[meteorite-list] Catch a Shooting Star on Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 30 Apr 2008 15:10:29 -0700 (PDT)
Message-ID: <200804302210.PAA28095_at_zagami.jpl.nasa.gov>

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CONTACTS

Dr Apostolos Christou
Armagh Observatory
College Hill
Armagh BT61 9DG
Northern Ireland
E-mail: aac (at) star.arm.ac.uk

EMBARGOED UNTIL 0001 BST, 2 April 2008

Ref.: PN 08/20 (NAM 11)

Catch a shooting star on Mars

A team of scientists led by Armagh Observatory have, for the first time,
detected a storm of shooting stars on Mars.

The detections were made using predictions of when meteor showers should
occur as the orbit of Mars intersects with debris from comet 79P/du
Toit-Hartley. These predictions were cross-referenced with observations of
activity in the Martian ionosphere by NASA's Mars Global Surveyor (MGS)
satellite.

Dr Apostolos Christou, who is presenting the results at the RAS National
Astronomy Meeting in Belfast on Wednesday 2nd April, said, "Just as we can
predict meteor outbursts at Earth, such as the Leonids, we can also predict
when meteor showers are going to occur at Mars and Venus. We believe that
shooting stars should appear at Venus and Mars with a similar brightness to
those we see at Earth. However, as we are not in a position to watch them in
the Martian sky directly, we have to sift through satellite data to look for
evidence of particles burning up in the upper atmosphere."

Observations of meteor showers, caused when a planet passes through the
dusty trail left by a comet as it moves along its orbital path, give
insights into the age, size and composition of particles ejected from the
comet's nucleus, the ejection velocity, as well as general information about
the structure and history of the comet itself. Roughly four times more
comets approach the orbit of Mars than the Earth's and a high proportion of
these are Jupiter Family Comets. Mars therefore offers a significant
opportunity to improve our understanding of meteor showers and Jupiter
Family Comets.

When meteor particles burn up in a planet's atmosphere, metals contained
within them are ionised to form a layer of plasma. On Earth, this layer has
an altitude of approximately 95-100 kilometres and on Mars the layer is
predicted to be around 80-95 kilometres above the Martian surface. Meteor
showers leave a narrow layer of plasma superimposed on top of the main
plasma layer, caused by meteors that are general debris from the Solar
System.

Christou and his colleagues developed a model to predict meteor showers
caused by the intersection of Mars with dust trails from comet 79P/du
Toit-Hartley. From the model, the team identified six predicted meteor
showers since the MGS satellite entered into orbit around Mars in 1997.
Although the metallic ions cannot be observed directly by MGS instruments,
evidence for the plasma layer can be inferred by monitoring electron density
in the Martian atmosphere using the spacecraft's radio communication system.

Out of the six predicted showers, ionospheric data from MGS was only
available for the outbursts in April 2003 and March 2005.

In the April 2003 data, the team found that an ionospheric disturbance
appeared at the exact time of the predicted meteor outburst. The height of
the disturbance corresponded with the predicted altitude for the formation
of the metallic ion layer and its width and multi-peaked shape were similar
to structures observed in the Earth's ionosphere linked to the Perseid
meteor shower.

For the 2005 data, no features were observed near or immediately after the
predicted meteor shower. Dr Christou says, "We speculate that we don't see
anything in the 2005 data because the meteors burned up deeper in the
atmosphere where their ionisation is less efficient. If we are going to get
a clear picture of what is going on, we need more optical and ionospheric
observations of meteor showers at both the Earth and Mars so we can
establish a definitive link between cause and effect. Equally importantly,
we need further observations of Martian meteor showers, either from orbit or
from the planet's surface, to confirm our predictions. Finally, we need to
improve our prediction model by tracking more comets that might cause meteor
showers on Mars."

Dr Christou is now investigating the possibilities of making observations
with Europe's ExoMars mission, which is due to land on Mars in 2015.

NOTES FOR EDITORS

RAS NATIONAL ASTRONOMY MEETING
The RAS National Astronomy Meeting (NAM 2008) is hosted by Queen's
University Belfast. It is principally sponsored by the RAS and the STFC. NAM
2008 is being held together with the UK Solar Physics (UKSP) and
Magnetosphere, Ionosphere and Solar-Terrestrial (MIST) spring meetings.

COMET 79P/DU TOIT-HARTLEY
Comet 79P/du Toit-Hartley was discovered by D. du Toit in April 1945 but
then went unobserved during subsequent apparitions for nearly 40 years. In
1982, Malcolm Hartley discovered two comets, 1982b and 1982c, which were
later identified as fragments of du Toit's 1945 discovery. 1982b faded
rapidly, but the remaining fragment has been observed in December 1986 and
March 2003.

JUPITER FAMILY COMETS
The Jupiter Family Comets (JFCs) are short period comets with an orbital
period of less than 20 years. Their orbits are controlled by Jupiter and
many are believed to originate from the Edgeworth-Kuiper Belt, a vast
population of small icy bodies that orbit just beyond Neptune. Famous JFCs
include Comet 81P/Wild 2, which was encountered by the Stardust spacecraft
in January 2004 and Comet Shoemaker-Levy 9, which broke up and collided with
Jupiter in July 1994.

IMAGES

[http://www.ras.org.uk/images/stories/press/NAM08/79Plocation.jpg (943KB)]
Comet 79P/du Toit-Hartley. Credit: Las Cumbres Observatory Global Telescope
Network/Faulkes Telescope Project"

[http://www.ras.org.uk/images/stories/press/NAM08/HDTV_LEO28mm_1.jpg (68KB)]
Leonid meteor shower. Credit: Shinsuke Abe and Hajime Yano, ISAS

[http://www.ras.org.uk/images/stories/press/NAM08/layer_location.jpg
(261KB)]
Polar view of the Northern Hemisphere of Mars (actually a topographic map
compiled using data another instrument on MGS, MOLA) annotated with the
geographical location of the two detections and that of Viking Lander 2 for
reference. Credit: MOLA Science Team/Christou

[http://mars.jpl.nasa.gov/mgs/gallery/images/mgs-mons.jpg (12MB)]
Mars Global Surveyor. Image credit: NASA/JPL-Caltech

[http://www.ras.org.uk/images/stories/press/NAM08/test5551.gif (6KB)]
Intersection of Comet 79P/du Toit-Hartley with the orbit of Mars in April
2003. Courtesy: NASA JPL/Caltech

[http://www.ras.org.uk/images/stories/press/NAM08/radio_occ2.jpg (95KB)]
Radio occultation
Received on Wed 30 Apr 2008 06:10:29 PM PDT