41 research outputs found
The high-energy spectrum of the nearby planet-hosting inactive mid-M dwarf LHS 3844
To fully characterize the atmospheres, or lack thereof, of terrestrial
exoplanets we must include the high-energy environments provided by their host
stars. The nearby mid-M dwarf LHS 3844 hosts a terrestrial world which lacks a
substantial atmosphere. We present a time series UV spectrum of LHS 3844 from
1131-3215A captured by HST/COS. We detect one flare in the FUV, which has an
absolute energy of 8.96+/-0.79e28 erg and an equivalent duration of 355+/-31 s.
We extract the flare and quiescent UV spectra separately. For each spectrum we
estimate the Ly-alpha flux using correlations between UV line strengths. We use
Swift-XRT to place an upper limit on the soft X-ray flux and construct a
differential emission model (DEM) to estimate flux that is obscured by the
interstellar medium. We compare the DEM flux estimates in the XUV to other
methods that rely on scaling from the Ly-alpha, Si IV, and N V lines in the UV.
The XUV, FUV, and NUV flux of LHS 3844 relative to its bolometric luminosity is
log10(Lband/LBol) = -3.65, -4.16, and -4.56, respectively, for the quiescent
state. These values agree with trends in high-energy flux as a function of
stellar effective temperature found by the MUSCLES survey for a sample of
early-M dwarfs. Many of the most spectroscopically accessible terrestrial
exoplanets orbit inactive mid- to late-M dwarfs like LHS 3844. Measurements of
M dwarf high-energy spectra are preferable for exoplanet characterization, but
are not always possible. The spectrum of LHS 3844 is a useful proxy for the
current radiation environment for these worlds.Comment: Published in AJ; HLSPs now availabl
Chd8 Mutation Leads to Autistic-like Behaviors and Impaired Striatal Circuits
Autism spectrum disorder (ASD) is a heterogeneous disease, but genetically defined models can provide an entry point to studying the molecular underpinnings of this disorder. We generated germline mutant mice with loss-of-function mutations in Chd8, a de novo mutation strongly associated with ASD, and demonstrate that these mice display hallmark ASD behaviors, macrocephaly, and craniofacial abnormalities similar to patient phenotypes. Chd8[superscript +/–] mice display a broad, brain-region-specific dysregulation of major regulatory and cellular processes, most notably histone and chromatin modification, mRNA and protein processing, Wnt signaling, and cell-cycle regulation. We also find altered synaptic physiology in medium spiny neurons of the nucleus accumbens. Perturbation of Chd8 in adult mice recapitulates improved acquired motor learning behavior found in Chd8[superscript +/–] animals, suggesting a role for CHD8 in adult striatal circuits. These results support a mechanism linking chromatin modification to striatal dysfunction and the molecular pathology of ASD.National Science Foundation (U.S.) (1122374)National Science Foundation (U.S.) (2013169249)National Institute of Mental Health (U.S.) (F31-MH111157)Howard Hughes Medical Institute (NS046789)Simons Foundation Autism Research Initiative (306063)Simons Foundation Autism Research Initiative (6927482)National Institute of Mental Health (U.S.) (5DP1-MH100706)National Institute of Mental Health (U.S.) (1R01-MH110049)Nancy Lurie Marks Family Foundation (6928117)Howard Hughes Medical Institute (NS046789
CRISPR-Cas9 Knockin Mice for Genome Editing and Cancer Modeling
CRISPR-Cas9 is a versatile genome editing technology for studying the functions of genetic elements. To broadly enable the application of Cas9 in vivo, we established a Cre-dependent Cas9 knockin mouse. We demonstrated in vivo as well as ex vivo genome editing using adeno-associated virus (AAV)-, lentivirus-, or particle-mediated delivery of guide RNA in neurons, immune cells, and endothelial cells. Using these mice, we simultaneously modeled the dynamics of KRAS, p53, and LKB1, the top three significantly mutated genes in lung adenocarcinoma. Delivery of a single AAV vector in the lung generated loss-of-function mutations in p53 and Lkb1, as well as homology-directed repair-mediated Kras[superscript G12D] mutations, leading to macroscopic tumors of adenocarcinoma pathology. Together, these results suggest that Cas9 mice empower a wide range of biological and disease modeling applications.National Science Foundation (U.S.). Graduate Research Fellowship (Grant 1122374)Damon Runyon Cancer Research Foundation (Fellowship DRG-2117-12)Massachusetts Institute of Technology. Simons Center for the Social Brain (Postdoctoral Fellowship)European Molecular Biology Organization (Fellowship)Foundation for Polish Science (Fellowship)American Society for Engineering Education. National Defense Science and Engineering Graduate FellowshipNational Science Foundation (U.S.). Graduate Research FellowshipMassachusetts Institute of Technology (Presidential Graduate Fellowship)Human Frontier Science Program (Strasbourg, France) (Postdoctoral Fellowship)National Human Genome Research Institute (U.S.) (CEGS P50 HG006193)Howard Hughes Medical InstituteKlarman Cell ObservatoryNational Cancer Institute (U.S.) (Center of Cancer Nanotechnology Excellence Grant U54CA151884)National Institutes of Health (U.S.) (Controlled Release Grant EB000244)National Heart, Lung, and Blood Institute (Program of Excellence in Nanotechnology (PEN) Award Contract HHSN268201000045C)Massachusetts Institute of Technology (Poitras Gift 1631119)Stanley CenterSimons Foundation (6927482)Nancy Lurie Marks Family Foundation (6928117)United States. Public Health Service (National Institutes of Health (U.S.) R01-CA133404)David H. Koch Institute for Integrative Cancer Research at MIT (Marie D. and Pierre Casimir-Lambert Fund)MIT Skoltech InitiativeNational Cancer Institute (U.S.) (Koch Institute Support (Core) Grant P30-CA14051)National Institute of Mental Health (U.S.) (Director’s Pioneer Award DP1-MH100706)National Institute of Neurological Disorders and Stroke (U.S.) (Transformative R01 Grant R01-NS 07312401)National Science Foundation (U.S.) (Waterman Award)W. M. Keck FoundationKinship Foundation. Searle Scholars ProgramKlingenstein FoundationVallee FoundationMerkin Foundatio
The K2-3 system revisited: testing photoevaporation and core-powered mass loss with three small planets spanning the radius valley
Multi-planet systems orbiting M dwarfs provide valuable tests of theories of
small planet formation and evolution. K2-3 is an early M dwarf hosting three
small exoplanets (1.5-2.0 Earth radii) at distances of 0.07-0.20 AU. We measure
the high-energy spectrum of K2-3 with HST/COS and XMM-Newton, and use
empirically-driven estimates of Ly-alpha and extreme ultraviolet flux. We use
EXOFASTv2 to jointly fit radial velocity, transit, and SED data. This
constrains the K2-3 planet radii to 4% uncertainty and the masses of K2-3b and
c to 13% and 30%, respectively; K2-3d is not detected in RV measurements. K2-3b
and c are consistent with rocky cores surrounded by solar composition envelopes
(mass fractions of 0.36% and 0.07%), H2O envelopes (55% and 16%), or a mixture
of both. However, based on the high-energy output and estimated age of K2-3, it
is unlikely that K2-3b and c retain solar composition atmospheres. We pass the
planet parameters and high-energy stellar spectrum to atmospheric models.
Dialing the high-energy spectrum up and down by a factor of 10 produces
significant changes in trace molecule abundances, but not at a level detectable
with transmission spectroscopy. Though the K2-3 planets span the small planet
radius valley, the observed system architecture cannot be readily explained by
photoevaporation or core-powered mass loss. We instead propose 1) the K2-3
planets are all volatile-rich, with K2-3d having a lower density than typical
of super-Earths, and/or 2) the K2-3 planet architecture results from more
stochastic processes such as planet formation, planet migration, and impact
erosion.Comment: 15 pages, 7 figure, published in AJ, HLSPs at
https://archive.stsci.edu/hlsp/mstarpanspe
Transiting Exoplanet Studies and Community Targets for JWST's Early Release Science Program
The James Webb Space Telescope will revolutionize transiting exoplanet
atmospheric science due to its capability for continuous, long-duration
observations and its larger collecting area, spectral coverage, and spectral
resolution compared to existing space-based facilities. However, it is unclear
precisely how well JWST will perform and which of its myriad instruments and
observing modes will be best suited for transiting exoplanet studies. In this
article, we describe a prefatory JWST Early Release Science (ERS) program that
focuses on testing specific observing modes to quickly give the community the
data and experience it needs to plan more efficient and successful future
transiting exoplanet characterization programs. We propose a multi-pronged
approach wherein one aspect of the program focuses on observing transits of a
single target with all of the recommended observing modes to identify and
understand potential systematics, compare transmission spectra at overlapping
and neighboring wavelength regions, confirm throughputs, and determine overall
performances. In our search for transiting exoplanets that are well suited to
achieving these goals, we identify 12 objects (dubbed "community targets") that
meet our defined criteria. Currently, the most favorable target is WASP-62b
because of its large predicted signal size, relatively bright host star, and
location in JWST's continuous viewing zone. Since most of the community targets
do not have well-characterized atmospheres, we recommend initiating preparatory
observing programs to determine the presence of obscuring clouds/hazes within
their atmospheres. Measurable spectroscopic features are needed to establish
the optimal resolution and wavelength regions for exoplanet characterization.
