Browsing by Subject "planets and satellites: composition"

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A Correlation Between The Eclipse Depths Of Kepler Gas Giant Candidates And The Metallicities Of Their Parent Stars
(2012-06) Dodson-Robinson, Sarah E.; Dodson-Robinson, Sarah E.
Previous studies of the interior structure of transiting exoplanets have shown that the heavy-element content of gas giants increases with host star metallicity. Since metal-poor planets are less dense and have larger radii than metal-rich planets of the same mass, one might expect that metal-poor stars host a higher proportion of gas giants with large radii than metal-rich stars. Here I present evidence for a negative correlation at the 2.3 sigma level between eclipse depth and stellar metallicity in the Kepler gas giant candidates. Based on Kendall's tau statistics, the probability that eclipse depth depends on star metallicity is 0.981. The correlation is consistent with planets orbiting low-metallicity stars being, on average, larger in comparison with their host stars than planets orbiting metal-rich stars. Furthermore, since metal-rich stars have smaller radii than metal-poor stars of the same mass and age, a uniform population of planets should show a rise in median eclipse depth with [M/H]. The fact that I find the opposite trend indicates that substantial changes in the gas giant interior structure must accompany increasing [M/H]. I investigate whether the known scarcity of giant planets orbiting low-mass stars could masquerade as an eclipse depth-metallicity correlation, given the degeneracy between metallicity and temperature for cool stars in the Kepler Input Catalog. While the eclipse depth-metallicity correlation is not yet on firm statistical footing and will require spectroscopic [Fe/H] measurements for validation, it is an intriguing window into how the interior structure of planets and even the planet formation mechanism may be changing with Galactic chemical evolution.
Hdo And SO2 Thermal Mapping On Venus: Evidence For Strong SO2 Variability
(2012-07) Encrenaz, T.; Greathouse, T. K.; Roe, H.; Richter, M.; Lacy, J.; Bezard, B.; Fouchet, T.; Widemann, T.; Lacy, J.
We have been using the TEXES high-resolution imaging spectrometer at the NASA Infrared Telescope Facility to map sulfur dioxide and deuterated water over the disk of Venus. Observations took place on January 10-12, 2012. The diameter of Venus was 13 arcsec, with an illumination factor of 80%. Data were recorded in the 1344-1370 cm(-1) range (around 7.35 mu m) with a spectral resolving power of 80 000 and a spatial resolution of about 1.5 arcsec. In this spectral range, the emission of Venus comes from above the cloud top (z = 60-80 km). Four HDO lines and tens of SO2 lines have been identified in our spectra. Mixing ratios have been estimated from HDO/CO2 and SO2/CO2 line depth ratios, using weak neighboring transitions of comparable depths. The HDO maps, recorded on Jan. 10 and Jan. 12, are globally uniform with no significant variation between the two dates. A slight enhancement of the HDO mixing ratio toward the limb might be interpreted as a possible increase of the D/H ratio with height above the cloud level. The mean H2O mixing ratio is found to be 1.5 +/-0.75 ppm, assuming a D/H ratio of 0.0312 (i.e. 200 times the terrestrial value) over the cloud deck. The SO2 maps, recorded each night from Jan. 10 to Jan. 12, show strong variations over the disk of Venus, by a factor as high as 5 to 10. In addition, the position of the maximum SO2 mixing ratio strongly varies on a timescale of 24 h. The maximum SO2 mixing ratio ranges between 75 +/-25 ppb and 125 +/-50 ppb between Jan. 10 and Jan. 12. The high variability of sulfur dioxide is probably a consequence of its very short photochemical lifetime.