Uranus is Finally Being Revisited

Issue 7, Volume 113

By Frances Schwarz 

Uranus, the butt of all planetary science jokes. Despite its unfortunate name, planetary scientists from across the country named Uranus “one of the most intriguing bodies in the solar system” in a nationwide survey this April. The scientists agreed that a trip to Uranus should be planetary exploration’s first priority. This is a great feat for the underappreciated planet, which was visited for the first and only time in 1986. In fact, Uranus is so mysterious that its long-time categorization as an ice giant—an enormous planet made of elements heavier than hydrogen or helium—might not even be true.

Recent interest in Uranus was expressed through the decadal survey, which gathers a committee of planetary scientists once a decade to propose missions that NASA should undertake. This survey is organized by the National Academy of Sciences, Engineering, and Medicine at the request of NASA. While NASA and Congress, which funds NASA, are not bound to the survey, its top mission priorities are almost always carried out.

At a virtual town hall on August 18th, shortly after the decadal survey released on April 19th, NASA announced that they were working toward initiating a trip to Uranus, along with a very rough timeline for the mission. The trip to Uranus has been deemed a flagship mission, or one reserved exclusively for NASA’s most distinguished spacecraft, and will thus take a long time to get off the ground. According to the timeline, studies could begin as early as the fiscal year 2023, launch in the early 2030s, and arrival in the 2040s.

Such a trip was proposed largely to answer the many mysteries surrounding Uranus: its extreme axial tilt, its odd magnetic field, its interior, which is suspected to be most likely ice or rock, and more. More importantly, many exoplanets, or planets beyond our solar system, are around the same size as Uranus. This means that a trip to Uranus would allow us to study planets of a class that abounds in our galaxy. Certain exoplanets, for example, may show signs of life that we can interpret and explore further, making the potential value of the mission far beyond our expectations.

Topping the decadal survey truly is an accomplishment for lowly Uranus, which, aside from being known as the solar system’s backside, has also been publicized as excessively boring. As Forbes put it in 2017, when the legendary interstellar probe Voyager 2 flew past the planet in 1986, “the most remarkable part of the story was how unremarkable Uranus appeared.” Indeed, while the 70s and 80s were rife with extravagant photos of planets like Jupiter with its swirling cloud stripes or Mars with its grand ice caps, Uranus appeared to be nothing more than a pale blue dot.

The explanation for its plainness seemed simple. Though Uranus can fit roughly 68 Earth within its volume, it is minuscule compared to Saturn and Jupiter, rendering it unable to produce its own internal heat. The only heat it has is from the Sun, leaving its upper atmosphere at an unwavering 58 kelvins.

Don’t stop reading yet, however. Voyager 2 visited Uranus at its solstice, when the planet was at its most shy. Uranus is the only planet in the solar system to rotate on its side, with even its rings and moons orbiting perpendicular to the plane of the solar system. Around Uranus’s solstices—the points in a planet’s orbit at which its axis of rotation is directed toward the star it orbits—hypothetical aliens in Uranus’s north pole bask in long-time sunlight while those in the south huddle in the dark. During Uranus’s equinoxes—the points at which a planet’s slanted axis is not tilted toward the star it orbits—aliens in the south pole see the Sun for the first time in decades and find themselves experiencing both night and day. Decades? Indeed: Uranus takes 84 Earth years to orbit the sun.

As for the reason why Uranus’s photographic debut in 1986 fell flat, Uranus’s temperatures during solstice produce a haze of methane, which floats to the top of Uranus’s atmosphere and hides exciting activity below. In fact, this methane haze makes up only one percent of Uranus’ atmosphere.

However, Uranus surprised astronomers during its 2007 equinox with a new suit. As Uranus moves toward equinox and the south pole cools off in a long overdue night, the methane haze sinks into the lower atmosphere, leaving the uppermost layer transparent the following day. This revealed a number of exciting features: a vast stormy cloud cap over the north pole, atmospheric bands of contrasting color, Neptune-like cloud activity, and even 13 faint rings, likely from shattered or spaghettified moons. And yes, spaghettification is a real astronomical term that describes the state of an object being vertically stretched as it encounters extreme gravitational fields.

By visiting Uranus, insight into its unusual seasons will certainly be valuable, though there are equally great mysteries ahead. Uranus shocked researchers when Voyager 2 revealed that the line connecting the planet’s magnetic north and south poles was tilted 59 degrees to the planet’s axis of rotation, instead of lining up roughly with the planet’s poles. Oddly enough, Neptune has a similarly misguided magnetic field. The reason why remains unknown.

Scientists aren’t certain about how Uranus ended up with its lopsided rotation. The general opinion is that Uranus was battered by various space rocks early in its formation until it flipped onto its side. However, recent research suggests that the loss of a large moon early in its life could have done the trick. The fact that the other planets emerged with stubbornly upright positions despite suffering severe astronomical beatings has typically been explained by Uranus’s bad luck.

Perhaps most embarrassingly for planetary scientists, Uranus might not be an ice giant after all. The current belief is that Uranus is composed of mostly liquid water, methane, and ammonia. Yet, a mixture of rock and gas shares a similar density with this trio, meaning that planetary scientists could have actually been observing rock and gas all along. It’s possible that if Uranus and Neptune formed from the collision of rock-dominated objects as opposed to the slow collection of ice floating on dust grains by gravity, these planets would be more rocky than icy, making them rock giants.

Ultimately, Uranus is long overdue on a checkup, and the fact that it is finally getting one after being pushed to the back burner in favor of Mars missions and the James Webb Telescope is no small feat for the underdog planet. Over the next few decades, we may see gorgeous photos of the planet, a fair number of news articles on Uranus’s surprises, a number of additions to textbooks describing ice giants, and maybe even an alien or two on one of Uranus’s moons, which are fascinating worlds in their own ways. In the meantime, the best that space enthusiasts can do is twiddle their thumbs and hope that NASA makes it to Uranus by 2045. After all, an equinox is approaching, and that methane haze only stays transparent for so long.