Astronomers have uncovered a third planet orbiting Proxima Centauri, the closest star to our Solar System, located just 4.2 light-years away. Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile, researchers detected faint signals of an object completing a five-day orbit around the star. The signals were later confirmed as a planet using the ESPRESSO spectrograph, ensuring they weren’t caused by the star’s activity.

Named Proxima d, this exoplanet is remarkable for its size—at just a quarter of Earth’s mass, it is the smallest and lightest planet identified in the Proxima Centauri system. The planet orbits about 4 million kilometers from its host star, less than a tenth of Mercury’s distance from the Sun. Although it orbits near Proxima Centauri’s habitable zone, the actual conditions on the planet remain uncertain.

Proxima d joins the previously discovered planets Proxima Centauri b and Proxima Centauri c, making this star system a focal point for studying planetary diversity and habitability beyond our Solar System.

Proxima Centauri’s system is a top candidate for future interstellar exploration due to its proximity and intriguing planetary lineup. Proxima Centauri b, discovered in 2016, is an Earth-sized planet located within the star’s habitable zone, offering the potential for liquid water on its surface. In contrast, Proxima Centauri c is a super-Earth or mini-Neptune with a mass seven times that of Earth, but its distant orbit makes it unlikely to support life.

Proxima d adds a new dimension to the system’s diversity. Its small size and rocky nature suggest it may resemble terrestrial planets like Earth. Furthermore, the discovery underscores the capabilities of the radial velocity technique used with instruments like ESPRESSO, which can detect lightweight exoplanets that might host life.

As lead researcher João Faria noted, the proximity of the Proxima Centauri system makes it an exceptional case for deeper study and eventual exploration. Future missions could offer unprecedented insights into the formation and potential habitability of planets in this system.

This discovery, published in the journal Astronomy & Astrophysics, highlights the abundance of small, rocky planets in the galaxy. According to Pedro Figueira, an ESPRESSO instrument scientist, this technique could unveil many such planets, which are thought to be the most common type in the universe.

With advancements in space travel and observation technologies, the Proxima Centauri system represents a stepping stone toward understanding exoplanets and the possibility of extraterrestrial life.