Mark Megahan
When two asteroids smack a planet at the same time, it leaves distinct patterns in the crater. Astrophysicists study some obscure and tedious things but once in a while it teaches us something important. For instance the shock waves combine in strange ways to create ridges formed like the infamous “bumblebee ejecta” pattern.
Two asteroids at the same time
The dead dinosaurs we pump out of the ground to fuel our cars would agree that an asteroid impact can pack quite a wallop. It gets even worse when two or more asteroids hit the same place at the same time.
A groundbreaking new study in the journal “Icarus” takes a look at the way it happens on Mars. A team of researchers nearly worked themselves blind pouring over crater field photos with a magnifying glass.
After they got done, the team had a list of “hundreds of craters” which appear to be the result of binary asteroids. That’s what they call it when one hunk of rock circles another the way the moon orbits the Earth.
According to Dmitrii Vavilov at the Côte d’Azur University in France, the study’s lead author, “they’re really difficult to find.” The very first time a binary asteroid system was discovered, astronomers didn’t believe it.
Back in 1993, NASA’s Galileo craft was on it’s way out to Jupiter. Along the way, it spotted asteroid “Ida.” When the mission team found a second asteroid in the vicinity, “they were so confused.”
University of Maryland astronomer Harrison Agrusa recalls people “were debating if something was wrong with the camera.” Ida and her companion “Dactyl” checked out as the first of many confirmed pairs of asteroids. “It set off a big shock wave in the community.”
One in every six
After doing some survey work, the experts decided that “1 in every 6 asteroids — around 16 percent — is part of a binary system.” Most of the ones we know about are found in our own solar system “particularly in the asteroid belt between Mars and Jupiter.”
One pair is scheduled for a visit later this year, “Didymos and its small companion, Dimorphos.”
Everyone knows asteroids hit all the space real estate on a regular basis. So, that means a bunch of binary ones should land, too. Finding such craters on the moon is really difficult because there are too many craters on the airless surface to start with. On Earth our weather scours away all traces in no time.
There is a good candidate for one here at home, though. “the Lockne crater in Sweden and a smaller crater nearby called Målingen.” The scientists “dated these structures very exactly and saw that they formed at exactly the same age,” about 450 million years ago, relates Jens Ormö from the Astrobiology Center in Spain.
Mars is a happy medium where craters stick around but there aren’t an overwhelming number of them. Some have been visible for billions of years. Thanks to high resolution images, courtesy of the Mars orbiters, Vavilov and his team were able to scour through “nearly 32,000 craters larger than 4 kilometers across to hunt for crater pairs.”
They found 150 pairs which seem like examples. They form in patterns recognizable as “tear-drop craters, where the two craters overlap; peanut craters, where they are connected at their edges; and doublet craters, where there is a gap between the two.”
Shock waves from the impacts of the two asteroids could bang together, “creating a raised ridge between the two craters or some high-pressure locations.” As the debris blasts out and falls back, it can create an unmistakable “bumblebee” pattern.
