Browsing by Subject "planets and satellites: atmospheres"

Now showing 1 - 7 of 7

Discovery Of A Low-Luminosity, Tight Substellar Binary At The T/Y Transition
(2015-04) Dupuy, Trent J.; Liu, Michael C.; Leggett, S. K.; Dupuy, Trent J.
We have discovered that the brown dwarf WISE J014656.66+423410.0 is a close binary (0 ''.0875 +/- 0 ''.0021, 0.93(-0.16)(+0.12) AU) from Keck laser guide star adaptive optics imaging. Our photometry for this system reveals that both components are less luminous than those in any known substellar binary. Combining a new integrated-light spectrum (T9p) and resolved YJH-band photometry from Keck allows us to perform spectral decomposition and assign component types of T9 and Y0. Many of the unusual features in the spectrum might be explained by high surface gravity: Y-band peak broadened to the blue; J-band peak broadened to the red; H-band peak shifted slightly to the red; and red Y - J colors. Interestingly, the very low component luminosities imply that the T9 primary is unexpectedly cold (T-eff = 345 +/- 45 K assuming an age of 10 Gyr), making it approximate to 100 K cooler than any other late-T dwarf and comparable to Y dwarfs. One intriguing explanation for this apparent discrepancy is that the J- and H-band spectral features that trigger the transition from T to Y spectral types are highly gravity dependent. This can be tested directly in the very near future by orbit monitoring. We constrain the orbital period to be less than or similar to 10 yr by combining evolutionary-model-based mass estimates for the components (approximate to 12-21M(Jup), 1 sigma at 10 Gyr) with a statistical constraint on the semimajor axis (less than or similar to 1.3 AU). Such a period is shorter than any other known T/Y transition binary, meaning that WISE J0146+4234AB will likely yield a dynamical mass within the next few years.
HDO And SO2 Thermal Mapping On Venus II. The So2 Spatial Distribution Above And Within The Clouds
(2013-11) Encrenaz, T.; Greathouse, T. K.; Richter, M. J.; Lacy, J.; Widemann, T.; Bezard, B.; Fouchet, T.; deWitt, C.; Atreya, S. K.; Lacy, J.
Sulfur dioxide and water vapor, two key species of Venus photochemistry, are known to exhibit significant spatial and temporal variations above the cloud top. In particular, ground-based thermal imaging spectroscopy at high spectral resolution, achieved on Venus in January 2012, has shown evidence for strong SO2 variations on timescales shorter than a day. We have continued our observing campaign using the TEXES high-resolution imaging spectrometer at the NASA InfraRed Telescope Facility to map sulfur dioxide over the disk of Venus at two different wavelengths, 7 mu m (already used in the previous study) and 19 mu m. The 7 mu m radiation probes the top of the H2SO4 cloud, while the 19 mu m radiation probes a few kilometers below within the cloud. Observations took place on October 4 and 5, 2012. Both HDO and SO2 lines are identified in our 7-mu m spectra and SO2 is also easily identified at 19 mu m. The CO2 lines at 7 and 19 mu m are used to infer the thermal structure. An isothermal/inversion layer is present at high latitudes (above 60 N and S) in the polar collars, which was not detected in October 2012. The enhancement of the polar collar in October 2012 is probably due to the fact that the morning terminator is observed, while the January data probed the evening terminator. As observed in our previous run, the HDO map is relatively uniform over the disk of Venus, with a mean mixing ratio of about 1 ppm. In contrast, the SO2 maps at 19 mu m show intensity variations by a factor of about 2 over the disk within the cloud, less patchy than observed at the cloud top at 7 mu m. In addition, the SO2 maps seem to indicate significant temporal changes within an hour. There is evidence for a cutoff in the SO2 vertical distribution above the cloud top, also previously observed by SPICAV/SOIR aboard Venus Express and predicted by photochemical models.
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.
Seasonal Variability In The Ionosphere Of Uranus
(2011-03) Melin, H.; Stallard, T.; Miller, S.; Trafton, L. M.; Encrenaz, T.; Geballe, T. R.; Trafton, L. M.
Infrared ground-based observations using IRTF, UKIRT, and Keck II of Uranus have been analyzed as to identify the long-term behavior of the H-3(+) ionosphere. Between 1992 and 2008 there are 11 individual observing runs, each recording emission from the H-3(+) Q branch emission around 4 mu m through the telluric L' atmospheric window. The column-averaged rotational H-3(+) temperature ranges between 715 K in 1992 and 534 K in 2008, with the linear fit to all the run-averaged temperatures decreasing by 8 K year(-1). The temperature follows the fractional illumination curve of the planet, declining from solstice (1985) to equinox (2007). Variations in H-3(+) column density do not appear to be correlated to either solar cycle phase or season. The radiative cooling by H-3(+) is similar to 10 times larger than the ultraviolet solar energy being injected to the atmosphere. Despite the fact that the solar flux alone is incapable of heating the atmosphere to the observed temperatures, the geometry with respect to the Sun remains an important driver in determining the thermospheric temperature. Therefore, the energy source that heats the thermosphere must be linked to solar mechanisms. We suggest that this may be in the form of conductivity created by solar ionization of atmospheric neutrals and/or seasonally dependent magnetospherically driven current systems.
A Stringent Upper Limit To SO2 In The Martian Atmosphere
(2011-06) Encrenaz, T.; Greathouse, T. K.; Richter, M. J.; Lacy, J. H.; Fouchet, T.; Bezard, B.; Lefevre, F.; Forget, F.; Atreya, S. K.; Lacy, J. H.
