NASA may be closing down its grand plan to study a piece of an asteroid up close, but the researchers who focus on near-Earth objects aren’t turning their backs on massive space boulders.

They say it’s just a matter of time before we’ll be forced to head off a threatening asteroid. On Friday, they’ll be calling attention to the challenge — and what scientists and activists are doing to address it.

For the past two years, the organizers of Asteroid Day have focused on June 30 as a time to turn an international spotlight on planetary defense. The date marks the anniversary of the Tunguska explosion, a presumed asteroid strike that destroyed half a million acres of forest in Siberia in 1908.

This year, with the United Nations’ encouragement, 190 countries around the world are planning a total of more than 700 Asteroid Day events, ranging from planetarium shows and virtual reality tours to a 24-hour streaming video marathon.

Seattle’s Museum of Flight is hosting Asteroid Awareness Day, which will feature fun activities for the kids and live-stream lectures for the grownups.

One of the organizers of the worldwide Asteroid Day event is former NASA astronaut Ed Lu, executive director of the nonprofit B612 Foundation’s Asteroid Institute.

More than a decade ago, Lu proposed a method for diverting an asteroid that was on a long-term collision course for Earth, by stationing a spacecraft near the asteroid and letting its gravitational attraction pull the asteroid ever so gently into a non-threatening trajectory.

The “gravity tractor” concept would have been tested during NASA’s Asteroid Redirect Mission, or ARM, which had been planned for the mid-2020s. The Obama administration championed ARM, but now that President Donald Trump is in the White House, it’s being defunded.

Despite ARM’s cutoff, Lu says other studies focusing on how to deflect potentially threatening asteroids will move forward.

“We still think a test of a gravity tractor would be very useful,” he told GeekWire.

Lu points to future space shots such as the European Space Agency’s Asteroid Impact Mission and NASA’s Double Asteroid Redirection Test, or DART, which is designed to smash a probe into an asteroid and see how much its trajectory changes. NASA’s OSIRIS-REx mission, launched last September, aims to bring bits of an asteroid back to Earth for study in 2023.

NASA says the data produced during ARM’s planning stages will be used to guide preparations for future missions. “Asteroid encounter mission concepts remain of interest due to the broad array of benefits for the human and robotic exploration, science, planetary defense and asteroidal resources communities,” the space agency said in this month’s ARM update.

Concerns about asteroid threats have risen to fossil evidence suggesting that cosmic impacts were behind ancient mass extinctions — including the demise of the dinosaurs 65 million years ago — as well as more recent events such as 2013’s Chelyabinsk meteor explosion and 1908’s Tunguska blast.

Scientists estimate that a Tunguska-scale impact might happen every few centuries or so on average. NASA is already tracking more than 15,000 near-Earth asteroids, and Czech astronomers recently reported a new source of potentially hazardous space debris.

The asteroid-tracking game is likely to become more complex in the 2020s, when the Large Synoptic Survey Telescope, or LSST, goes into full swing in Chile. The University of Washington’s DIRAC Institute and the B612 Foundation’s Asteroid Institute are already bracing for what’s expected to be a flood of LSST asteroid discoveries.

Alan Fitzsimmons, an astrophysicist from Queen’s University Belfast who’s part of Europe’s NEOshield-2 project, says scientists and engineers are making great strides in detecting asteroids – and adds a caveat that’s fitting for Asteroid Day.

“Astronomers find Near-Earth asteroids every day, and most are harmless,” he said in a news release. “But it is still possible the next Tunguska would take us by surprise, and although we are much better at finding larger asteroids, that does us no good if we are not prepared to do something about them.”

Stay tuned for more Asteroid Day coverage from GeekWire over the week ahead.