What NASA plans to do about asteroids

Every once in a while, we hear the unsettling news that a large asteroid is passing near Earth. And often, we also hear that the rock was only discovered just before the flyby. The close calls are a reminder of how vulnerable our planet really is.

Now we know what NASA intends to do about it. The agency's new plan outlines how it will defend against asteroid strikes.

The plan focuses on detection, meaning telescopes and software. Asteroids have predictable orbits, so once one is spotted, scientists can quickly tell whether it will ever pose a threat and when is the best time to try to deflect it.

SEE MORE: Congressman Dana Rohrabacher Is Very Worried About Surprise Asteroids

And if a threat is found? Some options to deflect an asteroid are subtle, like gravity tractors, where a spacecraft uses its own small gravitational field to nudge an asteroid onto a different orbit.

Others are less subtle, like smashing a spacecraft into the asteroid at high speed to knock it off course. And yes, blowing an asteroid up with a nuke is a real option.

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IN SPACE - JULY 10: This handout image provided by the European Space Agency, transmitted by the space craft Rosetta, shows the asteroid Lutetia at closest approach July 10, 2010 between Mars and Jupiter in outer space. Lutetia, about which little is known although it was discovered in 1852, is believed to be 83.3 miles (134 kilometers) in diameter. The Rosetta, which was launched in 2004, flew by Lutetia tonight at a distance of 1,900 miles (3,200 kilometers). (Photo by ESA 2010 MPS for OSIRIS Team via Getty Images)

This Dawn framing camera (FC) image of Asteroid Vesta shows Licinia crater, which is the large crater in the center of the image. Licinia has a fresh, sharp rim that is scalloped in shape. Around the side of Licinia crater there are many streaks of dark and bright material cascading towards the crater's center. This image is located in Vesta's Floronia quadrangle, in Vesta's northern hemisphere. NASA's Dawn spacecraft obtained this image with its framing camera on Oct. 11, 2011. (Photo by: Universal History Archive/UIG via Getty Images)

The large asteroid Vesta is shown in this image taken by NASA's Dawn spacecraft. Astronauts and scientists are training in waters off Key Largo, Florida as part of NASA Extreme Environment Mission Operations (NEEMO) which is meant to test equipment and man's reactions for a human rendezvous with an asteroid. (Miami Herald/MCT via Getty Images)

IN SPACE - JULY 10: This handout photo illustration provided by the European Space Agency, transmitted by the space craft Rosetta, shows the final sequence of images before the closest approach of the asteroid Lutetia July 10, 2010 between Mars and Jupiter in outer space. Lutetia, about which little is known although it was discovered in 1852, is believed to be 83.3 miles (134 kilometers) in diameter. The Rosetta, which was launched in 2004, flew by Lutetia tonight at a distance of 1,900 miles (3,200 kilometers). (Photo by ESA 2010 MPS for OSIRIS Team via Getty Images)

NASA's Dawn spacecraft obtained this image with its framing camera on July 17, 2011. It was taken from a distance of about 9,500 miles (15,000 kilometers) away from the protoplanet Vesta. Each pixel in the image corresponds to roughly 0.88 miles (1.4 kilometers). (Photo by: Universal History Archive/UIG via Getty Images)

Image of the Vesta Ateroid. This Dawn framing camera (FC) image of Vesta shows linear grooves and ridges in Vesta's regolith. These linear features generally run diagonally across the image from the top left to the bottom right. They are less than 1 kilometer (0.6 mile) in width and some have lengths that extend across the entire image. This image is located in Vesta's Tuccia quadrangle, in Vesta's southern hemisphere. NASA's Dawn spacecraft obtained this image on April 8, 2012. (Photo by: Universal History Archive/UIG via Getty Images)

As NASA's Dawn spacecraft takes off for its next destination, this mosaic synthesizes some of the best views the spacecraft had of the giant asteroid Vesta. Dawn studied Vesta from July 2011 to September 2012. The towering mountain at the south pole -- more than twice the height of Mount Everest -- is visible at the bottom of the image. The set of three craters known as the 'snowman' can be seen at the top left. (Photo by: Universal History Archive/UIG via Getty Images)

Asteroid 2015 TB145 is depicted in eight individual radar images collected on Oct. 31, 2015 between 5:55 a.m. PDT (8:55 a.m. EDT) and 6:08 a.m. PDT (9:08 a.m. EDT). (Photo via NASA/JPL-Caltech/GSSR/NRAO/AUI/NSF)

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The report also says NASA is now confident that all the largest asteroids — the ones big enough to cause worldwide damage — have already been found and that none are a threat.

And for smaller asteroids, early detection could give years to prepare for an impact if it can't be deflected.

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