- Astronomers found a new class of exoplanets orbiting too close to their host stars.
- These so-called super-Earths consist largely of aluminum, calcium and their oxides such as ruby and sapphires.
Most planets and exoplanets (planets outside our solar system) were born when stars like the Sun were surrounded by a disc-shaped cloud of gas and dust. These planets are thought to have formed inside this disc only.
As the disc-shaped cloud cooled, all building blocks condensed. Most of these building blocks were formed in areas where materials like silicon, magnesium, and iron condensed billions of years ago.
The resulting planets contain composition similar to that of Earth. Almost all super-Earths (exoplanets with masses up to 10 times higher than Earth’s) have been born in those regions.
Recently, researchers at the University of Zurich studied three new candidates of super-Earth and found that they were formed close to their host star at temperatures higher than 1200 K. They consist of aluminum, calcium and their oxides such as ruby and sapphire.
The Three Super-Earths
One of the three candidates is HD 219134 b. It lies 21 light-years away in the Cassiopeia constellation. The exoplanet orbits its star every 3 days and is 5 times more massive than the Earth.
Unlike our planet, it doesn’t have a massive iron core but is rich in aluminum and calcium. Since the planet also contains aluminum oxides including rubies and sapphires, it most likely shimmers red to blue.
Numerous materials on this planet are still in the gaseous state because regions close to the star are much hotter. The researchers applied a new model to visualize the formation of this planet at such high temperatures.
The results showed that the planet hardly contains any iron, thus it cannot have an Earth-like magnetic field. And Since its inner structure is very different, its atmosphere and cooling behavior will differ from those of usual super-Earths.
The other two candidates are WASP-47 e and 55 Cancri e. They both revolve around their host star so closely that their surface temperatures reach 3000 K. Due to their high stellar irradiation, they might have lost their gaseous envelope long ago.
Artistic impression of 55 Cancri e | ESA/Hubble
The situation is a bit different on HD219134 b: it’s less hot but has a more complex structure. Researchers weren’t able to identify the reason behind its low density: it could be due to the planet’s position (relative to its host star) or its magma oceans.
They Don’t Have Diamonds
In addition to this exotic composition discovered in a new class of super-Earths, the team is also correcting the previous image of 55 Cancri e, which made headlines as the ‘diamond in the sky’, in 2012.
According to earlier studies, the exoplanet consisted mostly of carbon. Now, researchers have abandoned this hypothesis on the basis of recent observations. The supposed diamond planet has turned into a ruby planet.