Hot Super Neptune LTT 9779b: A Mysterious Exoplanet Unveiled
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Chapter 1: Introduction to LTT 9779b
Astronomers have recently observed a puzzling hot super Neptune, LTT 9779b, which defies expectations as observed by the Transiting Exoplanet Survey Satellite (TESS).
This exoplanet is significantly larger than Earth, boasting a size nearly five times that of our planet. Its surface temperatures are so extreme that they far exceed those of Venus, the hottest planet in our solar system. Discovered only a year ago, LTT 9779b's existence raises questions about its stability and longevity.
Hot Neptunes are typically described as planets similar in size to Neptune or slightly larger, located in close proximity to their stars. Conventional wisdom suggests that such planets should be unstable due to the intense heat from their stars, which would likely strip away their atmospheres.
According to Ian Crossfield, an assistant professor of physics and astronomy at the University of Kansas, “This planet experiences such intense radiation from its star that its temperature exceeds 3,000 degrees Fahrenheit, potentially leading to a complete evaporation of its atmosphere. Yet, our observations from the Spitzer Space Telescope reveal its atmosphere through the infrared light it emits.”
Section 1.1: Characteristics of Hot Neptunes
Similar to the well-known hot Jupiters, hot Neptunes are predominantly gaseous but are considerably less massive. LTT 9779b has a mass approximately 30 times that of Earth and orbits its star six times closer than Earth does to the Sun. The star at the center of this system is about 75% as massive as our Sun, while LTT 9779b itself is slightly smaller than our own star.
Subsection 1.1.1: Extreme Conditions on LTT 9779b
The planet orbits its star in a region known as the "Neptune desert," where a year on LTT 9779b lasts less than 24 hours. This rapid orbit is just one of the many extreme characteristics of this unusual world. Crossfield notes, “This planet lacks a solid surface, and its temperatures are even higher than those of Mercury. Not only would lead melt in its atmosphere, but so too would platinum, chromium, and stainless steel.”
The TESS spacecraft has provided invaluable insights into exoplanets across the galaxy. Image credit: NASA’s Goddard Space Flight Center/CI Lab. This exoplanet was among the first Neptune-sized worlds identified by TESS. Researchers conducted the initial spectral study of a TESS-discovered planet, creating the first temperature map of a TESS planet with an atmosphere.
Crossfield elaborates, “Infrared light allows us to determine temperatures and identify the hotter and cooler regions of this planet. Unlike Earth, where temperatures peak in the afternoon, this planet reaches its highest temperature around noon.”
Section 1.2: The Search for Habitable Planets
“One in 200 stars has habitable Earth-like planets surrounding it — in the galaxy, half a billion stars have Earth-like planets going around them — that’s huge, half a billion. So when we look at the night sky, it makes sense that someone is looking back at us.” — Michio Kaku
LTT 9779b has been found to be cooler than previously anticipated, implying that its atmosphere may be cloud-covered, efficiently radiating heat back into space. Typically, Neptune-sized planets found in such close orbits to their stars are remnants of larger Jupiter-like worlds or massive rocky planets that have lost their atmospheres.
Chapter 2: Future Studies on LTT 9779b
Researchers highlight the significance of studying smaller planets that represent more typical outcomes of planet formation. “Although most of the measurements conducted to date have focused on large, massive hot Jupiters, there is significant interest in exploring the atmospheres of smaller planets, such as the ultra-hot Neptune LTT 9779b, a rare inhabitant of the Neptune desert,” as noted in an article published in the Astrophysical Journal Letters on October 26.
As advancements in technology continue, astronomers are beginning to unravel the mysteries surrounding the atmospheres of smaller exoplanets. Several questions persist about LTT 9779b and hot Neptunes as a whole.
“What enables this planet to maintain its atmosphere? How did it form initially? Was it once larger and has since lost a portion of its atmosphere? If that’s the case, why is its atmosphere not merely a scaled-down version of those found on larger ultra-hot exoplanets? And what other components might its atmosphere contain?” Crossfield inquires.
James Maynard, the founder and publisher of The Cosmic Companion, currently resides in Tucson, where he lives with his wife, Nicole, and their cat, Max.
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