GJ 229B was the first T dwarf to be discovered in 1995, and its spectrum has been more thoroughly observed than that of most other brown dwarfs. Yet a full spectroscopic analysis of its atmosphere ...has not been done with modern techniques. This spectrum has several peculiar features, and recent dynamical estimates of GJ 229B’s mass and orbit have disagreed widely, both of which warrant closer investigation. With a separation of tens of astronomical units from its host star, GJ 229B falls near the border of the planet and stellar population formation regimes, so its atmosphere could provide clues to formation processes for intermediate objects of this type. In an effort to resolve these questions, we performed retrievals on published spectra of GJ 229B over a wide range of wavelengths (0.5–5.1 μm) using the open-source APOLLO code. Based on these retrievals, we present a more precise mass estimate of 41.6 ± 3.3MJ and an effective temperature estimate of 869 +5 −7 K, which are more consistent with evolutionary models for brown dwarfs and suggest an older age for the system of >1.0 Gyr. We also present retrieved molecular abundances for the atmosphere, including replicating the previously observed high CO abundance, and discuss their implications for the formation and evolution of this object. This retrieval effort will give us insight into how to study other brown dwarfs and directly imaged planets, including those observed with JWST and other next-generation telescopes.
Strong Release of Methane on Mars in Northern Summer 2003 Mumma, Michael J; Villanueva, Geronimo L; Novak, Robert E ...
Science (American Association for the Advancement of Science),
02/2009, Letnik:
323, Številka:
5917
Journal Article
Recenzirano
Living systems produce more than 90% of Earth's atmospheric methane; the balance is of geochemical origin. On Mars, methane could be a signature of either origin. Using high-dispersion infrared ...spectrometers at three ground-based telescopes, we measured methane and water vapor simultaneously on Mars over several longitude intervals in northern early and late summer in 2003 and near the vernal equinox in 2006. When present, methane occurred in extended plumes, and the maxima of latitudinal profiles imply that the methane was released from discrete regions. In northern midsummer, the principal plume contained ~19,000 metric tons of methane, and the estimated source strength (greater-than-or-equal0.6 kilogram per second) was comparable to that of the massive hydrocarbon seep at Coal Oil Point in Santa Barbara, California.
Investigating Possible Binarity for GJ 229B Howe, Alex R.; Mandell, Avi M.; McElwain, Michael W.
Astrophysical journal. Letters,
07/2023, Letnik:
951, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
GJ 229B, the first type-T brown dwarf to be discovered, has presented a tension between comparisons with evolutionary models and the larger-than-expected mass and radius values derived from ...spectroscopic and astrometric observations. We examine the hypothesis that GJ 229B is actually a binary substellar object by using two grid-based fits using evolutionary models to explore the range of mass ratios of the possible binary components. We find that the best-fit component values are most consistent with a roughly 2:1 binary mass ratio and an age range of 2–6 Gyr. The observed temperatures, masses, and apparent radii match expected values from evolutionary models for a binary much better than a single-object model, but more detailed observations and modeling are needed to definitively confirm the binary hypothesis.
Abstract
Recent investigations have demonstrated the potential for utilizing a new observational and data-analysis technique for studying the atmospheres of nontransiting exoplanets with combined ...light that relies on acquiring simultaneous, broad-wavelength spectra and resolving planetary infrared emission from the stellar spectrum through simultaneous fitting of the stellar and planetary spectral signatures. This new data-analysis technique, called planetary infrared excess (PIE), holds the potential to open up the opportunity for measuring mid-infrared (MIR) phase curves of nontransiting rocky planets around the nearest stars with a relatively modest telescope aperture. We present simulations of the performance and science yield for a mission and instrument concept that we call the MIR Exoplanet CLimate Explorer, a concept for a moderately sized cryogenic telescope with broad wavelength coverage (1–18
μ
m) and a low-resolution (
R
∼ 50) spectrograph designed for the simultaneous wavelength coverage and extreme flux measurement precision necessary to detect the emission from cool rocky planets with PIE. We present exploratory simulations of the potential science yield for PIE measurements of the nearby planet Proxima Centauri b, showing the potential to measure the composition and structure of an Earth-like atmosphere with a relatively modest observing time. We also present overall science yields for several mission architecture and performance metrics, and discuss the technical performance requirements and potential telescope and instrument technologies that could meet these requirements.
We report 78 secondary eclipse depths for a sample of 36 transiting hot Jupiters observed at 3.6 and 4.5 μm using the Spitzer Space Telescope. Our eclipse results for 27 of these planets are new, and ...include highly irradiated worlds such as KELT-7b, WASP-87b, WASP-76b, and WASP-64b, and important targets for James Webb Space Telescope such as WASP-62b. We find that WASP-62b has a slightly eccentric orbit (e cos w = 0.00614 ± 0.00064), and we confirm the eccentricity of HAT-P-13b and WASP-14b. The remainder are individually consistent with circular orbits, but we find statistical evidence for eccentricity increasing with orbital period in our range from 1 to 5 days. Our day-side brightness temperatures for the planets yield information on albedo and heat redistribution, following Cowan & Agol (2011). Planets having maximum day-side temperatures exceeding ∼2200 K are consistent with having zero albedo and a distribution of stellar irradiance uniformly over the day-side hemisphere. Our most intriguing result is that we detect a systematic difference between the emergent spectra of these hot Jupiters as compared to blackbodies. The ratio of observed brightness temperatures, Tb(4.5)/Tb(3.6), increases with equilibrium temperature by 100 ± 24 parts-per-million per Kelvin, over the entire temperature range in our sample (800–2500 K). No existing model predicts this trend over such a large range of temperature. We suggest that this may be due to a structural difference in the atmospheric temperature profiles of real planetary atmospheres as compared to models.
