On July 8, 2011 the Space Shuttle Atlantis launched for the very last time. On that historic day, as the world watched its last ascent up into orbit and commentators discussed the program’s contributions to space flight and scientific research over 20 years, the shuttle helped spawn one last experiment.
As the shuttle reached a height of about 70 miles over the east coast of the U.S., it released – as it always did shortly after launch – 350 tons of water vapor exhaust.
As the plume of vapor spread and floated on air currents high in Earth’s atmosphere, it crossed through the observation paths of seven separate sets of instruments. A group of scientists, reporting in online in the Journal of Geophysical Research on August 27, 2012, tracked the plume to learn more about the airflow in the Mesosphere and Lower Thermosphere (MLT) — a region that is typically quite hard to study. The team found the water vapor spread much faster than expected and that within 21 hours much of it collected near the arctic where it formed unusually bright high altitude clouds of a kind known as polar mesospheric clouds (PMCs). Such information will help improve global circulation models of air movement in the upper atmosphere, and also help with ongoing studies of PMCs.