Uranus: the coolest destination in the solar system

Let’s dismiss it now. Any comments that might come to mind when you hear the name of the seventh planet from the sun pronounced in a certain way, keep them to yourself. No laughs. Absolutely no wisecracks-shit. No jokes! This is a serious story about Uranus.

Because it’s a big day for Uranus. Once a decade, NASA asks the National Academies of Sciences, Engineering, and Medicine to convene a panel of planetary scientists to decide the country’s priorities for future missions to the solar system. And the latest report, released today, has brought this outer planet to the fore. According to the powers that be, the top priority for the next decade of space exploration is to spend several billion dollars on a shiny new flagship mission to Uranus.

Uranus deserves closer examination. Only one spacecraft, Voyager 2, has ever visited the planet, and that was in 1986, with technology developed in the 1970s. The visit was short; Uranus was a stop on the mission’s grand tour of the solar system, and the probe made its observations while on the move. What scientists are now recommending is a mission designed specifically to study everything related to the Uranian system, including the planet, its moons and its rings – yes, Uranus has rings!

Given our lowbrow humor history with Uranus – which is pronounced Your-uh-nus, by the way, one would assume that we know our cosmic neighbor quite well. But even with the best space telescopes, it’s difficult to study a planet twice as far from Earth as Saturn, and much smaller than the ringed planet. Although we know more about the universe than ever before, we still don’t understand one of the planets in our own solar system.

Name any aspect of the Uranian system, and planetary scientists can give you a list of unanswered questions about it. Scientists suspect that Uranus, like Neptune, is made up of different types of ice, gas, and rock, but they can’t say anything for sure about the makeup of its hazy atmosphere or the structure of its interior. Unlike the other planets, Uranus spins sideways, which means summers of constant sunshine and winters of total darkness; it was probably knocked down by a giant impact eons ago, but what kind? Planetary scientists have no idea how its magnetic field works and they really like to know how magnetic fields work. These rings, what are they? they or they made of? And the moons of Uranus – could any of them have subterranean oceans? Voyager images showed the side planet as a mostly featureless bluish orb, but telescope observations over the past two decades have captured intriguing bursts of cloud activity in its atmosphere. What is all this about?

The Uranus mission – if NASA decides to follow the space science community’s suggestion – would mean putting a spacecraft into orbit around the planet, and even launching a probe into its atmosphere. With Voyager, “it’s almost like driving next to a person and having a few seconds to look at them,” Jonathan Fortney, an astronomer at UC Santa Cruz, told me. “Do you feel like you would have a good understanding of who they were?” A spacecraft-in-residence, on the other hand, is like “spending years talking to them and getting to know their idiosyncrasies,” he said.

By getting to know Uranus, planetary scientists can learn about a class of planets called ice giants. The space community is already familiar with the workings of terrestrial planets in our solar system, such as Earth and Mars, and NASA is already planning new missions to Venus. Scientists also have a good grasp of Saturn and Jupiter, our gas giants, thanks to dedicated missions that have spent years orbiting these planets. But Uranus and Neptune, the ice giants? These pages of our cosmic understanding are nearly blank.

Which is especially frustrating for scientists, because ice giants could be one of the most common planets in the galaxy. Research on exoplanets – planets beyond our solar system – has shown that gas giants like Saturn and Jupiter are rare, but worlds the size of Uranus and Neptune are everywhere. So before anyone can understand the ice giants out there, scientists would have to take a closer look at one of our own. Planetary scientists chose Uranus over Neptune for practical reasons; Neptune, which since 2006 has the distinction of being the furthest planet from our solar system (well, it depends on who you ask), is further away. “They’re both absolutely fascinating, and they’re not the same,” Amy Simon, a NASA planetary scientist who studies ice giants, told me. For example, Uranus, despite being closer to the sun, is actually cooler than Neptune – and, you guessed it, scientists aren’t sure why either. But with the rocket systems currently in operation, Uranus is easier to reach.

Any mission to the outer planets still takes a little time. If a Uranus mission were to launch in 2031, the first opportunity suggested by the National Academies report, it would not reach the planet until the end of this decade. Later, and the spacecraft would arrive in the 2040s. But planetary scientists are used to playing the long game, Heidi Hammel, an astronomer at the Association of Universities for Research in Astronomy, told me. Hammel worked on the Voyager mission during the Uranus flyby, and by the time this new mission reaches its goal, “I’ll be watching from the porch of the retirement home of retired planetary scientists,” she joked. . Maybe NASA would let her falter in mission control, she said, to watch a new generation of researchers bask in the experiment. She knows how wonderful it is to see a world appear in real time. And she and her colleagues only spotted Uranus 36 years ago. This time, if NASA indeed makes a dedicated mission to Uranus a priority, humanity can stick around for a while. “I guarantee you that when we get there,” Hammel said, “the young scientists working there are going to see things they never even imagined.”

Arline J. Mercier