Farewell, LADEE. The NASA spacecraft has crashed into the lunar surface after months spent measuring moon dust and testing laser-based broadband. NASA says the probe made impact on 17 April sometime between 4.30 and 7.22 pm UTC.
LADEE launched from Wallops Island, Virginia, on 6 September 2013 and settled into lunar orbit about a month later. The mission's goals were few and specific: test a broadband communications system between Earth and the moonMovie Camera; analyse the moon's thin atmosphere; and investigate the cause of a strange pre-sunrise glow seen by some Apollo moonwalkers.
The spacecraft's main mission ended in early March, and shortly thereafter it ran out of the fuel needed to keep it in orbit. Since LADEE could not come home, NASA intentionally crashed the probe into the far side of the moon, away from historically important sites like the Apollo landing zones.
Mission managers sent the orbiter a signal to turn off all its science instruments on 11 April and set the craft on course for a crash landing. But the moon's gravity field is very uneven, and variations in the field affected LADEE's path as it descended. That meant no one could predict ahead of time exactly when or where on the far side it would crash, just that it should happen sometime before 21 April.
Netflix on the moon
About the size of a vending machine, the probe smashed into the moon while travelling at about 5800 kilometres per hour. Mission managers think it broke up during its descent, and the pieces should have left visible marks on the moon's surface. The Lunar Reconnaissance Orbiter will be searching for the resulting features in the coming months.
Although the mission was relatively brief, LADEE was highly productive. The laser-based communication system worked wonderfully, says team member Mihaly Horanyi at the University of Colorado, Boulder.
"We had a really high rate of data transmission. You could have watched Netflix on the moon if you wanted to," he says. Future versions of this technology could stream high-definition video from space probes or from human missions into deep space.
The LADEE team also found that the moon is engulfed in a cloud of dust that is being constantly refreshed by impacts from micrometeorites. "People expected this, but this is the first time we've actually made measurements," says Horanyi. Similar small impacts should churn up dust on other rocky bodies in the solar system, so studying the size distribution of the lunar particles could help in planning for future missions to an asteroid or Mars.
Astronaut moonbeams
However, the team is still not sure what caused the mysterious lunar rays seen by Apollo astronauts. The best theory is that solar radiation gives some particles of fine, glassy moon soil a positive charge, which repels the grains upwards. Gravity pulls those grains back down even as new particles float up, creating fountains of electrostatic dust that would reflect light. The effect should be stronger at twilight, which is when astronauts reported the lunar beams.
The dust particles involved would be too small for LADEE to have seen directly, but the craft was able to look for the electrical current that should be coursing through such dust fountains. However, the current it saw was two orders of magnitude too low to account for the Apollo astronaut's horizon glow.
LADEE may have seen evidence of the dust fountains in its last week of operation, as it spiralled closer to the lunar surface. But for now, mission managers have bid the spacecraft a bittersweet farewell.
"It delivered what it was supposed to," says Horanyi. "Unfortunately, all good things come to an end."
LADEE launched from Wallops Island, Virginia, on 6 September 2013 and settled into lunar orbit about a month later. The mission's goals were few and specific: test a broadband communications system between Earth and the moonMovie Camera; analyse the moon's thin atmosphere; and investigate the cause of a strange pre-sunrise glow seen by some Apollo moonwalkers.
The spacecraft's main mission ended in early March, and shortly thereafter it ran out of the fuel needed to keep it in orbit. Since LADEE could not come home, NASA intentionally crashed the probe into the far side of the moon, away from historically important sites like the Apollo landing zones.
Mission managers sent the orbiter a signal to turn off all its science instruments on 11 April and set the craft on course for a crash landing. But the moon's gravity field is very uneven, and variations in the field affected LADEE's path as it descended. That meant no one could predict ahead of time exactly when or where on the far side it would crash, just that it should happen sometime before 21 April.
Netflix on the moon
About the size of a vending machine, the probe smashed into the moon while travelling at about 5800 kilometres per hour. Mission managers think it broke up during its descent, and the pieces should have left visible marks on the moon's surface. The Lunar Reconnaissance Orbiter will be searching for the resulting features in the coming months.
Although the mission was relatively brief, LADEE was highly productive. The laser-based communication system worked wonderfully, says team member Mihaly Horanyi at the University of Colorado, Boulder.
"We had a really high rate of data transmission. You could have watched Netflix on the moon if you wanted to," he says. Future versions of this technology could stream high-definition video from space probes or from human missions into deep space.
The LADEE team also found that the moon is engulfed in a cloud of dust that is being constantly refreshed by impacts from micrometeorites. "People expected this, but this is the first time we've actually made measurements," says Horanyi. Similar small impacts should churn up dust on other rocky bodies in the solar system, so studying the size distribution of the lunar particles could help in planning for future missions to an asteroid or Mars.
Astronaut moonbeams
However, the team is still not sure what caused the mysterious lunar rays seen by Apollo astronauts. The best theory is that solar radiation gives some particles of fine, glassy moon soil a positive charge, which repels the grains upwards. Gravity pulls those grains back down even as new particles float up, creating fountains of electrostatic dust that would reflect light. The effect should be stronger at twilight, which is when astronauts reported the lunar beams.
The dust particles involved would be too small for LADEE to have seen directly, but the craft was able to look for the electrical current that should be coursing through such dust fountains. However, the current it saw was two orders of magnitude too low to account for the Apollo astronaut's horizon glow.
LADEE may have seen evidence of the dust fountains in its last week of operation, as it spiralled closer to the lunar surface. But for now, mission managers have bid the spacecraft a bittersweet farewell.
"It delivered what it was supposed to," says Horanyi. "Unfortunately, all good things come to an end."
