P. R. Christensen's research while affiliated with Arizona State University and other places

Publications (530)

Article
Full-text available
Bennu, the target of the OSIRIS‐REx mission, is an asteroid with compositions analogous to low petrologic type CI, CM, CR, and/or ungrouped carbonaceous chondrites. Asteroids like Bennu provide information about the building blocks of the early Solar System. Analysis of the mid‐infrared remote sensing data informs mineral quantification. We apply a...
Article
Carbonaceous asteroids, such as (101955) Bennu, preserve material from the early Solar System, including volatile compounds and organic molecules. We report spacecraft imaging and spectral data collected during and after retrieval of a sample from Bennu’s surface. The sampling event mobilized rocks and dust into a debris plume, excavating a 9-m-lon...
Article
Full-text available
The OSIRIS‐REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) spacecraft sampled asteroid (101955) Bennu on 20 October 2020 and will return the collected regolith to Earth in 2023. Before sample collection, spectral observations of four regions of interest on Bennu's surface were acquired at high spatial...
Article
Full-text available
AIM: The SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery. METHODS: This was an international prospective cohort study of consecutive colorectal cancer patients...
Article
Full-text available
Planetary surfaces can be complex mixtures of coarse and fine particles that exhibit linear and nonlinear mixing behaviors at mid‐infrared (MIR) wavelengths. Machine learning multivariate analysis can estimate modal mineralogy of mixtures and is favorable because it does not assume linear mixing across wavelengths. We used partial least squares (PL...
Article
Full-text available
There is little evidence around the potentially protective role of previous Bacillus Calmette-Guerin (BCG) vaccination on postoperative mortality in patients with perioperative SARS-CoV-2 vaccination. Prior BCG vaccination did not protect SARS-CoV-2 infected patients against postoperative pulmonary complications and 30-day mortality.
Article
Full-text available
Background: Surgery is the main modality of cure for solid cancers and was prioritised to continue during COVID-19 outbreaks. This study aimed to identify immediate areas for system strengthening by comparing the delivery of elective cancer surgery during the COVID-19 pandemic in periods of lockdown versus light restriction. Methods: This internati...
Article
Context. Asteroid (101955) Bennu is the target of NASA’s Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission. The spacecraft’s instruments have characterized Bennu at global and local scales to select a sampling site and provide context for the sample that will be returned to Earth. These o...
Article
Full-text available
Background Surgical services are preparing to scale up in areas affected by COVID-19. This study aimed to evaluate the association between preoperative SARS-CoV-2 testing and postoperative pulmonary complications in patients undergoing elective cancer surgery. Methods This international cohort study included adult patients undergoing elective surge...
Article
Full-text available
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Article
Full-text available
Thermal inertia and surface roughness are proxies for the physical characteristics of planetary surfaces. Global maps of these two properties distinguish the boulder population on near-Earth asteroid (NEA) (101955) Bennu into two types that differ in strength, and both have lower thermal inertia than expected for boulders and meteorites. Neither ha...
Article
Full-text available
Background: Ileus is common after elective colorectal surgery, and is associated with increased adverse events and prolonged hospital stay. The aim was to assess the role of non-steroidal anti-inflammatory drugs (NSAIDs) for reducing ileus after surgery. Methods: A prospective multicentre cohort study was delivered by an international, student-...
Article
Full-text available
Establishing the abundance and physical properties of regolith and boulders on asteroids is crucial for understanding the formation and degradation mechanisms at work on their surfaces. Using images and thermal data from NASA’s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we show...
Article
Full-text available
Early spectral data from the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission reveal evidence for abundant hydrated minerals on the surface of near-Earth asteroid (101955) Bennu in the form of a near-infrared absorption near 2.7 µm and thermal infrared spectral features that are most sim...
Article
Full-text available
The OSIRIS-REx Thermal Emission Spectrometer (OTES) will provide remote measurements of mineralogy and thermophysical properties of Bennu to map its surface, help select the OSIRIS-REx sampling site, and investigate the Yarkovsky effect. OTES is a Fourier Transform spectrometer covering the spectral range 5.71–100 μm (1750–100cm−1) with a spectral...
