火星漫游者在这个红色行星的地表下探测到了原始生命的迹象

火星的漫游者好奇号已经在红色行星上发现了一个潜在的生命迹象——这个星球历史上对于甲烷气体的最高水平的测量结果。

地球上,甲烷主要来源于呼出甲烷的微生物。按照NASA的推测,隐藏在火星地壳下面的生物可能也是最近的测量结果的原因。但是现在请别过于兴奋,因为生命不是对于这个发现的唯一的可能解释。NASA指出,甲烷也能够由岩石和水之间的化学反应产生。

“从我们现在的测量结果来看,我们没有方法去判断甲烷的来源是生物还是地质。”位于绿地、马里兰州的NASA戈达德航天中心的主要研究者保罗马哈菲在一项声明中说道。

况且,这个破纪录的甲烷测量结果和地球上的甲烷含量的平均值相比较也显得更逊色。

好奇号测出的火星上的甲烷含量是10亿方分之21(ppb)。相比较而言,地球的甲烷含量接近1860ppb。

好奇号在过去曾经检测到过甲烷,虽然含量比这次要低很多。火星上甲烷含量的平均值接近于10的9次方分之7。可是根据NASA,甲烷含量确实随着季节的变化而升高或降低。这个模式提供了关于甲烷的来源的潜在的证据。在火星的冬季,甲烷含量减少。在夏天,它们的含量再次增多。科学家们知道,在红色行星的地壳底下躺着一层冰。也许在夏季,冰融化了,向火星的大气层释放出原来被困在冰层中的甲烷其气泡(与地球北极地区的冰冻土层在自己融化的同时向大气层释放出甲烷气体相似)。按照NASA的推测,这些甲烷气泡有可能是生命的遗迹。

甲烷不是火星曾经拥有古代生命适宜的环境的唯一证据。在2012年,好奇号与火星一个河床里识别出了存在了30亿年的水的化学痕迹。其后一年,科学家们在由好奇号于相同地点附近采集的岩石样本中认出了生命的一些化学组成部分。

欧洲航天局的微量气体轨道飞行器已经在火星轨道飞行了一年多了,还没有测量出一点甲烷。通过与微量气体轨道飞行器小队合作,NASA的科学家们希望最终解决火星上甲烷的秘密,并找到这种天然气的来源。

本文来自于

Mars Rover Detects Primordial Signs of Life Under the Red Planet’s Surface

By Isobel Whitcomb, Live Science Contributor | June 24, 2019 03:41pm ET

The Mars rover Curiosity has uncovered a potential sign of life on the Red Planet — the planet’s highest-ever measurement of a natural gas called methane.

On Earth, methane primarily comes from microbes, who breathe out the gas. It’s possible that life-forms hiding under Mars’ crust are also responsible for this latest measurement, according to NASA. But don’t get too excited — yet. Life isn’t the only potential explanation for the finding. Methane is also created by chemical reactions between rocks and water, according to NASA. [9 Strange, Scientific Excuses for Why Humans Haven’t Found Aliens Yet]

“With our current measurements, we have no way of telling if the methane source is biology or geology,” principal investigator Paul Mahaffy of NASA’s Goddard Spaceflight Center in Greenbelt, Maryland, said in a statement.

Plus, even this record-high methane measurement pales in comparison with average methane levels on Earth. Curiosity measured methane concentrations of 21 parts per billion (ppb) on Mars. In comparison, Earth’s methane concentrations are close to 1,860 ppb.

Curiosity has detected methane in the past, albeit at much lower concentrations. The average level on Mars is close to 7 ppm. But methane levels do appear to rise and fall seasonally, according to NASA. And this pattern offers a potential clue about the source of the methane. During the Martian winter, concentrations fall. In the summer, they rise once more. Scientists know that beneath the Red Planet’s crust lies a layer of ice. Perhaps, in summer, ice thaws, releasing trapped bubbles of methane into the atmosphere (similar to the way Earth’s arctic permafrost releases methane into the atmosphere as it melts). These methane pockets could be a relic of ancient life, according to NASA.

Methane isn’t the only evidence that Mars was once hospitable to ancient life. In 2012, Curiosity identified chemical traces of 3 billion-year-old water in a Martian streambed. The following year, scientists identified some of the chemical building blocks of life in a rock sample collected by Curiosity near that same site.

The European Space Agency’s Trace Gas Orbiter has been in orbit around Mars for over a year and has yet to measure any methane. By partnering with the Trace Gas Orbiter team, NASA scientists hope to eventually solve the Mars methane mystery and find the source of the natural gas.

火星上的漫游者在红色行星的地表下探测到了生命原始的迹象

火星的漫游者好奇号已经在红色行星上发现了一个潜在的生命迹象——这个星球历史上甲烷气体的最高浓度的测量结果。

地球上,甲烷主要来源于呼出甲烷的微生物。根据NASA,隐藏在火星地壳下面的生物可能也是最近的测量结果的原因。但是现在请别过于兴奋。生命不是对于这个发现的唯一可能的解释。根据NASA,甲烷也能够由岩石和水之间的化学反应产生。

“从我们现在的测量结果来看,我们没有方法去判断甲烷的来源是生物还是地质原因。”位于绿地、马里兰州的NASA戈达德航天中心的主要研究者保罗马哈菲说道。

再说,即使这个破纪录的甲烷测量结果和地球上的甲烷含量的平均值相比较也显得逊色。

好奇号测出的火星上的甲烷含量是10的9次方分之21。相比较而言,地球的甲烷含量接近10的9次方分之1860。

好奇号在过去已经检测到过甲烷,虽然含量比这次要低很多。火星上甲烷含量的平均值接近于10的9次方分之7。可是根据NASA,甲烷含量确实随着季节的变化而升高或降低。这个模式提供了关于甲烷的来源的潜在的证据。在火星的冬季,甲烷含量减少。在夏天,它们的含量再次增多。科学家们知道,在红色行星的地壳底下躺着一层冰。也许在夏季,冰融化了,向火星的大气层释放出原来被困在冰层中的甲烷其气泡(与地球北极地区的冰冻土层在自己融化的同时向大气层释放出甲烷气体相似)。根据NASA,这些甲烷气体有可能是生命的遗迹。

