A newly expanded asteroid-alert system operated by the University of Hawaii Institute for Astronomy can now scan the entire sky every 24 hours for dangerous asteroids that could strike Earth with short notice.

The NASA-funded Asteroid Terrestrial-impact Last Alert System — ATLAS for short — has added two recently built Southern Hemisphere telescopes, in South Africa and Chile, to its existing Northern Hemisphere telescopes, on Haleakala on Maui and Mauna Loa on Hawaii island.

“An asteroid that hits the Earth can come at any time from any direction, so ATLAS is now all the sky, all the time,” John Tonry, a professor with the UH astronomy institute, and the project’s principal investigator, said in a UH news release.

The system can provide one day’s warning for a 20-meter-diameter asteroid, which would be capable of destroying a city. Larger asteroids can be seen when farther away, so ATLAS can provide up to three weeks’ warning for a 100-meter asteroid, which officials say would be big enough to cause regional devastation 10 times the scale of Tonga’s recent volcanic eruption.

The four-telescope system has become the first surveillance system for hazardous asteroids capable of monitoring the entire dark sky every 24 hours. The two southern telescopes can observe at night when it is daytime in Hawaii. So far, the system has discovered more than 700 near-Earth asteroids and 66 comets, the institute said.

While other surveillance systems such as UH’s Pan-STARRS look for much larger objects visible when they’re still years away, the ATLAS system is built to detect smaller, fast-moving objects in close range that the other systems might miss, UH associate astronomer Roy Gal told the Honolulu Star-­Advertiser.

If an object poses a threat, he said, ATLAS could possibly give people time to evacuate away from the projected impact area.

The new telescopes were built with $3.8 million from NASA at Sutherland Observing Station in South Africa — in partnership with the South African Astronomical Observatory — and El Sauce Observatory in Chile, in a multi-institutional collaboration. UH scientists were able to supervise assembly remotely during the pandemic.

The ATLAS project in 2013 received $5.4 million to build the two Hawaii telescopes and operate them until 2018, and then $2.2 million to operate them through 2020, Larry Denneau, institute astronomer and ATLAS co-principal investigator, told the Star-­Advertiser. An extension grant of $5.5 million will carry the project through 2025.

The facilities on Haleakala and Mauna Loa became fully operational in 2017. The two added telescopes will take a few more weeks or months to become fully operational.

Denneau, in a statement, called the surveillance for near-Earth objects “a cooperative global effort. … All these systems have different specialties, and together they are working to keep us safe from hazardous asteroids that could strike anywhere from days to decades into the future.”