Nearly mile-wide 'double asteroid' to pass Earth's vicinity tonight

J. H. Osborne • May 25, 2019 at 2:00 PM

An unusual “double asteroid” is nearing Earth’s vicinity and will pass us by Saturday, May 25. It consists of a primary space rock just under a mile wide, with a 0.3-mile-wide companion asteroid — which some are calling an “asteroid moon” — orbiting it, according to a press release issued Friday by The Farmers’ Almanac listing these facts from contributing astronomer Joe Rao:

• Named 1999 KW4, the object is an Aten-type space rock, meaning that its orbit brings it between the orbits of Venus and Earth and will actually cross Earth’s orbit. (It would not be good if the asteroid and our planet were to arrive at that crossing point in space at the same time.) This double asteroid completes an orbit around the sun once every 6.18 months (188 days).

• NASA animation of the orbit can be viewed online.

• Most of us will NOT be able to see 1999 KW4 as it streaks past Earth on Saturday evening.

• At 7:05 p.m. EDT, 1999 KW4 will pass 3,219,955 miles from Earth — or about 13.5 times the distance of the moon from our planet. By comparison, the destructive meteoroid that exploded in the sky over Chelyabinsk, Russia, in February 2013 was only about 65 feet wide. Of course, that meteoroid made contact with Earth. This “double asteroid,” estimated to be 80 times larger, will not.

• According to the catalog of near-Earth objects (NEOs) kept by the Minor Planet Center, this passing will mark the closest currently known approach by an object this large. The next large asteroid to approach Earth will be in June 2027— 1990 MU — at about 4 miles across, at 12 lunar distances (2.86 million miles from Earth).

Who will be able to see it?

• There are some assiduous amateur astronomers who will take the initiative and make the attempt to locate 1999 KW4 soon after darkness falls on Saturday evening. But most of us who are inexperienced observers with unsophisticated equipment probably won’t be able to spot 1999 KW4. It’s simply much too faint. Even at its very brightest, it will be around only 12th magnitude, or 250 times fainter than the faintest star that you can see with your unaided eye. And that’s when it will be at its very closest to Earth.

• Astronomers intend to use both NASA’s Goldstone 230-foot radar antenna, located in the Mojave Desert, and the 1,000-foot radar dish at Arecibo Observatory in Puerto Rico to bounce radio waves off the asteroid in an attempt to accurately determine its size.

• Today, we know that our planet is literally in a celestial shooting gallery. And it is not a matter of “if” an asteroid impacts our planet, but when.

• In fact, there are nearly 2,000 PHAs (potentially hazardous asteroids) that have the potential of colliding with Earth, and 1999 KW4 is one of them. New ones are being found all the time.