mardi 16 juin 2015

Moon Engulfed in Permanent, Lopsided, Dust Cloud












NASA - LADEE Mission patch.

June 16, 2015

New science results from NASA’s Lunar Atmosphere and Dust Environment Explorer, or LADEE, mission indicate that the moon is engulfed in a permanent, but lopsided, dust cloud that increases in density when annual events like the Geminids meteor shower spew shooting stars, according to a new study led by University of Colorado Boulder.

LADEE discovered dust clouds around the Moon

"Knowledge about the dusty environments in space has practical applications," said CU-Boulder physics Professor Mihaly Horanyi. "Knowing where the dust is and where it is headed in the solar system could help mitigate hazards for future human exploration, including dust particles damaging spacecraft or harming astronauts."

The cloud was discovered using data from a detector on board LADEE called the Lunar Dust Experiment (LDEX) designed and built by CU-Boulder. LDEX charted more than 140,000 impacts during the six-month long mission, which launched in September 2013 and orbited the moon for about six months. NASA’s Ames Research Center in Moffett Field, California, was responsible for spacecraft design, development, testing and mission operations, in addition to managing the overall mission.

“It's been over a year since LADEE completed its fully successful mission by impacting the lunar surface as planned on April 18, 2014,” said LADEE project scientist at Ames, Rick Elphic. “The LADEE science team has been busy analyzing the returned data, figuring out how the exosphere breathes and changes, and how the moon's tenuous dust shroud varies in time and space.”

According to Horanyi, the cloud is primarily made up of tiny dust grains kicked up from the moon’s surface by the impact of high-speed, interplanetary dust particles. A single dust particle from a comet striking the moon’s surface lofts thousands of smaller dust specks into the airless environment, and the lunar cloud is maintained by regular impacts from such particles.

“Identifying this permanent dust cloud engulfing the moon was a nice gift from this mission,” said Horanyi, the principal investigator on LDEX and the lead author of the study. “We can carry these findings over to studies of other airless planetary objects like the moons of other planets and asteroids.”

A paper on the subject appears in the June 17 issue of Nature. Co-authors on the study include Jamey Szalay, Sascha Kempf, Eberhard Grun and Zoltan Sternovsky from CU-Boulder, Juergen Schmidt from the University Oulu in Finland, and Ralf Srama from the University of Stuttgart in Germany.

Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft orbiting the Moon

The first hints of a cloud of dust around the moon came in the late 1960s when NASA cameras aboard unmanned moon landers captured a bright glow during lunar sunsets. Several years later, Apollo astronauts orbiting the moon reported a significant glow above the lunar surface when approaching sunrise, a phenomenon brighter than the sun alone should have been able to create at that location.

Since the new findings don’t square with the Apollo reports of a thicker, higher dust cloud, conditions back then may have been somewhat different. The dust on the moon -- which is dark and sticky and regularly dirtied the suits of moonwalking astronauts -- was created over several billion years as interplanetary dust particles incessantly pounded the rocky lunar surface.

Many of the cometary dust particles impacting lunar surface are traveling at thousands of miles per hour in a retrograde, or counterclockwise orbit around the sun, the opposite orbital direction of the solar system’s planets. This causes high-speed, near head-on collisions with the dust particles and the moon’s leading surface as the Earth-moon system travel together around the sun.

For more information about Lunar Atmosphere and Dust Environment Explorer (LADEE) mission, visit: http://www.nasa.gov/mission_pages/ladee/main/index.html

Images, Text, Credits: NASA.

Greetings, Orbiter.ch

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