Authors– Manu Mehta and Raghavendra Pratap Singh

An exoplanet, short for extrasolar planet, is a planet that orbits a star outside our solar system. These planets follow the same physical laws – orbiting stars and varying widely in size and composition. When you look up at the night sky and see countless stars, it’s amazing to think that many of them likely have their own systems of planets. Some of these exoplanets may be massive gas giants, while others could be rocky worlds, possibly similar to Earth, in size or in temperature. Exploring the exoplanets is like opening a cosmic book filled with the stories of far-off, hidden realms. It is our way of asking: Are we alone? Is Earth truly unique, or just one example of many potentially habitable worlds scattered across the galaxy? How do planetary systems like ours come together, and what shapes their evolution over billions of years? Venturing beyond our solar system to study distant planets helps us understand how worlds like Earth form and evolve, while also fuelling our quest to find life amid the endless expanse of the cosmos. Telescopes like Kepler, TESS, and the James Webb Space Telescope (JWST), along with databases like the NASA Exoplanet Archive, have been instrumental in advancing this research.

Globally, databases and services such as NASA’s Exoplanet Archiveand theExoplanet Follow-up Observing Program (ExoFOP), ESA’s Planetary Science Archive (PSA), Japan’s ExoKyoto database, China’s AstroCloud, and collaborative platforms like Exo-MerCat collectively advance exoplanet discovery, characterization, and data integration (Tinetti et al., 2018; Notsu et al., 2017; Gao et al., 2015; Bashi et al., 2020; Christiansen et al., 2025). For stars, we can gather data on key characteristics such as mass, radius, temperature, luminosity, anddistance from Earth(Akeson et al., 2013). For exoplanets, the Archive can help to determine important features like planetary radius, mass, andorbital period. By combining radius and mass, we can estimate a planet’s density, which reveals whether it is likely to be rocky like Earth or gas-rich like Jupiter (Winn & Fabrycky, 2015). These databases also provide information on a planet’s equilibrium temperature, which depends on the star’s brightness and the planet’s distance from it, giving us clues about surface conditions and potential habitability. In some cases, we can even study a planet’s atmosphereusing spectroscopy during transits, revealing the presence of gases like water vapor, carbon dioxide, ormethane, which are important for understanding a planet’s environment (Madhusudhan, 2019). As an illustration, Figure 1 displays the exoplanet mass (scaled w.r.t. Earth mass) vs orbital period based on the catalogue of exoplanets data from NASA Exoplanet Archive; where the colours represent the equilibrium temperature while the size of the data point circles represents the relative size of the exoplanets (w.r.t. Earth radius). Please note that only planets with estimated equilibrium temperature and radius data are shown in Figure 1; solar system planets are also depicted for reference.

Figure 1: Exoplanet mass (scaled w.r.t. Earth mass) vs orbital period (in log scale); colours represent the equilibrium temperature and sizes of the data point circles represent the relative size of the exoplanets w.r.t. Earth (NASA Exoplanet Archive)

For studies requiring precise stellar and exoplanet parameters and smaller uncertainties, one can refer to more refine, well-characterized, homogeneous datasets like CKS (California-Kepler Survey), that includes only the transiting Kepler mission targets, observed with high-resolution spectroscopy. In Figure 2, we illustrate the exoplanet radii vs. orbital period using the CKS dataset, colour-coded by the incident stellar flux (without any screening checks) which shows that close-in planets get extreme irradiation. Hot Jupiters, super Earths, sub Neptunes and hot Neptune deserts along with some of our solar system planets (shown as white filled circles) are also depicted. Further meaningful screening can be applied to investigate the demographies as reported in recent studies by Petigura et al. (2022) and Lee (2025).  

Figure 2: Exoplanet radius (scaled w.r.t. Earth radius) vs orbital period; colours represent the incident stellar flux (w.r.t. Earth Flux) in log scale (CKS dataset)

References:

Akeson, R. L., et al. (2013). The NASA Exoplanet Archive: Data and Tools for Exoplanet Research. Publications of the Astronomical Society of the Pacific, 125(930), 989–999.
Bashi, D., et al. (2020). Exo-MerCat: A Merged Exoplanet Catalog. Astronomy & Astrophysics, 633, A120.
Christiansen, J. L., Akeson, R. L., Ciardi, D. R., & Gelino, C. R. (2025). The NASA Exoplanet Archive and Exoplanet Follow-up Observing Program: Data, Tools, and Usage. arXiv.
Gao, C., et al. (2015). AstroCloud: A Cyber-Infrastructure for Astronomy Research. Research in Astronomy and Astrophysics, 15(11), 1943–1952.
Lee, J. J. (2025). Where Are the Universe’s Missing Planets? Scientific American.
Madhusudhan, N. (2019). Exoplanetary Atmospheres: Key Insights, Challenges, and Prospects. Annual Review of Astronomy and Astrophysics, 57, 617–663.
Notsu, Y., et al. (2017). ExoKyoto: Exoplanet Database of Kyoto University. Publications of the Astronomical Society of Japan, 69(6), 98.
Petigura, E. A., et al. (2022). The California-Kepler Survey. X. The Radius Gap as a Function of Stellar Mass, Metallicity, and Age. The Astronomical Journal, 163(4), 179.
Tinetti, G., et al. (2018). The Ariel Space Mission. Experimental Astronomy, 46, 135–209.
Winn, J. N., & Fabrycky, D. C. (2015). The Occurrence and Architecture of Exoplanetary Systems. Annual Review of Astronomy and Astrophysics, 53, 409–447.