74 research outputs found
Prebiotic chemistry and atmospheric warming of early Earth by an active young Sun
This is the author accepted manuscript. The final version is available from Nature Publishing Group via the DOI in this recordNitrogen is a critical ingredient of complex biological molecules. Molecular nitrogen, however, which was outgassed into the Earth's early atmosphere, is relatively chemically inert and nitrogen fixation into more chemically reactive compounds requires high temperatures. Possible mechanisms of nitrogen fixation include lightning, atmospheric shock heating by meteorites, and solar ultraviolet radiation. Here we show that nitrogen fixation in the early terrestrial atmosphere can be explained by frequent and powerful coronal mass ejection events from the young Sun - so-called superflares. Using magnetohydrodynamic simulations constrained by Kepler Space Telescope observations, we find that successive superflare ejections produce shocks that accelerate energetic particles, which would have compressed the early Earth's magnetosphere. The resulting extended polar cap openings provide pathways for energetic particles to penetrate into the atmosphere and, according to our atmospheric chemistry simulations, initiate reactions converting molecular nitrogen, carbon dioxide and methane to the potent greenhouse gas nitrous oxide as well as hydrogen cyanide, an essential compound for life. Furthermore, the destruction of N 2 , CO 2 and CH 4 suggests that these greenhouse gases cannot explain the stability of liquid water on the early Earth. Instead, we propose that the efficient formation of nitrous oxide could explain a warm early Earth.We thank three referees for constructive suggestions that improved the manuscript. This work was supported by NASA GSFC Science Task Group 263 funds. V. Airapetian performed the part of this work while staying at ELSI/Tokyo Tech
GaN-Based Detector Enabling Technology for Next Generation Ultraviolet Planetary Missions
The ternary alloy AlN-GaN-InN system provides several distinct advantages for the development of UV detectors for future planetary missions. First, (InN), (GaN) and (AlN) have direct bandgaps 0.8, 3.4 and 6.2 eV, respectively, with corresponding wavelength cutoffs of 1550 nm, 365 nm and 200 nm. Since they are miscible with each other, these nitrides form complete series of indium gallium nitride (In(sub l-x)Ga(sub x)N) and aluminum gallium nitride (Al(sub l-x)Ga(sub x)N) alloys thus allowing the development of detectors with a wavelength cut-off anywhere in this range. For the 2S0-365 nm spectral wavelength range AlGaN detectors can be designed to give a 1000x solar radiation rejection at cut-off wavelength of 325 nm, than can be achieved with Si based detectors. For tailored wavelength cut-offs in the 365-4S0 nm range, InGaN based detectors can be fabricated, which still give 20-40x better solar radiation rejection than Si based detectors. This reduced need for blocking filters greatly increases the Detective Quantum efficiency (DQE) and simplifies the instrument's optical systems. Second, the wide direct bandgap reduces the thermally generated dark current to levels allowing many observations to be performed at room temperature. Third, compared to narrow bandgap materials, wide bandgap semiconductors are significantly more radiation tolerant. Finally, with the use of an (AI, In)GaN array, the overall system cost is reduced by eliminating stringent Si CCD cooling systems. Compared to silicon, GaN based detectors have superior QE based on a direct bandgap and longer absorption lengths in the UV
Life Beyond the Solar System: Space Weather and Its Impact on Habitable Worlds
The search of life in the Universe is a fundamental problem of astrobiology
and a major priority for NASA. A key area of major progress since the NASA
Astrobiology Strategy 2015 (NAS15) has been a shift from the exoplanet
discovery phase to a phase of characterization and modeling of the physics and
chemistry of exoplanetary atmospheres, and the development of observational
strategies for the search for life in the Universe by combining expertise from
four NASA science disciplines including heliophysics, astrophysics, planetary
science and Earth science. The NASA Nexus for Exoplanetary System Science
(NExSS) has provided an efficient environment for such interdisciplinary
studies. Solar flares, coronal mass ejections and solar energetic particles
produce disturbances in interplanetary space collectively referred to as space
weather, which interacts with the Earth upper atmosphere and causes dramatic
impact on space and ground-based technological systems. Exoplanets within close
in habitable zones around M dwarfs and other active stars are exposed to
extreme ionizing radiation fluxes, thus making exoplanetary space weather (ESW)
effects a crucial factor of habitability. In this paper, we describe the recent
developments and provide recommendations in this interdisciplinary effort with
the focus on the impacts of ESW on habitability, and the prospects for future
progress in searching for signs of life in the Universe as the outcome of the
NExSS workshop held in Nov 29 - Dec 2, 2016, New Orleans, LA. This is one of
five Life Beyond the Solar System white papers submitted by NExSS to the
National Academy of Sciences in support of the Astrobiology Science Strategy
for the Search for Life in the Universe.Comment: 5 pages, the white paper was submitted to the National Academy of
Sciences in support of the Astrobiology Science Strategy for the Search for
Life in the Univers
Demonstration of an off-axis parabolic receiver for near-range retrieval of lidar ozone profiles
During the 2017 Ozone Water Land Environmental Transition Study (OWLETS), the
Langley mobile ozone lidar system utilized a new small diameter receiver to
improve the retrieval of near-surface signals from 0.1 to 1 km in altitude.
