Depth 19 · Rocky exoplanet

Proxima Centauri b

Proxima Centauri b is the closest known exoplanet, circling the red dwarf Proxima Centauri, the nearest star to the Sun. It orbits within its star's habitable zone, where liquid water could exist in principle, although intense flares from the star may make conditions harsh.

Fact sheet

Type

Exoplanet about as massive as Earth, likely rocky, orbiting a red dwarf

Distance

About 4.25 light-years from the Sun

Size

Minimum mass about 1.07 times Earth's; its radius has not been measured (NASA gives an estimate of about 1.0 Earth radius)

Constellation

Centaurus

Position in the sky

Right ascension 14h 30m, declination −62° 41′

Seeing it from Earth

Neither the planet nor its star can be seen with the naked eye; Proxima Centauri is a faint red dwarf in the southern constellation Centaurus that needs a telescope, and the planet itself has only been detected indirectly.

On the voyage

Depth 19, in the Nearby stars section of the route, between Alpha Centauri and Barnard's Star

Things to know

• The planet was announced in 2016 by the Pale Red Dot campaign, which used the HARPS spectrograph at ESO's La Silla Observatory to detect the tiny back-and-forth wobble the planet causes in its star. ESO
• It completes an orbit every 11.2 days at only about 5% of the Earth-Sun distance, yet it still sits in the habitable zone because Proxima Centauri is so much dimmer than the Sun. ESO
• The planet was confirmed in 2020 with the more precise ESPRESSO instrument on ESO's Very Large Telescope, which later also revealed a second, smaller planet, Proxima d, with about a quarter of Earth's mass and a five-day orbit. ESO
• Chandra X-ray observations suggest a planet in Proxima's habitable zone receives on average about 500 times more X-rays than Earth, and around 50,000 times more during a big flare. NASA Chandra
• Tidal forces probably keep one side of the planet facing its star in permanent daylight while the other side stays dark. ESO

Sources

• NASA Science – Proxima Centauri b (exoplanet catalog)
• ESO – Planet found in habitable zone around nearest star (eso1629)
• ESO – New planet detected around star closest to the Sun (eso2202)
• NASA Exoplanet Archive – Proxima Cen system overview