Other initiatives from our proposed ERS program include testing the instrument
brightness limits and performing phase-curve observations.(Abridged)Comment: This is a white paper that originated from an open discussion at the
Enabling Transiting Exoplanet Science with JWST workshop held November 16 -
18, 2015 at STScI (http://www.stsci.edu/jwst/science/exoplanets). Accepted
for publication in PAS
A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b
Close-in giant exoplanets with temperatures greater than 2,000 K (''ultra-hot
Jupiters'') have been the subject of extensive efforts to determine their
atmospheric properties using thermal emission measurements from the Hubble and
Spitzer Space Telescopes. However, previous studies have yielded inconsistent
results because the small sizes of the spectral features and the limited
information content of the data resulted in high sensitivity to the varying
assumptions made in the treatment of instrument systematics and the atmospheric
retrieval analysis. Here we present a dayside thermal emission spectrum of the
ultra-hot Jupiter WASP-18b obtained with the NIRISS instrument on JWST. The
data span 0.85 to 2.85 m in wavelength at an average resolving power of
400 and exhibit minimal systematics. The spectrum shows three water emission
features (at 6 confidence) and evidence for optical opacity,
possibly due to H, TiO, and VO (combined significance of 3.8).
Models that fit the data require a thermal inversion, molecular dissociation as
predicted by chemical equilibrium, a solar heavy element abundance
(''metallicity'', M/H = 1.03 solar), and a
carbon-to-oxygen (C/O) ratio less than unity. The data also yield a dayside
brightness temperature map, which shows a peak in temperature near the
sub-stellar point that decreases steeply and symmetrically with longitude
toward the terminators.Comment: JWST ERS bright star observations. Uploaded to inform JWST Cycle 2
proposals. Manuscript under review. 50 pages, 14 figures, 2 table
Early Release Science of the exoplanet WASP-39b with JWST NIRCam
Measuring the metallicity and carbon-to-oxygen (C/O) ratio in exoplanet
atmospheres is a fundamental step towards constraining the dominant chemical
processes at work and, if in equilibrium, revealing planet formation histories.
Transmission spectroscopy provides the necessary means by constraining the
abundances of oxygen- and carbon-bearing species; however, this requires broad
wavelength coverage, moderate spectral resolution, and high precision that,
together, are not achievable with previous observatories. Now that JWST has
commenced science operations, we are able to observe exoplanets at previously
uncharted wavelengths and spectral resolutions. Here we report time-series
observations of the transiting exoplanet WASP-39b using JWST's Near InfraRed
Camera (NIRCam). The long-wavelength spectroscopic and short-wavelength
photometric light curves span 2.0 - 4.0 m, exhibit minimal systematics,
and reveal well-defined molecular absorption features in the planet's spectrum.
Specifically, we detect gaseous HO in the atmosphere and place an upper
limit on the abundance of CH. The otherwise prominent CO feature at 2.8
m is largely masked by HO. The best-fit chemical equilibrium models
favour an atmospheric metallicity of 1-100 solar (i.e., an enrichment
of elements heavier than helium relative to the Sun) and a sub-stellar
carbon-to-oxygen (C/O) ratio. The inferred high metallicity and low C/O ratio
may indicate significant accretion of solid materials during planet formation
or disequilibrium processes in the upper atmosphere.Comment: 35 pages, 13 figures, 3 tables, Nature, accepte
Photochemically-produced SO in the atmosphere of WASP-39b
Photochemistry is a fundamental process of planetary atmospheres that
regulates the atmospheric composition and stability. However, no unambiguous
photochemical products have been detected in exoplanet atmospheres to date.
Recent observations from the JWST Transiting Exoplanet Early Release Science
Program found a spectral absorption feature at 4.05 m arising from SO
in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass
(0.28 M) gas giant exoplanet orbiting a Sun-like star with an equilibrium
temperature of 1100 K. The most plausible way of generating SO in
such an atmosphere is through photochemical processes. Here we show that the
SO distribution computed by a suite of photochemical models robustly
explains the 4.05 m spectral feature identified by JWST transmission
observations with NIRSpec PRISM (2.7) and G395H (4.5). SO
is produced by successive oxidation of sulphur radicals freed when hydrogen
sulphide (HS) is destroyed. The sensitivity of the SO feature to the
enrichment of the atmosphere by heavy elements (metallicity) suggests that it
can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an
inferred metallicity of 10 solar. We further point out that
SO also shows observable features at ultraviolet and thermal infrared
wavelengths not available from the existing observations.Comment: 39 pages, 14 figures, accepted to be published in Natur