Robotic explorers have found signs of long-lost water on Mars and extensive ice still present on the dwarf planet Ceres — evidence that water truly is almost everywhere we look.
The results were announced last week at the fall meeting of the American Geophysical Union — the world's largest gathering of Earth and space scientists. There, NASA scientists discussed the results from several of the dozen space probes currently exploring the universe beyond our planet.
Curiosity finds boron on Mars
The rover Curiosity has been trundling across the Martian landscape for more than four years. But recently, the plucky robot rolled onto a patch of ground with veins of calcium sulfate, in the form of the mineral gypsum, running through it. Hiding within those veins was the element boron, which usually appears only in once-flooded sites where the water has evaporated away.
According to scientists at the Los Alamos National Laboratory, the discovery in Mars's Gale Crater suggests that there was once liquid water on the Red Planet — and that the water was habitable. The calcium sulfate and boron could only precipitate out of water that was between 32 and 140 degrees Fahrenheit and was not too acidic.
The boron was identified by a ChemCam built at Los Alamos. The camera works by shooting a laser at a rock, exciting the electrons of the atoms within it. Those electrons then emit distinctive wavelengths of light, depending on the element; by reading the spectrum that shines back at it, the instrument can figure out what elements the rock contains.
This was the first discovery of boron on Mars, and the latest finding suggesting that Mars used to be much wetter, warmer and far less hostile than it is now.
Gale crater — a 100-mile-wide canyon with Denali-sized Mount Sharp at its center — is thought to be the site of a former lake. As Curiosity climbs the slopes of Mount Sharp, it has found varying levels of clay, boron and other types of rock. These variations could hint at the lake environment that may have existed there billions of years ago.
“There is so much variability in the composition at different elevations, we’ve hit a jackpot,” Caltech geologist John Grotzinger, Curiosity's chief scientist, said in a statement.
Scientists have been seeking evidence of past or present life on Mars for four decades, without success. But the boron finding adds to the evidence that the planet may have had the kinds of dynamic environments that are known to support organisms on Earth.
“A sedimentary basin such as this is a chemical reactor,” Grotzinger said. “Elements get rearranged. New minerals form and old ones dissolve. Electrons get redistributed. On Earth, these reactions support life.”
Dawn detects hidden ice on Ceres
In the asteroid belt between Mars and Jupiter, the space probe Dawn has been surveying the rocky, icy body known as Ceres. The dwarf planet is the largest thing in the asteroid belt, and it's pocked with craters deep enough that their interiors are cast in permanent shadow.
Dawn scientists announced at AGU that they have new evidence that some of Ceres's craters act as cold traps that accumulate pockets of permanent water ice. In addition, the protoplanet has huge amounts of ice just below its rocky surface and may even have a slushy ocean of liquid water in its interior.
This means that Ceres is less like fellow asteroid-belt inhabitant Vesta, a dry rocky world that Dawn visited before the current phase of its mission, than it is like the icy moons that exist in the outer part of the solar system.
“It's pointing toward Ceres being a really interesting object,” Carol Raymond, Dawn's deputy principal investigator, said at a news conference. “Similar to Europa or Enceladus in terms of its habitability potential.”
Europa and Enceladus, moons of Jupiter and Saturn, respectively, are thought to contain liquid water oceans in their interiors and are considered prime targets in the search for life beyond Earth.
During its approach in early 2015, Dawn spotted two extremely bright spots inside craters that looked as if they could be highly reflective ice. But further investigation revealed that the bright patches contained salt, not water — drying up NASA's hopes that Ceres might be a wet place.
But the dwarf planet does have about 600 other “persistently shadowed regions” — craters whose interiors never see the sun. Astrobiologist Norbert Schörghofer called them “Ceres' darkest secrets.” Once Dawn arrived in orbit, it was able to probe these secret spots — and found that they did have water ice hiding within them.
Ice has been found in craters on other worlds, like Mercury and the moon, but that water was thought to have arrived via impacts from space. The origins of Ceres's crater ice is more mysterious. One theory is that it comes from water frozen in Ceres's crust.
A second investigation by Dawn found that the dwarf planet has huge amounts of hydrogen in the form of frozen water (water molecules have two atoms of hydrogen and one oxygen). This ice is hiding just below the surface, filling pores in the planet's rocky crust. Data from Dawn suggests that about 10 percent of the weight of the planet's top meter of material comes from ice.
The discovery of abundant ice supports the idea that Ceres once held liquid water that was heated by a radioactive core. As the body cooled, Ceres's heavier rocks fell to the interior, while lighter water rose to the surface, then froze.
Dawn scientists say that further investigation of this ice could reveal clues about Ceres's past and the role of water in the early history of the solar system.
“By finding bodies that were water-rich in the distant past, we can discover clues as to where life may have existed in the early solar system,” Raymond said in a statement.