Amid the large universe extension studying exoplanets, planets orbiting a star besides the Sun, has become one of the most popular and quickly evolving branch of astronomy. Every time such a discovery is made, one feels that the capability of the universe to harbor other forms of life outside the earth is possible. Welcome to the blog dedicated to one of the most intriguing topics – exoplanets: their definition, discovery, and the most recent advancements that expand the limits of knowledge.

What Are Exoplanets?

Asteroids are small, solid objects that can be found in the narrow region between a planet and the sun; on the other hand, exoplanets also known as extrasolar planets are celestial objects that revolve around stars and just like the Earth revolves around the sun. The first ever discovery of an exoplanet was in 1992 when two planets where found to revolve round a pulsar, a type of neutron star. Since then, encouragingly, several thousand other exoplanets have been discovered all owing to improvements in the technology and ways of observation. By August 2024, more than five thousand exoplanets have been discovered, and several thousand remain merely as candidates.

Super-Earths are different in size and mass, as well as they can orbit at different distances to their host stars. Some are gaseous such as Jupiter and others are terrestrial similar to the earth. There are many types of exoplanets, which gave rise to new classifications, including “super-Earth” – the planet that is larger than Earth but is composed of rocks, and “hot Jupiter” – the large gas giant that orbits very close to its star.

How Are Exoplanets Discovered?

It is not an easy process to detect exoplanets since they are extremely far away and moreover, they are embedded in the brightness of the star that they orbit. However, astronomers have developed several ingenious methods to detect these elusive worlds: 

Transit Method: This is by far the most effective and commonly applied approach. It relates to the observation of the variation of the brightness of a star with time. The planet’s size will affect the star brightness; if the planet crosses our line of sight to the star, then the brightness will slightly reduce. In this way, astronomers are able to deduce the existence of a planet and even it size and its path of movement around the stars.

Radial Velocity Method: This measurement method is also called the Doppler method and is based on the fact that a star also ‘wobbles’ due to the gravitational pull of an orbiting planet. As with any other object, if the star is approaching or receding, this will cause the light emitted by the star to change in frequency and therefore it will be able to be studied.

Direct Imaging: This procedure involves the use of direct imaging to take real images of exoplanets with the starlight being occulted. Direct imaging of exoplanets is relatively difficult and many a times restricted to large planets in remote distances from their stars; but despite its limitations, due to recent technological developments this method is becoming more feasible.

Gravitational Microlensing: If a star moves in front of another star the gravitational force of this foreground star bends the light of the background star and forms a lens. That is, if a planet orbits around the foreground star, then an additional peak appears in the light curve.

The Search for Habitable Worlds

The discovery of HZ Worlds Is one of the most important aims of exoplanet studies since scientists search for exoplanets with the possibility of maintaining life. The concept of the star ‘s ‘habitable zone’ or ‘the ‘Goldilocks zone,’ is the range of temperature within which liquid water is possibly present on the surface of a planet.

What Are Exoplanets?

The detection of extrasolar planets in the zone with Liquid Water also gave rise to the idea about other forms of life in the universe. For instance, Proxima Centauri b, a planet with the size of Earth around the nearest star, is in the habitable area and has attracted much attention to become the object of further research. Also, the TRAPPIST-1 system consisting of seven Earth-sized planets of which first three planets are in the habitable zone have aroused the scientist’s interest and the public’s imagination.

Recent Developments in Exoplanetary Science

Exoplanet research is a growing and expanding field with the discover and development of new technologies and topics happening frequently. Here is how it looks in early 2024:

JWST's Exoplanet Observations: The JWST, which was launched in December 2021, has been a game changer on the exoplanets’ field. JWST, which has highly effective infrared potential, allows observing exoplanets to a greater extent. One of the first achievements of this instrument was taking the spectrum of the atmosphere of the massive hot gaseous flat planet WASP-96b which lies at a distance of 1,150 light years from the Earth. Water vapor and clouds were characterized, as well as evidence of haze, in the planet’s atmosphere according to JWST.

New Exoplanets Discovered by TESS: TESS, launched in 2018, has also been a very productive mission, that searches for planets transiting the stars . TESS has found well over 300 exoplanets some of these are attractive; Earth-sized in the habitable zones of their host-stars. Among these, one must mention TOI-700 d: it is an Earth-sized planet in the habitable zone of a nearby star, so its further study should be interesting.

Advances in Direct Imaging: The current technology is enhancing the possibility of direct imaging, and astronomers are envisioning that it is possible to capture images of other little and faint exoplanets. The Extremely Large Telescope at present under construction at Paranal, Chile is likely to have a major role to play in this front. Having a diameter of 39 meters of the primary mirror, ELT will be able to resolve Earth-like exoplanets and study the composition of their atmospheres.

Exomoons and Exo-Rings: Whereas most discoveries were made regarding planets, there is increasing concern for the search and study of exomoons and exo-rings. The discovery of an exomoon candidate orbiting the planet Kepler-1625b has given the scientists new directions for investigation. Spherical astrophysical remains research of exomoons into the possible existence of habitable conditions and the further evolution of overseas planetary systems.

Machine Learning and AI in Exoplanet Research: The large volumes of data produced in the latest missions including Kepler, TESS and JWST have resulted in the use of the artificial intelligence, and machine learning on exoplanets. Such tools are applied for light curves analysis, possible exoplanets detection, and their properties’ forecast. That is why AI is useful to improve the speed of the discovery process at which it is possible to work through data.

The Search for Biosignatures: However, one of the most prospective fields of exoplanets study is the search for biosignatures – any signs of life. The researchers are concentrating on the surveys of the atmospheres of the exoplanets; the presence of gases such as oxygen, methane, and carbon oxides are searched for as these may be released by living organisms. The discovery of such biosignatures would be significant and would make humans possibly the first species to know the existence of life in other planets.

The Future Evolution of Exoplanet Hunting

Looking to the future the discovery of other planets in the galaxy will be one of the most important pursuits of mankind. Subsequent missions including the ESA’s ARIEL (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) mission which is proposed to be launched in 2029 will investigate the atmospheres of several hundred exoplanets in order to understand the chemical dynamics of their atmospheres and the suitability of exoplanets for hosting life.

Similarly, the prospects of next generation telescopes such as the NASA’s Habitable Worlds Observatory can help in imaging the Earth like planets around neighborhood stars and for the detection of life. These missions, combined with ongoing advancements in AI, spectroscopy, and observational techniques, will bring us closer to answering one of humanity's most profound questions: What about all you guys around the earth: are there any other living beings in this galaxy?

What Are Exoplanets?