Latest "Fossil" News
Stalked Spheriods Adorn Rocks at Fram Crater
Opportunity Rover arrived at Fram Crater on Sol 84 (April 19, 2004), after
traveling about 450 meters (.3 miles) from the landing point at Eagle Crater. Four days
later, it departed for Endurance Crater, by then just 250 meters away. While at Fram
Crater, the rover took several hundred images with its Panoramic Camera, many of which
show rocks studded with spheroids perched on slender stalks. The complete set of images
from Fram Crater can be found at the Opportunity Raw Images page, listed under Sol 84, 85,
86, and 87:
Below: Fram Crater (see map) as viewed by
Opportunity's left front hazard camera on Sol 85. The large rock in the foreground is
named Pilbara. The crater Endurance can be seen on the horizon in the upper right. Notice
the rover wheels in the bottom corners of the photo. The original image has been cropped
and the shadow cast by the rover has been lightened in this version. You can download the
full-size raw image here:
|Above: color composite of the rock Pilbara, after it was ground by the
RAT (Rock Abrasion Tool). This is a cropped version of the full image, which was made from
3 separate images taken by Opportunity's panoramic camera through 480, 530, and 600
nanometer filters. The original image is available here:
Below: 2x detail from the top right quadrant of the Pilbara post-RAT image. Note that in the 3 insets at right, the angles made by the 3 "berries" and their corresponding shadows are all the same. This indicates that the object in the topmost inset (colored in red) is free-standing, and has an extraordinarily long root-like stalk. Certainly, this stalk must be composed of a harder substance than the material that once encased it, despite the apparent color similarity of the stalk and the surrounding rock.
|Above: 3-D stereogram of the same object shown above it in color. For
instructions on how to view stereograms in 3-D, go to the mars_fossils
The left image is a gray-scale version of the color image of Pilbara shown above. The right image is a composite made by combining 3 raw images taken by the right Pancam on Sol 88. The composite has greater clarity than the individual images. The original right Pancam images can be downloaded here:
|Above: 2x close-up from the lower right quadrant of the Pilbara composite
image. Note that the objects circled in red point in the opposite direction from those
circled in yellow. Also, the spheroid circled in cyan seems to have 2 tails. The green
dashed line shows the location of a ridge-line that runs along most of the top surface of
Pilbara. All of this suggests that the wind flow at the boundary layer might be in
opposite directions on either side of the ridge line. A further speculation is that the
well-defined stalks form when the wind flow is closely aligned with a pre-existing grain
structure in the sedimentary layers.
Below: stereogram showing the same area of Pilbara. Again, the left image is a gray-scale version of the color Pilbara photo, and the right side image is a composite of 3 right Pancam images.
|Above: stereogram of the pre-RAT Pilbara rock. This image suggests that
the stalks facing toward or away from the viewer might have been formed by episodic winds
travelling in opposite directions on different occasions. At such times, the
spheroid-stalk structures on the leeward side would be relatively protected from erosion.
On the windward side, the hard spheroids would protect the softer rock behind them, and as
the rock was abraded away, the spheroids would be left projecting from the receding rock
surface on a column of softer rock. At times of lighter, and variable winds, the columns
might then be slowly reduced in diameter until they acquired the forms of the objects seen
in the photos.
In summation, my theory is that the stalks are formed when powerful winds, that blow only in specific directions, are interspersed with more gentle winds that blow in random directions. Alternatively, the stalks might simply be the fossilized remnants of long-dead martian organisms!
The image on the right was rotated 5 degrees counter-clockwise to bring the images into
better alignment. The original raw images can be downloaded here:
|Above: stereogram showing the left-most corner of the rock Pilbara.
Notice that the stalk and spheroid just below the image center is oriented at nearly a
right angle to the stalked spheroid in the upper right quadrant. Again, could this be due
to a difference in the direction of the prevailing winds at the two locations, or are the
stalks pre-existing structures buried in the rock? Original images for this stereogram are
the same as for the stereograms near the top of this page.
Below: stereogram showing part of the rock just northeast of Pilbara. In this lucky shot, the normally buried structures of two stalks are revealed, just below where the stalks enter the rock. The original images for this stereogram are the same as for the first 2 stereograms shown on this page.
|Below: mosaic of a small area of Fram Crater, a short distance south of
the rock Pilbara. (Visible in the photo at the top of this page, on the far-right side.)
Notice that the spheroids with stalks point in at least 2 different directions, despite
the lack of any large rocks in the area that might divert the wind flow. It seems unlikely
that wind direction alone could explain the orientation of the spheriod stalks. Five
separate areas of the mosaic have been enlarged 1.5x and combined with right-eye views to
make stereograms, which are displayed below. Notice the strange drooping spheroid-stalk in
the center of the first stereogram.
Here are the raw images used to make the mosaic and stereograms: