Study Finds Space Shuttle Exhaust Creates Night-shining Clouds

Exhaust from the main engines of NASA’s space shuttle, which is about 97 percent water vapor, can travel to the Arctic in Earth’s thermosphere, the highest part of the atmosphere, where it forms ice to create clouds that shine at night, according to a new study. The thermosphere is above 88 kilometers [55 miles] altitude. The clouds settle to around 82 kilometers [51 miles] altitude in the layer directly below, called the mesosphere. The stratosphere and the troposphere lie in that order below the mesosphere.
From American Geophysical Union:Study Finds Space Shuttle Exhaust Creates Night-shining Clouds

WASHINGTON – Exhaust from the main engines of NASA’s space shuttle, which is about 97 percent water vapor, can travel to the Arctic in Earth’s thermosphere, the highest part of the atmosphere, where it forms ice to create clouds that shine at night, according to a new study.

The thermosphere is above 88 kilometers [55 miles] altitude. The clouds settle to around 82 kilometers [51 miles] altitude in the layer directly below, called the mesosphere. The stratosphere and the troposphere lie in that order below the mesosphere.

Michael H. Stevens, a research physicist at the Naval Research Laboratory in Washington and the paper’s lead author, reports that exhaust from the shuttle and other launch vehicles may help explain how some of these mysterious clouds are formed. The paper, co-authored by scientists in Sweden and Germany, appears in the current issue of the journal Geophysical Research Letters, published by the American Geophysical Union.

Noctilucent clouds, sometimes called polar mesospheric clouds when observed from space, are too thin to be seen by the naked eye in broad daylight. However, they shine at night when the Sun’s rays hit them from below the horizon, when the atmosphere under them is dark. They typically form in the cold, summer polar mesosphere and are made of water ice particles.

The study uses data from the Naval Research Laboratory’s Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI) instrument, launched on the shuttle for eight days of observation in August 1997. MAHRSI allowed scientists to follow the plume’s rapid poleward movement and then to observe a discrete region of ice clouds as it appeared in the Arctic near the end of the mission. Stevens and his colleagues found that the water contained in these clouds was consistent with the amount injected into the thermosphere by the shuttle during its ascent from Cape Canavaral, Florida.

“This study is important because it shows that there is a new source of water ice for the polar upper atmosphere,” said Stevens, lead scientist for MAHRSI. “Our results indicate that the water vapor released by launch vehicles can end up in the Arctic mesosphere.”

About half of the water vapor exhaust from the shuttle’s main fuel tank is injected into the thermosphere, typically at altitudes of 103 to 114 kilometers [64 to 71 miles]. Stevens and colleagues found that this water vapor can be transported all the way to the Arctic in a little over a day, much faster than predicted by models of atmospheric winds. There is currently no explanation for why the water moves so quickly.

The researchers also discuss observations from a ground-based experiment in Norway, which measured water vapor moving toward the Arctic Circle. These observations reveal the passage of a large plume of water vapor overhead a little over a day after the same shuttle launch (STS-85), confirming the plume trajectory inferred from the MAHRSI measurements.

As the water vapor moves to the Arctic it falls from the warmer thermosphere down to colder levels in the mesosphere. Over the North Pole in the summer, mesospheric temperatures can plummet below minus 140 Celsius [minus 220 Fahrenheit], the lowest in Earth’s atmosphere. At these temperatures, water vapor condenses into ice particles and forms clouds.

“The amount of water found here is tiny compared to the amount in the lower atmosphere,” Stevens said. “But the long term effects in the upper atmosphere have yet to be studied.”

The Office of Naval Research and NASA’s Office of Space Science funded the study.

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Notes for journalists:

Journalists and public information officers of scientific institutions (only) may obtain a copy of this paper upon request to Emily Crum: [email protected].

Title: “Polar mesospheric clouds formed from space shuttle exhaust”

Citation: Stevens, M. H., J. Gumbel, C. R. Englert, K. U. Grossmann, M. Rapp, and P. Hartogh, Polar mesospheric clouds formed from space shuttle exhaust, Geophys. Res. Lett., 30(10),1546, doi:10.1029/2003GL017249,2003.

Contact information for author:
Michael S. Stevens: [email protected] or +1 (202) 404-7226


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