We know that there are planets in our solar system. However, prior to 1992 (when the first discovery of a planet outside our solar system also known as exoplanet), planetary systems other than our own were supposed to be true but there was no evidence given. Real discoveries came with advancing technology which put us on the verge of answering pressing questions: “Do other Earths exist?”, “Are they common?”, “Do they have signs of life?”

Exoplanets are planets that are essentially outside our own solar system. The prefix “exo” comes from the Greek and means outside; these planets are lightyears away from us and so far, Astronomers have confirmed more than 4000 exoplanets. These planets don’t necessarily orbit stars. While most of them do, Astronomers discovered a type of planets called Rogue Planets, and these are planets with no associated star in vicinity and are believed to just be roaming the universe without an orbit. The concept that there may be worlds beyond Earth goes back more than 2000 years, with Epicurus (ca. 300 BCE) asserting, “There are infinite worlds both like and unlike this world of ours. We must believe that in all worlds there are living creatures and plants and other things we see in this world” (Seager, 2010)

First Discovery of Exo Planets

The year 1995 was the dawn of discoveries. The new explorers, rather than considering seagoing vessels for discovering continents, used telescopes for discovering planets that revolved around distant stars. Numerous extra-solar planets or exoplanets have been discovered including those that appear to be other potential earths, together with strange objects that have no resemblance to any planet in the solar system. Two of these explorers were recently awarded with a Nobel Prize, Didier Queloz and Michel Mayor, for their discovery in 1995. Actually, this discovery ranges back to 1992 when the first exoplanet was discovered by astronomers. However, it did not come in a form they had expected and anticipated (Winn, 2019).

In general, neutron stars are recognized as the second densest type of object, second to black holes in the universe. They are formed when a star dies and it explodes outward because of the collapse of its core. In simple words, the star becomes too large for continuing on and it expels its energy into the space. For this detonation, the core is the ground zero and when it collapses, it either becomes a black hole or a neutron start in accordance with the size of the star. Some neutron stars are referred to as pulsars for their consistent pulses in the form of radio frequencies. They can be thought of as a drummer producing regular beats. Actually, these pulses are so consistent and regular that if they do not come at the right time and interval, it tells astronomers that something is strange.

In 1992, a breakthrough offered strong evidence about the existence of exoplanets. Dale Frail and Aleksander Wolszczan considered PSR B1257+12 and it should have pulsed approximately 0.006219 seconds. However, regularity was missing in the pulses. Still, those off-beats had a regular pattern and after an intensive study, the astronomers explained why such a thing was occurring: there were two plants surrounding it. One planet was four times and the other was three times the whole mass of earth and they seemed to rotate around every 98 and 67 days. It can be said that pulsar stars in between a chimera and zombie. Usually, when a star explodes, the planets in that specific system are either flung out or destroyed by a shockwave. However, once the violence settles down, the dust and gas re-condense. In effect, this means that three planets existing in B1257 might be made out of parts of those planets which came from planets even before them. Considering the extreme radiations in these systems, no one has thought that life could exist in B1257 system.

Thus, while the discovery of 1992 was a great news, it indicated that astronomers had the very first verified planets around another planet or star. However, there was no proof of planets around a main star such as Sun. Gradually, a real observation was made in 1995. Didier Queloz was working with Michel Mayor, his advisor on the search and exploration of extrsolar planets using radial velocity or wobbles. It would not be wrong to say that his discovery was a chance coincidence. For instance, out of a catalogue of various signatures of radial velocity, an F-type star was chosen by him that was 50 light-years away. Actually, he was attempting to calibrate his code and opted for the start as a potential candidate. That is when it fell into place when a strong signal began to be received every four days. In accordance with measurements, its mass was near or equal to Jupiter which indicated that the object was certainly a planet. Although astronomers consider it possible to possess such periods, they did not expect to find one in such a short period of time (Wenz, 2019).

All at Once versus One at a Time

The early days of detection of exoplanets were marked by their extensive focus on star-based analysis using radial velocity and it made radial velocity one of the most effective techniques of finding exoplanets. As of March 2018, 746 worlds have been discovered. There are some other methods as well such direct imaging for finding exoplanets but they are limited to young and large planets. The most successful method of finding exoplanets has been the transit technique. In the same time frame as the headcount of radial velocity, it found 2,789 planets. There exist 3,705 planets so 75 percent of all the discovered planets is made up by transiting planets. However, Kepler is a spacecraft that has found 2,648 of these planets. If the worlds discovered by Kepler are taken out then only 1,000 planets are left to be worked with and that is because Kepler worked as a survey of a small sky patch, counting all transits that it could. It has been shown by Kepler that planets were not rare and there are trillions out in the universe waiting to be discovered.

