The European Space Agency (ESA) said on 2 August that the fly-by of a 100-metre-wide asteroid last month illustrates the need to increase Earth’s asteroid detection capabilities.
Dubbed “2019 OK”, the football field-sized asteroid came within 65 000 km of the Earth’s surface during its closest approach – about one fifth of the distance to the Moon. It was detected just days before it passed Earth, although archival records from sky surveys show it had previously been observed but wasn’t recognised as a near-Earth asteroid.
Asteroids the size of “2019 OK” are relatively common but hit Earth once every 100,000 years. ESA said that its planned network of Flyeye telescopes will allow astronomers to detect risky space rocks in order to provide early warnings.
The ESA observed the asteroid just before its flyby, by requesting two separate telescopes in the International Scientific Optical Network (ISON) take images of the space rock. With these observations, asteroid experts at the ESA were able to extract precise measurements of the position and movement of the rocky body.
“With the ISON observations we were able to determine the distance of the close approach incredibly accurately,” explained Marco Micheli from the ESA’s Near-Earth Object Coordination Centre. “In fact, with a combination of observations from across the globe, the distance is now known to better than one kilometre!”
The asteroid was first discovered by the Southern Observatory for Near-Earth Asteroids Research (SONEAR) just a day before its close approach. Observations of “2019 OK” were independently confirmed by other observatories, including the Arecibo radar in Puerto Rico and a third telescope in the ISON network.
Since the discovery, with knowledge of where the asteroid would have been and by searching for it by eye, existing images were found in the Pan-STARRS and ATLAS sky survey archives. Both surveys had in fact captured the asteroid in the weeks before the flyby, but the slow space rock appeared to move just a tiny amount between images, and was therefore not recognised.
“This ‘un-recognition’ of an asteroid, despite it being photographed will be used to test the software going into ESA’s upcoming asteroid-hunting telescope, the Flyeye,” Rüdiger Jehn, ESA’s Head of Planetary Defence, said.
Eyes on the sky
Scientists know of – and are tracking – thousands of asteroids in the Solar System, so why was this one discovered so late? Unfortunately, there is currently no single obvious reason, apart from its slow motion in the sky before close approach.
“2019 OK” travels in a highly elliptical orbit, taking it from within the orbit of Venus to well beyond that of Mars. This means that the time it spends near Earth, and is detectable with current telescope capabilities, is relatively short.
The ESA, the US National Aeronautics and Space Administration (NASA), and other agencies and organisations around the globe – both professional and amateur – discover new asteroids every day, which constantly increases scientists’ understanding of the number, distribution and movement of orbiting “rocky bodies”.
Asteroids the size of “2019 OK” size are relatively common in our Solar System but hit Earth on average only every 100,000 years. Travelling in a highly elliptical orbit that takes it within the orbit of Venus, this asteroid won’t come close to Earth again for at least another 200 years.
Planetary Defence at the ESA
According to the ESA, it’s planned developments should mean that by 2030, Europe will be able to:
- provide early warning for dangerous asteroids larger than 40 m in size, about three weeks in advance;
- deflect asteroids smaller than 1 km if known more than two years in advance.
The ESA’s planned network of Flyeye telescopes is expected to significantly help in the global search for risky space rocks, which is necessary to provide early warnings. The agency’s Hera mission – currently being designed to test asteroid deflection for the first time – will look to develop the ESA’s capacity to knock asteroids off a dangerous path.
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