Universe Today
When the
Opportunity rover
landed on Mars on January 25th, 2004, its mission was only meant to last for about 90 Earth days. But the little rover that could has exceeded all expectations by remaining in operation (as of the writing of this article) for a total of 13 years and 231 days and traveled a total of about 50 km (28 mi). Basically,
Opportunity
has continued to remain mobile and gather scientific data 50 times longer than its designated lifespan.
And according to a
recent announcement
from NASA's Mars Exploration Program (MEP), the rover managed to survive yet another winter on Mars. Having endured the its eight Martian winter in a row, and with its solar panels in encouragingly clean condition, the rover will be in good shape for the coming dust-storm season. It also means the rover will live to see its 14th anniversary, which will take place on January 25th, 2018.
On Mars, a single year lasts the equivalent of
686.971 Earth days (or 1.88 Earth years). And s
ince Mars' axis is inclined 25.19° to its orbital plane (compared to Earth's axial tilt of just over 23°), Mars also experiences seasons. However, these tend to last about twice as long as the seasons on Earth. And of course, the seasons on Mars' are also much colder, with temperatures averaging about -63 °C (-82°F).
[caption id="attachment_138077" align="aligncenter" width="580"]
Enhanced-color view of ground sloping downward to the right in "Perseverance Valley", taken by the Pancam on the Opportunity rover in October of 2017. Credits: NASA/JPL-Caltech/Cornell Univ./Arizona State Univ
[/caption]
As Jennifer Herman, the power subsystem operations team lead for
Opportunity
at NASA's Jet Propulsion Laboratory, recalled in a NASA MEP
press statement
:
At present, both the
Opportunity
and
Spirit
rover are in Mars' southern hemisphere. Here, the Sun appears in the northern sky during the fall and winter, so the rovers need to tilt their solar-arrays northward. Back in 2004, the
Spirit
rover had lost the use of two of its wheels, and could therefore not maneuver out of a sand trap it had become stuck in. As such, it was unable to tilt itself northward and did not survive its fourth Martian winter (in 2009).
However,
Opportunity'
s current position -
Perseverance Valley
, a fluid-carved region on the inner slope at the edge of the Endeavour Crater - meant that it was well-positioned to keep working through late fall and early winter this year. This was ensured by the stops the rover made at energy-favorable locations, where it would inspect local rocks, examine the valley's shape and image the surrounding area, all the while absorbing ample energy from the Sun.
[caption id="attachment_138076" align="aligncenter" width="580"]
Image of the floor of Endeavour Crater, taken by NASA's Mars Exploration Rover Opportunity on Nov. 11th, 2017, about a week before Opportunity's eighth Martian winter solstice. Credits: NASA/JPL-Caltech/Cornell Univ./Arizona State Univ
[/caption]
Five months ago, the rover entered the top of the valley, which runs eastward down the inner slope of the Endurance Crater's western rim. Since that time,
Opportunity
has been conducting stops between drives at north-facing sites, which are situated along the southern edge of the channel. The rover team calls the sites "lily pads", since these places are spots that the rover need to hop across during its mission.
This is necessary, given that
Opportunity
does not rely on a radioisotope thermoelectric generator like
Curiosity
does. While winter conditions affect the use of electrical heaters and batteries on both rovers,
Opportunity
is different in that it's activities are more subject to seasonal change. Whereas
Curiosity
will simply allocate less energy to performing tasks in the winter,
Opportunity
needs to pick its routes to ensure it stays powered up.
During some of its previous winters, the
Opportunity
rover was not as well-situated as it currently is. During its fifth winter (2011-2012) the rover spent 19 weeks at one spot because no other places that allowed for a northward-facing tilt were available within driving distance. On the other hand, its first winter (2004-2005) was spent in the southern half of the Endurance Crater, where all grounds are favorable since they face north.
As the person who is chiefly responsible for advising other mission scientists on how much energy
Opportunity
has available on each Martian day (sol) for conducting activities like driving and observing - a task she performs for
Curiosity
as well - Herman understand the relationship between power usage and the seasons all too well. "Relying on solar energy for
Opportunity
keeps us constantly aware of the season on Mars and the terrain that the rover is on, more than for
Curiosity,
" she said.
[caption id="attachment_114565" align="aligncenter" width="580"]
A self-portrait of the Opportunity rover shortly after dust cleared its solar panels in March 2014. Credit: NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.
[/caption]
Another factor which can influence
Opportunity
's power supply is how much dust is in the sky and how much of it gets onto the rover's solar arrays. This is highly-dependent on prevailing wind conditions, which can both stir up dust storms and clear away dust deposits on the rover - basically, they are a real mixed blessing! During autumn and winter in the southern-hemisphere, the skies are generally clear where
Opportunity
operates.
Spring and summer is when the storms are most common in Mars' southern hemisphere, though they don't happen every year. The latest example took place in 2007, which led to a severe reduction in the amount of sunlight (and hence, solar energy)
Spirit
and
Opportunity
were able to receive. This required both rovers to enact emergency protocols and reduce the amount of operations and communications they conducted.
The amount of dust on the rover's solar arrays going into autumn can also vary from year to year. This year, the array was dustier than in all but one of the previous Martian autumns it experienced. Luckily, as Herman
explained
, things worked out for the rover:
[caption id="attachment_138078" align="aligncenter" width="580"]
Image of the Opportunity rover's front wheel, taken on June 9th, 2004, inside the Endurance Crater. Credit: NASA/JPL/Cornell
[/caption]
In the coming months, the
Opportunity
team hopes to investigate how the Perseverance Valley was cut into the rim of the Endeavor crater. As Matt Golombek, an Opportunity Project Scientist at JPL,
related
:
With its eighth winter finished and
Opportunity
still in good working order, we can expect the tenacious rover to keep turning up interesting finds on Mars. These include clues about Mars' warmer, wetter past, which likely included a standing body of water in the Endeavor crater. And assuming conditions are favorable in the coming year, we can expect that
Opportunity
will continue to push the boundaries of both science and its own endurance!
Further Reading: NASA
