- weight
- 0.19 g
- sun
- 8.3× wider
- sky
- warm white
Illustration computed from this world’s measured and derived values, not a photograph.
K2-138 f
K2-138 f is a confirmed sub-Neptune exoplanet 661 ly from Earth in the constellation Aquarius, discovered in 2017 by K2.
Transit: spotted by the tiny, repeating dip in its star’s light each time the planet crosses in front of it.
Standing on K2-138 f, you would weigh about 81% less than you do on Earth. Its yellow, Sun-like star looks 8.3× 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 13 days, and at an estimated 380°C (716°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
Low gravity, 0.19 times Earth's. A child who grew up here could become strikingly tall and lightly built, about 1.4x taller than on Earth: a 5 ft 10 in adult could stand nearer 8 ft 1 in, with long limbs and slender bones.
- Bones
- Light and slender
- With little weight to carry, the growing skeleton lays down far less bone, the way astronauts' bones thin in months of low gravity.
- Heart
- Unhurried
- With less weight pulling blood down toward the feet, the heart has far less work to do.
- Movement
- Bounding and springy
- So little weight means each step would carry the body up and forward in long, floating strides.
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 380°C (716°F), sound would travel roughly 51% 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 380°C (716°F), far too hot for liquid water on the surface.
- !Far too little gravity, 0.19 times Earth's, to hold a breathable atmosphere: effectively an airless vacuum.
- !Its star delivers about 51 times the sunlight Earth gets, a blinding, sterilizing glare.
- !Likely tidally locked: one hemisphere in endless day, the other in permanent night.
A playful read of K2-138 f’s measured and computed values, not a real advisory.
How long to get there · 661 ly away
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 K2-138 f?
K2-138 f's surface gravity is about 0.19 times Earth's.
How much would you weigh on K2-138 f?
Someone who weighs 150 pounds on Earth would weigh about 29 pounds on K2-138 f.
How far is K2-138 f from Earth?
K2-138 f lies about 661 light-years from Earth.
How long would it take to get to K2-138 f?
At the speed of NASA's Parker Solar Probe, the fastest craft ever built, the journey would take about 1.0 million years.
How hot is K2-138 f?
K2-138 f's equilibrium temperature, the balance it reaches from its star's light alone before any greenhouse warming, is about 380°C (716°F).
How long is a year on K2-138 f?
K2-138 f completes one orbit of its star in 13 days.
Illustration generated from K2-138 f's confirmed parameters, not a photograph.