114 research outputs found
A Search for Magnesium in Europa's Atmosphere
Europa's tenuous atmosphere results from sputtering of the surface. The trace element composition of its atmosphere is therefore related to the composition of Europa's surface. Magnesium salts are often invoked to explain Galileo Near Infrared Mapping Spectrometer spectra of Europa's surface, thus magnesium may be present in Europa's atmosphere. We have searched for magnesium emission in the Hubble Space Telescope Faint Object Spectrograph archival spectra of Europa's atmosphere. Magnesium was not detected and we calculate an upper limit on the magnesium column abundance. This upper limit indicates that either Europa's surface is depleted in magnesium relative to sodium and potassium, or magnesium is not sputtered as efficiently resulting in a relative depletion in its atmosphere
Limits on Clouds and Hazes for the TRAPPIST-1 Planets
The TRAPPIST-1 planetary system is an excellent candidate for study of the
evolution and habitability of M-dwarf planets. Transmission spectroscopy
observations performed with the Hubble Space Telescope (HST) suggest the
innermost five planets do not possess clear hydrogen atmospheres. Here we
reassess these conclusions with recently updated mass constraints and expand
the analysis to include limits on metallicity, cloud top pressure, and the
strength of haze scattering. We connect recent laboratory results of particle
size and production rate for exoplanet hazes to a one-dimensional atmospheric
model for TRAPPIST-1 transmission spectra. Doing so, we obtain a
physically-based estimate of haze scattering cross sections. We find haze
scattering cross sections on the order of 1e-26 to 1e-19 cm squared are needed
in hydrogen-rich atmospheres for TRAPPIST-1 d, e, and f to match the HST data.
For TRAPPIST-1 g, we cannot rule out a clear hydrogen-rich atmosphere. We also
modeled the effects an opaque cloud deck and substantial heavy element content
have on the transmission spectra. We determine that hydrogen-rich atmospheres
with high altitude clouds, at pressures of 12mbar and lower, are consistent
with the HST observations for TRAPPIST-1 d and e. For TRAPPIST-1 f and g, we
cannot rule out clear hydrogen-rich cases to high confidence. We demonstrate
that metallicities of at least 60xsolar with tropospheric (0.1 bar) clouds
agree with observations. Additionally, we provide estimates of the precision
necessary for future observations to disentangle degeneracies in cloud top
pressure and metallicity. Our results suggest secondary, volatile-rich
atmospheres for the outer TRAPPIST-1 planets d, e, and f.Comment: 15 pages, 3 figures, 2 tables, accepted in the Astronomical Journa
Exploring the Atmosphere of Neoproterozoic Earth: The Effect of O on Haze Formation and Composition
Previous studies of haze formation in the atmosphere of the Early Earth have
focused on N/CO/CH atmospheres. Here, we experimentally
investigate the effect of O on the formation and composition of aerosols
to improve our understanding of haze formation on the Neoproterozoic Earth. We
obtained in situ size, particle density, and composition measurements of
aerosol particles produced from N/CO/CH/O gas mixtures
subjected to FUV radiation (115-400 nm) for a range of initial
CO/CH/O mixing ratios (O ranging from 2 ppm to 0.2\%).
At the lowest O concentration (2 ppm), the addition increased particle
production for all but one gas mixture. At higher oxygen concentrations (20 ppm
and greater) particles are still produced, but the addition of O
decreases the production rate. Both the particle size and number density
decrease with increasing O, indicating that O affects particle
nucleation and growth. The particle density increases with increasing O.
The addition of CO and O not only increases the amount of oxygen in
the aerosol, but it also increases the degree of nitrogen incorporation. In
particular, the addition of O results in the formation of nitrate bearing
molecules. The fact that the presence of oxygen bearing molecules increases the
efficiency of nitrogen fixation has implications for the role of haze as a
source of molecules required for the origin and evolution of life. The
composition changes also likely affect the absorption and scattering behavior
of these particles but optical properties measurements are required to fully
understand the implications for the effect on the planetary radiative energy
balance and climate.Comment: 15 pages, 3 tables, 8 figures, accepted in Astrophysical Journa
Organic Hazes as a Source of Life’s Building Blocks to Warm Little Ponds on the Hadean Earth
Over 4 billion years ago, Earth is thought to have been a hazy world akin to Saturn’s moon Titan. The organic hazes in the atmosphere at this time could have contained a vast inventory of life’s building blocks and thus may have seeded warm little ponds for life. In this work, we produce organic hazes in the lab in atmospheres with high (5%) and low (0.5%) CH4 abundances and analyze the solid particles for nucleobases, amino acids, and a few other organics using GC/MS/MS to obtain their concentrations. We also analyze heated (200°C) samples from the high methane organic haze experiment to simulate these particles sitting on an uninhabitable surface. Finally, we use our experimental results and estimates of atmospheric haze production as inputs for a comprehensive numerical pond model to calculate the concentrations of nucleobases from organic hazes in these environments. We find that organic hazes typically provide up to 0.2-6.5 μM concentrations of nucleobases to warm little ponds for potentially habitable Hadean conditions. However, without seepage, uracil and thymine can reach ∼100 μM concentrations, which is the present lower experimental limit to react these species to form nucleotides. Heating samples leads to partial or complete decay of biomolecules, suggesting that biomolecule stockpiling on the hot surface is unlikely. The ideal conditions for the delivery of life’s building blocks from organic hazes would be when the Hadean atmosphere is rich in methane, but not so rich as to create an uninhabitable surface
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