22 research outputs found
Testing Earth-like atmospheric evolution on exo-Earths through oxygen absorption: required sample sizes and the advantage of age-based target selection
Life has had a dramatic impact on the composition of Earth's atmosphere over
time, which suggests that statistical studies of other inhabited planets'
atmospheres could reveal how they co-evolve with life. While many evolutionary
pathways are possible for inhabited worlds, a possible starting hypothesis is
that most of them evolve similarly to Earth, which we propose could lead to a
positive "age-oxygen correlation" between the ages of inhabited planets and the
fraction which have oxygen-rich atmospheres. We demonstrate that
next-generation space observatories currently under consideration could test
this hypothesis, but only if the stellar age distribution of the target sample
is carefully considered. We explore three possible parameterizations of the
age-oxygen correlation, finding that they yield similar results. Finally, we
examine how abiotic oxygen sources could affect the results, and discuss how
measuring the age-dependence of oxygen could shed light on whether it is a
reliable biosignature. Future efforts can expand upon this groundwork by
incorporating detailed models of the redox balance of terrestrial planets and
its dependence on stellar and planetary properties.Comment: 13 pages, 3 figures, accepted to Ap
A Thousand Earths: A Very Large Aperture, Ultralight Space Telescope Array for Atmospheric Biosignature Surveys
An outstanding, multidisciplinary goal of modern science is the study of the diversity of potentially Earth-like planets and the search for life in them. This goal requires a bold new generation of space telescopes, but even the most ambitious designs yet hope to characterize several dozen potentially habitable planets. Such a sample may be too small to truly understand the complexity of exo-earths. We describe here a notional concept for a novel space observatory designed to characterize 1000 transiting exo-earth candidates. The Nautilus concept is based on an array of inflatable spacecraft carrying very large diameter (8.5 m), very low weight, multiorder diffractive optical elements (MODE lenses) as light-collecting elements. The mirrors typical to current space telescopes are replaced by MODE lenses with a 10 times lighter areal density that are 100 times less sensitive to misalignments, enabling lightweight structure. MODE lenses can be cost-effectively replicated through molding. The Nautilus mission concept has a potential to greatly reduce fabrication and launch costs and mission risks compared to the current space telescope paradigm through replicated components and identical, lightweight unit telescopes. Nautilus is designed to survey transiting exo-earths for biosignatures up to a distance of 300 pc, enabling a rigorous statistical exploration of the frequency and properties of life-bearing planets and the diversity of exo-earths.Gordon and Betty Moore Foundation; NASA's Science Mission DirectorateThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
ACCESS: A Visual to Near-infrared Spectrum of the Hot Jupiter WASP-43b with Evidence of , but no evidence of Na or K
We present a new ground-based visual transmission spectrum of the hot Jupiter
WASP-43b, obtained as part of the ACCESS Survey. The spectrum was derived from
four transits observed between 2015 and 2018, with combined wavelength coverage
between 5,300 \r{A}-9,000 \r{A} and an average photometric precision of 708 ppm
in 230 \r{A} bins. We perform an atmospheric retrieval of our transmission
spectrum combined with literature HST/WFC3 observations to search for the
presence of clouds/hazes as well as Na, K, H, and planetary
absorption and stellar spot contamination over a combined spectral range of
5,318 \r{A}-16,420 \r{A}. We do not detect a statistically significant presence
of Na I or K I alkali lines, or H in the atmosphere of WASP-43b. We
find that the observed transmission spectrum can be best explained by a
combination of heterogeneities on the photosphere of the host star and a clear
planetary atmosphere with . This model yields a log-evidence of
higher than a flat (featureless) spectrum. In particular, the
observations marginally favor the presence of large, low-contrast spots over
the four ACCESS transit epochs with an average covering fraction and temperature contrast . Within the planet's atmosphere, we recover a log
volume mixing ratio of , which is consistent with
previous abundance determinations for this planet.Comment: 27 pages, 18 figures, 7 tables. Accepted for publication in AJ.
