Evidence of mafic silicates in the blue unit of Phobos: Vis-NIR analogs within the C and Xc-type asteroid taxonomy
Year: 2026
Type: article
Abstract: Context. The composition of Phobos’ blue unit is poorly constrained due a lack of diagnostic spectral features. A ≈1 μm absorption was tentatively identified in past studies, but there has not been a conclusive detection. This situation has precluded the identification of spectroscopic analogs, thus preventing accurate compositional analyses. Aims. The aim of this study is to validate the ≈1 μm absorption in the Phobos blue unit and identify novel asteroidal spectral analogs that fully reproduce its spectral shape. Methods. We validated a Phobos blue unit spectrum from Mars Express/OMEGA with TGO/CaSSIS photometry, whose absolute accuracy is well established, and identified novel asteroidal analogs. Results. The OMEGA and CaSSIS datasets show agreement within 1 σ , confirming the 1 μm band at ≥3 σ for the first time. We identified novel improved asteroidal analogs belonging to the C-complex and Xc types in the SMASSII taxonomy. Conclusions. The 1 μm absorption, suggesting the presence of mafic silicates in the Phobos blue unit, and the identification of C and Xc-type analogs support an exogenous origin, providing key compositional information for the future JAXA/MMX mission.
Source: Astronomy and Astrophysics
Institutions: Osservatorio Astronomico di Padova, National Institute for Astrophysics, University of Padua, Centre National de la Recherche Scientifique, Université Paris Cité, Université Paris Sciences et Lettres, Observatoire de Paris, Sorbonne Université, The Open University, Brown University, Western University
Language: English
Subfield: Space and Planetary Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Awards: BACKGROUND: THE MIT-HAWAII NEAR EARTH OBJECT SURVEY (MITHNEOS) HAS BEEN SYSTEMATICALLY MEASURING NEO NEAR-INFRARED SPECTRA USING SPEX ON THE 3-METER NASA IRTF SINCE 2000. SINCE INCEPTION THIS PROGRAM HAS MEASURED NEAR-INFRARED SPECTRA OF OVER 700 NEAR-EARTH OBJECTS. WE HAVE OBSERVED ~3% OF THE KNOWN DELTA-V<7 KM/S POPULATION REPRESENTING ABOUT 270 NEOS 80 OF WHICH HAVE DELTA-V<6 KM/S. THE SURVEY HAS ALSO OBTAINED SPECTRA FOR ~15% OF THE KNOWN PHA POPULATION OR ABOUT 270 OBJECTS. ALL SPECTRAL OBSERVATIONS FROM THIS CAMPAIGN ARE MADE PUBLICLY AVAILABLE FOR THE COMMUNITY SHORTLY AFTER OBSERVATION AT HTTP://SMASS.MIT.EDU. OBSERVATIONS AND ANALYSIS FROM THIS PROGRAM HAVE HAD A LARGE IMPACT ON NEO SCIENCE SUCH AS: 1) ENHANCED UNDERSTANDING OF SPACE WEATHERING AND REFRESHING MECHANISMS (VERNAZZA ET AL. 2009 NATURE. BINZEL ET AL. 2010 NATURE DEMEO ET AL. 2014) 2) METEORITE-NEO LINKS AND NEO-MAIN BELT SOURCE REGION LINKS (VERNAZZA ET AL 2008 NATURE. THOMAS C.A.&BINZEL R. P. 2010) 3) CHARACTERIZATION OF EXTREMELY SMALL AND RAPIDLY ROTATING NEOS (POLISHOOK ET AL. 2012) 4) DEVELOPMENT OF TECHNIQUES TO DETERMINE ALBEDO AND SPIN ORIENTATION FROM THERMAL EMISSION PAST 2 MICRONS (RIVKIN ET AL. 2005 MOSKOVITZ ET AL. 2017) AND 5) THE VIS+NEAR-INFRARED SPECTRAL TAXONOMY USED BY THE COMMUNITY TO CLASSIFY ASTEROIDS (DEMEO ET AL. 2009). GOALS AND OBJECTIVES: THE PROGRAMMATIC OBJECTIVE OF THIS WORK IS TO SPECTRALLY CHARACTERIZE LOW DELTA-V NEOS AND PHAS. WE WILL MEASUREM 500 NEOS OVER A 5 YEAR PERIOD INCLUDING 150 LOW DELTA-V AND 150 PHA TARGETS. SCIENCE OBJECTIVES OF THIS PROGRAM ARE: 1) COMPOSITIONAL CHARACTERIZATION THROUGH TAXONOMIC CLASSIFICATION AND MINERALOGIC ANALYSIS 2) ALBEDO ESTIMATES FROM MODELING OF THERMAL EMISSION PAST TWO MICRONS. 3) IDENTIFICATION OF METEORITE ANALOGS 4) CHARACTERIZATION OF THE NEO POPULATION AND SUB-POPULATIONS INCLUDING MISSION ACCESSIBLE (LOW DELTA-VELOCITY TARGETS) POTENTIALLY HAZARDOUS ASTEROIDS (PHAS) AND DORMANT COMETS. 5) ANALYSIS OF THE CHANGE IN COMPOSITION OF THE NEO POPULATION AS A FUNCTION OF SIZE. 6) EXPLORATION OF C-COMPLEX DATA TO IDENTIFY DIAGNOSTIC SPECTRAL CHARACTERISTICS AT NEAR-INFRARED WAVELENGTHS. APPROACH AND METHODOLOGY: TARGET SELECTION WILL BE BASED ON NEOS OBSERVABLE ON REQUESTED NASA IRTF OBSERVING DATES BY SEARCHING AMONG LOW DELTA-V TARGETS AND PHAS. DATA WILL BE REDUCED USING THE AUTOSPEX PIPELINE THAT HAS BEEN CONSISTENTLY USED FOR THIS PROGRAM FOR WELL OVER A DECADE. SPECTRAL CLASSIFICATION WILL BE PERFORMED USING THE BUS-DEMEO CLASSIFICATION SYSTEM. SCIENTIFIC ANALYSIS WILL USE ESTABLISHED TECHNIQUES AND TOOLS WHERE APPROPRIATE SUCH AS PRINCIPAL COMPONENT ANALYSIS THERMAL MODELING OF SPECTRAL EMISSION TAILS MINERALOGICAL MODELING AND SPACE WEATHERING MODELING AND COMPARISON WITH THE RELAB METEORITE DATABASE. RELEVANCE AND APPROPRIATENESS TO SOLAR SYSTEM OBSERVATIONS NEOO: THE PROPOSED WORK IS RELEVANT AND APPROPRIATE TO THE SOLAR SYSTEM OBSERVATIONS NEOO PROGRAM BECAUSE AS THE PROGRAM SPECIFIES WE WILL PERFORM NEW GROUND-BASED OBSERVATIONS OF NEAR EARTH OBJECTS TO CHARACTERIZE THEIR COMPOSITIONS. THIS PROGRAM ALSO SUPPORTS THE NASA HUMAN EXPLORATION AND OPERATIONS MISSION DIRECTORATE IN THAT IT PRIORITIZES OBSERVATIONS OF LOW DELTA VELOCITY ORBITS RELATIVE TO EARTH. BECAUSE THE PROPOSED WORK FOCUSES SOLELY ON THE NEAR EARTH OBJECT POPULATION THE NEOO PROGRAM ELEMENT IS THE MOST APPROPRIATE. THE OBSERVATIONS AND OBJECTIVES OF THIS PROGRAM CANNOT BE ACHIEVED BY CURRENT SPACECRAFT MISSIONS., G3816273892
OpenAlex ID: W7214935553