Astronomers find that two exoplanets may be mostly water

A workforce led by UdeM astronomers has discovered proof that two exoplanets orbiting a pink dwarf star are “water worlds,” planets the place water makes up a big fraction of the amount. These worlds, positioned in a planetary system 218 light-years away within the constellation Lyra, are not like any planets present in our solar system.

The workforce, led by Ph.D. scholar Caroline Piaulet of the Trottier Institute for Analysis on Exoplanets (iREx) on the Université de Montréal, revealed an in depth research of a planetary system often called Kepler-138 within the journal Nature Astronomy right this moment, December 15.

Piaulet, who’s a part of Björn Benneke’s analysis workforce, noticed exoplanets Kepler-138c and Kepler-138d with NASA’s Hubble and the retired Spitzer space telescopes and found that the planets—that are about one and a half instances the dimensions of the Earth—may very well be composed largely of water. These planets and a planetary companion nearer to the star, Kepler-138b, had been found beforehand by NASA’s Kepler House Telescope.

Water wasn’t instantly detected, however by evaluating the sizes and lots more and plenty of the planets to fashions, they conclude {that a} vital fraction of their quantity—as much as half of it—needs to be made from supplies which can be lighter than rock however heavier than hydrogen or helium (which represent the majority of gas giant planets like Jupiter). The most typical of those candidate supplies is water.

“We beforehand thought that planets that have been a bit bigger than Earth have been massive balls of steel and rock, like scaled-up variations of Earth, and that is why we referred to as them super-Earths,” defined Benneke. “Nevertheless, we have now now proven that these two planets, Kepler-138c and d, are fairly completely different in nature: an enormous fraction of their complete quantity is probably going composed of water. It’s the first time we observe planets that may be confidently recognized as water worlds, a kind of planet that was theorized by astronomers to exist for a very long time.”

With volumes greater than 3 times that of Earth and lots more and plenty twice as massive, planets c and d have a lot decrease densities than Earth. That is stunning as a result of a lot of the planets simply barely greater than Earth which have been studied intimately thus far all gave the impression to be rocky worlds like ours. The closest comparability to the 2 planets, say researchers, can be among the icy moons within the outer solar system which can be additionally largely composed of water surrounding a rocky core.

“Think about bigger variations of Europa or Enceladus, the water-rich moons orbiting Jupiter and Saturn, however introduced a lot nearer to their star,” defined Piaulet. “As a substitute of an icy floor, Kepler-138 c and d would harbor giant water-vapor envelopes.”

Researchers warning the planets might not have oceans like these on Earth instantly on the planet’s floor. “The temperature in Kepler-138c’s and Kepler-138d’s atmospheres is probably going above the boiling level of water, and we anticipate a thick, dense ambiance made from steam on these planets. Solely beneath that steam ambiance there may doubtlessly be liquid water at excessive stress, and even water in one other phase that happens at excessive pressures, referred to as a supercritical fluid,” Piaulet mentioned.

Just lately, one other workforce on the College of Montreal discovered one other planet, referred to as TOI-1452 b, that would doubtlessly be lined with a liquid-water ocean, however NASA’s James Webb House Telescope will likely be wanted to review its ambiance and ensure the presence of the ocean.

A brand new exoplanet within the system

In 2014, information from NASA’s Kepler House Telescope allowed astronomers to announce the detection of three planets orbiting Kepler-138, a red dwarf star within the constellation Lyra. This was primarily based on a measurable dip in starlight because the planet momentarily handed in from of their star, a transit.

Benneke and his colleague Diana Dragomir, from the College of New Mexico, got here up with the concept of re-observing the planetary system with the Hubble and Spitzer space telescopes between 2014 and 2016 to catch extra transits of Kepler-138d, the third planet within the system, in an effort to research its ambiance.

Whereas earlier NASA Kepler space telescope observations solely confirmed transits of three small planets round Kepler-138, Piaulet and her workforce have been stunned to seek out that the Hubble and Spitzer observations prompt the presence of a fourth planet within the system, Kepler-138e.

This newly discovered planet is small and farther from its star than the three others, taking 38 days to finish an orbit. The planet is within the liveable zone of its star, a temperate area the place a planet receives simply the correct amount of warmth from its cool star to be neither too scorching nor too chilly to permit the presence of liquid water.

The character of this extra, newly discovered planet, nonetheless, stays an open query as a result of it doesn’t appear to transit its host star. Observing the exoplanet’s transit would have allowed astronomers to find out its measurement.

With Kepler-138e now within the image, the plenty of the beforehand recognized planets have been measured once more by way of the transit timing-variation technique, which consists of monitoring small variations within the exact moments of the planets’ transits in entrance of their star attributable to the gravitational pull of different close by planets.

The researchers had one other shock: they discovered that the 2 water worlds Kepler-138c and d are “twin” planets, with nearly the identical measurement and mass, whereas they have been beforehand regarded as drastically completely different. The closer-in planet, Kepler-138b, then again, is confirmed to be a small Mars-mass planet, one of many smallest exoplanets recognized so far.

“As our devices and methods develop into delicate sufficient to seek out and research planets which can be farther from their stars, we would begin discovering much more water worlds like Kepler-138 c and d,” Benneke concluded.