Lately, I’ve been trying to learn as much as I can about the planet Uranus and its moons. It’s been a real challenge. Only one spacecraft has ever visited the Uranian System, and that was back in 1986.
When I do research on most other objects in the Solar System, I usually find plenty of good, highly detailed information to work with. Geology, chemistry, meteorology (sometimes), seismology (sometimes), astrobiology (more often than you’d think)…. But when it comes to the moons of Uranus… well, we know what color they are!
Today, I’d like to introduce you to Umbriel. She’s sort of dark grey. All the moons of Uranus are grey, but Umbriel is the darkest shade of grey out of them all. In fact, that’s basically what the name Umbriel means: darkness.
According to this paper, Umbriel’s dark grey color might be caused by carbon compounds. Imagine there’s coal or charcoal dust sprinkled all over Umbriel’s surface. That’s basically what we think we’re looking at, except unlike coal or charcoal, Umbriel’s carbon compounds probably formed due to the photolysis and/or radiolysis of carbon dioxide, not because of biological activity.
But that dark coloration appears to be only skin-deep. Near the equator, Umbriel has a lighter, icier-looking surface feature. It’s believed to be the result of a relatively recent asteroid or comet impact. The color change probably means we’re seeing subsurface material that hasn’t undergone photolysis yet. Officially, that surface feature is known as Wunda Crater. Unofficially, it’s called the fluorescent Cheerio. Seriously, I’m not making that up.
Sending a spacecraft to Uranus is a costly and technologically challenging endeavor. That’s why we’ve only done it once. But if/when another Uranus mission does get off the ground, investigating that fluorescent Cheerio should be a top priority. Anything that can tell us what lies beneath the surface of an icy moon like Umbriel is worth a closer look.