The Moon has two tails of particles streaming in its wake. Data from NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE), which spent seven months orbiting the moon in 2013 and 2014, has revealed a second tail of nanoscale dust particles. The finding follows the discovery of the first lunar tail in 1999, when ground-based telescopes spotted a faint stream of sodium gas stretching out behind the moon for hundreds of thousands of miles.

Anthony Colaprete, who is in charge of LADEE’s spectrometer instrument, wanted to get a closer look at the sodium tail, so positioned LADEE on the dark side of the moon and pointed it away from the sun. The spectrometer works by looking at the patterns of light wavelengths that different substances emit or reflect. In this position, the instrument picked up the sodium, but there also seemed to be something else, a brighter signal in the blue and ultraviolet wavelengths.

After eliminating other possibilities, the team found that the best explanation for their signal was a tail of dust grains, each around 10 nanometres in size, trailing away from the moon for thousands of miles. “We think it is a robust observation,” says Colaprete, who presented the work at the Lunar and Planetary Science Conference (LPSC) in The Woodlands, Texas, on 16 March.

These grains are too small to be seen by LADEE’s Lunar Dust Experiment, which is designed to collect floating dust particles. There is also no chance of seeing the tail from Earth since the particles are very spread out, with less than a thousandth of a gram of material per square meter. But Jack Schmitt, who was an astronaut on the Apollo 17 mission, attended the LPSC session and said he thought the dust tail could explain a strange glow the crew observed from orbit at lunar sunrise.

But how is this dust getting so far away from the moon? Colaprete thinks asteroids crashing into the lunar surface are throwing up tiny particles, and then radiation pressure from the sun is pushing them further away, which is why the tail is in the opposite direction to the sun.

If the same is true of other bodies in the solar system, it could give us a way to study their surfaces without having to land: collect their tails rather than landing on them. “This is something that should be applicable to any airless bodies,” says Colaprete. This includes asteroids, the moons of Mars and the dwarf planet Ceres. “If you could gather it over time, you could analyse it as a measure of the surface.”

Posted by: Soderman/SSERVI Staff
Source: DREAM2 Team/ NewScientist.com/Jacob Aron

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