[Paper Review] H2O- and OH-bearing minerals in the Martian regolith: Analysis of 1997 observations from HST/NICMOS

E. Z. Noe Dobrea, J. F. Bell+2 more|ArXiv.org|Dec 3, 2002

Planetary Science and Exploration64 references17 citations

TL;DR

This study analyzes Hubble Space Telescope/NICMOS observations from July 1997 to investigate hydration states in the Martian regolith, using narrow- and medium-band near-infrared filters at ~60 km/pixel resolution. It identifies spectrally distinct terrains across Acidalia Planitia and adjacent regions, finding evidence for H2O- or OH-bearing minerals in northern Acidalia and intermediate albedo terrain, but not in southern dark terrains, suggesting regional variations in surface hydration.

ABSTRACT

We have analyzed observations of the Acidalia hemisphere of Mars taken by the Hubble Space Telescope's Near-Infrared Camera Multi-Object Spectrograph (HST/NICMOS) during July of 1997 (Ls = 152 degrees, northern Martian summer). The data consist of images at ~60 km/pixel resolution, using both narrow- and medium-band filters specifically selected to allow us to study the hydration state of the Martian surface. Calibration was performed by comparison to Phobos-2 ISM observations of overlapping regions, and atmospheric gas correction was performed by modeling the atmosphere for each pixel using a line-by-line radiative transfer code coupled with the MOLA altimetry data. Our results indicate the presence of at least three spectrally different large-scale (>1000 km diameter) terrains corresponding to the dark regions of northern Acidalia, the southern hemisphere classical dark terrain, and the classical intermediate terrain adjacent to southern Acidalia. We also identified two other spectrally unique terrains, corresponding to the northern polar ice cap, and to the southern winter polar hood. Comparisons with mineral spectra indicate the possibility of different H2O- or OH-bearing (i.e., hydroxides and/or hydrates) minerals existing both in northern Acidalia and in the nearby intermediate albedo terrain. Hydrated minerals do not appear to be spectrally important components of the southern hemisphere dark terrains imaged by HST in 1997.

Motivation & Objective

• To assess the hydration state of the Martian surface using Hubble Space Telescope/NICMOS data from July 1997.
• To identify large-scale terrains with distinct spectral signatures indicative of hydrated minerals.
• To compare observed spectra with mineral standards to infer the presence of hydroxides or hydrates.
• To correct for atmospheric interference and surface albedo effects to isolate surface hydration signals.
• To determine spatial variations in hydration across the Acidalia region and adjacent terrains.

Proposed method

• Acquired near-infrared images using HST/NICMOS with narrow- and medium-band filters tuned to detect H2O and OH absorption features.
• Calibrated data using Phobos-2 ISM observations of overlapping regions to ensure spectral consistency.
• Applied line-by-line radiative transfer modeling with MOLA altimetry to correct for atmospheric gas absorption on a pixel-by-pixel basis.
• Performed spectral analysis to identify terrains with unique absorption features indicative of hydration.
• Compared observed spectra with laboratory mineral spectra to assess the likelihood of specific H2O- or OH-bearing phases.
• Mapped spatial distributions of spectrally distinct regions, including polar caps and seasonal polar hoods.

Experimental results

Research questions

• RQ1 What is the spatial distribution of hydration features in the Acidalia hemisphere of Mars based on 1997 HST/NICMOS data?
• RQ2 Are H2O- or OH-bearing minerals detectable in the northern and southern dark terrains of Acidalia?
• RQ3 How do atmospheric and surface albedo effects influence the interpretation of hydration signals in the data?
• RQ4 Which large-scale terrains exhibit spectrally unique signatures consistent with hydrated minerals?
• RQ5 What are the implications of the absence of strong hydration features in southern dark terrains for Martian surface processes?

Key findings

• Three large-scale (>1000 km diameter) terrains with distinct spectral signatures were identified: northern Acidalia, southern classical dark terrain, and adjacent intermediate albedo terrain.
• Two additional spectrally unique regions were detected: the northern polar ice cap and the southern winter polar hood.
• Evidence for H2O- or OH-bearing minerals was found in northern Acidalia and the nearby intermediate albedo terrain, based on spectral comparisons with mineral standards.
• No significant hydration features were detected in the southern hemisphere dark terrains imaged in 1997, indicating these regions lack spectrally dominant hydrated minerals.
• The spectral differences suggest regional heterogeneity in surface hydration, with potential implications for past or present water activity.
• Atmospheric correction using line-by-line radiative transfer and MOLA data significantly improved the accuracy of surface hydration detection.