NASA/JPL
Images from Mars show deposits of minerals like opals in magenta and blue.
Images from Mars show deposits of minerals like opals in magenta and blue.
Still puzzling over how warm and wet Mars may have onc e been, scientists are now seeing global mineralogical signs that the planet was at least occasionally wet for the first two billion years of its existence.
In an article in the November issue of the journal Geology, scientists working with data from NASA’s Mars Reconnaissance Orbiter report that they have spotted widespread deposits of opals and related minerals on the surface of Mars.
+ This image from Mars show claylike deposits, in green.
Opals belong to a class of minerals known as hydrated silicas, with water molecules wedged into silicon-based minerals like quartz. The formation of hydrated silicas requires liquid water.
Most interesting is that the opal deposits lie in areas that appear to have formed onl y about two billion years ago. Previously, spacecraft have detected other water-bearing minerals like clays in regions that date back more than 3.5 billion years. Mars, like the other planets in the solar system, is about 4.5 billion years old.
“The water was more widespread and extended to younger times,” said Scott L. Murchie, a staff scientist at Johns Hopkins’ Applied Physics Laboratory and the principal investigator for the orbiter’s spectrometer, which found the opal evidence.
In July, Dr. Murchie and other scientists reported that the orbiter had detected vast deposits of the claylike minerals on the older terrains. Images also showed ancient lakebeds with accumulations of the minerals, indicating standing water persisted for thousands of years.
The presence of water on Mars has been known for many years; its ice caps, easily visible from space, are largely made of frozen water. The unanswered question is how often the ice has melted. The Phoenix Mars Lander, now nearing the end of its six-month mission, is exploring whether the arctic ice has melted in recent millennia.
The most intriguing possibility is that Mars, when it was less than a billion years old, was warm enough for lakes and oceans of liquid water ? and with that, the possibility of life. The planet’s landforms offer compelling evidence for flowing water: immense canyons and channels, dried-up river deltas.
“I think most people agree there was lots of water on the surface in the first few hundred million years,” said Maria Zuber, a professor of geophysics at the Massachusetts Institute of Technology. “It’s later on when I get confused, although I’m confused about the whole thing. That’s what makes it interesting.”
Some scientists have suggested that rare catastrophic floods carved the landforms, either in the aftermath of an impact by an asteroid or comet or by underground water ? melted by residual volcanic warmth ? bursting to the surface.
Those who believe that liquid water was more persistent were nonetheless perplexed when earlier spacecraft detected onl y small quantities of carbonates, minerals that should have formed in large amounts from reactions involving carbon dioxide and liquid water.
But data collected by the two Mars rovers, Spirit and Opportunity, show a highly acidic environment that prevented the formation of carbonates. “That part of the story is fairly well agreed upon,” Dr. Zuber said.
The two rovers have also found signs of past water. Opportunity found hydrated sulfates in the Meridiani Planum rocks; Spirit found opal-like minerals similar to those spotted by the Reconnaissance Orbiter from space.
But planetary scientists are still trying to explain the transition of Mars from lots of water to today’s cold and dry climate. In fact, they are still trying to explain how it ever had lots of liquid water. Even if young Mars were enshrouded in a thick atmosphere of carbon dioxide belched by giant volcanoes, climatologists have had trouble coaxing enough global warming in their computer simulations to push temperatures above the melting point of ice.
James F. Kasting, a professor of geosciences at Penn State, believes he may have figured out how to warm up Mars. In research that he will present in December at a meeting of the American Geophysical Union, the key may be nitrogen dioxide.
In his climate models, carbon dioxide did act as a greenhouse gas, trapping heat near the surface, but it also reflected shorter wavelengths of light back into space, limiting the amount of heating. His models peaked at about minus-40 degrees Fahrenheit. Nitrogen dioxide, which is also released by volcanic eruptions, reduces the reflectivity of Mars in the models. With more light absorbed, temperatures jumped 100 degrees. “That would be more than you need,” Dr. Kasting said.
He said he still needed to demonstrate that the nitrogen dioxide would mix throughout the atmosphere rather than remain in pockets around the volcanoes.
Even if scientists figure out the water question, they have another problem: what happened to the Martian air? The climate models suggest early Mars had an atmosphere denser than Earth’s. Now, it’s a faint wisp.
“Well, we don’t know,” Dr. Zuber said. “One day we’re going to nail that one . There’s a whole bunch of things on my list of things to do.”
Mars
NASA
Earth
NASA
NASA
Temperatures on the daylight side of Mercury can reach 850 degrees Fahrenheit and plunge to minus-300 degrees on the night side. Mercury rotates slowly: one rotation takes 59 days, or two-thirds of a Mercury year, which is 88 days in length. It has a large iron core and thin outer crust, which leads many planetary scientists to believe that a large collision early in the solar system stripped away much of the outside of Mercury.
Venus (Planet)
NASA/JPL
Jupiter (Planet)
A Planet Denser Than Earth
Despite being the size of Jupiter and made mostly of hydrogen, a planet around a star 440 light-years away is denser than Earth, astronomers at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., announced. The astronomers were able to measure the size of the planet, designated HAT-P-2b, because it passes directly in front of the star every 5 days and 15 hours, causing it to dim slightly. HAT-P-2b, in the constellation Hercules, is more than eight times the mass of Jupiter, and the immense gravity crushes the planet down to its relatively small size and Earth-like density.
Saturn (Planet)
NASA/JPL
Uranus (Planet)
NASA
A collection of articles
Pluto (Dwarf Planet)
NASA
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