The three known planets of the star HR8799, as imaged by the Hale Telescope. The light from the central star was blanked out

Have you ever stared at the stars and wondered about the vastness of space? You must’ve pondered the question are we the only beings out there? Astronomy has come a long way from believing that we are the only world to being the center of the universe to being a small spec of dust in a seemingly infinitely Universe. In our long journey along the advancements of Astronomy we have discovered many heavenly objects including planets, stars, comets etc. not just in our Solar system but outside our solar system as well, and yet the hunt for discovering more and more celestial objects continues. One of the aims of this never-ending quest being the discovery of another planet harboring life as our own.

Exoplanets are one such group of celestial objects discovered during this quest of uncovering the truths about the Universe. Exoplanets are planets which exist outside our Solar system. What makes Exoplanets such an interesting group of celestial objects is that they cannot produce their own light hence they are often too dim to be observed even with the most powerful of telescopes we have. But by observing the various effects the exoplanets exert on the physical properties around it, it is possible to hypothesize the existence of such planets and furthermore confirm its existence using other known methods of observations.

For centuries scientists, philosophers, and science fiction writers suspected that extrasolar planets existed, but there was no way of knowing whether they existed, how common they were, or how similar they might be to the planets of our Solar System. Various detection claims made in the nineteenth century were rejected by astronomers.

The first confirmation of detection of an exoplanet occurred in 1992. This was followed by the confirmation of a different planet, originally detected in 1988. As of 24 April 2020, there are 4,255 confirmed exoplanets in 3,146 systems, with 695 systems having more than one planet. The closest exoplanet found is Proxima Centauri b, which was confirmed in 2016 to orbit Proxima Centauri, the closest star to our Solar System. Even still it is 4.25 light years away from Earth (light from Proxima Centuari B will take 4.25 years to reach Earth)

Generally, exoplanets are named using the parent star around which they revolve. For example, the first exoplanet discovered was named HIP 65426b as it revolves around the star HIP 65426. The parent star is considered HIP 65426a. Any subsequently discovered exoplanets will be named c, d etc.

The exoplanet HIP 65426b — the first discovered planet around star HIP 65426

The most interesting aspects about exoplanets are the methods and techniques used for their detection. There are many methods used for exoplanet detection each having its own merits. One single method is not accredited as the best method of detection, instead the method is chosen depends on the general distances concerned and the sizes of the exoplanet and brightness of the parent star concerned and many other factors as such.

One such method is the method of radial velocity. Any two masses which revolve around each will revolve around a common center of mass. Hence a planet that revolving around a star if large enough, the plant may cause the sun to move in a smaller orbit of its own around the planet. Hence when the star moves away and toward the earth it causes the lengthening and shortening of the wavelength of the light emitted from the star. This is known as Dopplers effect ( The same reason why you hear sound at a higher frequency when you hear an ambulance coming toward you and a lower frequency when going away) This variation in the observed wavelength can be used to find the velocity of revolution of the parent star and using the period taken to observe these variations, the mass and the relative position of the exoplanet can be calculated.

Graph of Radial Velocity for exoplanet 18 Delphini B

Another method is Gravitational microlensing. Ever since Einstein’s theory of relativity gravity is regarded to bend space time itself. In simpler terms, bodies with large masses with a large enough gravitational pull can essentially attract light rays towards it just like the Earth attracts an apple detached from a tree. So, the pathway of light becomes bent and distorted due to large masses and tend to act as a lens, and even smaller distortions can occur due to smaller mass bodies such as exoplanets. This phenomenon is known as gravitational microlensing. The distortions of a distant light source can then be studied in order to detect the presence of exoplanets.

Transit photometry is another such popular method. When a planet revolving around a star may happen to come in front of the star (between the star and the observer on earth) this phenomenon is known as planetary transits. During the transit period the light emitted from the star is diminished and this can be shown as evidence as the presence of exoplanets. Using the period of the transit and the amount of light that is diminished we can pinpoint the location the planet and also make estimations of its mass.

The above are just a few examples of the many methods used in the detection of exoplanets. As the size and quality of the telescopes we use improve and the improvements in new techniques of Astronomical observations the detection of exoplanets are becoming increasingly common and more accurate.

As more planets are discovered, the field of exoplanetology continues to grow it will ultimately tackle the prospect of the presence life on planets beyond the Solar System. At cosmic distances, detection of life is quite a challenge but we can safely assume a potentially habitable planet must orbit a stable star at a distance within which sufficient atmospheric pressure can support liquid water at their surfaces.

But in the this vastly infinite Universe one thing you can guarantee about exoplanets is that we will find more of them!!

~Nethsara Kekulawala~


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