甲烷不是火星曾经拥有古代生命适宜的环境的唯一证据。在2012年,好奇号与火星一个河床里识别出了存在了30亿年的水的化学痕迹。接下来一年,科学家们在由好奇号于相同地点附近采集的岩石样本中认出了生命的一些化学组成部分。

欧洲航天局的微量气体轨道飞行器已经在火星周围的轨道待了一年多了,还没有测量出一点甲烷。通过与微量气体轨道飞行器小队合作,NASA的科学家们希望最终解决火星上甲烷的秘密,并找到这种天然气的来源。

 

本文来自于:

Mars Rover Detects Primordial Signs of Life Under the Red Planet’s Surface

Mars Rover Detects Primordial Signs of Life Under the Red Planet's Surface
NASA’s Curiosity rover has found a sky-high amount of methane while sampling in Mars’ Gale Crater (shown here).

Credit: NASA

The Mars rover Curiosity has uncovered a potential sign of life on the Red Planet — the planet’s highest-ever measurement of a natural gas called methane.

On Earth, methane primarily comes from microbes, who breathe out the gas. It’s possible that life-forms hiding under Mars’ crust are also responsible for this latest measurement, according to NASA. But don’t get too excited — yet. Life isn’t the only potential explanation for the finding. Methane is also created by chemical reactions between rocks and water, according to NASA. [9 Strange, Scientific Excuses for Why Humans Haven’t Found Aliens Yet]

“With our current measurements, we have no way of telling if the methane source is biology or geology,” principal investigator Paul Mahaffy of NASA’s Goddard Spaceflight Center in Greenbelt, Maryland, said in a statement.

Plus, even this record-high methane measurement pales in comparison with average methane levels on Earth. Curiosity measured methane concentrations of 21 parts per billion (ppb) on Mars. In comparison, Earth’s methane concentrations are close to 1,860 ppb.

Curiosity has detected methane in the past, albeit at much lower concentrations. The average level on Mars is close to 7 ppm. But methane levels do appear to rise and fall seasonally, according to NASA. And this pattern offers a potential clue about the source of the methane. During the Martian winter, concentrations fall. In the summer, they rise once more. Scientists know that beneath the Red Planet’s crust lies a layer of ice. Perhaps, in summer, ice thaws, releasing trapped bubbles of methane into the atmosphere (similar to the way Earth’s arctic permafrost releases methane into the atmosphere as it melts). These methane pockets could be a relic of ancient life, according to NASA.

Methane isn’t the only evidence that Mars was once hospitable to ancient life. In 2012, Curiosity identified chemical traces of 3 billion-year-old water in a Martian streambed. The following year, scientists identified some of the chemical building blocks of life in a rock sample collected by Curiosity near that same site.

The European Space Agency’s Trace Gas Orbiter has been in orbit around Mars for over a year and has yet to measure any methane. By partnering with the Trace Gas Orbiter team, NASA scientists hope to eventually solve the Mars methane mystery and find the source of the natural gas.

全火星地下水系统的首个证据

WatersofMars二十年以前,火星曾经是否有过大量储存的液态水的问题依然备受争议。当前,这个讨论变成了对自然和液态水的体积的评估,例如液态水在哪里以及对于在火星上寻找生命(或生命留下来的物质)的努力有什么暗示。欧洲空间局的科学家们已经公布了火星快车对一些位于火星北半球的封闭的坑洞的观测结果。

作为作家中的领袖和荷兰的乌德勒支大学弗兰克林·萨莱斯说道:“早期的火星是一个充满水的世界,但是当该行星扥气候变化时,这些水从地表退回来了,形成了‘地下水 ’和水池。由于水的规模和角色还存争议,因此在这个研究中,我们记录了这些水,而且我们寻找到了火星上首个全星球的地下水系统的地质的证据。”

在从4000米到4500米深的范围内,被撞击出的坑洞的底部显示了只有水的存在下才会形成的特征。变化的深度的发现说明随着时间的变迁,水的高度改变了,并且渐渐降低。

GlobalGroundwater

坑洞中水的高度与人们所猜想的火星海洋里被提议的水的高度在一条直线,这证明了一个位于北方大平原(显示在上面的图中)的全球性大洋曾经覆盖火星北半球的三分之一。另外一种猜测也是可能的,就是至少两个覆盖全球的大洋在不同时期出现过——一个是连绵而辽阔的,存在于这颗行星早期时,另一个是更小、更浅的、不连续的(或者是河湖系统),有可能在大量火山作用或其他地热的活动加热了受困于地表以下的冰块时短时间地存在过。

火星上的地下水系统的存在可与这些假说兼容。火山口湖通过和我们在地球上看到的相同的地下水系统相互联系在一起。这个共同点是为什么我们相信火星长期地拥有显著的液态水的一个主要因素。我们已经找到了一些岩石,这些岩石在地球上的形成依靠液态水的存在和说明水力驱动侵蚀的地形的大规模特征,而水力驱动侵蚀的地形和液态水的存在曾经对改变火星的地貌景观有显著的作用。

在火星的古代时期转变到赫斯珀里亚时期后,这种活动迅速减少,而赫斯帕里亚时期也是火星被相信已经变得比以前干旱很多的时间。挪亚时代后的亚马逊河时期的特点是寒冷,这是现在仍然影响并支配这个星球的寒冷的火星环境。

已知的是大量的冰仍旧存在于这颗行星的北极,一个湖泊被相信依旧残留在南极的冰盖下面,这个湖泊和地球上南极洲中数英里冰层底下 的液态湖相似。任何依然存在于火星上的液态水在这个时候可能被更好地描述成“在火星里”。液体的痕迹会在地表偶尔出现,但是曾经却没有观测到大量的自由流动的水。

相同的团队也发现了5个特定的坑洞,在这几个坑里含有对于地球上生命的起源很普遍的矿物质,包括各种各样的黏土、碳酸盐与硅酸盐。这种流域有可能成为寻找火星上曾经可能存在的生命的主要位置。

本文来源于:

First Evidence of Global Groundwater System Found on Mars

Twenty years ago, the question of whether Mars ever had large reserves of liquid water was still open to debate. Today, the discussion has shifted to an evaluation of the nature and size of those reserves, where they existed, and what this implies for any effort to find life (or the remains of it) on the Red Planet. Scientists with the European Space Agency have released the results of Mars Express’ observation of some 24 deep, enclosed craters in the northern hemisphere of Mars.

