There are over 9000 extrasolar planets that are awaiting confirmation. While most of these planets are Jupiter- or Neptune-sized gas giants or rocky planets, a significant number have been planets where water makes up a significant part of their mass fraction. These planets are unlike anything we have seen in the Solar System and raise a lot of questions.
There are two water worlds in a single planetary system located about 218 light-years away in the constellation Lyra. The team found that the exoplanets are lighter than rocky ones but heavier than gas ones. The discovery was made using data from two space telescopes.
The leader of the team was a PhD candidate with the iREx. Professor Benneke is an advisor at iREx and he was with her. Their paper was published in the journal Nature Astronomy.
To determine the composition of intermediate-sized exoplanets, which are between Earth and Neptune in terms of size, Piaulet used transit and eclipse data from several telescopes. Water worlds are much larger than Earth but have lower densities. In a recent NASA press release, Benneke explained.
“We previously thought that planets that were a bit larger than Earth were big balls of metal and rock, like scaled-up versions of Earth, and that’s why we called them super-Earths. However, we have now shown that these two planets, Kepler-138c and d, are quite different in nature and that a big fraction of their entire volume is likely composed of water. It is the best evidence yet for water worlds, a type of planet that was theorized by astronomers to exist for a long time.”
A third exoplanet (Kepler-198b) was detected by the transit method used to discover the exoplanets in this study. The idea of observing the planetary system with Hubble and Spitzer was brought up by Benneke and Diana. The team was able to constrain the size of Kepler-198c and d by using 13 transit observations.
The host star's radial velocity was measured with the HIRES at the W.M.Keck Observatory. The team was able to constrain the size and mass of Kepler-198c and d, which led them to estimate the Earth's mass. The findings show that the two planets are almost the same in size and mass.
Their estimates show that these exoplanets have lower densities than Earth. Up to half of their volumes are made up of volatile elements like water. Most of the exoplanets studied have appeared to be rocky. Some of the icy moons in the outer solar system would be compared by researchers.
The bodies are mostly composed of water and other volatiles around a rocky-metallic core. Interior oceans under a layer of surface ice are different from surface oceans. Piaulet said that as well.
“Imagine larger versions of Europa or Enceladus, the water-rich moons orbiting Jupiter and Saturn, but brought much closer to their star. Instead of an icy surface, they would harbor large water-vapor envelopes. The temperature in Kepler-138d’s atmosphere is likely above the boiling point of water, and we expect a thick, dense atmosphere made of steam on this planet. Only, under that steam atmosphere there could potentially be liquid water at high pressure, or even water in another phase that occurs at high pressures, called a supercritical fluid.”
The team noted that there is evidence of a fourth planet in the data from the Hubble and Spitzer telescopes. The planet takes 38 days to complete a circle around its host star and appears to be similar in size to Mars. The characteristics of this planet are poorly constrained since it doesn't appear to transit its star. Astronomers will be able to find more water worlds that are farther away from their stars with the help of next- generation telescopes.
The JWST has demonstrated a key capability since it began observing the universe. The first clear evidence of carbon dioxide in this planet's atmosphere was found in the spectrum. A new method for constraining the atmospheric temperatures of exoplanets was developed while at iREx. Astronomers will be able to measure a key indicator of planetary habitability.
Nature Astronomy is read further.
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