University of California, Santa Cruz

About: University of California, Santa Cruz is a education organization based out in Santa Cruz, California, United States. It is known for research contribution in the topics: Galaxy & Population. The organization has 15541 authors who have published 44120 publications receiving 2759983 citations. The organization is also known as: UCSC & UC, Santa Cruz.

A synthesis of Martian aqueous mineralogy after 1 Mars year of observations from the Mars Reconnaissance Orbiter

Abstract: Martian aqueous mineral deposits have been examined and characterized using data acquired during Mars Reconnaissance Orbiter's (MRO) primary science phase, including Compact Reconnaissance Imaging Spectrometer for Mars hyperspectral images covering the 0.4–3.9 μm wavelength range, coordinated with higher–spatial resolution HiRISE and Context Imager images. MRO's new high-resolution measurements, combined with earlier data from Thermal Emission Spectrometer; Thermal Emission Imaging System; and Observatoire pour la Mineralogie, L'Eau, les Glaces et l'Activitie on Mars Express, indicate that aqueous minerals are both diverse and widespread on the Martian surface. The aqueous minerals occur in 9–10 classes of deposits characterized by distinct mineral assemblages, morphologies, and geologic settings. Phyllosilicates occur in several settings: in compositionally layered blankets hundreds of meters thick, superposed on eroded Noachian terrains; in lower layers of intracrater depositional fans; in layers with potential chlorides in sediments on intercrater plains; and as thousands of deep exposures in craters and escarpments. Carbonate-bearing rocks form a thin unit surrounding the Isidis basin. Hydrated silica occurs with hydrated sulfates in thin stratified deposits surrounding Valles Marineris. Hydrated sulfates also occur together with crystalline ferric minerals in thick, layered deposits in Terra Meridiani and in Valles Marineris and together with kaolinite in deposits that partially infill some highland craters. In this paper we describe each of the classes of deposits, review hypotheses for their origins, identify new questions posed by existing measurements, and consider their implications for ancient habitable environments. On the basis of current data, two to five classes of Noachian-aged deposits containing phyllosilicates and carbonates may have formed in aqueous environments with pH and water activities suitable for life.

Using FU Orionis Outbursts to Constrain Self-Regulated Protostellar Disk Models

Abstract: One dimensional, convective, vertical structure models and one dimensional, time dependent, radial diffusion models are combined to create a self-consistent picture in which FU~Orionis outbursts occur in young stellar objects (YSOs) as the result of a large scale, self-regulated, thermal ionization instability in the surrounding protostellar accretion disk. By fitting the results of time dependent disk models to observed time scales of FU~Orionis events, we estimate the magnitude of the effeciency of the effective viscous stress in the inner disk (r < 1 AU) to be, in accordance with the ad hoc ``alpha'' prescription, 10^{-4} where hydrogen is neutral and 10^{-3} where hydrogen is ionized. We hypothesize that all YSOs receive infall onto their outer disks which is steady (or slowly declining with time) and that FU~Orionis outbursts are self-regulated, disk outbursts which occur only in systems which transport matter inward at a rate sufficiently high to cause hydrogen to be ionized in the inner disk. We estimate a critical mass flux of 5x10^{-7} solar masses / year {\it independent of the magnitude of alpha} for systems with one solar mass, three solar radius central objects. Infall accretion rates in the range of (1-10)x10^{-6} solar masses per year produce observed FU~Orionis time scales consistent with estimates of spherical molecular cloud core collapse rates.