“Early Mars was a watery world, but as the planet’s climate changed this water retreated below the surface to form pools and ‘groundwater,’” says lead author Francesco Sales of Utrecht University in the Netherlands. “We traced this water in our study, as its scale and role is a matter of debate, and we found the first geological evidence of a planet-wide groundwater system on Mars.”

The floor of the impact craters showed features that could only have formed in the presence of water, at depths ranging from 4,000 to 4,500 meters. The various depth findings show that the water level changed and receded over time.

The water level in the craters aligns well with the proposed water level in the Mars ocean hypothesis, which argues that a global ocean situated in the Vastitas Borealis (pictured above) once covered the northern third of Mars. It’s also possible that at least two global oceans existed on Mars at different points — one vast and persistent, during the earliest days of the planet, and a smaller, shallower, and less-persistent ocean (or system of rivers and lakes) that may have temporarily existed when vast amounts of volcanism or other geothermal activity heated ice trapped below ground.

The existence of a groundwater system on Mars is compatible with these hypotheses. Crater lakes would have attached to each other through the same types of groundwater systems we see on Earth. Such commonalities are a major component of why we believe Mars supported significant amounts of liquid water for long periods of time. We’ve found rocks whose formation on Earth depends on the presence of liquid water and large-scale features of the terrain that indicate water-driven erosion once played a significant role in weathering the Martian landscape.

The incidence of such activity drops off sharply after Mars’ Noachian period transitions into the Hesperian, which is also when Mars is believed to have become much drier. The Amazonian period that followed the Noachian is characterized by the cold, arid Martian conditions that still dominate the planet today.

Substantial amounts of ice are known to still exist at the planet’s north pole, and a lake is believed to still remain beneath the south polar ice cap, similar to the liquid lakes under miles of ice in Antarctica on Earth. Any liquid water still existing on Mars might be better described as being in Mars at this point, given the depths at which it would be located. Traces of liquid are occasionally found at the surface, but no significant amount of free-running water has ever been observed.

The same team also spotted five specific craters where mineral ingredients believed to be common to the rise of life on Earth also exist, including various clays, carbonates, and silicates. Such basins could be prime locations for searching for the life that may have existed on Mars.

由于尘埃降落到在火星上,机遇号漫游者仍然是失踪的。

         由于操控者正在准备发起联系,因此这个漫游者还没有报到。Opportunity rover still MIA as dust settles on Mars

我们在火星上看到的最大的一次沙尘暴现在正在逐渐结束,给机遇号将快速得到足够的功率 去重新开启和地球的正常联系带来了希望。从六月至今,这个漫游者已经失去了联系,控制者也在准备好去尝试使漫游者回复NASA的深空探测网发送的命令。

和更大的好奇号漫游者不同,机遇号由太阳能供电。当现在的沙尘暴渐渐包围了整个火星的大气层时,为它提供能量的太阳光逐渐变淡。机遇号已经有几个月不能够得到足够的能量去维持在正常的功能,导致它转换到了休眠模式。一旦它经历了这次在6月的转换,这个漫游者就有了足够的功率和地球上的操作人员实现应答了。

基于大气层的状况,那些操作人员预测在不久的未来那个电源很有可能是充足的。可是,这个漫游者的情况会有一些无法把握的事情,这意味着它将不会像预期的那样进行联系。最简单的可能是沙尘暴在漫游者的太阳能控制板上沉积了足够的尘埃,使它一直远离充足电量的程度。那能够把它从睡眠的返回推延到最后一颗尘埃离开大气层,或者甚至造成电量停留在低的状态,直到附近的风清理了控制板。

当然,那一切假设每件事情都在正常地运行。机遇号的电量很有可能降得太低了,以至于它的机载时钟停止运转。如果是那种情况,那么就没有方法去得知这个漫游者什么时候会努力重新连接建立联系。这是操作人员正在准备给它发送命令去建立联系的缘故之一,到了那时就不能等待漫游者去应答了。

在休眠的过程中,一些电量或联络的硬件设备也有可能出故障了。操作者认为漫游者现在待着的位置会保持足够温暖,能使一些主板上加热器将继续维持部件在被估计的温度或其以上,所以问题基本上是部件是旧的而且它们已经在火星上的14年的条件是艰苦的。

在状况好到能使它产生足够的功率以回应后,NASA将持续尝试去联络漫游者45天。如果在那个时段里没有响应,漫游者的操控者将只会再用几个额外的月份来被动地听它。

Opportunity rover still MIA as dust settles on Mars

The rover has not checked in as controllers are getting ready to trigger contact.

One of the largest dust storms we’ve ever seen on Mars is finally winding down, raising hopes that the Opportunity rover will soon be able to obtain enough power to resume normal contact with Earth. At this point, there’s been no contact with the rover since June, and controllers are getting ready to attempt to get the rover to respond to commands sent over NASA’s Deep Space Network.

Unlike the larger Curiosity rover, Opportunity is solar-powered. And as the current dust storm gradually grew to encompass the entirety of Mars’ atmosphere, the sunlight that powered it gradually faded out. For several months, Opportunity hasn’t been getting enough powerto maintain normal function, causing it to shift into a hibernation mode. Once it underwent this shift back in June, the rover has been waiting for enough power to start checking in with its operators here on Earth.

Based on the atmospheric conditions, those operators expect that power is likely to be sufficient in the very near future. There are a number of uncertainties regarding the rover’s condition that could mean it won’t be making contact as expected, however. The simplest possibility is that the storm deposited enough dust on the rover’s solar panels to keep them from reaching sufficient power levels. That could delay its return from hibernation until the last of the dust is out of the atmosphere, or it could even cause the power to stay low until local winds clean the panels off.

