An asteroid hurtled across Earth's orbit at a distance of only 3 million miles last week in a passing that planetary scientists consider a close encounter. The asteroid, dubbed 1990 MF, made one of the closest crossings of Earth orbit observed in 50 years. It had been tracked since Jet Propulsion Laboratory planetary scientist Eleanor Helin discovered it June 26.
Scientists estimated the rocky object's diameter at 300 to 1,000 feet and said the radiant asteroid accelerated to 22,000 m.p.h. at its closest approach. Initial calculations indicate the asteroid has an elongated orbit of 161 million miles that takes two years and four months to complete.
Last year, the closest asteroid orbit yet known came within about 470,000 miles of the Earth.