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 The asteroid, estimated to be about 1,300 feet (400 meters) in
diameter, will shoot past the planet at 22 miles (35 km) per second
at around 1 p.m. (1700 GMT) on Halloween afternoon. Known as 2015
TB145, it will come within about 300,000 miles (480,000 km) of
Earth, farther away than the moon but relatively close by cosmic
measures.
Astronomers hope to capture radar images and other measurements of
the asteroid during the encounter, a rarity for scientists who
typically rely on expensive robotic space probes to gather
information about such rocky bodies. Scientists expect to learn
about the asteroid’s shape, dimensions, surface features and other
characteristics.
 "The close approach of 2015 TB145 ... coupled with its size,
suggests it will be one of the best asteroids for radar imaging
we'll see for several years," Lance Benner, an astronomer at NASA’s
Jet Propulsion Laboratory in Pasadena, California, said in an
article posted on the U.S. space agency's website.
Aside from pure scientific value, the encounter may help engineers
develop better tracking techniques and countermeasures for asteroids
that may be on a collision course with Earth.
Small space rocks rain down on Earth constantly, with most
disintegrating as they blaze through the atmosphere.
About 65 million years ago, an asteroid or comet roughly six miles
(10 km) in diameter crashed into what is now Mexico’s Yucatan
peninsula, triggering global climate changes that killed off the
dinosaurs along with about 75 percent of life that existed at the
time, scientists say.
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More recently, a 65-foot-wide (20 m) asteroid broke apart over
Chelyabinsk, Russia, in February 2013, shattering windows and
damaging buildings. More than 1,000 people were injured by flying
debris.
NASA is working to map potentially dangerous asteroids and comets
that pass within 30 million miles (48 million km) of Earth.
Asteroid 2015 TB145 was discovered less than three weeks ago.
“That such a large object, capable of doing significant damage if it
were to strike our planet, was discovered only 21 days before
closest approach demonstrates the necessity for keeping daily watch
of the night sky,” Detlef Koschny, an astronomer with the European
Space Agency, said in a statement.
(Editing by Frank McGurty and Tom Brown)
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