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Patience for Uranus | The planetary society

The long way back to Uranus

The road back to Uranus is paved with a complex mix of science and politics.

Every 10 years, the National Academy of Sciences enlists committees of top planetary scientists to help create a report outlining the community’s top scientific questions and a priority list of missions to answer them. These reports are known as the decennial survey. They are used by NASA, the White House, and Congress during the budget-making process to decide which missions to fund next.

Getting a mission to Uranus or Neptune on the community radar has been a challenge for scientists studying ice giants. For the past few decades, NASA has focused on the search for life. A flagship mission from Uranus made it the 2013 ten-year surveybut it was prioritized behind Europa Clipper and Mars Sample Return.

These missions are currently in development, paving the way for a Uranus mission to top the list of flagships in the 2023 ten-year surveypublished in April 2022. The survey recommends starting official work on the mission, which could have a price tag of $4.2 billion, as early as 2024.

Interest in Uranus has been boosted by the discovery of more than 5,000 exoplanets — planets orbiting other stars. A third of them are gaseous worlds the size of Uranus or Neptune. This means that studying Uranus or Neptune would give us considerable insight into what is currently the most common type of exoplanet we have discovered.

Simon, NASA’s planetary atmospheres expert, said a Uranus mission designed to study all aspects of the system would revive interest in the outer planets, which has waned since NASA’s Cassini mission ended in Saturn in 2017.

“With the end of Cassini, not as much is happening in the outer solar system anymore,” she said. “So I think for the community it will be a very good thing to have this mission that touches on so many different areas.”

under the clouds

While the outer planets were gobbling up material early in the solar system, Uranus and Neptune’s positions farther from the Sun allowed them to absorb additional portions of ice water, ammonia, and methane. Methane in Uranus’ atmosphere absorbs red light, giving the planet its blue-green appearance.

A Uranus mission would carry a probe to dive into the planet’s atmosphere and measure its composition, including the specific isotopes of each element. Isotopes, which are variations in the number of neutrons within the same element, act like fingerprints that would allow scientists to determine where Uranus formed and what conditions were like in the early days of the solar system, although before life appeared on Earth.

Jupiter and Saturn may have originally formed farther from the Sun than their current locations, while Uranus and Neptune may have formed closer to the Sun. About 4 billion years ago, the giant planets began jostling for position, pushing Uranus and Neptune toward their current locations.

At some point, Uranus went sideways. While Earth has a modest 23 degree tilt that gives us our seasons, Uranus’ axis of rotation is tilted 98 degrees. Essentially, the planet rolls around the solar system sideways.

It is not known what caused this. Gravitational resonances between Uranus and Saturn may have caused Uranus to wobble until it fell. Another popular theory is that a giant proto-world crashed into the planet. A new Uranus mission will seek evidence of what happened deep under the planet’s icy clouds, where its magnetic field is generated.