Last  year, scientists found the "hottest" planet to date, with a surface  temperature of 4,000 degrees Celsius. Although not as good as the sun,  it also surpassed most stars. In what way does the material exist in this magical form? On  the morning of August 16th, Beijing time, a Swiss team published a  paper in the world's top academic journal Nature, which found iron vapor  and titanium vapor in the atmosphere of the hottest planet.

The  planet is located in Cygnus, about 650 light-years from Earth, and was  found by the North KELT Telescope in Arizona, USA, and was named  KELT-9b. The  temperature of the star KELT-9 is more than 10,000 degrees Celsius,  almost twice the sun, and the KELT-9b is only one-thirtieth of the  distance from the Earth. This results in a surface temperature of 4,000 degrees Celsius for KELT-9b, which is hotter than most stars.

The "hottest planet" has attracted the interest of scientists. What constitutes its atmosphere? Under such extreme conditions, what kind of evolution has it experienced?

Researchers  at the University of Berne, Switzerland, have recently completed a  theoretical analysis that shows extreme temperature and radiation  conditions that most molecules on the planet cannot exist and can only  exist as atoms. This  is because, at such high temperatures, collisions occur between the  particles, breaking the chemical bonds of the constituent molecules. The  team also theoretically predicted the human telescope conditions and  was able to observe the gaseous metal atoms in the KELT-9b atmosphere.

On  the night of July 31-August 1, 2017, scientists from the Department of  Astronomy at the University of Rib, Switzerland, used the Galileo  National Telescope in La Palma, Spain to observe the transit of the  KELT-9b. The  so-called transit day refers to the phenomenon that when the planet  glides through the surface of the star in the field of view of the  telescope, it causes the brightness of the star to drop. The KELT-9b is very close to the star and will revolve every 36 hours. During  the transit, a small portion of the light from the star is screened by  the planet's atmosphere, and scientists can use spectrometers to analyze  the composition of the planet's atmosphere. Just  as a prism splits the sun into seven colors, the spectrometer breaks  down the light that stars pass through the planet's atmosphere into a  spectrum. Substances in the planet's atmosphere, thus leaving a unique "fingerprint" in the spectrum.

Iron  is one of the most abundant transitional metal elements in the  universe. However, most of the iron elements on exoplanets are mixed  with gaseous oxides or fine dust particles, which is difficult to detect  directly. This  time, the experimental scientists found the neutral iron atoms and  single-ion iron in the atmosphere of KELT-9b according to the  predictions of theoretical scientists.

Jens  Hoeijmakers, who led the study, said that after digging deep into the  data, they also discovered that another metal vapor leaves a fingerprint  in the spectrum: titanium.

KELT-9b represents a new class of planets called "super hot Jupiter." In the same environment, most of the planets will evaporate, and KELT-9b is one of the few cases to survive. This  time, humans have seen a glimpse of the atmosphere of this type of  planet, confirming that the high temperature will decompose most of the  molecules. In  the future, it will continue to play a unique "laboratory" for  scientists to study the evolution of planets under high temperature and  high radiation.