[meteorite-list] Colliding Atmospheres: Mars vs Comet Siding Spring

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 12 Aug 2014 14:09:44 -0700 (PDT)
Message-ID: <201408122109.s7CL9il7000895_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/science-news/science-at-nasa/2014/12aug_marscomet/

Colliding Atmospheres: Mars vs Comet Siding Spring
NASA Science News
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!"

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."

Brain, 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 at NASA
Received on Tue 12 Aug 2014 05:09:44 PM PDT