Prabal Saxena's research while affiliated with NASA Johnson Space Center and other places

Publications (28)

Preprint
Full-text available
Simulations of exoplanet albedo profiles are key to planning and interpreting future direct imaging observations. In this paper we demonstrate the use of the Planetary Spectrum Generator to produce simulations of reflected light exoplanet spectra. We use PSG to examine multiple issues relevant to all models of directly imaged exoplanet spectra and...
Article
Full-text available
The era of atmospheric characterization of terrestrial exoplanets is just around the corner. Modeling prior to observations is crucial in order to predict the observational challenges and to prepare for the data interpretation. This paper presents the report of the TRAPPIST Habitable Atmosphere Intercomparison workshop (2020 September 14-16). A rev...
Preprint
Full-text available
The era of atmospheric characterization of terrestrial exoplanets is just around the corner. Modeling prior to observations is crucial in order to predict the observational challenges and to prepare for the data interpretation. This paper presents the report of the TRAPPIST Habitable Atmosphere Intercomparison (THAI) workshop (14-16 September 2020)...
Article
Full-text available
Early in the Moon's history volcanic outgassing may have produced a periodic millibar level atmosphere (Needham and Kring 2017). We examined the relevant atmospheric escape processes and lifetime of such an atmosphere. Thermal escape rates were calculated as a function of atmospheric mass for a range of temperatures including the effect of the pres...
Preprint
Early in the Moon's history volcanic outgassing may have produced a periodic millibar level atmosphere (Needham and Kring, 2017). We examined the relevant atmospheric escape processes and lifetime of such an atmosphere. Thermal escape rates were calculated as a function of atmospheric mass for a range of temperatures including the effect of the pre...
Preprint
Full-text available
Using the Andrade-derived Sundberg-Cooper rheology, we apply several improvements to the secular tidal evolution of TRAPPIST-1e and the early history of Pluto-Charon under the simplifying assumption of homogeneous bodies. By including higher-order eccentricity terms (up to and including $e^{20}$), we find divergences from the traditionally used $e^...
Preprint
Full-text available
This White Paper presents a mission concept called MIRECLE - the Mid-InfraRed Exoplanet CLimate Explorer. With a moderately sized aperture of 2 meters, broad wavelength coverage (4 - 25 um), and next generation instruments, MIRECLE will be capable of efficiently characterizing a statistically significant sample of terrestrial planets, many of which...
Preprint
Full-text available
While the Earth and Moon are generally similar in composition, a notable difference between the two is the apparent depletion in moderately volatile elements in lunar samples. This is often attributed to the formation process of the Moon and demonstrates the importance of these elements as evolutionary tracers. Here we show that paleo space weather...
Article
Full-text available
Highly volcanic exoplanets, which can be variously characterized as 'lava worlds', 'magma ocean worlds', or 'super-Ios' are high priority targets for investigation. The term 'lava world' may refer to any planet with extensive surface lava lakes, while the term 'magma ocean world' refers to planets with global or hemispherical magma oceans at their...
Article
Full-text available
The geophysics of extrasolar planets is a scientific topic often regarded as standing largely beyond the reach of near-term observations. This reality in no way diminishes the central role of geophysical phenomena in shaping planetary outcomes, from formation, to thermal and chemical evolution, to numerous issues of surface and near-surface habitab...
Article
Full-text available
The Origins Space Telescope (OST) is one of four mission concepts currently being studied by NASA in preparation for the Astrophysics 2020 Decadal Survey. With active cooling (~4 K), OST will be sensitive in mid- to far-IR wavelengths, using imaging and spectroscopy to probe the furthest reaches of our galaxies, trace the path of water through star...
Article
A primary goal of direct imaging techniques is to spectrally characterize the atmospheres of planets around other stars at extremely high contrast levels. To achieve this goal, coronagraphic instruments have favored integral field spectrographs (IFS) as the science cameras to disperse the entire search area at once and obtain spectra at each locati...
Conference Paper
Full-text available
A primary goal of direct imaging techniques is to spectrally characterize the atmospheres of planets around other stars at extremely high contrast levels. To achieve this goal, coronagraphic instruments have favored integral field spectrographs (IFS) as the science cameras to disperse the entire search area at once and obtain spectra at each locati...
Conference Paper
Full-text available
Direct imaging of exoplanets has become a priority in the field of exoplanet discovery and characterization due to its ability to directly obtain evidence about a planet’s atmosphere and some bulk properties. Features such as atmospheric composition, structure and clouds are just some of the planetary properties obtainable from directly imaged spec...
Article
Full-text available
The Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies (PISCES) is a high contrast integral field spectrograph (IFS) whose design was driven by WFIRST coronagraph instrument requirements. We present commissioning and operational results using PISCES as a camera on the High Contrast Imaging Testbed at JPL. PISCES has demonstrated abi...
Article
We create the first quantitative model for the early lunar atmosphere, coupled with a magma ocean crystallization model. Immediately after formation, the moon's surface was subject to a radiative environment that included contributions from the early Sun, a post-impact Earth that radiated like a mid-type M dwarf star, and a cooling global magma oce...
Article
We examine the relevance of tidal heating for large Trans-Neptunian Objects, with a focus on its potential to melt and maintain layers of subsurface liquid water. Depending on their past orbital evolution, tidal heating may be an important part of the heat budget for a number of discovered and hypothetical TNO systems and may enable formation of, a...
Article
The population of known extrasolar planets includes giant and terrestrial planets that closely orbit their host star. Such planets experience significant tidal distortions that can force the planet into synchronous rotation. The combined effects of tidal deformation and centripetal acceleration induces significant asphericity in the shape of these...

