Of all the planets in our solar system, Uranus is arguably one of the most unique and mysterious. Its discovery by astronomer William Herschel in 1781 marked the first location of a planet using a telescope, although ironically, Herschel initially thought the planet had merely been a star, or perhaps a comet.
Subsequent observations by astronomer Johann Elert Bode would eventually confirm the planetary status of the mysterious celestial object, which Herschel proposed naming Georgium Sidus in honor of King George III. The idea was vetoed, and Bode’s choice of naming the planet after the Greek god of the sky won out in the end.
Along with Neptune, Uranus is one of two planets known as ice giants—a planet composed of elements heavier than hydrogen or helium—whose mass is comprised of materials that include methane, ammonia, and water surrounding a rocky core. Despite its status as an “ice giant,” the composition of Uranus is mostly rather warm and fluid, and there is hardly anything about the temperature of its core, which clocks in at an estimated 9,000 degrees Fahrenheit.
Despite this, Uranus remains a cold and windy locale. Possessing the third largest diameter in our solar system, the planet is also curious on account of its rotation at what is almost a 90-degree angle to relative to its orbit. Thus, the plant has the appearance of a “rolling” motion with its orbit, rather than the vertical spin of our own planet.
Uranus is host to 27 small moons, as well as 13 rings which, arguably, are its most curious feature. In fact, some astronomers have called the planet’s rings nearly invisible, and seemingly impossible on account of the way that they seemingly defy the expectations of astronomers.
The planet’s 13 rings are divided into two sets — the inner rings of which are mostly dark and narrow, while its two remaining outer rings are a striking rusty red ring encircled by an outermost ring resembling Saturn’s blue E ring. Belts of dust particulate also rest outside some of the planet’s larger rings.
Despite the fact that so much is known and can be observed about the rings of Uranus, astronomers have experienced ongoing difficulties accounting for their appearance and behavior. One problem has to do with their composition: if the rings are composed of tiny bits of matter, it would have been expected that within a mere few decades that these rings would have continued to spread into a series of much wider rings.
Of course, in the centuries since its discovery, the rings of Uranus appear to have remained intact, although they have only been officially known to exist since 1977 when a trio of astronomers, James Elliot, Jessica Mink and Ted Dunham, made the discovery from aboard the Kuiper Airborne Observatory, which at the time had been fitted with a special infrared telescope. Despite this being the occasion of the “official” discovery of Uranus’s rings, earlier observations date as far back to Herschel, who also claimed to have seen them. In an entry dated February 22, 1789, the astronomer had written of his observations of the planet that “A ring was suspected.” An additional claimed observation of rings encircling Uranus also occurred again in 1847, though this account remains somewhat more questionable.
Indeed, if observations of the rings of Uranus appear to have been made for more than two centuries, it would seem unlikely that they were a recent formation, at least by human standards of the passage of time. Another curiosity has to do with the fact that the rings are nearly invisible, as their “official” discovery required the use of an infrared telescope. Astronomers have long contended that the rings of Uranus should be brighter and easily visible like those of its neighbor, Saturn.
The peculiar darkness of the rings encircling Uranus have prompted some astronomers in the past to consider whether they might actually not be rings at all, but instead tiny single satellites (i.e. moons) producing trace amounts of gas as they coast along in their orbits. This idea, proposed in the later 1970s by Thomas Van Flandern, would seemingly have accounted for some of the curious features noted about the planet’s rings.
Notably, Van Flandern had also been an early proponent of the idea that the so-called “Face on Mars” had indeed been a construction of ancient extraterrestrials and other less conventional ideas related to modern astronomy, and following the Voyager 2 probe’s visit to Uranus in 1986, images clearly detailing the Uranian rings seemed to have confirmed their identity once and for all.
Today, astronomers believe that the rings are indeed a recent formation, celestially speaking. Sometime in the last 600 million years, the rings are likely to have originated from collisions that broke apart several of its past moons, the particulate remains of which are believed to constitute the faint rings that are visible today.
And yet, astronomers still can’t determine what, precisely, holds the rings in place. An early theory bearing some similarity to that of Van Flandern had involved the presence of so-called “shepherd moons” near each ring which exerted enough gravity to help them maintain their placement. However, by 1986 with the Voyager 2 probe’s visit to the planet, only one pair of shepherd moons were detected around the planet’s brightest ring.
Despite our growing body of knowledge about our solar system and its unique qualities, many characteristics of our planetary neighbors remain mysterious, and arguably, Uranus remains a very special case in this regard.
The post The Uranian Mystery: Astronomers Are Still Puzzled by this Ice Giant’s Odd Rings first appeared on Mysterious Universe.