Mars Express radar reveals complex structure in ionosphere of Mars(Forwarded)

ESA News
http://www.esa.int

30 November 2005

Mars Express radar reveals complex structure in ionosphere of Mars

MARSIS, the radar on board ESA's Mars Express, has performed its first
sounding of the Martian ionosphere --- the upper part of the atmosphere --
and found a number of unexpected features.

Like solid surfaces and layers of material, atmospheres of planets can be
probed by radar. In their analyses of these data for Mars, scientists are
exploring the connection between the ionosphere's structure and the
behaviour of the magnetic fields permeating the crust of the Red Planet.

MARSIS has been collecting ionospheric data, mostly during Martian
day-time observations, since this summer. Radio signals emitted by the
radar are reflected in the form of echoes when they encounter a region of
the ionosphere where the natural frequency of the plasma -- the gas of
charged particles that composes the ionosphere -- matches that of the
radar.

"This radio-echo sounding technique works especially well with a
horizontally stratified ionosphere like that of Mars," says Donald
Gurnett, lead Co-Investigator for MARSIS ionospheric studies.

MARSIS scientists have discovered the presence of a number of unexpected
hyperbola-shaped oblique echoes, facing downwards. These are different
from the vertical echoes normally expected from the upper interface of the
ionosphere.

By comparing the MARSIS map of these echoes with maps of the Martian
crustal magnetic field from Mars Global Surveyor's data, scientists noted
that the ionospheric areas from which the oblique echoes are generated
correspond to areas of strong magnetic fields in the crust of the planet.

This provides further strong evidence for an intimate connection between
the ionosphere and the crustal, localised magnetic fields. Where the
crustal magnetic field becomes almost vertical, charged particles in the
ionosphere tend to concentrate in an upward bulge-structure that gives
rise to the oblique echo when hit by the MARSIS radio waves.

"In particular, we believe that the creation of the bulge, which locally
increases the height of the ionosphere, has to do with the heating caused
by the charged particles (electrons) carried by the solar wind. These
penetrate the ionosphere along the vertical magnetic field peak and
contribute to increasing the local density of particles," says Gurnett.

However, the crustal magnetic fields cannot account for all the oblique
echoes observed, even if they are responsible for the majority of them. In
future analyses, the MARSIS scientists intend to explore other mechanisms
for the production of the oblique echoes. These include wind-driven
atmospheric waves excited by topographic features and various types of
wave-like structures in the atmosphere caused by the interaction with the
solar wind.

MARSIS is sensitive to the magnetic fields in a totally different and
unexpected way. The pulses of radar energy excite the thin plasma in the
local vicinity of the spacecraft and the resulting signals oscillate at a
frequency dependent on the magnetic field strength. In this way MARSIS is
adding to the data about the crustal magnetic fields obtained by other
spacecraft.

Other unexpected echoes have also been recorded by MARSIS. For example,
unusual reflections recorded in the night-side of Mars that would be
impossible in a horizontally stratified atmosphere, may indicate the
presence of low density 'holes' in the ionosphere, like those observed in
the night-side of Venus.

MARSIS measurements so far also allowed a good preliminary description of
the way the ionosphere reacts when the solar activity, and the consequent
bombardment of charged particles, increase. For instance, this is observed
when some surface reflections during the ionospheric probing vary in
intensity following solar flares, such as those that occurred on 7 and 15
September this year.

"Understanding how the ionosphere behaves, and how it allows the
propagation of radio-waves in different ionospheric conditions, is also
very important to properly plan the radar sounding of the subsurface.
Processing and interpreting the subsurface signals depends on
understanding the influence of the ionosphere," concludes Giovanni
Picardi, MARSIS Principal Investigator.

Note to editors

These findings appear on line in Science, on 30 November 2005, in an
article called 'Radar soundings of the ionosphere of Mars'.

The authors a D.A. Gurnett, D.L. Kirchner, R.L. Huff, D.D. Morgan, A.M.
Persoon, T.F. Averkamp and F. Duru (Dept. of Physics and Astronomy, Univ.
of Iowa, USA); E. Nielsen (Max Planck Institute for Solar System Research,
Lindau, Germany); A. Safaeinili and J.J. Plaut (NASA/JPL, Pasadena, USA);
G. Picardi (Univ. of Rome, La Sapienza, Italy).

Mars Express was launched on 2 June 2003 and has been orbiting Mars since
December 2003. On 19 September, ESA took the decision to extend the
mission by one additional Martian year (23 months), as of December 2005.

For more information

Giovanni Picardi, MARSIS Principal Investigator
Univ. di Roma La Sapienza'
E-mail: picar @ infocom.uniroma1.it

Jeff Plaut, MARSIS co-Principal Investigator, NASA/JPL
E-mail: plaut @ jpl.nasa.gov

Donald Gurnett, MARSIS Co-Investigator for ionosphere studies
Univ. of Iowa, USA
E-mail: donald-gurnett @ uiowa.edu

Agustin Chicarro, ESA Mars Express Project Scientist
E-mail: agustin.chicarro @ esa.int

Fred Jansen, ESA Mars Express Mission Manager
E-mail: fjansen @ rssd.esa.int

Enrico Flamini, ASI Mars Express Mission Manager
E-mail: enrico.flamini @ asi.it

Related articles

* At Saturn and Titan
http://www.esa.int/SPECIALS/Cassini-Huygens/index.html
* Looking at Mars
http://www.esa.int/SPECIALS/Mars_Express/index.html
* Buried craters and underground ice -- Mars Express uncovers depths of
Mars

http://www.esa.int/SPECIALS/Results_...ZTULWFE_0.html
* Mars Express evidence for large aquifers on early Mars

http://www.esa.int/SPECIALS/Results_...1UULWFE_0.html
* Mars Express discovers new layer in Martian ionosphere

http://www.esa.int/SPECIALS/Results_...AUULWFE_0.html

Related links

* Mars Express instruments
http://www.esa.int/SPECIALS/Mars_Exp...C75V9ED_0.html
* Huygens instruments
http://www.esa.int/SPECIALS/Cassini-...W82VQUD_0.html
* Cassini instruments
http://www.esa.int/SPECIALS/Cassini-...182VQUD_0.html

[NOTE: Images and an audio clip supporting this release are available at
http://www.esa.int/SPECIALS/Results_...4UULWFE_1.html
]