Citations

... For direct imaging and secondary eclipse models, the code performs the radiative transfer across the visible hemisphere with adequate weights. They employ either a disk sampling methodology that divides the observable hemisphere into sections of similar incidence/emission angles, in the form of rings centered at the sub-observer point or a standard Gauss-Chebyshev disk integration method (Saxena et al. 2021). PSG has been used for post-processing transit spectroscopy from GCM output (e.g., May et al. 2021). ...
... Moreover, there always exists an uncertainty in GCM parameters, and this is acutely felt in theoretical studies of exoplanetary atmospheres due to the extreme paucity of observational data. This demands exploration of the model behavior over a range of parameters and configurations, alongside model intercomparisons (Polichtchouk et al. 2014;Yang et al. 2019;Fauchez et al. 2021a). ...
... The results show three main sources of water ice on the moon (Anand, 2010), including comets or small celestial bodies that hit the moon, the reduction reaction of hydrogen in the solar wind with ferrous oxide in the lunar soil, and the moon's interior. Water ice mainly exists in the form of bound water, ice-soil cement or pure ice layer in the surface and subsurface layer of the lunar soil in the PSR (Hurley et al., 2021). However, due to the multi-solution of remote sensing detection data, the characteristics of the occurrence, content, and depth distribution of water ice cannot be determined (Siqi et al., 2020;Li et al., 2018). ...
... Based on various friction mechanisms involved, several viscoelastic models have been proposed and constrained by means of laboratory experiments (e.g., Faul et al., 2004;Gribb and Cooper, 1998;Jackson, 2005;Jackson and Faul, 2010;Takei et al., 2014). Most of the experimental studies have focused devoted to the tidal dynamics of the icy systems such as Trans-Neptunian Objects, including both the Pluto-Charon binary and Kuiper belt objects (e.g., Arakawa et al., 2021;Bierson et al., 2020;Renaud et al., 2021;Rhoden et al., 2020;Saxena et al., 2018), and the Galilean moons, Iapetus and Enceladus (e.g., Beuthe, 2019;Kamata and Nimmo, 2017;Shoji et al., 2014;Spencer, 2013;Tyler, 2014Tyler, , 2009Tyler, , 2011. All these bodies are either presently tidally active or experienced significant tidal activity in their history. ...
... In contrast 1D simulations can often be run on a modern desktop computer or laptop to obtain useful approximations to the atmospheric structure and processes. Indeed, 1D DSMC models have been applied to a wide variety of planetary atmospheres including complex and transient processes: gravity waves in Mars' atmosphere (Leclercq et al., 2020); coupling to fluid models of Pluto's lower atmosphere (Tucker et al., 2012; cooling in multi-component atmospheres induced via escaping H 2 , Carberry Mogan et al., 2020; thermal and non-thermal processes in Europa's atmosphere ; the Moon's early volcanic atmosphere (Tucker et al., 2021); the collapse and reformation of Io's atmosphere during and after eclipse (Moore et al., 2009); volatile loss from Kuiper Belt Objects (Johnson et al., 2015); and cometary coma (Combi, 1996); to name several. Furthermore, 1D DSMC simulations can be used to evaluate standard analytic models: e.g., Jeans escape (Volkov et al., 2011b), as well as its transition to hydrodynamic escape (Volkov et al., 2011a); the exobase approximation (Tucker et al., 2016); and energy-limited escape . ...
... We found that these processes can remove only 0.5 PAN at most even assuming an EUV level 500 times higher than at present, which is significantly smaller than the excess atmospheric N estimated above. This level of EUV corresponds to so-called fast-rotating young Sun model, but previous studies focusing on volatile contents on Venus (Lammer, Leitzinger, et al., 2020;Lammer, Scherf, et al., 2020) and the Moon (Saxena et al., 2019) concluded that the EUV level of the young Sun is likely to be less active than a moderate rotator, whose EUV level was ≃100 times that of the current Sun. For this EUV level, neither 14 N nor 15 N can be removed by EUVdriven escape. ...
... This study was initiated at GSFC in spring 2018, followed by a JPL Team A study in May 2018, the first GSFC science meeting May 14-15, 2019, and a Team X study at JPL the following week. Starshades have been well studied for the Exo-S [2-4], WFIRST [5][6][7][8][9][10][11] and HabEx [8,[12][13][14][15][16] missions recently, and in the past for JWST, UMBRAS [17], BOSS [18], New Worlds Explorer [19, 20], and THEIA [21] ...
... Comparison of the estimates and images for iteration 0 in the cube mode experiment. The bottom row contains broadband data which is calculated via Eqn.(15). The left column contains the estimates where the top two rows are calculated by the estimator. ...
... These are likely to be relatively easy rocky exoplanets to characterize due to their preferential occurrence in short orbital periods, their bright flux in the infrared, and spectroscopy of volcanic gases. Henning et al. (2018) suggested that highly volcanic worlds could become second only to habitable worlds in terms of scientific and public interest. ...
... For total-power detection, usually a large number of pixels are required to increase the observation efficiency and mapping speed [8]. For example, the SCUBA2 instrument [9] has 10 4 pixels and the OST satellite [10] requires 10 5 pixels for its far- infrared imager. In the astronomical detection field, KIDs have attracted great interest and have been developed rapidly in the last decade. ...