Meteor impacts are far less random than most scientists assumed, according to a new analysis of Earth-strike meteors.
The research, reported on the pre-press astrophysics website ArXiv.org, concluded that meteor impacts are more likely to occur at certain times of the year when Earth's orbit takes us through streams of meteoroids.
The majority of meteors analysed hit the Earth in the second half of the year, say the researchers, brothers Carlos and Raúl de la Fuente Marcos of the Complutense University of Madrid.
"This lack of randomness is induced by planetary perturbations, in particular Jupiter's, and suggests that some of the recent, most powerful Earth impacts may be associated with resonant groups of Near Earth Objects and/or very young meteoroid streams," they report.
Meteoroid streams can be generated by the break-up of an asteroid or comet.
A planet or moon can also affect nearby asteroids and meteors, herding them into loose orbits called 'resonant streams', which can be broken up by big planets such as Jupiter and Saturn.
The study is based on 33 meteor impact events detected between 2000 and 2013 by infrasound acoustic pressure sensors, operated by the Comprehensive Nuclear-Test-Ban Treaty Organization.
The sensors are designed to detect clandestine nuclear tests, but also pick up meteor impacts with an explosive energy in excess of a thousand tonnes of TNT.
The researchers looked at when and where each of the 33 meteors hit the Earth, as this enabled them to determine where it might have come from.
They found 17 impacts occurred in the northern hemisphere and 16 in the south; 25 impacts occurred within 40 degrees north or south of the equator, while only eight occurred at higher latitudes.
Significantly, the authors found a 21 per cent difference in meteor timing, with 20 impacts across the second half of the year compared to just 13 hits in the first six calendar months.
For people in the southern hemisphere, June was the most likely month for a meteor to hit the Earth, while September and October were the least likely. Overall though, more meteor impacts were recorded in the second half of the year -- 12 compared to four in the first six months.
North of the equator, November was the most likely month for a meteor hit while May and June were the least likely. Distribution was pretty even throughout the year with nine meteors occurring in the first half of the year and eight in the second half.
However, the authors believe the timing will change as old meteoroid streams dissipate and new ones form.
More data needed
This theory makes sense says Dr Simon O'Toole of the Australian Astronomical Observatory.
"What we had always assumed up until this paper, was that meteor impacts were random, occurring at any time and in any place," says O'Toole.
"This new work points to asteroids orbiting out near Jupiter, getting disrupted from their orbits by the planet's gravitational perturbations, and this can have an impact for us here on Earth."
However, O'Toole is concerned that the study is based on only 33 individual impact events.
"It's a very interesting paper, but 33 events is a statistically small sample range," says O'Toole.
"This needs far more data."