Illustration: Rebecca Zisser/Axios

Scientists continue to find dangerous asteroids in Earth's vicinity, but to fully capture the threat these nearby space rocks pose, they need tools that aren't in operation now and may not be for years to come.

Driving the news: Last week, an asteroid large enough to destroy a city buzzed by Earth not long after scientists first spotted it.

Why it matters: Astronomers have detected less than half of the estimated 25,000 near-Earth objects thought to be 459 feet in size or greater.

  • Asteroid strikes are exceedingly rare, but if one of these relatively large space rocks were to impact a populated area, it could cause significant citywide or regional damage.

Where it stands: Because of that danger, Congress mandated that by 2020 NASA find at least 90% of large asteroids that could hit Earth. NASA isn't on track to meet that goal but has found about 90% of all near-Earth asteroids that are 3,281 feet in size or greater.

  • A report released by the National Academies in June suggests the best way for NASA to meet that goal is to use a space-based infrared telescope like NEOCam.
  • However, that new mission reportedly doesn't have the funding it needs.
  • NASA's NEOWISE telescope currently in orbit today does hunt for asteroids in infrared light, but it's nearing the end of its operational life and it wasn't designed for this purpose.
  • Public polls find Americans believe asteroid tracking should be a top priority for NASA.

How it works: Detecting asteroids in infrared light is effective because many of the space rocks are dark to the naked eye but shine brightly in thermal infrared.

  • A space-based system is also well-suited for this work because it doesn't rely on it being nighttime on Earth to scan the skies, NASA scientist Tom Statler told Axios.
  • Instead of simply looking in optical or infrared wavelengths of light, it might also one day be possible to use artificial intelligence to pick out the signal from the noise to find those space rocks.

The catch: Experts think there's no one method that will find, track and characterize all of the potentially dangerous asteroids near our planet, but instead it will be necessary to use both ground-based and space-based telescopes.

  • Asteroid tracking also requires a fair bit of follow-up observation, so ground-based systems will be needed for those follow-ups even if a new telescope is launched to space.

What's next: Scientists are trying to figure out what can be done if a dangerous asteroid is found speeding on a collision course with Earth.

  • In 2021, NASA is planning to launch its DART mission to intercept a space rock and test asteroid deflection technology.
  • "To avoid an impact, you would need to change the arrival time of an asteroid by 7 minutes; either speed it up by 7 minutes, or slow it down by 7 minutes," planetary astronomer Andy Rivkin of Johns Hopkins University told Axios.

The bottom line: The risk of an asteroid strike is low, but the consequences would be high if one were on a collision course with Earth.

  • "It's something to be smart about, but it's not a matter of fear," Statler said.

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