This new receiver utilizes a single 90 ∘ fiber-coupled, off-axis
parabolic mirror resulting in a compact form that is easy to align. The
single reflective surface offers the opportunity to easily expand its use to
multiple wavelengths for additional measurement channels such as visible
wavelength aerosol measurements. Detailed results compare the performance of
the receiver to both ozonesonde and in situ measurements from a UAV platform,
validating the performance of the near-surface ozone retrievals. Absolute
O3 differences averaged 7 % between lidar and ozonesonde data
from 0.1 to 1.0 km and yielded a 2.3 % high bias in the lidar data, well
within the uncertainty of the sonde measurements. Conversely, lidar
O3 measurements from 0.1 to 0.2 km averaged 10.5 % lower than
coincident UAV O3. A more detailed study under more stable
atmospheric conditions would be necessary to resolve the residual instrument
differences reported in this work. Nevertheless, this unique added capability
is a significant improvement allowing for near-surface observation of ozone.</p
Transmission spectrum of Venus as a transiting exoplanet
On 5-6 June 2012, Venus will be transiting the Sun for the last time before
2117. This event is an unique opportunity to assess the feasibility of the
atmospheric characterisation of Earth-size exoplanets near the habitable zone
with the transmission spectroscopy technique and provide an invaluable proxy
for the atmosphere of such a planet. In this letter, we provide a theoretical
transmission spectrum of the atmosphere of Venus that could be tested with
spectroscopic observations during the 2012 transit. This is done using
radiative transfer across Venus' atmosphere, with inputs from in-situ missions
such as Venus Express and theoretical models. The transmission spectrum covers
a range of 0.1-5 {\mu}m and probes the limb between 70 and 150 km in altitude.
It is dominated in UV by carbon dioxide absorption producing a broad transit
signal of ~20 ppm as seen from Earth, and from 0.2 to 2.7 {\mu}m by Mie
extinction (~5 ppm at 0.8 {\mu}m) caused by droplets of sulfuric acid composing
an upper haze layer above the main deck of clouds. These features are not
expected for a terrestrial exoplanet and could help discriminating an
Earth-like habitable world from a cytherean planet.Comment: 4 pages, 3 figures, 1 table. Figure 3 and Table 1 will be only
available on-line. Table 1 will be fully available at the CDS. Accepted for
publication in Astronomy and Astrophysics (Letter
Impact of Space Weather on Climate and Habitability of Terrestrial Type Exoplanets
The current progress in the detection of terrestrial type exoplanets has
opened a new avenue in the characterization of exoplanetary atmospheres and in
the search for biosignatures of life with the upcoming ground-based and space
missions. To specify the conditions favorable for the origin, development and
sustainment of life as we know it in other worlds, we need to understand the
nature of astrospheric, atmospheric and surface environments of exoplanets in
habitable zones around G-K-M dwarfs including our young Sun. Global environment
is formed by propagated disturbances from the planet-hosting stars in the form
of stellar flares, coronal mass ejections, energetic particles, and winds
collectively known as astrospheric space weather. Its characterization will
help in understanding how an exoplanetary ecosystem interacts with its host
star, as well as in the specification of the physical, chemical and biochemical
conditions that can create favorable and/or detrimental conditions for
planetary climate and habitability along with evolution of planetary internal
dynamics over geological timescales. A key linkage of (astro) physical,
chemical, and geological processes can only be understood in the framework of
interdisciplinary studies with the incorporation of progress in heliophysics,
astrophysics, planetary and Earth sciences. The assessment of the impacts of
host stars on the climate and habitability of terrestrial (exo)planets will
significantly expand the current definition of the habitable zone to the
biogenic zone and provide new observational strategies for searching for
signatures of life. The major goal of this paper is to describe and discuss the
current status and recent progress in this interdisciplinary field and to
provide a new roadmap for the future development of the emerging field of
exoplanetary science and astrobiology.Comment: 206 pages, 24 figures, 1 table; Review paper. International Journal
of Astrobiology (2019
Validation of the TOLNet lidars: the Southern California Ozone Observation Project (SCOOP)
The North America-based Tropospheric Ozone Lidar Network (TOLNet)
was recently established to provide high spatiotemporal vertical profiles of
ozone, to better understand physical processes driving tropospheric ozone
variability and to validate the tropospheric ozone measurements of upcoming
spaceborne missions such as Tropospheric Emissions: Monitoring Pollution
(TEMPO). The network currently comprises six tropospheric ozone lidars, four
of which are mobile instruments deploying to the field a few times per year,
based on campaign and science needs. In August 2016, all four mobile TOLNet
lidars were brought to the fixed TOLNet site of JPL Table Mountain Facility
for the 1-week-long Southern California Ozone Observation Project (SCOOP).
