Titan News 2020
January 17, 2020 : Some Researchers May Have Solved The Mystery Of The Reversed Spin Of The Huygens Probe During Its Atmospheric Descent
About 15 years ago, on January 14, 2005, the Huygens probe released from the Cassini orbiter performed an atmospheric descent and landed on the surface of Saturn's largest moon Titan for the first time in history. The Huygens probe which was proposed by ESA and ASI had separated from the Cassini spacecraft proposed by NASA at the end of December 2004. During the atmospheric plunge of January 14, 2005, the Huygens probe started to spin the wrong way and engineers and researchers had not anticipated that configuration. That mystery may have been solved thanks to recent tests or simulations. In fact, during the atmospheric journey, some instruments of the probe may have generated an unexpected torque opposite to that engendered by the 36 angled vanes of the Huygens probe. The vanes played a key role since they were used to control the rotation of the probe during its descent inside the deep and thick atmosphere of the giant moon. The atmosphere of Titan like the atmosphere of Venus or like the atmosphere of Mars makes any parachute useful for any probe that dives to the surface.
Researchers have been in a position to determine that two devices of the Huygens probe, the Separation Subsystem (SEPS) and the Radar Altimeter (RA) antennae, actually engendered an unexpected torque opposite to that generated by the multiple vanes. That phenomenon was strengthened due to the alteration of the gas flow around the atmospheric probe by the vanes which led to a rise in the amplitude of the « negative torque ». Let's point out that the negative torque corresponds to the effect that made the Huygens module flip its direction of rotation. The unexpected effect turned out to exceed the influence of the vanes. It is crucial for engineers to clearly understand the mechanisms that led to the unexpected configuration in the prospect of the development of future probes sent to extraterrestrial atmospheres like the atmosphere of Venus, Mars, Titan or the four Gas Giants. The behavior of any atmospheric probe can engender scientific failures. That's why engineers and scientists must be in a position to anticipate any scenario during the complex phase of the atmospheric descent.
The image above represents a mosaic of aerial views of Titan's landscape obtained from the DISR of the Huygens probe during its atmospheric plunge on January 14, 2005. The views were acquired at an altitude of approximately 8 km and the resolution of the landscape features is about 20 meters per pixel. One can clearly notice a sharp contrast between bright hills composed of a network of dark channels and a dark plain which seems quite uniform. The Cassini-Huygens mission represented the outcome of a collaboration between ESA, NASA and ASI. Image credit: ESA/NASA/JPL/University of Arizona.
January 7, 2020 : A New Research Work Involving Takahiro Iino Reveals That ALMA Has Measured The 14N/15N Isotopic Ratio In CH3CN Of The Opaque Atmosphere Of Titan
A new research work proposed on January 7, 2020 by a team of researchers composed of Takahiro Iino, Hideo Sagawa and Takashi Tsukagoshi and presented in Arxiv reveals the measurement of the 14N/15N isotopic ratio in CH3CN in the atmosphere of Saturn's largest moon Titan via ALMA. The planetologists were in a position to detect submillimeter rotational transitions of CH3C15N found at the 338 GHz band in the spectra of Titan's opaque atmosphere thanks to the analysis of archival data collected by the Atacama Large Millimeter/submillimeter Array (ALMA). A comparison between those observations and the simultaneously observed CH3CN lines at the 349 GHz band, which allow us to study the area from the altitude of 160 km to the altitude of about 400 km, allowed the researchers to deduce the value of the ratio 14N/15N in CH3CN at about 125. The level of accuracy remains limited but it allows the scientists to advance that the value of 14N/15N for CH3CN is higher than the values that have been previously determined and theoretically predicted for HCN and HC3N. The difference may be related to the different N2 dissociation factors whose impact depends on the altitude as proposed by a recent photochemical model.
The isotopic ratio between 14N and 15N can vary in the various nitriles present in Titan's atmosphere. The differences are closely related to the production processes of the molecules. The dissociation processes of N2 can be generated via the action of ultraviolet light from the Sun, via the action of magnetospheric electrons or via the action of galactic cosmic rays. Regarding the nitrile CH3CN, a photochemical model predicted a value of 120-130 in the lower part of the stratosphere for the isotopic ratio 14N/15N. The expected value is much higher than that for the nitriles HCN and HC3N which is, approximately, between 67 and 94. The value of 125 for the ratio 14N/15N in the molecule CH3CN which was measured by ALMA appears clearly higher than the value measured and predicted for the ratio 14N/15N in the molecules HCN and HC3N. The dissociation factors which depend on the altitude must be considered. Researchers are particularly interested in the chemistry of Titan's complex atmosphere which represents, to a certain extent, a soup of various molecules, elements or ions and which may resemble the atmosphere of the Early Earth.
The image in the upper part of the table reveals a raw image of Titan's disk obtained from the Cassini spacecraft on December 14, 2009. The image whose file name is N00148433.jpg was acquired using the CL1 filter and the MT3 filter. The view had not been validated or calibrated. A validated or calibrated view was going to be archived with the Planetary Data System proposed by NASA. The image in the lower part of the table represents a colorized version of the raw image. Credit for the raw image: NASA/JPL-Caltech/Space Science Institute. Credit for the colorization of the raw image: Marc Lafferre, 2020.
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