![]() Migration could explain the planet, too, but only if it migrated during the star’s main sequence lifetime. ![]() “First, the stellar flux in XUV may be significantly lower or absorbed less efficiently than existing models predict, preventing severe atmospheric erosion even if the planet has not changed its orbit or radius since formation.” If the star isn’t as powerful as thought, then that could explain how the planet has held onto its atmosphere for so long. The authors say that the explanation could lie in incorrect models of stellar flux. How was it able to hold onto its mass for so long while being so close to its star? “Thus, assuming that the planet did not experience migration or inflation after a system age of 20 Myr, most or all of the planet’s atmosphere should have been stripped over its lifetime,” the authors write. Outliers like these are important because they can define Nature’s limits and help scientists build better models.Ĭurrent models can’t explain TIC 365102760 b and instead show that there should be nothing left by now but a core. There is only a small handful of Neptune-size planets orbiting a post-main sequence star, and it’s the only hot Neptune orbiting this type of star. “The old age and high equilibrium temperature yet remarkably low density of this planet suggests that its gaseous envelope should have been stripped by high-energy stellar irradiation billions of years ago,” the authors write. Its temperature is 4700 Kelvin (4400 C 8,000 F.) Considering all these factors, TIC 365102760 b should be nothing but a planetary core by now. The star is ancient, a red giant about 7.2 billion years old, and is 1.2 times as massive as the Sun. With a density that low, the planet shouldn’t be hanging onto its atmosphere. Even though it’s about half the radius of Jupiter, its density is only 0.06 that of Jupiter’s. The planet, named TIC 365102760 b, is not very dense. This hot Neptune is so close to its star that it completes an orbit in only 4.2 days. The lead author is Samuel Grunblatt from the Department of Physics and Astronomy at Johns Hopkins University. The paper is “An unlikely survivor: a low-density hot Neptune orbiting a red giant star.” In new research, astronomers from the USA and Australia presented their discovery of another hot Neptune. A 2015 paper concluded that the planet is losing mass and leaving a trail of hydrogen behind it as the star strips away its atmosphere. Researchers are still puzzling over Gliese 436 b and trying to understand how it held onto its atmosphere for this long. Astronomers found it in 2004, five years before the Kepler mission changed exoplanet science forever. ![]() The first hot Neptune astronomers found is Gliese 436 b. They’re not massive enough to hold onto their atmospheres in the face of all the stellar radiation. Hot Jupiters are so massive that they can hang on to their atmospheres with some success.īut Neptune-size planets are much less massive than Jupiter-size planets, and really, hot Neptunes just shouldn’t exist. When a gas planet gets too close to its star, the star can strip the gaseous atmosphere away. But the hot Neptune tag isn’t used much because there aren’t many of them.Ī hot Neptune is a gaseous planet that is extremely close to its star, just as a hot Jupiter is. Other classifications are used in space science, too, like hot Jupiter. On their Exoplanet Discovery Dashboard, NASA groups exoplanets into these categories: Neptune-like, Gas Giant, Super-Earth, and Terrestrial. ![]() With over 5,300 confirmed exoplanets, scientists are getting a handle on the makeup of the exoplanet population. The more exoplanets we find, the better we understand the exoplanet population. ![]()
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