339 research outputs found
A Limited Habitable Zone for Complex Life
The habitable zone (HZ) is commonly defined as the range of distances from a
host star within which liquid water, a key requirement for life, may exist on a
planet's surface. Substantially more CO2 than present in Earth's modern
atmosphere is required to maintain clement temperatures for most of the HZ,
with several bars required at the outer edge. However, most complex aerobic
life on Earth is limited by CO2 concentrations of just fractions of a bar. At
the same time, most exoplanets in the traditional HZ reside in proximity to M
dwarfs, which are more numerous than Sun-like G dwarfs but are predicted to
promote greater abundances of gases that can be toxic in the atmospheres of
orbiting planets, such as carbon monoxide (CO). Here we show that the HZ for
complex aerobic life is likely limited relative to that for microbial life. We
use a 1D radiative-convective climate and photochemical models to circumscribe
a Habitable Zone for Complex Life (HZCL) based on known toxicity limits for a
range of organisms as a proof of concept. We find that for CO2 tolerances of
0.01, 0.1, and 1 bar, the HZCL is only 21%, 32%, and 50% as wide as the
conventional HZ for a Sun-like star, and that CO concentrations may limit some
complex life throughout the entire HZ of the coolest M dwarfs. These results
cast new light on the likely distribution of complex life in the universe and
have important ramifications for the search for exoplanet biosignatures and
technosignatures.Comment: Revised including additional discussion. Published Gold OA in ApJ. 9
pages, 5 figures, 5 table
Presynchronizing PGF2α and GnRH injections before timed artificial insemination CO-Synch + CIDR program
Fixed-time artificial insemination is an effective management tool that reduces the
labor associated with more conventional artificial insemination programs requiring
detection of estrus. The 7-day CO-Synch + controlled internal drug release (CIDR)
insert protocol has been shown to effectively initiate estrus and ovulation in cycling
and non-cycling suckled beef cows, producing pregnancy rates at or greater than 50%
in beef cows. The gonadotropin-releasing hormone (GnRH) injection that begins the
CO-Synch + CIDR program initiates ovulation in a large proportion of cows, particularly
anestrous cows. The CIDR, which releases progesterone intravaginally, prevents
short estrous cycles that usually follow the first postpartum ovulation in beef cows. Our
hypothesis was that inducing estrus with a prostaglandin injection followed 3 days later
with a GnRH injection, 7 days before applying the 7-day CO-Synch + CIDR protocol,
might increase the percentage of cycling cows that would exhibit synchronous follicular
waves after the onset of the CO-Synch + CIDR protocol. We also hypothesized that
the additional GnRH injection would increase the percentage of anestrous cows that
would ovulate, thereby increasing pregnancy outcomes
Earth as an Exoplanet. II. Earth's Time-variable Thermal Emission and Its Atmospheric Seasonality of Bioindicators
We assess the dependence of Earth's disk-integrated mid-infrared thermal
emission spectrum on observation geometries and investigate which and how
spectral features are impacted by seasonality on Earth. We compiled an
exclusive dataset containing 2690 disk-integrated thermal emission spectra for
four different full-disk observing geometries (North & South Pole centered and
Africa & Pacific centred equatorial views) over four consecutive years. The
spectra were derived from 2378 spectral channels in the wavelength range from
3.75 to 15.4 micron (nominal resolution 1200) and were recorded by
the Atmospheric Infrared Sounder aboard the Aqua satellite. We learned that
there is significant seasonal variability in Earth's thermal emission spectrum,
and the strength of spectral features of bio-indicators, such as N2O, CH4, O3
and CO2 depends strongly on both season and viewing geometry. In addition, we
found a strong spectral degeneracy with respect to the latter two indicating
that multi-epoch measurements and time-dependent signals may be required in
order to fully characterize planetary environments. Even for Earth and
especially for equatorial views, the variations in flux and strength of
absorption features in the disk-integrated data are small and typically
10%. Disentangling these variations from the noise in future exoplanet
observations will be a challenge. However, irrespectively of when the planet
will be measured (i.e., day or night or season) the results from mid-infrared
observations will remain the same to the zeroth order which is an advantage
over reflected light observations.Comment: 21 pages, 15 Figures, 3 Table
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