اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدMapping Vinyl Cyanide and Other Nitriles in Titans Atmosphere Using ALMA
345
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Vinyl cyanide (C$_2$H$_3$CN) is theorized to form in Titans atmosphere via high-altitude photochemistry and is of interest regarding the astrobiology of cold planetary surfaces due to its predicted ability to form cell membrane-like structures (azotosomes) in liquid methane. In this work, we follow up on the initial spectroscopic detection of C$_2$H$_3$CN on Titan by Palmer et al. (2017) with the detection of three new C$_2$H$_3$CN rotational emission lines at submillimeter frequencies. These new, high-resolution detections have allowed for the first spatial distribution mapping of C$_2$H$_3$CN on Titan. We present simultaneous observations of C$_2$H$_5$CN, HC$_3$N, and CH$_3$CN emission, and obtain the first (tentative) detection of C$_3$H$_8$ (propane) at radio wavelengths. We present disk-averaged vertical abundance profiles, two-dimensional spatial maps, and latitudinal flux profiles for the observed nitriles. Similarly to HC$_3$N and C$_2$H$_5$CN, which are theorized to be short-lived in Titans atmosphere, C$_2$H$_3$CN is most abundant over the southern (winter) pole, whereas the longer-lived CH$_3$CN is more concentrated in the north. This abundance pattern is consistent with the combined effects of high-altitude photochemical production, poleward advection, and the subsequent reversal of Titans atmospheric circulation system following the recent transition from northern to southern winter. We confirm that C$_2$H$_3$CN and C$_2$H$_5$CN are most abundant at altitudes above 200 km. Using a 300 km step model, the average abundance of C$_2$H$_3$CN is found to be $3.03pm0.29$ ppb, with a C$_2$H$_5$CN/C$_2$H$_3$CN abundance ratio of $2.43pm0.26$. Our HC$_3$N and CH$_3$CN spectra can be accurately modeled using abundance gradients above the tropopause, with fractional scale-heights of $2.05pm0.16$ and $1.63pm0.02$, respectively.
قيم البحث
اقرأ أيضاً
We report the first spectroscopic detection of ethyl cyanide (C$_2$H$_5$CN) in Titans atmosphere, obtained using spectrally and spatially resolved observations of multiple emission lines with the Atacama Large Millimeter/submillimeter array (ALMA). T
he presence of C$_2$H$_5$CN in Titans ionosphere was previously inferred from Cassini ion mass spectrometry measurements of C$_2$H$_5$CNH$^+$. Here we report the detection of 27 rotational lines from C$_2$H$_5$CN (in 19 separate emission features detected at $>3sigma$ confidence), in the frequency range 222-241 GHz. Simultaneous detections of multiple emission lines from HC$_3$N, CH$_3$CN and CH$_3$CCH were also obtained. In contrast to HC$_3$N, CH$_3$CN and CH$_3$CCH, which peak in Titans northern (spring) hemisphere, the emission from C$_2$H$_5$CN is found to be concentrated in the southern (autumn) hemisphere, suggesting a distinctly different chemistry for this species, consistent with a relatively short chemical lifetime for C$_2$H$_5$CN. Radiative transfer models show that most of the C$_2$H$_5$CN is concentrated at altitudes 300-600 km, suggesting production predominantly in the mesosphere and above. Vertical column densities are found to be in the range (2-5)$times10^{14}$ cm$^{-2}$.
The hydrogen cyanide (HCN) molecule in the planetary atmosphere is key to the formation of building blocks of life. We present the spectroscopic detection of the rotational molecular line of nitrile species hydrogen cyanide (HCN) in the atmosphere of
Saturn using the archival data of the Atacama Large Millimeter/Submillimeter Array (ALMA) in band 7 observation. The strong rotational emission line of HCN is detected at frequency $ u$ = 354.505 GHz (>4$sigma$ statistical significance). We also detect the rotational emission line of carbon monoxide (CO) at frequency $ u$ = 345.795 GHz. The statistical column density of hydrogen cyanide and carbon monoxide emission line is N(HCN)$sim$2.42$times$10$^{16}$ cm$^{-2}$ and N(CO)$sim$5.82$times$10$^{17}$ cm$^{-2}$. The abundance of HCN and CO in the atmosphere of Saturn relative to the H$_{2}$ is estimated to be f(HCN)$sim$1.02$times$10$^{-9}$ and f(CO)$sim$2.42$times$10$^{-8}$. We discussed possible chemical pathways to the formation of the detected nitrile gas HCN in the atmosphere of Saturn.
