By Sean Henahan, Access Excellence

Caption: Lunar Image from Clementine

Late last year, researchers announced (Science (29 November 1996))  that the Clementine spacecraft returned data suggesting tat there might be a mass of frozen water near the moon's south pole. This prompted discussions about the possibility of primitive lunar life forms as well as possible ways this water might be utilized by lunar explorers. Now however, new detailed radar images of the north and south poles of the moon have failed to confirm the earlier announcement.

"We don't see anything that suggests ice.  We don't think there is any obvious evidence from the Arecibo radar images for the presence of water-ice at the poles of the moon," said Donald B. Campbell, Cornell University professor of astronomy and associate director of the National Astronomy and Ionosphere Center (NAIC), which operates the Arecibo Observatory under a cooperative agreement with the National Science Foundation. .

The observations, taken at Arecibo Observatory in Puerto Rico in 1992 and just now released do actually indicate a number of small areas less than a half-square-mile in size throughout the polar regions whose
radar reflection could be interpreted as ice.  However, some of these features occur in areas near the poles that are sunlit and similar features are seen in radar images taken of clearly sunlit areas much closer to the moon's equator.  It is much more likely that their radar reflection properties are due to very rough surfaces associated with the steep slopes of impact craters than with ice deposits, the researchers said.

The Arecibo data studied the moon polar regions at the same radio wavelength -- 13 centimeters -- as Clementine and at a similar viewing angle, but with a resolution of 125 meters, or 400 feet, much greater than the resolution used in the Clementine studies. Previous studies of the planet Mercury showed patterns believed to suggest ice deposits on the surface facing away from the Sun.

"We were hoping to see a similar situation for the moon, with unambiguous, bright spots at the poles," Campbell said.  "With Mercury it's pretty clear.  But with the moon we didn't see  anything like that.  Our contention is that the surface roughness is a much better candidate for the signatures we're seeing.  However, neither Arecibo nor Clementine observed all  the areas that are in permanent shadow and there is still the possibility that there are ice deposits in the bottoms of deep craters."

Arecibo Observatory, which recently completed a $27 million upgrade that will be dedicated on June 14, is operated by Cornell University's National Astronomy and Ionosphere Center under a cooperative agreement with the NSF. It is the world's largest single dish radio telescope, with a 1,000-foot antenna and, when combined with a new one-megawatt transmitter, forms the world's most powerful radar.

MEANWHILE, ON JUPITER...

When the Galileo's atmospheric probe was released into the Jovian atmosphere (Dec. 7, 1995,)  researchers fully expected to find water. Instead, the probe reported bone dry conditions. It now appears that serendipity brought the probe to a dry area of the planet, but that other areas are indeed soaking wet.

Caption:  Jupiter Equatorial Region True and false color views of Jupiter from NASA's Galileo spacecraft show an equatorial 'hotspot' on Jupiter. These images cover an area 34,000 kilometers by 11,000 kilometers (about
21,100 by 6,800 miles)

"We had suspected that the probe landed in the Sahara Desert of Jupiter. But the new data show there is moisture in the surrounding areas. Jupiter is not as dry overall as we thought." '' Andrew Ingersoll, a planetary science professor at the California Institute of Technology, told reporters Thursday at NASA's Jet Propulsion Laboratory. Now new data from Galileo confirms, "Jupiter is wet," he reported.

The probe originally entered a clearing in the clouds -- a dry spot through which deeper, warmer layers could be seen. By studying various areas, including those resembling the probe entry site, the Galileo orbiter has helped scientists understand the probe results. In fact, the air around a dry spot has 100 times more water than the dry spot itself, according to Dr. Robert Carlson, of NASA's Jet Propulsion Laboratory, principal investigator for the imaging spectrometer instrument onboard Galileo.

Such dry spots cover less than 1 percent of the Jovian atmosphere, and appear to be regions where the winds converge and create a giant downdraft. In fact, the water content of the giant, gaseous planet varies at least as much as the moisture varies from place to place on Earth.

"Winds rise from the deep atmosphere and lose water and ammonia," explained Dr. Glenn Orton, a Galileo interdisciplinary scientist at JPL and co-investigator on the photopolarimeter- radiometer instrument. "At the top, when they converge and drop back down, nothing is left to condense back into clouds, and a dry clearing is created. These dry spots may grow and diminish, but they recur in the same places, possibly because of the circulation patterns on Jupiter."

Ingersoll said the dry spots are found in a band in the northern hemisphere at 5 to 7 degrees latitude. When the Galileo probe was released near the tops of the clouds, it found dry air underneath. But at other locations, the weather might be rather Earth-like. In the months since the probe's descent, Galileo mission scientists have debated whether the dry conditions it encountered were due to the downdraft concept, or whether Jupiter's water had somehow been concentrated deep in the gas planet's interior as it formed and evolved four billion years ago.

"There was a cosmo- chemical explanation and a meteorological explanation, and our latest analysis clearly favors the idea that the dry spots are a consequence of weather-related activity. Fifty miles below the cloud tops, we could expect thunderstorms, lightning and rain. But in contrast to Earth, individual Jovian storms and weather systems sometimes last for months, years or even centuries. The Great Red Spot, for example, has existed for at least the 300 years that we've been aware of it," Ingersoll noted.

Ingersoll is not optimistic about finding life on Jupiter. Despite the relatively warm temperatures and the presence of water on Jupiter, he said it is "highly unlikely" that the planet could sustain life in its thick, gaseous environment without any solid surface. He expressed the opinion that any Jovian life forms would have to hover, and "while we might imagine an advanced life form that could adapt, pre-biotic compounds would not survive in that environment and, therefore, evolution could not take place there."

The new lunar information appeared in the June 6, 1997 issue of Science. The Jupiter data was released during a press conference at JPL in Pasadena.