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An animation shows what the orbit looks like.
Credit: Dr. Steven Ostro et al./NASA
A very large asteroid with its own little moon will pass near the Earth tonight (May 25) – close enough so that, with preparation and quality telescope, amateur astronomers can spot it in the process of hiding the stars.
This lunar-asteroid system, called 1999 KW4, consists of two rocks. The largest is about 1.3 km wide according to NASA and has the shape of a top. The smaller one is longer and extends 0.57 km (0.55 km) along its largest dimension. It points in the direction of the length towards its much bigger twin.
Together, the asteroid and its minimoon will cross the Earth at such a strange and steep angle that NASA has described them as "less accessible … for a space mission of any known binary asteroid close to the Earth". [Doomsday: 9 Real Ways Earth Could End]
But that does not mean that they are not interesting to watch.
The two asteroids will be closest to Earth at 19:05 EDT (11:05 GMT), while they will be only 5,182,015 kilometers (5,182,015 km) from the surface of the planet. It's more than a dozen times the distance between the Earth and the Moon in its orbit around our planet, and far too far for the space rocks to pose a threat. In fact, this is the fourth approach that binary asteroids have made to Earth since their discovery in 1999, and not the closest one. This is not the first time, according to EarthSky, that astronomers are planning to create radar images of these asteroids as they pass.
A series of radar images taken in 2001 with NASA's Goldstone radar telescope shows 1999 KW4.
Credit: Dr. Steven Ostro et al./NASA
On May 25, 2001, according to NASA, asteroids dropped 6.7% closer to Earth than they did this time, at a distance of 4,836,798 km (3,005,447 miles). In 17 years, on May 25, 2036, the rocks will pass 55.2% closer to Earth, at a distance of just 1,443,511 miles (2,323,106 km), which poses no additional threat.
These big rocks are frequent travelers in the vicinity of our planet for a long time.
"1999 KW4's approach to 0.05 AU from the Earth several times a century," says NASA's report on this subject. "This trend has existed since at least [the year] 1600 [to] 2500. " [Black Marble Images: Earth at Night]
"UA" refers to "astronomical units", a unit equal to the distance between the Earth and the sun. So 0.05 AU equals one twentieth of the distance between the Earth and the sun, about 7 650 000 km (7 650 000 km). The two asteroids have passed even closer to Earth, without incident, several times a century since William Shakespeare wrote, and they will continue to do so until this article is at least 500 years old.
EarthSky announced that, at the closest approach to the space rocks, they would be most visible in the southern hemisphere, appearing as rapidly moving shadows against the stars in the constellation of Puppis. Both asteroids will remain visible for several days, according to EarthSky. North American asteroid hunters can locate objects near the Hydra constellation on the evening of May 27th.
NASA said its global defense coordination office will continue to monitor asteroids closely.
Originally published on Science live.
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