This past Saturday, NASA launched Lucy, a probe to explore an asteroid in the main belt of our solar system. The craft will continue on to a group of asteroids called Trojans out near Jupiter. Taking 12 years, it will be the first mission to visit so many different objects in the solar system.

Also in October, a Canadian woman woke to find a meteorite had crashed through her roof and hit her bed, missing her head by mere inches, illustrating the connection between the building blocks of the solar system and our own precarious existence.

Rocks in space are called asteroids, and when they enter Earth’s atmosphere, they create a fiery display as they start to burn in the atmosphere. We call them meteors because these “shooting stars” were originally thought to be a local weather phenomenon; hence, the same root as the word meteorology. If you find a piece of one of these on the ground — or your pillow — we call those rocks “meteorites.”

It takes just one glance at the full moon to see that these types of space rocks have impacted planets throughout the solar system’s history. Given that you can see the craters on the lunar surface, you know some of them were quite large, causing immense devastation upon impact.

Would it surprise you to know such impacts are relatively common? The last really large one happened on Earth about 65 million years ago, and they occur on average about once every 50 million to 100 million years. In other words, we are due, geologically speaking.

That’s why NASA runs a program to hunt for near earth objects (NEOs), which tracks the location of all the known asteroids that cross Earth’s orbit. While it is rare for both Earth and an asteroid to occupy the same space at the same time, we see them whiz past us frequently. By tracking them, we can predict when they might hit Earth, and possibly do something about it.

That is the reason for another NASA mission, launching in November. Called DART, it plans to visit an orbiting pair of asteroids and use an explosive to slightly alter the path of the smaller one. Instruments will then measure the effect, allowing scientists to gauge how much force may be needed to deflect an asteroid that happens to be on a collision course with Earth.

Lately, NASA has been doing a lot of asteroid exploration. In 2018, its OSIRIS-REx mission visited a 1,600-foot-diameter asteroid known as Bennu with the goal of returning a sample for study on Earth. It’s also important to note there is a 1 in 2,700 chance that Bennu will impact Earth in 2182. While that may seem like long odds, these objects are constantly pushed and pulled by the gravity of other things in the solar system, so keeping track of them is pretty important. And in case you don’t have enough to worry about these days, you can keep track of NASA’s efforts by visiting the Center for Near Earth Object Studies. They keep a list of all of the known objects that come close to Earth.

It’s only a matter of time before one of them comes close enough to hit us. NASA has identified more than 90% of them, which still leaves a lot of undiscovered space rocks. In fact, back in 2013, while we watched the close approach of a known NEO, an unknown asteroid blew up over Chelyabinsk, Russia. This object was “only” the size of a school bus, but the air burst shattered windows and caused other damage on the ground. So we are keeping an eye out for NEOs and, soon, sending a probe to test our ability to deflect one if there ever is a need.

This says nothing about comets. Those icy bodies come out of nowhere from the outer solar system, giving us very little warning of an impending impact. The last large one was the Tunguska event in 1908, which flattened over 800 square miles of forest, an air burst equivalent to a 12 megaton nuclear explosion. We think it was a comet because no meteorites from the event have ever been found, something you’d expect if the impactor was more ice than rock. Even if we include comets, the chance of experiencing a massive asteroid impact in your lifetime is extremely unlikely.

But it’s still far more likely than waking up next to a meteorite on your pillow.

Dr. John Armstrong is a Weber State University professor of physics. Twitter: @ByJCArmstrong

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