What it may sound like a huge disaster, destroying the $263 million dollar spacecraft was NASA’s intention from the start. At 8:59 p.m. CDT April 17, the agency confirmed the probe had impacted the moon’s surface.
The Lunar Atmosphere and Dust Explorer or LADEE (pronounced ‘laddie’) began circling the moon last fall, its mission to study dust in its extremely rarefied lunar atmosphere. Much of the dust sputters off the surface during meteorite impacts, while some may be lofted into the sky by electrostatic forces active when the sun rises along the day-night borderline called the terminator.
Prior to crashing, mission controllers gradually lowered the spacecraft’s orbit to study the moon’s near surface dust environment in ever more detail. While the moon lacks the atmosphere to slow a spacecraft and “drag” it down to the surface (like what happens at Earth), nature worked her wonders all the same. The moon’s gravity field is “lumpy”, with lighter, less dense regions alternating with denser concentrations of rock beneath the surface. Low-orbiting probes, perturbed by variations in pull of gravity are soon brought down.
“At the time of impact, LADEE was traveling at a speed of 3,600 miles per hour – about three times the speed of a high-powered rifle bullet,” said Rick Elphic, LADEE project scientist at Ames. “There’s nothing gentle about impact at these speeds — it’s just a question of whether LADEE made a localized craterlet on a hillside or scattered debris across a flat area. It will be interesting to see what kind of feature LADEE has created.”
NASA plans to work with the Lunar Reconnaissance Orbiter (LRO) team to overfly and capture an image of the impact site. LADEE struck the moon on the farside, a safe distance from any historic landing sites, all of which have been on the lunar nearside. Because radio communications can’t be received from the farside, NASA mission controllers had to wait for an hour during each ultra-low orbital pass. If LADEE began sending data again, they knew it was still “alive”. When LADEE didn’t show up at the planned time Thursday, the mission was declared over.
Scientists will be analyzing the data from the probe for a long, long time, but there are some preliminary results:
* LADEE survived the chill-inducing lunar eclipse earlier this week, demonstrating the spacecraft’s ability to endure low temperatures and a drain on batteries as it, and the moon, passed through Earth’s deep shadow.
* LADEE’s Lunar Dust EXperiment (LDEX) experiment detected an increase in the number of dust particles in the moon’s exosphere during the Geminid meteor shower in mid-December 2013. The LDEX dust impacts are thought to be due to the ejecta, or spray, of particles that result when the Geminid meteoroids slam into the lunar surface. The exosphere or dilute lunar atmosphere contains dust particles as well as gases from the solar wind.
* The Ultraviolet and Visible light Spectrometer (UVS) carried out a series of before and after observations looking for effects of the Chinese Chang’e 3 landing in December and meteor showers. Analysis revealed an increase in sodium connected with the Geminids, as well as evidence of increased light scattering due to dust but no clear signal from the Chang’e 3 landing.
The UVS also has been monitoring specific wavelengths of light emitted by atomic oxygen, and has seen emissions that may indicate the presence of both iron and titanium in the lunar exosphere. All three are elements found in the lunar soil called regolith but have never been seen in the moon’s atmosphere before.