We present spectrally and spatially-resolved maps of HNC and HC$_3$N emission from Titans atmosphere, obtained using the Atacama Large Millimeter/submillimeter Array (ALMA) on 2013 November 17. These maps show anisotropic spatial distributions for bo
th molecules, with resolved emission peaks in Titans northern and southern hemispheres. The HC$_3$N maps indicate enhanced concentrations of this molecule over the poles, consistent with previous studies of Titans photochemistry and atmospheric circulation. Differences between the spectrally-integrated flux distributions of HNC and HC$_3$N show that these species are not co-spatial. The observed spectral line shapes are consistent with HNC being concentrated predominantly in the mesosphere and above (at altitudes $zgtrsim 400$ km), whereas HC$_3$N is abundant at a broader range of altitudes ($zapprox70$-600 km). From spatial variations in the HC$_3$N line profile, the locations of the HC$_3$N emission peaks are shown to be variable as a function of altitude. The peaks in the integrated emission from HNC and the line core (upper-atmosphere) component of HC$_3$N (at $zgtrsim300$ km) are found to be asymmetric with respect to Titans polar axis, indicating that the mesosphere may be more longitudinally-variable than previously thought. The spatially-integrated HNC and HC$_3$N spectra are modeled using the NEMESIS planetary atmosphere code and the resulting best-fitting disk-averaged vertical mixing ratio (VMR) profiles are found to be in reasonable agreement with previous measurements for these species. Vertical column densities of the best-fitting gradient models for HNC and HC$_3$N are $1.9times10^{13}$ cm$^{-2}$ and $2.3times10^{14}$ cm$^{-2}$, respectively.
The Cassini-Huygens mission measured the chemical abundances of the major components of Titans atmosphere, and analyses of the data revealed several as-yet unexplained anomalies in the methane and hydrogen profiles. We model the deceleration and abla
tion of meteors in Titans atmosphere to examine whether meteor energy deposition could explain, in part, two of these anomalies. Our simulations vary meteor entry mass, trajectory angle, and velocity, and follow changes in all three as our meteors descend into a realistic Titan atmosphere. For the smallest particles, which deliver the most mass and therefore energy to Titan, we find that the altitudes where energy deposition peaks correspond to those of the observed chemical anomalies. In the region directly above the anomalies, energy deposition by meteors is greater than energy deposition from ultraviolet photons, which are typically responsible for methane dissociation. Finally, we calculate the total amount of energy available for chemical reactions in question. Total meteor energy deposited is swamped by daytime ultraviolet light, but of course is the dominant source of energy for atmospheric chemistry at the relevant altitudes during the night.
Titan harbors a dense, organic-rich atmosphere primarily composed of N$_2$ and CH$_4$, with lesser amounts of hydrocarbons and nitrogen-bearing species. As a result of high sensitivity observations by the Atacama Large Millimeter/submillimeter Array
(ALMA) in Band 6 ($sim$230-272 GHz), we obtained the first spectroscopic detection of CH$_3$C$_3$N (methylcyanoacetylene or cyanopropyne) in Titans atmosphere through the observation of seven transitions in the $J = 64rightarrow63$ and $J = 62rightarrow61$ rotational bands. The presence of CH$_3$C$_3$N on Titan was suggested by the Cassini Ion and Neutral Mass Spectrometer detection of its protonated form: C$_4$H$_3$NH$^+$, but the atmospheric abundance of the associated (deprotonated) neutral product is not well constrained due to the lack of appropriate laboratory reaction data. Here, we derive the column density of CH$_3$C$_3$N to be (3.8-5.7)$times10^{12}$ cm$^{-2}$ based on radiative transfer models sensitive to altitudes above 400 km Titans middle atmosphere. When compared with laboratory and photochemical model results, the detection of methylcyanoacetylene provides important constraints for the determination of the associated production pathways (such as those involving CN, CCN, and hydrocarbons), and reaction rate coefficients. These results also further demonstrate the importance of ALMA and (sub)millimeter spectroscopy for future investigations of Titans organic inventory and atmospheric chemistry, as CH$_3$C$_3$N marks the heaviest polar molecule detected spectroscopically in Titans atmosphere to date.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
