About the image. Drawn with a dark crust split by glowing magma, after the lava-ocean interpretation of Spitzer and JWST data. The temperature is measured; the surface itself has never been seen.
61×as wide as our Sun looks from Earth
2 400×the light Earth gets
Almost certainly tidally locked: the star stays put
The sky from 55 Cancri e
55 Cancri A would look 61× as wide as the Sun does from Earth, and the planet gets 2 400× as much light as Earth gets.
Its colour comes from its surface temperature of 5 172 K (4 900 °C); the Sun's is about 5 772 K (5 500 °C).
55 Cancri e is almost certainly tidally locked: one side always faces the star.
There are no sunrises. Where you stand decides where the star hangs, overhead on the day side, low at the edge, gone on the night side.
Apparent size = star radius ÷ orbit; light = size² × (temperature ÷ 5 772 K)⁴. Both from the values on this page. The landscape is imagined.
55 Cancri e is one of the most extreme small planets known. It is a super-Earth almost twice Earth’s width, orbiting so close to its star that one trip around takes less than 18 hours. It is almost certainly tidally locked: one hemisphere always faces the star, the other is in permanent night.
A magma ocean
Spitzer mapped the planet’s heat in 2016 and found an average dayside temperature of about 2 700 K (2 430 °C), hot enough to melt rock. Infrared results announced in 2017 pointed to a global lava ocean under an atmosphere. In 2024 a team led by Renyu Hu used the James Webb Space Telescope to measure its thermal glow and ruled out a thin atmosphere of vaporised rock. What they found instead looks like a real volatile atmosphere, likely rich in carbon dioxide or carbon monoxide, possibly fed by gas bubbling out of the magma below.
The diamond planet
In 2012 Nikku Madhusudhan and colleagues proposed that the planet might be carbon-rich rather than oxygen-rich like Earth, with perhaps a third of its mass in carbon, some of it as diamond. The headline stuck. The idea has never been confirmed and needs further observations.
In 2015 the planet received an official name, Janssen, after the Dutch spectacle-maker linked to the invention of the telescope.
Its orbit, to scale
55 Cancri e goes around once every 17.7 hours, at 0.01544 AU from its star. The whole view is tiny on Solar System scale: Mercury orbits the Sun about 25 times farther out than the outermost orbit shown here.
55 Cancri e: dayside temperature (2016). Logarithmic scale from 100 K to 10 000 K. Reference values: NASA, IAU.
How long to get there?
55 Cancri e is about 41 light-years away.
Light299 792 km/s41 years
Breakthrough Starshotplanned light sail, 20% of light speed205 years
Parker Solar Probefastest spacecraft so far, 192 km/s64 018 years
Voyager 1leaving the Solar System, 17 km/s723 028 years
At Voyager 1's speed the trip would take about 9 038 human lifetimes of 80 years. Bars are on a logarithmic scale. Speeds: NASA, Breakthrough Initiatives.
Your weight on 55 Cancri e
On 55 Cancri e
Gravity there is about 2.27× Earth's. Calculated from the measured mass and radius.
Gallery
Artist's impressions rendered from the same model as the view at the top of this page.
Timeline
2004Discovered from its star's wobble at McDonald Observatory.
2012A carbon-rich, partly diamond interior is proposed.
2015Named Janssen in the IAU NameExoWorlds contest.
2016Spitzer maps a dayside around 2 700 K (2 430 °C).
2024JWST finds signs of a real atmosphere, likely rich in CO₂ or CO.
Questions people ask
Is 55 Cancri e made of diamond?
That was proposed in 2012, when one study suggested the planet could be carbon-rich with diamond inside. It has never been confirmed.
How long is a year on 55 Cancri e?
About 17.7 hours. It orbits its star more than once every Earth day.
Is 55 Cancri e covered in lava?
Its dayside is hot enough to melt rock, and the evidence points to a magma ocean under an atmosphere.