(ORDO NEWS) — Astronomers have discovered for the first time an incandescent planet the size of Neptune, with a year that lasts less than Earth days. Until recently, the existence of such celestial bodies was considered almost impossible.
The discovery is described in a scientific article published in the journal Nature Astronomy.
Some worlds are located so close to their sun that they make a complete revolution around it in less than one Earth day. They are called ultrashort planets. This is not so uncommon in the Galaxy: for example, among the sun-like stars, such exoplanets have about every two hundredths.
But a planet so close to a star is glowing under its rays. And if the rocky world is threatened with a maximum loss of atmosphere, then the gas or ice body risks literally evaporating.
It is not surprising that so far only small rocky planets or, conversely, gas giants the size of Jupiter have been found in such proximity to stars. The latter survive in the hot embrace of the luminary due to their powerful gravity, which prevents matter from escaping into space.
But ice bodies like Neptune are almost never found near stars. They are not massive enough and not refractory enough to withstand the proximity of a star.
True, in recent years, astronomers have nevertheless discovered several hot Neptunes. This is, for example, GJ 3470b, orbiting a red dwarf in 3.3 Earth days and earning the glory of a planet evaporating at record rates. Another example is NGTS-4b, heated to a thousand degrees Celsius, making one revolution around its sun every 1.3 Earth days.
However, the recently discovered planet LTT 9779b is much more surprising. It has a radius of 4.6 terrestrial and a mass of 29 terrestrial, that is, belongs to the class of Neptune. And this is the first Neptune with a really ultra-short period: only 19 hours.
Moreover, its parent star LTT 9779 is sun-like, that is, more massive and hotter than the red dwarfs prevailing in the Galaxy.
As a result, the LTT 9779b temperature exceeds 1,700 degrees Celsius. In connection with this discovery, astronomers propose to introduce a new class of planets: ultra-hot Neptunes (by analogy with ultra-hot Jupiters).
An amazing celestial body was discovered by the orbiting space telescope TESS using the transit method. Its existence has already been confirmed by ground-based observations by the radial velocity method.
Based on the mass and radius of this incandescent world, experts believe that 6-12% of its mass falls on the atmosphere of hydrogen and helium. But why hadn’t he lost her until now, being so close to the star? After all, the luminary LTT 9779 (and, therefore, its entire system) is about two billion years old.
One possible explanation is that the unusual exoplanet has only recently settled dangerously close to the luminary. The gravitational effect of other (not yet discovered) planets or a passing star could move it from its previous orbit.
It is also possible that LTT 9779b was originally not Neptune but Jupiter. But the tidal forces of the star gradually destroyed it, forcing it to lose a significant part of its mass. Calculations show that such a scenario cannot be discounted, although it does require a few unlikely coincidences.
Fortunately, the star LTT 9779 is located just 260 light-years from Earth (a stone’s throw from galactic standards). This means that using the most powerful telescopes, astronomers can study this system in great detail. This will help uncover the secret of an amazing planet that should not exist, but it does exist.
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