by Uranus, the seventh planet from the Sun, orbits in the outer solar system, about 3.2 billion kilometers (2 billion miles) from Earth. It is a huge world: four times the diameter of the Earth, with 15 times its mass and 63 times its volume.
Uranus, which has not been visited by spacecraft for more than 35 years, inhabits one of the least explored regions of our solar system. Although scientists have learned some things about it from telescopic observations and theoretical work since Voyager 2’s flyby in 1986, the planet remains an enigma.
It is easy to divide the solar system into two large groups: an inner zone with four rocky planets and an outer zone with four giant planets. But nature is, as always, more complicated. Uranus and Neptune, the eighth planet from the Sun, are very different from the others. Both are ice giants, composed largely of compounds such as water, ice, ammonia and methane; They are places where the average temperature is -320 to -350 degrees Fahrenheit (-212 Celsius).
Through recent discoveries of exoplanets (worlds outside our solar system that are trillions of kilometers away), astronomers have learned that ice giants are common throughout the galaxy. They challenge our understanding of planetary formation and evolution. Uranus, comparatively close to us, is our cornerstone for learning about them.
A new mission
Many in the space community – like me – are urging NASA to launch a robotic spacecraft to explore Uranus. In fact, the 2023 decadal survey of planetary scientists ranked that trip as the top priority for a new NASA flagship mission.
This time, the spacecraft wouldn’t simply pass by Uranus on its way to somewhere else, as Voyager 2 did. Instead, the probe would spend years orbiting and studying the planet, its 27 moons and its 13 rings.
You may be wondering why send a spacecraft to Uranus and not Neptune. It’s a question of orbital architecture. Because of the positions of both planets over the next two decades, a spacecraft from Earth will have an easier trajectory to follow to reach Uranus than Neptune. Launched at the right time, the orbiter would reach Uranus in about 12 years.
These are just some of the basic questions that a Uranus orbiter would help answer: What exactly is Uranus made of? Why is Uranus tilted on its side, with its poles pointing almost directly toward the Sun during the summer, which is different from all the other planets in the solar system? What is generating Uranus’ strange magnetic field, which is shaped differently than Earth’s and is misaligned with the direction of the planet’s spin? How does atmospheric circulation work in an ice giant? What do the answers to all these questions tell us about how ice giants form?
Despite the progress scientists have made on these and other questions since Voyager 2’s flyby, there is no substitute for direct, up-close, and repeated observations from an orbiting spacecraft.
The rings and those moons
The rings around Uranus, probably made of dirty ice, are thinner and darker than those around Saturn. A Uranus orbiter would look for “ripples” in them, similar to waves on a lake. Finding them would allow scientists to use the rings as a giant seismometer to help us understand the interior of Uranus, one of its great secrets.
The moons, mostly named after literary characters from the writings of Shakespeare and Pope, are made primarily of frozen mixtures of ice and rock. Five of the moons are particularly compelling. Miranda, Ariel, Umbriel, Titania and Oberon are large enough to be spherical and treated as miniature worlds in their own right.
During its flyby, Voyager 2 took low-resolution images of the moons’ southern hemispheres. (Its northern hemispheres, still invisible, remain one of the main unexplored frontiers of our solar system.) Those images include photographs of ice volcanoes on Ariel, a tantalizing hint of past geological and tectonic activity and, possibly, groundwater.
The possibility of oceans and life.
Which leads to 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, may be an ocean world hosting large underground bodies of liquid water miles away. depth. surface. Finding out if any of the moons have oceans is one of the main objectives of the mission.
This is one reason why an orbiter would likely carry a magnetometer, to detect the electromagnetic interactions of a subsurface ocean as one of its moons travels through Uranus’s magnetic field. Instruments to measure the moons’ gravitational fields and cameras to study the geology of their surface would also be useful.
Liquid water is an essential requirement for life as we know it. If oceans are detected, scientists will want to look for other ingredients for life on the moons, such as energy, nutrients and organic matter.
It’s not a done deal
No launch date has been set for the mission and there is still no official approval from NASA for its funding. The cost would likely amount to more than $1 billion.
One critical factor to consider: The cosmos operates on its own schedule, and spacecraft trajectories toward Uranus will change over the years as the planets move throughout their orbits. Ideally, NASA would launch a mission in 2031 or 2032 to maximize trajectory desirability and minimize travel time. That period of time is shorter than it may seem; It takes years of planning (and years more of building the spacecraft) to be ready for launch. That is why now is the time to start the process and fund a mission to this fascinating world.
This article is republished from The Conversation, an independent, nonprofit news organization bringing you trusted data and analysis to help you understand our complex world. Do you 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.