Surfur-bearing molecules have been found at the surface of Mars by the Viking lander, the Spirit and Opportunity rovers, and the OMEGA infrared spectrometer aboard Mars Express. However, no gaseous sulfur-bearing species have ever been detected in the Martian atmosphere. We search for SO2 signatures in the thermal spectrum of Mars at 7.4 mu m using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). Data were obtained on Oct. 12, 2009 (Ls = 353 degrees), in the 1350-1360 cm(-1) range, with a spatial resolution of 1 arcsec (after convolution over three pixels along the N-S axis and two steps along the E-W axis) and a resolving power of 80 000. To improve the signal-to-noise ratio (S/N), we co-added the Martian spectrum around the positions of nine selected SO2 transitions with a high S/N and no telluric contamination. From a mean spectrum, averaged over 35 pixels in the region of maximum continuum, we infer a 2 sigma upper limit of 0.3 ppb to the SO2 mixing ratio, assuming that our instrumental errors are combined according to Gaussian statistics. Our upper limit is three times lower than the upper limit derived by Krasnopolsky (2005, Icarus, 178, 487), who used the same technique on previous TEXES data. In addition, we derive an upper limit of 2 ppb at each spatial pixel of the region observed by TEXES, which covers the longitude ranges 50 E-170 E for latitudes above 30 N, 100 E-170 E for latitudes between 0 and 30 N, and 110 E-170 E for latitudes between 15 S and 0. The non-detection of localized SO2 sources in the observed area is consistent with a homogeneous distribution being expected around equinox for non-condensible species with a lifetime longer than the global mixing time. In view of the typically large SO2/CH4 ratio observed in terrestrial volcanoes, and assuming a comparable volcanic composition for Mars and the Earth, our result reaffirms that a volcanic origin is unlikely for any methane in the Martian atmosphere.
Variability in A Young, L/T Transition Planetary-Mass Object
(2015-11) Biller, Beth A.; Vos, Johanna; Bonavita, Mariangela; Buenzli, Esther; Baxter, Claire; Crossfield, Ian J. M.; Allers, Katelyn; Liu, Michael C.; Bonnefoy, Mickael; Deacon, Niall; Brandner, Wolfgang; Schlieder, Joshua E.; Dupuy, Trent; Kopytova, Taisiya; Manjavacas, Elena; Allard, France; Homeier, Derek; Henning, Thomas; Dupuy, Trent
As part of our ongoing NTT SoFI survey for variability in young free-floating planets and low-mass brown dwarfs, we detect significant variability in the young, free-floating planetary-mass object PSO J318.5-22, likely due to rotational modulation of inhomogeneous cloud cover. A member of the 23 +/- 3 Myr beta Pic moving group, PSO J318.5-22 has T-eff = 1160(-40)(+30) K and a mass estimate of 8.3 +/- 0.5 M-Jup for a 23 +/- 3 Myr age. PSO J318.5-22 is intermediate in mass between 51 Eri b and beta Pic b, the two known exoplanet companions in the beta Pic moving group. With variability amplitudes from 7% to 10% in J(S) at two separate epochs over 3-5 hr observations, we constrain the rotational period of this object to >5 hr. In K-S, we marginally detect a variability trend of up to 3% over a 3 hr observation. This is the first detection of weather on an extrasolar planetary-mass object. Among L dwarfs surveyed at high photometric precision (<3%), this is the highest amplitude variability detection. Given the low surface gravity of this object, the high amplitude preliminarily suggests that such objects may be more variable than their high-mass counterparts, although observations of a larger sample are necessary to confirm this. Measuring similar variability for directly imaged planetary companions is possible with instruments such as SPHERE and GPI and will provide important constraints on Formation. Measuring variability at multiple wavelengths can help constrain cloud structure.
Water Vapor Map Of Mars Near Summer Solstice Using Ground-Based Infrared Spectroscopy
(2010) Encrenaz, T.; Greathouse, T. K.; Bezard, B.; Fouchet, T.; Lefevre, F.; Montmessin, F.; Bitner, M.; Kruger, A.; Richter, M. J.; Lacy, J. H.; Forget, F.; Atreya, S. K.; Lacy, J. H.
Ground-based spatial mapping of Mars provides a unique way to retrieve the global distribution of minor atmospheric species and to study transient phenomena or possible variations with the local hour. We have obtained an instantaneous map of water vapor on Mars near summer solstice (Ls = 80 degrees) using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF) at Mauna Kea Observatory. Data have been obtained in the 1230-1245 cm(-1) range (lambda = 8.1 mu m), with a spatial resolution of 1.1 arcsec (after convolution) and a spectral resolution of 0.012 cm(-1) (R = 10(5)). The map has been retrieved from the line depth of a weak HDO transition, compared with the line depth of a weak CO(2) nearby transition. The TEXES map exhibits a strong maximum around the northern pole, as expected from previous observations and from climate model predictions. More interestingly, it shows longitudinal variations, both at high northern latitudes and at mid-latitudes, in close agreement with the predictions of the Global Climate Model developed at the Laboratoire de Meteorologie Dynamique (LMD GCM). The inferred water vapor mixing ratio is also in good agreement with the model predictions. The longitudinal variations at mid latitudes show a general enhancement toward the east. They do not seem to be due to the effect of local hour, but can be explained by dynamical effects generated by the topography. The map of surface temperatures, inferred from the continuum flux, is surprisingly different from the map expected from the climate models; the source of this discrepancy is still unclear.