Tiny grit making up much of one of Saturn’s rings may have come from the planet’s moon Enceladus (En-SELL-ah-dus). These mineral particles likely formed in scalding water bubbling from rock below the moon’s ice-capped ocean, new lab studies suggest.
In Earth’s oceans, that sort of heating shows up at sites known as hydrothermal vents. There, openings in hot rock release plumes of scalding water. Similar vents also may occur deep below the ocean on Enceladus, researchers now conclude. If true, that might mean conditions there could support life.
Hsiang-Wen Hsu is a planetary scientist at the University of Colorado Boulder. He and his colleagues used data collected by NASA’s Cassini spacecraft. It has orbited Saturn since 2004. Hsu’s team measured the size and makeup of tiny grit detected in Saturn’s E ring. This ring is the second in from the outer edge, and one of Saturn’s widest. Tiny grains of silicon dioxide — also called silica — make up most of this ring’s particles, the researchers found.
Finding silica was an important clue. It often develops when rock comes into contact with water.
To recreate this process in the lab, Hsu’s team started with a powdery mix of minerals. All are common in asteroids and comets. Under heat and pressure, the scientists left the mix to stew in cocktails of water, ammonia and sodium bicarbonate. (That last chemical is also known to cooks as baking soda.) After several months, different concentrations of silica had formed.
Next, Hsu’s group identified what chemical reactions had cooked up the silica. The experts also calculated the lowest temperature at which the silica could form. Their answer: 90° Celsius (194° Fahrenheit). That is nearly boiling. The new results suggest a huge source of heat must reside at the seafloor of the ocean on Enceladus.
Hsu and his coworkers shared their findings in the March 12 issue of Nature.
Once formed on the ocean floor, the silica bits probably travel upward toward the surface of the ocean on Enceladus. From there, warm plumes of water erupt from the ocean through cracks in the moon’s icy shell. Those geysers likely blast silica grit into space.
“This is an extraordinary claim,” says Christopher Glein. A geochemist at the University of Toronto in Canada, he did not work on the new study. Glein agrees that the silica likely formed through the interaction of rock and water on Enceladus. Still, he has doubts about whether the moon is hydrothermally active and generating its own heat.
It is hard to produce such high temperatures on Enceladus, he explains. The most likely source of the heat inside this moon is friction. The gravity of Saturn squishes and stretches the moon. That morphing generates a lot of heat. Still, it is not enough to bring things close to a boil, he suspects.
One way to test Hsu’s claim would be to look for molecular hydrogen (H2). On Earth, seawater interacts with rock at some hydrothermal vents to produce high concentrations of this molecule. If there is hydrothermal activity on Enceladus, Cassini could detect H2 in its geysers, says Glein.
It may turn out the water on Enceladus isn’t that hot. But that won’t necessarily rule out this moon as a host for simple life. Whenever water and rock mix on Earth, no matter what the temperature, energy becomes available that life can use, Glein says. Adding heat only creates more opportunities. “Organisms like to take advantage of those situations,” Glein says.
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ammonia A colorless gas with a nasty smell. Ammonia is a compound made from the elements nitrogen and hydrogen. It is used to make food and applied to farm fields as a fertilizer. Secreted by the kidneys, ammonia gives urine its characteristic odor. The chemical also occurs in the atmosphere and throughout the universe.
asteroid A rocky object in orbit around the sun. Most orbit in a region that falls between the orbits of Mars and Jupiter. Astronomers refer to this region as the asteroid belt.
comet A celestial object consisting of a nucleus of ice and dust. When a comet passes near the sun, gas and dust vaporize off the comet’s surface, creating its trailing “tail.”
debris Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.
friction The resistance that one surface or object encounters when moving over or through another material (such as a fluid or a gas). Friction generally causes a heating, which can damage the surface of the materials rubbing against one another.
geochemistry A science that deals with the chemical composition of and chemical changes in the solid material of Earth or of another celestial body (such as the moon or Mars). Someone who works in this field is known as a geochemist.
geyser A vent (opening) in Earth’s surface that intermittently sends up a tall spray of steam and/or hot water. The sometimes explosive discharge of water and steam is propelled by the geothermal heating of water below ground.
gravity The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.
hydrogen The lightest element in the universe. As a gas, it is colorless, odorless and highly flammable. It’s an integral part of many fuels, fats and chemicals that make up living tissues.
hydrothermal vent Openings at the bottom of the ocean or a lake where hot water emerges from deep inside the earth. The water is rich in minerals and chemicals that can nourish ecosystems of worms, clams, microbes and other organisms.
mineral The crystal-forming substances, such as quartz, apatite, or various carbonates, that make up rock. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in certain regular three-dimensional patterns).
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
NASA (National Aeronautics and Space Administration) Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It has also sent research craft to study planets and other celestial objects in our solar system.
organism Any living thing, from elephants and plants to bacteria and other types of single-celled life.
planet A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and it must have cleared other objects out of the way in its orbital neighborhood. To accomplish the third feat, it must be big enough to pull neighboring objects into the planet itself or to sling-shot them around the planet and off into outer space. Astronomers of the International Astronomical Union (IAU) created this three-part scientific definition of a planet in August 2006 to determine Pluto’s status. Based on that definition, IAU ruled that Pluto did not qualify. The solar system now consists of eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
plume The movement of some gas or liquid, under the direction of gravity, winds or currents. It may be in air, soil or water. It gets its name from the fact that it tends to be long and relatively thin, shaped like a large feather.
reactive (in chemistry) The tendency of a substance to take part in a chemical process, known as a reaction, that leads to new chemicals or changes in existing chemicals.
Saturn The sixth planet out from the sun in our solar system. One of the four gas giants, this planet takes 10.7 hours to rotate (completing a day) and 29 Earth years to complete one orbit of the sun. It has at least 53 known moons and 9 more candidates awaiting confirmation. But what most distinguishes this planet is a broad and flat plane of seven rings that surrounds it.
silica A mineral, also known as silicon dioxide, containing silicon and oxygen atoms. It is a basic building block of much of the rocky material on Earth and of some construction materials, including glass.
silicon A nonmetal, semiconducting element used in making electronic circuits. Pure silicon exists in a shiny, dark-gray crystalline form and as a shapeless powder.
sodium bicarbonate Also known as baking soda, this white, chemical powder occurs naturally. Its formula is NaHCO3. It also has been used as a natural product to extinguish small electrical and grease fires. When ingested, this chemical can help settle upset stomachs. Indeed, it is the main ingredient of many antacids sold in grocery stores.