A team led by UdeM astronomer has found evidence that two exoplanets are water worlds, planets where water makes up a large portion of the volume. These worlds are located in a planetary system that is 218 light-years away from our solar system.
A detailed study of a planetary system was published in the journal Nature Astronomy.
The planets, which are about one and a half times the size of the Earth, were discovered by a member of the research team. The planets and a planetary companion were discovered by NASA.
Water wasn't directly detected, but by comparing the sizes and mass of the planets to models, they conclude that a significant fraction of their volume should be made of materials that are lighter than rock. Water is the most common material.
"We used to think 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 Benneke. We have shown that the two planets, Kepler-138c and d, are not the same as nature would have you believe. It's the first time we've seen planets that can be confidently identified as water worlds.
The densities of planets c and d are less than Earth's. Most of the planets that have been studied have been found to be rocky like ours. Some of the icy moons in the outer solar system that are mostly composed of water would be the closest comparison to the planets.
"Imagine larger versions of Enceladus, the water-rich moons around Jupiter andSaturn, but brought much closer to their star," said Piaulet. The water-vapor envelopes would be different than the icy surface of Kepler-138c and d.
The oceans on Earth are not directly at the planet's surface, according to researchers. We expect a thick, dense atmosphere to be made of steam on the planets. There could be liquid water under that steam atmosphere, or water in another phase that occurs at high pressures, called a supercritical fluid.
A team at the University of Montreal found another planet, called TOI 1452 b, that could be covered with a liquid-water ocean, but it will take a NASA telescope to confirm the existence of the ocean.
There is a new planet in the system.
Astronomers were able to announce the detection of three planets around a red dwarf star with the help of data from NASA. The dip in starlight was the basis for this.
The idea of re-observing the planetary system with the Hubble and Spitzer space telescopes was brought up by Benneke and Diana.
While earlier NASA Kepler space telescope observations only showed transits of three small planets around the system, Piaulet and her team were surprised to find out that there was more than one planet in the system.
This planet is small and far away from its star than the others, and it takes 38 days to complete a circle around it. The planet is not too hot or too cold to allow liquid water on it's surface.
The nature of this new planet is an open question because it doesn't seem to transit its star. Calculating the exoplanet's size would have been possible.
The mass of the previously known planets were measured again using the transit timing-variation method, which involves tracking small variations in the precise moments of the planets's transit in front of their star.
The researchers were surprised to find that the two water worlds are almost the same size and mass. One of the smallest planets known to date is confirmed to be a small Mars-mass planet.
"As our instruments and techniques become sensitive enough to find and study planets that are farther from their stars, we might start finding a lot more water worlds," Benneke said.
There is evidence for the volatile-rich composition of a planet. The article can be found at www.nature.com/articles/s.
Journal information: Nature Astronomy
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