We're obsessed with the idea that somewhere out there in space there might be other places just like Earth — we'd even settle for remotely like Earth.
Now, an international team of astronomers have spotted a planet with a stratosphere: a layer in the upper atmosphere where temperature increases with altitude, and the closest thing you can get to an ozone layer.
This particular exoplanet — with the catchy name WASP-121b — is an ultrahot gas giant 880 light years away.
Earth's atmosphere consists of layers that can be delineated by temperature. The stratosphere is warmer than the troposphere, which is just above the surface. Exoplanets could, in theory, have stratospheres, but the only way to determine this is via the analysis of their chemical properties using remote sensing.
A previous claim has been made for an exoplanet having a stratosphere, but this remains open to question for a bunch of reasons - including the high variability of its host star.
Thomas Evans and team reported observations of WASP-121b made in November 2016 and January 2017 using the Hubble Space Telescope and the Spitzer space telescope, that show features in the emission lines corresponding to water. This lead researchers to conclude that the planet has a stratosphere.
The researchers say the temperature inversion is probably caused by the presence of vanadium oxide, with weaker evidence for titanium oxide. The WASP-121b spectrum is the first exoplanet to show spectrally resolved features of a stratosphere in emission.
In plain terms: the researchers think these atmospheric layers exist because of the chemical signatures they've detected from the infra-red radiation emitted by the planet.
These 'hot Jupiter' planets are relatively easy to study, according to experts - so refining our techniques on these before using them on cooler, potentially habitable planets is a good idea.
So, hey, maybe we're a little way off packing our bags. But it's cool to think about, right?