In 2019 a work by Hellard et al. discussed the possibility of measuring the Love number of transiting hot Jupiters using HST/STIS. A tentative measurement of for WASP-121b was published in the same work.
The planetary orbit is inclined to the equatorial plane of the star by 8.1°.
Reanalysis of aggregated spectral data was published in June 2020. Neutral magnesium, calcium, vanadium, chromium, iron, and nickel, along with ionized sodium atoms, were detected. The low quality of available data preclude a positive identification of any molecular species, including water. The atmosphere appears to be significantly out of chemical equilibrium and possibly escaping. The strong atmospheric flows beyond the Roche lobe, indicating ongoing atmosphere loss, were confirmed in late 2020.
In 2021, the planetary atmosphere turned out to be slightly more blue and less absorbing, which may be an indication of planetary weather patterns. By mid-2021, the presence of ions of iron, calcium, chromium, vanadium and calcium in planetary atmosphere was confirmed.
^ abAtmospheric Rossiter-McLaughlin effect and transmission spectroscopy of WASP-121b with ESPRESSO, 2020, arXiv:2011.01245
^Gibson, Neale P.; Merritt, Stephanie; Nugroho, Stevanus K.; Cubillos, Patricio E.; de Mooij, Ernst J. W.; Mikal-Evans, Thomas; Fossati, Luca; Lothringer, Joshua; Nikolov, Nikolay; Sing, David K.; Spake, Jessica J.; Watson, Chris A.; Wilson, Jamie (2020). "Detection of Fe I in the atmosphere of the ultra-hot Jupiter WASP-121b, and a new likelihood-based approach for Doppler-resolved spectroscopy". Monthly Notices of the Royal Astronomical Society. 493 (2): 2215. arXiv:2001.06430. Bibcode:2020MNRAS.493.2215G. doi:10.1093/mnras/staa228. S2CID210714233.
^Mikal-Evans, Thomas; Sing, David K.; Kataria, Tiffany; Wakeford, Hannah R.; Mayne, Nathan J.; Lewis, Nikole K.; Barstow, Joanna K.; Spake, Jessica J. (2020). "Confirmation of water emission in the dayside spectrum of the ultrahot Jupiter WASP-121b". Monthly Notices of the Royal Astronomical Society. 496 (2): 1638–1644. arXiv:2005.09631. Bibcode:2020MNRAS.496.1638M. doi:10.1093/mnras/staa1628. S2CID218684532.
^Hoeijmakers, H. J.; Seidel, J. V.; Pino, L.; Kitzmann, D.; Sindel, J. P.; Ehrenreich, D.; Oza, A. V.; Bourrier, V.; Allart, R.; Gebek, A.; Lovis, C.; Yurchenko, S. N.; Astudillo-Defru, N.; Bayliss, D.; Cegla, H.; Lavie, B.; Lendl, M.; Melo, C.; Murgas, F.; Nascimbeni, V.; Pepe, F.; Ségransan, D.; Udry, S.; Wyttenbach, A.; Heng, Kevin (2020), Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) IV. A spectral inventory of atoms and molecules in the high-resolution transmission spectrum of WASP-121 b, arXiv:2006.11308
^Gemini/GMOS Optical Transmission Spectroscopy of WASP-121b:signs of variability in an ultra-hot Jupiter, 2021, arXiv:2103.05698
^An inventory of atomic species in the atmosphere of WASP-121b using UVES high-resolution spectroscopy, 2021, arXiv:2106.15394