New data confirms and localizes uplifted lunar dust as seen by Apollo astronauts

The uncertainty of science: In a paper released today, scientists reveal the detection of electrostatic dust events on the Moon similar to those observed by Apollo astronauts, and find that these events might not be global but instead confined to craters during twilight. From the abstract:

Lunar horizon glows observed by the Apollo missions suggested a dense dust exosphere near the lunar terminator. But later missions failed to see such a high‐density dust exosphere. Why the Apollo missions could observe so large number of dust grains remains a mystery. For the first time, we report five dust enhancement events observed by the Lunar Dust Experiment on board Lunar Atmosphere and Dust Environment Explorer [LADEE] mission, which happen near a twilight crater with dust densities comparable to the Apollo measurements. Moreover, the dust densities are larger on the downstream side of the crater and favor a higher solar wind temperature, consistent with an electrostatic dust lofting from the negatively charged crater floor. We also check the Apollo observations and find similar twilight craters, suggesting that the so‐called dust exosphere is not a global phenomenon but just a local electrified dust fountain near twilight craters.

The dust clouds the astronauts thought they saw near the horizon have been theorized to be dust uplifted by static electricity. However, all later missions had so far failed to detect this phenomenon, until now. That the result also pinpoints the location and ties it to twilight is important for future missions to the Moon. Astronauts can thus minimize any damage by this dust by shutting down operations during lunar twilight periods.

LADEE impact site located

Lunar Reconnaissance Orbiter has spotted the impact crater formed when engineers sent the probe LADEE crashing into the lunar surface in April 2014.

Compared with asteroid and meteoroid impacts on the moon, LADEE was actually traveling pretty slow, ‘only’ 3,800 miles per hour (1,700 meters per second). That combined with the relatively low mass and density of the spacecraft, a fairly neat crater of only 10 feet (3 meters) across was created. The crater barely registered in LROC’s image resolution, making it a very difficult task to identify the fresh man-made divot.

As the NASA lunar probe LADEE nears its planned end — where it will crash onto the Moon — the scientists running it admit that they have as yet been unable to solve its primary scientific question about levitating lunar dust.

As the NASA lunar probe LADEE nears its planned end — where it will crash onto the Moon — the scientists running it admit that they have as yet been unable to solve its primary scientific question about levitating lunar dust.

A major goal of the mission was to understand a bizarre glow on the Moon’s horizon, spotted by Apollo astronauts just before sunrise. “So far we haven’t come up with an explanation for that,” project scientist Rick Elphic, of NASA’s Ames Research Center in Moffett Field, California, said at a media briefing on 3 April. One leading idea is that the Sun’s ultraviolet rays cause lunar dust particles to become electrically charged. That dust then lofts upwards, forming a cloud that caught the light and the astronauts’ eyes.

LADEE carries an instrument that measures the impact of individual dust particles, as well as the collective signal from smaller particles. Lunar scientists had expected a certain amount of tiny dust to explain what the Apollo astronauts saw. But LADEE didn’t find it. “We did measure a signal that indicates that the amount of lofted dust has to be at least two orders of magnitude below the expectations that were based on the Apollo reports,” says Mihály Horányi, the instrument’s principal investigator, who is at the University of Colorado. Perhaps the dust lofting happens only occasionally, he suggests, and the astronauts were in just the right place at the right time to see it.

This remains an important question. Knowing what caused that horizon glow and knowing how often it occurs is essential knowledge for any future lunar base or research station.

In an engineering test, LADEE successfully used a laser to beam information back from the Moon this past weekend.

In an engineering test, LADEE successfully used a laser to beam information back from the Moon this past weekend.

Lasers could enhance space communications and lead to radical changes in spacecraft design. Today’s spacecraft communicate with radio, but radiofrequency wavelengths are so long that they require large dishes to capture the signals. Laser wavelengths are 10,000 times shorter than radio, the upshot being that a spacecraft could deliver much more data then even the best modern radio system. For scale, NASA says that the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft that’s carrying this laser experiment would take 639 hours to download an average-length HD movie using ordinary S-band communications. LLCD could download the film in less than eight minutes.

Orbital Sciences has issued an update on its Antares launch schedule, with the launch window now set for September 14-19.

The competition heats up: Orbital Sciences has issued an update on its Antares launch schedule, with the launch window for the Cygnus demonstration mission to ISS now set for September 14-19.

They announced this on July 10, but I am only now catching up. The launch could happen sooner, if there are delays to the launch of NASA’s LADEE moon probe. Right now the two launches are coordinated to have LADEE launch first.