The Solar Storm That Lit Up Uranus

By the end of this article, you will understand how scientists predicted space weather billions of miles away to catch bizarre, off-center auroras on Uranus.

In September 2017, the Sun unleashed a massive coronal mass ejection. Scientists knew this solar storm was heading for Uranus, but it would take two months to cross the solar system. This gave them a rare chance to prepare. They pointed the ‘Hubble Space Telescope’, along with giant Earth-based telescopes like the ‘Very Large Telescope’ (VLT) and ‘Gemini North’, at the distant ice giant. When the storm finally hit in November, Hubble captured a Surprise: a bright, intense spot of Far-Ultraviolet light near the planet’s southern pole. They had successfully predicted and caught an alien aurora in action, triggered by the pressure wave of the solar wind!

Original Paper: ‘Analysis of HST, VLT and Gemini Coordinated Observations of Uranus Late 2017’

This event provided a unique opportunity to investigate the auroral response of the asymmetric Uranian magnetosphere.
— L. Lamy et al.

This is NOT like the auroras on Earth, which form neat, glowing rings around our North and South poles. Because Uranus rotates on its side, its magnetic field is wildly tilted and messy. The Salient Idea here is that Uranus’s auroras appear as patchy, transient spots rather than perfect halos. While looking for these spots, scientists also searched for near-infrared light from an ion called H3+. They expected to see concentrated glowing from the aurora. Instead, they found the H3+ glowing broadly across the entire southern hemisphere. This wide glow wasn’t an aurora; it was the planet’s upper atmosphere naturally heating up as it approached its summer season.

Why does this matter to us? Auroras are the visible footprints of a planet’s magnetic shield interacting with the solar wind. Without Earth’s magnetic field, our atmosphere would be stripped away by these exact same solar storms. By studying Uranus’s highly tilted, asymmetrical magnetic field, we learn how magnetic shields work in extreme, twisted configurations. The auroras on Uranus act like glowing flare guns, showing us exactly where the invisible magnetic lines are bending and snapping. Understanding this twisted space weather helps us better appreciate the perfectly balanced magnetic bubble that protects life here on Earth.

Uranus’s auroras act like glowing flare guns, revealing the invisible physics of its magnetic shield.
— NorthernLightsIceland.com Team

Coordinating this observation was no easy task. It required Knowledge and Tools spread across the globe and in orbit. Astronomers used computer models to calculate exactly when the solar wind would hit Uranus. Then, they had to secure highly coveted time on ‘Hubble’ in space, the ‘Chandra’ X-ray observatory, ‘VLT’ in Chile, and ‘Gemini North’ in Hawaii. By analyzing specific wavelengths of light—Far-Ultraviolet and Near-Infrared—they could literally peel back the layers of Uranus’s atmosphere. It was a triumph of international teamwork, proving we can forecast and observe space weather billions of miles away.

These new high resolution images reveal H3+ from the whole disc, but show no evidence of localized auroral emission in the infrared.
— Research Team

Q: Could I see the auroras on Uranus if I flew a spaceship there?
A: Probably not with your bare eyes! The auroras observed in this study radiate in Far-Ultraviolet and Near-Infrared light, which are completely invisible to human vision. You would need special sensor goggles to see the light show.

Q: Why did it take two months for the solar storm to reach Uranus?
A: Uranus is located about 1.8 billion miles from the Sun. Even though the solar storm travels at over a million miles per hour, the sheer scale of the solar system means it takes months for that energy to cross the void.