[X] My Assistant

[djellison]

As I understand it - these types of instruments can only detect a transition between layers.

i.e. you could have a iceberg sat on the surface, but it would only tell you about the change between the iceberb and the surface under it - not the actual material itself.

Doug

[Decepticon]

This becomes less and less exciting.

[deglr6328]

Hmm well that's kind of a letdown. Though we ARE extrapolating from the slightest bit of information here and it isn't totally incongruous with the epithermal neutron flux mapping data from odyssey. Theres lots more H in the southern hemisphere....

[RNeuhaus]

Hmm well that's kind of a letdown. Though we ARE extrapolating from the slightest bit of information here and it isn't totally incongruous with the epithermal neutron flux mapping data from odyssey. Theres lots more H in the southern hemisphere....

That graph shows that the Meridiani Planum and Gusev Crater (slight higher than MP) have a middle level of quantity of Hydrogen.

For subsurface probing, MARSIS must operate under 800 kilometres altitude from the Martian surface, while for ionospheric sounding MARSIS provides acceptable results from a distance of up to 2000 kilometres. The radar vertical depth resolution is 150 metres (in the free space), while echo profiles of the subsurface are acquired at a lateral spacing of about 5 to 9 km, depending on the spacecraft altitude.

The MARSIS radar is designed to operate around the pericentre of the orbit, when the spacecraft is closer to the planet’s surface. In each orbit available to MARSIS, the radar is switched on for 36 minutes around this pericentre point, dedicating the central 26 minutes to subsurface observations and the first and last five minutes of the slot to active ionosphere sounding.

Nighttime is the environmental condition favourable to subsurface sounding, as the ionospheric plasma frequency is lowest. The ionosphere is more energised during the daytime and disturbs the radio signals used for subsurface observations. Although even during the daytime, the MARSIS instrument can detect signals from the surface and subsurface after proper ionospheric corrections are made.

The above is an extract from ESA and it does not mention about the places to be examined by MARSIS.

Does the Mars Express only scans the subsurface of northern plains or any place?

Rodolfo

[Guest_BruceMoomaw_*]

Cheerier news on the initial MARSIS results from an upcoming paper at the Fall 2005 AGU meeting ( http://www.agu.org/cgi-bin/SFgate/SFgate?&...t;P13C-02" ):

"The MARSIS radar has been performing nominally since turn-on. Echoes from the surface are typically strong, with signal-to-noise ratios in the range of 30-50 dB. Later returns from off-nadir topographic clutter are evident and easily modeled using MOLA topography data. Many late echoes are observed that cannot be explained as topographic clutter. These features are under investigation as potential subsurface interfaces."

So it's seeing SOMETHING under the surface, even if we don't yet know what it is. As for Rodolfo's question about which parts of Mars' surface will be scanned by MARSIS:

"As the periapsis of the Mars Express orbit migrates toward the south pole, the polar layered deposits and related landforms will be observed by MARSIS on the nightside. In addition, numerous targets of interest in the southern mid-latitudes will be acquired during the nightside, including the floors of Hellas and Argyre basins, and the regions of strong remnant crustal magnetization."

[deglr6328]

It always somehow seemed a little unbelieveable to me that a tiny transmitter putting out ~15W could actually have enough energy to bounce off the surface of a planet a few 100s of miles away and return useful and (apparently) detailed data on surface structure. Hmm. I guess it must be pretty radio quiet way up there.

[Rakhir]

Besides MARSIS on Mars Express, another experiment is under way searching for ice in Mars underground.
They are using the SRI International's 46-meter (150-foot) radio telescope working in tandem with the Mars Odyssey UHF radio system.

More details at : http://mars.jpl.nasa.gov/odyssey/spotlight/20051024.html

Rakhir

[Adam]

http://www.esa.int/esaCP/SEM30WTLWFE_index_0.html

[Decepticon]

This was just a article about how it works.

Once again no real news.





Yeah yeah I'm grumpy again.