We report the detection of transits by the 3.1 M Jup companion to the V = 8.17 G0V star HD 17156. The transit was observed by three independant observers on Sep. 9/10, 2007 (two in central Italy and one in the Canary Islands), who obtained detections at confidence levels of 3.0σ, 5.3σ, and 7.9σ, respectively. The observations were carried out under the auspices of the Transitsearch.org network, which organizes follow-up photometric transit searches of known planet-bearing stars during the time intervals when transits might be expected to occur. Analyses of the 7.9σ data set indicates a transit depth d = 0.0062 ± 0.0004 and a transit duration t = 186 ± 5 min. These values are consistent with the transit of a Jupiter-sized planet with an impact parameter b = a cos i/R ∼ 0.8. This planet occupies a unique regime among known transiting extrasolar planets, both as a result of its large orbital eccentricity (e = 0.67) and long orbital period (P = 21.2 d). The planet receives a 26-fold variation in insolation during the course of its orbit, which will make it a useful object for characterizing exoplanetary atmospheric dynamics.

The results of observations of the spatial and temporal variation of water vapor during the Viking primary mission are reported. The instrument, the Mars atmospheric water detector (Mawd), is a five‐channel grating spectrometer operating in the 1.4‐μm water vapor bands. The seasonal period covered here is the northern summer solstice to the following equinox. The global water vapor, mapped at low resolution at approximately 1‐month intervals, has been observed to undergo a gradual redistribution, the latitude of maximum column abundance moving from the northern polar area to the equatorial latitudes, and the integrated global atmospheric vapor content remaining constant. The peak abundances (∼100 precipitable microns) occurred over the dark material of the circumpolar region. The summer residual cap is dirty water ice; at the season of maximum vapor the atmosphere above it is saturated and has a stable lapse rate, of temperature. High‐resolution maps show local structure controlled by abrupt changes of surface elevation, suggesting that large variations at a given latitude are orographie in nature and only occur in association with features whose horizontal scale is small in comparison to the product of the atmospheric relaxation time and the local mean wind speed. These results are at variance with the low‐resolution global maps, however, which seem to show topographic control even at the regional scale. Attempts to isolate the diurnal variation of the vapor have shown a variety of effects at different latitudes and locations; scattering by dust and condensate particles obscures the intrinsic diurnal variation of the vapor phase. The large diurnal variation reported from earth‐based measurements may be largely an observational effect.

Observations of the latitude dependence of water vapor made from the Viking 2 orbiter show peak abundances in the latitude band 70 degrees to 80 degrees north in the northern midsummer season (planetocentric longitude approximately 108 degrees ). Total column abundances in the polar regions require near-surface atmospheric temperatures in excess of 200 degrees K, and are incompatible with the survival of a frozen carbon dioxide cap at martian pressures. The remnant (or residual) north polar cap, and the outlying patches of ice at lower latitudes, are thus predominantly water ice, whose thickness can be estimated to be between 1 meter and 1 kilometer.

This paper describes an investigation of a potential weakness in DES which leads to a statistical property observable in plaintextciphertext pairs and dependent on the key. However, the number of encryptions of known plaintext needed to exploit this property i s comparable to the number of encryptions of an exhaustive k ey search, so the \weakness" is mainly of theoretical interest.

Analysis of observations made from the Viking 1 Orbiter indicates that the water vapor over the Viking 1 landing site is uniformly mixed with the atmosphere and not concentrated near the surface. The analysis incorporates the effects of atmospheric scattering and explains why previous earth‐based observations showed a strong diurnal variation in water content. It also explains the lack of an early morning fog and removes the necessity of daily exchange of large amounts of water between the surface and the atmosphere. A water vapor volume mixing ratio of 1.5×10−4 is inferred for the Viking 1 site in late summer.