Updated affiliation
ACCESS: An optical transmission spectrum of the high-gravity, hot Jupiter HAT-P-23b
We present a new ground-based visible transmission spectrum of the
high-gravity, hot Jupiter HAT-P-23b, obtained as part of the ACCESS project. We
derive the spectrum from five transits observed between 2016 and 2018, with
combined wavelength coverage between 5200 {\AA} - 9269 {\AA} in 200 {\AA} bins,
and with a median precision of 247 ppm per bin. HAT-P-23b's relatively high
surface gravity (g ~ 30 m/s^2), combined with updated stellar and planetary
parameters from Gaia DR2, gives a 5-scale-height signal of 384 ppm for a
hydrogen-dominated atmosphere. Bayesian models favor a clear atmosphere for the
planet with the tentative presence of TiO, after simultaneously modeling
stellar contamination, using spots parameter constraints from photometry. If
confirmed, HAT-P-23b would be the first example of a high-gravity gas giant
with a clear atmosphere observed in transmission at optical/NIR wavelengths;
therefore, we recommend expanding observations to the UV and IR to confirm our
results and further characterize this planet. This result demonstrates how
combining transmission spectroscopy of exoplanet atmospheres with long-term
photometric monitoring of the host stars can help disentangle the exoplanet and
stellar activity signals.Comment: 28 pages, 18 Figures, accepted for publication in AJ. arXiv admin
note: text overlap with arXiv:1911.0335
ACCESS: A featureless optical transmission spectrum for WASP-19b from Magellan/IMACS
The short period (-day) transiting exoplanet WASP-19b is an exceptional
target for transmission spectroscopy studies, due to its relatively large
atmospheric scale-height ( km) and equilibrium temperature ( K). Here we report on six precise spectroscopic Magellan/IMACS
observations, five of which target the full optical window from m
and one targeting the m blue-optical range. Five of these datasets
are consistent with a transmission spectrum without any significant spectral
features, while one shows a significant slope as a function of wavelength,
which we interpret as arising from photospheric heterogeneities in the star.
Coupled with HST/WFC3 infrared observations, our optical/near-infrared
measurements point to the presence of high altitude clouds in WASP-19b's
atmosphere in agreement with previous studies. Using a semi-analytical
retrieval approach, considering both planetary and stellar spectral features,
we find a water abundance consistent with solar for WASP-19b and strong
evidence for sub-solar abundances for optical absorbers such as TiO and Na; no
strong optical slope is detected, which suggests that if hazes are present,
they are much weaker than previously suggested. In addition, two spot-crossing
events are observed in our datasets and analyzed, including one of the first
unambiguously detected bright spot-crossing events on an exoplanet host star.Comment: 20 pages (plus 5 for the Appendix), 17 figures, 5 tables. MNRAS, in
pres
ACCESS & LRG-BEASTS: a precise new optical transmission spectrum of the ultrahot Jupiter WASP-103b
We present a new ground-based optical transmission spectrum of the ultrahot
Jupiter WASP-103b (K). Our transmission spectrum is the result
of combining five new transits from the ACCESS survey and two new transits from
the LRG-BEASTS survey with a reanalysis of three archival Gemini/GMOS transits
and one VLT/FORS2 transit. Our combined 11-transit transmission spectrum covers
a wavelength range of 3900--9450A with a median uncertainty in the transit
depth of 148 parts-per-million, which is less than one atmospheric scale height
of the planet. In our retrieval analysis of WASP-103b's combined optical and
infrared transmission spectrum, we find strong evidence for unocculted bright
regions () and weak evidence for HO (), HCN
(), and TiO (), which could be responsible for
WASP-103b's observed temperature inversion. Our optical transmission spectrum
shows significant structure that is in excellent agreement with the extensively
studied ultrahot Jupiter WASP-121b, for which the presence of VO has been
inferred. For WASP-103b, we find that VO can only provide a reasonable fit to
the data if its abundance is implausibly high and we do not account for stellar
activity. Our results highlight the precision that can be achieved by
ground-based observations and the impacts that stellar activity from F-type
stars can have on the interpretation of exoplanet transmission spectra.Comment: 33 pages, 17 figures, 7 tables. Accepted for publication in A
ACCESS: Confirmation of no potassium in the atmosphere of WASP-31b
We present a new optical (400-950nm) transmission spectrum of the hot Jupiter
WASP-31b (M=0.48 MJ; R= 1.54 RJ; P=3.41 days), obtained by combining four
transits observations. These transits were observed with IMACS on the Magellan
Baade Telescope at Las Campanas Observatory as part of the ACCESS project. We
investigate the presence of clouds/hazes in the upper atmosphere of this planet
as well as the contribution of stellar activity on the observed features. In
addition, we search for absorption features of the alkali elements Na I and K
I, with particular focus on K I, for which there have been two previously
published disagreeing results. Observations with HST/STIS detected K I, whereas
ground-based low- and high-resolution observations did not. We use equilibrium
and non-equilibrium chemistry retrievals to explore the planetary and stellar
parameter space of the system with our optical data combined with existing
near-IR observations. Our best-fit model is that with a scattering slope
consistent with a Rayleigh slope (alpha=5.3+2.9-3.1), high-altitude clouds at a
log cloud top pressure of -3.6+2.7-2.1 bars, and possible muted H2O features.
We find that our observations support other ground-based claims of no K I.
Clouds are likely why signals like H2O are extremely muted and Na or K cannot
be detected. We then juxtapose our Magellan/IMACS transmission spectrum with
existing VLT/FORS2, HST/WFC3, HST/STIS, and Spitzer observations to further
constrain the optical-to-infrared atmospheric features of the planet. We find
that a steeper scattering slope (alpha = 8.3+/-1.5) is anchored by STIS
wavelengths blueward of 400 nm and only the original STIS observations show
significant potassium signal.Comment: Accepted 14 September 2020 by A