All that, of course, assumes everything’s working normally. There’s a good chance that Opportunity‘s power dropped so low that its on-board clock shut down. If that’s the case, then there’s no way of knowing when the rover will try to re-establish contact. That’s one of the reasons that operators are preparing to send it commands to establish contact rather than waiting for the rover to try to check in.

There’s also the chance that some power or communication hardware failed during the hibernation. Operators expect that the location the rover is in will stay warm enough that some small onboard heaters will keep components at or above the temperatures they’re rated for, so the issue is primarily that the components are old and the conditions have been harsh for the 14 years they’ve been on Mars.

NASA will continue attempts to contact the rover for 45 days after the conditions are good enough for it to generate sufficient power to respond. If there’s no response during that period, the rover’s controllers will just passively listen for it checking in for several additional months.

NASA的洞察号着陆器正在红色行星上正式地开展搜寻地震的工作

This image from NASA's InSight Mars lander, taken on Jan. 7, 2019, shows the SEIS seismograph instrument deployed on the Martian surface to measure Marsquakes.

根据建造此地震仪的法国航天局的说法,这个用于叫做SEIS的内部结构地震实验的超级灵敏地震仪已经通过了最初的实验,目前工作正常。

“这是一个具有历史意义的时刻,也是地球物理学重大的希望,”法国航天局的官员正式说道。“美国的NASA在1975年发射的海盗1和海盗2航天飞船上都带着一个地震仪。其中的一个地震仪的功能失效,另一个地震仪安装在舱面上,由于它对风产生的周围的背景噪声过于敏感而没能检测到火星的震动。SEIS是此类仪器中第一个被放置在火星地表上的。”

洞察号着陆器于11月26日在火星上登陆。12月19日,它用像起重机的机器手臂使SEIS在火星的地表上展开。洞察号将迅速地在SEIS地震仪上面安装一个特殊的盖子覆盖住SEIS地震仪之上,以使它免受火星上的风和极端的温度的侵扰。

法国航天局的官员说道,自从NASA的阿波罗17号在月球上登陆后宇航员哈里森·施密特有效地利用那次任务的阿波罗月球表面实验包——一个含有月球地震仪的传感器组件以来,SEIS是第一个开始在另一个世界里成功地开始工作的地震仪。

SEIS由三个钛球体中的超静谧的振动传感器组成,被置于真空中。一个用来给它的系统供电的电子拴绳和加热器在1月6日被配置好。根据法国航天局,SEIS传感器“正在开始记录每分钟的地面移位”。

洞察号的SEIS是这个着陆器将要调动的两个工具中的一个。另外一个是用来挖掘的一个工具,叫做具有热流和物理特性的探头,或者HP3。执行航天任务的科学家们将要利用敏感的地震仪去检测火星震和陨石的撞击、研究火星内部的结构;利用HP3记录着关于热量如何在这个星球的地表里移动的。为了帮助科学家们研究这个行星的震动,洞察号也要做一个无线电实验。

NASA在2018年5月份发射了85千万美元的洞察号着陆器(它的名字是使用地震勘探、测地学和热量转移的简称)。人们期待它能用至少一个火星年——大约两个地球年的时间来研究火星的内部。

NASA’s InSight Lander on Mars Is Now Hunting for Marsquakes

This image from NASA’s InSight Mars lander, taken on Jan. 7, 2019, shows the SEIS seismograph instrument deployed on the Martian surface to measure Marsquakes.

NASA’s InSight Mars lander is officially hunting for quakes on the Red Planet.

The lander’s ultrasensitive seismometer, called the Seismic Experiment for Interior Structure (SEIS), has passed its initial tests and is working working well, according to the French space agency CNES, which built the lander’s instrument.

“This is a historic moment and a great hope for geophysics,” CNES officials said in a statement. “The two U.S. Viking 1 and Viking 2 missions launched by NASA in 1975 were each carrying a seismometer. One failed to function, while the other — fixed to the deck of the lander — was unable to measure Mars’ seismic activity as it was too sensitive to the background noise generated by winds. SEIS is thus the first instrument of its kind to be placed on the surface of the Red Planet.” [NASA’s InSight Mars Lander: Full Coverage]

The InSight lander touched down on Mars Nov. 26 and used its crane-like robotic arm to deploy the SEIS instrument on the Martian surface on Dec. 19. On Jan. 1, InSight celebrated the new year by testing the seismograph, CNES officials said. InSight will soon deploy a special cover over the SEIS instrument to protect it from the Martian wind and extreme temperatures.

SEIS is the first seismometer to successfully begin work on another world since NASA’s Apollo 17 moon landing in 1972, when astronaut Harrison Schmitt deployed a that mission’s Apollo Lunar Surface Experiments Package — a sensor suite that included a lunar seismometer, CNES officials said. SEIS is made up of three ultraprecise seismic sensors surrounded by a vacuum inside a titanium sphere. An electronic tether to power its systems and heaters was deployed on Jan. 6, and the SEIS sensors “are beginning to record minute ground displacements.” according to CNES.

InSight’s SEIS instrument is one of two tools the lander will deploy on the surface of Mars. The other is a burrowing tool called the Heat Flow and Physical Properties Probe, or HP3. Mission scientists will use the sensitive seismometer to detect Marsquakes, meteorite impacts and to study the structure of the interior of Mars, with the HP3 tool recording observations on how heat moves through the planet’s surface. InSight also carries a radio experiment to help scientists study the planet’s wobble.

NASA launched the $850 million InSight lander (its name is short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) in May 2018. It is expected to study the interior of Mars for at least one Martian year, which is about the equivalent of two Earth years.

