Solar Hurricane Tear Comet Tail Off
Pastor Dale Morgan
NASA Satellite Sees Solar Hurricane Tear Comet Tail Off*
by Andy Freeberg
Washington DC (SPX) Oct 02, 2007
NASA's STEREO satellite captured the first images ever of a collision
between a solar "hurricane", called a coronal mass ejection (CME), and a
comet. The collision caused the complete detachment of the comet's
plasma tail. Comets are icy leftovers from the solar system's formation
billions of years ago. They usually hang out in the cold, distant
regions of the solar system, but occasionally a gravitational tug from a
planet, another comet, or even a nearby star sends them into the inner
solar system.
Once there, the sun's heat and radiation vaporizes gas and dust from the
comet, forming its tail. Comets typically have two tails, one made of
dust and a fainter one made of electrically conducting gas, called plasma.
CMEs are large clouds of magnetized gas ejected into space by the sun.
They are violent eruptions with masses upwards of a few billion tons
traveling anywhere from 100 to 3,000 kilometers per second (62 to 1,864
miles/second). They have been compared to hurricanes because of the
widespread disruption they can bring when directed at Earth; CMEs are
known to cause geomagnetic storms that can present hazards for
satellites, radio communications, and power systems.
Comet Encke was traveling within the orbit of Mercury when a CME
scrunched the tail and eventually tore it off the comet. Scientists at
the Naval Research Laboratory (NRL) made the observations using the
Heliospheric Imager (HI) in NRL's Sun Earth Connection Coronal and
Heliospheric Investigation (SECCHI) telescope suite aboard NASA's Solar
Terrestrial Relations Observatory (STEREO)-A spacecraft.
Scientists have been aware of this spectacular phenomenon, the
disconnection of the entire plasma tail of a comet, for some time.
However, the conditions that lead to these events remained a mystery.
Scientists suspected that CMEs could be responsible for some of the
disconnection events, but the interaction between a CME and a comet had
never been directly observed. Because the HI instrument can take many
images rapidly, and the images are very detailed, scientists were able
to obtain a series of images of the comet and tail disconnection as the
event occurred.
The researchers combined the images into a movie. This never-before-seen
movie was recorded on April 20, 2007, when a CME encountered comet
Encke. The observations reveal the brightening of the comet tail as the
CME swept by and its subsequent disconnection and transport by the CME
front.
A preliminary analysis suggests that the tail was ripped away when
magnetic fields bumped together in an explosive process called "magnetic
reconnection." Oppositely directed magnetic fields around the comet
"bumped into each" by the magnetic fields in the CME. Suddenly, these
fields linked together--they "reconnected"--releasing a burst of energy
that rent the comet's tail. A similar process takes place in Earth's
magnetosphere during geomagnetic storms fueling, among other things, the
Northern Lights.
"The comet had its own space weather event," said Angelos Vourlidas,
Lead author and Researcher with the Naval Research Laboratory,
Washington, DC. "We think it experienced a magnetic reconnection event
very similar to what Earth experiences when CMEs impact our own
protective magnetosphere."