Space-rock strikes the Moon at 38,000 miles per hour

Observers of January’s total eclipse of the Moon glimpsed a much rarer, shorter-lived bonus event. Appearing as a small flash on the lunar surface — a meteorite struck the moon as onlookers on Earth observed.

The flash from the impact of the meteorite on the eclipsed Moon, seen as the dot at the top left (indicated by the arrow in the image), as recorded by two of the telescopes operating in the framework of the MIDAS Survey from Sevilla (Spain) on 2019 January 21. ( J. M. Madiedo / MIDAS)

Observers of January’s total eclipse of the Moon glimpsed a much rarer, shorter-lived bonus event. Appearing as a small flash on the lunar surface — a meteorite struck the moon as onlookers on Earth observed.

Spanish astronomers believe that the space rock collided with the Moon at 61,000 kilometres (or ~38,000 miles) an hour, blasting out a crater 10 to 15 metres in diameter.

Total lunar eclipses take place when the Moon moves completely into the shadow of the Earth, taking a red colour — the result of scattered sunlight refracted through the Earth’s atmosphere — but is much darker than normal.

This, the most recent lunar eclipse took place on 21 January 2019, with observers in North and South America and Western Europe enjoying the best view. At 0441 GMT — just after the total phase of the eclipse began — a flash was seen on the lunar surface. Amateur astronomers reported that the flash — attributed to a meteorite impact — was bright enough to be seen with the naked eye.

Professor Jose Maria Madiedo of the University of Huelva and Dr Jose L. Ortiz of the Institute of Astrophysics of Andalusia operate the Moon Impacts Detection and Analysis System (MIDAS). MIDAS — which uses eight telescopes in the south of Spain to monitor the lunar surface — was able to capture video footage from MIDAS recorded the moment of impact.

The impact flash lasted 0.28 seconds and is the first ever filmed during a lunar eclipse, despite a number of earlier attempts.

Madiedo, says: “Something inside of me told me that this time would be the time.”

He also adds that he was impressed when he observed the event —with it being brighter than most of the events regularly detected by the survey.

A close-up of the impact ( J. M. Madiedo / MIDAS)

Unlike the Earth, the Moon has little to no atmosphere for objects to pass through before reaching the surface. This means that smaller objects which would burn up or break apart before striking Earth are able to hit the Moon’s surface.

As these impacts take place at huge speeds, the rocks are instantaneously vaporised at the impact site, producing an expanding plume of debris whose glow can be detected by telescopes here on Earth as short-duration flashes.

The MIDAS telescopes observed the impact flash at multiple wavelengths, providing an amazingly detailed analysis of the event. Madiedo and Ortiz were able to conclude that the incoming rock had a mass of 45kg, measured 30 to 60 centimetres across. It impacted the surface at 61,000 kilometres an hour — close to the crater Lagrange H, near the west-south-west portion of the lunar limb.

The impact energy of even this tiny object yielded the equivalent of 1.5 tonnes of TNT — enough to create a crater up to 15 metres across — about the size of two double-decker buses side by side. The ejected debris is estimated to have reached a peak temperature of 5400⁰C — roughly the same as the surface of the Sun.

Madiedo continues: “It would be impossible to reproduce these high-speed collisions in a lab on Earth. Observing flashes is a great way to test our ideas on exactly what happens when a meteorite collides with the Moon.”

Madiedo and Ortiz of the Institute of Astrophysics of Andalusia publish their results in a new paper in Monthly Notices of the Royal Astronomical Society.

The team plan to continue monitoring meteorite impacts on the lunar surface, not least to understand the risk they present to astronauts, set to return to the Moon in the next decade.