NASA的火星好奇号着陆器发现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,发现它的孔隙度原来所想的要更大。

一个科考队设法改变了一个监测运动状况的设备的用途,该设备帮助NASA的好奇号漫游者导航,它被改造后应用于测量这颗红色行星重力场的变化范围。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,夏普山是一个奇异的山丘,该着陆器一直在盖尔陨坑的中央探索它。

“这个研究有一点像此类型中的第一个。”霍普金斯大学研究报告的作家凯文路易斯说道。“它是在地球和月球之外另一个的行星中第一个引力测线。

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,由于航天飞船离火星地表太远而不能拍摄到一张精细的图像。所以即使好奇号漫游者已经在这颗红色星球上待了六年多了,科学家和工程师们一起工作,主要给好奇号提供一个新的仪器。

就像路易斯解释的一样,引力只不过是加速度。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常用的加速度一样——既可以用来航行,也可以用来得知车的方向。因此,通过使用着陆器的加速计,这个团队能够测量来自各处地下岩层的重力“牵引”。

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。

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。

“如果你在月亮上用一个望远镜观察火星,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一次性地充满沉积物。”

因此,当好奇号的重力数据表明这个想法是根本不可能的时候,人们都极其惊讶。这是因为即使那里石头的密度极其小,它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,那么就像路易斯所说的那样,样式中的孔隙就会在数吨的石头下面,基本上被挤扁。

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,引出了‘盖尔陨坑的历史以及远古时期火星赤道上的环境状况是怎样的’这个谜团。”与之不同的是,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,这又是在此类尺度上的又一次科技演示,并可以在未来对火星的地表下面提供全新的洞察力。”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。

本文来源于:

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.
curiosity1

This 2016 Curiosity rover selfie shows the vehicle at the “Okoruso” drilling site on Mount Sharp’s Naukluft Plateau. The Martian scene is a mosaic of images taken with the arm-mounted Mars Hands Lens Imager (MAHLI).

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.

火星上的气候是什么样的?

NASA的一个新机器人正在冒着极端气温的风险去学习有关这颗红色行星的知识。

InSight at work on the Martian surface.

         NASA的一个前往火星的新任务将第一次提供火星每天的气候报告,而现在火星上物体的严寒完全是另一个级别。依据这个任务的网站,目前为止,已记录的温度最高达到15华氏度,最低下降到零下149华氏度。

         洞察号着陆器这个机器人真可怜——它必须待在那里并记录那些令人憎恶的寒流。这个着陆器位于火星赤道北边的埃律西昂平原,NASA称此平原为“一个平坦的、光滑的平面”。根据NASA,洞察号是第一个对所谓火星的“内宇宙空间”进行彻底的研究的机器人,这个研究叫做“它的地壳、地幔和地核”,而洞察号则表示运用地震侦查、测地学和热量转移的火星内部探索。该航天局说,这个研究能够帮助确认火星和其他多岩石的行星——诸如金星、水星和我们的地球是如何在跨越40亿年中形成的。用表明其名称的工具时,这个着陆器将测量这个行星上“维持生命所必需的痕迹”——它的脉搏、反射作用和温度——这每个测量对象能告诉我们火星的构成以及它和地球的构成有什么不同。

An Australian dust devil, which likely has nothing on one of its Martian counterparts.

          这个着陆器使用一组叫做辅助负载子系统的传感器来对火星的气候作出评估,不仅允许我们在这里、在上跟随着此次任务,而且也帮助科学家们改善他们的研究。火星温度的波动能歪曲陆器的地震仪和热量探测器的测量结果,因此持续记录例如气压和风等数据能帮助科学家们判断火星镇是否真得正在发生,或者仪器只是在从不相关的变化中记录“噪音”。辅助负载子系统将在每个火星日——被称为太阳日的每秒钟测量大气压、气温、风和磁场,持续至少两个地球年,允许足够的时间去解释季节的变化。(一个太阳日大约有24小时39分钟长。)

          这个气压传感器在记录低压的旋风——被认为是小尘暴的时证明自己很有用,而小尘暴在火星的地表留下了清晰可见的条痕。根据一个印刷所出版的,我们确实在地球上看见了小尘暴,但是火星尘暴的变化范围却更加壮观——记录的高度在36英里之间,有时甚至达到直径超过300英尺的高度。

         该任务并不标志科学家们第一次作为火星的气象学家,可是它将提供一个外行星领域宽广的气候报告,这个报告也有可能从根本上帮助我们学习到更多关于我们的星球的知识。

本文来源于:

What’s the Weather Like on Mars?

A new NASA robot is braving extreme temperatures to learn about the Red Planet.

A NEW NASA MISSION TO the Red Planet will, for the first time, provide a daily weather report from Mars, where things right now are a whole other level of cold. So far, according to the mission’s website, recorded temperatures have maxed out at 15 degrees Fahrenheit and dipped as far as 140 degrees below zero.

So pity the InSight lander, the robot that has to sit there and register these abominable chills. The lander is located at Elysium Planitia, what NASA calls “a flat, smooth plain” just north of the planet’s equator. InSight—which stands for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport—is, according to NASA, the first robot to conduct an in-depth study of Mars’s so-called “inner space”: “its crust, mantle, and core.” This research, the agency said, can help establish how Mars and other rocky planets—like Mercury, Venus, and our very own—formed over four billion years ago. Using the tools indicated in its name, the lander will measure the planet’s “vital signs”: its pulse, its reflexes, and its temperature—each of which can teach us about Mars’s composition, and how it compares to Earth’s.

The lander uses a group of sensors called the Auxiliary Payload Subsystem (APSS) to take stock of the planet’s weather, allowing us to follow along with the mission from here on Earth while also helping the scientists sharpen their research. Mars’s temperature swings can distort measurements taken by the lander’s seismometer and heat probe, so continuously tracking things such as air pressure and wind can help scientists determine whether a “marsquake” is actually occurring, or whether the instruments are simply recording “noise” from unrelated changes in the weather. APSS will be measuring the air pressure, air temperature, wind, and magnetic field for every second of every Martian day—known as a sol—for at least two Earth years, allowing enough time to account for seasonal variations. (One sol runs for approximately 24 hours and 39 minutes.)

The air pressure sensors have also proven useful in tracking low-pressure whirlwinds known as “dust devils,” which have left visible streaks on the planet’s surface. While we do see our own dust devils on Earth, the Martian variety are, according to a press release, far more imposing—registering heights of between three and six miles and, sometimes, diameters of more than 300 feet.

This mission does not mark the first time that scientists have taken on the role of Martian meteorologists, but it will provide a newly extensive extraterrestrial weather report that, ultimately, may help us learn more about our own planet, too.

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.

