Solstizio d'inverno su Marte

Winter Solstice on Mars: Rovers Look Forward to A Second Martian Spring
August 07, 2006

Like the fabled tortoise that, in the race with the hare, moves slowly
yet accomplishes much, NASA’s Mars Exploration Rover Spirit has
continued to make progress little by little, while essentially running
in place.

Eking out a steady stream of scientific data as solar power levels have
plunged to a seasonal low during the rover’s second Martian mid-winter,
Spirit has discovered meteorites that might otherwise have been missed
and completed work on a 360-degree, full-color panorama of its
surroundings. The rover has collected long-term observations of the
Martian atmosphere, rocks, and soils under varying conditions of
sunlight, temperature, and wind.

“Spirit has conducted a regular routine of scientific observations,”
said Jake Matijevic, rover engineering team chief, “though they haven’t
been very extensive each day because the energy levels don’t allow
After the solstice, we’ll turn the rover to investigate a different
of the surface. We’ll move very carefully to preserve our tilt toward
the sun.”

The winter solstice falls on Tuesday, Aug. 8, 2006, Spirit’s 923rd sol,
or Martian day, of exploration. Since April, the rover has been parked
on an outcrop known as “Low Ridge Haven,” tilted 11 degrees to the

Opportunity Continues Trek

On the opposite side of the planet, Spirit’s twin, Opportunity,
continues to advance toward Victoria Crater, the largest crater yet
visited on the surface of Mars. While exploring Martian plains north of
the equator, Opportunity, too, has experienced lower power levels
the southern hemisphere winter, though not to the same degree as

Opportunity recently arrived at another, smaller crater known as
Crater,” which is 35 meters (115 feet) wide. Scientists plan to spend
some time examining rocks that were excavated onto the surface during
the impact that formed the crater. Opportunity is collecting full-color
panoramic images of the site.

Like Spirit, Opportunity will have more power for science operations as
the days grow longer before and after the vernal equinox on Feb. 8,
2006, when the lengths of the day and night will be equal. On Earth,
vernal equinox is considered the official start of spring.

No Stranger to Adversity

As the sun moves toward zenith and power levels increase, the biggest
challenge for Spirit will be mobility. Last March, Spirit’s right front
wheel stopped working. Engineers safely navigated the rover to its
winter haven, in part because they had learned to drive Spirit
alternatively backward and forward on five wheels in 2004, when
the right front wheel temporarily began drawing excess power.

Using this maneuver, the rover dragged the ailing wheel behind the
vehicle, carving a trench in the sand.

Rover handlers are optimistic that Spirit will be able to explore all
but the steepest or sandiest terrain.

“I think we should be able to drive Spirit 10 to 15 meters (30 to 45
feet) a day when solar power is restored to optimum levels,” observed
Matijevic. “Sandy areas are going to have to be treated as obstacles.
We’ll be looking for routes that are not too rocky but that also do not
have much sand.”

Looking Ahead

Bruce Banerdt, project scientist for the mission, said team members
looking forward to collecting more science data as a result of having
more electrical power. NASA recently agreed to extend the Mars
Exploration Rover mission for another year starting in October.

“When Spirit has sufficient energy, which may be early September, we’re
thinking about turning the rover about 30 degrees to get a better look
at the bright soil churned up by the rover’s right front wheel,”
said. “We’ll look at the chemical composition to see if it’s made of
sulfate salts like other deposits we’ve visited. We’ll have excellent
data from the 13-filter, panoramic camera images to guide us to
promising targets for further study.”

The ascending sun will also bring warmer temperatures - warmer, that
for Mars. The coldest day of the Martian year will probably be the same
as the shortest day, said Matijevic. Unlike Earth, Mars does not have a
thick atmosphere to buffer changes in temperature. Though Spirit is not
awake to measure the coldest temperatures in the middle of the night,
models estimate that Spirit’s solar panels have recently experienced
frigid temperatures of about -104 degrees C (-155 F.).

Location, however, does make a difference. Being stationed on a
heat-absorbing rock has probably kept the rover slightly warmer than it
would have been out on the sands of the “Inner Basin,” he added.

Though surviving on Mars is always a challenge, there have been no
surprises this winter. Energy levels and operating temperatures have
been in agreement with what engineers predicted. “Our experiences this
winter are very similar to what we experienced last winter,” said