Tallest, deepest, hottest, weirdest: Our solar system is a place of extremes. In a new book, The 50 Most Extreme Places in Our Solar System, authors David Baker and Todd Ratcliff take readers on a sightseeing tour of gas giants, icy moons, and the heat-blasted inner planets. Here we present a sampling of our favorite extraordinary locales.
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.
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!"
Here on Earth we're impressed by the Pacific Ocean's Marianas Trench, which reaches a depth of 6.8 miles. But the ocean on the Jupiter moon of Europa put ours to shame. Although Europa is covered in a thick crust of scarred and cross-hatched ice, measurements made by NASA's Galileo spacecraft and other probes strongly suggest that a liquid ocean lies beneath that surface. Some measurements put the ocean's depth at 62 miles. The interior is warmed, researchers believe, by the tidal stresses exerted on Europa by Jupiter and several other large moons, as well as by radioactivity.
Europa's huge liquid ocean makes it one of the most promising places to look in the search for extraterrestrial life. NASA and the European Space Agency are therefore hard at work on a joint mission that may launch in 2020, and which will examine Jupiter, Europa, and another moon named Ganymede. A major objective is to determine the thickness of Europa's ice crust, which has implications for the moon's potential to sustain life.
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.
Even Bob Dylan never imagined a hard rain like this.
The ice giant planets Uranus (left) and Neptune (right) differ from the gas giants Jupiter and Saturn in composition; they contain mostly "ices" of water, ammonia, and methane. And that makes for interesting planetary interiors: In the mantles of Neptune and Uranus, high temperatures probably break methane into its components of hydrogen and carbon. Astronomers think that intense pressures may then squeeze the free carbon into crystalline latices, aka diamonds. As Baker and Ratcliff explain: "Diamond hail, as small as salt grains or as large as boulders, may steadily rain through the liquid mantle and pummel the rocky core. The core may be covered in a thick layer of diamonds, more massive than any diamond mine on Earth."
So far, the diamond rains of Uranus and Neptune are theoretical, and planetary scientists say they need more data before they can determine whether or not this bizarre phenomenon actually occurs. Unfortunately, no spacecraft are currently scheduled to go and explore these remote worlds.
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.
Mars has not only the deepest valley in our solar system, but also the mightiest mountain. The Martian volcano Olympus Mons reaches a towering height of 27 miles, or three times the height of our own Mount Everest.
This prodigious peak probably formed in the same way that our own volcanoes do: by sitting over a "hot spot" where plumes of hot rock rise up from the planet's interior. But it was able to grow taller than any earthly volcano because Mars lacks plate tectonics, Baker and Ratcliff explain. On Earth, the tectonic plates act like "a conveyor belt over a hot flame," they write. "Volcanoes form, die out, and form anew as the plate moves over the hot spot, producing a long chain of volcanoes." With no moving plates on Mars, Olympus Mons likely sat above a hot, volcano-forming plume for a very long time.
When NASA's Cassini spacecraft was on its way to Saturn in the late 1990s it swung by Earth for a gravitational assist. From a distance of 55,000 miles above the Earth's surface, the probe detected the radio wave bursts that are a signal of terrestrial lightning. (A lightning bolt emits electromagnetic radiation at a variety of wavelengths, including visible light and radio waves.) As Cassini continued to head toward Saturn in the early 2000s, the spacecraft's controllers got a shock. From 100 million miles away, the probe detected radio pulses indicating powerful lightning storms of Saturn. The radio signal was about a million times more powerful than the one it received from Earth.
For years the Saturnian superbolts weren't seen directly, but the radio busts indicated that they occur in a region called Storm Alley in the planet's southern hemisphere. This image shows one bright tempest in that area, the so-called Dragon Storm. Finally, this spring, Cassini captured the first images of lightning flashes on Saturn.
This beautiful image shows our magnetically hyperactive sun, ornamented with bright solar flares, arcs, and plasma streamers. The electrically charged plasma in the sun's outer layers creates turbulent bubbles the size of Texas, which generate local magnetic fields.
These magnetic field structures are often outlined by glowing plasma, because charged particles flow along magnetic field lines. That's why bright filaments outline sunspots, which are regions where plasma is trapped by intense magnetic fields, and cools down. Where magnetic field lines cross, they can release tremendous bursts of energy known as solar flares and even larger blasts called coronal mass ejections (CMEs). A single CME can fling as much as 10 percent of the sun's corona (its outer atmosphere) into space at intense speeds.
Our sister planet Venus is about the same size, density, and composition as Earth, and when its thick atmosphere was first discovered, alien-hunters wondered if it harbored lush jungles and exotic life. In fact, Venus is a hellishly hot world governed by clouds of sulfuric acid.
Venus is 26 million miles closer to the sun than Earth, but that's not the only reason it's so blazingly hot. The planet has been baked by runaway global warming. In the greenhouse effect, solar radiation reaches the planet's surface, and the planet releases some of that energy by emitting infrared radiation. But on Venus, the thick clouds and a dense atmosphere that's composed primarily of carbon dioxide trap the heat and prevent it from escaping into space. Venus's surface temperature is 860 degrees Fahrenheit, making it the hottest planetary surface in our solar system.
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.