Perhaps the image of Uranus just below helps explain why the planet has been treated so sparsely in science fiction. Even this Voyager view shows us a featureless orb, and certainly in visible light the world has little to make it stand out other than its unusual axis of rotation, which is tilted so that its polar regions are where you would expect its equator to be. Geoff Landis’ “Into the Blue Abyss” (2001) is the best fictional treatment I know, but the fog-shrouded Uranus of Stanley G. Weinbaum’s “The Planet of Doubt” (1935) has its own charms, though obviously lacking the scientific verisimilitude of the Landis tale.
My admiration for Gerald Nordley’s “Into the Miranda Rift” (1993) is unabated, taking us into this strange world’s most dramatic moon, while I should also mention Kim Stanley Robinson’s visit to Uranus in Blue Mars (1997), where the moon is established as a protected wilderness site while the rest of the Uranian satellite system is under colonization. Fritz Leiber’s “Snowbank Orbit” (1962) explores aero-braking at Uranus, while Larry Niven’s A World Out of Time (1976) maneuvers the planet to adjust the Earth’s own orbit.
Image: The planet Uranus as seen by Voyager 2, which flew closely past the seventh planet in January of 1986. Credit: NASA/JPL.
I will spare you the 1962 film Journey to the Seventh Planet and move on to new work on Uranus out of the Georgia Institute of Technology, where researchers have discovered that the magnetosphere of the planet ‘flips on and off like a light switch’ (according to this Georgia Tech news release) as it rotates along with the planet. In one orientation, the solar wind flows into the magnetosphere, which later closes to deflect that same wind away from Uranus.
Rotating on its side, Uranus also has a magnetic field that is off-centered and tilted 60 degrees from its axis of rotation. What we wind up with is rapid rotational reorientation, keeping the field strength turbulent. Carol Paty (Georgia Tech), a co-author of the study, puts the matter this way:
“Uranus is a geometric nightmare. The magnetic field tumbles very fast, like a child cartwheeling down a hill head over heels. When the magnetized solar wind meets this tumbling field in the right way, it can reconnect and Uranus’ magnetosphere goes from open to closed to open on a daily basis.”
Compare this with the Earth, where the magnetic field is nearly aligned with the planet’s spin axis, which means that the magnetosphere spins along with the Earth’s rotation. Even so, disruptive events can occur because of geomagnetic storms. A strong solar storm disrupting the magnetic fields of the solar wind can reconfigure Earth’s field from closed to open, rearranging the local magnetic topology to allow a surge of solar energy to enter the system. Such reconnection happens throughout the Solar System, and occurs when the direction of the heliospheric magnetic field is opposite to a planet’s magnetospheric alignment.
Geomagnetic storms produced by coronal mass ejections slamming into Earth’s magnetic field can produce spectacular aurora events while playing havoc with radio communications. Reconnection drives the entire process, happening in the presence of plasma, which carries its own magnetic fields in a constantly adjusting dance between charged particles and fields. Sudden changes in the alignment of the magnetic field lines convert the stored energy of the magnetic fields into heat and kinetic energy that drives particles along the field lines.
Image: Magnetic reconnection (henceforth called “reconnection”) refers to the breaking and reconnecting of oppositely directed magnetic field lines in a plasma. In the process, magnetic field energy is converted to plasma kinetic and thermal energy. Credit: Magnetic Reconnection Experiment.
Thus a surge of energy enters the system. Such magnetic reconnection should produce auroras at various latitudes on Uranus even if they are a challenge to observe from Earth. The Georgia Tech team’s numerical models predict the most likely places on the planet for reconnection, working with Voyager 2 data from the 1986 flyby. Lead author Xin Cao comments:
“The majority of exoplanets that have been discovered appear to also be ice giants in size. Perhaps what we see on Uranus and Neptune is the norm for planets: very unique magnetospheres and less-aligned magnetic fields. Understanding how these complex magnetospheres shield exoplanets from stellar radiation is of key importance for studying the habitability of these newly discovered worlds.”
The paper is Cao and Paty, “Diurnal and seasonal variability of Uranus’s magnetosphere,” published online by the Journal of Geophysical Research: Space Physics 27 June 2017 (abstract).