To avoid patches of knife-edged rocks, the mission has taken an alternative path up Mount Sharp.
NASA’s Curiosity Mars rover spent most of March climbing the “Greenheugh Pediment” – a gentle slope capped by rubbly sandstone. The rover briefly summited this feature’s north face two years ago; now on the pediment’s southern side, Curiosity has navigated back onto the pediment to explore it more fully.
But on March 18, the mission team saw an unexpected terrain change ahead and realized they would have to turn around: The path before Curiosity was carpeted with more wind-sharpened rocks, or ventifacts, than they have ever seen in the rover’s nearly 10 years on the Red Planet.
Ventifacts chewed up Curiosity’s wheels earlier in the mission. Since then, rover engineers have found ways to slow wheel wear, including a traction control algorithm, to reduce how frequently they need to assess the wheels. And they also plan rover routes that avoid driving over such rocks, including these latest ventifacts, which are made of sandstone – the hardest type of rock Curiosity has encountered on Mars.
The team nicknamed their scalelike appearance “gator-back” terrain. Although the mission had scouted the area using orbital imagery, it took seeing these rocks close-up to reveal the ventifacts.
“It was obvious from Curiosity’s photos that this would not be good for our wheels,” said Curiosity Project Manager Megan Lin of NASA’s Jet Propulsion Laboratory in Southern California, which leads the mission. “It would be slow going, and we wouldn’t have been able to implement rover-driving best practices.”
为了避免出现刀锋状的岩石，该任务选择了另一条通往夏普山的道路。
美国国家航空航天局的好奇号火星探测车在三月份的大部分时间里都在攀登“格林黑格山麓”——一个由碎石砂岩覆盖的缓坡。两年前，火星车简要总结了这一特征的北面；现在，在山墙的南面，好奇号又回到了山墙上，对它进行了更全面的探索。
但在3月18日，任务团队看到前方的地形发生了意想不到的变化，意识到他们将不得不掉头：好奇号之前的道路上覆盖着比他们在火星上近10年来所见过的更多的风蚀岩石。
在任务的早些时候，这些事实破坏了好奇号的车轮。从那时起，罗孚工程师找到了减缓车轮磨损的方法，包括牵引力控制算法，以减少他们需要评估车轮的频率。他们还计划了漫游者路线，以避免驶过这些岩石，包括这些最新的岩石，它们是由砂岩制成的，这是好奇号在火星上遇到的最坚硬的岩石类型。
该团队将其鳞状外观命名为“鳄鱼背”地形。虽然该任务使用轨道图像对该地区进行了侦察，但需要近距离观察这些岩石才能揭示事实。
“从好奇号的照片中可以明显看出，这对我们的车轮不好，”负责此次任务的南加州NASA喷气推进实验室的好奇号项目经理梅根·林说。“这将是一个缓慢的过程，我们将无法实施路虎驾驶最佳实践。”
The gator-back rocks aren’t impassable – they just wouldn’t have been worth crossing, considering how difficult the path would be and how much they would age the rover’s wheels.
So the mission is mapping out a new course for the rover as it continues to explore Mount Sharp, a 3.4-mile-tall (5.5-kilometer-tall) mountain that Curiosity has been ascending since 2014. As it climbs, Curiosity is able to study different sedimentary layers that were shaped by water billions of years ago. These layers help scientists understand whether microscopic life could have survived in the ancient Martian environment.
Why Greenheugh?
The Greenheugh Pediment is a broad, sloping plain near the base of Mount Sharp that extends about 1.2 miles (2 kilometers) across. Curiosity’s scientists first noticed it in orbital imagery before the rover’s landing in 2012. The pediment sticks out as a standalone feature on this part of Mount Sharp, and scientists wanted to understand how it formed.
It also sits nearby the Gediz Vallis Ridge, which may have been created as debris flowed down the mountain. Curiosity will always remain in the lower foothills of Mount Sharp, where there’s evidence of ancient water and environments that would have been habitable in the past. Driving across about a mile (1.5 kilometers) of the pediment to gather images of Gediz Vallis Ridge would have been a way to study material from the mountain’s uppermost reaches.
