Exoplanets are planets that lie outside our Solar System . Because they do not emit light of their own and due to their great distance from Earth , exoplanets are very difficult to detect. However, advances in detection techniques, using telescopes, have allowed more than 4200 planets to be discovered since 1992, some of them very similar to Earth.
The search for exoplanets is not simple. To find them, it takes a long time of observation, a bit of luck and a certain amount of time to analyze the images, so until the present moment |1| , there are 4284 exoplanets confirmed by NASA , in addition to another 5573 that lack confirmation.
How are exoplanets detected?
There are three techniques that are most efficient for detecting exoplanets, these methods are known as:
- radial velocity method,
- gravitational microlensing method,
- transit method.
The radial velocity method consists of measuring the wobble that an orbiting planet causes in a star. The gravitational pulls produced by the planet cause the light emitted by the star to undergo a small variation, due to the Doppler effect of electromagnetic waves .
The gravitational microlensing detection method is based on Einstein’s general relativity . When a massive star passes in front of another star, its gravity causes the light to be deflected, the distortions that appear in the star’s image magnify it, as when we look through a lens and see a magnified image.
Finally, the transit method consists of measuring the variation in the star’s brightness when a planet passes in front of it, as occurs in an eclipse . By detecting minute variations in brightness, astronomers are able to infer:
- the translation period,
- the orbit radius,
- the composition of the atmosphere (if there is one),
- the size of the planet.
Closest exoplanets to Earth
Most known exoplanets are very distant from Earth. According to NASA data, there are at least 97 known exoplanets that are located 10 parsecs away from us (about 32.6 light-years).
Based on the latest findings released by the US space agency, the closest exoplanets to Earth are in orbit around the star Proxima Centauri , the closest star to the Sun , whose distance to us is approximately 4.2 light-years. . Want to know more about these distance measurements? Access our text on astronomical units .
With the technology we have today, it is still not possible to say that there is life on any of the known exoplanets . However, astronomers are able to identify which exoplanets have climatic conditions, diameter, mass, atmosphere and light incidence similar to those of Earth, in this way, they are able to list which exoplanets can be considered “habitable”, in other words, which are able to support life.
Among the more than 4000 exoplanets discovered:
- 1457 are similar to Neptune ,
- 1339 are gas giants, as are Saturn and Jupiter ,
- 1320 are super-earths, that is, they are telluric, as they have rocky soil, however, they are much larger and more massive than Earth ,
- about 160 of the exoplanets discovered are terrestrial, meaning they have rocky cores and are solid like Earth, Mars and Venus .