In 2016, a number of astronomers who had been working under secrecy determined that they had seemingly found the closest system of exoplanet to Earth and it was orbiting around Proxima Centauri. Their work was added into other systems and in 2018, they found an evidence of another exoplanet (Haynes, 2020).

Methods of Exo Planets

There are a number of methods which have been used for discovering and finding exoplanets and they include:

Radial Velocity of Exo Planets

A star with a planet will seemingly move in its own obit according to the gravity of the planet. Due to it, there are variations or changes in the speed with which the star seems to move away or towards the earth. It is possible to deduce radial velocity from the displacement in the spectral lines of the parent star because of the Doppler Effect. The method of radial-velocity determines these changes and variation for confirming the presence of a planet with the use of binary mass function. Until 2012, this method was recognized as the most productive and useful technique for discovering planets. The transmit method, after 2012, became the most effective method.

Transit Photometry of Exo Planets

Although information about the mass of a planet is provided by the radial velocity method, the radius of the planet can be determined by the photometric method. For instance, if a planet seems to cross in front of the disk of parent star, then the observed brightness of the star decreases by a small amount, in accordance with the sizes of the planet and star. Actually, this method has two drawbacks. First of all, it is possible to observe planetary transits when the obit of planet is aligned perfectly from the vantage point of the astronomer. Meanwhile, the second drawback is a high rate and likelihood of false detections. Still, the main benefit of transit method is that the planet’s size can be identified from the light curve. Usually, when it is combined with the method of radial velocity, an astronomer can determine and identify the density of the plane. Through this, the astronomer can learn something about the physical structure of the planet as well. In addition to it, the transit technique allows the astronomer to study the transiting planet’s atmosphere. In general, when the star is transited by the planet, light from the star seems to pass through the planet’s upper atmosphere.

Relativistic Beaming of Exo Planets

Actually, an individual novel technique of detecting exoplanets from variations in light makes the use of observed flux’s relativistic beaming from the star because of its motion. It is also referred to as Doppler boosting or Doppler beaming. As the star is tugged by the planet with its gravitation, the brightness and density of protons change from the viewpoint of the observer. Similar to the method of radial velocity, it does not need a precise spectrum of a star. Therefore, it can be utilized easily for finding planets around distant and fast-rotating stars. A major disadvantage or drawback of this technique is that the effect of light variation is very small.

Ellipsoidal Variations of Exo Planets

Similar to the relativistic beaming technique, it helps in determining the planet’s minimum mass, and its sensitivity seems to rely on the orbital inclination of the planet. This method is suitable for discovering and finding those planets around stars which have seemingly left the main structure or sequence (Fischer, et al., 2015).

Conclusion of Exo Planets

Overall, it can be said that exoplanets are planets that are essentially outside our own solar system. The prefix “exo” comes from the Greek and means outside; these planets are lightyears away from us and so far, Astronomers have confirmed more than 4000 exoplanets. The most successful method of finding exoplanets has been the transit technique. In the same time frame as the headcount of radial velocity, it found 2,789 planets. There exist 3,705 planets so 75 percent of all the discovered planets is made up by transiting planets. However, Kepler is a spacecraft that has found 2,648 of these planets. Still, there are trillions of planets that are waiting to be discovered with the use of better technologies.

References of Exo Planets

Fischer, D. A., Howard, A. W., Laughlin, G. P., Macintosh, B., Mahadevan, S., Sahlmann, J., & Yee, J. C. (2015). Exoplanet detection techniques. arXiv preprint arXiv:1505.06869.

Haynes, K. (2020). How Many Exoplanets Have Been Discovered, and How Many Are Waiting to Be Found? Retrieved from DiscoverMagazine: https://www.discovermagazine.com/the-sciences/how-many-exoplanets-have-been-discovered-and-how-many-are-waiting-to-be

Seager, S. (2010). Exoplanets. University of Arizona Press.

Wenz, J. (2019). How the first exoplanets were discovered. Retrieved from Astronomy: https://astronomy.com/news/2019/10/how-the-first-exoplanets-were-discovered

Winn, J. N. (2019). Who Really Discovered the First Exoplanet? Retrieved from Scientificamerican: https://blogs.scientificamerican.com/observations/who-really-discovered-the-first-exoplanet/