Universe Today

Image credit: NASA/JPL

It turns out that Mars has been hiding its water underneath a layer of dry ice. By tracking the seasonal changes at Mars northern ice cap, NASA’s Mars Odyssey spacecraft has watched how a layer of carbon dioxide permafrost comes and goes. When the permafrost dissipates in the Spring, Mars reveals a soil layer mixed with large amounts of water ice. In some places, the water ice content is more than 90% by volume. During the winter, the dry ice permafrost can reach more than a metre in thickness.

NASA’s Mars Odyssey spacecraft is revealing new details about the intriguing and dynamic character of the frozen layers now known to dominate the high northern latitudes of Mars. The implications have a bearing on science strategies for future missions in the search of habitats.

Odyssey’s neutron and gamma-ray sensors have tracked seasonal changes as layers of “dry ice” (carbon-dioxide frost or snow) accumulate during northern Mars’ winter and then dissipate in the spring, exposing a soil layer rich in water ice– the martian counterpart to permafrost.

Researchers used measurements of martian neutrons combined with height measurements from the laser altimeter on another NASA spacecraft, Mars Global Surveyor, to monitor the amount of dry ice during the northern winter and spring seasons.

“Once the carbon-dioxide layer disappears, we see even more water ice in northern latitudes than Odyssey found last year in southern latitudes,” said Odyssey’s Dr. Igor Mitrofanov of the Russian Space Research Institute (IKI), Moscow, lead author of a paper in the June 27 issue of the journal Science. “In some places, the water ice content is more than 90 percent by volume,” he said. Mitrofanov and co-authors used the changing nature of the relief of these regions, measured more than 2 years ago by the Global Surveyor’s laser altimeter science team, to explore the implications of the changes.

Mars Odyssey’s trio of instruments, called the gamma-ray spectrometer suite, can identify elements in the top meter (3 feet) or so of Mars’ surface. Mars Global Surveyor’s laser altimeter is precise enough to monitor meter-scale changes in the thickness of the seasonal frost, which can accumulate to depths greater than a meter. The new findings show a correlation in the springtime between Odyssey’s detection of dissipating carbon dioxide in latitudes poleward of 65 degrees north and Global Surveyor’s measurement of the thinning of the frost layer in prior years.

“Odyssey’s high-energy neutron detector allows us to measure the thickness of carbon dioxide at lower latitudes, where Global Surveyor’s altimeter does not have enough sensitivity,” Mitrofanov said. “On the other hand, the neutron detector loses sensitivity to measure carbon-dioxide thickness greater than one meter (3 feet), where the altimeter obtained reliable data. Working together, we can examine the whole range of dry-ice snow accumulations.”

“The synergy between the measurements from our two ‘eyes in the skies of Mars’ has enabled these new findings about the nature of near-surface frozen materials, and suggests compelling places to visit in future missions in order to understand habitats on Mars,” said Dr. Jim Garvin, NASA’s Lead Scientist for Mars Exploration.

Another report, to be published in the Journal of Geophysical Research-Planets, combines measurements from Odyssey and Global Surveyor to provide indications of how densely the winter layer of carbon-dioxide frost or snow is packed at northern latitudes greater than 85 degrees. The Odyssey data are used to estimate the mass of the deposit, which can then be compared with the thickness to obtain a density. The dry-ice layer appears to have a fluffy texture, like freshly fallen snow, according to the report by Dr. William Feldman of Los Alamos National Laboratory, N.M., and 11 co-authors. The study also found that once the dry ice disappears, the remaining surface near the pole is composed almost entirely of water ice.

“Mars is constantly changing,” said Dr. Jeffrey Plaut, Mars Odyssey project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. With Mars Odyssey, we plan to examine these dynamics through additional seasons, to watch how the winter accumulations of carbon dioxide on each pole interact with the atmosphere in the current climate regime.”

Mitrofanov’s co-authors include researchers at the Institute for Space Research of the Russian Academy of Science, Moscow; MIT, Cambridge, MA; NASA’s Goddard Space Flight Center, Greenbelt, Md.; TechSource, Santa Fe, N.M.; and NASA Headquarters, Washington. Feldman’s co-authors include researchers at New Mexico State University, Las Cruces; Cornell University, Ithaca, N.Y.; and Observatoire Midi-Pyrenees, Toulouse, France.

