It may sound like science-fiction, but scientists have concluded that an incredibly hot exoplanet may have rain comprised of liquid metal, ruby, and sapphire. In new research published by the journal Nature Astronomy, a team of international researchers explored the nightside hemisphere of an exoplanet for the first time, developing a 3D model of the atmosphere to make the interesting observations. The study is the first of its kind, with findings that may pave the way for similar work in the future when the James Webb Space Telescope is fully operational.
The planet in question is known as WASP-121b, and it can be found 855 light-years away from Earth. It’s a gaseous giant that orbits close to its star, and it is in fact tidally locked, much like the moon is locked to the Earth – thus, one side of WASP-121b is incessantly seared by its star, while the other is dark and cooler (although still a very warm 1,500 degrees). The top of the atmosphere is at 2,500 degrees, the temperature at which iron exists in gas rather than solid form. It orbits its star every 1.27 days, one of the shortest ever detected, and it’s about the closest distance it could be to the star without the gravity tearing the planet apart.
Some of these clouds may be red or blue in colour as a result of their potential gemstone composition
A team from the Massachusetts Institute of Technology observed WASP-121b using a spectroscopic camera aboard the Hubble Space Telescope, studying both the night side (which always faces away) and the day side. They employed a clever observational approach, observing the sunlight that passed through the atmosphere, which revealed some of the chemicals present. Obviously, water clouds can’t form in these temperatures, but metals in a gaseous state will condense in such environments. The team measured the spectrum of the exoplanet at all viewing angles, inferring a temperature map that offers some potential explanations for questions about WASP-121b.
They concluded that the planet boasts clouds made up of metals like magnesium, chromium, vanadium, and, importantly for this research, aluminium. Aluminium condenses into the mineral corundum, from which both ruby and sapphire are made. It is possible, then, that some of these clouds may be red or blue in colour as a result of their potential gemstone composition, and that liquid gems could be raining on the nightside of the planet.
The study also answered some mysteries about the exoplanet. Previous studies indicated the presence of metals in the dayside atmosphere, but the temperature there is hot enough to vaporise metals. This would indicate that metal clouds are blown across the nightside hemisphere by winds in excess of 18,000km/h, and the new data provides direct evidence for these winds. The observational data shows that the hottest region of the dayside atmosphere was slightly to the east of the ‘noon’ point, indicating that the gas must be getting heated at noon but then blown eastwards before it has a chance to re-emit the thermal radiation to space.
Studies of exoplanets, such as this one, will be revolutionised by the success of the James Webb Space Telescope
Thomas Mikal-Evans, of the Max Planck Institute for Astronomy, explained that the study also explains some previous unusual observations. He said: “Previous observations showed that titanium was missing from the atmosphere, but its chemical cousin vanadium was present in the atmosphere. Since these two atoms are chemically similar, it seemed odd that we’d observe one but not the other. Our new data reveals for the first time that the temperatures on the night side hemisphere drop low enough for titanium and aluminium gas to precipitate and rain down to deeper layers of the atmosphere, whereas vanadium precipitates at lower temperatures making it harder for it to rain out.”
Studies of exoplanets, such as this one, will be revolutionised by the success of the James Webb Space Telescope. As Mikal-Evans notes: “Despite the discovery of thousands of exoplanets, we’ve only been able to study the atmospheres of a small fraction due to the challenging nature of the observations. So far, most of these measurements have provided limited information, such as basic details on the chemical composition or average temperature in specific subregions of the atmosphere.” But, the new telescope can see more light and detect more molecules than Hubble, and it will examine smaller planets too, paving the way for more exciting discoveries to come.