by Gideon Marcus
Every so often, serendipity chooses what I write about. Last month, the Traveler family Journeyed to the Seventh Planet in film. Then, the Good Doctor wrote about the giant planet in his science fact article in The Magazine of Fantasy and Science Fiction. And now, in this month's Galaxy, Willy Ley tells of the origin of the the names of our celestial neighbors, Uranus included.
And there's a 7th Planet-sized gap in my series on the planets of the solar system. Who am I to fight fate?
How much could we know about a world that is twice as far away from us as Saturn? The answer is at once "more than you'd think" and "less than we'd like."
Uranus is a small green disc when viewed through a telescope. In fact, the planet is technically visible with the naked eye, but it is so small that it is no surprise that it wasn't discovered until 1781. Over the course of several late-Winter nights, a German expatriate living in England named William Herschel saw the fuzzy circle of Uranus slowly travel among the fixed tableau of the stars. He thought he'd found a comet. But its orbit and characteristics made it apparent that it was, in fact, the first new planet discovered in thousands of years.
Herschel tried to name the planet after his King, George III, just as Galileo had tried to name the Jovian moons he had discovered after his sovereigns, the De Medici family. Others tried to name the planet after Herschel, himself! In the end, a name of classical derivation won out – and what more fitting name than the father of Saturn, who was, himself, father of Jupiter, who was father of Mercury, Venus, and Mars?
Uranus hugs the ecliptic, the plane of the solar system, more closely than any of the other planets. Using older observations of Uranus from before the object was recognized as a planet, astronomers quickly determined the new planet's year: 84 years. We are fortunate that Uranus has moons (five of them, the latest discovered just 14 years ago), for we are able to determine the mass of the planet from the length of time it takes for the moons to orbit their parent. There are 15 Earths of mass in the planet, the least of the four giant planets. Nevertheless, you could fit 60 Earths inside Uranus. That makes it the second-smallest in volume (Neptune has a volume of 40 Earths).
You can tell how long the day of a planet is using a spectroscope, which breaks up light into its component wavelengths. The waves of light coming from the side of a planet rotating toward us are compressed and made bluer. The side going away reflects redder light. This is the Doppler Effect – the same phenomenon that makes train whistles seem to rise and fall as the locomotives approach and recede. Uranus' day is just under 11 hours long. This is slightly longer than Saturn's, and shorter than Neptune's.
So in terms of raw physical characteristics, Uranus is kind of a middlin' gas giant. But there is one feature that makes it absolutely unique among the planets. Thanks again to the trek of Uranus' moons, we know that the planet is tipped way over on its side with respect to the ecliptic – a whopping 98 degrees! Compare that to Earth's slightly wobbled 23 degrees. As you may know, this tilt is responsible for our planet's seasons; imagine what kind of severe seasons Uranus must have! The Poles of the seventh planet are in perpetual sunlight for 21 years, in darkness for the same amount of time.
Exploring the Planets, 1958, Roy A. Gallant
An observer on the surface of Uranus, if such a thing exists, probably wouldn't be able to tell the difference. There is a 3000 mile thick atmosphere that we know contains methane, thanks again to the spectroscope. Below that is an ocean of increasingly slushy hydrogen some 6000 miles thick. By the time you get to solid ground, whatever that be made of, you can be sure that no light penetrates. As at the bottom of terrestrial oceans, the surface of Uranus must be seasonless.
Now, while the edge of Uranus' atmosphere is a chilly 300 degrees below zero (Fahrenheit), it is certain that things heat up as one goes deeper into the pressure cooker of the planet's gaseous envelope. It is even possible that an ocean of water floats at some level of the giant's composition, though we'll never know until we go there.
Exploring the Planets, 1958, Roy A. Gallant
The last bit we know about Uranus is a piece of negative information. Over the last decade or so, we have turned the giant dishes pf radio telescopes toward the heavens and discovered all sorts of staticy emanations, some associated with things we can see, and some appearing to radiate from nowhere. Jupiter, it turns out, is a chatty subject on the radio. Uranus, however, is not.
By the way, my favorite aspect of Uranus is the naming of its moons. They are (closest in to farthest out) Miranda, Ariel, Umbriel, Titania, and Oberon. Unlike Jove's mistresses that orbit Jupiter and the elder Titans that circle Saturn, Uranus' moons are named after the literary creations of Shakespeare and Pope. The most ancient of Gods is thus attended by some of humanity's more recent fairies.
There you have it: virtually the entire sum of knowledge we have about the 7th planet. Not a whole lot for nearly 200 years of observation. However, I suspect that, with powerful rockets like the Saturn at our disposal, it won't be long before Uranus gets a new moon, one with a NASA sticker (or perhaps, a Sickle and Hammer) on the side. Then we'll truly learn about this mysterious, grand, tipped-over world.
Classics Illustrated. Illustrated by Torres, Angelo, Kirby, Jack, and Glanzman, Sam. To the Stars!