Washington: Scientists have for the first time captured images of auroras above the giant ice planet Uranus, finding further evidence of just how peculiar a world that distant planet is.
Detected by means of carefully scheduled observations from the Hubble Space Telescope, the newly witnessed Uranian light show consisted of short-lived, faint, glowing dots – a world of difference from the colourful curtains of light that often ring Earth`s poles.
In the new observations, which are the first to glimpse the Uranian aurora with an Earth-based telescope, the researchers detected the luminous spots twice on the dayside of Uranus – the side that`s visible from Hubble.
Previously, the distant aurora had only been measured using instruments on a passing spacecraft. Unlike auroras on Earth, which can turn the sky greens and purples for hours, the newly detected auroras on Uranus appeared to only last a couple minutes.
In general, auroras are a feature of the magnetosphere, the area surrounding a planet that is controlled by its magnetic field and shaped by the solar wind, a steady flow of charged particles emanating from the sun. Auroras are produced in the atmosphere as charged solar wind particles accelerate in the magnetosphere and are guided by the magnetic field close to the magnetic poles – that`s why the Earthly auroras are found around high latitudes.
But contrary to the Earth – or even Jupiter and Saturn – “the magnetosphere of Uranus is very poorly known,” said Laurent Lamy, with the Observatoire de Paris in Meudon, France, who led the new research.
His team includes researchers from France, the United Kingdom, and the United States.
Auroras on Uranus are fainter than they are on Earth, and the planet is more than 4 billion kilometers (2.5 billion miles) away. Previous Earth-bound attempts to detect the faint auroras were inconclusive. Astronomers got their last good look at Uranian auroras 25 years ago when the Voyager 2 spacecraft whizzed past the planet and recorded spectra from of the radiant display.
“This planet was only investigated in detail once, during the Voyager flyby, dating from 1986. Since then, we`ve had no opportunities to get new observations of this very unusual magnetosphere,” Lamy noted.
The researchers suspect that the unfamiliar appearance of the newly observed auroras is due to Uranus` rotational weirdness and peculiar traits of its magnetic axis. The magnetic axis is both offset from the center of the planet and lists at an angle of 60 degrees from the rotational axis – an extreme tilt compared to the 11 degree difference on Earth.
Scientists theorize that Uranus`s magnetic field is generated by a salty ocean within the planet, resulting in the off-center magnetic axis.
A better understanding of Uranus` magnetosphere could help scientists test their theories of how Earth``s magnetosphere functions, Lamy added.
The results will be published Saturday in Geophysical Research Letters, a journal of the American Geophysical Union.