Article
Gale crater is the landing site of the Mars Science Laboratory (MSL) rover, Curiosity. Here we present Thermal Emission Imaging System Visible Imaging Subsystem (THEMIS-VIS) mosaics in gray scale and in false color of Gale crater. We use these data products, in addition to THEMIS thermal infrared decorrelation stretch (DCS) mosaics, thermal inertia...
Article
We investigated the area to the northwest of the Isidis impact basin (hereby referred to as "NW Isidis") using thermal infrared emission datasets to characterize and quantify bulk surface mineralogy throughout this region. This area is home to Jezero crater and the watershed associated with its two deltaic deposits in addition to NE Syrtis and the...
Article
Following the most recent updates to the Mars Odyssey Thermal Emission Imaging System daytime and nighttime infrared global mosaics, a colorized global map was produced that combines the thermophysical information from the nighttime infrared global mosaic with the morphologic context of the daytime infrared global mosaic. During the validation of t...
Article
The OSIRIS-REx Thermal Emission Spectrometer (OTES) will provide remote measurements of mineralogy and thermophysical properties of Bennu to map its surface, help select the OSIRIS-REx sampling site, and investigate the Yarkovsky effect. OTES is a Fourier transform spectrometer covering the spectral range 5.71 - 100 {\mu}m (1750 - 100 cm-1) with a...
Article
Full-text available
In May of 2011, NASA selected the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) asteroid sample return mission as the third mission in the New Frontiers program. The other two New Frontiers missions are New Horizons, which explored Pluto during a flyby in July 2015 and is on its way for a fly...
Article
Full-text available
With the advent of exoplanetary astronomy and the ongoing discovery of terrestrial-type planets around other stars, our own solar system becomes a key testing ground for ideas about what factors control planetary evolution. In particular, what allows a planet to be both within a potentially habitable zone and sustain habitability over long geologic...
Article
Full-text available
Recurring Slope Lineae (RSL) are dark streaks that appear on steep slopes on the martian surface. While their apparent movement suggests liquid flow, remote sensing studies have not found evidence of fresh water. Some RSL have been observed at temperatures below the freezing point of water; if liquid water is present, therefore, it is likely in the...
Article
In this study, we investigate the fluvial, sedimentary, and volcanic history of Margaritifer basin and the Uzboi-Ladon-Morava (ULM) outflow channel system. This network of valleys and basins spans more than 8000 km in length, linking the fluvially dissected southern highlands and Argyre Basin with the northern lowlands via Ares Vallis. Compositiona...
Article
The colocation of southern-hemisphere RSL and local chloride deposits was measured to assess the role of chloride brines as mechanisms of RSL formation.
Article
The geologic history of the northern plains of Mars has been extensively debated. Specifically, the Vastitas Borealis Formation (VBF) represents an enigmatic surface unit that exhibits flow morphologies at its boundary, extensive surface fracturing, tens of thousands of small mounds, and unique crater morphologies. Here, we test the hypothesis that...
Article
A local olivine-rich exposure provides insight into the relationship between widespread mafic exposures and the circum-Chryse chaos terrain and fluvial systems.
Conference Paper
Here we present TIR spectral evidence that the high-silica component of TES surface type 2 could be explained by weathering rinds on basalt glass.
Article
Mars surface properties (e.g., grain size, induration, layering, chemistry) strongly affect thermal conductivity. Lab improves interpretation of temperature datasets.
Article
The correlation between MSL and ODY ground temperature measurements is very good. In situ data provide insight into the local scale variability in geology.
Article
The large ULM fluvial system on Mars has substantial amounts of olivine-rich bedrock, which has significant implications for fluvial and sedimentary history.
Article
Sedimentary deposits associated with the circum-Chryse outflow channels are identified in the shallow subsurface of Chryse and Acidalia Planitiae, Mars.
Article
Flat-floored craters have long been recognized on Mars with early work hypothesizing a sedimentary origin. More recently, high-resolution thermal inertia measurements show that these craters contain some of the rockiest materials on the planet, inconsistent with poorly consolidated sedimentary materials. In this study, the distribution, physical pr...
Article
The diversity of investigations of planetary surfaces, especially Mars, using in situ instrumentation over the last decade is unprecedented in the exploration history of our solar system. The style of instrumentation that landed spacecraft can support is dependent on several parameters, including mass, power consumption, instrument complexity, cost...
