Toward the Formation of Carbonaceous Refractory Matter in High Temperature Hydrocarbon-Rich Atmospheres of Exoplanets Upon Micrometeoroid Impact

Abstract

We report on laboratory simulation experiments mimicking the chemical processing of model atmospheres of exoplanets containing C3 and C4 hydrocarbons at moderate temperatures of 400 K upon interaction of catalytic surfaces of micrometeoroids. By utilizing an ultrasonic levitator device and heating singly levitated particles under simulated microgravity conditions, Raman spectroscopy is utilized as a non-invasive tool to probe on line and in situ the conversion of C3 and C4 hydrocarbons to refractory carbonaceous matter on the surfaces of levitated particles. Secondary Ion Mass Spectrometry and electron microscopic imaging were also conducted to gain further insight into the elementary composition and structures of the refractories formed. Our results provide compelling evidence that in the presence of a catalytic surface, which can be supplied in the form of micrometeoroids and atmospheric dust particles, hydrocarbon gases present in the atmospheres of exoplanets can be converted to refractory, carbon-rich carbonaceous matter of mainly graphitic structure with a carbon content of at least 90% at elevated temperatures. This finding might explain the low methane to carbon monoxide (CH 4-CO) ratio in the hot Neptune GJ 436b, where the abundant methane photochemically converts to higher order hydrocarbons and ultimately to refractory graphite-like carbon in the presence of a silicon surface.

COMPLEX HYDROCARBON CHEMISTRY IN INTERSTELLAR AND SOLAR SYSTEM ICES REVEALED: A COMBINED INFRARED SPECTROSCOPY AND REFLECTRON TIME-OF-FLIGHT MASS SPECTROMETRY ANALYSIS OF ETHANE (C2H6) AND D6-ETHANE (C2D6) ICES EXPOSED TO IONIZING RADIATION

“…Recently, Lorenzi et al (2016) suggested that the discoloration of Pluto along with Makemake and Eris may be due to COMs, and our present study shows that this is very likely just from the simple ethane ice. Dangi et al (2015) has shown that under model atmospheric conditions containing C3 and C4, hydrocarbons interact catalytically with surfaces of micrometeroids to produce a carbonaceous refractory layer, which can account for the hydrocarbon sequestration.…”

Design and Performance of an Acoustic Levitator System Coupled with a Tunable Monochromatic Light Source and a Raman Spectrometer for In Situ Reaction Monitoring

“…Furthermore, a levitator can be used to probe the differences between the physical and chemical processes on the bulk samples and the surfaces of sub-millimeter size levitated particles. 5 , 12 Such tiny particles floating in the given gas medium provide ideal laboratory conditions simulating the dust particles or droplets in the atmospheres of planets and exoplanets. 5 Moreover, the levitated particle can respond quickly to temperature and radiation perturbations due to their small total heat and radiation dose capacity.…”

“… 5 , 12 Such tiny particles floating in the given gas medium provide ideal laboratory conditions simulating the dust particles or droplets in the atmospheres of planets and exoplanets. 5 Moreover, the levitated particle can respond quickly to temperature and radiation perturbations due to their small total heat and radiation dose capacity. Hence, a levitation device provides a versatile platform to study the physical and chemical processes without support structures as well as creates less-contingent sample trapping requirements, such as electric charge and refractive index.…”

“…In such laboratory experiments, gas–surface, heterogeneous reactions are of particular interest to investigate cloud and haze dynamics. 5 , 15 In a gas–surface reaction investigation, reactions of unsaturated hydrocarbon gases on the surface of silicon single particle had been performed, 4 where selected hydrocarbon gases are adsorbed on the surface and polymerized to refractory carbonaceous compounds whose spectroscopic signatures matched with the meteoritic sample providing insights into the possible formation conditions of the carbonaceous compounds in the meteoritic sample. A model mechanistic computational study 16 showed that 1,3-butadiene (H 2 CHCHCH 2 ) can adsorb exothermically on the silicon surface propagated by a second H 2 CHCHCH 2 molecule adsorption with further release of energy.…”

“…In recent years, acoustic levitation − has been utilized in a range of scientific disciplines including but not limited to analytical chemistry, astrochemistry, materials science, and pharmaceuticals. ,− Acoustic levitation has also been used in contactless mixing of two droplets to initiate a chemical reaction , and to transport protein crystal samples in crystallography experiments . In acoustic levitation, a liquid droplet, a solid particle, or a suspension is levitated slightly below the pressure nodes of the ultrasonic standing wave.…”