Mars is cooler, clearer, and drier than the Red Planet was a couple of decades ago, according to new data released last week, which include this collection of the first Mars opposition images taken since the Hubble Space Telescope (HST) was repaired in December 1993. Related spectroscopic studies also reveal that the abundance of ozone in Mars' atmosphere has increased threefold at equatorial levels. "Mars is in a very different climate regime than it was a couple decades ago," when the Viking spacecraft visited the planet, says Steven Lee of the University of Colorado at Boulder. What's more, the average global temperature has dropped 20 K since the mid-1970s, largely due to the settling of dust particles, which absorb sunlight and warm the atmosphere. In fact, Mars is about 3 times less dusty than it was during the Viking visit. Lee notes, "We just happened to visit Mars when it was dusty, and now the dust has settled out."
Scientists estimate that Mars' climate has been very stable over the past 1.5 years. Observations of Mars' atmosphere may help shed light on processes at work in Earth's atmosphere, scientists say. "It gives us a way to do almost experimental planetology," says Anne L. Kinney, of the Space Telescope Science Institute. The three HST images were obtained through a narrowband red filter (673 nm) with the Wide Field/Planetary Camera-2 instrument. The spatial resolution near the sub-Earth point - the latitude and longitude on Mars closest to Earth - is about 25 km/pixel, comparable to the resolution of many of the far-encounter sequence images obtained by the Mariner and Viking spacecraft. Features on the scale of individual craters can be clearly seen, and there are obvious lanes, gaps and irregularities in the north polar cap. All images were corrected for standard bias and flat variations, and a spatial deconvolution function was applied to allow the maximum potential spatial resolution to be realized.
(A) The top image was taken February 24, 1995, at 1708 UT. The central meridian longitude is 275°, and the season is late northern spring (Ls = 64°). The sub-Earth latitude at this time was 17.5°. Thus the residual north polar cap is tilted toward Earth, exposing the entire north polar region.
(B) The middle image was taken February 25, 1995, at 0114 UT. Here the central meridian is 33°. This view centers on the dark northern hemisphere feature Acidalia, which is probably a vast basaltic sand sheet, on the basis of Viking and previous ground-based data. The view is centered almost exactly on the landing site of the upcoming NASA Mars Pathfinder mission to fly in late 1996. Craters in southern Chryse Planitia and craters and wind streaks in Arabia Planitia, southeast of Acidalia, are indicative of the spectacular detail resolved in these images. The Valles Marineris canyon system can be clearly seen near the morning (left) limb, just below center as a narrow, dark albedo feature.
(C) The bottom image was taken February 25, 1995, at 0915 UT. The central meridian here is 151°. This view centers on the Amazonis regions just west of the volcano Olympus Mons. Olympus itself can be discerned by a ring of bright material, probably related to its basal scarp. The three Tharsis volcanos can also be discerned in the image. Images at blue wavelengths indicate that there was substantial afternoon cloud activity associated with all of these orographic features; much of the brighter, wispy structure seen in the image in this region may be caused by clouds that appear bright in the red because they contain some component of bright red dust. In general, there are far fewer details in this image because this hemisphere is dominated by bright, ferric-rich, "desert" region rather than by darker, more ferrous-rich, basaltic units.—Steve Lee and Mike Wolff of the University of Colorado (CU) and Jim Bell of NASA Ames performed image processing for these data. The University of Toledo's Phil James is the principal investigator of the science team analyzing these data, which includes CU researchers Lee, Wolff, and Todd Clancy, Lowell Observatory's Leonard Martin, and NASA's Bell.
Return to Science and
Society
Return to Starting
Point