Article
This work studies the variability of martian surface properties through the creation of a global thermal inertia map from THEMIS infrared images.
Article
Decompression melting of the mantle via impact excavation is an important, widespread, and ancient process that has dramatically shaped the surface of Mars.
Conference Paper
The high-silica component of TES Surface Type 2 is shown to be consistent with leached glass, based on lab spectra and global correlation with near-IR spectra.
Article
The mound of material in Gale Crater formed by tectonic uplift rather than sedimentary deposition and erosion.
Article
The clay stratigraphy at Mawrth Vallis, Mars, is interpreted as a paleosol sequence. Soil mineralogy indicates climate transitions and surface environments.
Article
Analysis of seasonal data from the Mars Global Surveyor Thermal Emission Spectrometer (TES) shows a significant increase in thermal inertia during autumn, winter and spring in the middle and high latitudes of Mars. At each stage of the northern seasonal polar cap's recession in spring a distinct high thermal inertia (HTI) annulus arises around the...
Article
Models of Thermal Emission Spectrometer (TES) data suggest that poorly-crystalline weathering products allophane and aluminosilicate gel occur in several low-albedo regions of Mars. The presence of allophane in TES models indicates that the martian surface experienced low-temperature chemical weathering at low water-to-rock ratios and mildly acidic...
Article
Full-text available
OSIRIS-REx is an asteroid sample-return mission that was selected by NASA in May 2011 as the third New Frontiers Mission. The name is an acronym that captures the scientific objectives of the mission: Origins, Spectral Interpretation, Resource Identification, and Security Regolith Explorer. OSIRIS-REx will Rendezvous with near-Earth asteroid 101955...
Article
This work describes the interpretation of THEMIS-derived thermal inertia data at the Eberswalde, Gale, Holden, and Mawrth Vallis Mars Science Laboratory (MSL) candidate landing sites and determines how thermophysical variations correspond to morphology and, when apparent, mineralogical diversity. At Eberswalde, the proportion of likely unconsolidat...
Article
We review the evidence for regolith on the surface of our target asteroid (101955) 1999 RQ36 and provide an overview of our sampling strategy.
Article
The stratigraphy and mineralogy at Mawrth Vallis may be consistent with ancient clay-rich soils on Earth, suggesting that Mawrth Vallis may preserve a geochemical record of several million years of evolving climates and habitable environments.
Conference Paper
Full-text available
Spectral libraries are an integral part of planetary surface remote sensing. Thermal emission spectra have been collected for whole-rock specimens of meteorites representing chondritic and achondritic groups, with asteroid assessment applicability.
Article
We report several new occurrences of dikes in Thaumasia Planum, which have distinct thermophysical and compositional characteristics. They are important for understanding the magmatic properties and processes in early martian geological time.
Article
Full-text available
A new atlas of Mars includes base maps created from merged, multiple datasets, global views of geology and composition, and features of interest in each region.
Article
MGS TES surface-atmosphere separation methods are improved by removing minor CO_2 and water vapor absorptions and working with an expanded spectral range. One of the new advantages is ability to assess global spectral variability at >1300 cm^-^1.
Article
We present initial results from the development of a microscopic thermal emission spectrometer and its application to igneous planetary analog materials. Additionally, we also illustrate its utility as a non-destructive micro-analysis technique.
Article
The Arizona State University (ASU) School of Earth and Space Exploration's Mars Space Flight Facility (MSFF) and 100 Cities Project, in collaboration with the United Nations Global Pulse initiative are utilizing NASA multispectral satellite data to visualize and analyze socioeconomic characteristics and human activity in Uganda. The Global Pulse in...
Article
A relatively thin, global or semi-global, rocky, olivine-rich layer has been identified. We propose that the most likely scenario for the formation of a layer with these characteristics and extent is directly related to a mega-impact event.
Article
There is a need for a software tool that has the ability to display and analyze various types of earth science and social data through a simple, user-friendly interface. The J-Earth software tool has been designed to be easily accessible for download and intuitive use, regardless of the technical background of the user base. This tool does not requ...