液态水“河”在火星上被揭示

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研究人员已经在火星上发现了大量现存的液态水域的证据。

他们相信,这是一个坐落在这颗行星南极的冰冠底下的湖泊,它大概有20公里(12英里)宽。

以前的研究发现了在火星地表漂浮着的、断断续续的、液态水的可能迹象,但是这是当今在火星上的第一个持续出现的水域的迹象。

那些如被NASA好奇号探测器发现的河床显示,在过去,水在火星的地表上是存在的。

不过,后来这个星球的气候由于它薄薄的大气层已经变冷了,使大部分水封锁在冰里。

这个结果特别令人兴奋,因为科学家已经用了很长时间来寻找火星上现有的液态水的迹象,可是它们亦或没有寻找到液态水,亦或产生了不明确的发现。它也将会使那些正在研究地球以外生命的可能的人们感兴趣——虽然这个结果还没有提高寻找生命的堵住。它将会激起那些正在研究地外生命可能性的人们的兴趣 – 虽然它对寻找生命还没有真正的贡献(还没发挥作用)。

这个发现是通过使用欧洲航天机构的火星快捷轨道飞行器的雷达系统Marsis去完成的。

“它有可能不是一个非常大的湖泊。”来自意大利国家天体物理学机构的罗伯特·奥罗赛教授说,他领导这个研究。

Marsis不能够确定那层水有可能有多厚,但这个研究队估计它最小有1米。

“这真的称得上是一个水域。一个湖泊,而不是在地球特定的冰川上充溢在岩石和冰之间的融水”奥罗赛教授补充道。

火星上的水域是怎么被找到的呢?

诸如Marsis这样的雷达系统通过发出一个信号并且检查什么东西反射了回来,去检测这颗行星的地表和附近的次表层。

雷达上部持续的白色线条

在白线底下,研究人员在冰下面1.5公里处发现了不同寻常的东西。

“在浅蓝色中你可以看到从底部来的反射比从表层来的反射要强烈。对我们而言,这对水的存在来讲,是能够说明问题的迹象。”奥罗赛教授说道。

这对生命而言意味着什么?

现在来讲还没有确切的东西。

来自开放大学的马尼什·帕特尔博士解释道:“我们早已经知道,火星的地表对生命是不适于居住的,就如我们知道的一样。因此,现在在火星上寻找生命是在次表层。”

“这是我们不被有害的射线照到的地方。这里能够让我们得到足够的保护。这里的温度和压强上升到更有利的高度。最重要的是,这使得对生命来讲至关重要的液态水的存在成为可能。”

“跟踪水”这个原则是太空生物学的关键——太空生物学是对地球以外潜在的生命的研究。

所以,尽管这个调查发现说明水是现在就有的,它们没有证明任何更深入的东西。

“我们没有更加接近于真正的探测到生命,”帕特尔博士告诉BBC新闻。“但是这个调研结果所能做的,是给予我们在火星上寻找水的位置范围。这就像是一个宝藏地图——除了在这种情况下将会有大量在点上做X的记号。”

水的温度和化学性质也能对任何潜在的火星生物造成一定的困难。

为了在如此冷的条件下保持着液体的状态(研究团队估计在它接触上边的冰的地方温度有零下30摄氏度到零下10摄氏度)这里的水很有可能含有大量溶解进里面的盐。

“可信的是,这里的水有可能是极其寒冷的、浓缩的盐水。这对生命而言是很有挑战性的。”一位来自英国圣安德鲁斯的天体物理学家克莱尔博士的表兄解释说。

我们接下来要做什么?

虽然它的存在为那些对火星上过去或现在生命的可能性感兴趣的人们提供了令人激动的设想,这个湖泊的特征必须先通过进一步的研究来被核实。

“现在需要做的”来自开放大学的玛特·巴尔梅博士解释道,“是在其他地域重复这个测量出来的尺寸,用来寻找相似的信号,如果可能,为了使其他的解释方法被解释——可以指望——把一些解释方法排除掉。”

科学家们在之前已经宣布,他们在南极洲的沃斯托克湖被埋藏的深处里发现了细菌的生命,但是在火星上挖掘的确会促进并形成一个既耗资也耗时的工程。

“到达那里并且得到最终的证据去说明这的确是一个湖泊,这将不是一个简单的任务。”奥罗赛教授说道。

“它将会需要在那里飞行一个能够向1.5公里厚的冰里挖掘的机器人。这一定将会需要一些科技的发展,而此时此刻这是无法得到的。”

Researchers have found evidence of an existing body of liquid water on Mars.

What they believe to be a lake sits under the planet’s south polar ice cap, and is about 20km (12 miles) across.

Previous research found possible signs of intermittent liquid water flowing on the martian surface, but this is the first sign of a persistent body of water on the planet in the present day.

Lake beds like those explored by Nasa’s Curiosity rover show water was present on the surface of Mars in the past.

However, the planet’s climate has since cooled due to its thin atmosphere, leaving most of its water locked up in ice.

The result is exciting because scientists have long searched for signs of present-day liquid water on Mars, but these have come up empty or yielded ambiguous findings. It will also interest those studying the possibilities for life beyond Earth – though it does not yet raise the stakes in the search for biology.

The discovery was made using Marsis, a radar instrument on board the European Space Agency’s (Esa) Mars Express orbiter.

“It’s probably not a very large lake,” said Prof Roberto Orosei from the Italian National Institute for Astrophysics, who led the study.

Marsis wasn’t able to determine how thick the layer of water might be, but the research team estimate that it is a minimum of one metre.

“This really qualifies this as a body of water. A lake, not some kind of meltwater filling some space between rock and ice, as happens in certain glaciers on Earth,” Prof Orosei added.

How was it found?

Radar instruments like Marsis examine the surface and immediate subsurface of the planet by sending out a signal and examining what is bounced back.

The continuous white line at the top of the radar results above marks the beginning of the South Polar Layered Deposit; a filo pastry-like accumulation of water ice and dust.

Beneath this, researchers spotted something unusual 1.5km under the ice.

“In light blue you can see where the reflections from the bottom are stronger than surface reflection. This is something that is to us the telltale sign of the presence of water,” says Prof Orosei.

What does this mean for life?

Nothing definitive. Yet.

