Universe Today
It's been a time of milestones for Mars rovers lately! Last month (on
January 26th, 2018
), NASA announced that the
Curiosity
rover had spent a total of
2,000 days on Mars
, which works out to 5 years, 5 months and 21 days. This was especially impressive considering that the rover was only intended to function on the Martian surface for 687 days (a little under two years).
But when it comes to longevity, nothing has the
Opportunity
rover beat! Unlike
Curiosity,
which relied on a
Multi-Mission Radioisotope Thermoelectric Generator
(MMRTG) for power, the solar-powered Opportunity
recently witnessed
its five-thousandth sunrise on Mars. This means that the rover has remained in continuous operation for 5000 sols, which works out to 5137.46 Earth days.
This five-thousandth sunrise began on Friday, Feb. 16th, 2018 - roughly 14 Earth years (and 7.48 Martian years) after the rover first landed. From its position on the western rim of the Endeavour Crater, the sunrise appeared over the basin's eastern rim, about 22 km (14 mi) away. This location, one-third of the way down "Perseverance Valley", is more than 45 km (28 mi) from
Opportunity's
original landing site.
[caption id="attachment_136596" align="aligncenter" width="580"]
Mosaic view looking down from inside the upper end of "Perseverance Valley" on the inner slope of Endeavour Crater's western rim. Credit: NASA/JPL/Cornell/Marco Di Lorenzo/Ken Kremer/kenkremer.com
[/caption]
This is especially impressive when you consider that the original science mission was only meant to last 90 sols (92.47 Earth days) and NASA did not expect the rover to survive its first Martian winter. And yet, the rover has not only survived all this time, it continues to send back scientific discoveries from the Red Planet. As John Callas, the Opportunity Project Manager at NASA's Jet Propulsion Laboratory, explained in a NASA
press release
:
For instance, the rover has provided us with 225,000 images since its arrival, and revealed that ancient Mars was once home to extensive groundwater and surface water. Beginning in 2008, it began working its way across the Endeavour Crater in order to get a glimpse deeper into Mars' past. By 2011, it had reached the crater's edge and confirmed that mineral-rich water once flowed through the area.
At present, researchers are using
Opportunity
to investigate the processes that shaped Perseverance Valley, an area that descends down the slope of the western rim of Endeavour Crater. Here too,
Opportunity
has learned some fascinating things about the Red Planet. For instance, the rover has conducted observations of possible "rock stripes" in the valley, which could be indicative of its valley's origin.
[caption id="attachment_138579" align="aligncenter" width="580"]
Textured rows on the ground in this portion of "Perseverance Valley" are under investigation by NASA's Mars Exploration Rover Opportunity. Credits: NASA/JPL-Caltech
[/caption]
These stripes are of interest to scientists because of the way they resemble rock stripes that appear on mountain slopes here on Earth, which are the result of repeated cycles of freezing and thawing on wet soil. On Mauna Kea, for example, soil freezes every night, but is often dry due to the extreme elevation. This causes soils that have high concentrations of silt, sand and gravel to expand, pushing the larger particles up.
These particles then form stripes as they fall downhill, or are moved by wind or rainwater, and cause the ground to expand less in this space. This process repeats itself over and over, creating a pattern that leads to distinct stripes. As
Opportunity
observed, there are slopes within the Perseverance Valley where soil and gravel particles appear to have formed into rows that run parallel to the slope, alternating between rows that have more and less gravel.
In the case of the Perseverance Valley's stripes, scientists are not sure how they formed, but think they could be the result of water, wind, downhill transport, other processes, or a combination thereof. Another theory posits that features like these could be the result of changes in Mars tilt (obliquity) which happen over the course of hundreds of thousands of years.
During these periods, Mars' axial tilt increases to the point where water frozen at the poles will vaporize and become deposited as snow or frost nearer to the equator. As Ray Arvidson, the Opportunity Deputy Principal Investigator at Washington University,
explahttps://www.nasa.gov/feature/jpl/long-lived-mars-rover-opportunity-keeps-finding-surprisesined
:
[caption id="attachment_138581" align="aligncenter" width="580"]
Stone stripes on the side of a volcanic cone on Mauna Kea, Hawaii, which are made of small rock fragments that are aligned downhill. These are formed when freeze-thaw cycles lift them out of the finer-grained regolith and move them to the sides, forming stone stripes. Credits: Washington University in St. Louis/NASA
[/caption]
Having the chance to investigate these features is therefore quite the treat for the
Opportunity
science team. "Perseverance Valley is a special place, like having a new mission again after all these years." said Arvidson. "We already knew it was unlike any place any Mars rover has seen before, even if we don't yet know how it formed, and now we're seeing surfaces that look like stone stripes. It's mysterious. It's exciting. I think the set of observations we'll get will enable us to understand it."
Given the state of the Martian surface, it is a safe bet that wind is largely responsible for the rock stripes observed in Perseverance Valley. In this respect, they would be caused by sand blown uphill from the crater floor that sorts larger particles into rows parallel to the slope. As Robert Sullivan, an Opportunity science-team member of Cornell University,
explained
:
Despite being in service for a little over 14 years, and suffering its share of setbacks,
Opportunity
is once again in a position to reveal things about Mars' past and how it evolved to become what it is today. Never let it be said that an old rover can't reveal new secrets! If there's one thing
Opportunity
has proven during its long history of service on Mars, it is that the underdog can make some of the greatest contributions.
Further Reading: NASA
,
NASA (2)
