Last year, while the Cassini spacecraft was still orbiting Saturn, NASA’s Hubble Space Telescope (HST) captured a stunning view of the planet’s northern aurora, which, after being combined with Cassini data, was just released as an image and video.
When Saturn experienced its summer solstice on May 24, 2017, meaning its north pole was tilted toward the Sun, both Hubble and Cassini observed and measured the northern aurora.
Although the aurora appears blue, it actually glows in ultraviolet wavelengths, which can only be seen from space. When hydrogen gas at the north pole interacts with energetic electrons generated by the planet’s powerful magnetic field, intense auroras are created. Because Saturn rotates rapidly on its axis, with a Saturn “day” taking just 11 hours, the auroras’ appearances constantly change.
The actual image and video released by NASA are composites that include images of the aurora taken in early 2018 and transformation of the May 2017 photos from ultraviolet wavelengths to visible light.
One of Cassini’s last images before it plunged into Saturn’s atmosphere last September revealed a never-previously-seen auroral storm produced by interactions between plasma in the planet’s magnetosphere and its upper atmosphere.
The spacecraft also tracked an arc-shaped structure within the aurora as it grew and eventually disappeared.
In a paper published in the journal Geophysical Research Letters, Cassini scientists noted the aurora bears a striking resemblance to auroras seen on Earth and attributed its creation to the solar wind, a stream of charged particles emanating from the Sun.
From the combined observations of both Hubble and Cassini, scientists learned that Saturn’s aurora strongly peaked just prior to the planet’s midnight, then did so again around dawn. Both midnight and dawn auroral spikes also occur on Earth.