Dr Manish Patel from the Open University explained: “We have long since known that the surface of Mars is inhospitable to life as we know it, so the search for life on Mars is now in the subsurface.

“This is where we get sufficient protection from harmful radiation, and the pressure and temperature rise to more favourable levels. Most importantly, this allows liquid water, essential for life.”

This principle of following the water is key to astrobiology – the study of potential life beyond Earth.

So while the findings suggest water is present, they don’t confirm anything further.

“We are not closer to actually detecting life,” Dr Patel told BBC News, “but what this finding does is give us the location of where to look on Mars. It is like a treasure map – except in this case, there will be lots of ‘X’s marking the spots.”

The water’s temperature and chemistry could also pose a problem for any potential martian organisms.

In order to remain liquid in such cold conditions (the research team estimate between -10 and -30 Celsius where it meets the ice above), the water likely has a great many salts dissolved in it.

“It’s plausible that the water may be an extremely cold, concentrated brine, which would be pretty challenging for life,” explained Dr Claire Cousins, an astrobiologist from the University of St Andrews, UK.

What next?

While its existence provides a tantalising prospect for those interested in the possibility of past or present life on Mars, the lake’s characteristics must first be verified by further research.

“What needs to be done now,” explained Dr Matt Balme from the Open University, “is for the measurements to be repeated elsewhere to look for similar signals, and, if possible, for all other explanation to be examined and – hopefully – ruled out.

“Maybe this could even be the trigger for an ambitious new Mars mission to drill into this buried water-pocket – like has been done for sub-glacial lakes in Antarctica on Earth,” he added.

Scientists have previously claimed to find bacterial life in the buried depths of Antarctica’s Lake Vostok, but drilling on Mars would make for an ambitious project indeed.

“Getting there and acquiring the final evidence that this is indeed a lake will not be an easy task,” said Prof Orosei.

“It will require flying a robot there which is capable of drilling through 1.5km of ice. This will certainly require some technological developments that at the moment are not available.”

宇航员在火星上发现幽灵沙丘

环绕着火星飞行的机器人轨道飞行器已经得到了幽灵沙丘的照片。它们是一些坑洞,科学家们相信在那里曾经出现过这个红色荒漠世界里的高大月牙形沙丘。

火星是一个荒漠般的星球,非常像地球上的一些沙漠,但是比地球寒冷很多。火星的沙漠拥有大量的沙丘,从小沙丘到高耸的、峭壁般的、被细腻的沙粒覆盖的沙丘。但是——虽然大量种类的沙丘已经从轨道飞行器和火星漫游者里看见了,最近仍然十分活跃,正在逐步成为火星的风景——现在另外一种沙丘也在火星上被发现了。科学家们把它们称作幽灵山丘,它们极其古老。他们在2018年7月10日的«地球空间»里报告了这个发现。新的研究论文刚刚在地球物理研究杂志中发表。

这些沙丘在今天并不是活跃的沙丘。更确切地说,它们是以前古老的沙丘在其被侵蚀后留下来的、在地上像坑洞般的洼地。大量这样新月形的坑洞被发现了,每个大约有美国国会大厦那么大。西雅图华盛顿大学的行星地貌学家、做新研究的作家麦肯齐·戴解释道:

这些坑洞的任意一个都不足以告诉你那是一个沙丘或者它是从覆盖着大片古老沙丘的地方来的。可是当你将它们放在一起时,它们有太多火星上和地球上的沙丘的共同点以至于你必须运用一些极好的解释方法来去说明它们不仅仅只是沙丘。

幽灵沙丘是怎样形成的呢?在地球上,幽灵沙丘有可能已经部分地被熔岩或者用水传播的泥沙掩埋。对于这种火星的幽灵沙丘,当岩浆或泥沙变硬时,它们保持沙丘的轮廓。然后,沙丘剩下的上部就会被风侵蚀并将其冲刷走,只留下原来的沙丘“模型”般的轮廓。现在它们看起来像有着坚固边缘的坑洞。

火星上这些沙丘的存在对它很久以前是什么样的状况提供了更多的证据,特别是风。正如戴指出的:

关于幽灵沙丘的一件很酷的事情是它们能够确切地告诉我们火星上的风在形成时的古老过去是和现在截然不同的。那时的风与现在的不同,这一事实告诉我们火星上的环境状况在长时间里不是一成不变的,在过去的20亿年中它们已经改变了,我们需要知道这些事情去解释火星上的地质。

火星幽灵沙丘是人们在希腊平原流域和诺克提斯迷宫的轨道照片中被发现的。它们和2016年在爱达荷州东部发现的蛇江平原相似。戴和合著者大卫·凯特林仅仅在轨道里拍的诺克提斯迷宫的图片中就发现有多于480个潜在的幽灵沙丘模型,在希腊平原上的轨道图片发现有多于300个的沙丘模型。诺克提斯迷宫是一个在太阳系已知最大的峡谷,位于水手号谷西部混乱无序的高原区域。希腊平原是一个位于火星南半球的巨大火山口。它跨越的距离多于1678英里(2700公里)。它的年龄为40亿,是撞击而成的。

火星上的幽灵沙丘的形状是月牙形,就像地球上的新月形沙丘,这意味着原来的沙丘可能会和火星和地球上最普遍的类型新月形沙丘很相像。月牙形的“角”或尖端指着盛行风的方向。这种沙丘往往会在几乎或完全没有植被的平坦地势上形成。每个地点都有那么多坑洞的事实预示着:它们是曾经活跃的沙丘场的遗迹。正如戴指出的:

因为沙丘都是在同一个风的体系里形成、移动,所以你会预料到沙丘都是朝同一个方向的。因此形状和大小就能告诉我们这些是它们来自于远古的沙丘系统的特点。

对火星上幽灵沙丘的分析表明原始的沙丘是很庞大的——在诺克提斯迷宫里大约有130英尺(40米)高,在希腊平原上的大约有246英尺(75米)高。通过比较,好奇号探测器在盖尔撞击坑的夏普山山脚附近研究了一系列的沙丘。纳米布沙丘大概有16英尺(5米)高。

