The Milky Way could be a wetter place than we know it.
A new analysis of exoplanets orbiting red dwarf stars suggests that we may have lost a group of “water worlds” — wet planets whose composition is up to 50 percent water.
Not all of these worlds will be covered in a file global liquid oceans; Scientists predict, for many of them, that the water will be associated with the wet minerals. However, this discovery may have implications for our search for life outside the solar system.
“It was a surprise to see evidence of so many water worlds orbiting the most common type of star in the galaxy,” Astronomer Raphael Locke says: from the University of Chicago.
“It has dire consequences for the search for habitable planets.”
Although we Not a single red dwarf can be seen with the naked eyeThese stars are incredibly numerous. Small, cool, and dim red dwarfs account for, at most, only about half the Sun’s mass.
Its low fusion rate gives it the longest-lived of all stars; At 13.8 billion years old, the universe was not old enough for a red dwarf star to live a full 100 billion year old.
An estimated 73 percent of the stellar population in the Milky Way is made up of red dwarf stars. Just think about that for a moment. When you go out to stargaze, in a cold field or on the roof of a truck in the desert on a warm summer night, you can’t even see most of the stars in the sky.
Because they are dim and red in color, finding exoplanets in orbit around red dwarfs is difficult. Only a small percentage of 5,084 confirmed exoplanets At the time of writing, they are found around red dwarf stars.
However, our instruments are getting more sophisticated than ever – enough for scientists to be able to discern dozens of tiny worlds orbiting these tiny stars.
There are two main signals that scientists look at to characterize an exoplanet. The first is a regular faint dimming of starlight as the orbiting exoplanet passes between us and the star.
The second is lengthening and shortening the wavelengths of light from the star by a minute, as the orbiting exoplanet causes a faint gravitational pull.
If you have these measurements, and you know how far away the star is (and thus how much light it is emitting), you can measure the radius and mass of an exoplanet — two properties by which astronomers can derive the density of an exoplanet.
This density can be used to infer the composition of an exoplanet. The lower density likely means an exoplanet with a lot of atmosphere, like a gas giant. A higher density would likely mean a rocky world, such as Earth, Venusor Mars.
Locke and his colleague, astronomer Enrique Ballet of the Institute of Astrophysics in the Canary Islands and the University of La Laguna in Spain, conducted a study of the density of 43 exoplanets orbiting red dwarf stars.
Usually, these exoplanets have been divided into two categories: rocky exoplanets and gaseous planets with thick atmospheres. But Luque and Pallé have seen the emergence of a strange third class: exoplanets that are too dense to be gaseous, but not dense enough to be purely rocky either.
Their conclusion was that the rocky composition of these mid-range exoplanets had mixed with something lighter… like water, perhaps. But, while it’s tempting to imagine a world full of stormy seas, these planets are so close to their stars that there is no liquid water on their surfaces.
If their water were at the surface, it would swell into the atmosphere, making it larger in diameter, and less dense.
“But we don’t see that in the samples,” Luke says. “This indicates that the water is not in the form of a surface ocean.”
Alternatively, these worlds could look something like another object in the solar system – Jupitermoon Ganymede, which is roughly half rock and half water, with the water hidden under an icy rocky crust. Or they could be somewhat similar the moon (although more humid), to which water molecules are attached glass and metal.
However, these worlds have retained their waters, if the team’s conclusions are correct, the discovery indicates that these worlds could not have formed in the place where they formed. Instead, they had to have formed far from their stars, out of rocks and ice, and migrate inland to their current positions.
However, without further evidence, it is impossible at this point to make a judgment in favor of this model one way or another.
“Let’s put aside this potential for discovering alien life forms,” astronomer Joanna Teske of the Carnegie Institution for Science wrote. In a related perspective“Measuring the compositional diversity of planets around red dwarf stars—the most common type of star in the Milky Way—is important for piecing together the complex puzzle of minor planet formation and evolution.”
The search was published in Sciences.