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Illustrative Image. Source: LLC/Alamy
On the night of March 13th, 1781, William Herschel was peering through his telescope in the backyard of his New King Street home in Bath, England, when he noticed a faint, unusual object near the star Zeta Tauri. He observed it for several nights and realized it was moving slowly compared to the background stars. The astronomer initially thought he had found a comet, but later accurately determined it to be a distant planet. This planet was later named Uranus. This achievement earned Herschel a spot in the Royal Society, a knighthood, and lasting astronomical acclaim.
Studies have revealed that Uranus is a highly peculiar world. The planet is tilted compared to the other planets in our solar system. And while it’s not the farthest planet from the sun, it is the coldest planet in our solar system.
Uranus also experiences extreme seasons. Each pole spends decades basking in continuous sunlight before transitioning to decades of complete darkness. If someone were born near Uranus’s pole during the autumn season, they would have to wait 42 years until spring to see the sun for the first time. Moreover, Uranus is the only planet named after a Greek god rather than a Roman one. (Uranus is the grandfather of Zeus.)
Despite the astronomical oddities and extremes of this planet, humans have made very few efforts to get up close to Uranus. Only one robotic probe has visited, in 1986—the United States’ Voyager 2 spacecraft—though it merely conducted a flyby exploration of the solar system. The data revealed a massive, strange, pale blue world with an atmosphere composed of hydrogen, helium, and methane, numerous moons, and a powerful magnetic field. And that is nearly all that humans know about Uranus.
However, that is about to change. Earlier this year, the United States National Academy of Sciences published a report urging NASA to send a probe to Uranus, considering it a top-priority mission for the next decade. These reports are released every ten years and carry significant influence, meaning that NASA is now under substantial pressure to design and fund such a mission.
For enthusiasts of Uranus, this is exciting news. Professor Leigh Fletcher from the University of Leicester states, “It’s very exciting news. There are very few places in the solar system that we have so little knowledge about, such as Uranus. The inner planets of the solar system have been visited many times, including Earth and Mars. Even the remote, small planets like Pluto have been surveyed. So, a Uranus mission would fill in a gap in our understanding of the processes that formed the solar system.”
Astronomers categorize the planets of the solar system into three basic groups. One group comprises the rocky planets—Mercury, Venus, Earth, and Mars—that orbit close to the sun. Further out are the gas giants—Jupiter and Saturn—huge worlds made primarily of hydrogen and helium. Then, on the solar system’s outskirts, there’s Uranus and its partner, Neptune, the second and farthest planets from the sun. These two are called the ice giants because they’re massive (though not as massive as Jupiter and Saturn) and formed from icy material. Importantly, they harbor a lot of icy-making molecules like methane, water, and others within their atmospheres and interiors.
These characteristics have always been considered intriguing but not compelling enough for special attention—until astronomers started studying other star systems and found ice giants like Uranus and Neptune all over the place. Fletcher adds, “It’s genuinely fascinating: when we look at planets around other stars, we see so many planets among them that resemble Uranus and Neptune.” Or as Jonathan Fortney, a planetary scientist at the University of California, Santa Cruz, puts it, “Nature seems to love making planets like these.”
The reasons for the prevalence of these ice giants in our galaxy remain unknown. Fletcher says, “However, there’s clearly something important about planets like Uranus and Neptune. And it’s important that we have two planets representing the most common planet type in the galaxy, right here in our solar system. However, their composition, nature, and origins still remain a mystery. It’s time to care about them.”