by Uranus, the seventh planet from the Sun, orbits in the outer solar system, about two billion miles (3.2 billion kilometers) from Earth. It is a huge world – four times the diameter of Earth, with 15 times the mass and 63 times the volume.
Unvisited by spacecraft for more than 35 years, Uranus resides in one of the least explored regions of our solar system. Although scientists have learned a few things about it from telescopic observations and theoretical work since the Voyager 2 flyby in 1986, the planet remains an enigma.
It is easy to divide the solar system into two large groups: an inner belt with four rocky planets and an outer belt with four giant planets. But nature, as usual, is more complicated. Uranus and Neptune, the eighth planet from the Sun, are very different from the others. Both are ice giants, composed mostly of compounds such as water, ice, ammonia and methane; they are places where the average temperature is minus 320 to minus 350 degrees Fahrenheit (minus 212 Celsius).
Through the recent discovery of exoplanets – worlds outside our solar system trillions of miles away – astronomers have learned that ice giants are common throughout the galaxy. They challenge our understanding of planetary formation and evolution. Uranus, which is close to us, is our cornerstone to learn about.
New mission
Many in the space community – like me – are urging NASA to send a robotic spacecraft to explore Uranus. In fact, a 2023 decennial survey of planetary scientists ranked such a trip as the highest priority for NASA’s new flagship mission.
This time, the spacecraft would not simply fly past Uranus on its way somewhere else, as Voyager 2 did. Instead, the probe would spend years orbiting and studying the planet, which 27 moons and their 13 rings.
You may wonder why a spacecraft goes to Uranus and not Neptune. It is an object of orbital architecture. Because of the positions of the two planets over the next two decades, a spacecraft from Earth will have an easier path to follow to reach Uranus than Neptune. Launched at the right time, the orbiter would reach Uranus in 12 years.
Here are some of the basic questions that Uranus’ orbit would help answer: What, exactly, is Uranus made of? Why is Uranus tilted on its side, with its poles pointing almost directly towards the Sun during the summer – unlike all the other planets in the solar system? What generates Uranus’s peculiar magnetic field, which is shaped differently than Earth and is not aligned with the direction the planet rotates? How does atmospheric circulation work on an ice giant? What do the answers to these questions tell us about how ice giants form?
Despite the progress scientists have made on these and other questions since the Voyager 2 flight, there is no substitute for direct, close-up and repeated observations from an orbiting spacecraft.
Those rings and moons
The rings around Uranus, probably made of dirty ice, are thinner and darker than those around Saturn. The orbit of Uranus would find “currents” in them, like waves on a lake. If found, it would allow scientists to use the rings as a giant seismometer to help us learn about the interior of Uranus, one of its great secrets.
The moons, which are mainly named after literary characters from the writings of Shakespeare and Pope, are made mainly of frozen mixtures of ice and rock. Five of the moons are particularly strong. Miranda, Ariel, Umbriel, Titania and Oberon are big enough to be spherical and treated as miniatures in their own right.
During its flyby, Voyager 2 took low-resolution images of the moon’s southern hemisphere. (Its as-yet-unseen northern hemisphere is one of the great unexplored frontiers of our solar system.) Among those images are photographs of ice volcanoes on Ariel – a tantalizing hint of geological and tectonic activity at the time passed around and, perhaps, water under the surface.
The possibility of oceans and life
The result is one of the most exciting parts of the mission: Many planetary scientists theorize that Ariel, and perhaps most or all of the other five moons, could be an ocean world with vast underground bodies of liquid water miles below the icy solid. surface. One of the major goals of the mission is to find out if any of the moons have oceans.
That’s one reason an orbiter might carry a magnetometer – to detect the electromagnetic interactions of a subsurface ocean as one of its moons travels through Uranus’ magnetic field. Instruments to measure the moon’s gravitational fields and cameras to study its surface geology would also help.
Liquid water is an essential requirement for life as we know it. If the oceans are found, scientists will want to look for other ingredients for life on the moon – such as energy, nutrients and organic matter.
Not a done deal
No launch date has been set for the mission, and funding has yet to be officially approved by NASA. The cost would probably be more than a billion dollars.
One critical factor to consider: The cosmos operates on its own timetable, and the trajectories of those spacecraft to Uranus will change over the years as the planets move along their orbits. Ideally, NASA would launch a mission in 2031 or 2032 to maximize trajectory utility and minimize travel time. That period of time is less than it seems; It takes years of planning – and years of building the spacecraft – to be ready for launch. That’s why now is the time to start the process and fund a mission to this wonderful world.
This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. Like this article? Subscribe to our weekly newsletter.
It was written by: Mike Sori, Purdue University.
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Mike Sori receives funding from NASA.
