SEBASS: Nevada Test Site craters

Laurel Kirkland
Infrared Remote Sensing of Mars and Earth



Aerospace/LPI Remote Sensing Team


THIS SITE DESCRIBES:
1. Research in identification of materials using infrared spectroscopy on Mars and the Earth, at:
        The Lunar and Planetary Institute, a non-profit NASA research group, and
        The Aerospace Corporation, a non-profit lab managed by the Dept. of Defense.
2. Open visible/infrared spectral community meetings organized as a community service.

Contact information:
Lunar and Planetary Institute
3600 Bay Area Blvd., Houston, Texas 77058-1113
Office (281) 486-2112; Fax (281) 486-2162
email: kirkland@lpi.usra.edu


Recent Mars Analog Work:

Coso Hot Springs

China Lake Naval Air Weapons Station



A unique Mars analog location:
A portion of the Coso Hot Springs is shown above (click on the picture to enlarge). Coso Hot Springs are at the China Lake Naval Air Weapons Station, CA. In June 2005, we measured airborne infrared hyperspectral images covering the spectral ranges from 0.35-2.5 microns, 2.5-5 microns, and 7-13 microns. Concurrent with the airborne flights, we measured ground hyperspectral imagery.
What makes Coso Hot Springs an important Mars analog site.
1. The community needs analog sites to learn how to find past or current near-surface hydrothermal activity on Mars.
2. Restricted access has maintained this site for study.
3. The geology differs from other hot spring areas used for Mars analog work.
4. We have unique, high quality hyperspectral data (ground, airborne, and lab) to use to unravel matching data of Mars.


Neat Pictures! (Click to enlarge)
The hot springs come in various colors, including gray and bright red (image above). Some springs are quiet, and other bubble violently. Some vents do not currently have liquid water, but steam. The image below left shows hot spring overflow remnants. Below center shows an overview of the site during the airborne campaign. Below right shows temperature measurements of one of the gray springs.



Mars Analog Work:
Nevada Test Site Explosion Craters


Manmade explosion craters at the Nevada Test Site are unique Mars analog locations. We recently imaged craters there using airborne ("SEBASS") and rover-analog instruments ("RamVan"). Abstracts that discuss the work are in the Lunar and Planetary Science Conference, Jan 2005:

LPSC abstract: Airborne work

LPSC abstract: Rover analog work

SUMMARY
Craters can create windows into sub-surface geology. Hydrothermal alteration products that correlate with ejecta from small craters (<100 m deep) can flag possible near-surface hydrothermal activity. A region with such activity is a highly prized target for Mars exploration. These abstracts describe a unique airborne (satellite analog, see image at the top of this web site) and rover analog study that identified mineral indicators of hydrothermal activity exposed by manmade explosion craters in a basalt flow. This field development work draws mainly on operational expertise from outside NASA. One goal is to develop the operational foundation for routes to discovery for Mars.

Looking inside the explosion crater "Buckboard 12":

Opal coating exposed on ejecta at Buckboard 12



A Fine Surprise for the Opportunity Mars Rover:
Fine-grained Hematite


Boulder coated with fine-grained hematite.  

The Mars rover has found no evidence of coarse (gray) hematite. Instead, the data point toward fine-grained, consolidated hematite such as the mock specularite shown here:  

Ruler is 6"  


Preprint of our Geophy. Res. Letters Jan, 2004, now published.

Discovery.com article about the fine surprise.

Christensen et al. (JGR 105, 9632, 2000) conclude that coarse hematite (also called "gray hematite" or "specularite") is the only possible match to TES data. They stated any form of fine hematite (including fine hematite coatings) was not a possible match. Excitement over implied longstanding water to form the rare, coarse crystals led to selection of that site for the Opportunity rover.

The fine surprise: Spectra of fine-grained hematite match the TES data better than coarse (gray) hematite.
Our group has shown since 2001 that spectra of fine-grained, consolidated hematite match the TES signatures, and match them better than coarse hematite has been demonstrated to do. Our publications demonstrated the consistency at visible wavelengths, where consolidated, fine-grained hematite can be red or black. Forms of consolidated hematite include coatings, ferricrete (cemented hematite), compacted by pressure, or anything that places the fine crystals closer together than ~wavelength of the light. The rover is bearing out our predictions that the hematite is probably fine-grained (composed of material with <10 micron crystal size).

Fine-grained hematite matches Meridiani. Oops!

Why the grain size matters:
(1) It is unknown whether fine-grained hematite implies abundant water;
(2) It is unknown whether the fine-grained hematite formed any differently than elsewhere on the planet, or instead whether consolidation is what is rare at Meridiani. Fine-grained, unconsolidated hematite that is thought to be common on Mars, and to give it is rusty color.
(3) Consolidated hematite (e.g., coating, ferricrete) may explain the non-detection of coexisting aqueous alteration minerals and the lack of hematite wind streaks;
(4) Current "hematite abundance maps" may instead map the surface texture;
(5) Coatings may be of great astrobiology interest;
(6) Studies are needed to determine whether visible-infrared spectra can definitively distinguish fine-intimate from coarse hematite.

Additional details are in our GRL preprint.

An article about the fine surprise at Discovery.com.

