Weird Uranus Auroras Seen First Time From Earth

Wild leeks push through the dried leaves of the forest floor each April in Duluth's Hawk Ridge nature reserve. Photo: Bob King

The ground is snapping and popping. Ever hear this? On quiet evenings in the country in mid-spring, you can walk up to a roadside ditch along the edge of the forest and listen to green plants pushing up through last year’s leaves and grasses. It sounds like fire consuming tiny twigs. Green fire.

I used to think it was insects but I’ve looked with a flashlight and heard it for so many years I’m certain the sound is from plants on their way up and out. Not even night can hold back the call of the sun.

The sun reached out to Earth this week in the form of the aurora borealis. Uranus also displays auroras but as dots instead of arcs and curtains. Auroras were seen by the Voyager 2 spacecraft during it 1986 flyby of the planet, but this is the first time they’ve been spotted from Earth.

Uranus' northern lights have an unusual form and different location compared to Earth's due to the planet's unusually large tilt and offset magnetic field. Uranus faint ring system is also seen. Credit: Laurent Lamy

Using the Hubble Space Telescope, astronomers photographed dim dots of aurora glowing above Uranus’ pale blue cloudtops. The Uranian lights last only a few minutes at a time before fading away, making them even trickier to catch than the earthly variety.

Auroras on both Earth and Uranus are produced when charged particles (electrons and protons) from the sun enter a planet’s magnetosphere or protective magnetic envelope, and are guided into the polar atmosphere by the planet’s magnetic field.

Uranus' axis is tilted almost 98 degrees. During its 84-year orbit, first the north pole and then the south pole points toward the sun. In between, one side or another faces the sun. Credit: Smithsonian

Earth’s magnetic field is tipped just 11 degrees relative to the our axis of rotation. When the solar wind hits, the particles travel toward the north and south polar regions, which is why auroras are visible in Earth’s more northern and southern locations than nearer the equator.

Uranus is another place altogether. Its rotational axis is tilted 98 degrees compared to Earth’s modest 23.5. This means the planet literally rotates on its side like a bowling ball rolling down a lane. Its magnetic axis is way out of whack too – not only offset from the planet’s core but tilted 60 degrees relative to the rotation axis. Back during the Voyager 2 flyby, the planet’s south pole was pointed toward the sun with the magnetic poles far off to the sides. Voyager observed auroras on Uranus’ nightside resembling those on Earth.

The Earth, with its modestly-tipped rotation axis (blue arrowed line) and nearly north-pointing magnetic field axis, is a far cry from the extremes of Uranus.

Uranus has since moved along its orbit so that now its side faces the sun instead of a geographic pole. This happy circumstance means that one of the magnetic poles points directly at the sun.

When a big blast of solar wind left the sun in September 2011, the particles sped past Earth in 2-3 days, blew by Jupiter two weeks later and arrived at Uranus in mid-November, creating the odd dots of aurora that seem to lie near the equator. They’re really near the planet’s magnetic poles!

Uranus, you’re a mixed up planet, but we love you anyway. To read more about the new aurora discovery, click HERE.

2 Responses

  1. madscientist5580

    Interesting that you posted about this today. My wife and I have noticed this recently while walking the dog. I assumed it was frogs or insects, but there were so many places the sounds were coming from I envisioned the ground crawling with bugs. Tonight we actually investigated the rustling leaves. In moving the leaves we found nothing, but then there was rustle in the grass and glint in the beam of the flashlight…worms. They are extremely fast at pulling back into their hole, so any sound or vibration and they are gone.

    Our front yard safari also yielded a Predaceous Diving Beetle that was buzzing light in the garage. I got some pics but wow did he stink.

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