The polar ice caps have fully melted and the water level has risen to more than 5 miles, swallowing practically all of the land, in the post-apocalyptic action movie “Waterworld” from 1995.

Unlike any planet in our solar system, astronomers have discovered a pair of planets that are true “water worlds.”

They are somewhat bigger than Earth yet lack the solidity of rock. Despite this, they have a higher density than the gas-giantgiant outer planets that circle our Sun. What then are they composed of? The best explanation is that these exoplanets contain oceans that are at least 500 times deeper than those on Earth, which are only a wet surface on a rocky ball.

The wet planets revolve around the red dwarf star Kepler-138, which can be found 218 light-years distant in the constellation Lyra. 2014 saw the discovery of the planets thanks to NASA’s Kepler Space Observatory.

The planets must be mostly made of water, according to follow-up measurements made with the Hubble and Spitzer satellite observatories. It wasn’t possible to directly see the spectral signature of water. However, their density—which is determined by comparing their mass and size—is what led to this result.

In the world’s waters, don’t look for fish. There is probably no clear separation between the ocean surface and the planet’s atmosphere since they are both too warm and under a lot of pressure.

Astronomers have discovered proof that two exoplanets circling a star 218 light-years distant are “water worlds,” where water makes up a significant portion of the total planet. This evidence was discovered using data from NASA’s Hubble and Spitzer Space Telescopes. Credit: Paul Morris, Lead Producer at NASA Goddard Space Flight Center

The planets’ densities show that, despite the telescopes’ inability to directly examine their surfaces, they are heavier than gas-dominated planets but lighter than rock worlds.

Two exoplanets circling a red dwarf star have been identified as “water worlds,” where water makes up a significant portion of the planet’s mass, according to data discovered by a team headed by scientists at the University of Montreal. These planets are unlike any planet in our solar system and are situated in a planetary system 218 light-years distant in the constellation Lyra.

The group, led by Caroline Piaulet of the University of Montreal’s Trottier Institute for Research on Exoplanets (iREx), released a thorough analysis of this planetary system, also known as Kepler-138, on December 15 in the journal Nature Astronomy.

Exoplanets Kepler-138 c and Kepler-138 d may be mostly made of water, according to research by Piaulet and colleagues using NASA’s Hubble and the decommissioned Spitzer satellite observatories. These two planets as well as Kepler-138 b, a smaller planet partner located nearer to the star, have already been found by NASA’s Kepler Space Telescope. The latest investigation also discovered evidence of a fourth planet.

Image of the Kepler 138 Planetary System

Super-Earth Kepler-138 d is shown in the foreground in this picture. The planet Kepler-138 c is seen on the left, and Kepler-138 b, is visible in shadow transiting its star in the background. Red dwarf star Kepler 138 is 218 light-years distant. Kepler-138 c and Kepler-138 d, which are virtually similar in size, must be mostly made of water due to their low density. They cannot both be solid rocks since they are both twice as massive as Earth and only have around half the density. Based on evaluations of their bulk in relation to physical diameter They are distinct from all other major planets in our solar system and are regarded as a new kind of “water planet.” One of the tiniest known exoplanets, Kepler-138 b has the mass of Mars and the density of rock. Leah Hustak, NASA, and ESA (STScI)

Water wasn’t explicitly found at Kepler-138 c and d, but by comparing the planets’ sizes and weights to models, astronomers have come to the conclusion that up to half of their content should be composed of substances that are heavier than hydrogen or helium but lighter than rock (which constitute the bulk of gas giant planets like Jupiter). Water is the most prevalent of these potential materials.

Björn Benneke, research co-author and professor of astrophysics at the University of Montreal, said: “We previously assumed that planets that were a little bigger than Earth were gigantic balls of metal and rock, like scaled-up copies of Earth.

That’s why we dubbed them super-Earths. “However, we have now shown that the nature of these two planets, Kepler-138 c, and d, is significantly distinct from one another and that a significant portion of their total volume is most certainly made up of water. The existence of water worlds, a kind of planet that astronomers have long predicted to exist, is now supported by the strongest evidence yet.

Planets c and d have substantially lower densities than Earth while having volumes that are more than three times as large and masses that are twice as great.

This is unexpected considering that the majority of planets that are just marginally larger than Earth that have been thoroughly researched so far all seemed to be rocky worlds similar to our own. According to experts, several of the icy moons in the outer solar system that also has a rocky core and aismostly made of water would be the most comparable.

Piaulet said, “Consider bigger copies of Europa or Enceladus, the water-rich moons circling Jupiter and Saturn, but brought considerably closer to their star. They “would host enormous water-vapor envelopes rather than an ice surface.”

Earth and Kepler-138 Exoplanet Cross-Section

An artist’s conception of the Earth (left) and the exoplanet Kepler-138 d in cross-section (right). A thick layer of high-pressure water exists on Kepler-138 d in a variety of forms, including supercritical and potentially liquid water deep inside the planet and an extended water vapor envelope (shades of blue) above it. Like the Earth, this exoplanet has an interior made of metals and rocks (brown portion). More over half of its volume, or 1,243 miles, is made up of these water strata (2,000 kilometers). The oceans on Earth, in contrast, have an average depth of less than 2.5 miles and contain a minimal amount of liquid water (4 kilometers). Credit goes to Benoit Gougeon of the University of Montreal.

The waters on the planet’s surface may not be similar to those on Earth, according to researchers. We anticipate a thick, dense atmosphere formed of steam on Kepler-138 d since the planet’s atmosphere is most likely above the boiling point of water. Only in that steam environment could there possibly be high-pressure liquid water or even water in another phase that happens at high pressures, known as a supercritical fluid, according to Piaulet.

Astronomers announced the discovery of three planets around Kepler-138 in 2014 thanks to data from NASA’s Kepler Space Telescope. This was predicated on the planet briefly passing in front of its star, which caused a significant reduction in brightness.

The University of New Mexico’s Diana Dragomir and Benneke had the notion to re-observe the planetary system between 2014 and 2016 using the Hubble and Spitzer space telescopes in order to observe the atmosphere of Kepler-138 d, the third planet in the system, more closely.

Kepler-138 c and d, two potential water planets, are not found in the habitable zone, which is the region surrounding a star where temperatures permit liquid water to exist on the surface of a rocky planet. However, scientists also discovered proof of a brand-new planet in the system, Kepler-138 e, in the habitable zone in the Hubble and Spitzer data.

This recently discovered planet takes 38 days to complete an orbit and is smaller and located farther away from its star than the other three. However, because it doesn’t seem to transit its host star, the nature of this extra planet is still unknown. Astronomers may have measured the exoplanet’s size by observing its transit.

With Kepler-138 e in the picture, the masses of the previously identified planets were once more determined using the transit timing-variation method. This technique involves monitoring minute changes in the precise moments of the planets’ transits in front of their star that are brought on by the gravitational pull of other nearby planets.

Another surprise for the researchers was that, contrary to what was previously believed, the two water worlds Kepler-138 c and d are really “twin” planets, almost identical in size and mass. On the other hand, Kepler-138 b, the planet that is closer in, is proven to be a tiny Mars-mass planet and one of the tiniest exoplanets that have been discovered so far.

“We could start discovering a lot more of these water worlds as our tools and approaches grow sensitive enough to identify and analyze planets that are further from their stars,” Benneke said.