NASA的火星好奇号着陆器寻找到关于神秘的夏普山的证据。

通过对好奇号的一个航行工具进行改进,科学家们已经分析了着陆器下面的岩石的密度,发现它比原来想象的要更潮湿。

一个科考队改变了一个监测运动状况的设备的用途,并将其应用于测量这颗红色行星重力的变化范围。在这个过程中,科学家们发现着陆器底下的岩石比原来认为的要有更多的小孔。这提供了神秘的夏普山的形成的一些证据。夏普山是这个着陆器已经在盖尔陨坑的中央探索过的奇异山丘。

“这个研究是这个类型中的第一个。”霍普金斯大学研究报告的作家凯文路易斯说道。“它是除了地球和月球之外的行星中第一个引力侧线。”

在地球上,地质学家通常用这类仪器来研究潜藏在地下的岩石。但是在火星上,研究者只能从绕轨道飞行的航天飞船上获得这种重力的数据,而航天飞船离火星地表太远以至于不能拍摄到一张精细的图像。所以科学家和工程师们一起工作,主要是给好奇号一个新的一起——即使他已经在这颗红色星球上待了六年多了。

就像路易斯解释的一样,引力只是加速度。好奇号配备有加速计——就像用在苹果手机和其他电子产品上面的——既可以用来航行,也可以用来得知车的方向。因此,通过运用着陆器的加速计,这个团队能够测量从地表底下的岩层传来的变化的重力拖船。

从亚丽桑大立州大学毕业的一个队员特拉维斯加布里埃尔在一封电子邮件中说道:“引力的测量……给这个行星上一块特别的区域提供一个放大镜。这就是地表上重力的测量在地球地质的工具腰带中是一个主要工具的原因。”所以,通过将好奇号发送去爬位于火星的盖尔陨坑中间一个高3英里(高5公里)的夏普山,这个团队能够发现这个地区的密度以及夏普山在过去是怎样的形成的。

火星的地质情况

在过去,研究者们认为盖尔陨坑的底部在很久以前有可能埋藏在数英里的岩石下面。

“如果你从一个望远镜中观察月亮,你会注意到在大多数大型坑洞中央的小山峰——盖尔陨坑也是一样的。但是盖尔陨坑中的山峰比个的边缘要更高。这导致科学家们相信他曾经充满沉淀。”

因此,当好奇号的重力数据表明这个想法是不可能的时,简直就是一个惊讶。这是因为那里石头的密度极其小,即使里面实际的矿物质很稠密。这意味着岩石中充溢着使其变得多孔的空洞。

如果盖尔陨坑曾经被充溢到边缘上,那么岩石中的那些小孔就会被挤出。就像路易斯所说的,在数吨的石头下面。

加布里埃尔补充说:“我们现在认为盖尔陨坑只是部分地被充满了,提供了‘盖尔陨坑的历史以及远古时期火星赤道上的环境状况’这一关键板块。”相反地,这个团队认为在更暖和的时候,风可能已经把残骸吹到坑里;在寒冷的夜晚中,风又使残骸被吹到坑外,在数百万年里逐渐形成夏普山。

这可能不将是我们最后一次听说到好奇号新的重力设备。“在我们的分析中,我们也证实了这个加速计检测火星上的地震的能力,而这又是在此类尺度上的另一个科技证明,并可以在未来给火星的地表下面提供全新的洞悉。”加布里埃尔补充道。

这个研究将会于2月1日(周五)发表在杂志《科学》中。

NASA’s Mars Curiosity rover finds clues about mysterious Mount Sharp

By tweaking one of Curiosity’s navigational tools, scientists have analyzed the density of the rock beneath the rover, finding it’s more porous than previously thought.

By Chelsea Gohd  |  Published: Friday, February 01, 2019

A team of researchers managed to repurpose a movement-detecting device that helps NASA’s Curiosity rover navigate and use it to measure variations in the Red Planet’s gravitational field. In the process, the scientists discovered that the rocks beneath the rover are more porous than previously suspected. This offers clues into the mysterious formation Mount Sharp, a strange hill the rover has been exploring in the center of Gale Crater.

“This study is a little bit of the first of its kind,” said study author Kevin Lewis of Johns Hopkins University. “It’s the first gravity traverse on the surface of another planet other than the Earth and the moon.”

On Earth, geologists commonly use such instruments to study rocks lurking beneath the surface. But on Mars, researchers could only get this kind of gravity data from orbiting spacecraft, which are too far away to get a detailed picture. So scientists and engineers worked together to essentially give Curiosity a new scientific instrument — even after more than six years on the Red Planet.

As Lewis explains, gravity is really just acceleration. And Curiosity is equipped with accelerometers — like the ones commonly used in iPhones and other electronics — which are used both to drive and get the vehicle’s orientation. So, by using the rover’s accelerometers, the team was able to measure varying gravitational “tugs” from subsurface rock layers.

“Gravity measurements … provide a magnifying lens into one particular area of the planet’s subsurface,” Travis Gabriel, a team member and graduate student at Arizona State University, said in an email. “This is why surface measurements of gravity are a staple tool in an Earth geologist’s toolbelt.” So, by sending Curiosity to climb Mount Sharp, a 3-mile-tall (5-km-tall) mountain in the middle of Mars’ Gale crater, the team was able to uncover the density of the area’s rocks and how Mount Sharp likely formed.

Martian geology

In the past, researchers thought the floor of Gale Crater was probably buried beneath miles of rock long ago.

“If you look through a telescope at the moon, you’ll notice central peaks in most of the large craters – Gale Crater is no different,”Gabriel said. “However, (Gale’s) central peak stands taller than the crater’s rim, which leads scientists to believe it was filled to the brim with sediments at one time.”

So it came as a surprise when Curiosity’s gravity data showed this idea just isn’t possible. That’s because the rocks there have a surprisingly low density, even though the actual minerals in the rocks are fairly dense. This implies the rocks are riddled with empty pockets that make them porous.

If Gale Crater had ever been filled to the brim, those pores in the rocks would have been essentially “squished out,” as Lewis put it, beneath tons of rock.

“We think Gale Crater was filled only partially, providing a critical piece of the puzzle that is the history of Gale crater and the ancient environmental conditions at the equator of Mars,” Gabriel added. Instead, the team suggests winds may have blown debris into the crater in the warmer day hours and out of the crater during the cold night, gradually forming Mount Sharp over many millions of years.

And this probably won’t be the last time we hear about Curiosity “new” gravity instrument. “In our analysis, we also demonstrated the capacity of the accelerometers to measure martian earthquakes, which is yet another technology demonstration with these units and can provide new insights in the subsurface of Mars in the future,” Gabriel added.

The research will be published in the journal Science on Friday, Feb. 1.

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