[meteorite-list] Close Comet Flyby Threw Mars' Magnetic Field Into Chaos (MAVEN)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 15 Mar 2016 16:10:08 -0700 (PDT)
Message-ID: <201603152310.u2FNA8IE028750_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?feature=5747

Close Comet Flyby Threw Mars' Magnetic Field Into Chaos
Jet Propulsion Laboratory
March 9, 2016

Fast Facts:

* NASA's newest Mars orbiter, MAVEN, arrived just in time for a comet's
close flyby of Mars in 2014.

* The powerful magnetic field around the comet temporarily merged with
-- and overwhelmed -- Mars' weak magnetic field.

Just weeks before the historic encounter of comet C/2013 A1 (Siding Spring)
with Mars in October 2014, NASA's Mars Atmosphere and Volatile Evolution
(MAVEN) spacecraft entered orbit around the Red Planet. To protect sensitive
equipment aboard MAVEN from possible harm, some instruments were turned
off during the flyby; the same was done for other Mars orbiters. But a
few instruments, including MAVEN's magnetometer, remained on, conducting
observations from a front-row seat during the comet's remarkably close
flyby.

The one-of-a-kind opportunity gave scientists an intimate view of the
havoc that the comet's passing wreaked on the magnetic environment, or
magnetosphere, around Mars. The effect was temporary but profound.

"Comet Siding Spring plunged the magnetic field around Mars into chaos,"
said Jared Espley, a MAVEN science team member at NASA's Goddard Space
Flight Center in Greenbelt, Maryland. "We think the encounter blew away
part of Mars' upper atmosphere, much like a strong solar storm would."

Unlike Earth, Mars isn't shielded by a strong magnetosphere generated
within the planet. The atmosphere of Mars offers some protection, however,
by redirecting the solar wind around the planet, like a rock diverting
the flow of water in a creek. This happens because at very high altitudes
Mars' atmosphere is made up of plasma -- a layer of electrically charged
particles and gas molecules. Charged particles in the solar wind interact
with this plasma, and the mingling and moving around of all these charges
produces currents. Just like currents in simple electrical circuits, these
moving charges induce a magnetic field, which, in Mars' case, is quite
weak.

Comet Siding Spring is also surrounded by a magnetic field. This results
from the solar wind interacting with the plasma generated in the coma
- the envelope of gas flowing from a comet's nucleus as it is heated by
the sun. Comet Siding Spring's nucleus -- a nugget of ice and rock measuring
no more than about one-third mile (half a kilometer) -- is small, but
the coma is expansive, stretching out more than 600,000 miles (a million
kilometers) in every direction. The densest part of the coma -- the inner
region near the nucleus -- is the part of a comet that's visible to telescopes
and cameras as a big fuzzy ball.

When comet Siding Spring passed Mars, the two bodies came within about
87,000 miles (roughly 140,000 kilometers) of each other. The comet's coma
washed over the planet for several hours, with the dense inner coma reaching,
or nearly reaching, the surface. Mars was flooded with an invisible tide
of charged particles from the coma, and the powerful magnetic field around
the comet temporarily merged with -- and overwhelmed -- the planet's own
weak one.

"The main action took place during the comet's closest approach," said
Espley, "but the planet's magnetosphere began to feel some effects as
soon as it entered the outer edge of the comet's coma."

At first, the changes were subtle. As Mars' magnetosphere, which is normally
draped neatly over the planet, started to react to the comet's approach,
some regions began to realign to point in different directions. With the
comet's advance, these effects built in intensity, almost making the planet's
magnetic field flap like a curtain in the wind. By the time of closest
approach -- when the plasma from the comet was densest -- Mars' magnetic
field was in complete chaos. Even hours after the comet's departure, some
disruption continued to be measured.

Espley and colleagues think the effects of the plasma tide were similar
to those of a strong but short-lived solar storm. And like a solar storm,
the comet's close passage likely fueled a temporary surge in the amount
of gas escaping from Mars' upper atmosphere. Over time, those storms took
their toll on the atmosphere.

"With MAVEN, we're trying to understand how the sun and solar wind interact
with Mars," said Bruce Jakosky, MAVEN's principal investigator from the
University of Colorado's Laboratory for Atmospheric and Space Physics
in Boulder. "By looking at how the magnetospheres of the comet and of
Mars interact with each other, we're getting a better understanding of
the detailed processes that control each one."

This research was published in Geophysical Research Letters.

For more information about MAVEN, visit:

www.nasa.gov/maven


Media Contact

Elizabeth Zubritsky
NASA Goddard Space Flight Center, Greenbelt, Md.
301-614-5438
elizabeth.a.zubritsky at nasa.gov

2016-065
Received on Tue 15 Mar 2016 07:10:08 PM PDT