are we alone in the universe? This is one of the great questions that has plagued humankind since we began looking at the stars. Today, thanks to scientific and technological advances, Not only do we know that there are thousands of planets outside our solar system, but many of them could resemble—at least a little—Earth.
The discovery of exoplanets has revolutionized modern astronomyBut finding distant worlds is not enough; the big ambition is to determine whether any of them might harbor lifeIn this article, we explain how scientists detect exoplanets, what they look for in them to determine their potential habitability, and where we are currently at.
What is an exoplanet and how is it detected?
Un An exoplanet is a planet that orbits a star other than the Sun., that is, it is outside our solar system. To the naked eye, these worlds are invisible due to the enormous brightness of its host stars, but astronomers have developed ingenious techniques to detect them and even study some details of their atmosphere.
The most used method is transit method, consisting of observe small decreases in the brightness of a star when a planet passes in front of it. This decrease in light indicates that a planet is crossing the visible face of its star from our point of view and allows infer its size and orbit.
Another widely used method is that of radial velocity, which measures how a star wobbles slightly due to the gravitational pull of a planet that orbits it. This technique allows calculating the minimum mass of an exoplanet.
It is also used gravitational microlensing, which takes advantage of the gravitational effect of a massive object, like a star or planet, to amplify the light from a more distant starThis technique has been useful for detecting planets that cannot be discovered using other methods.
The combination of these techniques has made it possible to identify more than 5.200 exoplanets To date, according to updated NASA data, from gas giants like Jupiter to rocky super-Earths.
What makes a planet habitable?
The possibility of a planet being able to support life as we know it depends on various factorsOne of the most important is that it is in the habitable zone of its star, also known as the “Goldilocks zone.” This is the region where temperatures allow the presence of liquid water on the surface., provided the planet has a suitable atmosphere.
However, the habitability It does not depend only on the Distance to the sunOther elements are also important, such as:
- The stability of the host star: Very active or unstable stars can emit large amounts of harmful radiation.
- The composition of the atmosphere: an atmosphere dense can help regulate the temperature y protect against cosmic radiation.
- Presence of a magnetic field: helps to protect the planet's surface against the solar wind and cosmic particles.
- Age of the system: how much more old, greater possibility that satisfaction have had time to evolve.
Planets like the super-Earths (plus larger than Earth but more smaller than Neptune) and the mini-Neptunes (with atmospheres dense) are being considered as interesting candidates even though our solar system does not contain planets with those characteristics.
Biosignatures: chemical signs of life
Once a planet has been detected in the habitable zone, the next step is to analyze its atmosphere in search of biosignatures, that is, gases or compounds that could be produced by life forms.
The three main biomarkers known as the “triplet of life” are:
- Oxygen (O2): Generated by photosynthesis on Earth, and therefore considered a strong indicator of life.
- Ozone (O3): present in the Earth's atmosphere, acts as ultraviolet ray filter and usually lives in balance with oxygen.
- Methane (CH4): produced by processes biological and geological, but its presence together with oxygen may be indicative of biological activity.
Other relevant gases that can be found in exoplanet atmospheres are steam, the carbon dioxide and the chloromethane, all of them studied through spectroscopic analysis with advanced space telescopes.
A recent line of research proposes that low levels of carbon dioxide combined with the presence of ozone can be a strong evidence of liquid water on the surface of a planet, which would increase its chances of habitability.
The role of space telescopes
The path toward detecting habitable worlds has been made possible, in large part, by space missions such as:
- Kepler: detected more than 2.600 exoplanets during their mission, many by the transit method.
- TESS: Follow Kepler's legacy and search for exoplanets close to the size of Earth.
- James Webb (JWST): It is currently the telescope more advanced to analyze exoplanet atmospheres using infrared spectra.
El JWST It has instruments such as NIRSpec y MIRI that allow to detect the atmospheric composition of distant exoplanets with great precision. It has been key in detecting levels of water vapor, carbon dioxide e even thermal patterns.
Outstanding cases of potentially habitable exoplanets
Some of the most interesting worlds located so far include:
- HD 20794 d: a super earth 20 light-years away in the constellation of Eridanus, discovered by HARPS and confirmed by ESPRESSO.
- Proxima d: located on the closest star to the Solar System, it has a mass less than Earth and was also detected by ESPRESSO.
- Trappist-1 system: only 40 light years away, contains seven Earth-sized planets, with three in habitable areaIt is one of the main objectives of the James Webb Telescope due to its proximity and orbital conditions.
- HD 85512b: its atmosphere has low levels of carbon dioxide, adequate temperature (25ºC) and high presence of oxygen, making it a great candidate to host life.
Color of alien vegetation and other indirect signs
Not everything is about gases. Scientists have also studied the possibilities of identifying alien vegetation by analyzing the reflected light. On Earth, for example, the chlorophyll reflects more in near infrared, generating the call “red line”. Detect this pattern on another planet it could be a test photobiological life.
El star type It also plays a role: in cooler stars (type M), vegetation could have evolved to be darker, even black, to better absorb infrared radiation, while in hotter stars (type F), it could have reddish or orange tones.
Current limitations and upcoming advances
Although advances in detection and analysis are significant, We still cannot confirm the existence of life on other planets.. Although we can measure the atmosphere, temperatures or masses, There is not yet the possibility of traveling directly to those worlds nor send probes to study them in detail.
La modern astrobiology works on probabilities, not certainties. Therefore, new missions and projects are being developed, such as:
- Habitable Worlds Observatory (HWO): under development by NASA to directly study some 25 candidate exo-Earths.
- LIFE Project: a European space interferometer that will analyse the habitability of rocky exoplanets.
- Breakthrough Starshot: proposes sending ultra-fast probes to Proxima Centauri to study its planets in situ.
Although we are still far from setting foot on a world outside the solar system, The ability to search for life from here is a developing reality.Thanks to telescopes like Webb, we're getting closer to determining whether we share this universe with other life forms.
From the first discoveries in the 90s to the present day, We have made progress in the detection of distant planets and in the analysis of key aspects for the existence of life.. Chemical signals, thermal patterns, the color of vegetation to atmospheric winds They open a new window for identifying worlds with the potential to harbor life. This knowledge could mark the first step toward understanding whether we are alone in this cosmic vastness.
