Frozen: Ice on Earth and Well Beyond
Icy Hearts: A heart-shaped calving front of a glacier in Greenland (left) and Plutoâs frozen plains (right). Credits: NASA/Maria-Jose Viñas and NASA/APL/SwRI
From deep below the soil at Earthâs polar regions to Plutoâs frozen heart, ice exists all over the solar systemâŠand beyond. From right here on our home planet to moons and planets millions of miles away, weâre exploring ice and watching how it changes. Hereâs 10 things to know:
1. Earthâs Changing Ice Sheets
An Antarctic ice sheet. Credit: NASA
Ice sheets are massive expanses of ice that stay frozen from year to year and cover more than 6 million square miles. On Earth, ice sheets extend across most of Greenland and Antarctica. These two ice sheets contain more than 99 percent of the planetâs freshwater. However, our ice sheets are sensitive to the changing climate.
Data from our GRACE satellites show that the land ice sheets in both Antarctica and Greenland have been losing mass since at least 2002, and the speed at which theyâre losing mass is accelerating.
2. Sea Ice at Earthâs Poles
Earthâs polar oceans are covered by stretches of ice that freezes and melts with the seasons and moves with the wind and ocean currents. During the autumn and winter, the sea ice grows until it reaches an annual maximum extent, and then melts back to an annual minimum at the end of summer. Sea ice plays a crucial role in regulating climate â itâs much more reflective than the dark ocean water, reflecting up to 70 percent of sunlight back into space; in contrast, the ocean reflects only about 7 percent of the sunlight that reaches it. Sea ice also acts like an insulating blanket on top of the polar oceans, keeping the polar wintertime oceans warm and the atmosphere cool.
Some Arctic sea ice has survived multiple years of summer melt, but our research indicates thereâs less and less of this older ice each year. The maximum and minimum extents are shrinking, too. Summertime sea ice in the Arctic Ocean now routinely covers about 30-40 percent less area than it did in the late 1970s, when near-continuous satellite observations began. These changes in sea ice conditions enhance the rate of warming in the Arctic, already in progress as more sunlight is absorbed by the ocean and more heat is put into the atmosphere from the ocean, all of which may ultimately affect global weather patterns.
Snow extends the cryosphere from the poles and into more temperate regions.
Snow and ice cover most of Earthâs polar regions throughout the year, but the coverage at lower latitudes depends on the season and elevation. High-elevation landscapes such as the Tibetan Plateau and the Andes and Rocky Mountains maintain some snow cover almost year-round. In the Northern Hemisphere, snow cover is more variable and extensive than in the Southern Hemisphere.
Snow cover the most reflective surface on Earth and works like sea ice to help cool our climate. As it melts with the seasons, it provides drinking water to communities around the planet.
Tundra polygons on Alaskaâs North Slope. As permafrost thaws, this area is likely to be a source of atmospheric carbon before 2100. Credit: NASA/JPL-Caltech/Charles Miller
Permafrost is soil that stays frozen solid for at least two years in a row. It occurs in the Arctic, Antarctic and high in the mountains, even in some tropical latitudes. The Arcticâs frozen layer of soil can extend more than 200 feet below the surface. It acts like cold storage for dead organic matter â plants and animals.
In parts of the Arctic, permafrost is thawing, which makes the ground wobbly and unstable and can also release those organic materials from their icy storage. As the permafrost thaws, tiny microbes in the soil wake back up and begin digesting these newly accessible organic materials, releasing carbon dioxide and methane, two greenhouse gases, into the atmosphere.
Two campaigns, CARVE and ABoVE, study Arctic permafrost and its potential effects on the climate as it thaws.
Did you know glaciers are constantly moving? The masses of ice act like slow-motion rivers, flowing under their own weight. Glaciers are formed by falling snow that accumulates over time and the slow, steady creep of flowing ice. About 10 percent of land area on Earth is covered with glacial ice, in Greenland, Antarctica and high in mountain ranges; glaciers store much of the worldâs freshwater.
Our satellites and airplanes have a birdâs eye view of these glaciers and have watched the ice thin and their flows accelerate, dumping more freshwater ice into the ocean, raising sea level.
The nitrogen ice glaciers on Pluto appear to carry an intriguing cargo: numerous, isolated hills that may be fragments of water ice from Plutoâs surrounding uplands. NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Plutoâs most famous feature â that heart! â is stone cold. First spotted by our New Horizons spacecraft in 2015, the heartâs western lobe, officially named Sputnik Planitia, is a deep basin containing three kinds of ices â frozen nitrogen, methane and carbon monoxide.
Models of Plutoâs temperatures show that, due the dwarf planetâs extreme tilt (119 degrees compared to Earthâs 23 degrees), over the course of its 248-year orbit, the latitudes near 30 degrees north and south are the coldest places â far colder than the poles. Ice would have naturally formed around these latitudes, including at the center of Sputnik Planitia.
