NASA’s Hubble and Spitzer Space Telescopes Just Discovered Two Exoplanets That May be Mostly Water

Finding an Earth-like planet with the potential of sustaining any form of life has remained the primary goal of most space agencies. To take this goal even further, NASA has successfully launched several powerful space Telescopes including Hubble and Spitzer. 

A team of scientists led by Caroline Piaulet of the Institute for Research on Exoplanets (iREx) at the University of Montreal has discovered two exoplanets orbiting around a red dwarf star. These scientists observed closely and realized that these two exoplanets are mostly occupied with large fractions of water that fill the entire planet. These types of planets are referred to as water worlds by astronomers across the globe.

Using the Hubble and Spitzer Space Telescopes to examine even further, astronomers discovered that these water worlds are located in a Planetary system that is 218 light-years away in the constellation Lyra. The researchers marveled as they have not seen this type of planetary system in our system before. 

What You Should Know About These Planets

These planets were known to exist in a planetary system named Kepler-138. This system has three planets (Kepler-138b, Kepler-138c, and Kepler-138d) around its orbit. Kepler-138b was the first planet to be discovered on this planetary system by the Kepler Space Telescope in 2014. The two water worlds that exist in this planetary system are named Kepler-138c and Kepler-138d.

Piaulet and colleagues recently used NASA’s Hubble and the retired Spitzer space telescopes to discover Kepler-138c and Kepler-138d as two water words orbiting around their host star Kepler-138. Unlike Kepler-138b with a smaller size, Kepler-138c and Kepler-138d are quite larger. The new study also reveals evidence of the existence of the fourth planet. 

Caroline Piaulet and her colleagues did not discover water directly on the surface of Kepler-138c and d. However, they compared the sizes and masses of the exoplanets to models before concluding that a larger fraction of their volume which may reach up to half of its size is occupied by materials that are lighter than rock but heavier than hydrogen or helium. The astronomers conclude that the most common material that matches the description of their discovery is water.

“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,” said Björn Benneke, study co-author and professor of astrophysics at the University of Montreal. “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.”

Kepler-138c and d have lower densities than Earth. But they both have masses twice as big as Earth and volumes more than three times that of Earth. However, astronomers were amazed by the existence of these planets. Most planets discovered in the past with similar sizes were spotted to be rocky worlds. Scientists that participated in this study used Europa or Enceladus to express the nature of these newly discovered water worlds.

“Imagine larger versions of Europa or Enceladus, the water-rich moons orbiting Jupiter and Saturn, but brought much closer to their star,” explained Piaulet. “Instead of an icy surface, they would harbor large water-vapor envelopes.”

Based on the scientific observations of these planets, researchers that participated in this study revealed that the planets may not have oceans directly on their surfaces as we have on Earth.

 “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,” Piaulet said. However, future observations will enable scientists to completely understand more about Kepler-138 and its three planets.

How Kepler-138 and its Planets Were Discovered Using Kepler Space Telescope

NASA’s Kepler Space telescope looked deep into Interstellar Space and spotted a Star named Kepler-138 with three planets orbiting around it in 2014. Scientists used the data obtained by the sophisticated telescope to announce the new discovery to space lovers. Astronomers finalized this data based on the measurable dip in starlight as the planet occasionally moves across the front of its host star from the view of the Kepler space telescope.

After the discovery, astronomers began to wonder how to obtain more information from exoplanets discovered by Kepler. Benneke and his partner Diana Dragomir from the University of New Mexico later came up with the idea of re-observing the planetary system with Hubble and Spitzer Space Telescopes. These re-observations lasted between 2014 and 2016. The astronomers focused more on catching the transits of Kepler-138d, which is the third planet in the planetary system. their goal is to study the atmosphere of this planet.

After Benneke and his colleagues have completed their observation, Piaulet and his team of astronomers decided to use the same telescopes to recently observe the planetary system. From their recent observations, they discovered that the two water worlds do not exist in the goldilocks zone of their host star. Keep in mind that the goldilocks zone or habitable zone is the region around a star that has suitable temperatures which would allow liquid water to exist on the surface of a rocky planet.

However, the data provided by Hubble and Spitzer telescopes enable the researchers to discover that Kepler-138c and d do not orbit around Kepler-138 in a habitable zone. Instead, both space telescopes allowed astronomers to discover evidence of a new planet in the system that orbits the star in the Goldilocks zone. Scientists named this newly spotted exoplanet Kepler-138e. This newly discovered planet is farther away from Kepler-138 that the other three planets orbiting around the star.

It is also smaller in size and takes about 38 days to complete an orbit around the host star. However, astronomers will likely conduct more observations in this planetary system to make more discoveries for humanity. After the study, the team of scientists led by Caroline Piaulet of the Institute for Research on Exoplanets iREx) at the University of Montreal, published a detailed study of this planetary system, in the journal Nature Astronomy today. You can check out their observations to learn more about this discovery.


Discovering water worlds in deep space often gives humans the hope of finding other forms of life outside Earth. Hopefully, we will advance technologically as a civilization and build technologies that will enable us to explore some of these water worlds and make discoveries for ourselves. What do you think about this discovery?

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1 thought on “NASA’s Hubble and Spitzer Space Telescopes Just Discovered Two Exoplanets That May be Mostly Water”

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