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.
{ 6 comments… read them below or add one }
Can someone explain why the explanation has to be an impact and cannot just be “wobble” due to [transient] non uniform composition? Is it a matter of the size of the forces, or the time needed to deliver the change, or some completely different factor?
Alex
I do not know… conservation of angular moment perhaps? The angle of the proto planetary disk would have defined the angle of the spin ( axis perpendicular to the disk) and assuming the disk was in a near circular orbit, the speed of the spin should have to do with the mass of the accumulated body, and the distance from the center of gravity of the disk ( where the sun was forming), and the total mass and distribution of matter in the protodisk. looking at the rest of the planets, things look pretty regular.
I’m curious if anyone has ever run the math on the results of an extrasolar body passing through the protoplanetary disk. It seems intuitive that a brown dwarf or “rogue planet” passing through could have tugged Uranus’ axis into its inclination if approaching from galactic north to south through the disk. It would also seem that this would result in reduced mass for moon formations as the body would attract material out of the solar system with it, which seems to be the case according to the wikipedia article: “The Uranian satellite system is the least massive among those of the gas giants.” [http://en.wikipedia.org/wiki/Moons_of_Uranus#Characteristics_and_groups]
Any thoughts on other possible effects of this scenario?
@jkittle
Except that it was noted that the impact with Uranus also shifted the satellite orbits with its axial change, which conventionally shouldn’t happen with simple models of dynamics and conservation of momentum.
Alex – so true.
Perhaps the moons are debris from the collision. it there were two collisions one might see two distinct populations of satellites.
We need to observe more solar systems to figure out how this all works.
I am waiting so see if they can identify any moons of some of these extra- solar gas giants that seem so ubiquitous among the stars.
For Saturn and Jupiter the interiors are hot enough they is probably no solid surface, below the think hydrogen helium atmospheres. Is it possible Uranus has a LIQUID and /or solid surface as one goes deeper? What about Neptune? given the lower gravity and temperature why are we not considering the possibility of ( microbial) life in the complex oceans of these “ice giants?”
Astrophoto: The Distant Worlds of Uranus and Neptune by Rolf Wahl Olsen
by Dianne Castaneda on October 9, 2011
Rolf Wahl Olsen captured this photo of the Uranus and Neptune system on October 3, 2011. Uranus and Neptune are currently the two farthest planets from the Sun after Pluto was demoted to a dwarf planet.
“The image was taken with my 10″ f/5 Serrurier truss Newtonian and is a composite of short exposures for the planet discs and longer exposures for the fainter moons. Miranda, the smallest of Uranus’ five larger moons, was very close to Uranus when the image was taken and therefore lost in the glare of the planet itself in the long exposure image used to capture the moons. The orbits of the moons were added to illustrate the scale and orientation of the two systems as viewed from Earth, with South being towards the top of the image.
Both Uranus and Neptune are so far away from us that their angular diameters are only a few arcseconds, being 3.7″ and 2.3″ respectively. This makes it extremely difficult to discern any details on then and they nearly always appear as tiny cyan/blue balls except when imaged by large observatories or the Hubble Space Telescope. In fact, the entire orbit of Triton would easily fit behind the disc of Mars when the latter is at opposition. Still, with relatively modest equipment it is possible to get a good glimpse of these fascinating icy worlds.”
http://www.universetoday.com/89445/astrophoto-the-distant-worlds-of-uranus-and-neptune-by-rolf-wahl-olsen/