New views of Uranus’ auroras and rings

The auroras are the white areas in this composite image via ESA/Hubble & NASA, L. Lamy / Observatoire de Paris.

Here are two new composite images of our sun’s 7th major planet, Uranus – combining observations by the Hubble Space Telescope and the Voyager 2 spacecraft – showing both the planet’s ring system and its auroras. Does it look like the rings orbit over Uranus’ poles to you? They don’t. They lie above the planet’s equator, but Uranus itself lies nearly sideways with respect to the plane of its orbit around the sun. NASA released these new images on April 10, 2017, explaining that:

Auroras are caused by streams of charged particles like electrons that come from various origins such as solar winds, the planetary ionosphere, and moon volcanism. They become caught in powerful magnetic fields and are channeled into the upper atmosphere, where their interactions with gas particles, such as oxygen or nitrogen, set off spectacular bursts of light.

Every major planet in our solar system, except Mercury, is known to have auroras. But – much like the mysteriously shifting northern or southern lights seen from Earth’s surface – the auroras on other planets are endlessly fascinatingly.

The Voyager 2 spacecraft discovered Uranus’ auroras as it swept past the planet in 1986, on what ultimately became its Grand Tour of the outer solar system. The Hubble Space Telescope got an earlier image of Uranus’ auroras, too, in 2011, becoming the first Earth-based telescope to do so.

To this day, however, Uranus’ auroras are not well studied.

In 2012 and 2014 a team led by an astronomer from Paris Observatory took a second look at Uranus’ auroras using the ultraviolet capabilities of the Space Telescope Imaging Spectrograph (STIS) installed on Hubble. NASA said:

They tracked the interplanetary shocks caused by two powerful bursts of solar wind traveling from the sun to Uranus, then used Hubble to capture their effect on Uranus’ auroras — and found themselves observing the most intense auroras ever seen on the planet. By watching the auroras over time, they collected the first direct evidence that these powerful shimmering regions rotate with the planet. They also re-discovered Uranus’ long-lost magnetic poles, which were lost shortly after their discovery by Voyager 2 in 1986 due to uncertainties in measurements and the featureless planet surface.

Bottom line: This is a composite image of Uranus by the Voyager 2 spacecraft, plus two different observations made by Hubble, one for Uranus’ ring and one for the auroras.

April 12, 2017

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