The last 25 years have seen the discovery of thousands of exoplanets around stars in our galaxy, but more than 99% of them are in the vicinity of smaller stars.
Most of the exoplanets that have been observed are the size of Jupiter or larger. There are some stars in the night sky that are A type.
According to the University of California, Berkeley, there is a new Neptune-sized planet around one of these stars.
The newly discovered planet has a longer orbital period than most discovered to date, which makes it more difficult to find. If a Neptune-sized planet were to sit close to a bright A-type star, it would be stripped of its gas in a matter of hours.
It was not known if this theory extended to hotter stars because of the lack of planets around some of the best stars.
Steven Giacalone is a graduate student at UC Berkeley. This is the hottest star we know of with a small planet. It's interesting because these types of planets are hard to find, and we're not going to find many like them in the foreseeable future.
The desert is hot.
The discovery of 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 many unseen cores within the hot Neptune zone that are waiting to be discovered.
The researchers concluded in their paper that there could be a pileup of remnant Neptunian cores around the stars.
It adds to our understanding of how planetary atmospheres evolve.
How do planets retain their atmospheres over time is a big question. Are we looking at the atmosphere of the planets when we look at them? Is it possible that the atmosphere was outgassed over time? We can change the ratio of X-ray to ultraviolet light on planets if we can look at them with different amounts of light.
Giacalone and Dressing reported their discovery in a paper that was accepted for publication.
It's well known that Neptune-sized planets are less massive than expected. It's not known if this holds for planets around A- type stars.
Smaller F, G, K and M dwarfs are A-type stars. Close-in planets around sun-like stars get more X-ray and ultraviolet radiation than close-in planets around A-type stars.
It is possible that the hot Neptune desert also extends to A-type stars. Understanding the physics of atmospheric mass loss and investigating the formation and evolution of small planets is what this result is about.
HD 56414 b was detected by NASA as it transited its star. Dressing, Giacalone and their colleagues were able to confirm that HD 56414 was an A-type star by using the 1.5 meter telescope operated by the Small and Moderate Aperture Research Telescope System.
The star is about one-quarter the distance between Earth and the sun, but the planet has a much larger radius. Our sun is 4.5 billion years older than the system.
The researchers modeled the effect that radiation from the star would have on the planet and found that it would likely survive for a billion years.
According to Giacalone, Jupiter-sized planets are less susceptible to photoevaporation because their core is large enough to hold onto their hydrogen gas.
He said there was a balance between the central mass of the planet and the atmosphere. The planet is large enough to hold on to its atmosphere. The atmosphere is still puffy even though the planet is not as big, so they can lose their atmosphere more easily.
Giacalone and Dressing continue to search for more Neptune-sized exoplanets around A-type stars in hopes of finding others in or near the hot Neptune desert to understand where these planets form in the accretion disk during star formation.
More information: Steven Giacalone et al, HD 56414 b: A Warm Neptune Transiting an A-type Star, The Astrophysical Journal Letters (2022). DOI: 10.3847/2041-8213/ac80f4 , iopscience.iop.org/article/10. … 847/2041-8213/ac80f4 Journal information: Astrophysical Journal Letters
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