The 1,400 asteroids, whose orbits are given a web-like appearance in the spirograph, are considered fairly dangerous but are not expected to pose an imminent threat for at least another 100 years.
The ‘potentially hazardous asteroids’ (PHA) are large – estimated at about 460ft or 140m in size – and can reportedly pass within 4.7million miles of the Earth’s orbit.
In these terms – that’s pretty close.
‘By monitoring these PHAs and updating their orbits as new observations become available, we can better predict the close-approach statistics and thus their Earth-impact threat.’
In February of this year a PHA known as 2012 DA14 passed Earth within a margin of 17,200 miles, which is closer than some satellites in geosynchronous orbit. The asteroid was 150ft in diameter and passed safely.
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