bones, muscle, and heart would all grow heavier just to stand and move.
- Bones
- Thick and dense
- More weight to bear forces the skeleton to grow denser and stronger all through childhood.
- Heart
- Large and powerful
- Pushing blood upward against stronger gravity demands a bigger, harder-working heart.
- Movement
- Low and deliberate
- A fall under this gravity lands hard, so movement stays slow, planted, and careful.
A playful thought experiment from this world’s gravity, not a prediction about any real person. No human has ever grown up off Earth, so no one truly knows; the direction (taller in low gravity, shorter and stockier in high) follows how growing bodies respond to weight.
Hear how a voice sounds herea computed acoustic demo
Your voice would sound high and thin, almost cartoonish.
Assuming Earth-like air at this world's temperature of about 364°C (687°F), sound would travel roughly 49% faster than on Earth, so your voice would sound high and thin, almost cartoonish. The real atmosphere is unknown, so this is a best guess.
A real voice sample, pitch-shifted (tempo held constant) to suggest the acoustics: a playful approximation, not a precise simulation. Voice: Lingua Libre / Vealhurl, CC BY-SA 4.0.
- !Blistering at about 364°C (687°F), far too hot for liquid water on the surface.
- !Gravity is 2.4 times Earth's, so every movement is a strain and a fall could be fatal.
- !Likely tidally locked: one hemisphere in endless day, the other in permanent night.
A playful read of HD 21520 b’s measured and computed values, not a real advisory.
How long to get there · 258 ly away
No other confirmed planets here yet. New ones auto-appear as telescopes report.
Zoom out: star → system → (soon) galaxy arm, host black hole, and a real image of the host galaxy.
Matched telescope & eyepiece recommendations are coming. Any product links will carry a clear affiliate disclosure.
What is the gravity on HD 21520 b?
HD 21520 b's surface gravity is about 2.4 times Earth's.
How much would you weigh on HD 21520 b?
Someone who weighs 150 pounds on Earth would weigh about 365 pounds on HD 21520 b.
How far is HD 21520 b from Earth?
HD 21520 b lies about 258 light-years from Earth.
How long would it take to get to HD 21520 b?
At the speed of NASA's Parker Solar Probe, the fastest craft ever built, the journey would take about 402,912 years.
How hot is HD 21520 b?
HD 21520 b's equilibrium temperature, the balance it reaches from its star's light alone before any greenhouse warming, is about 364°C (687°F).
How long is a year on HD 21520 b?
HD 21520 b completes one orbit of its star in 25 days.
Illustration generated from HD 21520 b's confirmed parameters, not a photograph.