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NASA mission detects first seismic waves traveling through the center of Mars
When quakes rumbled on Mars and a meteorite smacked into the red planet during the past four years, NASA’s InSight lander collected soundwaves that helped reveal secrets of the Martian interior.
During these events, InSight detected for the first time seismic waves traveling through the Martian core. Now, scientists have used the lander’s data to determine that Mars has a liquid iron-alloy core that also includes lightweight elements such as sulfur and oxygen, as well as smaller amounts of hydrogen and carbon.
Developing a greater understanding of the Martian interior can help scientists learn more about how rocky planets such as Earth and Mars form, how the two planets differ, and the factors that help make other planets habitable for life.
A study detailing the findings was published Monday in the journal Proceedings of the National Academy of Sciences.
“In 1906, scientists first discovered the Earth’s core by observing how seismic waves from earthquakes were affected by traveling through it,” said study coauthor Vedran Lekic, associate professor of geology at the University of Maryland, College Park, in a statement. “More than a hundred years later, we’re applying our knowledge of seismic waves to Mars. With InSight, we’re finally discovering what’s at the center of Mars and what makes Mars so similar yet distinct from Earth.”
Planetary core offers clues on evolution
Earth has a liquid outer core and a solid inner core, but the Martian core appears to be made entirely from liquid. Mars’ core is also slightly denser and smaller than scientists believed, with a radius of approximately 1,106 to 1125 miles (1,780 to 1,810 kilometers).
“You can think of it this way; the properties of a planet’s core can serve as a summary about how the planet formed and how it evolved dynamically over time,” said study coauthor Nicholas Schmerr, associate professor of geology at the University of Maryland, College Park in a statement.
“The end result of the formation and evolution processes can be either the generation or absence of life-sustaining conditions. The uniqueness of Earth’s core allows it to generate a magnetic field that protects us from solar winds, allowing us to keep water. Mars’ core does not generate this protective shield, and so the planet’s surface conditions are hostile to life.”
Mars currently lacks a magnetic field, but there are traces of magnetism that linger in the Martian crust. The traces lead scientists to believe that Mars likely once supported a potentially habitable environment, but evolved over time to become an inhospitable frozen desert.
“It’s like a puzzle in some ways,” Lekic said. “For example, there are small traces of hydrogen in Mars’ core. That means that there had to be certain conditions that allowed the hydrogen to be there, and we have to understand those conditions in order to understand how Mars evolved into the planet it is today.”
Initially, the InSight mission, the first to study the interior of Mars, was only supposed to last for about two years. But NASA extended the mission for another two years.
“The extra mission time certainly paid off,” said lead study author Dr. Jessica Irving, senior lecturer in Earth sciences at the University of Bristol in the United Kingdom, in a statement.
“We’ve made the very first observations of seismic waves travelling through the core of Mars. Two seismic signals, one from a very distant marsquake and one from a meteorite impact on the far side of the planet, have allowed us to probe the Martian core with seismic waves. We’ve effectively been listening for energy travelling through the heart of another planet, and now we’ve heard it.”
The InSight mission continued to collect data about Mars until the very end, falling silent in December 2022 after dust blocked its solar panels from receiving necessary sunlight. But the treasure trove of data the lander collected during four years on the Martian surface has changed the way scientists understand the red planet.
“InSight will continue to influence how we understand the formation and evolution of Mars and other planets for years to come,” Lekic said.
注释：
meteorite: n
表示" 陨石；流星"，means "stony or metallic object that is the remains of a meteoroid that has reached the earth's surface"，如：He discovered an unusual meteorite. 他发现了一块奇异的陨石。
smack: v
表示" 用掌击；拍打"，means " strike sb with the open hand;slap"，如：Don't you dare smack my children! 你敢掴我的孩子!
alloy: n
表示" 合金"，means " a metal that consists of two or more different metals mixed together"，如：Brass is an alloy of copper and zinc. 黄铜是铜和锌的合金。
trove: n
表示" 贵重发现物；珍藏品"，means "treasure of unknown ownership found hidden (usually in the earth"，如：Mogao Grottoes is a veritable treasure trove of cultural relics.莫高窟还是一座名副其实的文物宝库。
中文简要说明：
过去4年来，美国航天总署（NASA）透过「洞察号」（InSight）着陆器，搜集到许多关于火星地震的数据，藉此解开火星核心的秘密，证实火星缺乏磁场，不利生命生存。这项研究的结果发表在最新一期《美国国家科学院院刊》（Proceedings of the National Academy of Sciences，PNAS）。
美国有线新闻网（CNN）报导，自从2018年「洞察号」降落在火星以来，已经观测到上千次火星震，包括2021年12月24日因流星撞击，引起震度高达4级的地震。透过分析这些震波通过火星核心的时间，研究人员估算出火星具有一个液态的铁合金核心，其中包括硫和氧等轻质元素，以及少量的氢和碳。
马里兰州大学地质学副教授莱基克（Vedran Lekic）说，「1906年，科学家透过观察地震穿过地心的波动，首次发现了地球的核心。」「100多年后，我们把地震波的知识应用在火星上……终于发现火星看似像地球，实际上两者却存在极大的差异。」
研究指出，地球是由一个液态外核和固态内核组成，但火星的核心似乎完全是液态的，半径大约介于1,780至1,810公里之间，体积比科学家过去预估的来得小，密度也更高。
此外，地心的独特性使它可以产生磁场，保护地球免受太阳风的伤害，同时把水留在地表。而火星的地壳虽然也存在磁力的痕迹，但随着时间的推移，现在火星的核心已无法产生磁场，因此火星表面变成了荒凉、冰冻的沙漠，不再适合生命居住。
这项研究的共同作者、马里兰州大学地质学副教授史梅尔（Nicholas Schmerr）说，「从一个星球的核心，可以看出它是如何形成，以及如何随时间动态演变。」尽管人类移民火星的可能性微乎其微，但科学家认为，了解火星的组成和演化方式，仍有助于增进我们对宇宙的理解，进而找到可能存在生命的行星。
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