Seems to discover many outer planets that shrinks, solves the “missing link” in Planet EvolutionFour planets have been found in Milky Waywhich is a large and diverse place with a variety of outer planets that have been identified so far, which are quite different from what we find in our solar system.
One such planet is the minor planet Neptune, which is the most common type of world discovered by the Kepler mission, but is noticeably absent from our little corner of the galaxy.
These are worlds larger than Earth, and less massive than Neptune, but still surrounded by a dense atmosphere similar to the forage of Neptune, which consists of hydrogen and helium. Interestingly, these exoplanets appear to be at least twice the radius of the Earth.
Scientists believe that this gap exists because, above a certain critical limit, exoplanets have enough mass to hold a large primordial atmosphere that amplifies their size, putting them in the category of mini-Neptunes. On the other hand, the super-terrestrial planets do not have enough mass, and either they lost their primordial atmosphere, or they never started with it.
The next question is if these exoplanets started with primitive atmospheres, how were they lost?
One potential pathway, called core-supported mass loss, is the internal heat from planet formation, where gravitational binding energy is converted into heat that ejects the primordial atmosphere, and the other is called photoevaporation, where intense X-rays and ultraviolet rays from the young star remove The atmosphere of the outer planets.
Determining any of these scenarios, turning mini-Neptune into super-Earths requires observing the leaking exoplanets, and determining the rate at which they lose mass.
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A team of researchers led by astronomer Michael Zhang of the California Institute of Technology (Caltech) used spectroscopic analysis to study the atmospheres of four young planets close to Neptune, orbiting orange dwarf stars, to determine the rate at which these exoplanets leak helium into space.
These four include a single planet called TOI 560b, which is 2.8 times the diameter of Earth, whose analysis Zhang and colleagues published earlier this year.
The other three are new, TOI 1430.01, 2.1 times the size of Earth; TOI 1683.01, 2.3 times the size of Earth; and TOI 2076b, 2.52 times the size of Earth.
The team found that all four planets had large outflows of helium, at a rate consistent with photo-evaporation, rather than a loss of mass with primary energy.
In addition, this rate of loss is enough to strip the atmosphere of these exoplanets in just a few hundred million years, the team found – a very short time scale in cosmic contexts.
The team says that their findings suggest that most of the small Neptune planets that orbit around Sun-like stars may turn into super-Earths, and do so by photoevaporation.
“We conclude that many, if not all, of these planets will lose their hydrogen-rich envelopes and become super-Earths,” Chang and colleagues write in their peer-reviewed paper.
He added: “Our results show that most young Neptunes orbiting Sun-like stars have primitive atmospheres, and that photoevaporation is an effective mechanism for stripping these atmospheres and turning these planets into super-Earths.”
