(
SKY NEWS) Astronomers following the so-called "doomsday" asteroid
Apophis which could collide with Earth have discovered it is 20% bigger
than previously thought.
Previous estimates put the asteroid's average diameter at 270 metres
(877 feet) representing a mass that would equal the energy release of a
506-megatonne bomb, according to Nasa figures.
The
European Space Agency
(ESA) said its Herschel telescope had scanned the space rock as it
headed towards its closest fly-by with the planet in years on Wednesday.
In a two-hour observation, Herschel returned a diameter of 325 metres
(1,056 feet), with a range of 15 metres (48.75 feet) either way, the ESA
said.
"The 20% increase in diameter, from 270m to 325m translates into a 75%
increase in our estimates of the asteroid's volume or mass," said Thomas
Mueller, of the Max Planck Institute for Extra-terrestrial Physics in
Garching, Germany, who led the data analysis.
Named after the god of evil, darkness and destruction in Egyptian
mythology, Apophis sparked a scare when it was first detected in 2004.
Early calculations suggested a 2.7% chance of the space rock hitting
Earth in 2029 - the highest ever for an asteroid, but the risk was
swiftly downgraded after further observations.
It is expected to pass even closer to the planet on April 13, 2036, according to
Nasa's Jet Propulsion Laboratory (JPL) in Pasadena, California.
The object is being tracked by astronomers to help them fine tune the 2029 and 2036 risks of a collision.
Herschel, using thermal sensors, also found that Apophis is darker than previously thought, the ESA added.
Only 23% of light that falls on it is reflected, and the rest is
absorbed by the asteroid. Previous estimates of this reflectivity, known
as albedo, were put at around 33%.
This discovery is important because asteroids experience something
called the Yarkovsky effect, or an increase in thrust that comes from
alternate heating and cooling as the rock slowly turns in space.
Over time, this momentum can change the body's trajectory as it moves through the Solar System.
On February 15, a 57-metre (185-feet) asteroid, 2012 DA14, will skim
the planet at just 34,500km (21,600 miles), making the narrowest
approach so far of any detected asteroid.
Read more article
here.