Scorching hot planet with metallic clouds discovered

Astronomers announced on Monday the discovery of an incredibly hot planet with unique characteristics. Situated over 260 light years away from Earth, this distant world is exceptionally reflective, reflecting 80 percent of the light emitted by its host star. In fact, it rivals Venus, the brightest celestial object in our night sky after the Moon, in terms of its shininess.

Known as LTT9779b, this Neptune-sized planet was first detected in 2020. It has a remarkably close orbit around its star, completing one revolution in just 19 hours. Due to its proximity, the side of the planet facing its star reaches an incredibly scorching temperature of 2,000 degrees Celsius. Scientists initially believed that such extreme heat would prevent cloud formation on the planet.

However, contrary to expectations, LTT9779b does possess clouds. Researchers from France’s Cote d’Azur Observatory, who published their findings in the journal Astronomy and Astrophysics, compared the cloud formation to condensation in a bathroom after a hot shower. They explained that the planet’s atmosphere became oversaturated with a mixture of metal and silicate, similar to the materials used to make glass. This created a situation analogous to steam forming in a bathroom from hot water, resulting in the formation of metallic clouds in the planet’s atmosphere.

Surviving ‘Neptune desert’

In addition to its unique reflective properties, the planet’s size and location make it an outlier among exoplanets. Typically, exoplanets with orbits shorter than 24 hours are either gas giants much larger than Earth or rocky planets half its size. However, LTT9779b resides in a region known as the “Neptune desert,” where planets of its size are not expected to be found. This makes its existence quite remarkable, defying conventional expectations.

“It’s a planet that defies expectations,” remarked Parmentier. Normally, planets of this nature would have their atmospheres stripped away by the intense stellar radiation, leaving behind barren rocky surfaces. However, the presence of metallic clouds on LTT9779b acts as a shield, reflecting light and protecting the atmosphere from being blown away. The comparison was drawn to the shields seen in old Star Trek films, safeguarding the ships from harm.

This research is considered a significant milestone as it sheds light on how a Neptune-sized planet can survive in the challenging conditions of the Neptune desert. The European Space Agency’s Cheops space telescope, launched in 2019, played a crucial role in measuring the planet’s reflectivity. By observing the light before and after LTT9779b passed behind its star, the telescope enabled scientists to assess its reflective properties accurately. The Cheops mission’s primary objective is to investigate exoplanets discovered outside our Solar System.