arXiv subjects

Sanjay S. Limaye

Publications and source records attributed to Sanjay S. Limaye.

6 recordsLinked to original sources

arXiv2026

Altered Cosmic Organics as Venus' Ultraviolet Absorbers

Venus' ultraviolet (UV) absorbers significantly contribute to the atmosphere's energy budget. However, the composition of these absorbers remains a mystery. Here, we show that mixtures of polycyclic aromatic hydrocarbons (PAHs) and iron-bearing compounds, analogs of altered cometary dust, excellently match Venus' spectra from the cloud tops to the sub-cloud atmosphere across the UV and visible wavelengths. The molecular compositions for the cloud tops (5-10 ring PAHs and ferric chloride), decomposed cloud aerosols (3-4 ring PAHs and acid ferric sulfate), and sub-cloud atmosphere (5-10 PAHs and ferric hydroxy sulfates) are consistent with the stepwise alteration of cosmic dust. These steps include sourcing of the PAHs and iron from thermally unablated and ablated dust particles, respectively, reactions with sulfuric acid in the clouds, and thermal decomposition below the clouds. Geologically short timelines of cosmic influx (minimum of 600 and 3 kyr) would respectively yield the cloud top carbon and iron concentrations. Hence, we propose a unified origin for Venus' absorbers, which may arise from cometary dust via altitude-dependent alteration pathways from the mesosphere to the surface, with PAHs serving as the primary UV absorbers and iron compounds as the dominant absorbers by mass.

astro-ph.EP↗

arXiv2022

The CO$_2$ Profile and Analytical Model for the Pioneer Venus Large Probe Neutral Mass Spectrometer

We present a significantly updated CO$_2$ altitude profile for Venus (64.2-0.9 km) and provide support for a potential deep lower atmospheric haze of particles (17 km and lower). We extracted this information by developing a new analytical model for mass spectra obtained by the Pioneer Venus Large Probe (PVLP) Neutral Mass Spectrometer (LNMS). Our model accounts for changes in LNMS configuration and output during descent and enables the disentanglement of isobaric species via a data fitting routine that adjusts for mass-dependent changes in peak shape. The model yields CO$_2$ in units of density (kg m-3), isotope ratios for $^{13}$C/$^{12}$C and $^{18}$O/$^{16}$O, and 14 measures of CO$_2$ density across 55.4-0.9 km, which represents the most complete altitude profile for CO$_2$ at 60 km towards the surface to date. The CO$_2$ density profile is also consistent with the pressure, temperature, and volumetric gas measurements from the PVLP and VeNeRa spacecraft. Nominal and low-noise operations for the LNMS mass analyzer are supported by the behaviors (e.g., ionization yields, fragmentation yields, and peak shapes) of several internal standards (e.g., CH$^{3+}$, CH$^{4+}$, $^{40}$Ar$^+$, $^{136}$Xe$^{2+}$, and $^{136}$Xe$^+$), which were tracked across the descent. Lastly, our review of the CO$_2$ profile and LNMS spectra reveals hitherto unreported partial and rapidly clearing clogs of the inlet in the lower atmosphere, along with several ensuing data spikes at multiple masses. Together, these observations suggest that atmospheric intake was impacted by particles at 17 km (and lower) and that rapid particle degradation at the inlet yielded a temporary influx of mass signals into the LNMS.

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arXiv2021

Venus' Mass Spectra Show Signs of Disequilibria in the Middle Clouds

We present a re-examination of mass spectral data obtained from the Pioneer Venus Large Probe Neutral Mass Spectrometer. Our interpretations of differing trace chemical species are suggestive of redox disequilibria in Venus' middle clouds. Assignments to the data (at 51.3 km) include phosphine, hydrogen sulfide, nitrous acid, nitric acid, carbon monoxide, hydrochloric acid, hydrogen cyanide, ethane, and potentially ammonia, chlorous acid, and several tentative PxOy species. All parent ions were predicated upon assignment of corresponding fragmentation products, isotopologues, and atomic species. The data reveal parent ions at varying oxidation states, implying the presence of reducing power in the clouds, and illuminating the potential for chemistries yet to be discovered. When considering the hypothetical habitability of Venus' clouds, the assignments reveal a potential signature of anaerobic phosphorus metabolism (phosphine), an electron donor for anoxygenic photosynthesis (nitrite), and major constituents of the nitrogen cycle (nitrate, nitrite, ammonia, and N2).

astro-ph.EP↗

arXiv2018

Nightside Winds at the Lower Clouds of Venus with Akatsuki/IR2: Longitudinal, local time and decadal variations from comparison with previous measurements

We present measurements of the wind speeds at the nightside lower clouds of Venus from observations by JAXA's mission Akatsuki during 2016, complemented with new wind measurements from ground-based observations acquired with TNG/NICS in 2012 and IRTF/SpeX in 2015 and 2017. Zonal and meridional components of the winds were measured from cloud tracking on a total of 466 Akatsuki images of Venus acquired by the camera IR2 using the 2.26-$\mathrm{μm}$ filter, with spatial resolutions ranging 10--80 km per pixel and covering from 2016 March 22 to October 31. More than 149,000 wind vectors were obtained with an automatic technique of template matching, and 2,947 wind vectors were inferred with the manual procedure. The meridional profiles for both components of the winds are found to be consistent with results from the Venus Express mission during 2006--2008, although stronger wind variability is found for the zonal component at equatorial latitudes where Akatsuki observations have better viewing geometry than Venus Express. The zonal winds at low latitudes also suggest a zonal variability that could be associated with solar tides or vertically propagating orographic waves. Finally, the combination of our wind measurements from TNG/NICS, IRTF/SpeX and Akatsuki images with previously published and based in data from 1978 to 2017 suggests variations of up to 30 m s$^{-1}$ in the winds at the lower clouds of the Venus nightside.

astro-ph.EP↗

arXiv2018

Adiabatic Lapse Rate and Static Stability in the Venus Atmosphere calculated from Real Gas Mixture Models

It is known that the ideal gas equation of state is not valid in the lower atmosphere of Venus where surface pressures reach 9 MPa and surface temperatures approach 750K. Moreover, the presence of a small amount of nitrogen slightly complicates the calculation of thermodynamic properties of the real gas mixture present in the atmosphere. Previous calculations of the adiabatic lapse rate in the Venus atmosphere have used approximations to estimate the adiabatic lapse rate. Here, we calculate the adiabatic lapse rate more accurately by using multi-parameter mixture models formulated in reduced Helmholtz free energy to account for the real gas mixture effects. Our results show small differences from the Seiff et al. (1980) values for the adiabatic lapse rate which may be significant where the Venus atmosphere is close to being neutral. For accurate knowledge of the static stability for atmosphere circulation, a local value of the adiabatic lapse rate is necessary.

astro-ph.EP↗

arXiv2016

Rational Approximation Formula for Chandrasekhar's H-function for Isotropic Scattering

We first establish a simple procedure to obtain with 11-figure accuracy the values of Chandrasekhar's H-function for isotropic scattering using a closed-form integral representation and the Gauss-Legendre quadrature. Based on the numerical values of the function produced by this method for various values of the single scattering albedo and the cosine of the azimuth angle of the direction of radiation emergent from or incident upon a semi-infinite scattering-absorbing medium, we propose a rational approximation formula, which allows us to reproduce the correct values of the H-function within a relative error of 2.1/100000 without recourse to any iterative procedure or root-finding process.

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