In the search for extraterrestrial life there are three questions that astronomers try to answer before any other. Is it a rocky planet? Does it receive an amount of energy similar to that of the Earth? And is it close enough to be able to study its atmosphere in the future? Until now, very few worlds could answer yes to all three.
But a new study has just made GJ 3378 b, located just 25 light years away from us, one of the most promising candidates discovered to date. The new observations indicate that It has an 85% chance of being a rocky planet, receives approximately 90% of the radiation that Earth receives from the Sun, and is only 2.3 times Earth’s mass.much smaller than thought. Together, these three characteristics place it among the most interesting exoplanets to search for signs of habitability.
The study, published in The Astrophysical Journaldoes not prove that life exists in this world. But it does significantly change our expectations of him. The main advance of the analysis, led by Michael Endl, focuses precisely on a new estimate of the planet’s mass. Until now, astronomers estimated that GJ 3378 b had about 5.2 Earth masses. A planet that size usually falls into a category known as mini-Neptunes: worlds enveloped by thick atmospheres of hydrogen and helium, without a solid surface where liquid water can accumulate.
The new observations, made with the Habitable-zone Planet Finder (HPF) and NEID spectrographs, reduce that figure to 2.31 Earth masses, a more than 55% decrease from previous estimates. It may seem like a simple statistical adjustment, but in astronomy it represents an enormous change: scientists point out the extreme threshold of rocky planets to those with 5 times the Earth’s mass. Halving it is a very strong indicator.
According to the models used by Endl’s team, that new mass is what makes GJ 3378 b about 85% likely to be a rocky planet. That is to say, goes from looking more like a small Neptune than Earth to becoming a true super-Eartha type of planet considered much more favorable for hosting liquid water and, potentially, life.
But the mass is not the only promising aspect. By making more refined calculations about the planet’s orbit, They have calculated that it receives about 92% of the radiation that the Earth receives from the Sun. This figure is especially striking because it means that the amount of energy that reaches its surface would be very similar to that on Earth. In other words, if you have a suitable atmosphere, the temperatures could allow liquid water to exist for long periods. And even so, that does not guarantee that it is habitable. The composition of the atmosphere, the activity of its star, the presence of a magnetic field or the geological history of the planet remain decisive factors. However, receiving practically the same energy as our planet places it within the so-called habitable zone.
Another important factor is that GJ 3378 b orbits a red dwarf, a type of star much smaller and cooler than the Sun. These stars have an obvious advantage: their lower brightness makes it easier to detect planets similar in size to Earth. But they also pose a problem: During much of their life they are very active and can emit powerful flares capable of slowly eroding the atmospheres of nearby planets.
This is precisely why it is so important to study this world in greater detail. If it has managed to preserve a stable atmosphere despite the activity of its star, its chances of being habitable would increase considerably. And that is the next step. Just 25 light years away, GJ 3378 b practically belongs in our galactic neighborhood. This proximity will allow future telescopes, such as the Habitable Worlds Observatory from NASA, try to directly study its atmosphere in search of possible biosignatures: gases whose presence could be related to biological processes.
For now, we don’t know if the planet supports oceans, a dense atmosphere, or any form of life. But each new measurement brings it a little closer to the profile of the world that astronomers have been trying to find for decades. Because, If an ideal candidate had to be designed to begin the search for life, it would probably have three characteristics very similar to those of GJ 3378 b: be a rocky planet, receive an amount of energy similar to that of Earth, and be close enough to study its atmosphere with next-generation telescopes.