Exoplanets – planets outside our Solar System – continue to provide astronomers with fascinating glimpses of other worlds, including the one designated WASP-76b. On this inferno-like planet, almost the size of Jupiter, the daytime surface temperatures are hot enough to vaporize iron, which could fall as rain on the slightly cooler night side.
Now researchers have given WASP-76b another look and concluded that it might actually be hotter than previously thought. Key to that conclusion is the discovery of ionized calcium, which would need "significantly hotter" conditions to form than have previously been outlined in studies.
As we know from previous research, temperatures on the surface of WASP-76b are thought to climb to around 4,400 degrees Fahrenheit (2,246 Celsius) on the daytime side – but that might be something of an underestimation if the new and updated temperature profile turns out to be more accurate.
"We're seeing so much calcium; it's a really strong feature," says astrophysicist Emily Deibert from the University of Toronto in Canada. "This spectral signature of ionized calcium could indicate that the exoplanet has very strong upper atmosphere winds, or the atmospheric temperature on the exoplanet is much higher than we thought."
Discovered in 2016, WASP-76b is known as a 'hot Jupiter' exoplanet because it's so close to its star – an orbit takes just 1.8 Earth days. It's around 640 light-years away from our position in the Universe. It's also tidally locked, meaning the same side of the planet always faces its star, itself slightly hotter than our Sun.
Here the researchers used data from the Gemini North Telescope in Hawaii to look at the moderate temperature zone of the planet, the border between day and night. They used a process of transit spectroscopy, where the light of an exoplanet's star shines through its atmosphere, all the way back to Earth.
The quality and composition of that light enable us to make calculations about the atmosphere at a variety of different depths. In this case, the team was able to identify a rare trio of spectral lines, readings that indicate the presence of ionized calcium.
"It's remarkable that with today's telescopes and instruments, we can already learn so much about the atmospheres – their constituents, physical properties, presence of clouds and even large-scale wind patterns – of planets that are orbiting stars hundreds of light-years away," says astronomer Ray Jayawardhana from Cornell University in New York.
Spectroscopy techniques such as the one used here enable astronomers to discover all kinds of secrets about exoplanets hundreds of light-years (or more) away: everything from the details of the planet's rotation to the wind patterns on the surface.
That means that as more and more of these exoplanets are discovered and cataloged, researchers can group them for easier reference. Ultimately we end up learning more about our place in the Universe and where we might find other forms of life.
This study is part of a multi-year project looking at a minimum of 30 exoplanets, called Exoplanets with Gemini Spectroscopy (ExoGemS). Once the project is completed, experts should have a much better idea of the diversity of atmospheres that exist on these distant and exotic worlds.
"As we do remote sensing of dozens of exoplanets, spanning a range of masses and temperatures, we will develop a more complete picture of the true diversity of alien worlds – from those hot enough to harbor iron rain to others with more moderate climates, from those heftier than Jupiter to others not much bigger than the Earth," says Jayawardhana.
The research has been published in the Astrophysical Journal Letters.