余存火星大气仍在变化中

标签:
杂谈 |
分类: 科学与技术 |
2013.04.10

美国航空航天局火星漫游车好奇号上的桅杆相机(Mast Camera)拍摄的拼接图像显示了经过白平衡调色的夏普山(Mount Sharp),天空颜色超蓝,但地势清晰
华盛顿——火星已经失去了原有的大部分大气,但美国航空航天局(NASA)火星漫游车“好奇号”(Curiosity)最近的发现表明,余存大气仍然相当活跃。
美国航空航天局4月8日的新闻简报表示,漫游车团队成员当天在维也纳(Vienna)举行的2013年欧洲地球科学联盟大会(European Geosciences Union 2013 General Assembly)上报告了各种发现。
4月份更强有力的证据表明,[火星]气体从大气层顶的逐渐脱离导致火星失去大部分原有大气。
在4月1日那一周,好奇号火星样本分析(Sample Analysis at Mars)仪通过浓缩提取气体程序分析了一份火星大气样本。分析结果提供了有史以来最精确的火星大气中氩同位素的测量数据。同位素是具有不同原子量的同一元素变体。
密歇根大学安阿伯分校(University of Michigan, Ann Arbor)参加火星样本分析的研究员苏什尔•阿特莱雅(Sushil Atreya)说:“可以说,我们发现了火星大气受损最明确、最强有力的特征。”
火星样本分析发现,火星大气中较轻的稳定同位素(氩-36)大约是较重的氩-38含量的四倍。这消除了来自1976年美国航空航天局维京项目(Viking Project)和从火星陨石中提取的少量氩气所得的测量数据对于火星大气比率的不确定性。按照太阳和木星氩同位素测量的估计数据,火星这一比率比太阳系的原始比率要低得多。这表明火星上发生的过程使较轻的同位素比较重的同位素损失更大。
好奇号使用西班牙提供的漫游车环境监测站(Rover Environmental Monitoring Station)测量当今火星大气的多项变量。虽然自从八个月前开始测量以来,火星的日常气温呈稳步升高,并且与漫游车的位置无密切关联,但漫游车所经不同地方的湿度明显不同。这些是首次对火星湿度的系统测量数据。
盖尔陨坑(Gale Crater)内未发现尘暴痕迹,但漫游车环境监测站传感器在执行使命最初的100个火星日期间检测到许多旋风模式,不过没有早些时候的使命在同样的时间长度内检测到的那么多。马德里(Madrid)天体生物学中心(Centro de Astrobiología)漫游车环境监测站的首席研究员哈维尔•戈梅斯-埃尔维拉(Javier Gómez-Elvira)说:“旋风发生在几秒钟内,十分快速,应该结合压力、温度和风力振荡进行验证,有时候还要考虑紫外线辐射的减少。”
好奇号的激光发射化学摄像(Chemistry and Camera)仪已经检测了由风吹散的尘埃。瞄准每个目标的初始激光脉冲都击中尘埃。激光的能量清除尘埃,暴露底层物质,但初始激光脉冲也提供了有关尘埃的信息。
法国图卢兹(Toulouse)天体物理学和行星研究所(Institut de Recherche en Astrophysique et Planétologie)化学摄像副首席研究员(ChemCam Deputy Principal Investigator)西尔维斯特•莫里斯(Sylvestre Maurice)说:“我们知道,火星因尘埃中含有铁氧化物而呈红色。化学摄像揭示了火星尘埃中复杂的化学成分,包括可能以羟基或水分子形式存在的氢。”
漫游车上的组合仪器分析了火星大气和地面之间可能的水分子交换,包括中子动态反照率测量仪(Dynamic Albedo of Neutrons)。此仪器在中子动态反照率首席研究员伊戈尔•米特罗法诺夫(Igor Mitrofanov)的领导下由俄罗斯提供。
在4月余下的日子,好奇号将执行日常项目,这些项目指令已在3月用中子动态反照率测量仪、漫游车环境监测站和辐射评估探测器(Radiation Assessment Detector)发送给好奇号。在四个星期中,从地球角度看,当火星绕到接近太阳背面时,好奇号不会收到新的指令。这种几何轨迹大约每26个月出现一次,被称为火星合日(Mars Solar Conjunction)。
位于帕萨迪纳市(Pasadena)的加州理工学院(California Institute of Technology)火星科学实验室项目(Mars Science Laboratory Project)的科学家约翰•戈洛辛格(John Grotzinger)说:“火星合日后,好奇号将凿钻其现在所在之处的另一块岩石,但目标尚未选定。科学团队将在火星合日期间就此进行讨论。”
美国航空航天局的火星科学实验室项目正利用好奇号来研究盖尔陨坑内的环境历史,火星科学实验室项目发现盖尔陨坑的条件很久以前适合微生物生存。好奇号2012年8月携带10种科学仪器登陆火星,开始执行为期两年的重要使命。美国航空航天局的喷气推进实验室(Jet Propulsion Laboratory)是加州理工学院的分部,为位于华盛顿的美国航空航天局科学项目理事会(Science Mission Directorate)管理这一项目。
有关好奇号使命的更多信息,可见美国航空航天局网站: http://www.jpl.nasa.gov/msl, http://www.nasa.gov/msl 和 http://mars.jpl.nasa.gov/msl。您也可以在脸谱网(Facebook)和推特(Twitter)上关注好奇号使命进展。
Read more: http://iipdigital.usembassy.gov/st/chinese/article/2013/04/20130410145534.html#ixzz2QDtDgB63
Remaining Martian Atmosphere Still Dynamic
09 April 2013
This mosaic of images from the Mast Camera (Mastcam) on NASA’s Mars rover Curiosity shows Mount Sharp in a white-balanced color adjustment that makes the sky look overly blue but shows the terrain.
