16 July 1997
10:30 am Pacific Daylight Time
|The latest from the
Sagan Memorial Station
MISSION STATUS - 15 July 1997, 12:00 noon PDT
The Mars Pathfinder flight team today reported
on a very successful night of data transmission, receiving an unprecedented
90 megabits of data on the chemical makeup of a boulder nicknamed Yogi,
atmospheric measurements and nearly all remaining portions of a 360-degree
color panorama image of the landing site.
Last night's downlink sessions contained detailed information on the chemistry
of Yogi taken by the rover after a second attempt to position its alpha
proton X-ray spectrometer against the rock. The new data also included
measurements of the aerosol content of the Martian atmosphere, which was
used in parallel with new Hubble Space Telescope images of Mars to characterize
changes in regional and global weather patterns in the last three weeks.
Recent incidents in which the Pathfinder lander's computer reset itself
were discussed by Glenn Reeves, flight software team leader. According
to Reeves, computer resets have occurred a total of four times during the
mission -- on July 5, 10, 11 and 14. The flight team has attempted to avoid
future resets by instructing the computer to handle one activity at a time
-- "serializing" activities -- rather than juggling a number
of activities at once.
The team continues to troubleshoot the problem by testing all of the sequences
leading up to reset in JPL's Mars Pathfinder testbed; considering changes
in the flight software that would allow for immediate recovery if the flight
computer were to reset itself; and modifying operational activities to
minimize data loss if a reset should occur again. "In a sense, the
reset itself is not harmful because it brings us back into a safe state,"
said Reeves. "But it does cause a disruption of the operational activities."
Among the science highlights, the Pathfinder mineralogy team presented
new information about Barnacle Bill, a very roughly textured rock, and
Yogi, a much larger boulder nearby, which was successfully measured last
Yogi, low in quartz content, appears to be more primitive than Barnacle
Bill, "having not gone through the cooking that Barnacle Bill and
other andesites have gone through," said Dr. James Greenwood, University
of Tennessee, a member of the mineralogy science team. Although these observations
are very preliminary, Yogi appeared to be more like the common basalts
found on Earth. The next rock to be studied is "Scooby Doo,"
followed by others, including "Half Dome," "Wedge,"
"Shark" and "Flat Top," all located in a different
region of the landing site. Some are near the lander petal on which Sojourner
flew to Mars.
Observations from the Earth-orbiting Hubble Space Telescope revealed a
lot of surface-atmospheric transport activity. A dust storm detected in
Vallis Marineris just prior to Pathfinder's landing, for instance, had
all but vanished within two weeks according to new Hubble images, noted
Dr. Steven Lee, University of Colorado, a Hubble investigator. Some of
the dust from that regional storm had diffused to the Pathfinder landing
site, which was consistent with recent Pathfinder atmospheric opacity measurements.
In observations taken between May 18 and July 11, the amount of dust near
the Pathfinder landing site had nearly tripled. "There's obviously
a lot of very rapid transport going on here, with some of the dust diffusing
toward the landing area," Lee said. "This is consistent with
Pathfinder observations on the surface."
The increase in atmospheric dust appears to be diminishing the amount of
cloudiness, Lee added. Clouds observed near the southern polar hood had
begun to decrease in the most recent Hubble images as the dust diffused
throughout the southern hemisphere. The Hubble team estimated that these
clouds were relatively low, hovering around 15 to 16 kilometers (9 to 10
miles) above the surface, because the tips of some Martian volcanoes could
be seen peeking through the cloud tops.
On Pathfinder's 11th Martian day -- or Sol 11 -- Earth rise at the Martian
landing site was at 4:07 p.m. Pacific Daylight Time on Monday, July 14,
followed by sunrise at 7:16 p.m. PDT. The flight team radioed commands
to the Pathfinder lander beginning at 7:40 p.m. PDT. Data were downlinked
from Pathfinder's lander from 9:02 to 9:35 p.m. PDT using the lander's
low-gain antenna; this session included the spectrometer data on Yogi.
A second downlink session, on the lander's high-gain antenna, began at
1:20 a.m. and ran until 5:10 a.m. PDT, with a half-hour break in the middle
while the antenna was adjusted; this session included the new portions
of the color panorama image. Earth set was at 5:46 a.m. and sunset was
at 8:15 a.m. PDT.