火星漫游者已经展开

NASA（美国国家航空航天局）的飞船“勇气”号已经降落在火星表面将要开始它的使命

火星漫游者“勇气”号将要开始对这颗红色行星进行探险，它成功地于星期四上午在火星表面展开。

它的第一个目标是位于着陆地点东北大约250米处的一个无名环形山。流星碰撞所产生的低气压应该已经暴露了比“勇气”号着陆地点大的古谢夫(Gusev)环形山更早更原始的岩石。科学家希望它包含能证明古谢夫曾经是一个被水灌满的湖的矿石，这就是寻找火星上生命的第一步。

“我们会小心地靠近，” 康乃尔大学的史蒂夫·斯库里斯(Steve Squyres)、“勇气”号上科学设备的首席调查员说。越过环形山的嘴唇可能会被证明是一项挑战。

“勇气”号在过去的10天中一直在为这趟实地旅行做准备。由于其中的一个用于保护飞船的安全气囊在着陆时没有完全把气放光，因此漫游者只能慢慢地横着身子把自己移到一个更好的位置以便离开登陆仓平台。在过去的几年中，NASA的科学家已经在沙箱里进行了500多次的模拟着陆演习。

他们还使用了“勇气”号传回的照片重构了它的外维虚拟环境, (因此得以) 练习操纵(这个)装置在地形中行动。这些模拟在“勇气”号的冒险活动中还在继续。

“勇气”号的所有的科学设备已经展开，它的全景照相机已经拍摄了一些照片。登陆仓和漫游者之间有一条最后的脐带（一个炸药闸刀将会切断它），这是一条用于提供电力和数据传输的电缆。“我们已经松开了我们的联系并且即将开始漫游。”JPL飞行主管克里斯·列维奇(Chris Lewicki)说。

寻找水

“勇气”号上装备有一台可以在岩石上钻5毫米微型钻机，一台尘埃收集器以及一系列能够决定矿物的结晶结构以及元素构成的工具。它的红外照相机已经探测到了土壤中的痕量的碳酸盐和硅酸盐，直接暗示着湖底的沉积物可能就是由它们形成的。

位于科罗拉多州Boulder的西南研究所的空间科学家马克·布洛克(Mark Bullock)解释说这些碳酸盐可能形成了覆盖在尘埃粒子上的一薄层水。他说如果你正在搜寻能够养育生命的条件的证据，你就需要找到数目可观的矿石，这些矿石只能够在一池水里才能形成，比如方解石晶体。

但是至今，布洛克对于“勇气”号传回的地形照片还是感到迷惑。“这是一块非常平坦的区域，几乎没有岩石。在我看来，这不太像湖床。”他说。他还补充说，这些小岩石不太像散开的残骸，虽然有人曾经认为它们可能是。

玛丽亚·祖柏(Maria Zuber)是一位麻省理工的地球物理学家，帮助绘制了“勇气”号的着陆地点的地图，她同意这块区域当凑近看时不太像在轨道上看时那样像湖床这样一种观点。“问题在于，由于地球上没有保存了40亿年的古代湖床，因此我们无法将它和地球上的比较。”她说。

祖柏说最能证明古谢夫曾经是湖泊的方法莫过于在岩石中找到沉积物的层理。为此，“勇气”号可能将需要接近大约3千米以外的一系列山脉，在那儿在岩石的纵剖面上可能可以看到层理。但是那个距离是漫游者的设计行驶距离的5倍。工程师们不愿意把登陆仓降落得离那些山更近一些是因为那样会增大意外地撞上山的可能性。“我不能告诉你我们即将到达这些山，”斯库里斯说，“但是我们正在向它们移动。”

这个185千克的漫游者将在接下来的两天内到达那个小的环形山。它的最高速度是每秒5厘米，但是由于程序设定了每10秒停下来评估一下它的位置，因此实际前进速度要慢得多。

NASA预期在到达环形山24小时以内会得到“勇气”号的第一份土壤分析结果，48小时以内会得到第一份岩石数据。“勇气”号的姐妹，“机遇”号，将于1月24号降落在火星的另一侧。■

Mars rover rolls out Mark Peplow

NASA’s craft Spirit has hit the dirt and is set to go.  

The Mars rover Spirit is set to begin its exploration of the red planet, having successfully rolled out onto the Martian surface Thursday morning.

Its first target is a nameless crater that lies about 250 metres northeast of the landing site. The depression, created by a meteor impact, should have exposed rock that is older and more pristine than that in the larger Gusev crater that Spirit landed in. Scientists hope it will contain minerals that prove water once filled Gusev — the first step in the search for life on Mars.

"We'll be careful as we approach," says Steve Squyres of Cornell University, principal investigator for the science instruments on Spirit. Going over the lip of a crater could prove a challenge.

Spirit has spent the past ten days preparing for its field trip. One of the airbags that protected the craft as it landed did not fully deflate, so the rover had to slowly edge itself into a better position to leave the lander platform. NASA scientists rehearsed the roll-off manoeuvre in a sandbox mock-up more than 500 times over the past few years.

They have also used Spirit's photos to create a virtual 3-D replication of its environment, and have been practising manoeuvring the craft through that terrain. Those simulations will continue as Spirit rolls off on its adventure.

All of Spirit's scientific instruments have unfolded, and its panoramic camera has already taken some shots. An explosive guillotine has severed the final umbilicus between the rover and the lander — a cord that provided a boost of power and allowed for data flow. "We've cut loose our ties and we're ready to rove," says JPL flight director Chris Lewicki.

Searching for water

Spirit comes equipped with a tiny drill that can bore 5 mm into rock, a dust collector and an array of tools that can determine the crystal and elemental structure of minerals. Its infrared camera has already detected traces of carbonates and silicates in the soil, a tantalizing hint that they may have formed as sediments in the bottom of a lake.

Space scientist Mark Bullock of the Southwest Research Institute in Boulder, Colorado, explains that these carbonates could have formed in the thin films of water that coat dust particles. If you're looking for evidence of conditions that could foster life, you need to find sizeable chunks of minerals, such as calcite crystals, that could only have formed in pools of water, he says.

But Bullock is puzzled so far by Spirit's pictures of the terrain. "It's a very uniform field of little rocks. It doesn't look much like a lake bed to me," he says. The tiny rocks don't look like scattered debris, he adds, which is what one might expect.

Maria Zuber, a geophysicist at the Massachusetts Institute of Technology who helped map Spirit's landing site, agrees that the area looks less like a lake bed from close up that it did from orbit. "The trouble is, there are no pristinely preserved 4-billion-year-old lake beds on Earth that we can compare it with," she says.

The best proof that Gusev once held a lake would be to find sedimentary layering in the rock, says Zuber. To see that, Spirit would probably need to get close to a range of hills about three kilometres away, where layering might be visible in vertical planes of rock. But that's five times as far as the rover was designed to drive. Engineers were reluctant to land the craft closer to the hills as it would have increased the chance of accidentally crashing into them. "I cannot tell you we're going to reach those hills," says Squyres. "But we're going to go towards them."

The 185-kg rover should reach the small crater within the next two days. It has a top speed of 5 cm per second, but will actually make much slower progress as it is programmed to stop every 10 seconds to reassess its location.

    NASA expects to have Spirit's first soil readings within 24 hours of reaching the crater, and the first rock data within about 48 hours. Spirit's sister craft, Opportunity, is due to land on the opposite side of Mars on 24 January.