Using Hubble
telescope, team led by UCLA researcher gathers data on size, speed and path of
debris
UCLA
Newsroom:
Images of comet 332P
breaking apart, captured by the Hubble Space Telescope.
Astronomers
have captured the sharpest, most detailed observations of a comet breaking
apart 67 million miles from Earth, using NASA’s Hubble Space Telescope. The
discovery is published online today in Astrophysical Journal Letters.
In
a series of images taken over three days in January 2016 (view
the animation), Hubble showed 25 fragments consisting of a mixture
of ice and dust that are drifting away from the comet at a pace equivalent to
the walking speed of an adult, said UCLA astrophysicist David Jewitt, who led
the research team.
The images suggest that the roughly 4.5-billion-year-old comet, named 332P/Ikeya-Murakami, or comet 332P, may be spinning so fast that material is ejected from its surface. The resulting debris is now scattered along a 3,000-mile-long trail, larger than the width of the continental United States.
These
observations provide insight into the volatile behavior of comets as they
approach the sun and begin to vaporize, unleashing powerful forces.
“We
know that comets sometimes disintegrate, but we don’t know much about why or
how,” Jewitt said. “The trouble is that it happens quickly and without warning,
so we don’t have much chance to get useful data. With Hubble’s fantastic
resolution, not only do we see really tiny, faint bits of the comet, but we can
watch them change from day to day. That has allowed us to make the best
measurements ever obtained on such an object.”
The
three-day observations show that the comet shards brighten and dim as icy
patches on their surfaces rotate into and out of sunlight. Their shapes change,
too, as they break apart. The icy relics comprise about four percent of the
parent comet and range in size from roughly 65 feet wide to 200 feet wide. They
are separating at only a few miles per hour as they orbit the sun at more than
50,000 miles per hour.
The
Hubble images show that the parent comet changes brightness frequently,
completing a rotation every two to four hours. A visitor to the comet would see
the sun rise and set in as little as an hour, Jewitt said.
The
comet is much smaller than astronomers thought, measuring only 1,600 feet
across, about the length of five football fields.
Comet
332P was discovered in November 2010, after it surged in brightness and was
spotted by two Japanese amateur astronomers.
Based
on the Hubble data, the research team suggests that sunlight heated the surface
of the comet, causing it to expel jets of dust and gas. Because the nucleus is
so small, these jets act like rocket engines, spinning up the comet’s rotation,
Jewitt said. The faster spin rate loosened chunks of material, which are
drifting off into space. The research team calculated that the comet probably
shed material over a period of months, between October and December 2015.
Jewitt
suggested that some of the ejected pieces have themselves fallen to bits
in a kind of cascading fragmentation. “We think these little guys have a short
lifetime,” he said.
Hubble’s
sharp vision also spied a chunk of material close to the comet, which may be
the first salvo of another outburst. The remnant from still another flare-up,
which may have occurred in 2012, is also visible. The fragment may be as large
as comet 332P, suggesting the comet split in two. But the remnant wasn’t
spotted until Dec. 31, 2015, by a telescope in Hawaii.
That
discovery prompted Jewitt and colleagues to request Hubble Space Telescope time
to study the comet in detail.
“In
the past, astronomers thought that comets die when they are warmed by sunlight,
causing their ices to simply vaporize away,” Jewitt said. “But it’s starting to
look like fragmentation may be more important. In comet 332P we may be seeing a
comet fragmenting itself into oblivion.”
The
researchers estimate that comet 332P contains enough mass for 25 more
outbursts. “If the comet has an episode every six years, the equivalent of one
orbit around the sun, then it will be gone in 150 years,” Jewitt said. “It’s
just the blink of an eye, astronomically speaking. The trip to the inner solar
system has doomed it.”
The
icy visitor hails from the Kuiper belt, a vast swarm of objects at the
outskirts of our solar system. As the comet traveled across the system, it was
deflected by the planets, like a ball bouncing around in a pinball machine, until
Jupiter’s gravity set its current orbit, Jewitt said.
Co-authors
include Harold Weaver Jr., research professor at the Johns Hopkins University
Applied Physics Laboratory.