April 13, 2012
Auroras Seen Dancing Around On Uranus
Scientists have seen auroras dancing around above the giant ice planet Uranus by using the Hubble Space Telescope.
The Uranian light show consisted of short-lived, faint, glowing dots, a show completely different than that seen on planet Earth.The researchers detected the luminous spots twice on the dayside of Uranus, which is the side that is visible to Hubble.
Unlike auroras on Earth, the newly detected auroras on Uranus appear to only last a couple of minutes.
Auroras are a feature of the magnetosphere, which is the area surrounding the planet that is controlled by its magnetic field and shaped by solar wind.
The cosmic light show is produced in the atmosphere as charged solar wind particles acerbate in the magnetosphere and are guided by the magnetic field close to the magnetic poles.
However, Laurent Lamy, with the Observatoire de Paris in Meudon, France, who led the new research, said Uranus' magnetosphere is "very poorly known."
Auroras on Uranus are fainter than they are on Earth, and the planet is over 2.5 billion miles away. The planet's light show was only seen vaguely one time before, 25 years ago when Voyager 2 spacecraft flew by the planet.
“This planet was only investigated in detail once, during the Voyager flyby, dating from 1986," Lamy said in a press release. "Since then, we´ve had no opportunities to get new observations of this very unusual magnetosphere."
Uranus is different than other planets when it comes to the orientation of its rotation axis, spinning as if it was knocked on its side.
The researchers believe the unfamiliar appearance of the newly observed auroras is because of the planet's unusual rotation and peculiar traits of its magnetic axis.
The planet's magnetic axis is both offset form the center of the planet and lists at an angle of 60 degrees from the rotational axis. This is compared to the 11 degree difference on Earth.
Conditions in 2011 were set up perfectly for scientists to observe the auroras on the distant planet. Earth, Jupiter and Uranus were lined up last year so that the solar wind could flow from the Sun, past Earth and Jupiter, and then head toward Uranus.
Once the Sun produced several large bursts of charged particles in mid-September, the researchers used Earth-orbiting satellites to monitor the solar wind's local arrive two to three days later.
Two week after the solar wind arrived, it sped past Jupiter at 310 miles per second. After that, the researchers calculated that the charged particles would be reaching Uranus in mid-November, so they scrambled to reserve time on the Hubble Space Telescope.
Having a better understanding of Uranus' magnetosphere could help scientists test their theories of how Earth's magnetosphere functions, according to Fran Bagenal, a planetary scientist with the University of Colorado in Boulder.
“We have ideas of how things work on Earth and places like Jupiter and Saturn, but I don´t believe you really know how things work until you test them on a very different system," she said in a press release.
The researchers published their findings in the journal of the American Geophysical Union, Geophysical Research Letters.
Image Caption: These composite images show Uranus auroras, which scientists caught glimpses of through the Hubble Space Telescope in 2011. Credit: Laurent Lamy