At first glance, exoplanet 55 could be looked at as just another normal exoplanet. The mass of this exoplanet is about 8.63 Earth masses with a diameter that is about twice that of Earth. It is in the orbit of its sun host 55 Cancri A. It takes less than 18 hours for this exoplanet to complete an orbit. Lastly, exoplanet 55 has a striking resemblance to Neptune. By all standards, it seems like an ordinary hot Neptune. In turn, the composition of it that much like Uranus and Neptune. Although exoplanet’s size is closer to the ice giants, it’s only slightly denser than Saturn.
These characteristics of exoplanet 55 are what would cause one two take a long second glance at it. These characteristics are not typical of an exoplanet. So what is so special about it? The answer is water, more specifically water vapor.
Hannah Wakeford, a postdoc at NASA Goddard, says, “That the planet is primarily made of a rocky core and a dense envelope of water, with a hydrogen helium atmosphere of about 15-30 percent the mass of the planet.” Furthermore, exoplanet 55 has a low metallicity that resembles Jupiter despite its low Neptune mass.
The formation of this planet was probably different from the ice giants it is compared to. The abundance of its water vapor and the lack of heavy elements suggest a snug formation close on to the star.
Wakeford goes on to say that exoplanet 55 formed closer to its star than similar mass planets Neptune and Uranus in our solar system, thus resulting in a low metallicity atmosphere.