Article
On Earth, vast deposits rich in phyllosilicates are commonly created during soil formation, or pedogenesis. When soils are preserved in the stratigraphic record as paleosols, they become valuable resources for terrestrial geologists because paleosol isotopes, mineralogy, and chemical weathering profiles can be used to reconstruct ancient surface en...
Article
Roughly 80 images of our planet are captured every day from the Geostationary Operational Environmental Satellite 13 (GOES-13), a geosynchronous weather satellite, which covers the Atlantic side of the western hemisphere. The GOES-13 multichannel imager measures radiant energy and reflected solar energy from the Earth's surface and atmosphere in fi...
Article
A wealth of terrestrial remote sensing data has been collected and made public over the years from a variety of missions, but accessing this data and performing analysis on it has often been a time consuming and problematic task. J-Earth is a geospatial application that provides a quick and consistent means of accessing many terrestrial datasets wh...
Article
The mosaicking of global planetary data sets allows for the examination of local, regional, and global scale processes on all planetary bodies. Processing techniques that allow us and other users to crate mosaics of tens of thousands of images are documented along with the associated errors introduced by each image-processing algorithm. These techn...
Article
Full-text available
The weathering of meteorites found on Mars involves chemical and physical processes that can provide clues to climate conditions at the location of their discovery. Beginning on sol 1961, the Opportunity rover encountered three large iron meteorites within a few hundred meters of each other. In order of discovery, these rocks have been assigned the...
Article
Full-text available
Models of TES and Mini-TES spectra with libraries containing allophanes and gel suggest these weathering products occur in several regions of Mars. The presence of allophane indicates that weathering has proceeded under moderate pH conditions.
Article
Allophane is an alteration product of volcanic glass and a clay mineral precursor that is commonly found in basaltic soils on Earth. It is a poorly-crystalline or amorphous, hydrous aluminosilicate with Si/Al ratios ranging from ~0.5-1 [Wada, 1989]. Analyses of thermal infrared (TIR) spectra of the Martian surface from TES show high-silica phases a...
Article
The hyperarid (< 2 mm/yr MAP) Atacama Desert of northern Chile is a widely accepted terrestrial analog for the surface of Mars. Sulfate and chloride deposits are present in uncommonly high abundances throughout the Atacama. The formation and preservation of these evaporite deposits are a direct result of the arid-hyperarid climate of the region fro...
Article
We present measurements of the altitude and eastward velocity component of mesospheric clouds in 35 imaging sequences acquired by the Mars Odyssey (ODY) spacecraft’s Thermal Emission Imaging System visible imaging subsystem (THEMIS-VIS). We measure altitude by using the parallax drift of high-altitude features, and the velocity by exploiting the ti...
Article
J-Earth is a Geographic Information Systems (GIS) application used for viewing and processing satellite and airborne remote sensing data and includes NASA imagery such as ASTER, Landsat, MODIS, TIMS, as well as other geological, ecological, and social datasets. The J-Earth team is working with the National Science Foundation-funded Central Arizona-...
Article
Phyllosilicates were first identified on Mars by the OMEGA spectrometer on Mars Express and found to be widespread in ancient terrains by the CRISM spectrometer on Mars Reconnaissance Orbiter. They are indicators of water in the environment, which is important for understanding martian climate. But the quantitative abundance of phyllosilicates, suc...
Article
NASA's Mars Program and Arizona State University's Mars Education Program have partnered with Mars mission teams and Mars Principal Investigator Dr. Phil Christensen to develop and promote an ongoing STEM-based opportunity for students to become active participants in the exploration of the Red Planet. The Mars Student Imaging Project (MSIP) has, s...
Article
Our society currently is facing a number of major environmental challenges, most notably the threat of climate change. A multifaceted, interdisciplinary approach involving physical and social scientists, engineers and decisionmakers is critical to adequately address these complex issues. To best facilitate this interdisciplinary approach, data and...
Article
It has been suggested that allophane or related poorly crystalline aluminosilicates are present on Mars, and that they comprise the high-silica phase detected by the Thermal Emission Spectrometer (TES) in Surface Type 2 materials (Kraft et al., 2003; Michalski et al., 2005). Using new laboratory spectra of allophanic materials, we (Rampe et al., th...