When I heard June 30 was Asteroid Day, I wasn’t sure whether I was supposed to celebrate, duck and cover, or listen to Aerosmith. Asteroids seem to be walking (okay, barreling through space) contradictions. They are simultaneously common rocks and a wealth of new information. They could destroy us, but they may have enabled life. We like them close, but not too close.
Our solar system contains millions of asteroids, rocky objects ranging in size from tiny to several hundred miles across. Most of them hang their hat in the asteroid belt between Mars and Jupiter. Some are spherical, most are irregularly shaped. Zoom in on one and you’ll likely see craters or pits from where they’ve been hit or collided with other objects during the last 4.6 billion years. These rocks hold the history of our solar system.
When the asteroids get too close to Mars or Jupiter, or each other, they can get thrown out of orbit and onto collision paths with other objects. This is when things get risky. You’ve probably seen the movies, so let’s just say it’s in our best interest to be on alert. I’m sure the dinosaurs would agree.
Space agencies, academic research groups, and citizen scientists are looking out for us with ground-based telescope and a space-based NASA satellite. Information on potential hazards goes to a global database run by the International Astronomical Union’s Minor Planet Center. The objects are classified and appropriate follow-up ensues by NASA and others.
So far we’ve cataloged more than 14,500 near-Earth objects (mostly asteroids, but some are comets). We know about most, maybe all, of the really big ones, 3 miles across or more, but even the small ones could cause serious damage and there are likely hundreds of thousands (millions?) of them to be discovered. An impact by an object larger than 0.5 miles across could have worldwide effects, according to NASA, and 80 feet across or larger could have serious local impacts.
If you want to keep tabs on the danger level, check out NASA’s Asteroid Watch Widget. Here you’ll find out about the asteroids and comets coming within 4.6 million miles of us, which is roughly 20 times as far from us as the moon. According to the site, “an object larger than about 150 meters [492 feet] that can approach the Earth to within this distance is termed a potentially hazardous object.” If you want the information within reach at all times, try the “Asteroid Tracker” app. If you have your own telescope, why not be an Asteroid Data Hunter?
|An illustration of a massive asteroid crashing into Earth. The Earth may have experienced such gigantic impacts in its youth. Image Credit: Don Davis, NASA|
Not all near objects are ominous. Recently a telescope on Hawaii that surveys the sky for asteroids, Pan-STARRS, found a small asteroid that seems to circle the Earth while orbiting the sun. This near-Earth companion has been with us for almost a century, thanks for noticing, and looks to be for many more. It ranges from 38-100 times as far from us as the moon and is probably 100-300 feet across, so not in the hazard range.
It’s true that if the odds are not in our favor, an asteroid could mean the end of life as we know it. But we may also have asteroids to thank for creating conditions on Earth that support life. A team of scientists from the Southwest Research Institute recently proposed a mechanism by which primordial asteroids smashing into our planet during its first billion years could have stabilized the temperature on the Earth, enabling liquid water despite a faint sun. This may have also given us sulfur, a key element of life. Asteroids may also be responsible for most of the Earth’s water and other building blocks of life. Ongoing missions to study current samples and visit more asteroids should provide greater insight into these possibilities.
|NASA’s Asteroid Redirect Mission, currently in development, involves a robotic mission to a large near-Earth asteroid, collecting a giant boulder, redirecting it into orbit around the moon, and sending astronauts there in the 2020s. |
Image Credit: NASA
A key component of Asteroid Day is the 100X Declaration—a declaration signed by notable scientists like Kip Thorne, Jill Tarter, Brian Cox, Bill Nye, and 15,000+ others—that advocates for dramatically improving the rate at which we are discovering and tracking asteroids. You can read it here, and sign it if you’d like. The campaign was co-founded by astrophysicist and Queen guitarist Brian May, and in 2016 there are hundreds of events planned worldwide—ranging from talks to exhibits to movie screenings and music. If there’s not an event near you, don’t panic, you can honor the day with your favorite of the many cheesy, end-of-the-world impact movies.