A 1,000-mile cloud on Mars may reveal physics never seen in nature

Every morning during the Martian spring and summer, a thin and extremely long cloud emerges, only to disappear again. The wispy formation appears near the volcano Arsia Mons and gradually elongates until it reaches over 1,000 miles—about the distance from New York to Kansas City as the crow flies—before dissipating. This cycle then repeats for several months.

在火星的春季和夏季，每天早晨都会出现一朵细长且极长的云，随后又消失不见。这种纤细的云层出现在阿尔西亚山（Arsia Mons）附近，并逐渐拉长，直到延伸超过1000英里（大约是从纽约到堪萨斯城的直线距离），然后消散。这个周期会持续数月之久。

Since it was first recorded by a probe in 2018, scientists have been unable to find a plausible explanation for the existence of this cloud, often referred to as the Arsia Mons Elongated Cloud (AMEC). Until now. Recently, researchers successfully modeled the cloud’s formation for the first time, their results suggesting that it may be driven by a physical process that has never been directly observed in any planet’s atmosphere.

自2018年探测器首次记录到这一现象以来，科学家们一直无法为这朵通常被称为“阿尔西亚山延伸云”（AMEC）的云层找到合理的解释。直到现在，研究人员首次成功模拟了该云层的形成过程，结果表明它可能是由一种在任何行星大气层中都从未被直接观测到的物理过程所驱动的。

“We found that we needed to include some exotic physics… physics that, while included in textbooks, is treated as theoretical and usually thought not to happen in nature. It certainly hasn’t been seen in action before,” Jorge Hernández-Bernal, a planetary scientist at Paris’ Sorbonne Université and lead author of the study, said in a press release. “Once we included this physics in our simulations, the AMEC emerged just as we hoped.”

“我们发现需要引入一些奇异的物理学……这些物理学虽然被写进教科书，但通常被视为理论，且被认为不会在自然界中发生。它肯定从未在实际中被观测到过，”巴黎索邦大学的行星科学家、该研究的主要作者豪尔赫·埃尔南德斯-贝尔纳尔（Jorge Hernández-Bernal）在新闻稿中表示，“一旦我们将这些物理学原理纳入模拟，AMEC就如我们所期望的那样出现了。”

On Earth, clouds usually form when water vapor creates droplets or ice crystals in the presence of tiny particles, such as dust or salt. The new study, published in Nature Geoscience, instead suggests AMEC could be forming through so-called homogeneous nucleation, where vapor changes directly into ice crystals on its own without any help from debris.

在地球上，云层通常是在微小颗粒（如灰尘或盐分）存在的情况下，由水蒸气形成液滴或冰晶而产生的。发表在《自然-地球科学》杂志上的这项新研究则表明，AMEC可能是通过所谓的“均相成核”过程形成的，即水蒸气在没有任何杂质辅助的情况下，直接自行转变为冰晶。

“It’s akin to droplets of condensation appearing in the middle of a room, rather than on a window,” Hernández-Bernal explained. “It’s wholly unexpected.” This phenomenon requires extreme conditions—a sharp temperature drop of 30° Celsius within 10 minutes and high relative humidity. The Arsia Mons volcano also plays a key role. When wind current hits the 65,000-foot-tall volcano, it creates a powerful wave that launches moist air high in the atmosphere in a matter of minutes.

“这就像冷凝水滴出现在房间中央，而不是窗户上一样，”埃尔南德斯-贝尔纳尔解释道，“这完全出乎意料。”这种现象需要极端条件——在10分钟内气温骤降30摄氏度，且具有高相对湿度。阿尔西亚山火山也起到了关键作用。当气流撞击这座6.5万英尺高的火山时，会产生强大的波浪，在几分钟内将潮湿空气推向高层大气。

Scientists have assumed a similar phenomenon could occur in the upper atmospheres of other planets, including Venus and even Earth, but it has never been observed. That’s not too surprising given the extreme air humidity required for this phenomenon, which is more than 100,000 times greater than any value measured on Earth. Before this modeling, it was not known that these humidity levels existed on Mars either.

科学家们曾推测，类似的现象可能发生在包括金星甚至地球在内的其他行星的高层大气中，但从未被观测到。考虑到该现象所需的极端空气湿度（比地球上测量到的任何数值都要高出10万倍以上），这并不令人惊讶。在进行此次模拟之前，人们也不知道火星上存在这种湿度水平。

“We don’t have nearly as much information about Mars’ atmosphere as we do about Earth’s, so reproducing the AMEC to this degree is a big success,” said Hernández-Bernal, adding, “the result is remarkable.”

“我们对火星大气的了解远不如对地球大气的了解，因此能将AMEC模拟到这种程度是一个巨大的成功，”埃尔南德斯-贝尔纳尔补充道，“这一结果非常了不起。”