The eponymous ‘they’ strike again. You may know ‘them’ from such a sentence as “Well, you know what they say”, but this time ‘they’ are a team of international researchers lead by Exeter’s own Dr. Tom Evans. Their most recent research, conducted using NASA’s Hubble space telescope has discovered the most significant evidence to date of an exoplanet sporting a highly mathematically fashionable stratosphere. Solid evidence of such an exoplanet has eluded astronomers all over the world for some time.

Perhaps the beginning of a type of reconnaissance for space travel.     

Just quickly though, before we look at this in more detail, allow me to tell you that an exoplanet is simply a planetary body outside of our solar system, an ‘extra-solar planet’. And a stratosphere is an atmospheric layer surrounding a planet that gets hotter as its altitude increases.

With definitions out the way, we can set the scene with some facts. The exoplanet in question is called WASP-121b, a huge gas giant body 900 light years away that is alone in its system and orbits its star in just under 1.3 earth days. It is nicknamed ‘hot Jupiter’ because of its enormity, and the fact that it flies close enough to its star to reach temperatures of 2,500 Celsius. This is hot enough to vaporise and maintain gaseous iron.

Our researchers, utilising the Hubble telescope and a method of spectroscopy, found evidence that the upper layer of WASP-121b’s atmosphere is significantly higher than the lower part. This is a rare phenomenon in the vast coldness of space. The spectroscopy method works much like a human’s finger print, whereby different molecules emit different wavelengths of electromagnetic radiation (or ‘light’, for simplicity’s sake). We are then able to detect these wavelengths of light and compare them and their intensity to other known molecular fingerprints here on earth for identification and measurement purposes.

Massive planet infront of a rising star with a film of gaseous methane over its atmosphere
Jupiter Class Planet in a Tight Orbit. Source:

Specifically, our researchers used this method across space to receive and identify wavelengths of infrared radiation from WASP-121b’s atmosphere. They found that the molecules in the upper atmosphere glowed hot with the wavelengths of light that would be expected from a stratosphere, and thus were not blocked by cooler regions of the same molecules.

Using the same method, our researchers also found that the temperature difference between the upper and lower parts of 121b’s atmosphere is quite significant. As of yet they are uncertain regarding the cause of this extreme heating, but have some ideas. They indicated in this paper (and have given evidence on the idea in previous papers) that they predict the ultra-heating is due to vanadium oxide and titanium oxide gases in the atmosphere. These are gases capable of absorbing the star’s light, much like how ozone absorbs UV light from our sun.

This is hot enough to vaporise and maintain gaseous iron.

Now, you might think this is quite a niche discovery, but its significance to research into atmospheric physics and chemistry should not be understated. Professor David Sing, associate professor of astrophysics at Exeter and co-author of the paper, commented that “this new research is the smoking gun evidence scientists have been searching for when studying exoplanets”. He also noted that the discovery is a step forward in figuring out how planets behave under different conditions, research that will help us learn about the conditions on different planets.

This is perhaps the beginning of a type of reconnaissance for the distant prospects of space travel.


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