"Determining whether the hot Neptune desert also extends to A-type stars provides insight into the importance of near-ultraviolet radiation in governing atmospheric escape," she said. Close-in planets orbiting sun-like stars receive high amounts of both X-ray and ultraviolet radiation, but close-in planets orbiting A-type stars experience much more near-ultraviolet radiation than X-ray radiation or extreme ultraviolet radiation.
But whether this holds for planets orbiting A-type stars is not known because those planets are challenging to detect.Īnd an A-type star is a different animal from smaller F, G, K and M dwarfs. Giacalone and Dressing reported their discovery in a paper accepted by The Astrophysical Journal Letters and posted online.Īccording to Dressing, it's well-established that highly-irradiated, Neptune-sized planets orbiting less massive, sun-like stars are rarer than expected. Credit: Graphic by Steven Giacalone, using data courtesy of NASA Current techniques are limited to finding planets in close, short-period orbits, less than about 100 days.
The planets on this chart were discovered when they crossed in front of or transited their star, dimming its light. A new-found Neptune-sized planet (yellow star) suggests that they don't survive long enough to detect.
The discovery of what the researchers term a "warm Neptune" just outside the zone where the planet would have been stripped of its gas suggests that bright, A-type stars may have numerous unseen cores within the hot Neptune zone that are waiting to be discovered through more sensitive techniques.Īstronomers have found thousands of exoplanets (black dots) around stars in the Milky Way galaxy, but few Neptune-sized planets have been discovered in short-period orbits around their stars, creating what astronomers call a Hot Neptune desert (pink region, representing planets with radii 3-10 times that of Earth with orbital periods under 3 days). This planet's interesting first and foremost because these types of planets are really hard to find, and we're probably not going to find many like them in the foreseeable future." "In fact, this is the hottest star we know of with a planet smaller than Jupiter. "It's one of the smallest planets that we know of around these really massive stars," said UC Berkeley graduate student Steven Giacalone. While this theory has been proposed to explain so-called hot Neptune deserts around redder stars, whether this extended to hotter stars-A-type stars are about 1.5 to 2 times hotter than the sun-was unknown because of the dearth of planets known around some of the galaxy's brightest stars. The researchers suggest that an easier-to-find Neptune-sized planet sitting closer to a bright A-type star would be rapidly stripped of its gas by the harsh stellar radiation and reduced to an undetectable core. University of California, Berkeley, astronomers now report a new, Neptune-sized planet-called HD 56414 b-around one of these hot-burning, but short-lived, A-type stars and provide a hint about why so few gas giants smaller than Jupiter have been seen around the brightest 1% of stars in our galaxy.Ĭurrent exoplanet detection methods most easily find planets with short, rapid orbital periods around their stars, but this newly found planet has a longer orbital period than most discovered to date. Some of the brightest stars in the night sky, such as Sirius and Vega, are A-type stars. Few have been discovered around even more massive stars, such as A-type stars-bright blue stars twice as large as the sun-and most of the exoplanets that have been observed are the size of Jupiter or larger.
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