On 2013 September 11 at 20h07m28.s68 ± 0.s01 UTC, two telescopes operated in the framework of our lunar impact flashes monitoring project recorded an extraordinary flash produced by the impact on the Moon of a large meteoroid at selenographic coordinates 17 ?.2 ± 0 ?.2 S, 20 ?.5 ± 0 ?.2 W. The peak brightness of this flash reached 2.9 ± 0.2 mag in V and it lasted over 8 s. The estimated energy released during the impact of the meteoroid was 15.6 ± 2.5 tons of TNT under the assumption of a luminous efficiency of 0.002. This event, which is the longest and brightest confirmed impact flash recorded on the Moon thus far, is analysed here. The likely origin of the impactor is discussed. Considerations in relation to the impact flux on Earth are also made.
On Sept. 11, 2013, a pair of telescopes from a project called MIDAS (Moon Impacts Detection and Analysis System) monitored the blast from a meteoroid crashing into the lunar surface. The meteorite hit at a speed of 37,900 mph (61,000 km/h), gouging out a new crater roughly 131 feet (40 meters) wide in an ancient lava-filled lunar basin known as Mare Nubium. The energy released by the impact was comparable to an explosion of roughly 15 tons of TNT, and was at least three times more powerful than the largest previously observed event. The flash, which lasted for about 8 seconds, was about as bright as Polaris, the North Star. The high-speed collision was recorded on video and would have been clearly visible to anyone on Earth who happened to look at the moon at the right time.
The uncertainty of the impact is fairly high, the team who made the discovery said in their paper, and the team cautioned that specifics about the meteorite’s impact were difficult to nail down, in part because its origin cannot be determined. “Two sources have been considered for the impactor,” they write. “The event was compatible with the impact geometry of the September Epsilon Perseids minor shower, but it could also be associated with a sporadic meteorid.” If it was part of the September Epsilon Perseids meteor shower, it would have a very high velocity relative to the moon, and wouldn’t need as much mass to cause an impact with this energy. In this case, the rock would have been about 45kg and 36cm across. If, however, it was a sporadic meteoroid, the velocity would be lower and the mass greater, perhaps a mass of 450kg, and a diameter as large as 1.4 meters.
The MIDAS project has been running since 2009, and has an automated pipeline for identifying impacts. The statistics it has generated suggest that some early estimates of the rate at which Earth is bombarded may be low by as much as a factor of 10. In their paper, the team noted “Thus, the impact energy of the lunar impact flash would be equivalent to an impact energy of 28.3 ± 4.5 tons of TNT on Earth for the sporadic meteoroid and 24.3 ± 3.8 tons of TNT for the SPE meteoroid. So, by performing the corresponding surface area scaling between both bodies, the impact rate on Earth for events with an energy above these values would be of about 1680 ± 1050 events per year.”
“Our telescopes will continue observing the Moon as our meteor cameras monitor the Earth’s atmosphere,” said Madiedo and Ortiz in a press release. “In this way we expect to identify clusters of rocks that could give rise to common impact events on both planetary bodies. We also want to find out where the impacting bodies come from.”
A video of the impact has been posted on YouTube.