GJ 9827 d, an exoplanet akin to Neptune, was discovered in 2017. It has a diameter twice the size of Earth and is estimated to be much heavier, with a mass approximately 3.5 times that of our planet.

Publications of the Astronomical Society of the Pacific, Vol. 116, No. 823 (September 2004), pp. 876-885 (10 pages) ABSTRACT Water vapor, while usually a small contributor to the atmospheric ...