If you want to have a base on the moon, you鈥檇 better build sturdy walls. Lunar grit kicked up by meteorite impacts moves at the speed of a shotgun blast, posing a potential risk to future astronauts. But such high-speed projectiles need not be a show-stopper for long-term lunar missions, provided we beef up the structural integrity of buildings, rovers and spacesuits.
鈥淵ou have to have a suit or habitat design that can handle small meteors, and that may just as well handle these secondary ejecta particles,鈥� says Rob Suggs, head of the Lunar Impact Monitoring team at NASA鈥檚 Marshall Space Flight Center in Huntsville, Alabama.
The airless moon is already pockmarked with craters made by incoming space rocks, and the bombardment is ongoing. With low gravity and no air resistance, dirt from an impact can be scattered far and wide. NASA worried about the risks from impact debris during the Apollo era, but at the time little was known about how often objects hit the moon and the speed of any material they kick up.
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In 2006, NASA was working on the Constellation programme, which aimed to send humans back to the moon. The agency started its Lunar Impact Monitoring project to better understand the risks, which continued even after Constellation was cancelled. Ground-based observations have since catalogued more than 300 flashes from impacts on the lunar surface, caused by objects ranging in size from a golf ball to a bowling ball.
Pack your bags
One of the came on 17 March 2013, when an object weighing about 40 kilograms blasted an 18-metre-wide crater in the lunar surface. NASA鈥檚 Lunar Reconnaissance Orbiter had photographed the region before, so a team led by at Arizona State University in Tempe scanned the area again with LRO to see the impact鈥檚 effects. Speaking at a , this week, Robinson reports that they found 248 fresh 鈥渟plotches鈥� ranging from 2 to 14 metres in width, which must have been created by ejected material.
The debris field is spread within about 30 kilometres of the main crater. Assuming material was ejected at a 45-degree angle, Robinson鈥檚 team calculates that dirt must have initially been travelling at about 200 meters per second 鈥� the speed of a shotgun blast. Most of these particles are the size of small sand grains, but that could still be a real hazard for astronauts, says of Purdue University, who was not involved in the research.
A more precise rate of lunar impacts remains to be determined, but Robinson鈥檚 group has already found 20 more fresh craters since last year鈥檚 March impact, and they are now compiling data on their surrounding debris zones. 鈥淥nce we have 30 to 40 of these new craters, we will have really good statistics,鈥� he says.
Robinson adds that he thinks the risk from lunar 鈥渟cattershot鈥� is manageable for missions lasting days, and it can be overcome for projects lasting 10 years or more, as long as debris speeds are accounted for in future habitats or robotic experiments. In fact, knowing the potential dangers, he is ready to make the trip: 鈥淕ive me a ride and I will pack my bags immediately!鈥�
