Credit: NASA, ESA, and D. Jewitt (UCLA)
Credit: NASA, ESA, and D. Jewitt (UCLA)
NASA's Hubble Space Telescope has captured one of the sharpest, most
detailed observations of a comet breaking apart, which occurred 67
million miles from Earth.
In a series of images taken over a three-day span in January 2016,
Hubble revealed 25 building-size blocks made of a mixture of ice and
dust that are drifting away from the comet at a leisurely pace, about
the walking speed of an adult.
The observations 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 U.S.
These observations provide insight into the volatile behavior of
comets as they approach the sun and begin to vaporize, unleashing
dynamical forces. Comet 332P was 150 million miles from the sun,
slightly beyond the orbit of Mars, when Hubble spotted the breakup.
"We know that comets sometimes disintegrate, but we don't know much
about why or how they come apart," explained lead researcher David
Jewitt of the University of California at Los Angeles. "The trouble is
that it happens quickly and without warning, and 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. And that has allowed us to make the best
measurements ever obtained on such an object."
The three-day observations reveal 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 4 percent of the parent comet and range in size from roughly 65
feet wide to 200 feet wide. They are moving away from each other at a
few miles per hour.
The Hubble images show that the parent comet also changes brightness
cyclically, 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. The
comet is also 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, Kaoru
Ikeya and Shigeki Murakami.
Based on the Hubble data, the research team suggests that sunlight
heated up the comet, causing jets of gas and dust to erupt from its
surface. Because the nucleus is so small, these jets act like rocket
engines, spinning up the comet's rotation. 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 several months, between October and December 2015. Jewitt suggests
that even some of the ejected pieces have themselves fallen to bits in a
kind of cascading fragmentation. "Our analysis shows that the smaller
fragments are not as abundant as one might expect based on the number of
bigger chunks," he said. "This is suggestive that they're being
depleted even in the few months since they were launched from the
primary body. We think these little guys have a short lifetime."
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 icy remnant wasn't spotted until Dec. 31,
2015, by the Pan-STARRS (Panoramic Survey Telescope and Rapid Response
System) telescope in Hawaii, in work supported by the Near-Earth Object
Observations program in NASA's Planetary Defense Coordination Office.
That discovery prompted Jewitt and colleagues to request Hubble time to
look at the comet in detail. Around the same time, astronomers around
the world began to notice a cloudy patch of material near the comet,
which Hubble later resolved into the 25 pieces.
"In the past, astronomers thought that comets die when they are
warmed by sunlight, causing their ices to simply vaporize away," Jewitt
said. "Either nothing would be left over or there would be a dead hulk
of material where an active comet used to be. 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."
"Hubble's best previous glimpse at a fragmenting comet came during
Advanced Camera for Surveys (ACS) observations of
73P/Schwassmann-Wachmann 3 (73P) in April 2006," said collaborator
Harold Weaver of the Johns Hopkins University Applied Physics Laboratory
in Laurel, Maryland. "In those observations, Hubble witnessed a comet
with more than 60 named pieces. The Hubble images showed unprecedented
detail of 73P's breakup, but the comet wasn't observed long enough to
document the evolution of the fragments over time, unlike the case of
332P."
The researchers estimate that Comet 332P contains enough mass to
endure another 25 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 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. These icy relics are the leftover
building blocks from our solar system's construction. After nearly 4.5
billion years in this icy deep freeze, chaotic gravitational
perturbations from Neptune kicked Comet 332P out of the Kuiper Belt.
As the comet traveled across the solar 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 estimates that a comet
from the Kuiper Belt gets tossed into the inner solar system every 40 to
100 years.
The results will appear in the Sept. 15, 2016, issue of The Astrophysical Journal Letters.
The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency. NASA's Goddard Space Flight
Center in Greenbelt, Maryland, manages the telescope. The Space
Telescope Science Institute (STScI) in Baltimore, Maryland, conducts
Hubble science operations. STScI is operated for NASA by the Association
of Universities for Research in Astronomy in Washington, D.C.
Contacts
Felicia Chou
NASA Headquarters, Washington, D.C.
202-358-0257
felicia.chou@nasa.gov
Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
David Jewitt
University of California, Los Angeles, California
310-825-2521
jewitt@ucla.edu
Source: HubbleSite
