- KELT-9b is the hottest known exoplanet with a surface temperature of 4,300°C.
- It is so hot that even molecules of hydrogen gas (in the atmosphere) are torn to shreds on its dayside.
- The molecules reform when they flow around the planet’s nightside.
In 2017, astronomers detected a unique exoplanet using the Kilodegree Extremely Little Telescope. It orbits the early A-type star KELT-9, located nearly 670 light-years from Earth.
Dubbed KELT-9b, the exoplanet orbits too close to its star to sustain life. It is approximately 2.8 times more massive and 2 times larger than Jupiter. With 4,300 degrees Celsius surface temperature, KELT-9b is the hottest planet found so far.
Recently, a team of astronomers found something very interesting about this exoplanet, using NASA’s Spitzer space telescope. KELT-9b is so hot that even molecules of hydrogen gas (in the atmosphere) are torn to shreds on its dayside. These hydrogen gas molecules reform when their separated atoms flow around the nightside of the planet.
Although the planet’s nightside is incredibly hot, its slight cooling compared to the dayside allows hydrogen gas molecules to reform, until they flow back to the dayside, where they are split apart all over again.
How Did They Find It?
In this study, researchers showcased the increasing complexity of technology and examination required to analyze such very distant exoplanets. We have just begun to peer into the atmosphere of such distant worlds, probing the molecular meltdowns of the brightest and hottest.
To parse temperature profiles of KELT-9b, researchers used the Spitzer space telescope that captures data in infrared light to measure tiny fluctuations in heat. Several hours of observations revealed variations in the atmosphere as the exoplanet presents itself in phases while revolving around its host star, KELT 9.
Different views of the exoplanet enabled researchers to capture the difference between its nightside and dayside. The planet orbits too close to its star, and it takes only 1.5 days to complete one revolution around its star.
It is tidally locked, which means the planet presents only one face to its star for all time. On one side of KELT-9b, daytime lasts forever, while on the far side, nighttime lasts forever.
KELT-9b’s dayside temperatures reach 4,600 Kelvin, which is hotter than many low mass stars. The exoplanet receives intense radiation from its host star and is currently experiencing quick atmospheric escape.
KELT-9b orbiting its host star KELT-9 | Credit: NASA
KELT-9b is quite different from many other exoplanets, but there are few ultra-hot Jupiter where the same effect should be taking place.
Things We Don’t Know So Far
The team is currently trying to figure out how heat and gases flow from one side of the planet to the other. How this flow and radiation balance each other out?
Computer simulations have shown the behavior KELT-9b atmosphere in different temperatures: hydrogen molecules go through a process called dissociation (molecules torn apart) and recombination (molecules reassemble).
Moreover, the observations revealed that the ‘hot spot’ on the exoplanet’s dayside was shifted away from its anticipated location. To solve the mystery behind this shift, scientists will investigate the exoplanet in detail in the coming years.