Astronomers have narrowed the search for extraterrestrial life by identifying a focused group of Earth-like planets that may offer the most favourable conditions for habitability.

Drawing on updated stellar data and planetary records, researchers have compiled a catalogue of rocky exoplanets located within habitable zones – regions around stars where liquid water could potentially exist.

The study highlights 45 planets as the strongest candidates for supporting life, out of more than 6,000 confirmed exoplanets discovered to date. A further subset of 24 planets falls within a more restrictive definition of habitability, offering a refined framework for future observation and analysis.

Defining the habitable zone

The concept of the habitable zone remains central to the search for life beyond Earth.

It refers to the orbital region around a star where temperatures are neither too extreme for liquid water to persist on a planet’s surface. Water, widely considered essential for life as we know it, makes this zone a primary target for astronomers.

Using updated measurements from the European Space Agency’s Gaia mission alongside data from the NASA Exoplanet Archive, the research team reassessed known exoplanets to determine which ones fall within these critical boundaries.

The analysis also considered how much stellar energy each planet receives compared to Earth, a key factor in assessing surface conditions.

A refined list of Earth-like planets

Among the shortlisted worlds are several well-known exoplanets, including Proxima Centauri b, TRAPPIST-1f and Kepler-186f. The catalogue also introduces less prominent candidates such as TOI-715 b, expanding the pool of targets for future study.

Particular attention is given to a cluster of planets within the TRAPPIST-1 system – specifically TRAPPIST-1 d, e, f and g – which lie approximately 40 light-years from Earth.

Another notable candidate is LHS 1140 b, located around 48 light-years away. These planets are considered especially compelling due to their size, composition and position within their respective habitable zones.

However, researchers caution that being in the habitable zone does not guarantee habitability. A planet’s ability to retain an atmosphere plays a decisive role in maintaining surface water and regulating temperature.

Energy balance and Earth comparisons

A subset of the identified exoplanets receives levels of stellar radiation closely matching that of Earth. This group includes TRAPPIST-1 e, TOI-715 b, Kepler-442 b and Kepler-1652 b, among others.

Such similarities make them particularly valuable for comparative analysis, as they may offer insights into how Earth-like climates develop under similar energy conditions.

The study distinguishes between planets detected via transits, where a planet passes in front of its host star, and those identified through stellar “wobble,” a method that detects gravitational effects on stars.

Both detection techniques contribute to understanding planetary mass, orbit and potential atmospheric properties.

Testing the limits of habitability

Beyond identifying promising candidates, the catalogue is designed to probe the outer boundaries of the habitable zone itself.

Some planets sit near the inner edge, where excessive heat could strip away atmospheres, while others lie near the outer edge, where temperatures may be too low to sustain liquid water.

Planets such as K2-239 d and TOI-700 e are positioned to test the inner limits, while others like Kepler-441 b and TRAPPIST-1 g offer opportunities to study colder, outer-edge environments.

These edge cases are expected to help refine theoretical models that have guided habitability research since the 1970s.

The study also highlights planets with highly elliptical orbits, which experience significant fluctuations in stellar radiation.

These worlds may help answer a key question: whether a planet must remain consistently within the habitable zone, or if it can temporarily move in and out of it while still supporting life.

Implications for future observations

The catalogue arrives at a critical moment for observational astronomy, as a new generation of telescopes comes online.

Instruments such as the James Webb Space Telescope (JWST), the upcoming Nancy Grace Roman Space Telescope, and the Extremely Large Telescope are expected to play a central role in examining these Earth-like planets.

Future missions, including the Habitable Worlds Observatory and the proposed Large Interferometer for Exoplanets (LIFE), are also expected to build on this work by directly analysing planetary atmospheres for biosignatures – chemical indicators of life.

Observing small, rocky exoplanets remains technically challenging, particularly when attempting to detect atmospheric composition. However, the refined list provides a targeted set of candidates, improving the efficiency of these efforts.

Prioritising the search for life

Researchers involved in the study have already begun prioritising planets for detailed follow-up.

Among the most accessible targets are TRAPPIST-1 e and TOI-715 b, both of which orbit relatively small, dim stars. These conditions make it easier for telescopes to detect atmospheric signals as planets transit their host stars.

The TRAPPIST-1 system, in particular, has become a focal point for ongoing observation campaigns. Its compact arrangement of Earth-sized planets offers a rare opportunity to compare multiple potentially habitable worlds within a single system.

By refining the list of Earth-like planets and clarifying the limits of the habitable zone, astronomers are moving closer to answering one of science’s most enduring questions: whether life exists beyond Earth.