Researchers from the University of California, Berkeley recently discovered a new Neptune-sized exoplanet that is orbiting a massive bright star. Its discovery may help explain why finding such planets is rare.
Scientists believe that the massive bright star's harsh radiation could have stripped the gas layers of these Neptune-sized exoplanets. The process would have reduced the planets to a barely detectable core which is probably why scientists could not detect them.
Neptune-Sized Exoplanets Getting Stripped of Their Gaseous Atmospheres
The new Neptune-sized exoplanet is called HD 56414 b. Steven Giacalone, a graduate student at UC Berkeley, said in a statement that the recently discovered exoplanet is one of the smallest planets they found orbiting a massive star.
Neptune-sized exoplanets are usually hard to find and there might not probably be many like them in the near future if they all orbit a giant bright star, like HD 56414 b. Its star is one of the hottest stars that scientists know of, with a planet smaller than Jupiter orbiting it.
NASA's TESS mission spotted the planet, which is about 3.7 times the size of Earth. It is located too close to its star that it only takes about just 29 Earth days to complete one revolution.
Since the discovery of the first exoplanet about 30 years ago in 1992, astronomers have found many more and now the number reaches more than 5,000 planets that are orbiting their own stars. However, most exoplanets found were orbiting red dwarfs or stars that are slightly more massive than the average-sized Sun.
Additionally, many of these exoplanets were Jupiter-sized worlds and are orbiting close to their star. Very few are discovered orbiting massive stars, most likely the brightest, hottest, and short-lived ones. That means less than 1% of gas giants orbiting such stars are less massive than Jupiter.
They are identified as Neptune-sized exoplanets smaller than Jupiter but have the same "puffy" gaseous compositions. Giacalone explained that Jupiter-sized exoplanets or larger have a massive gravitational influence on their puffy atmosphere to prevent their gases from being extracted. But Neptune-sized exoplanets are not as massive and can easily lose their atmospheres.
New Neptune-Sized Exoplanet Orbiting a Bright Massive Star May Explain Why Finding Such Planets is Rare
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What Are Warm Neptunes?
Sapce.com reported that astronomers classify HD 56414 b as a "warm Neptune" because it lies outside the zone around its star, which would violently strip off the planet's atmosphere. The discovery implies that "hot Neptunes" in closer orbits to A-type stars may have already been separated from their outer layers and only left as smoldering cores.
Neptune-sized exoplanets orbiting less massive stars are rarer than expected and the lack of such worlds is called the "hot Neptune desert." Although, scientists are unsure whether it is because of the same reason as those which orbit A-type stars that removes their gas layers.
Courtney Dressing, a UC Berkeley assistant professor of astronomy, said that determining whether the hot Neptune desert also extends to A-type stars will give more insights into the importance of near-ultraviolet radiation. Resolving this mystery will need more sensitive instruments and methods, so hunting for Neptune-sized exoplanets orbiting A-type stars is needed.
For now, the discovery of HD 56414 b, a warm Neptune, could help astronomers better understand how these exoplanets evolve and where they form, whether inside or outside their star system. Researchers concluded that the proximity of this planet to its star means that radiation is stripping its gas layers.
They discussed their findings in full in the paper titled "HD 56414 b: A Warm Neptune Transiting an A-type Star," published in The Astrophysical Journal Letters.
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