[meteorite-list] Cometary Poison Gas Geyser Heralds Surprises

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 2 Nov 2010 17:36:58 -0700 (PDT)
Message-ID: <201011030036.oA30awYT015762_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/science-news/science-at-nasa/2010/02nov_epoxi2/

Cometary Poison Gas Geyser Heralds Surprises
NASA Science News

Nov. 2, 2010: As NASA's Deep Impact (EPOXI) probe approaches Comet
Hartley 2 for a close encounter on Nov. 4th, mission scientists are
certain of only one thing:

"We're about to be surprised," says principal investigator Mike A'Hearn
of the University of Maryland. "This comet is unlike any we've visited
before, and we don't know what we're going to find."

In recent years, international spacecraft have buzzed the cores of four
comets: Halley, Tempel 1, Borrelly and Wild 2. Deep Impact even blew a
hole in one of them (Tempel 1) to see what was beneath the surface.
Those previous flybys, however, may not have prepared researchers for
the comet at hand.

"Comet Hartley 2 is smaller yet much more active than the others,"
explains A'Hearn. "Although its core is only 2 km wide - about a third the
size of Tempel - it is spewing five times more gas and dust."

The comet has already shocked the science team by producing a massive
surge of CN, the cyanogen radical commonly known as "cyanide." Cyanide
itself wasn't the surprise; CN is a common ingredient of comet cores.
Rather, it was the size and purity of the outburst that has researchers
puzzled.

"The abundance of CN in the comet's atmosphere jumped by a factor of
five over an eight day period in September - that's huge," says A'Hearn.
"Curiously, however, there was no corresponding increase in dust."

This flies in the face of conventional wisdom. Comet cores are thought
to be a mish-mash of volatile ices, rock, and dust particles, generally
well mixed. When the ice evaporates to produce a jet of gas, dust
naturally comes along for the ride. Yet this outburst was pure gas.

"We have never seen this kind of activity in a comet before. The amount
of gas suggests a global event - but how could such an event occur without
dust? It's a mystery."

A'Hearn stresses that readers shouldn't worry about a "poisonous comet."
For one thing, Comet Hartley 2 is more than 11 million miles from Earth.
There's no direct contact between our planet and the comet's gaseous
shroud. Furthermore, the cyanide gas is very diffuse. If it did touch
Earth, it would not be able to penetrate our planet's dense atmosphere.

May of 1910 provides a relevant example: Astronomers had just announced
that Earth was passing through the cyanide-containing tail of Comet
Halley, triggering a minor panic. People walked the streets of New York
wearing gas masks, and unscrupulous merchants made a pretty penny
selling "comet pills" to counteract poisoning. Nothing happened. Even
direct contact with Halley's tail produced no ill effects.

The real significance of Hartley 2's cyanide surge is the tease.
Something mysterious is happening...and we're about to find out what.

The flyby officially begins on the evening of Nov. 3rd when Deep
Impact/EPOXI is about 18 hours from closest approach. During the early
stages of the encounter, all of the close-up images will be stored
onboard the spacecraft. This is because Deep Impact cannot
simultaneously point its high gain antenna toward Earth and its imagers
toward the comet.

Closest approach occurs around 10 am EDT on Nov.4th at a distance of 435
miles. About a half an hour later, the changing geometry of the
encounter will allow simultaneous communications and imaging. With its
big antenna once again pointing toward Earth, Deep Impact/EPOXI will
begin transmitting close-up pictures of Comet Hartley 2. The complete
data dump will take several hours.

"We will be waiting," said A'Hearn. "The best images won't reach Earth
until many hours after the actual encounter."

Data from the close approach will continue to download through the 6th
of November, but NASA will release preliminary results sooner than that.
A live press conference is scheduled for 4 pm EDT (1 pm PDT) on Nov. 4th.

Stay tuned to the EPOXI web site <http://epoxi.umd.edu/> for updates.


Author: Dr. Tony Phillips
Credit: Science at NASA
Received on Tue 02 Nov 2010 08:36:58 PM PDT