Exoplanet atmospheres

Abstract:

The first four complete spectra recorded by the near infrared mapping spectrometer (NIMS) instrument on the Galileo spacecraft in 1996 have been analyzed. These spectra remain the only ones which have been obtained at maximum resolution over the entire NIMS wavelength range of 0.7 - 5.2 μm. The spectra cover the edge of a "warm" spot at location 5°N, 85°W. We have analyzed the spectra first with reflecting layer models and then with full multiple scattering models using the method of correlated-k. We find that there is strong evidence for three different cloud layers composed of a haze consistent with 0.5-μm radius tholins at 0.2 bar, a cloud of 0.75-lim NH3 particles at about 0.7 bar, and a two-component NH4SH cloud at about 1.4 bars with both 50.0- and 0.45-μm particles, the former being responsible for the main 5-μm cloud opacity. The NH3 relative humidity above the cloud tops is found to decrease slightly as the 5-μm brightness increases, with a mean value of approximately 14%. We also find that the mean volume mixing ratio of ammonia above the middle (NtL4SH) cloud deck is (1.7± 0.1) × 10-4 and shows a similar, though less discernible decrease with increasing 5-μm brightness. The deep volume mixing ratios of deuterated methane and phosphine are found to be constant and we estimate their mean values to be (4.9± 0.2) × 10-7 and (7.7 ± 0.2) × 10-7, respectively. The fractional scale height of phosphine above the 1 bar level is found to be 27.1± 1.4% and shows a slight decrease with increasing 5-μm brightness. The relative humidity of water vapor is found to be approximately 7%, but while this and all the previous observations are consistent with the assumption that "hot spots" are regions of downwelling, desiccated air, we find that the water vapor relative humidity increases as the 5-μm brightness increases. Copyright 1998 by the American Geophysical Union.

Abstract:

A comparison between low-flux dayside and nightside spectra of Jupiter recorded by the Galileo near-infrared mapping spectrometer (NIMS) experiment gives the first accurate estimate of the solar reflected component at 5 μm, in the equatorial zone of Jupiter. A minimum flux level of about 0.6 μW cm-2 sr-1V/μm is found on the dayside, compared with 0.1 /μW cm-2 sr-1/μm on the nightside. These fluxes are 100-800 times lower respectively than the bright 5-μm thermal emission in the north equatorial belt (NEB) hot spots. The day/night difference can be interpreted as a solar reflected component from a cloud, presumably the ammonia cloud, with an albedo of the order of 15%, located at a pressure level of 0.79 bar or at higher altitudes (corresponding to cloud temperature of 160 K or lower). Compared to the measurements in hot spots made at other wavelengths from ground-based observations and from NIMS real time spectra, they imply a high cloud opacity in cold regions at atmospheric levels where the cloud optical depth in the hot spots is very low. The residual flux on the nightside arises from (1) a very small cloud transparency giving some access to deeper thermal emission or (2) as high-resolution solid-state imaging (SSI) images of Galileo suggest, to cloud inhomogeneities, with clearer regions of medium brightness temperatures, mixed with dark regions of much lower thermal emission. If the former have the same brightness as a typical hot spot, a filling factor of a few percent is sufficient to explain the observed flux level on the nightside cold regions. Copyright 1998 by the American Geophysical Union.

Abstract:

SINFONI, the SINgle Faint Object Near-infrared Investigation, is an instrument for the Very Large Telescope (VLT), designed to provide spectroscopy at the telescope diffraction limit in the near-infrared. This unique capability is achieved by combining two state-of-the-art developments, an integral field spectrometer (SPIFFI) and a curvature sensor based adaptive optics system (MACAO). SINFONI is a collaborative effort by the Max-Planck-Institut fur extraterrestrische Physik (MPE) and the European Southern Observatory (ESO).SINFONI will operate at the Cassegrain focus of Unit Telescope 1 (UT1) of the VLT, in conjunction with a Laser Guide Star (LGS) for almost complete sky coverage. It will provide integral field data cubes, with a hexagonal field of view ranging from similar to 1 " to 8 ", with corresponding pixel sizes of 0." 03 to 0." 25. The field of view contains 1024 spatial pixels, with similar to 100% filling factor in the focal plane. Spectra are obtained for each of the 1024 pixels. Spectral resolutions of R=2000 to R=4500 will be available, covering the J, H and K spectral windows. The high spectral resolution made will allow software OH suppression in the J and H bands. The detector is a 1024(2) HgCdTe HAWAII array from Rockwell. Spectroscopy of faint objects (m(K) < 21 and m(H) < 22) will be easily feasible.