An animation shows what the orbit looks like.
Picture credits: Dr. med. Steven Ostro et al./NASA
A very large asteroid with its own little moon will pass Earth this evening (May 25th) – close enough for amateur astronomers, with some preparation and a decent telescope, to see it erase the stars.
This moon asteroid system, called 1999 KW4, consists of two rocks. According to NASA, the big one is about 1.3 kilometers wide and has the shape of a gyroscope. The smaller one is elongated and extends over a length of 0.57 km. It shows lengthwise to its much larger twin.
Together, the asteroid and its minimoon will pass the Earth at such a strange, steep angle that NASA calls it "the least accessible … for a spacecraft mission of a known binary near-Earth asteroid." (Judgment Day: 9 Real Ways the Earth May End)
That does not mean that they are not interesting.
The two asteroids will pass Earth closest to Earth at 19:05 GMT (1105 GMT) when they are only 5,182,015 km from the surface of the planet. That's more than a dozen times the distance between the Earth and the Moon in its orbit around our planet and way too far for the space rocks to be a threat. In fact, this is the fourth approximation of binary asteroids to Earth since they were discovered in 1999, rather than the next. EarthSky is not the first time that astronomers are taking radar images of these asteroids as they pass by.
As early as May 25, 2001, NASA reported that the asteroids were about 6.7% closer to Earth at a distance of 4,836,798 km than this time. In seventeen years, on May 25, 2036, the rocks will travel closer to Earth at a distance of only 2,323,106 km 55.2%. Again, this is not a serious threat.
These big rocks have been flying a lot in the neighborhood of our planet for a long time.
"1999 KW4 approaches several times a century within 0.05 AU of the Earth," states NASA's report on the object. "This trend exists from at least (the year) 1600 (to) 2500." (Black Marble Pictures: Earth at Night)
"AU" refers to "astronomical units," a unit that corresponds to the distance between Earth and Sun. 0.05 AU equals one-twentieth of the distance between Earth and the Sun or about 7,480,000 km (4,650,000 miles). Several times in the century since William Shakespeare wrote, the two asteroids have come even closer to Earth without incident, and will continue to do so until that article is at least 500 years old.
EarthSky reported that they are most visible during the next approach of space rocks in the southern hemisphere, and appear as fast-moving shadows against stars in the constellation Puppis. The two asteroids, however, remain visible for several days, according to EarthSky. North American asteroid hunters can spot the objects on the evening of May 27 near the constellation Hydra.
NASA announced that its planetary defense coordination office will continue to closely monitor the asteroids.
Originally) released on Live Science,