New Horizons also saw strange ice formations resembling giant knife blades. This âbladed terrainâ contains structures as tall as skyscrapers and made almost entirely of methane ice, likely formed as erosion wore away their surfaces, leaving dramatic crests and sharp divides. Similar structures can be found in high-altitude snowfields along Earthâs equator, though on a very different scale.
This image, combining data from two instruments aboard our Mars Global Surveyor, depicts an orbital view of the north polar region of Mars. Credit: NASA/JPL-Caltech/MSSS
Mars has bright polar caps of ice easily visible from telescopes on Earth. A seasonal cover of carbon dioxide ice and snow advances and retreats over the poles during the Martian year, much like snow cover on Earth.
This animation shows a side-by-side comparison of CO2 ice at the north (left) and south (right) Martian poles over the course of a typical year (two Earth years). This simulation isnât based on photos; instead, the data used to create it came from two infrared instruments capable of studying the poles even when theyâre in complete darkness. This data were collected by our Mars Reconnaissance Orbiter, and Mars Global Surveyor. Credit: NASA/JPL-Caltech
During summertime in the planetâs north, the remaining northern polar cap is all water ice; the southern cap is water ice as well, but remains covered by a relatively thin layer of carbon dioxide ice even in summertime.
Scientists using radar data from our Mars Reconnaissance Orbiter found a record of the most recent Martian ice age in the planetâs north polar ice cap. Research indicates a glacial period ended there about 400,000 years ago. Understanding seasonal ice behavior on Mars helps scientists refine models of the Red Planetâs past and future climate.
8. Ice Feeds a Ring of Saturn
Wispy fingers of bright, icy material reach tens of thousands of kilometers outward from Saturnâs moon Enceladus into the E ring, while the moonâs active south polar jets continue to fire away. Credit: NASA/JPL/Space Science Institute
Saturnâs rings and many of its moons are composed of mostly water ice â and one of its moons is actually creating a ring. Enceladus, an icy Saturnian moon, is covered in âtiger stripes.â These long cracks at Enceladusâ South Pole are venting its liquid ocean into space and creating a cloud of fine ice particles over the moonâs South Pole. Those particles, in turn, form Saturnâs E ring, which spans from about 75,000 miles (120,000 kilometers) to about 260,000 miles (420,000 kilometers) above Saturnâs equator. Our Cassini spacecraft discovered this venting process and took high-resolution images of the system.
Jets of icy particles burst from Saturnâs moon Enceladus in this brief movie sequence of four images taken on Nov. 27, 2005. Credit: NASA/JPL/Space Science Institute
View of a small region of the thin, disrupted, ice crust in the Conamara region of Jupiterâs moon Europa showing the interplay of surface color with ice structures. Credit: NASA/JPL/University of Arizona
The icy surface of Jupiterâs moon Europa is crisscrossed by long fractures. During its flybys of Europa, our Galileo spacecraft observed icy domes and ridges, as well as disrupted terrain including crustal plates that are thought to have broken apart and âraftedâ into new positions. An ocean with an estimated depth of 40 to 100 miles (60 to 150 kilometers) is believed to lie below that 10- to 15-mile-thick (15 to 25 km) shell of ice.
The rafts, strange pits and domes suggest that Europaâs surface ice could be slowly turning over due to heat from below. Our Europa Clipper mission, targeted to launch in 2022, will conduct detailed reconnaissance of Europa to see whether the icy moon could harbor conditions suitable for life.
10. Crater Ice on Our Moon
The image shows the distribution of surface ice at the Moonâs south pole (left) and north pole (right), detected by our Moon Mineralogy Mapper instrument. Credit: NASA
In the darkest and coldest parts of our Moon, scientists directly observed definitive evidence of water ice. These ice deposits are patchy and could be ancient. Most of the water ice lies inside the shadows of craters near the poles, where the warmest temperatures never reach above -250 degrees Fahrenheit. Because of the very small tilt of the Moonâs rotation axis, sunlight never reaches these regions.
A team of scientists used data from a our instrument on Indiaâs Chandrayaan-1 spacecraft to identify specific signatures that definitively prove the water ice. The Moon Mineralogy Mapper not only picked up the reflective properties weâd expect from ice, but was able to directly measure the distinctive way its molecules absorb infrared light, so it can differentiate between liquid water or vapor and solid ice.
With enough ice sitting at the surface â within the top few millimeters â water would possibly be accessible as a resource for future expeditions to explore and even stay on the Moon, and potentially easier to access than the water detected beneath the Moonâs surface.
11. Bonus: Icy World Beyond Our Solar System!
With an estimated temperature of just 50K, OGLE-2005-BLG-390L b is the chilliest exoplanet yet discovered. Pictured here is an artistâs concept. Credit: NASA
OGLE-2005-BLG-390Lb, the icy exoplanet otherwise known as Hoth, orbits a star more than 20,000 light years away and close to the center of our Milky Way galaxy. Itâs locked in the deepest of deep freezes, with a surface temperature estimated at minus 364 degrees Fahrenheit (minus 220 Celsius)!
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