Planetary system · 2 known planets · Leo

K2-18

Its star: low after darkLow · east · 4° at 05:17

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Where is K2-18?

Times for LondonChange city

Low in the east, at most 4° up around 05:17 in Leo.

Rises: 04:51
Highest: 11:31
Sets: 18:16
Best after dark: 05:17 · 4°

Can I see K2-18?

No. The planets of K2-18 can’t be seen with the eye, binoculars or any amateur telescope: they are lost in their star’s light. What you can do is point toward the star.

From London tonight, the star K2-18 stays low while the sky is dark: at best 4° above the east horizon around 05:17. You’ll need a clear, flat view in that direction.

Why is K2-18 interesting?

K2-18 has 2 known planets, discovered between 2015 and 2017 by the radial velocity and primary transit methods.

What can you see?

Eyes

Direction only

Not visible.

Binoculars

Not visible.

Telescope

The star is around magnitude 13.5 and needs a telescope of about 200–250 mm and a detailed chart. The planets themselves can’t be seen with any backyard telescope.

What you’re likely to see, not what a space telescope photographs.

About

K2-18 is a red dwarf about 124 light-years away in Leo. Its planet K2-18 b is about two and a half times the size of Earth and orbits in its star’s habitable zone.

Water vapor was reported in its atmosphere in 2019. In 2023 the James Webb Space Telescope detected methane and carbon dioxide, and some researchers suggested the planet could have an ocean beneath a hydrogen-rich atmosphere.

Claims of a possible sign of life, a gas called dimethyl sulfide, have drawn wide attention but are unconfirmed and disputed by other researchers.

The planet was found by NASA’s K2 mission, the extended mission of the Kepler space telescope. K2-18 b is about eight to nine times Earth’s mass and orbits every 33 days.

It is probably not rocky like Earth. It may be a smaller version of Neptune, with a thick atmosphere, or a world with a deep ocean beneath a hydrogen-rich atmosphere.

The K2-18 system

Known planets of K2-18 (catalog values from exoplanet.eu)
Planet	Mass	Radius	Orbit	From star	Found	Method
K2-18 c	7.50 M⊕	—	8.96 days	0.06 AU	2017	Radial Velocity
K2-18 b	8.93 M⊕	2.37 R⊕	32.9 days	0.1429 AU	2015	Primary Transit

M⊕ / R⊕ = Earth masses / radii; M♃ / R♃ = Jupiter. Masses from radial velocity are often minimum masses. Data: The Extrasolar Planets Encyclopaedia, exoplanet.eu (CC BY 4.0).

Questions

Has life been found on K2-18 b?

No. Some researchers have reported a possible biosignature, but it is unconfirmed and disputed.

Can I see K2-18 b?

No. Even its star is faint.

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Sources: The Extrasolar Planets Encyclopaedia (CC BY 4.0); star chart: Wikidata (CC0). Positions computed for your place and time with astronomy-engine. Data & Licences