Japan’s MMX Mission Wants to Bring Martian Moon Samples Back to Earth

It’s difficult to imagine a more daunting journey than one to an alien moon named after the Greek god of fear—especially when three other attempts to make that journey have failed.

很难想象还有比前往一颗以希腊恐惧之神命名的外星卫星更艰巨的旅程了，尤其是考虑到此前已有三次尝试以失败告终。

And yet, as Japan’s space agency, JAXA, and its collaborators gear up to send a spacecraft to Mars’ formidably named moon, “all the members are filled with a quiet sense of excitement,” says Kiyoshi Kuramoto, who leads the mission’s slew of international scientists.

然而，随着日本宇宙航空研究开发机构（JAXA）及其合作伙伴准备向火星这颗名字令人望而生畏的卫星发射航天器，该任务国际科学家团队的负责人仓本清（Kiyoshi Kuramoto）表示：“所有成员心中都充满了平静的兴奋感。”

This mission, called the Martian Moons eXploration (MMX), is set to launch from Japan’s Tanegashima Space Center in the wee hours of Tuesday in Japan (Monday afternoon in the US). After almost a year of travel, the spacecraft will reach Mars and its two moons: Phobos, meaning fear in Greek, and Deimos, meaning dread. MMX will observe the pair from afar and collect samples from Phobos in a bid to answer a looming scientific question: How, exactly, did the moons come to be?

这项名为“火星卫星探测”（MMX）的任务定于日本时间周二凌晨（美国时间周一 pomeriggio）从日本种子岛宇宙中心发射。经过近一年的航行，航天器将抵达火星及其两颗卫星：火卫一（Phobos，希腊语意为“恐惧”）和火卫二（Deimos，意为“战栗”）。MMX将从远处观测这两颗卫星，并从火卫一采集样本，旨在回答一个悬而未决的科学问题：这些卫星究竟是如何形成的？

Researchers have been attempting similar gambits for decades. Since the 1980s, Russia has sent three probes to Phobos, all of which failed. Still, researchers are anxious to achieve this mission impossible because the origin of Phobos and its sibling remains a mystery. Some of their attributes, such as the pattern of visible light they reflect, suggest they are asteroids captured into Mars’ orbit by its gravity. But the moons’ circular orbits in line with the Martian equator indicate that they could have formed from debris left over from a collision between a nascent Mars and a gigantic asteroid, Tom Statler, MMX program executive at NASA, said at a press briefing.

几十年来，研究人员一直在尝试类似的壮举。自20世纪80年代以来，俄罗斯曾向火卫一发射过三枚探测器，但均以失败告终。尽管如此，研究人员仍渴望完成这项“不可能的任务”，因为火卫一及其“兄弟”的起源至今仍是一个谜。NASA的MMX项目执行官汤姆·斯塔特勒（Tom Statler）在新闻发布会上表示，它们的一些特征，例如反射可见光的模式，表明它们是被火星引力捕获的小行星；但这两颗卫星与火星赤道平齐的圆形轨道又表明，它们可能是由一颗原始火星与一颗巨大小行星碰撞后留下的碎片形成的。

The new mission is designed to help settle the debate by surveying Mars and the moons in detail using a suite of scientific instruments. With MMX’s MEGANE instrument, for instance, researchers will determine the elemental makeup of Phobos by measuring the neutrino particles and gamma rays it emits. If Phobos ends up having more volatile elements such as hydrogen or potassium, it could lean closer to the captured-asteroid hypothesis, while fewer volatiles could support the impact idea.

这项新任务旨在通过使用一套科学仪器详细勘测火星及其卫星，以帮助平息这场争论。例如，借助MMX的MEGANE仪器，研究人员将通过测量火卫一发射的中微子和伽马射线来确定其元素构成。如果火卫一含有更多氢或钾等挥发性元素，则可能更倾向于“捕获小行星”假说；而如果挥发性元素较少，则可能支持“碰撞”假说。

“We know nothing about Phobos’ elemental composition,” says David Lawrence, who leads the MEGANE team from Johns Hopkins University. “For me, that’s what’s exciting—making a measurement nobody’s done before.”

