Scientists Watch Mars Weather
Plans to terraform Mars to make it more like Earth have called for everything from nuclear detonations to colonization with primitive plants and cockroaches. But all the plans have called for a generous helping of one virtue: patience. Now NASA says the cold, dry, desert world may reward patience of heroic proportions with a more hospitable surface - and without human intervention.
Cameras aboard NASA's Mars Global Surveyor found that Mars' global climate changes significantly from one 687-day year to the next. (A Martian day is about equal to an Earth day.) The strongest evidence for change is the rapid widening of pits in Mars' southern polar ice cap, according to a paper to be published in the peer-reviewed journal, Science.
Mars' southern ice cap is crusted with dry ice, or solid carbon dioxide. Unlike water ice, dry ice sublimates; it quickly becomes a gas when warmed without passing through a liquid phase. Carbon dioxide is a powerful, heat-trapping greenhouse gas.
"This means the Mars environment we see today may not be what it was a few hundred years ago, and may not be what will exist a few hundred years in the future," said Dr. Michael Malin of Malin Space Science Systems in San Diego, in a statement.
If true, future probes sent to land on the Red Planet should be able to gather more evidence for the planet's evolution from the surface, he said. The pits also provide another reason to suspect water may have once flowed over the sands of Mars. And any sign of water encourages speculation that the seemingly dead planet may once have harbored life.
The Global Surveyor, which is on a mapping mission until April of 2002, also measured carbon dioxide snowfall over both poles with its laser altimeter and radio tracking system. The instruments profile the change of seasons on the planet, which are caused by the planet's tilted axis, much like on Earth. Up to two meters of dry ice 'snow,' which is denser than Earth's snow, fell in the arctic regions, according to a separate paper also published in Science.
The new data will help NASA choose future landing sites, said Dr. James Garvin, NASA's lead scientist for Mars exploration. A prime target for future probes will be hydrothermal vents, if they exist on Mars, Garvin said. Recent data indicate that Mars may be more geologically active than previously believed.
But planetary climate change on Mars as well as Earth isn't attributable to internal factors such as magma and axis tilting alone. The two planets' climates can be greatly influenced by solar activity, according to a new computer model from scientists at NASA's Goddard Institute for Space Studies in New York (also reported in Science).
According to the study, a lack of sunspots during the Middle Ages plunged Earth into a mini Ice Age.
Europe and North America were gripped by a 'Little Ice Age' for three hundred years, from the 1400s to the 1700s, the scientists said. During that period, there was little or no sunspot activity, which is a signal of the Sun's energy output, according to astronomers of the time. As few as 50 sunspots were sighted over a thirty year span, down from a typical 40,000 to 50,000 sunspots, with an 11-year cycle of waxing and waning activity, according to researchers.
As a result of the sun's energy deficit, western winds that normally carry warmer air from oceans to land during winters were reduced.
But like Mars, carbon dioxide was key to climate change on Earth. The paper's authors view the industrial releases of the greenhouse gas as a greater contributor to global warming today than the fine distinctions in the solar cycle.
The study was the first time scientists have looked at regional changes due to solar fluctuations, rather than a more static global temperature average.