An exoplanet is the name given to planets outside the Solar System orbiting another star. Exoplanets gained recognition in the scientific world with the discovery of 3 planets around a neutron star in 1992 by astrophysicists Aleksander Wolszczan and Dale Frail. In 1995, the first exoplanet orbiting the star 51 Pegasi was discovered by Genevan astronomers Michel Mayor and Didier Queloz. The planet, named 51 Pegasi b, had half the mass of Jupiter and orbited its star every 1 year and 4 days, being eight times closer to its star than the distance between the Sun and Mercury. To date, more than 4000 exoplanets have been discovered.
Exoplanets reflect light from their stars, similar to other planets in the solar system. The amount of light reflected by exoplanets is very small, making their detection akin to finding a needle in a haystack due to their extreme distance from us. Even the closest exoplanet discovered in 2016, Proxima Centauri, is approximately 4.2 light-years away from us. The vast majority of exoplanets have been discovered using two important methods.
The first method is the Doppler method. The planet’s small mass in relation to the star creates a slight circular orbit of the star. Astronomers observing the star with this method deduce the presence of
at least one planet orbiting it based on the way the star wobbles like a top.
Another method is when the exoplanet passes between us and the star. In this method, called the Transit method, the brightness of the star decreases for a certain period of time. Through this observation, it can be inferred that there is a planet orbiting the star by analyzing the changes in photometrics.
Thanks to observations made from both Earth and space, we can gather information about exoplanets and their systems. Space telescopes such as Kepler, Spitzer, and Hubble, utilized to detect exoplanets in
Earth’s orbit, have been surveying the sky since their launch. The Kepler telescope was retired on November 15, 2018, and replaced by a telescope named TESS, developed by MIT and capable of even more powerful scanning, which was sent into Earth’s orbit on October 18, 2018. Many exoplanets have been discovered through observations made using Very Large Telescopes from Earth (VLT).
Now, let’s address the most important question: Could there be life on these planets?
For life to exist on a planet within or outside the solar system, numerous conditions must align, perhaps hundreds of different situations. However, particularly in the search for exoplanets, the focus is on the “habitable zone” theory, which is one of these conditions. The habitable zone theory defines the distance of a planet from its star. If an exoplanet is as close to its star as Mercury is to the Sun, that planet will be scorching hot, and if it is as far away as Neptune, it will be extremely cold. Planets that can be considered habitable must have a distance from their star similar to the Earth’s distance from the Sun. This region is known as the habitable zone. Of course, the size of the star will affect the boundaries of this habitable zone. In a small dwarf star, this distance is reduced, while in a larger star, it is extended.
It’s essential to bear in mind that we cannot ascertain whether an exoplanet within the habitable zone contains life or supports life using the methods we know, or even contains water, which is the foundation of life consisting of 2 hydrogen and 1 oxygen atoms. These planets are very, very distant from us. With technology progressing every day, perhaps one day we will be able to examine these exoplanets more closely. Maybe we will discover life on the other side of the universe. However, even with what we know so far, the motivation to explore and discover is significant.
Now, you have much more information about exoplanets.