Once every ten years, NASA asks the National Academies of Science, Engineering and Medicine to bring together a number of planetary scientists to decide the priorities for future missions in the solar system. And according to the latest recently released report the top priority for the next decade of space exploration is to spend several billion dollars on a new flagship mission to Uranus. Why?
Only one spacecraft, Voyager 2, has ever visited the planet Uranus, and that was in 1986, with technology developed in the 1970s. The visit was brief: Uranus was one stopover on the mission’s grand tour of the solar system, and the probe made its observations while en route. What scientists now recommend is a mission specifically designed to study everything about the Uranian system, including the planet, its moons and its rings. Because yes, Uranus has rings.
Uranus is the seventh planet from the sun – between our Earth and Uranus are Mars, Jupiter and Saturn. Because the solar system is in constant motion, the distance between Earth and Uranus changes daily. At its closest, it’s still flying for 2.6 billion kilometers. For Mars, that’s about 55 million kilometers.
Even with the best space telescopes, it’s difficult to study a planet twice as far from Earth as Saturn, and much smaller than that ringed planet. Although we know more about the universe than ever before, Uranus is still largely a mystery. Name any aspect of the Uranian system and planetary scientists can give you a list of unanswered questions about it.
We know almost nothing
Scientists suspect that Uranus, like Neptune, is made of various ices, gases and rocks, but they can’t say for sure about the composition of the hazy atmosphere or the structure of its interior.
Unlike the other planets, Uranus rotates on its side, meaning summers with constant sunlight and winters of complete darkness. The planet was probably knocked over by a giant impact many eons ago, but what kind? Planetary scientists have no idea how the magnetic field works. The rings – what are they made of? And the moons of Uranus – could some of them have subterranean oceans?
Voyager’s images showed the side planet as a largely unremarkable, bluish sphere, but telescope observations over the past two decades have captured intriguing bursts of cloud activity in the atmosphere.
The Uranus mission — if NASA decides to take up the space science community’s suggestion — would mean placing a spacecraft in orbit around the planet and even dropping a probe into the atmosphere.
Ice giants are everywhere
By getting to know Uranus, planetary scientists can learn about a class of planets that ice giants are called. The space community is already fairly familiar with the workings of the terrestrial planets in our solar system, such as Earth and Mars, and NASA is already setting up new missions to Venus. Scientists also have a good handle on Saturn and Jupiter, our gas giants, thanks to dedicated missions that orbited those planets for years. But Uranus and Neptune, the ice giants? Those pages in our cosmic understanding are almost blank.
And that’s frustrating for scientists, because ice giants are arguably one of the most abundant planets in the Milky Way. Research on exoplanets – planets outside 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 need to take a closer look at one of our own ice giants.
We’ll be there by 2040 (maybe)
Planetary scientists chose Uranus over Neptune as their primary target for practical reasons. Neptune is further. Uranus, although the planet is closer to the sun, is actually colder than Neptune — and, you guessed it, scientists don’t know why that is either. But with the missile systems currently in use, Uranus is easier to reach.
Any mission to the outer planets still takes quite some time. If an Uranus mission were launched in 2031, the earliest chance suggested by the National Academies report, it wouldn’t reach the planet until the end of that decade.
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