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Special Feature
Asteroid with Six Comet-like Tails Surprises Astronomers
By NASA’s Amazing Space reporters
December 2013
T
he Hubble Space
Telescope has found an
odd-looking asteroid
with six comet-like tails of
dust streaming from its body
like spokes on a wheel.
Astronomers spotted the asteroid
in our solar system’s asteroid belt, a
reservoir of space rocks between the
orbits of Mars and Jupiter. Asteroids
are some of the leftover debris from
the construction of our solar system
5 billion years ago.
The object’s unusual appearance
has puzzled astronomers. Almost all
other known asteroids look like tiny
points of light and do not have tails
of dust trailing behind them. Tails are
normally seen trailing from comets,
when they orbit near the Sun.
Comets are made up of ice, dust, and
some rock. They hail from the outer
solar system and visit the inner solar
system during their journey around
Continued, page 2…
IMAGE: NASA, ESA, and D. Jewitt (UCLA)
The active asteroid and its surprising tails, September 10, 2013:
Many tails are visible here. Astronomers noticed that the tail structure changed
dramatically over two weeks. See page 2 to view the changes they saw.
Continued from page 1…
the Sun. As comets get closer to the
Sun, they develop tails when some of
their ice vaporizes and gets pushed
away from them.
An active asteroid and its surprising tails
Astronomers also noticed that the
tail structure of this oddball asteroid
changed dramatically over just two
weeks as it released dust. Hubble
images have shown that the ancient
asteroid, known as P/2013 P5, has
been ejecting dust periodically for at
least five months.
Why is the asteroid losing material?
Astronomers hypothesize that
over billions of years the asteroid
began rotating faster and faster,
eventually causing it to start
losing material from its surface.
The researchers do not think the
tails formed from a collision with
another asteroid. A collision would
cause a large cloud of dust to blast
into space all at once. A series of
Hubble telescope images, taken
over five months, has not shown
that type of catastrophic event.
Instead, calculations show that
the tails could have formed by a
series of dust ejection events, from
April 15 to Sept. 4. A rather curious
feature is that between the Hubble
observations on Sept. 10 and Sept.
23, the entire structure appeared to
have swung around.
So far, the asteroid has lost a
small amount of its mass. Its
nucleus, which measures 1,400
feet wide, is thousands of times
more massive than the observed
amount of ejected dust.
Astronomers will continue observing
the unusual object. Asteroids that
fall apart by spinning too fast may
be common in the asteroid belt. As
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Sept. 10, 2013
Sept. 23, 2013
Sept. 10, 2013
Sept. 23, 2013
IMAGE: NASA, ESA, and D. Jewitt (UCLA)
Astronomers were “completely knocked out” to see how the appearance of the
asteroid and its tails changed quickly. In just 13 days, it looked as if the entire
structure had swung around. In the lower two images, the tails and the direction
of the Sun have been labeled.
one researcher said, “In astronomy,
where you find one, you eventually
find a whole bunch more.”
Asteroid P/2013 P5 may be a
fragment of a larger asteroid that
broke apart in a collision roughly
200 million years ago. Many collision
fragments are in orbits similar to
that of P/2013 P5. Meteorites from
these bodies show evidence of
having been heated to as much
as 1,500 degrees Fahrenheit. This
evidence means the asteroid is
probably made up of rocks and does
not hold any ice as a comet does.
The asteroid was discovered as an
unusually fuzzy-looking object with
the Pan-STARRS survey telescope
in Hawaii. The multiple tails were
discovered in Hubble images taken
on Sept. 10, 2013.
Anatomy of a comet
Most comets start out as dusty
chunks of ice on the outer
edges of the solar system. Their
distinctive shape develops as they
get closer to the Sun.
As the nucleus warms up, the
evaporating ice forms a coma, a
bright, huge sphere of gas and
dust. The warmer it gets, the more
gas and dust vaporize from the
surface, until a tail may form.
gas and dust.
Space Telescope Science Institute, Graphics Dept.
3
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