Washington — Mars has lost much of its original atmosphere, but what’s left remains quite active, recent findings from NASA’s Mars rover Curiosity indicate.
Rover team members reported diverse findings April 8 at the
European Geosciences Union 2013 General Assembly, in Vienna, NASA
said in a news release the same day.
Evidence has strengthened during April that Mars lost much of its
original atmosphere by a process of gas escaping from the top of
the atmosphere.
Curiosity’s Sample Analysis at Mars (SAM) instrument analyzed an
atmosphere sample the week of April 1 using a process that
concentrates selected gases. The results provided the most precise
measurements ever made of isotopes of argon in the Martian
atmosphere. Isotopes are variants of the same element with
different atomic weights.
“We found, arguably, the clearest and
most robust signature of atmospheric loss on Mars,” said Sushil
Atreya, a SAM co-investigator at the University of Michigan, Ann
Arbor.
SAM found that the Martian atmosphere has about four times as much
of a lighter stable isotope (argon-36) compared to a heavier one
(argon-38). This removes previous uncertainty about the ratio in
the Martian atmosphere from 1976 measurements from NASA’s Viking
project and from small volumes of argon extracted from Martian
meteorites. The ratio is much lower than the solar system’s
original ratio, as estimated from argon-isotope measurements of the
sun and Jupiter. This points to a process at Mars that favored
preferential loss of the lighter isotope over the heavier
one.
Curiosity measures several variables in today’s Martian atmosphere
with the Rover Environmental Monitoring Station (REMS), provided by
Spain. While daily air temperature has climbed steadily since the
measurements began eight months ago and is not strongly tied to the
rover’s location, humidity has differed significantly at different
places along the rover’s route. These are the first systematic
measurements of humidity on Mars.
Trails of dust devils have not been seen inside Gale Crater, but
REMS sensors detected many whirlwind patterns during the first
hundred Martian days of the mission, though not as many as detected
in the same length of time by earlier missions. “A whirlwind is a
very quick event that happens in a few seconds and should be
verified by a combination of pressure, temperature and wind
oscillations and, in some cases, a decrease in ultraviolet
radiation,” said REMS Principal Investigator Javier Gómez-Elvira of
the Centro de Astrobiología, Madrid.
Dust distributed by the wind has been examined by Curiosity’s
laser-firing Chemistry and Camera (ChemCam) instrument. Initial
laser pulses on each target hit dust. The laser’s energy removes
the dust to expose underlying material, but those initial pulses
also provide information about the dust.
“We knew that Mars is red because of iron oxides in the dust,” said
ChemCam Deputy Principal Investigator Sylvestre Maurice of the
Institut de Recherche en Astrophysique et Planétologie in Toulouse,
France. “ChemCam reveals a complex chemical composition of the dust
that includes hydrogen, which could be in the form of hydroxyl
groups or water molecules.”
Possible interchange of water molecules between the atmosphere and
the ground is studied by a combination of instruments on the rover,
including the Dynamic Albedo of Neutrons (DAN), provided by Russia
under the leadership of DAN Principal Investigator Igor
Mitrofanov.
For the rest of April, Curiosity will carry out daily activities
for which commands were sent in March, using DAN, REMS and the
Radiation Assessment Detector (RAD). No new commands are being sent
during a four-week period while Mars is passing nearly behind the
sun, from Earth’s perspective. This geometry occurs about every 26
months and is called Mars solar conjunction.
“After conjunction, Curiosity will be drilling into another rock
where the rover is now, but that target has not yet been selected.
The science team will discuss this over the conjunction period,”
said Mars Science Laboratory Project Scientist John Grotzinger, of
the California Institute of Technology, Pasadena.
NASA’s Mars Science Laboratory Project is using Curiosity to
investigate the environmental history within Gale Crater, a
location where the project has found that conditions were long ago
favorable for microbial life. Curiosity, carrying 10 science
instruments, landed in August 2012 to begin its two-year prime
mission. NASA’s Jet Propulsion Laboratory, a division of Caltech in
Pasadena, manages the project for NASA’s Science Mission
Directorate in Washington.
For more about the mission, visit these NASA websites: http://www.jpl.nasa.gov/msl, http://www.nasa.gov/msl and http://mars.jpl.nasa.gov/msl . You can also follow the
mission on Facebook and on
Twitter.
Read more: http://iipdigital.usembassy.gov/st/english/article/2013/04/20130409145452.html#ixzz2QDtHpdFZ