This intercomparison campaign, which included 400 h of lidar measurements
and 18 ozonesonde launches, allowed for the unprecedented simultaneous
validation of five of the six TOLNet lidars. For measurements between 3 and
10 km a.s.l., a mean difference of 0.7 ppbv (1.7 %), with a
root-mean-square deviation of 1.6 ppbv or 2.4 %, was found between the
lidars and ozonesondes, which is well within the combined uncertainties of
the two measurement techniques. The few minor differences identified were
typically associated with the known limitations of the lidars at the profile
altitude extremes (i.e., first 1 km above ground and at the instruments'
highest retrievable altitude). As part of a large homogenization and quality
control effort within the network, many aspects of the TOLNet in-house data
processing algorithms were also standardized and validated. This thorough
validation of both the measurements and retrievals builds confidence as to the
high quality and reliability of the TOLNet ozone lidar profiles for many
years to come, making TOLNet a valuable ground-based reference network for
tropospheric ozone profiling.</p
Evaluating WRF-GC v2.0 predictions of boundary layer height and vertical ozone profile during the 2021 TRACER-AQ campaign in Houston, Texas
The TRacking Aerosol Convection ExpeRiment – Air Quality (TRACER-AQ) campaign probed Houston air quality with a comprehensive suite of ground-based and airborne remote sensing measurements during the intensive operating period in September 2021. Two post-frontal high-ozone episodes (6–11 and 23–26 September) were recorded during the aforementioned period. In this study, we evaluated the simulation of the planetary boundary layer (PBL) height and the vertical ozone profile by a high-resolution (1.33 km) 3-D photochemical model, the Weather Research and Forecasting (WRF)-driven
GEOS-Chem (WRF-GC). We evaluated the PBL heights with a ceilometer at the
coastal site La Porte and the airborne High Spectral Resolution Lidar 2
(HSRL-2) flying over urban Houston and adjacent waters. Compared with the
ceilometer at La Porte, the model captures the diurnal variations in the PBL heights with a very strong temporal correlation (R>0.7) and
±20 % biases. Compared with the airborne HSRL-2, the model exhibits a moderate to strong spatial correlation (R=0.26–0.68), with ±20 % biases during the noon and afternoon hours during ozone episodes. For land–water differences in PBL heights, the water has shallower PBL heights compared to land. The model predicts larger land–water differences than the observations because the model consistently underestimates the PBL heights over land compared to water. We evaluated vertical ozone distributions by comparing the model against vertical measurements from the TROPospheric OZone lidar (TROPOZ), the HSRL-2, and ozonesondes, as well as surface measurements at La Porte from a model 49i ozone analyzer and one Continuous Ambient Monitoring Station (CAMS). The model underestimates free-tropospheric ozone (2–3 km aloft) by 9 %–22 % but overestimates near-ground ozone (<50 m aloft) by 6 %-39 % during the two ozone episodes. Boundary layer ozone (0.5–1 km aloft) is underestimated by 1 %–11 % during 8–11 September but overestimated by 0 %–7 % during 23–26 September. Based on these evaluations, we identified two model limitations, namely the single-layer PBL representation and the free-tropospheric ozone underestimation. These limitations have implications for the predictivity of ozone's vertical mixing and distribution in other models.</p
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