A5007045086- Planetary Science and Exploration
- Astro and Planetary Science
- Space Exploration and Technology
- Space Science and Extraterrestrial Life
- Scientific Research and Discoveries
- Astronomy and Astrophysical Research
- Solar and Space Plasma Dynamics
- Spacecraft and Cryogenic Technologies
- Calibration and Measurement Techniques
- Spaceflight effects on biology
- Atmospheric Ozone and Climate
- Photocathodes and Microchannel Plates
- Stellar, planetary, and galactic studies
- Astrophysical Phenomena and Observations
- Geophysics and Gravity Measurements
- Ionosphere and magnetosphere dynamics
- Advanced Frequency and Time Standards
- Atmospheric and Environmental Gas Dynamics
- Mathematical and Theoretical Analysis
- Methane Hydrates and Related Phenomena
- Plasma Diagnostics and Applications
- Spacecraft Design and Technology
- Advanced Differential Geometry Research
- History and Developments in Astronomy
- Particle Detector Development and Performance
Laboratory for Atmospheric and Space Physics
2022-2024
University of Colorado Boulder
2022-2024
Boston University
2012-2024
University of Illinois Urbana-Champaign
2020-2022
Patna University
1929
Abstract Mars is believed to have lost much of its surface water 3.5 billion years ago, but the amounts that escaped into space and remain frozen in crust today are not well known. Hydrogen atoms extended martian atmosphere, some which escape planet's gravity, can be imaged through scattered solar UV radiation. Hubble Space Telescope (HST) images ultraviolet H Ly α emission now indicate coronal density steadily decreased by a factor roughly 40% over 4 weeks, far greater variation than had...
Hubble Space Telescope and Mars Express observed unexpected rapid changes in the Martian hydrogen exosphere involving a decrease scattered Lyman α intensity fall 2007 (solar longitude, Ls = 331°–345°). These detected were speculated to be combination of seasonal variation and/or dust storms lower atmospheric dynamics. Here we present observations 2014 over broad range heliocentric distances seasons (Ls 138°–232°) which indicate factor ~3.5 change brightness associated with ~5.4 escape flux...
Abstract The MAVEN IUVS instrument contains an echelle spectrograph channel designed to measure D and H Ly α emissions from the upper atmosphere of Mars. This has successfully recorded both emissions, which are produced by resonant scattering solar emission, over course most a martian year. fundamental purpose these measurements is understand physical principles underlying escape into space, thereby relate present‐day enhanced HDO/H 2 O ratio in bulk water history Variations independent flux...
Abstract In September 2017, an active region of the Sun produced a series strong flares and coronal mass ejection that swept past Mars producing enhanced ionization heating in upper atmosphere. Emissions from atmospheric hydrogen Lyman‐α were also at Mars. Temperatures derived neutral species scale heights used conjunction with H observations to simulate effects this space weather event on Martian properties exosphere. It was found abundance atmosphere decreased by ~25% escape rate increased...
The exosphere is the outermost layer of terrestrial atmosphere which mainly comprised atomic hydrogen (H) and extends from several hundreds kilometers (~500 km) to Earth radii (~60 RE). Knowledge 3-D structure spatial distribution H densities, especially during geomagnetic storms, crucial understand (i) mechanisms that may enhance its permanent escape space (ii) significant role in governing transient response plasma environment weather. Current analysis this vast neutral region carried out...
The Earth’s thermosphere plays a critical role in the response to space weather and satellite drag particular. relationship between thermospheric variability is relatively straightforward: A hotter results higher densities at all altitudes, directly increasing drag. Despite its crucial weather, there are presently no operational direct measurements of state. Instead, today, state can only be estimated by driving numerical models with known drivers, or assimilating spatiotemporally...
Abstract Auroral emissions are expected from the footprint of Callisto in Jupiter's upper atmosphere owing to known interaction its with magnetosphere, and observed auroral footprints other three Galilean satellites. The mapping along modeled magnetic field lines at Jupiter, however, places same latitude as main emissions, making it difficult detect. We analyzed ultraviolet images Jupiter taken using Hubble Space Telescope/Advanced Camera for Surveys instrument during a large observing...
The complex seasonal, dust, and atmospheric circulation patterns at Mars affect the abundance spatial extent of water its photo-dissociated atomic byproduct H. Recent observations by Atmosphere Volatile Evolution (MAVEN) mission have been used to constrain H exobase (200 km altitude) as well thermal global escape rate. MAVEN span last seven years encompass effects declining phase Solar Cycle 24 activating 25 from mid-perihelion Year (MY) 32 through most aphelion MY36. Results show that there...
Abstract Hubble Space Telescope (HST) observations of the Martian hydrogen exosphere in Lyman α are presented this paper for a period when Mars passed perihelion and southern summer solstice its orbit. The peak intensity exospheric brightness was recorded after went past perihelion, slightly solstice. increase as approached found to not be symmetric around peak, making it impossible fit H escape flux trend with single sinusoidal curve at perihelion. While short‐term (~30 Earth days) changes...