“我们对火卫一的元素组成一无所知，”来自约翰霍普金斯大学、负责MEGANE团队的大卫·劳伦斯（David Lawrence）说，“对我来说，这就是最令人兴奋的地方——进行前人从未做过的测量。”

These observations are “going to give us a hint at some of the answers to the really big questions we have about Phobos,” says Abigail Fraeman, an MMX team member at NASA’s Jet Propulsion Laboratory. “But really, the return samples are going to nail those questions.” After scoping out Phobos with its onboard instruments and a rover—which will land ahead of the spacecraft to explore the new terrain—the spacecraft will land on the moon to collect at least 10 grams of material using two different sampling methods. The goal is to bring them to Earth by 2031, which would make them the first ever samples returned from a moon other than our own.

NASA喷气推进实验室的MMX团队成员阿比盖尔·弗雷曼（Abigail Fraeman）表示，这些观测结果“将为我们关于火卫一的一些重大问题提供线索，但真正能解决这些问题的，还是返回的样本。”在利用机载仪器和一辆将先于航天器着陆以探索新地形的漫游车对火卫一进行勘察后，航天器将降落在该卫星上，并使用两种不同的采样方法收集至少10克物质。目标是在2031年前将样本带回地球，这将使其成为人类历史上首次从地球以外的卫星上带回的样本。

Researchers suspect Phobos’ surface soil contains Martian material, and analyzing it could paint a better picture of how the planet evolved over billions of years. But MMX will also provide insight into our solar system at large. Laboratory analysis of the samples will help determine the origin of leftover material from the early solar system and how it was transported, Statler said during the briefing.

研究人员怀疑火卫一的表层土壤中含有火星物质，对其进行分析可以更清晰地描绘出火星在数十亿年间的演化过程。但斯塔特勒在发布会上表示，MMX还将提供关于整个太阳系的见解，对样本的实验室分析将有助于确定早期太阳系残留物质的起源及其传输方式。

Undertaking this research will require overcoming daunting obstacles. Because scientists currently know little of Phobos’ surface, they can’t pick a landing spot until taking up-close observations of the moon, Kuramoto says. The mission also uses two sampling methods as a safeguard in case one fails, he adds. “Returning samples from a Martian moon is a world-first challenge that is not easy.”

开展这项研究需要克服艰巨的障碍。仓本清表示，由于科学家目前对火卫一的表面知之甚少，在进行近距离观测之前无法选择着陆点。他还补充说，该任务采用了两种采样方法作为保障，以防其中一种失败。“从火星卫星上带回样本是一项世界首创的挑战，绝非易事。”

Still, the number of researchers involved and their depth of expertise give the team confidence that it can succeed where others have failed. MMX is a feat of international collaboration with scientists from NASA, the European Space Agency, and Germany’s and France’s space agencies. “That kind of compounded set of expertise and contributions really helps make the mission objectives very achievable,” says Elliot Sefton-Nash, MMX project scientist at ESA.

尽管如此，参与的研究人员数量及其深厚的专业知识让团队有信心在他人失败的地方取得成功。MMX是国际合作的壮举，汇集了来自NASA、欧洲航天局（ESA）以及德国和法国航天机构的科学家。ESA的MMX项目科学家埃利奥特·塞夫顿-纳什（Elliot Sefton-Nash）表示：“这种复合型的专业知识和贡献确实有助于使任务目标变得非常可实现。”

JAXA also has a proven track record of successful sample-return missions. Despite some setbacks, its Hayabusa mission became the first mission to return a sample from the surface of a near-Earth object when it brought back material from asteroid Itokawa in 2010. Its successor, Hayabusa2, delivered samples from the primitive asteroid Ryugu in 2020. Many Hayabusa2 members have helped design the MMX mission, but sampling Phobos will be different—its orbit and gravity are different from Ryugu’s, for instance, Kuramoto says.

JAXA在样本返回任务方面也有着成功的记录。尽管经历了一些挫折，但其“隼鸟号”（Hayabusa）任务在2010年从丝川小行星（Itokawa）带回物质，成为首个从近地天体表面带回样本的任务。其继任者“隼鸟2号”（Hayabusa2）于2020年从原始小行星“龙宫”（Ryugu）带回了样本。仓本清表示，许多“隼鸟2号”的成员参与了MMX任务的设计，但对火卫一的采样将有所不同，例如其轨道和重力都与“龙宫”不同。

Still, “JAXA’s learned and achieved so much with their sample-return missions that they are really well positioned to be able to do this,” Fraeman says.

不过，弗雷曼表示：“JAXA通过之前的样本返回任务学到了很多，也取得了很大成就，他们完全有能力完成这项任务。”