A NASA-funded telescope network devoted to detecting space rocks that could crash into Earth will expand into the Southern Hemisphere, which currently lacks a large-scale asteroid-surveillance effort. The additional observatories will not only spot asteroids that could harm people, but also detect comets, supernovae and other benign celestial objects.

NASA confirmed on 13 August that it will provide US$3.8 million over the next 4 years to support the construction and operation of two asteroid-hunting observatories south of the Equator. Researchers plan to build one facility in South Africa, but are still deciding on a location for the second outpost. The observatories will join two existing telescopes on the islands of Maui and Hawaii as part of the Asteroid Terrestrial-impact Last Alert System (ATLAS), which is run by the University of Hawaii.

Three Northern Hemisphere observatories, including ATLAS, spotted more than 95% of the 2,057 near-Earth asteroids discovered in 2017. But these northern surveys are blind to roughly 30% of the southern sky — and to any asteroids in that region that could hit Earth.

“By placing telescopes in the Southern Hemisphere, you’ll enhance the ability to protect the planet,” says Tim Spahr of the astronomy consultancy NEO Sciences near Boston, Massachusetts. “There will always be things we can’t see from the north.”

Asteroid-spotting

A southern presence for ATLAS is also alluring to astronomers because the southern sky is rich in interesting objects. “If you want to look at the Galactic Centre, that’s where you want to be,” says Matthew Holman, director of the Minor Planet Center in Cambridge, Massachusetts. The forthcoming telescopes could yield data across the whole range of astrophysics, he says.

The southern ATLAS units’ primary purpose, however, will be to spot relatively small asteroids that bigger telescopes miss. The asteroid that scientists believe wiped out the dinosaurs was 9 kilometres in diameter, but much smaller space rocks can also inflict serious damage. The mid-air explosion of a 20-metre asteroid in 2013 resulted in burns, cuts and broken bones for people in the Chelyabinsk region of Russia. And researchers think that a 50-metre asteroid devastated thousands of square kilometres of Russian forest in the 1908 Tunguska event.

Large telescopes such as those that are part of the Catalina Sky Survey in Tucson, Arizona, excel at finding asteroids in the far reaches of the Solar System. But the current ATLAS telescopes shine at picking out small objects that are much closer to Earth — within 7.5 million kilometres of the planet. They do so by conducting relatively rapid scans of the entire sky, which gives researchers more opportunities to detect diminutive asteroids as soon as the objects are visible from the ground.

ATLAS also has software optimized to detect fast-moving objects. As a result, the network can spot asteroids roughly the size of the Chelyabinsk and Tunguska rocks a few days to a week before impact, says John Tonry, the founder and principal investigator of ATLAS, who is based at the University of Hawaii at Mānoa. in Honolulu. In early June, the system proved its mettle by providing data on the trajectory of a 1.8-metre asteroid called 2018 LA that swept over Africa. Researchers were subsequently able to find fragments of this space rock in Botswana . Since it started making observations in 2015, ATLAS has discovered 171 asteroids whose path brings them close to Earth’s orbit.

Establishing relatively inexpensive ATLAS systems in the south will enable astronomers “to cover the entire night sky every day or two to provide as much warning as we can”, says Lindley Johnson, planetary defence officer for NASA in Washington DC.

After the southern ATLAS observatories come online, “we’ll have close to round-the-clock coverage of the night sky”, says Larry Denneau, an ATLAS co-principal investigator at the University of Hawaii. “The more eyes you have looking, the better.”