Earlier this month, scientists at NASA's Jet Propulsion Laboratory noticed something: a previously unidentified asteroid heading this way.
The rock, called 2015 TB145, is somewhere between 290 meters and 650 meters (950 feet and 2,100 feet) in diameter, and experts expect it to pass within 300,000 miles of Earth on Oct. 31.
"On average, a similar close approach for an object of the size of 2015 TB145 happens once per decade," Davide Farnocchia, of JPL's Near-Earth Object Program, told CBS News.
The last time an asteroid came close to Earth was in January, when 2004 BL86 flew by at a distance of about 750,000 miles -- two-and-a-half times farther away. At the time, the next near approach wasn't expected for another 200 years, when 1999 AN10 makes a flyby in 2027.
Of the near-Earth asteroids (NEAs) cataloged at that time, 1999 AN10 was the next in line, Farnocchia said. But then NEO scientists spied 2015 TB145 on Oct. 10.
Farnocchia contended the new space rock was "not really" a surprise. "Since new objects are discovered on a daily basis, the list of close approachers is not static and gets updated correspondingly."
NASA-funded surveys have identified about 90 percent of near-Earth asteroids that are more than a kilometer across, he explained, but "we still have to find many of the sub-kilometer NEAs."
"It is perfectly normal to discover new NEAs of this size," he added.