Subj: Atomic Oxygen, Installment 1
Date: 9/7/00 2:30:35 PM Pacific Daylight Time
From: (James Cleland)



Today we begin a month-long journey into the wonders of something many of us have never heard of...Atomic Oxygen...very possibly both the creator and destroyer of life here on Earth, and elsewhere in the Solar System....and the Universe. The reason we will be learning about this interesting little substance is that this is what the scientists around the globe are currently looking at.

The story begins in The Great White North...Canada...home of hockey, high-alcohol beer, and Captain Kirk. As we in the United States strut about the world stage, Canadian scientists are as busy as Canada's national animal, studying the strange story of Atomic Oxygen. They go about their business, "under the radar", seeking to unravel the mysteries of this mysterious molecule.

Like most scientists, these fine researchers do not make it a habit to make the results of their work accessible to us non-scientists. It's not that their work is not's just that most of it consists of scientific "jargon", unreadable by those of us without PhD's. To make matters worse, most scientists jealously guard their own "turf", and rarely look outside there own discipline to see how their work fits into the "Big Picture". This is OUR job...and it's a big one. In many ways, it is a detective story, calling on each of us to stretch our abilities to the maximum. The effort should, however, prove quiet rewarding.

We will start our long journey in a little quonset hut belonging to NASA's little-known cousin, the Canadian Space Agency; and we will finish today's tour, far away...on the icy surface of an alien moon...and looking out in the distance to the dim, red dot that is Mars.

In that threadbare hut, as the bright leaves of the early Canadian Autumn begin to fall, senior CSA scientists are setting out on an ambitious new program, one meant to study our new "friend", Atomic Oxygen. Their mission is is to study "... the variability of atomic oxygen in the thermosphere, which is the mirror of ozone in the stratosphere. Canadian scientists have a long history of experience with the crucial role of atomic oxygen in the thermosphere, and WINDII has revealed the dominant role of dynamics in the distribution of atomic oxygen so that this problem can now be properly addressed. Thus, again, there is unique Canadian expertise and experience in this area. The oxygen chemistry and dynamics of this region couple strongly into those of the ozone region below.

Linking the troposphere and stratosphere is the question of troposphere-stratosphere exchange, addressing the issue of how surface causes link to middle atmosphere effects. Finally, the topic of waves addressed in the A program is extended in the B priority program through a study of the identification of the sources of gravity waves, a study which may improve the predictions of weather forecasting models."

There are, however, skeptics amongst us who harbor sinister doubts as to whether we are being told the whole story. To find out, we must first travel many millions of Jupiter's mysterious moon, Ganymede:

"Atomic hydrogen found escaping from Ganymede implies Jupiter's largest moon has large amounts of oxygen hovering over or locked up in its icy surface, according to University of Colorado observations with NASA's Galileo spacecraft.

Senior Researcher Charles Barth of CU-Boulder's Laboratory for Atmospheric and Space Physics said observations made with a CU ultraviolet spectrometer on Galileo indicate UV radiation is breaking down Ganymede's rock-hard ice into atomic hydrogen and atomic oxygen. Because atomic hydrogen is the lightest atom and Ganymede has a weak gravitational field, the hydrogen escapes while the atomic oxygen stays behind, said Barth.

Barth speculated the atomic oxygen forms molecular oxygen and ozone which may become trapped in the ice or form a very thin atmosphere above the surface of Ganymede. "If this process has been occurring for the past four billion years since Ganymede was formed, then the moon should have as much oxygen on its icy surface as Earth has in its atmosphere".

Galileo's ultraviolet spectrometer was designed and built at CU-Boulder under the direction of LASP Senior Researcher Charles Hord. Barth, a CU science team member on the spectrograph, presented the new results at the fall meeting of the American Geophysical Union in San Francisco Dec. 14 to Dec. 19.

With a diameter of 3,269 miles, Ganymede is the largest moon in the solar system and is about three-quarters the size of Mars. The moon, which has craters, basins and mountains, is believed to be made of rock and water ice. The surface temperatures of Ganymede hover at a chilly minus 186 degrees F.

The CU-Boulder spectrometer was pointed at Ganymede during a June 27 flyby, passing within 519 miles of the moon. The approach was 70 times closer than the approach of the Voyager 2 spacecraft to Ganymede in 1979.

The spectrometer data from the flyby was stored on a tape recorder onboard the spacecraft for about six weeks before being transmitted to Earth for analysis.

While previous observations with the Hubble Space Telescope have indicated there is oxygen at Ganymede, the direct observations of escaping hydrogen by the CU-Boulder team provide a mechanism for the presence of oxygen, Barth said.

A CU-Boulder team discovered atomic hydrogen escaping from Mars and ozone at its surface in 1969 using NASA's Mariner 6 spacecraft, a finding essentially identical to the new Ganymede discoveries, Barth said.

"Mars is an analog to Earth and Ganymede is an analog to Mars," Barth said. "Although the conditions on Ganymede are extremely cold, it would be interesting to see what processes might take place if there was a way to haul Ganymede into the orbit of Mars".

Having learned that our brothers and sisters in Canada are not the cold-hearted villains we thought, we can now begin our long voyage to Mars.... but we will be making some stops along the way. Next time: