A planet has been discovered 25 light-years from Earth, where the search for life will begin

Top story: the planet has turned out to be lighter than previously thought. This increases the likelihood that it is not a gaseous mini-Neptune, but a rocky ‘super-Earth’ — that is, a planet larger than Earth but still potentially similar to it in composition.

The new data have been published in a paper accepted for publication in *The Astrophysical Journal*.

What sort of planet is it?

GJ 3378 b orbits a red dwarf — a small, cool M-type star. Such a star is much smaller and fainter than the Sun, so the planet can be very close to it and still receive a moderate amount of light.

According to NASA, GJ 3378 b has a mass of about 2.3 times that of Earth, completes one orbit around its star in approximately 21.5 days, and is located at a distance of about 0.097 astronomical units from the star.

By way of comparison, Earth takes 365 days to orbit the Sun. However, for red dwarfs, the zone where it may be warm enough for liquid water is situated much closer to the star.

Why it was called ‘Earth-like’

When the planet was first described, its mass was estimated at approximately 5.26 times that of Earth, and its orbital period at nearly 24.7 days. New research, based on data from several spectrographs, has reduced the estimate of the minimum mass to 2.3 Earth masses and refined the orbital period to 21.45 days.

This is significant. The more massive a planet is, the greater the chance that it retains a dense gaseous envelope and is more like a mini-Neptune than Earth. A lighter planet is more likely to be rocky.

Put simply: previously, GJ 3378 b might have appeared to be too heavy a world with a thick atmosphere. Now it looks more like a planet that could, in theory, have a solid surface.

Why scientists will be looking for life there

The planet lies within its star’s so-called habitable zone. This is a region where, given the right atmosphere, liquid water could exist on the planet’s surface. And water is the key indicator for astrobiologists, because all life as we know it requires it.

But the ‘habitable zone’ does not mean that the planet is definitely suitable for life. It is only the first filter.

For a world to truly resemble Earth, other conditions are also required: an atmosphere, suitable pressure, not too much radiation, a stable climate, and chemical conditions that allow water to remain liquid.

What is the main risk?

The star GJ 3378 is a red dwarf. Such stars are very common in the Galaxy, which is why they are important in the search for life. But there is a problem: planets in their habitable zone orbit very close to the star.

This could mean intense radiation and the risk of atmospheric loss. In their new paper, the authors explicitly state that GJ 3378 b lies close to the so-called ‘cosmic shoreline’ – a notional boundary where planets orbiting red dwarfs may lose their atmospheres due to radiation exposure.

In other words, the planet has become more interesting, but not automatically safer. It may be rocky, but scientists still need to determine whether it has managed to retain its atmosphere.

How it was studied

The planet was studied using the radial velocity method. This means that astronomers do not see the planet directly, but measure how its gravity causes the star to wobble slightly.

To do this, they used data from the Habitable-zone Planet Finder infrared spectrograph on the Hobby-Eberly Telescope, as well as additional observations from NEID, CARMENES and SPIRou. A joint analysis of this data made it possible to determine the planet’s mass and orbit more precisely.

There is an important caveat: the radial velocity method provides the minimum mass of the planet. The actual mass may be higher if the orbit is tilted towards us in a certain way. Scientists are therefore cautious in their conclusions: GJ 3378 b has become a more promising candidate, but its nature still needs to be clarified.

Why 25 light-years is considered close

For a human, 25 light-years is an enormous distance. But for astronomers, this is the Sun’s immediate neighbourhood. It is precisely such planets that will be the first candidates for future powerful telescopes.

The closer a planet is, the greater the chance of studying its atmosphere in detail, if it has one. In the future, such objects may be observed by large, next-generation ground-based telescopes and space missions designed to search for signs of life.

GJ 3378 b is therefore significant not as a ‘second Earth’, but as the closest candidate worth investigating.

What scientists will be looking for next

The next big question is whether this planet has an atmosphere.

If it does have an atmosphere, future observations may look for water vapour, carbon dioxide, methane, oxygen or other chemical traces within it. But even the presence of such substances does not immediately prove the existence of life: they need to be analysed in conjunction with the conditions on the planet and the star’s activity.

For now, the correct way to put it is: GJ 3378 b has become a more interesting target for the search for life, but no life has been detected there.

Background

Red dwarfs are the most common stars in our Galaxy. Consequently, the question of whether the planets orbiting them could be habitable is one of the key issues in modern astronomy.

On the one hand, there are a great many such stars, and their planets are easier to detect. On the other hand, the proximity of planets to red dwarfs can be dangerous: flares and radiation can destroy the atmosphere.

GJ 3378 b falls precisely into this important category: a close super-Earth orbiting a red dwarf, within the zone where liquid water could potentially exist, but close to the boundary where the atmosphere may be at risk.

Source

Study: Paul Robertson et al., “A Revised Mass and Period for the Habitable Zone super-Earth GJ 3378 b: A Planet Straddling the Cosmic Shoreline”, The Astrophysical Journal, 2026.