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They call them wandering planets. They roam our starless galaxy, although they were not always alone. They are a type of exoplanet that until now had not been able to study in detail, as not many such worlds have been found. Something that changes from this week, as a team with Spanish participation has just announced the discovery of a hundred
free-floating planets
(in English,
free-floating planets
or FFPs).
As they explain this Wednesday in the journal
Nature Astronomy
, it is the largest population of wandering planets discovered to date.
"They are celestial objects with properties similar to planets that orbit around stars, but which have formed either as stars or planets, but which have been expelled and are
no longer attached to the star around which they formed
", describes David Barrado Navascués, researcher at the Center for Astrobiology (CAB / INTA-CSIC) and co-author of this international research.
As Núria Miret Roig, first author of the article, adds, "wandering planets are considered" objects up to 13 times the mass of Jupiter but not linked to any star. "
Locating them is not easy precisely because we cannot have the clue of the brightness of the stars.
These worlds are
several thousand times fainter, so they can only be detected with large diameter telescopes and very sensitive detectors.
The first candidates were discovered 20 years ago: "Since then we have been accumulating evidence about their nature and properties. But now we have identified them in a massive way", says Barrado, author of the book
Exoplanets and astrobiology: plus ultra
(The Cataract) .
Despite having known them for a couple of decades, their nature and origin remain unclear as there is no homogeneous sample of these worlds. Scientists believe that there are two mechanisms that can produce wandering planets. One of those mechanisms is that they form like stars by the gravitational collapse of small gas clouds, and the other is that they form like planets around stars and then are dynamically ripped or ejected.
All the planets described in this research "are concentrated in a very specific region, globally associated with a set of young stars, which allows us to know their age quite precisely," according to the scientist.
Specifically, they are about 400 light years from Earth: They are all at practically the same distance.
We can say that they are brothers of the same litter. "
Regarding the characteristics of these young planets, he affirms that "they are massive, hot and bright, compared to Jupiter and Saturn, the analogues of the Solar System."
There are none similar to Earth:
"All the planets we have detected are between 5 and 13 times the size of Jupiter.
They are gaseous and not rocky planets. Planets like Earth are impossible to detect at the moment at the distance of the region of our study, they don't shine enough, "explains Miret, who is currently doing a postdoc at the University of Vienna.
Astronomers believe that these types of starless worlds are abundant in number but not in the total mass they represent. "From our work, we can speculate that if the fraction of wandering planets that we have found in the studied region is similar in other regions of the Milky Way and if there are about 100,000 million stars in the Milky Way, then there should be between 2,000 and 3,000 million wandering planets. These numbers refer to planets between 5-13 times the mass of Jupiter, which are what we have detected in our study. However, we know that planets like Earth are more frequent, so it is conceivable that this number would be even higher ", points out Miret, who emphasizes that" these numbers are speculations and are not the main result "of his article presented in
Nature Astronomy.
Could Earth become a wandering planet in the future, and be ejected from the Sun?
"Not in principle. To become one, there would have to be a gravitational interaction with a very massive object that would cause its expulsion. Like a star that passes very close and causes an effect similar to that of a slingshot. But these events are very infrequent", Barrado clarifies.
Neither does Miret believe that it is a probable situation: "For the Earth to be ejected from the Solar System, a great gravitational instability would be necessary and at the moment this scenario is not foreseen, luckily!".
The
James Webb
Space Telescope
, which will be launched on Christmas Day if there are no further delays, will be able to help better study these starless planets, which, according to Miret, "have important implications for the formation and early evolution of planetary systems."
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