Infrared stealthy surfaces:
Why TES and THEMIS may miss substantial mineral deposits on Mars

preprint

Large mineral deposits with rough surfaces can remain undetected (e.g., "White Rock").
Previous researchers used laboratory spectra of pure, smooth-surfaced minerals to conclude that the current Mars infrared instruments (TES, THEMIS, and the rover MiniTES) will detect any mineral deposit that covers ~10% of a pixel. In contrast, we use real-world data to demonstrate that optically rough surfaces can remain undetected, including well-crystalline, regional mineral deposits, and rock outcrops at 100% exposure. Such rough materials are referred to as "infrared stealthy". Terrestrially, the most commonly observed infrared stealthy deposits are the most water soluble (e.g., carbonate, sulfate), while silicates are not typically infrared stealthy.



Three cases of spectral behavior impact current Mars interpretations:
Case 1: The minerals present remain undetected ("infrared stealthy"). White Rock is an example. This case impacts interpretations when minerals that are present are interpreted as absent.
Case 2: Variations in surface texture and abundance commonly have a similar impact on the spectral signature. The commonality confounds abundance mapping. For example, it is unknown whether "hematite abundance maps" reflect variations in abundance or surface texture. Increasing surface smoothness mimics increasing abundance.
Case 3: Physical effects alter the spectral band shape. This impacts all current compositional interpretations.

The 10% detection threshold that was once stated for TES/THEMIS is an idealized lower bound. Optically smooth materials will be well-represented in TES/THEMIS/Mini-TES identifications. Other materials will be comparatively underrepresented or missed. Surface roughness occurs on three broad scales, and roughness at the grain scale can be a primary variable in whether a mineral is detectable.

The results mean that interpretations that built on non-detection (e.g., as for "White Rock") will require reassessment. The impact on future measurement strategies (including Mini-TES) should also be openly assessed.

Stealthy surfaces



Authors: L. E. Kirkland, K. C. Herr, and P. M. Adams

Click here for a preprint (as Adobe PDF file)


His eminence was due to the flatness of the surrounding landscape. -John Stuart Mill

Some of Our Group

Our research focus:

Low ambiguity identification of surface materials in the field without ground truth (without physical sampling). This requires development of the foundation of the physics of spectral behavior through:
(1) Methodical measurement and analysis of field, airborne, and satellite spectrometer data
(2) Supporting analysis of laboratory spectra and sample characterization
(3) Analysis of the measurement protocols and instrumentation necessary for low ambiguity identification
Our research includes effects in the field that are rarely if ever reproduced in the laboratory environment, including from surface roughness, reflected downwelling radiance, and mixing.




Field work!

Terrestrial data:

Our unique range of instrumentation provides the greatest depth of data sets available for this research:
(1) unique airborne hyperspectral imaging using SEBASS (7.5-13.5 Ám).
(2) the only thermal infrared imaging field spectrometers (hyperspectral).
(3) laboratory spectrometer (hyperspectral) measurements.

Mars data:

(1) 1969 Mariner Mars Infrared Spectrometer (IRS)
(2) 1971 Mariner Mars Interferometer Spectrometer (IRIS)
(3) 1989 Phobos 2 Imaging Spectrometer for Mars (ISM)
(4) 1996 Mars Global Surveyor TES
(5) We do not typically use multi-spectral (radiometer) data, such as the 2001 Mars Odyssey THEMIS.

We also examine the calibrations, recover missing data and documentation, and make all recovered information publicly available to help open these investigations to all interested researchers.

More details on these data sets.


-March 16th, 2004: Community Lunch at LPSC-

Where and When it was Held:
During the Lunar and Planetary Science Conference (LPSC), Tuesday, March 16th, at the conference site. It was a chance for people to meet and to discuss issues of concern to the community, over sandwiches and soft drinks. The meeting was open to all interested researchers, and students were particularly encouraged to attend.

Attendance:
Approximately 110 people attended. This included many students, who were introduced to the full group at the start of the meeting

Speakers:
Topic: Moessbauer spectroscopy
Each of the Mars rovers carries a Moessbauer spectrometer, a multispectral visible imager, and a thermal infrared spectrometer. A basic understanding of Moessbauer spectroscopy will facilitate the community's capability to correlate results from visible-infrared data sets with Moessbauer interpretations.

Darby Dyar presented a tutorial and discussion of Moessbauer spectroscopy. Additional details are at the community meeting web site.




LPI sponsors these workshops to benefit the Mars spectral community. If you are interested in convening a workshop related to instrumentation, data sets, or research related to remote sensing of Mars, please contact Laurel Kirkland (kirkland@lpi.usra.edu), 281-486-2112.



PREVIOUS WORKSHOPS
March 2003: Mars Infrared Spectroscopy Community Meeting: LIBS and Raman
December 2002: Mars Infrared Spectroscopy: Laboratory and Field Community Data Sets
June 2002: Infrared Spectroscopy of Mars: From Theory and the Laboratory to Field Observations
June 1999: Spectroscopy of the Martian Surface: What Next?
Workshop reports




Proponents...sometimes cite the example of the academic community, where competing scholarship supposedly thrives in an honest marketplace for the truth. ... [That] is based on a misunderstanding of the nature of scholarship. Truth in scholarship depends on a combination of individual integrity and genuine insight. It thrives not because universities offer an exceptionally effective marketplace for ideas. Rather, it thrives because senior scholars occasionally have the integrity and self-confidence to encourage younger scholars to do innovative and creative work, sponsoring them rather than competing with them. -William Odom, in Fixing Intelligence.


LINKS

Society for Applied Spectroscopy

NASA Astrobiology Institute newsletter


Lunar and Planetary Institute home page