HILO — Students and enthusiasts alike gathered Friday at ‘Imiloa Astronomy Center for a presentation by a University of Hawaii at Manoa astronomer about preventing asteroids from striking the Earth.
Although part of ‘Imiloa’s Maunakea Skies lecture series, Friday’s presentation was unusual in that it featured a speaker not from the Big Island but from Maui: Richard Wainscoat, who works with the Pan-STARRS telescopes atop Haleakala.
Pan-STARRS, or Panoramic Survey Telescope and Rapid Response System, is an astronomical survey that scans the night skies for near-Earth objects — objects in space that are very roughly 1.3 times as far from Earth as the Earth is from the sun. The survey has one complete telescope and a second under construction and is responsible for nearly half of all near-Earth object discoveries in the past four years.
One of Pan-STARRS most recent and high-profile achievements was the 2017 discovery of the asteroid ‘Oumuamua, the first object detected passing through the solar system that originated from beyond it. Wainscoat hinted that ‘Oumuamua’s discovery might disprove a theory that most interstellar objects would be comets instead of asteroids, but declined to comment further, instead advising his audience to wait for his next publication.
Although ‘Oumuamua’s discovery is momentous, most of Pan-STARRS’ work is spent on objects closer to Earth. The near-Earth objects the survey tracks are caught in lengthy elliptical orbits around the sun, returning to visibility every couple of years.
While Wainscoat emphasized that there is no known asteroid on a collision course for the Earth, he did not sugarcoat the gravity of Pan-STARRS’ work: The asteroids Pan-STARRS tracks are potential planet-killers, with asteroids with diameters of 1 kilometer or more, having the potential to level cities or ecologically devastate the planet.
To illustrate this point, Wainscoat referred to past meteorite impacts: the dinosaur-killing Chicxulub impact 66 million years ago, which involved a meteorite thought to be 10-15 kilometers in diameter; the Manicouagan crater in Quebec, formed 214 million years ago by a 5-kilometer diameter meteorite; and the 1908 Tunguska event, where an asteroid detonated in the atmosphere above Siberia, flattening millions of trees over 830 square miles.
More recently, Wainscoat highlighted the Chelyabinsk meteor in 2013, where a 20-meter-wide rock exploded over Chelyabinsk, Russia, shattering windows and triggering car alarms from miles away. The Chelyabinsk meteor was the largest of the 556 asteroids to disintegrate in the Earth’s atmosphere between 1994 and 2013, and, had it been much bigger, would likely have caused fatalities, Wainscoat said.
Should such an asteroid impact be certain, Wainscoat said some options are available. Smaller asteroids will have shorter warning periods — 24 hours to a couple of days, maximum — but larger asteroids’ trajectories will ideally be known years in advance, allowing governments to formulate defense strategies.
One option would be a kinetic impactor: effectively a spacefaring battering ram, which would strike the asteroid in an effort to knock it off course. If done early enough, even a small deviation in trajectory could change a certain collision into a near-miss, although Wainscoat said an insufficient course correction could actually worsen the situation by shifting the impact site from an unpopulated area to a populated one.
Should the kinetic impactor fail, Wainscoat said the only other option available with current technology would be to detonate a nuclear weapon on the asteroid, saying it is the only known device that could provide more force than a kinetic impactor.
Despite the work of Pan-STARRS and other telescopes around the world, the Chelyabinsk event could not have been predicted, Wainscoat said. The meteor came from the direction of the sun, meaning no telescope could have detected the object within the blinding light of the star.
However, Wainscoat said, nearly all near-Earth objects 1 kilometer in diameter or greater have been located. Even as humanity’s ability to observe space grows, the number of large asteroid discoveries has decreased, suggesting that more than 90 percent of large near-Earth objects are accounted for.
Pan-STARRS will, when completed, have four telescopes on Haleakala, each equipped with a camera capable of recording almost 1.4 billion pixels per image. In addition, the Hawaii-based NASA survey ATLAS, or Asteroid Terrestrial-Impact Last Alert System, will construct additional telescopes in Chile and South Africa, allowing the survey to scan more of the sky without being hampered by poor weather in Hawaii.
These improvements, Wainscoat said, hopefully will allow all potentially dangerous near-Earth objects to be identified within a decade or so — although he noted that no telescope today can detect an asteroid against the light of the sun, or among the billion stars within the Milky Way.
Email Michael Brestovansky at mbrestovansky@hawaiitribune-herald.com.
