Among all the planets, Uranus seems to get the least play in science fiction, though it does have one early advocate whose work I’ve always been curious about. Although he wrote under a pseudonym, the author calling himself ‘Mr. Vivenair’ published a book about a journey to Uranus back in the late 18th Century. A Journey Lately Performed Through the Air in an Aerostatic Globe, Commonly Called an Air Balloon, From This Terraquaeous Globe to the Newly Discovered Planet, Georgium Sidus (1784) seems to be reminiscent of some of Verne’s work, even if it pre-dates it, in using a then cutting-edge technology (balloons) to envision a manned trip through space.
Image: Near-infrared views of Uranus reveal its otherwise faint ring system, highlighting the extent to which it is tilted. Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory.
When ‘Vivenair’ wrote, Uranus had just been discovered (by William Herschel in 1781). The author used it as the occasion for political satire, and not a very good one, according to critic James T. Presley, who described it in an 1873 article in Notes & Queries as ‘a dull and stupid satire on the court and government of George III.’ Vivenair evidently put the public to sleep, for Uranus more or less fades from fictional view for the whole of the 19th Century. More recent times have done better. Tales like Geoff Landis’ wonderful “Into the Blue Abyss” (2001) bring Uranus into startling focus, and Larry Niven does outrageous things with it in A World Out of Time (1976). But although it doesn’t hold up well as fiction, Stanley G. Weinbaum’s story about Uranus may sport the most memorable title of all: “The Planet of Doubt” (1935).
What better name for this place? The seventh planet has a spin axis inclined by a whopping 98 degrees in reference to its orbital plane — compare that to the Earth’s 23 degrees, or Neptune’s 29. This is a planet that is spinning on its side. Conventional wisdom has it that a massive collision is the culprit, but the problem with that thinking is that such a ‘knockout blow’ would have left the moons of Uranus orbiting at their original angles. What we see, however, is that the Uranian moons all occupy the same 98 degree orbital tilt demonstrated by their parent.
New work unveiled at the EPSC-DPS Joint Meeting in Nantes, France is now giving us some answers to this riddle. A team led by Alessandro Morbidelli (Observatoire de la Cote d’Azur) ran a variety of impact simulations to test the various scenarios that could account for Uranus’ tilt. It turns out that a blow to Uranus experienced when it was still surrounded by a protoplanetary disk would have reformed the entire disk around the new and highly tilted equatorial plane. The result would be a planetary system with moons in more or less the position we see today, as described in this news release.
But this is intriguing: Morbidelli’s simulations also produce moons whose motion is retrograde. The only way to get around this, says the researcher, is to model the Uranian event not as a single impact but as at least two smaller collisions, which would increase the probability of leaving the moons in their observed orbits. Given all this, some of our planet formation theories may need revision. Says Morbidelli:
“The standard planet formation theory assumes that Uranus, Neptune and the cores of Jupiter and Saturn formed by accreting only small objects in the protoplanetary disk. They should have suffered no giant collisions. The fact that Uranus was hit at least twice suggests that significant impacts were typical in the formation of giant planets. So, the standard theory has to be revised.”
The questions thus raised by the ‘planet of doubt’ may prove helpful in understanding how giant planets evolve. More on this when the paper becomes available.