Geoscience Reference
In-Depth Information
Fig. 1.1 A striking picture, setting the stage for planets and dunes,
with vibrant red sand and blue skies is familiar to millions as a
'desktop' background image for the Windows operating system. The
image shows the moon atop a dune. But not just a dune; after reading
this topic, we hope you will recognize avalanche lobes and two
generations of ripples in the foreground. What millions in the northern
hemisphere have probably not noticed is that the moon is 'upside
down'; there the moon is seen as in the inset on the right, with the
pattern of mare (dark impact basins). The reason that the moon above
the dune looks 'wrong' is that this dune picture is from the southern
hemisphere (perhaps Australia, but more likely Namibia.) Montage by
J. Zimbelman
Fig. 1.2 The first dunes recognized on another world. After the 1972
dust storm cleared, Mariner 9 snapped this image showing what at the
time was called a 'suspected dune mass' in the floor of the
Hellespontus crater. Note the curved edge of the image: the vidicon
TV cameras of the time could cause geometric distortion of the image,
which would be corrected by lining up the regular pattern of black dots
('reseau marks'). Note the gradient in dune size across the dunefield.
Also visible towards the upper right is a small impact crater, and (just
barely visible here, and not recognized at the time) some faint dust
devil tracks. Tick marks at the left are for synchronization in data
handling; the white dots across the dunefield are transmission errors.
Mariner 9 image DAS 09807429, processed by R. Lorenz
 
Search WWH ::




Custom Search