Cаrolіne Pіаᴜlet, Pһ.D. Stᴜdent аt Unіʋerѕіté de мontréаl jᴜѕt dіѕcoʋered 2 аlіen wаter worldѕ wіtһ oceаnѕ 500 tімeѕ deeрer tһаn Eаrtһ’ѕ

We met Caroline Piaulet, PhD student at the Trottier Institute for Exoplanet Research (iREx) at the University of Montreal (Canada).

The team led by Caroline Piaulet conducted a detailed study of the Kepler-138 planetary system. More specifically, he discovered two “water worlds”: two water-filled exoplanets orbiting a red dwarf star, about 218 light-years from Earth.A light year is approximately 9.46 trillion kilometers (5.88 trillion miles).

How did your fascination with exoplanets come about? Which exoplanet surprised you the most?

What sparked my passion for exoplanets was the discovery that we can not only find planets in the solar system but also study their composition and atmosphere! The fact that we can probe gases in the atmospheres of distant planets never ceases to amaze me. One of the exoplanets that surprised me most was definitely WASP-107b, the first planet I studied during my PhD: it is a planet the size of Jupiter but with a density so low that comparable to cotton candy – is that really crazy?

How do you study the atmospheres of these very distant planets? Can telescopes see only the shadows of exoplanets?

There are several ways to study the atmospheres of exoplanets, but the most common is called “transmission spectroscopy,” which is similar to the “shadow” idea you’re talking about. When a planet passes in front of its star from our perspective, it creates a “shadow” that temporarily causes us to see less of the star’s light.

We call these events “transits,” and they allow us to discover planets we didn’t know existed. When studying the atmosphere, we take advantage of the fact that during transit a small part of the star’s light is filtered through the planet’s atmosphere and imbued with signatures of the molecules and atoms present .

“Transmittance Spectroscopy” then involves analyzing the light we receive from the star during its passage between all its different colors and determining the unique imprint left in these This color is given by the molecules of the star’s atmosphere.

A research team from the University of Montreal led by you has discovered two “underwater worlds”. Two exoplanets are filled with water (Kepler-138c and Kepler-138d). What are the characteristics of these two exoplanets?

Our international team has discovered two “twin” planets (they have essentially the same size and mass) that are best explained as water worlds, i.e.where the majority of their volume is made up of water. If you think about Kepler-138d as we understand it today, imagine a large planet (about 1.5 times the size of Earth) with about half of its volume made up of water in various forms together. Starting from the top of the mountain, you will have to cross a layer of water 2000 km deep to reach the rocky interior.

The water layer would consist of an expanded atmosphere of water vapor, and as you go deeper, where the water is at higher pressure, you would reach an ocean that we call “supercritical”, instead because water is liquid.Supercritical water is essentially water vapor raised to such high pressure that it reaches a liquid state, but is not cold enough to condense into an ocean of liquid water.

We used the Hubble and Spitzer space telescopes and observed 13 new transits of Kepler-138 d. Our method involves using a very special configuration of the planets in the Kepler-138 system, which means that instead of passing in front of their star at regular intervals (e.g. every 5 days for a planet (it takes 5 days to rotate) , its star), the three planets Kepler-138 b, c and d sometimes pass by the star one hour earlier or later a little (a few minutes).

This odd behaviour actually originates in the planets regularly close to each other, which perturbs their mutual orbits ever so slightly to produce what we call transit-timing variations (TTVs). Using these TTVs, we are able to measure the planets’ masses, which enables us to infer their densities. Kepler-138 c and d have densities too low to be made up of only rock similarly to the Earth: although the Earth is covered in oceans, they are very shallow and do not impact its density. 

On the other hand, we demonstrated this low density could not be due to a hydrogen envelope, as hydrogen is very light and can be easily swept away by the star’s irradiation. A heavier molecule like water or methane is light enough to make for a low planet density, while being much more resistent to being stripped by the star’s energy – enough to explain the low densities of Kepler-138 c and d.

If we could walk on those two exoplanets, what would we see? What is their landscape like?

I believe my answer to question 3 above provides a partial answer. With such a large amount of water, you wouldn’t expect there to be a continent or rocky surface to walk on. The way I like to imagine these planets is to think of the icy moons of the outer solar system, where we think large oceans of water exist beneath their icy surfaces.

For Kepler-138 c and d, we can instead look at the analogues of our icy moons, but much larger and closer to the star, so instead of sheltered beneath the ice surface, the water is exposed again in a slightly expanded atmosphere.

We are discovering many exoplanets, and many of them are filled with water and in the habitable zone.Do you think the universe is full of life? Is there life everywhere?

From a purely probability standpoint, the ingredients necessary for the emergence of life are certainly present around many stars other than our Sun. If the question is “do I believe there is life somewhere in the Universe?” ”, so I believe that.

But the challenging task for us astronomers actually looking for the signatures of extraterrestrial life is to find signs that would unambiguously have to be produced by life and could not be a result of other processes such as chemistry or volcanism. Therefore, being able to answer this question based on scientific evidence for life – or lack thereof – is probably going to have to still wait a few more years.

Source: Nature Astronomy