What Are Asteroids? NASA Astronomers Are Finding More Near-Earth Objects Than Ever Before

Maybe you've seen the news: Not one but two asteroids are flying by Earth in the next few days. That seems like a lot, so what the heck is happening? Are we having a week of cosmically bad luck? Is the solar system angry at us? Are we all going to go the way of the dinosaurs before we even get to pull out the flip-flops again? And what even are asteroids anyway?

Asteroids are basically space debris, hunks of metal, clay, rock and water floating around the solar system. They're all much smaller than a planet or our Moon, no more than a couple hundred miles across. That means their gravity isn't strong enough to give them a smooth, round shape, so they are lumpy and lopsided instead. Most of them, tens of thouands all told, are tucked away in the asteroid belt, located between Mars and Jupiter, but there are plenty of strays wandering around the solar system—that's how we get asteroids making these close approaches to Earth, within just tens of thousands of miles of us.

03_02_asteroid How many asteroids are there? We don't even know. NASA

Naturally, astronomers are pretty interested in these asteroids that sneak by us, since they are well aware that collisions can be deadly. That's why since 1998, NASA has funded a special program dedicated to tracking down what are formally called "near-Earth objects." If you feel like you've seen a sharp uptick in coverage of asteroid flybys, this is why: Astronomers are finding and tracking more near-Earth objects than ever before. (None of the asteroids large enough to cause a global disaster like the impact that wiped out the dinosaurs are on track to collide with Earth any time soon.)

But that isn't just a matter of self-preservation that has scientists studying asteroids: These rocks may also hold the secrets of the birth of the solar system—and perhaps even of how life on Earth began. That's because scientists believe they haven't changed much in the past 4.6 billion years ago or so, since they never got lumped in to form planets. (If they had, or if they were somehow all smushed together now, they would be smaller than our Moon.) So studying asteroids can give us a better sense of what the early solar system looked like.

Read more: Record-Breaking 2,000 New Asteroids Approached Earth in 2017 and Astronomers Expect to Spot Even More in 2018

We have two main options for studying asteroids: staying here and going to them. It's a great year for asteroid visits, with Japanese and American spacecraft landing on two different asteroids and bringing tiny pieces of them home for scientists to study in the lab. But we can also study them as they pass by, shooting invisible radar beams at them and studying the reflection that returns to Earth.

And scientists aren't going to stop trying to spot new asteroids flying past Earth any time soon. "Asteroid discovery is just a fun project to be involved with," Eric Christensen, who leads the Catalina Sky Survey, an asteroid-hunting project at the University of Arizona, told Newsweek. "There's a lot of undiscovered asteroids to be found."