JPL manages the Mars Odyssey and Mars Global Surveyor missions for NASA’s Office of Space Science in Washington. Investigators at Arizona State University, the University of Arizona, and NASA’s Johnson Space Center, Houston, built and operate Odyssey science instruments. The Russian Aviation and Space Agency supplied the high-energy neutron detector and Los Alamos National Laboratory supplied the neutron spectrometer. NASA’s Goddard Space Flight Center supplied Global Surveyor’s laser altimeter. Information about NASA’s Mars exploration program is available online at: http://mars.jpl.nasa.gov

Original Source: NASA/JPL News Release

Image credit: Ron Wayman

Earth and Mars are rapidly converging, and are expected to reach their closest point on August 27, 2003. Already amateur astronomers with modest telescopes are reporting they can see features on the surface of Mars with greater clarity, including the planet’s polar ice caps. On August 27, the two planets will only be 56 million km apart; the closest they’ve been for 60,000 years. The planet is currently visible in the morning sky, but over the course of the summer it will move to the point that it’s easy to spot in the evening sky – it’ll be hard to miss since it’ll be nearly the brightest object in the sky.

Count slowly: one one-thousand, two one-thousand, three one-thousand…. You just got about 30 km closer to the planet Mars.

Earth and Mars are rapidly converging. On August 27, 2003–the date of closest approach–the two worlds will be 56 million km apart. That’s a long way by Earth standards, but only a short distance on the scale of the solar system. NASA, the European Space Agency and Japan are all sending spacecraft to Mars this year. It’s a good time to go.

Between now and August, Mars will brighten until it “blazes forth against the dark background of space with a splendor that outshines Sirius and rivals the giant Jupiter himself.” Astronomer Percival Lowell, who famously mapped the canals of Mars, wrote those words to describe the planet during a similar close encounter in the 19th century.

Already Mars is eye-catching. You can see it this month in the morning sky–bright, steady and remarkably red. Only Venus near the sun is brighter.

Amateur astronomers looking through backyard telescopes have reported in recent days great views of Mars’s south polar cap. Made of frozen water and carbon dioxide (“dry ice”), it reflects sunlight well. “I can see the polar ice vividly using my 8-inch telescope,” says Ron Wayman of Tampa, Florida. He’s also spotted “some faint darker-shaded areas on the surface.”

Such markings will become clearer in the weeks ahead. On June 1st Mars was 12.5 arcseconds across and it glowed like a -1st magnitude star. On August 27th it will be twice as wide (25 arcseconds) and six times brighter (magnitude -2.9).

Much has been made of the fact that the August 27th encounter with Mars is the closest in some 60,000 years. Neanderthals were the last to observe Mars so favorably placed. This is true. It’s also a bit of hype. Mars and Earth have been almost this close many times in recent history.

Some examples: Aug. 23, 1924; Aug. 18, 1845; Aug. 13, 1766. In each case Mars and Earth were approximately 56 million km apart.

Astronomers call these close encounters “perihelic oppositions.” Perihelic means Mars is near perihelion–its closest approach to the sun. (The orbit of Mars, like that of all planets, is an ellipse, so the distance between the sun and Mars varies.) Opposition means that the sun, Earth and Mars are in a straight line with Earth in the middle. Mars and the sun are on opposite sides of the sky. When Mars is at opposition and at perihelion–at the same time–it is very close to Earth.

August 27th is indeed the best perihelic opposition since the days of the Neanderthals, but it scarcely differs from other more recent ones. That’s fine because all perihelic oppositions of Mars are spectacular.

Mars is a morning planet now. You have to wake up early to see it. Soon, though, it will be more conveniently placed. By mid-July Mars will rise in the east around 11 p.m. local time. In late August it will appear as soon as the sun sets. It won’t be long before everyone can see Mars at a civilized hour.

We’ll be telling more stories about Mars in the weeks ahead. This one, though, is finished. Did you make it to the end? Congratulations! You’re now 2000 km closer to Mars.

Original Source: NASA Science Story