Abstract The high‐resolution echelle mode of the Imaging Ultraviolet Spectrograph (IUVS) instrument on Mars Atmosphere and Volatile Evolution mission has been designed to measure D H Lyman α emissions from Martian atmosphere obtain key information about physical processes by which water escapes into space. Toward this goal, absolute calibration is critical for determining densities, D/H ratio, escape flux water. made observations interplanetary hydrogen (IPH) along multiple look directions...
Abstract The enhanced ratio of deuterium to hydrogen on Mars has been widely interpreted as indicating the loss a large column water into space, and content upper atmosphere is now known be highly variable. variation in properties both indicative dynamical processes that produce these species propagate them altitudes where they can escape planet. Understanding seasonal variability D key understanding rate from Mars. Data 15 month observing campaign, made by Atmosphere Volatile Evolution...
Abstract Atomic H is a direct tracer of water loss at Mars. The recent discovery annual enhancements in its escape rate near perihelion, excess the previously established theory, indicates that Mars has lost substantial amounts to space. However, these rates are often estimated assuming thermal properties for exospheric atoms and therefore lower limit. Past analyses spacecraft observations delivered indirect evidence existence an energetic non‐thermal population without clear detection....
Abstract Measurements by multiple Mars Atmosphere and Volatile Evolution mission instruments, obtained between November 2014 2017, are analyzed to produce deuterium properties in the upper atmosphere of Mars. We show here, for first time, seasonal distribution variability D densities, temperatures, estimated Jeans escape rates at exobase (200 km). Within data constraints, it is found that variations similar northern southern hemispheres, peak near summer solstice. Trends Lyman‐α brightness,...
Abstract Recent Mars Atmosphere and Volatile EvolutioN (MAVEN) observations have shown unexpectedly large deuterium Lyman‐α emissions near the Martian southern summer solstice. The brightness can reach ∼10% of hydrogen below 200 km. In this study, we propose a method to estimate D/H ratio in upper atmosphere through analysis vertical profiles without ability spectrally separate two atomic emission lines. measured by MAVEN/IUVS at four periods are analyzed. During summer, derived ratios km...
Mars' water history is fundamental to understanding Earth-like planet evolution. Water escapes space as atoms, and hydrogen atoms escape faster than deuterium giving an increase in the residual D/H ratio. The present ratio reflects total Mars has lost. Observations with Atmosphere Volatile Evolution (MAVEN) Hubble Space Telescope (HST) spacecraft provide atomic densities rates for H D. Large increases near perihelion observed each martian year are consistent a strong upwelling of vapor....
Abstract The Mars Atmosphere and Volatile Evolution (MAVEN) mission instrument suite includes an ultraviolet echelle spectrograph with high‐spectral resolution designed to resolve D H Lyman‐α emissions. mode was previously characterized in the lab cruise phase had been calibrated using observations models of interplanetary hydrogen This work presents improved characterizations in‐orbit that allow for more robust detections faint emission line. Additionally, re‐calibrated simultaneous...
The spark spectrum of sulphur was measured quite thoroughly by Eder and Yalenta in the region λ 3028⋅32 to 5819⋅54 year 1904; they gave wave-lengths up third place decimals. In 1907, Sir Norman Lockyer showed that some stronger lines S + occur Rigel (β-Orionis, class B8), but not spectra either α-Cygni (Giant Ao) or Sirius (Dwarf Ao). After this time, no experimental theoretical work seems have been undertaken elucidate structure spectrum. 1924, Millikan Bowen published their data on vacuum...
The close approach of comet C/2013 A1 (Siding Spring) to Mars in 2014 October provided a unique opportunity observe dynamically new Oort cloud with potential for interaction planet's atmosphere. water-originating hydrogen coma the extended over 20 million km from nucleus. Determining properties this contributes characterizing comet's water content and production rate. present study analyzes data set high spectral resolution UV observations Siding Spring measured by Atmosphere Volatile...
Exospheric tomography is a computational 3-D imaging technique that provides the estimates of neutral density distributions terrestrial exosphere from space-based ultraviolet (UV) measurements. Variability densities during geomagnetically active conditions has been previously reported, motivating development time-dependent tomographic techniques can characterize both spatial and temporal scales these events. However, solving dynamic exospheric problem be challenging owing to its...
Arcus is a high-resolution soft X-ray and far-ultraviolet spectroscopy mission being developed for submission to NASA's inaugural Astrophysics Probe solicitation. makes simultaneous observations in these two critical wavelength regimes address broad range of science questions highlighted by the 2020 Astronomy Decadal Survey, from temperature composition missing baryons intergalactic medium evolution stars their influence on orbiting planets. This proceeding presents motivation performance...