Future NASA concept missions that are currently under study, like the Habitable Exoplanet Imaging Mission (HabEx) and the Large Ultra-violet Optical Infra Red Surveyor, could discover a large ...diversity of exoplanets. We propose here a classification scheme that distinguishes exoplanets into different categories based on their size and incident stellar flux, for the purpose of providing the expected number of exoplanets observed (yield) with direct imaging missions. The boundaries of this classification can be computed using the known chemical behavior of gases and condensates at different pressures and temperatures in a planetary atmosphere. In this study, we initially focus on condensation curves for sphalerite ZnS, H 2 O , CO 2 , and CH 4 . The order in which these species condense in a planetary atmosphere define the boundaries between different classes of planets. Broadly, the planets are divided into rocky planets (0.5-1.0 R⊕), super-Earths (1.0-1.75 R⊕), sub-Neptunes (1.75-3.5 R⊕), sub-Jovians (3.5-6.0 R⊕), and Jovians (6-14.3 R⊕) based on their planet sizes, and "hot," "warm," and "cold" based on the incident stellar flux. We then calculate planet occurrence rates within these boundaries for different kinds of exoplanets, planet, using the community coordinated results of NASA's Exoplanet Program Analysis Group's Science Analysis Group-13 (SAG-13). These occurrence rate estimates are in turn used to estimate the expected exoplanet yields for direct imaging missions of different telescope diameters.
Detecting H2O in exoplanet atmospheres is the first step on the path to determining planet habitability. Coronagraphic design currently limits the observing strategy used to detect H2O, requiring the ...choice of specific bandpasses to optimize abundance constraints. In order to examine the optimal observing strategy for initial characterization of habitable planets using coronagraph-based direct imaging, we quantify the detectability of H2O as a function of signal-to-noise ratio (S/N) and molecular abundance across 25 bandpasses in the visible wavelength range (0.5–1 μm). We use a preconstructed grid consisting of 1.4 million geometric albedo spectra across a range of abundance and pressure, and interpolate to produce forward models for an efficient nested sampling routine, PSGnest. We first test the detectability of H2O in atmospheres that mimic a modern-Earth twin, and then expand to examine a wider range of H2O abundances; for each abundance value, we constrain the optimal 20% bandpasses based on the effective S/N of the data. We present our findings of H2O detectability as functions of S/N, wavelength, and abundance, and discuss how to use these results for optimizing future coronographic instrument design. We find that there are specific points in wavelength where H2O can be detected down to 0.74 μm with moderate-S/N data for abundances at the upper end of Earth’s presumed historical values, while at 0.9 μm, detectability is possible with low-S/N data at modern Earth abundances of H2O.
Abstract
Techniques to retrieve the atmospheric properties of exoplanets via direct observation of their reflected light have often been limited in scope owing to computational constraints imposed by ...the forward-model calculations. We have developed a new set of techniques that significantly decrease the time required to perform a retrieval while maintaining accurate results. We constructed a grid of 1.4 million precomputed geometric albedo spectra valued at discrete sets of parameter points. Spectra from this grid are used to produce models for a fast and efficient nested sampling routine called PSGnest. Beyond the upfront time to construct a spectral grid, the amount of time to complete a full retrieval using PSGnest is on the order of seconds to minutes using a personal computer. An extensive evaluation of the error induced from interpolating intermediate spectra from the grid indicates that this bias is insignificant compared to other retrieval error sources, with an average coefficient of determination between interpolated and true spectra of 0.998. We apply these new retrieval techniques to help constrain the optimal bandpass centers for retrieving various atmospheric and bulk parameters from a LuvEx-type mission observing several planetary archetypes. We show that spectral observations made using a 20% bandpass centered at 0.73
μ
m can be used alongside our new techniques to make detections of H
2
O and O
2
without the need to increase observing time beyond what is necessary for a signal-to-noise ratio of 10. The methods introduced here will enable robust studies of the capabilities of future observatories to characterize exoplanets.
We present self-consistent three-dimensional climate simulations of possible habitable states for the newly discovered habitable-zone Earth-sized planet TOI-700 d. We explore a variety of atmospheric ...compositions, pressures, and rotation states for both ocean-covered and completely desiccated planets in order to assess the planet's potential for habitability. For all 20 of our simulated cases, we use our climate model outputs to synthesize transmission spectra, combined-light spectra, and integrated broadband phase curves. These climatologically informed observables will help the community assess the technological capabilities necessary for future characterization of this planet-as well as similar transiting planets discovered in the future-and will provide a guide for distinguishing possible climate states if one day we do obtain sensitive spectral observations of a habitable planet around an M star. We find that TOI-700 d is a strong candidate for a habitable world and can potentially maintain temperate surface conditions under a wide variety of atmospheric compositions. Unfortunately, the spectral feature depths from the resulting transmission spectra and the peak flux and variations from our synthesized phase curves for TOI-700 d do not exceed 10 ppm. This will likely prohibit the James Webb Space Telescope from characterizing its atmosphere; however, this motivates the community to invest in future instrumentation that perhaps can one day reveal the true nature of TOI-700 d and to continue to search for similar planets around less distant stars.
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