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Hawaii telescopes stand sentry against asteroids
It's the stuff of science fiction: a giant asteroid on a collision course with Earth, threatening humanity with extinction.
In 1998, not one, but two big-budget Hollywood movies explored the planet-killing scenario: "Deep Impact" (with Robert Duvall) and "Armageddon" (with Bruce Willis). But the plot has been successfully mined by storytellers for decades. Centuries, possibly.
True, the likelihood of Earth being struck by a catastrophically large asteroid in your lifetime is very low. But it's not zero. Stephen Hawking famously ranked it as the biggest threat facing planet Earth.
That's why we have the Panoramic Survey Telescope and Rapid Response System, or Pan-STARRS, scanning the skies from atop Haleakala on Maui.
Significant space sightings
Pan-STARRS is the world leader in finding Potentially Hazardous Asteroids (PHAs).
It was only last year that the threat of a potential asteroid strike made global headlines.
In July, Pan-STARRS discovered a 65-foot-long asteroid less than a week before it made its closest approach to Earth. In the end, it safely sailed by at a distance 1.7 times further from Earth than the moon, but it was exactly the kind of space surprise that keeps astronomers on their toes.
First coming online in December 2008, Pan-STARRS was specifically designed to find these threats, and it's very good at it. Pan-STARRS finds nearly as many Near Earth Objects (NEOs) and Potentially Hazardous Asteroids (PHAs) as the rest of the world's observatories combined.
From 2014 to 2019, Pan STARRS discovered about 250,000 new asteroids, more than 4,000 of them NEOs. And Pan-STARRS has found most of the largest and most dangerous known asteroids, those measuring more than 459 feet (140 meters) across.
It also set a record for the largest number of asteroids discovered in a single night.
"Pan-STARRS is our insurance policy against one of these asteroids that may have a completely catastrophic impact on Earth, such as the one that wiped out the dinosaurs," said Pan-STARRS principal investigator Ken Chambers in a video news release.
That asteroid is believed to have measured as large as nine miles across.
“It could arrive a thousand, ten-thousand, or one million years from now... or it could arrive tomorrow," Chambers said. "So we need to continually scan the sky to find these ones that might be potential objects."
PS1 and PS2, not PS4
PS2 and PS1 telescopes atop Haleakalā on the island of Maui.
The Pan-STARRS wide-field astronomical imaging system consists of the Pan-STARRS1 (PS1) and Pan-STARRS2 (PS2) telescopes, outfitted with 1.4- and 1.5-gigapixel cameras. That makes them the two largest astronomical cameras in the world.
When PS2 came online in 2018, it doubled the area observed, each telescope scanning all of the visible sky in four nights. A single Pan-STARRS image is 2 gigabytes in size, with each camera acquiring about 10 terabytes of data each night.
"The original plan for Pan-STARRS called for a single mount with four mirrors and four big cameras to replace the 88-inch telescope on Mauna Kea," IfA associate astronomer Roy Gal told me.
But that older telescope, named UH88, remains scientifically productive today, celebrating its 50th anniversary last year. So Pan-STARRS is today two separate telescopes in two separate domes, the second repurposed after a small Japanese telescope was decommissioned.
"So far there have been two data releases," Gal explained, one in 2016 and one in 2019. "The first is the entire static sky, imaged over and over, and the second included better static sky imagery as well as hundreds or thousands of images of each object captured over time."
The data also represents the largest volume of astronomical information ever released, at 1.6 petabytes. (A petabyte is one million gigabytes.) That's equivalent to two-billion digital photos, or 30,000 times the total content of Wikipedia.
"The Pan-STARRS team has had a huge impact on astronomy with a host of discoveries from the solar system to cosmology,” Chambers said. "These include the discovery of thousands of near-Earth objects, hundreds of Kuiper belt objects, dozens of comets, as well as ʻOumuamua, the first interstellar object."
Pan-STARRS discovered ʻOumuamua, the first known interstellar object.
Part of a network of sky watchers
While Pan-STARRS is the leading spotter of NEOs and PHAs, it's not alone.
"If you’re looking for Earth destroying asteroids, those will be found by Pan-STARRS or the Catalina Sky Survey," Gal said. "If you're looking for fast-moving, smaller asteroids that could wipe out a city, that's ATLAS."
Atlas has telescopes on Haleakala and Mauna Loa on Hawaii Loa, 100 miles apart, which scan the whole sky several times each night looking for moving objects. Researchers say it can provide a week's warning of an incoming, 5-megaton "city killer" asteroid.
You'll only get a day's warning for a 30-kiloton impact, however.
"That means UH is responsible for 75 percent of these discoveries," Gal noted. "Hawaii is the world leader of asteroids and comets."
Funding for the future
The Pan-STARRS program received a $15 million grant from NASA to continue its work, UH announced yesterday. The grant will support operations and research for the next three years.
"This NASA grant will enable us to continue our mission to protect the Earth from catastrophic asteroid impact as we scan the sky for anything that moves and everything that goes bang in the night," Chambers said in the announcement.
"The risk of one hitting in our lifetime is extremely small, so you shouldn’t lose any sleep over it," he added. "On the other hand, if we find it, the consequences are so severe and can threaten life on our planet."