Probing the surface environment of large T-type asteroids

Abstract

We probed the surface environment of large ($>$80 km in diameter) T-type asteroids, a taxonomic type relatively ill-constrained as an independent group, and discussed their place of origin. We performed spectroscopic observations of two T-type asteroids, (96) Aegle and (570) Kythera, over 2.8--4.0 $\mu$m using the Subaru telescope. With other T-types' spectra available in the literature and survey datasets, we strove to find commonalities and global trends in this group. We also utilised the asteroids' polarimetric data and meteorite spectra to constrain their surface texture and composition. Our targets exhibit red $L$-band continuum slopes similar to (1) Ceres and 67P/Churyumov-Gerasimenko, and have an OH-absorption feature with band centres $<$2.8 $\mu$m. (96) Aegle hints at a shallow N--H band near 3.1 $\mu$m and C--H band of organic materials over 3.4--3.6 $\mu$m, whereas no diagnostic bands of water ice and other volatiles exceeding the noise of the data were seen for both asteroids. The large T-type asteroids but (596) Scheila display similar spectral shapes to our targets. $\sim$50 \% of large T-types contain an absorption band near 0.6--0.65 $\mu$m likely associated with hydrated minerals. For T-type asteroids (except Jupiter Trojans) of all sizes, we found a weak correlation: the smaller the diameter and the closer the Sun, the redder the visible slope. The 2.9-$\mu$m band depths of large T-types suggest that they might have experienced aqueous alteration comparable to Ch-types but more intense than most of the main-belt asteroids. The polarimetric phase curve of the T-types is well described by a particular surface structure and their 0.5--4.0 $\mu$m reflectance spectra appear most similar to CI chondrites with grain sizes of $\sim$25--35 $\mu$m. Taken as a whole, we propose that large T-type asteroids might be dislodged roughly around 10 au in the early solar system.

Accepted for publication in Astronomy & Astrophysics

References in corpus (16)

• Solar System evolution from compositional mapping of the asteroid belt
• Terrestrial deuterium-to-hydrogen ratio in water in hyperactive comets
• Connecting Asteroids and Meteorites with visible and near-infrared spectroscopy
• Coupling dynamical and collisional evolution of small bodies II : Forming the Kuiper Belt, the Scattered Disk and the Oort Cloud
• Twenty years of SpeX: Accuracy limits of spectral slope measurements in asteroid spectroscopy
• How to find metal-rich asteroids
• Hybrid accretion of carbonaceous chondrites by radial transport across the Jupiter barrier
• Water abundance at the surface of C-complex main-belt asteroids
• Low-phase spectral reflectance and equivalent geometric albedo of meteorites powders
• Distant formation and differentiation of outer main belt asteroids and carbonaceous chondrite parent bodies
• A Possible Explanation for the Blue Spectral Slope Observed on B-type Asteroids
• Space Weathering of the 3-micron Phyllosilicate Feature induced by Pulsed Laser Irradiation
• Origins of colors variability among C-cluster main-belt asteroids
• An Update of the Correlation between Polarimetric and Thermal Properties of Cometary Dust
• Do twin spectral peaks of olivine particles in the thermal infrared diagnose their sizes and porosities?
• The appearance of a 'fresh' surface on 596 Scheila as a consequence of the 2010 impact event