Proxima Centauri d, Alpha Centauri C d or Proxima d is a planet orbiting the star Proxima Centauri, together with Proxima Centauri b and disputedly Proxima Centauri c it shares the title of the closest exoplanet to Earth, at about 4.2 light years (1.3 parsecs, 40 trillion kilometers) away in the Centaurus constellation.

The first sign of this planet was a weak 5.15 day-signal in radical velocity data detected during Very Large Telescope's exploration of Proxima b's mass. This was proposed as a planet on February 10, 2022 by Faria et al., and independently confirmed on July 29, 2025.

Characteristics

Proxima d is a sub-Earth at about one fourth its mass (or twice the mass of Mars). It formerly held the record for beng the least massive exoplanet, surpassed by Barnard's Star e in 2025.

The planet orbits its star at around 4.3 million kilometers away from its star, completing an orbit every 5.1 days. Its the closest planet to the star in the system

Because we don't know the planet's orbital inclination, we only know its minimum mass, which is about 0.26 M🜨. For example, assuming that the inclination is 47°, which would be coplanar with its star's rotation, it is around 0.36 M🜨.

With its proximity to the star, its very likely tidally locked, meaning that one side of the planet has an eternal day, and the other has an eternal night.

The planet's avearage temperature is around 87 °C, the temperatures in the polar regions might be much more habitable.

Proxima d has a magnetic field of around 16 G (for comparison, Earth's is only 0.25 - 0.65 G). This magnetic field also interacts with its star's magnetic field.