Astronomers have confirmed the existence of an infrared (IR) aurora on Uranus. This could help astronomers identify exoplanets that could support life, many of which are icy worlds. The presence of an infrared aurora on Uranus’ cold, outer planet has been confirmed for the first time by astronomers at the University of Leicester.
The discovery could shed light on the mysteries of our solar system’s magnetic fields, as well as whether distant worlds might support life.
The team of scientists, who were supported by the Science and Technology Facilities Council (STFC), obtained the first measurements of Uranus’s infrared (IR) aurora since studies began in 1992. While Uranus’ ultraviolet (UV) aurorae have been observed since 1986, there has been no confirmation of the IR aurora until now. The findings of the scientists have been published in the journal Nature Astronomy.
Uranus and Neptune are unusual planets in our solar system because their magnetic fields are misaligned with their spin axes. While scientists have yet to discover an explanation, clues may be found in Uranus’ aurora.
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.
Emma Thomas
Aurorae are caused by highly charged particles that are funneled down and collide with the atmosphere of a planet via the planet’s magnetic field lines. The Northern and Southern Lights are the most famous manifestations of this process on Earth. This aurora will emit light outside of the visible spectrum and in wavelengths such as infrared (IR) at planets such as Uranus, where the atmosphere is predominately a mix of hydrogen and helium.
The team used the Keck II telescope to take infrared auroral measurements by analyzing specific wavelengths of light emitted by the planet. They can then analyze the light (known as emission lines) from these planets, much like a barcode. The lines emitted by a charged particle known as H3+ in the infrared spectrum will vary in brightness depending on how hot or cold the particle is and how dense this layer of the atmosphere is. As a result, the lines act as a thermometer into the planet.
Their observations revealed distinct increases in H3+ density in Uranus’s atmosphere with little change in temperature, consistent with ionization caused by the presence of an infrared aurora. Not only does this help us better understand the magnetic fields of the outer planets of our own solar system, but it may also help in identifying other planets that are suitable of supporting life.
“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,” said lead author Emma Thomas, a PhD student in the University of Leicester School of Physics and Astronomy. According to one theory, this is caused by the energetic aurora, which generates and pushes heat from the aurora down towards the magnetic equator.
“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 analysing 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.
“This paper is the culmination of 30 years of auroral study at Uranus, which has finally revealed the infrared aurora and begun a new age of aurora investigations at the planet. Our results will go on to broaden our knowledge of ice giant auroras and strengthen our understanding of planetary magnetic fields in our solar system, at exoplanets and even our own planet.”
The findings may also provide scientists with insight into geomagnetic reversal, a rare phenomenon on Earth in which the north and south poles switch hemisphere locations.
“We don’t have many studies on this phenomenon, so we don’t know what effects it will have on systems that rely on the Earth’s magnetic field, such as satellites, communications, and navigation,” Emma adds. However, because of the unique misalignment of the rotational and magnetic axes, this process occurs every day on Uranus. Continued research into Uranus’ aurora will provide information on what to expect if Earth experiences a future pole reversal and what that will mean for its magnetic field.”
