Artist's impression of the impact.
(Screenshot by Michelle Starr/CNET Australia)
A meteoroid crashing into the surface of the moon caused an explosion so big, it was visible from Earth to the naked eye.
Space debris crashing into the moon isn't as uncommon as you might think. In fact, NASA scientists have been monitoring the moon for eight years for crashing meteoroids, observing hundreds every year. A collision seen on 17 March, however, has just taken the biscuit for the biggest explosion seen in the history of the program — so big, in fact, that it would have been visible to the naked eye from Earth.
Weighing around 40 kilograms and measuring about 30 to 40 centimetres across, the meteoroid hit the moon at a speed of over 90,000 kilometres (56,000 miles per hour), causing an impact equivalent to 5 tonnes of TNT explosive — and a flash nearly 10 times brighter than any seen by NASA's Meteoroid Environment Office — about as bright as a fourth-magnitude star.
This, it ought to be noted, is not from an explosion as we might consider them on Earth, where we have an atmosphere that allows gases to ignite. Instead, the light comes from superheated vapours and molten rock — and even a small piece of debris the size of a pebble can cause a crater a metre or two in diameter.
NASA's scientists believe the impact was part of a shower of meteoroids hitting the Earth and moon at the same time. "On the night of March 17, NASA and University of Western Ontario all-sky cameras picked up an unusual number of deep-penetrating meteors right here on Earth," Bill Cooke of NASA's Meteoroid Environment Office said. "These fireballs were travelling along nearly identical orbits between Earth and the asteroid belt."
When meteoroids enter the Earth's atmosphere, they become meteors; if they come into contact with Earth, they then become meteorites. Every day, about 91,000 kilograms (100 tonnes) of meteoroids enter the atmosphere, transformed by the heat of entry, most disintegrating before they hit the ground. Most of those that do fall all the way fall into the oceans, lakes, forests or other uninhabited areas.