While the ultraviolet aurora of Uranus has been observed since 1986, no confirmation of the infrared aurora had been observed until now.
The ice giants Uranus and Neptune are unusual planets in our solar system as their magnetic fields are misaligned with the axes in which they spin. While planetary scientists have yet to find an explanation for this, clues may lie in Uranus’ aurora.
Aurorae are caused by highly energetic charged particles, which are funneled down and collide with a planet’s atmosphere via the magnetic field lines.
On Earth, the most famous result of this process are the spectacles of the northern and southern lights.
At planets such as Uranus, where the atmosphere is predominately a mix of hydrogen and helium, this aurora will emit light outside of the visible spectrum and in wavelengths such as the infrared.
In the new research, University of Leicester Ph.D. student Emma Thomas and colleagues analyzed the near-infrared spectra of Uranus obtained with the NIRSPEC (Near-infrared Spectrograph) instrument on the Keck II telescope.
“From this, we can analyze the light — known as emission lines — from these planets, similar to a barcode,” they explained.
“In the infrared spectrum, the lines emitted by a charged particle known as H3+ will vary in brightness depending on how hot or cold the particle is and how dense this layer of the atmosphere is. Hence, the lines act like a thermometer into the planet.”
The Keck II observations revealed distinct increases in H3+ density in Uranus’ atmosphere with little change in temperature, consistent with ionization caused by the presence of an infrared aurora.
“The temperatures of all the gas giant planets, including Uranus, are hundreds of degrees Kelvin/Celsius above what models predict if only warmed by the Sun, leaving us with the big question of how these planets are so much hotter than expected?” Thomas said.
“One theory suggests the energetic aurora is the cause of this, which…
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