Why is this planet twice as hot as our sun?

A new study published in The Astrophysical Journal Letters seeks to answer several questions about exoplanets. As explained by our colleagues at Space.com, until the beginning of the 21st century only the planets of the solar system were known, that is, the small rocky planets of the inner solar system and the gas planets in the outer part.

However, thanks to our technological and scientific advances, particularly the appearance of ultra-light telescopes, we can observe very distant worlds belonging to other star systems.

A very high surface temperature

This is the case, for example, with the Kepler mission, during which we were able to know that some gas exoplanets, in contrast to the gas giants in our solar system, orbit relatively close to their star. These celestial bodies, nicknamed “hot” or “ultra-hot” Jupiter, can have very high surface temperatures.

Unfortunately, despite the colossal efforts of astronomers, we still do not know exactly how these objects are composed, the size of which is generally between that of Earth and Neptune.

Study physics under unique environmental conditions

It is therefore important to determine how these exoplanets were able to form and exist so close to their star. The researchers are also concentrating on studying their composition and the physical and chemical processes taking place there. Due to their peculiarities, which are sometimes beyond our knowledge, these worlds, which belong to other solar systems, allow the study of physics under environmental conditions that are not reproducible on Earth.

Kelt-9 b (HD 195689) is one of those exoplanets that are of great interest to scientists. The ultra-hot Jupiter type is exposed to the strong gravitational pull of its host star. The temperature on its surface is 10,000 degrees, almost twice as hot as our sun. In addition, its “locked” orbit (the same side always facing the star) creates a huge temperature difference between the dark side and the lighted side.

Some gaseous exoplanets orbit relatively close to their star. Artist’s impression of the exoplanet Kelt-9b. Photo credit: R. HURT (IPAC), NASA / JPL-CALTECH

Even more powerful telescopes for future missions

To study the atmosphere of exoplanets, scientists generally use two methods. The transit method consists of observing the planet as it passes in front of its star, thereby exposing its footprints. The other is implemented during a solar eclipse. This is because planets emit and reflect a small amount of light as they pass behind their star. Analysis of this light helps to understand the nature of the chemical elements that exist on the exoplanet.

In the case of Kelt-9b, for example, the observations made have shown the presence of complex molecules, suggesting that the atmospheres of these extreme worlds are determined by poorly understood processes. Interestingly, the next generation of space telescopes like the James Webb Space Telescope and the Ariel Mission are said to make it easier to study the atmosphere of planets outside the solar system.