沙丘除了提供极关于火星上古老的环境状况,它们也可能是一个寻找过去生命证据极好的地方。正如在新论文的概要中提到的:

火星上两处古老的沙丘被部分地掩埋,然后被风侵蚀而去,留下保留关于古老环境信息的沙丘状的洞穴。这些坑洞的边缘有可能含有古老沙丘的砂岩,能够成为一个寻找古代生命的证据的好地方。洞穴的形状也告诉我们以前的风是如何运动的。

正如戴也指出的:

我们知道地球上的沙丘能够维持生命,而且地球上的沙丘和火星上的很相似。有一个问题是火星有的但是地球没有的,这是地表的辐射。如果你在一个沙丘里面或者它的底部,而且你是一个有微生物特征的生命,那个沙丘正在保护你接触过多的辐射。现在,有可能没有任何东西生活在那个地方。可是如果火星上曾经有过什么东西,这是一个比普通的地方更好的观察地点。

最下面的一行:沙丘不仅在地球上很常见,它们也被在火星、金星、土星最大的卫星泰坦,甚至在格拉西缅科彗星上。现在另外一种沙丘被人们在火星上发现——形如洞穴的古老‘鬼沙丘’。它们曾经是活跃,大部分都是被侵蚀的沙丘的遗迹。它们和今天的沙丘有极强的相似性,甚至有可能拥有这颗红色行星过去生命的证据。

本文出处:Astronomers find ‘ghost dunes’ on Mars

Robot orbiters circling Mars have acquired images of ghost dunes. They’re pits where, scientists believe, tall crescent-shaped sand dunes once existed on this red desert world.

Mars is a desert planet, a lot like some deserts on Earth, but much colder. Also just like Earth, the Martian deserts have vast dunes, ranging from small sand ripples (technically not dunes) to towering, cliff-like true dunes of fine sand. But – while various types of dunes have been seen from orbit and up close by Mars rovers, currently still active and gradually making their way across the landscape – now another kind of dune has been found on Mars as well. Scientists call these ghost dunes, and they are very ancient. They reported the finding in GeoSpace on July 10, 2018. The new research paper was just published in the Journal of Geophysical Research: Planets.

These ghost dunes are not active dunes today. Rather, they are the remains of previous ancient dunes that left pit-like depressions in the ground after they eroded away. Hundreds of these crescent-shaped pits have been discovered, each about the size of the U.S. Capitol building. As Mackenzie Day, a planetary geomorphologist at the University of Washington in Seattle and an author of the new study, explained:

Any one of these pits is not enough to tell you that it’s a dune, or from an ancient dune field, but when you put them all together, they have so many commonalities with dunes on Mars and on Earth that you have to employ some kind of fantastic explanation to explain them as anything other than dunes.

How do ghost dunes form? On Earth, ghost dunes may have been partially buried by lava or water-borne sediments. For these Martian ghost dunes, when the lava or sediments hardened, they preserved the contours of the dunes. The remaining top portions of the dunes were then eroded away by winds, which scoured them out, leaving only the “mold” outlines of the former dunes. Now they look like pits with hardened edges.

These dunes’ existence on Mars provide more clues as to what conditions were like billions of years ago, in particular, winds. As Day noted:

One of the cool things about the ghost dunes is that they tell us, for sure, that the wind on Mars was different in the ancient past, when they formed. The fact that the wind was different [when the ghost dunes formed] tells us that the environmental conditions on Mars aren’t static over long time scales, they have changed over the past couple billion years, something we need to know to interpret the geology on Mars.

The Martian ghost dunes were found in orbital images of Hellas Planitia basin and Noctis Labyrinthus. They are similar to ones discovered in the Snake River Plain in eastern Idaho in 2016. More than 480 potential dune molds were discovered in orbital images of Noctis Labyrinthus alone, and more than 300 in Hellas Planitia, by Day and co-author David Catling. Noctis Labyrinthus is a region of jumbled plateaus just west of Valles Marineris, the largest-known canyon in the solar system. Hellas Planitia is a massive 4-billion-year-old impact crater over 1,678 miles (2,700 km) across in the southern hemisphere.

The shapes of the ghost dunes on Mars are crescents, just like barchan dunes on Earth, meaning that the original dunes would have been very similar to barchan dunes, the most common type on both Mars and Earth. The “horns” or tips of the crescents point in the direction of the prevailing wind. This type of dunes tends to form on flat terrain where there is little or no vegetation. The fact that there are so many of these pits in each location points to them being the remains of once-active dune fields. As Day noted:

They are all going the same way, which you would expect for dunes because they are all migrating and forming in the same wind regime. So just the shape and size tell us that these are features that are coming from an ancient dune system.

Analysis of the ghost dunes on Mars indicates that the original dunes were quite large – about 130 feet (40 meters) tall at Noctis Labyrinthus and 246 feet (75 meters) tall at Hellas basin. By comparison, the Curiosity rover has studied a series of dunes near the base of Mount Sharp in Gale Crater. The striking Namib Dune is about 16 feet (5 meters) tall.

As well as providing fascinating clues about ancient environmental conditions on Mars, these ghost dunes may also be a good place to search for evidence of past life. As mentioned in the summary in the new paper:

Ancient dunes in two places on Mars were partially buried and then eroded away, leaving behind dune-shaped pits that preserve information about the ancient environment. These pits may contain ancient dune sandstones around the edges of the pits and could be a good place to look for evidence of ancient life. The shapes of the pits also tell us how the winds behaved in the past.

And as Day noted also:

We know that dunes on Earth can support life, and dunes on Earth are very similar to dunes on Mars. One problem that Mars has that Earth doesn’t is the surface radiation. If you are inside a dune, or at the bottom of a dune, and you are microbial life, the dune is protecting you from a lot of that radiation. There is probably nothing living there now. But if there ever was anything on Mars, this is a better place than average to look.

Bottom line: As well as being common on Earth, dunes have also been found on Mars, Venus, Titan and even comet 67P. Now another type of dune has been discovered on Mars – “ghost dunes,” the pit-like remains of ancient, once-active dunes which have mostly eroded away. They bear a strong similarity to present-day dunes and may even hold clues to past life on the red planet.