The impact was observed by researchers from the University of Huelva and the Institute of Astrophysics of Andalusia (IAA-CSIC) and produced a glow brighter than the North Star
On 11 September 2013 a rock with a mass of a small car impacted the moon and produced a glow almost as shiny as the North Star. It has been the strongest impact detected to date, and its glow, which lasted eight seconds, has been the longest and most intense ever observed. Today, researchers from the University of Huelva and the Institute of Astrophysics of Andalusia (IAA-CSIC) published an analysis of the impact in the Monthly Notices of the Royal Astronomical Society.
“I was immediately aware that I was witnessing an extraordinary event,” says José María Madiedo, researcher at the University of Huelva (UHU), who detected the impact. The observation was made using two telescopes of the MIDAS (Moon Impact Detection and Analysis System) project, developed by Madiedo and José Luis Ortiz, of the Institute of Astrophysics of Andalusia (IAA-CSIC).
These impacts are primarily caused by comet fragments and asteroids orbiting around the sun, technically known as meteoroids. The earth has a protective atmosphere which stops most meteoroids on a collision trajectory from reaching its surface, but the moon has no such shield and even small fragments can impact its surface and make a crater.
Since this kind of collision happens at speeds of tens of thousands of kilometres per hour, rocks melt and vaporize instantly at the point of impact. “That is why we do not use the word meteorite when referring to these collisions, because that term implies the presence of fragments,” José Luis Ortiz (IAA-CSIC) explains. The shock provokes a rise in temperature which in turn produces a glow that is visible with telescopes from the earth and which lasts a fraction of a second on average—much less than the 8 second duration of the glow produced by the September 11th impact.
The analysis carried out by Madiedo and Ortiz estimates that the new crater may measure up to forty meters in diameter, and that the meteoroid in question had a mass of approximately four hundred kilograms and a diameter between 0.6 and 1.4 metres. These estimates depend primarily on a physical parameter called “luminous efficiency” which is thus far little understood. The impact occurred at a speed of around sixty one thousand kilometres per hour in a region known as Mare Nubium (sea of clouds), an old solidified lava basin about the size of the Iberian Peninsula.
The energy released during the impact was enormous: equivalent to the blast of some fifteen tons of TNT. That makes it at least three times more potent than the greatest impact on the moon detected to date by NASA, registered by that agency on 17 March last year.
The results of the analysis of the glow of these lunar impacts allow us to better estimate the frequency with which meteoroids collide with the earth. One of the conclusions of this research suggests that the frequency with which rocks of a size similar to that which impacted the moon on 11 September collide with our own planet may be up to ten times higher than what a large portion of the scientific community had thought until now.
Madiedo J.M., Ortiz J.L., Morales N., Cabrera-Caño J., A LARGE LUNAR IMPACT BLAST ON SEPTEMBER 11TH 2013, MNRAS, 2014.