Why Astronomers Want to Look for Earth’s Mini-Moons

A new, powerful telescope in Chile will be able to detect tiny asteroid chunks circling our planet, which could be a goldmine for researchers


The moon is not alone. Or at least theoretically it shouldn’t be. Researchers believe that our planet is potentially orbited by lots of “mini-moons,” little asteroids gripped by Earth’s gravity that swing around the planet for a little while before burning up in our atmosphere or being flung back into the cosmos.

Now, reports Amber Jorgenson at Discover, astronomers have called for a new project using the Large Synoptic Survey Telescope (LSST)—a device still under construction in Chile—to look for the mini-moons. Examining those little space rocks, they believe, could be a big boost to astronomy.

Astronomers involved in the Catalina Sky Survey first discovered that Earth had a tiny second moon—a space rock less than 10 feet in diameter—in 2006, but only by serendipitous chance. Any space rocks that get caught in Earth’s orbit are typically too small and moving too quickly for our current asteroid surveys to detect.

But if we could detect these bits of space debris when they enter our orbit, we could capture samples from the space rocks and bring them down to Earth to study, new research in the journal Frontiers in Astronomy and Space Science suggests. It would be faster, cheaper and more efficient than our big budget missions, including the current OSIRIS-REx sample and return mission to the asteroid Bennu and Japan’s Hyabusa 2 mission to the asteroid Ryugu, which take millions of dollars and years of planning and zipping through space to accomplish.

“At present we don't fully understand what asteroids are made of,” co-author Mikael Granvik, of Luleå University of Technology, Sweden, and the University of Helsinki, Finland, says in a statement. “Missions typically return only tiny amounts of material to Earth. Meteorites provide an indirect way of analyzing asteroids, but Earth's atmosphere destroys weak materials when they pass through. Mini-moons are perfect targets for bringing back significant chunks of asteroid material, shielded by a spacecraft, which could then be studied in detail back on Earth.”

According to the team, the LSST is a “dream instrument” for finding the fast-moving mini-moons because its massive mirror will be able to detect very faint objects and its field of view will allow it to survey the entire sky more than once a week, giving us a good heads up when a chunk of asteroid begins orbiting Earth. Once we find a few targets, the team suggests that we can begin using satellites to study them and shuttle the samples back to Earth.

George Dvorsky at Gizmodo reports that there are several big things we can learn from the mini-moons. First, we can finally get some basic information about small asteroids, like their interior structure and whether they are loosely held together like “sandcastles” or solid, rock-like objects. Interacting with mini-moons could also help us test planetary defense technology to keep us safe from bigger asteroids and comets, give us a way to test safety and operational procedures for future manned missions to larger asteroids, help fine tune navigation and guidance systems for spacecraft, and also help test commercial space-mining equipment.

"I hope that humans will someday venture into the solar system to explore the planets, asteroids and comets,” lead author Robert Jedicke, an astronomer at the University of Hawaii in Honolulu, says in the release. “And I see mini-moons as the first stepping stones on that voyage.”

That is, if mini-moons are even out there. No new mini-moons have been seen since 2006 and even that one, 2006 RH120, which some people believed may have been part of an Apollo-era rocket booster, zoomed around our planet for 13 months before heading off on its own orbit around the sun, though it is expected to come back for a visit later this century. In 2016, another little asteroid, 2016 HO3, was detected dodging the Earth, but it’s too far away to be considered a mini-moon. It also has a twisting path that is more like a strange cha-cha with the Earth than an orbit, but it's expected to keep us company for the next few centuries.