Colliding Atmospheres: Mars vs Comet Siding Spring
 
August 12, 2014:  On October 19, 2014, Comet Siding Spring will pass by Mars
only 132,000 km away--which would be like a comet passing about 1/3 of the
distance between Earth and the Moon.
 
The nucleus of the comet won't hit Mars, but there could be a different kind
of collision.
 
"We hope to witness two atmospheres colliding," explains David Brain of the
University of Colorado's Laboratory for Atmospheric and Space Physics (LASP). 
"This is a once in a lifetime event!"
 
https://www.youtube.com/watch?v=2R4yj7DtQbM&feature=youtu.be
 
A new ScienceCast video examines what might happen if the atmosphere of Comet
Siding Spring hits the atmosphere of Mars.  Play it
 
Everyone knows that planets have atmospheres.  Lesser known is that comets do,
too.  The atmosphere of a comet, called its "coma," is made of gas and dust
that spew out of the sun-warmed nucleus.  The atmosphere of a typical comet is
wider than Jupiter.
 
"It is possible," says Brain, "that the atmosphere of the comet will interact
with the atmosphere of Mars.  This could lead to some remarkable
effects-including Martian auroras."
 
The timing could scarcely be better.  Just last year, NASA launched a
spacecraft named MAVEN to study the upper atmosphere of Mars, and it will be
arriving in Sept. 2014 barely a month before the comet.
 
MAVEN is on a mission to solve a longstanding mystery: What happened to the
atmosphere of Mars?  Billions of years ago, Mars had a substantial atmosphere
that blanketed the planet, keeping Mars warm and sustaining liquid water on
its surface. Today, only a wispy shroud of CO2 remains, and the planet below
is colder and dryer than any desert on Earth. Theories for this planetary
catastrophe center on erosion of the atmosphere by solar wind.
 
"The goal of the MAVEN mission is to understand how external stimuli affect
the atmosphere of Mars," says Bruce Jakosky of LASP, MAVEN's principal
investigator. "Of course, when we planned the mission, we were thinking about
the sun and the solar wind.  But Comet Siding Spring represents an opportunity
to observe a natural experiment, in which a perturbation is applied and we can
see the response."
 
http://www.nasa.gov/mission_pages/maven/main/#.U-lkt2MYmsM
 
Click to visit the MAVEN home pageBrain, who is a member of the MAVEN science
team, thinks the comet could spark Martian auroras. Unlike Earth, which has a
global magnetic field that shields our entire planet, Mars has a patchwork of
"magnetic umbrellas" that sprout out of the surface in hundreds of places all
around the planet.  If Martian auroras occur, they would appear in the
canopies of these magnetic umbrellas.
 
"That is one thing that we will be looking for with both MAVEN and Hubble
Space Telescope," says Brain.  "Any auroras we see will not only be neat, but
also very useful as a diagnostic tool for how the comet and the Martian
atmosphere have interacted."
 
The atmosphere of the comet includes not only streamers of gas, but also dust
and other debris blowing off the nucleus at 56 kilometers per second relative
to Mars.  At that velocity, even particles as small as half a millimeter
across could damage spacecraft.  NASA's fleet of Mars orbiters including
MAVEN, Mars Odyssey and Mars Reconnaissance Orbiter will maneuver to put the
body of Mars between themselves and the comet's debris during the dustiest
part of the encounter.
 
"It's not yet clear whether any significant dust or gas will hit the Mars
atmosphere," cautions Jakosky. "But if it does, it would have the greatest
effects on the upper atmosphere."
 
Meteoroids disintegrating would deposit heat and temporarily alter the
chemistry of upper air layers.  The mixing of cometary and Martian gases could
have further unpredictable effects. Although MAVEN, having just arrived at
Mars, will still be in a commissioning phase, it will use its full suite of
instruments to monitor the Martian atmosphere for changes.
 
"By observing both before and after, we hope to determine what effects the
comet dust and gas have on Mars, if any," says Jakosky.
 
Whatever happens, MAVEN will have a ringside seat.
 
Credits:
Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit:
Science@NASA
 
 
Regards,
 
Roger

--- D'Bridge 3.99
 * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)