Heidelberg astronomers have discovered that Earth-like planets are remarkably common around the galaxy’s smallest stars, significantly boosting the prospects for finding habitable worlds nearby. This key finding comes from an international study using data from the CARMENES project and were published in Astronomy & Astrophysics.

The CARMENES spectrograph, developed at Heidelberg University’s Königstuhl Observatory and located in Spain, specifically targets M-dwarf stars. These stars, the most abundant type in the Milky Way, have masses less than half of our Sun’s. CARMENES detects planets by measuring the tiny stellar “wobbles” (radial velocity changes) caused by planetary gravitational pulls.

Analyzing 15 stars from a catalog of 2,200 M-dwarfs, the team discovered four new exoplanets. The largest is 14 times Earth’s mass, orbiting its star every 3.3 years. The other three are much smaller (1.03 to 1.52 Earth masses) and orbit very close to their stars, completing revolutions in just 1.43 to 5.45 days.

Crucially, statistical analysis revealed that stars with less than 0.16 solar masses (under one-sixth the Sun’s mass) host, on average, about two planets each with masses below three Earths. Larger planets are rarer, suggesting these stars preferentially form smaller, close-orbiting rocky worlds.

While none of the ~5,000 known exoplanets is a true Earth twin, these new planets meet critical mass (and implied rocky composition) criteria. Their proximity to cool M-dwarfs often places them within the theoretical habitable zone where liquid water could exist. Professor Andreas Quirrenbach (Heidelberg) highlighted the potential: the abundance and long-term stability of M-dwarfs make them prime candidates for hosting life-sustaining environments.

This study, involving researchers from multiple countries and funded by institutions including the EU and German Research Foundation, provides a strategic focus for the search for habitable exoplanets: look towards the smallest, most numerous stars.

Read the full article by Heidelberg University.