(ORDO NEWS) — Based on observations, HD-207496b is rapidly losing its gaseous envelope as it transitions from one exoplanet class to another.
The erosion of its atmosphere could explain the mysterious shortage of small planets in our Galaxy.
Today, thousands of distant exoplanets of various sizes and properties are known – from “mini-earths” with a diameter smaller than ours to gas giants much larger than Jupiter.
However, in the interval from one and a half to two radii of the Earth – between rocky earth-like bodies and small mini-Neptunes surrounded by a dense gaseous shell – there is a clear deficit.
Such planets are practically not found, which makes astronomers talk about the “failure among planets of small radius” and look for explanations for this mystery .
According to one hypothesis , this may be due to the too weak ability of such celestial bodies to hold a dense atmosphere.
Fluxes of particles and radiation from a nearby star cause rapid erosion of the gaseous envelope, as a result of which these worlds quickly “dry out”, turning into small super-Earths.
This idea was confirmed by new observations carried out by an international team of astronomers led by Susana Barros from the Portuguese University of Porto.
Scientists relied on data from the TESS space telescope, specially designed to search for exoplanets.
The candidate objects he finds are usually confirmed by additional observations, and this time such work was carried out using the 3.6-meter HARPS telescope of the European Southern Observatory.
Unlike TESS, which captures transits – the dimming of stars as the planets pass between them on us – HARPS is also able to notice slight fluctuations in the position of the star itself.
This allows us to more accurately estimate the mass of the planet that caused such fluctuations.
The main attention of astronomers was attracted by the system of the orange dwarf HD-207496, located 138 light years from us.
TESS discovered an exoplanet in its system, the size and orbit of which correspond to the very “failure”: HD-207496b makes one revolution around the star in 6.44 days, and its radius is only 2.25 times larger than the Earth’s.
HARPS observations helped to estimate the mass of the planet, which turned out to be 6.1 times the Earth’s. Based on these indicators, it is easy to calculate the average density of HD-207496b.
It amounted to 3.27 grams per cubic centimeter – noticeably less than that of our planet (5.51 grams per cubic centimeter).
This suggests that water and/or gaseous shells make up a much larger part of the exoplanet than that of the Earth.
Simulations of such a world have shown that HD-207496b’s atmosphere of helium and hydrogen cannot remain stable under such conditions.
Under the influence of a nearby star, it will completely evaporate in about half a billion years. The age of the star HD-207496 is estimated at just such a time.
It is possible that HD-207496b is undergoing such a transformation, but it is likely that it has already lost its atmosphere and is left surrounded by a “bare” ocean of water.
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