A newly discovered distant mini-Neptune planet may have its own atmosphere, ocean, or a combination of the two, even if it doesn’t last long. The extrasolar planet, or exoplanet, called HD-2047496 b, located about 77 light-years from Earth, revealed its features to astronomers when it crossed the face of its parent star.
The discovery could help scientists better understand how planetary systems evolve and why there is an absence of Neptune-sized worlds close to their parent stars in the Milky Way.
The team of planetary scientists from around the world was able to characterize the features of the exoplanet while analyzing data from its star collected by the High Accuracy Radial velocity Planet Searcher (HARPS). They combined this with data from the Transiting Exoplanet Survey Satellite (TESS), which revealed the brightness and wavelengths of light from the star HD-207496 and revealed the features of the exoplanet as it crossed or passed over its face.
Related: Exoplanets: worlds beyond our solar system
The astronomers were able to determine that HD-2047496-b, which has the alternative name TOI-1099 b, has a width of 2.25 times that of Earth, while its mass is about 6.1 times that of our planet. This means that the exoplanet is less dense than Earth, which led the team to classify it as a “mini-Neptune” – a planet less massive than Neptune but still similar to the solar system’s icy giant.
The team was also able to calculate that HD-2047496-b orbits its star at a distance of just 9.4 million kilometers in just 6.4 Earth days. But not everything about this newly discovered world is so certain.
HD-2047496-b likely has a rocky core mostly covered in water or gas, but the team doesn’t currently know which one, or whether it indeed has both. Models of the planet didn’t get them any closer to determining the exoplanet’s specifics, but instead also pointed to the fact that it could be water-rich, gas-rich, or both. But regardless of the nature of the material covering HD-2047496-b’s rocky core, the situation is likely temporary.
Although its host star HD-2047496 is only about 80% the mass of the Sun and 79% the width of our star, it is still large enough for its gravity to strip the exoplanet of its hydrogen and helium atmosphere, it suggested. model of the team. .
Most Neptune-like planets orbiting stars at such a close distance would have had their atmospheres stripped and their oceans boiled away. This is one of the proposed explanations for why Neptune-like worlds are rarely found close to their stars, a problem dubbed the “hot Neptunian desert.” The Neptune- or sub-Neptune-sized planets are thus reduced in size to rocky cores that correspond to so-called super-Earth exoplanets.
Read more: Why are there so few ‘hot Neptune’ exoplanets?
HD-2047496-b may have escaped this fate because its star is only 520 million years old, meaning the system it inhabits is relatively young, especially compared to our 4.6 billion year old solar system. Therefore, the star may not have had time to completely strip the planet’s atmosphere yet.
The astronomers calculate that if the planet’s atmosphere hasn’t been stripped yet, leaving only an ocean cover, it should be ripped away within the next 500 million years. This leaves HD-2047496-b as a rocky core covered with oceans, or as a completely barren, naked planetary core if it currently has no ocean-atmosphere mix.
The team favors an explanation for the planet being covered by a mix of atmosphere and ocean rather than just an ocean or just an atmosphere, but added that further research of this world is needed to determine its composition .
“Further observations of the possible atmosphere and/or mass loss would allow us to differentiate between these two hypotheses,” the authors wrote. to write (opens in new tab). “Such observations would determine whether the planet will remain above the jet gap or if it will shrink and be below the gap.”
The team’s research has been accepted for publication in the journal Astronomy & Astrophysics and is available in the paper repository arXiv. (opens in new tab)
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