Thread by @washingtonpost

If all goes well, the spacecraft that NASA plans to launch today will smash itself to bits against an asteroid.

If all goes absolutely perfectly, that impact will jostle the asteroid into a slightly different orbit. wapo.st/3r0vha9

Mission success would mean that for the first time, humans will have changed the trajectory of a celestial object.

Making history, however, is incidental. The real mission is to defend the planet. wapo.st/3r0vha9

The basic idea could not be simpler: Hit it with a hammer! But the degree of difficulty is high, in part because no one has ever actually seen the asteroid NASA plans to nudge.

It is a moonlet named Dimorphos that is about the size of a football stadium. wapo.st/3r0vha9

Why just bump it instead of blowing it apart? Because exploding a pile of ancient rock would be messy and unpredictable, said the mission’s coordination lead.

A small nudge now could ensure that an asteroid sails well wide of Earth years down the road. wapo.st/3r0vha9

No known asteroid large enough to cause damage on the ground has any significant chance of reaching our planet in the next 50 years, according to Paul Chodas, director of NASA’s Center for Near-Earth Object Studies.

The unknown ones are the wild cards. wapo.st/3r0vha9

Here’s a look at the tech that will be tested.

With rolled-up solar panels, an ion thruster and its own satellite paparazzi, the DART spacecraft carries quite a bit of sophisticated equipment, including some that NASA is testing for future missions. wapo.st/3r0vha9

The spacecraft will be launched as early as 1:21 a.m. EST Wednesday.

In 2024, the European Space Agency will launch a spacecraft named Hera to visit Dimorphos and investigate the crater that — fingers crossed — will be left by DART. wapo.st/3r0vha9