An infrared aurora has been spotted on Uranus for the very first time, providing insights into the strange magnetic fields that can be found on the solar system’s distant icy giants.
Down here on Earth, aurorae are caused by solar winds clashing with highly energetic charged particles in the atmosphere, resulting in the particles emitting light due to ionization. This is the process that creates the spectacle of the Northern and Southern Lights, the mesmerizing green and purple that swirl in the night sky near our planet's poles.
Different forms of aurora can be seen on other planets in our solar system too, most notably among the troubled skies of Jupiter and its moons. Ultraviolet aurorae were first seen on Uranus in 1986 when the Voyager 2 probe whizzed past, but this is the first time infrared aurora has been reported.
On planets like Uranus, the aurora will emit light outside the visible spectrum in wavelengths of light, such as infrared, because the atmosphere is predominately a mix of hydrogen and helium (unlike Earth's, which is mainly nitrogen and oxygen).
This means the infrared aurorae are invisible on Uranus to the human eye, so don’t expect any dazzling color displays like the ones we can enjoy. However, scientists were able to document them thanks to the work of the Keck II telescope in Hawaii, one of the largest optical-infrared telescopes on Earth.
The researchers analyzed specific wavelengths of light emitted from the planet, paying close attention to the infrared light beamed out from a charged particle known as H3+, which varies in brightness depending on the temperature of the particle and how dense this layer of the atmosphere is.
Their findings showed an 88 percent increase in H3+, density in Uranus’s atmosphere with little temperature change, which the researchers claim is “consistent with auroral activity generating increased ionization.”
“The temperature 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? One theory suggests the energetic aurora is the cause of this, which generates and pushes heat from the aurora down towards the magnetic equator,” Emma Thomas, lead study author and a PhD student in the University of Leicester School of Physics and Astronomy, said in a statement seen by IFLScience.
“A majority of exoplanets discovered so far fall in the sub-Neptune category, and hence are physically similar to Neptune and Uranus in size. This may also mean similar magnetic and atmospheric characteristics too. By analyzing Uranus's aurora which directly connects to both the planet's magnetic field and atmosphere, we can make predictions about the atmospheres and magnetic fields of these worlds and hence their suitability for life,” she added.
Uranus and the other ice giant Neptune are very unusual planets because they have wonky magnetic fields. For an unknown reason, their magnetic poles are not aligned with the axes of their rotational spin. Since aurora activity is closely linked to a planet's magnetic field, the researchers believe that this research could help unravel the mystery of crooked magnetic fields.
Likewise, the team says their results might help to illuminate some of Earth’s little-understood processes, such as geomagnetic reversal when the north and south poles effectively flip over.
“We don't have many studies on this phenomena and hence do not know what effects this will have on systems that rely on Earth's magnetic field such as satellites, communications and navigation. However, this process occurs every day at Uranus due to the unique misalignment of the rotational and magnetic axes. Continued study of Uranus's aurora will provide data on what we can expect when Earth exhibits a future pole reversal and what that will mean for its magnetic field,” explained Thomas.
The study is published in the journal Nature Astronomy.