Seek and ye shall find. Scientists studying the Earth's upper atmosphere
are finding more water vapor up there than current theories, which have
so far ignored the existence of small comets, predict. The latest report
comes from an ozone-watching satellite deployed and retrieved during the
flight of the space shuttle Discovery in August of 1997. One of the
instruments aboard the satellite, called
CRISTA-SPAS, is the
Middle
Atmospheric High Resolution Spectrograph Investigation (MAHRSI).
Robert Conway of the E.O. Hulburt Center for Space Research at Naval
Research Laboratory in Washington, DC was quoted in news reports as
saying that MAHRSI had found a "startling" amount of hydroxyl,
a product of the breakdown of water, above altitudes of 43 miles. One
explanation for the existence of all this water vapor at these altitudes,
Conway told questioning reporters, is the small comets proposed by
University of Iowa physicist Louis A. Frank.
Many news reports also stated--erroneously as it turns out--that "almost no hydroxyl" was detected when MAHRSI flew aboard CRISTA-SPAS during the flight of space shuttle Atlantis back in November of 1994. But a report by Conway et al., entitled " Satellite measurements of hydroxyl in the mesosphere" and published in Geophysical Research Letters in August of 1996, indicates that a peak in hydroxyl was detected near 43 miles during that flight, a finding which the authors realized was "in substantial disagreement" with current models.
Reports of excess water in the mesosphere are mounting and can no longer be ignored. The first hint of unexpected amounts of water vapor at high attitudes came in May of 1987, when John Olivero, then of Pennsylvania State University and now at Embry-Riddle Aeronautical University in Florida, and a graduate student named Dennis Adams presented their findings at the American Geophysical Union meeting in Baltimore. Olivero and Adams had analyzed their collection of data on water-vapor concentrations in the mesosphere obtained with a microwave radiometer and found temporary increases of the size and frequency one would expect if the small comets existed. Then late in 1996 a team led by James M. Russell III of Hampton University in Virginia reported on their reanalysis of data gathered by their Halogen Occultation Experiment (HALOE), aboard the Upper Atmosphere Research Satellite (UARS) launched in September 1991. The data from their experiment, which used solar occultation to measure the presence of H2O and other compounds in the mesosphere, revealed a peak in water vapor at an altitude of about 45 miles.
"It's high time for theoreticians to take into account the small comets and the water they deposit into the upper atmosphere and begin to revise their models of the atmosphere," says Frank.