“From a distance, we can see car-sized boulders that were transported down from higher levels of Mount Sharp – maybe by water relatively late in Mars’ wet era,” said Ashwin Vasavada, Curiosity’s project scientist at JPL. “We don’t really know what they are, so we wanted to see them up close.”
The Road Less Traveled
Over the next couple weeks, Curiosity will climb down from the pediment to a place it had previously been exploring: a transition zone between a clay-rich area and one with larger amounts of salt minerals called sulfates. The clay minerals formed when the mountain was wetter, dappled with streams and ponds; the salts may have formed as Mars’ climate dried out over time.
“It was really cool to see rocks that preserved a time when lakes were drying up and being replaced by streams and dry sand dunes,” said Abigail Fraeman, Curiosity’s deputy project scientist at JPL. “I’m really curious to see what we find as we continue to climb on this alternate route.”
Curiosity’s wheels will be on safer ground as it leaves the gator-back terrain behind, but engineers are focused on other signs of wear on the rover’s robotic arm, which carries its rock drill. Braking mechanisms on two of the arm’s joints have stopped working in the past year. However, each joint has redundant parts to ensure the arm can keep drilling rock samples. The team is studying the best ways to use the arm to ensure these redundant parts keep working as long as possible.
鳄鱼背上的岩石并非不可逾越——考虑到这条路有多困难，以及它们会使漫游者的车轮老化多少，它们根本不值得穿越。
因此，随着探测器继续探索夏普山，该任务正在为其绘制一条新路线。夏普山是一座3.4英里（5.5公里）高的山，好奇号自2014年以来一直在攀登。当它爬升时，好奇号能够研究数十亿年前由水形成的不同沉积层。这些层有助于科学家了解在古代火星环境中，微观生命是否能够存活。
为什么是格林豪斯？
格林黑格山麓是夏普山底部附近的一片宽阔、倾斜的平原，宽约1.2英里（2公里）。好奇号的科学家们在2012年探测器着陆前的轨道图像中首次发现了它。山墙在夏普山的这一部分作为一个独立的特征突出，科学家们想了解它是如何形成的。
它还坐落在格迪兹-瓦利斯山脊附近，这可能是由于泥石流从山上滚落而形成的。在夏普山（Mount Sharp）较低的山麓地带，人们的好奇心将一直存在，那里有证据表明古代的水和环境在过去是可以居住的。开车穿过山麓约一英里（1.5公里）的地方，收集格迪兹-瓦利斯山脊的图像，是研究该山最上游材料的一种方式。
“从远处看，我们可以看到汽车大小的巨石从夏普山的更高层向下移动——可能是在火星湿润时代的相对晚些时候被水冲下的，”好奇号在JPL的项目科学家阿什温·瓦萨瓦达（Ashwin Vasavada）说。“我们真的不知道它们是什么，所以我们想近距离观察它们。”
这条路人迹罕至
在接下来的几周里，“好奇号”将从山麓爬到它之前一直在探索的地方：一个粘土丰富的地区和一个含有大量盐类矿物硫酸盐的地区之间的过渡地带。粘土矿物是在山上比较潮湿、布满溪流和池塘时形成的；这些盐分可能是随着火星气候的逐渐干涸而形成的。
“看到保存了一段时间的岩石真的很酷，当时湖泊正在干涸，取而代之的是溪流和干燥的沙丘，”好奇号喷气推进实验室的副项目科学家阿比盖尔·弗雷曼说。“我真的很好奇，当我们继续沿着这条备用路线攀登时，我们会发现什么。”
好奇号的车轮将在更安全的地面上行驶，因为它离开了鳄鱼背地形，但工程师们正在关注月球车携带凿岩机的机械臂的其他磨损迹象。在过去的一年里，手臂两个关节上的制动装置已经停止工作。然而，每个接头都有多余的零件，以确保钻臂能够保存钻孔岩石样本。该团队正在研究使用手臂的最佳方法，以确保这些冗余部件尽可能长时间地工作。
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