A Longer View

NASA, ESA, Erich Karkoschka (LPL)

In 1986, the Voyager 2 spacecraft made a flyby of Uranus. It gave us the first detailed images of the distant world. What was once only seen as a featureless pale blue orb was revealed to be…well, a mostly featureless pale blue orb. The flyby gave astronomers plenty of data, but the images Voyager 2 returned were uninspiring. That’s because Voyager only viewed Uranus for a moment in time. Things change slowly on the ice giant world, and to study them you need to take a longer view.

One of the most distinct features of Uranus is that it’s a world on its side. While Earth’s axial tilt is about 23 degrees, Uranus has a 98-degree axial tilt. This means that during summer on Neptune, the Sun is always overhead, while the winter-side is always in darkness. And since it takes 84 years for Uranus to orbit the Sun, summer and winter on the planet each last four decades.

For the past 20 years, the Hubble Space Telescope has captured detailed images of Uranus from time to time, both in visible and infrared. This means we have a view of Uranus as its Northern Hemisphere transitions from early spring toward its midsummer in 2030. From these observations, we’ve learned that the polar regions have significantly less methane than the equatorial region. It’s the methane that gives Uranus its pale blue coloring. The north polar region is also brightening as it enters summer, meaning that the haze layer is growing as things get warmer. Uranus is no longer a featureless orb but has banded layers around its equator.

Astronomers will continue to observe Uranus as its seasons evolve. But one thing is clear. Voyager 2 revealed a featureless world simply because of bad timing. Perhaps it would be a good time to send another spacecraft to the outer solar system.