The Freakiest Places in the Solar System
1. WEIRDEST ROTATION
The Saturnian moon Hyperion is a lumpy thing, measuring about 255 x 163 x 137 miles in diameter along its three axes. Since moons of this size typically have enough gravity to pull them into a spherical shape, astronomers suggest that it may be a fragment of a larger moon that was shattered by an impact. The planet’s odd shape explains why the planet is, as Baker and Ratcliff put it, “a tumbling chaotic mess.” Most large moons are tidally locked, meaning that the same face of the moon always faces its planet. But Hyperion’s bizarre shape prevents such locking, because the gravitational torques from Saturn and the moon Titan tug at it unevenly.
Picture a canyon that stretches from San Francisco to Washington DC, and you’ll have an idea of the scope of Valles Marineris on Mars.
This enormous gorge was first spotted by the NASA spacecraft Mariner 9 in 1972, and the canyon was named in the spacecraft’s honor. It stretches 2,485 miles across the planet’s surface, and reaches depths of 6.2 miles (for comparison, our Grand Canyon plunges 1.1 miles down at its deepest point). Valles Marineris is thought to be a rift valley, formed by uplift when hot material from the Mars’s mantle bubbled up and stretched the planet’s crust.
The result: A rotation that’s impossible to predict. “The days are never the same,” the authors write. “Not only does the rotation rate (the length of day) vary erratically, but Hyperion’s north pole continually points to a different location in space.” Astronomers know the equation to predict the moon’s rotational motion, but small uncertainties in measurements of the moon’s initial location or velocity turn into large uncertainties over time. For Hyperion, the authors say, “it is completely impossible to predict the direction of its spin axis after about 300 days—it could be pointed anywhere!”
The Jovian moon Io is fascinating from a planetary science perspective—it’s the most volcanically active place in our solar system, and its surface is pockmarked with volcanic craters. But it wouldn’t be much fun to visit. Baker and Ratcliff write that “Jupiter’s moon Io smells like a jumbo rotten egg.” The stink is due to hydrogen sulfide on Io’s surface and in its upper atmosphere, and the moon owes its distinctive yellow and red coloration to sulfur compounds.
Volcanic eruptions are quite common on Io, and they constantly refresh the atmosphere’s supply of sulfur gas. The moon is highly active because it travels around Jupiter in a slightly elliptical orbit. As the moon repeatedly dances closer to and farther from the giant planet, Jupiter’s gravity produces tidal flexing in the moon’s interior that heats its mantle and causes violent explosions. In 2007 NASA’s New Horizons spacecraft flew by Io and observed a volcanic eruption with sulfur plumes that stretched 180 miles above the surface. The largest volcanic eruptions on Earth reach about 12 miles high.
This storm shows no inclination of blowing itself out. Jupiter’s Great Red Spot was first observed by the Italian astronomer Giovanni Cassini in 1665; while observations were sporadic in the 18th and early 19th centuries, many astronomers think the storm has been roaring for the 345 years since it was first seen. The immense storm is the size of three Earths, and the winds reach speeds topping 400 miles per hour.
How has it kept churning through the centuries? Baker and Ratcliff explain that its energy comes from Jupiter’s interior and smaller vortices. “Remarkably, Jupiter’s interior supplies 70 percent more energy to the cloud tops than the planet receives from the Sun,” they write. “Like a giant air compressor, gravitational contraction generates intense pressures and heat deep inside the planet. Powerful thunderstorms in Jupiter’s atmosphere channel much of this heat to the cloud tops.” Smaller storms are devoured by the Great Red Spot, which allows it to roar on.
Roll Cloud, Shelf Cloud
“Pink Meanie” Jellyfish
Photograph courtesy Don Demaria
Off the Florida Keys (map), hundreds of stinging tentacles dangle from a “pink meanie”—a new species of jellyfish with a taste for other jellies that was discovered in January.
Like other species in the genus Drymonema, the new jelly has an appetite for moon jellyfish, which the predators feed on almost exclusively as adults.
Adult Drymonema do the majority of their digestion using specialized “oral arms” that dangle alongside their tentacles. The oral arms exude digestive juices, which break down the prey, scientists said in January.
Published November 28, 2011