Science & Technology

How Do Scientists Predict Whether an Asteroid Will Hit Earth?

Don't worry, there's no asteroid hurtling toward the planet that we know of — but that's not to say that scientists aren't looking. Every day, hunters around the world use a clever combination of space telescopes and ground-based observatories to scour the skies for icy comets and rocky asteroids, especially ones that cruise close to Earth. And every observation, every simulation, helps Earthlings get a little more prepared for that odd interloper that could turn into a threat.

How Citizen Scientists Help With the Hunt

You've probably heard of the Hubble Space Telescope, that venerable observatory that has made amazing discoveries from noticing that the universe is accelerating to spotting new moons around the dwarf planet Pluto while the New Horizons spacecraft was on its way to the neighborhood. Hubble generally examines big objects that are very far away, but every so often, an asteroid photobombs the image. The small world crosses through the field of view and leaves behind a streak. It's a little annoying if you're trying to examine a faraway galaxy, but eminently useful if you're studying how asteroids move in space — and how close they're getting to Earth.

In fact, it's not just scientists who can make use of these extraterrestrial photobombs. You can, too. "Citizen scientists," which are people just like you who have a love of space but not necessarily degrees in the field, can help spot new asteroids in our solar system via a new, free initiative called Hubble Asteroid Hunters on the citizen scientist platform Zooniverse. Using archival images from the European Space Agency's Hubble Science archive, thousands of people examined those telltale streaks to better predict the paths of asteroids through space (and thereby predict whether that path will intercept with Earth). In the end, more than 1,300 separate trails have been identified from some 300,000 observations, many from people just like you. The project is now complete, but Zooniverse is always leading many other projects like it that you can take part in.

Planetary Defenders

Of course, full-time scientists are on the case, too. A few years ago, NASA added on to its existing asteroid search program, which relied on a network of partner telescopes, by centralizing the coordination under a Planetary Defense Coordination Office. The office acts as both a collector of the various observations and a place where people can make decisions about what to do about any threatening interlopers. And to be sure, NASA's not the only one — the agency is working with a group of international partners who each have their own telescopes and policy programs.

And we continue to learn more about asteroids during various missions, such as NASA's OSIRIS-REx spacecraft that's camped out around asteroid Bennu right now. Around 2023, that craft will return a precious sample of material to Earth for scientists to study up close in their laboratories. Learning more about what asteroids are made of makes it easier to deflect threatening ones should they ever come our way.

The agency plans to test asteroid deflection using a mission called DART (Double Asteroid Redirection Test). This mission will send a spacecraft to the double-asteroid 65803 Didymos and attempt to slam an impactor into the smaller of the two so fast that its orbit will change ever so slightly. After that, the team will monitor the deflected asteroid's orbit both from the ground and also through a European mission called Hera, which should perform a flyby in a few years.

These are all small steps to better characterize asteroids and to protect ourselves from them. There's even more coming down the line soon. NASA is trying to classify all city-killing asteroids that would have threatening orbits and a diameter of at least 140 meters (460 feet). In 2005, Congress directed the agency to complete 90 percent of the inventory by 2020.

While funding shortages have made that deadline all but impossible, NASA says that new telescopes such as the Large Synoptic Survey Telescope (LSST) and its newly announced asteroid-hunting telescope that launches in 2024 will help accelerate the search. Right now, we've only found about a third of the estimated population, but these dedicated asteroid hunters will accelerate the search to make a lot more progress in the next decade.

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Learn more about the scientists who search for Earth-killing space rocks in the TED book "Asteroid Hunters" by Carrie Nugent. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Elizabeth Howell November 22, 2019

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