What exactly are Mars’ two moons? Japan’s new mission will land on one to find out

Mars’ largely unexplored moons are getting their moment in the spotlight as a first-of-its-kind mission prepares to take flight.

The red planet has many unsolved riddles , but the Japanese-led Martian Moons eXploration project will focus solely on two of the biggest curiosities orbiting nearby. Phobos and Deimos have long baffled scientists, who have been eyeing the small, lumpy moons for clues about the early days of Mars.

NASA/JPL-Caltech/ASU/MSSS

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“This is kind of like one of the major outstanding mysteries of solar system formation, the origin of Phobos and Deimos, so we really do need a mission like MMX to figure this out,” said Dr. Daniel Glavin, senior scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and participating scientist on the MMX mission.

Previous Mars missions have observed the peculiar pair whenever convenient. Orbiters circling the red planet have snapped images of the rocky bodies over the years, while rovers including Curiosity and Perseverance have captured some fantastic “googly eye” eclipses when Phobos moved between Mars and the sun. But even after decades of observations, scientists still don’t know how Phobos and Deimos came to be.

NASA/JPL-Caltech/ASU/MSSS/SSI

“What are these little space potatoes? We can’t explain Phobos or Deimos right now. They shouldn’t exist, but they do,” said Dr. Abigail Fraeman, research scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “They’re super weird, they’re super small and they’re super puzzling.”

MMX is set to lift off aboard an H3 rocket from the Yoshinobu Launch Complex at the Japan Aerospace Exploration Agency’s Tanegashima Space Center in southwestern Japan’s Kagoshima Prefecture at 3:41 p.m. ET Monday (4:41 a.m. JST Tuesday).

The risky robotic mission is an international collaboration — including scientific instruments from NASA, the European Space Agency, France’s National Center for Space Studies and the German Aerospace Center — that aims to collect more than 0.4 ounces (10 grams) of material from Phobos and return to Earth in 2031.

The detailed observations and samples captured by MMX might reveal the missing pieces to Phobos and Deimos’ origin story — and could even unveil secrets about the red planet itself. If the samples contain pieces of Mars, MMX could potentially be the first mission to successfully bring back Martian material to scientists on Earth in a race alongside China.

American astronomer Asaph Hall discovered the red planet’s unusual moons in 1877. He named them after the two mythological sons of the Roman god Mars: Phobos , meaning fear, and Deimos, signifying dread.

Phobos is a doomed moon, drawing 6 feet (1.8 meters) closer to Mars every 100 years. Scientists expect the lumpy rock to crash into the planet in roughly 50 million years or break up into a rocky ring that stays in orbit. The object’s defining feature is Stickney crater — a gaping cavity, about 6 miles (9.7 kilometers) wide, that takes up approximately half of the tiny moon’s surface. Thousands of meteorite impacts have also scarred Phobos over time.

HiRISE/MRO/LPL (U. Arizona)/NASA

Meanwhile, more distant and diminutive Deimos is slowly spiraling away from Mars. The moon has a smoother surface than Phobos but is still heavily pockmarked and covered in a perplexing amount of dust .

Scientists are weighing two leading hypotheses about how these oddballs came to orbit around Mars. One concept suggests that a large object slammed into Mars, launching rocky material that coalesced into Phobos and Deimos, Glavin said. The other hypothesis purports that the two moons are asteroids that came too close to Mars and were drawn in by its gravity.

“None of our data fit either hypothesis correctly,” said Fraeman, who is also a participating scientist on MMX. Japan’s expedition to the enigmatic moons could find new data that supports one of the existing hypotheses or illuminate an entirely different formation backstory, Fraeman added.

The mission will primarily focus on scouting and visiting Phobos, the larger and closer of the two moons to Mars, but along the way it will also take images of Deimos to help scientists better understand similarities and differences between the fraternal moons.

Carrying a small rover named Idefix, the MMX spacecraft — a stack of three modules for propulsion, exploration and returning to Earth — will spend about a year traveling to Mars and then orbit Phobos for about three years.

A suite of instruments aboard the spacecraft’s lander, called the exploration module, will enable scientists to gather a variety of data, including measurements on terrain, minerals, chemical elements and space radiation. Two Super Hi-Vision cameras will take the highest-definition images of Mars and its moons in 4K and 8K.

The spacecraft will first deploy the Idefix rover, developed by the German Aerospace Center and France’s National Center for Space Studies, in early 2029. The robotic explorer will make initial observations that will help mission scientists and engineers determine sites for MMX’s four-legged lander to collect samples directly on Phobos.

The rover will drop from about 131 to 328 feet (40 to 100 meters) down to the surface of Phobos; the tiny moon’s weak gravity should cushion its fall and enable the rover to bounce before sticking its landing.

German Aerospace Center/DLR

After autonomously releasing its wheels and solar panels and maneuvering into an upright position, Idefix will embark on a 100-day mission. The gravity on Phobos is so weak that Idefix, which weighs roughly 55 pounds (25 kilograms), will only weigh about 0.5 ounces (15 grams) during its surface operations.

The drink crate-size rover will scout out areas of scientific interest and potential safe landing spots. The mission team will then select two separate sites for the MMX lander to touch down.

Images taken by current orbiters show that Phobos appears to have one lighter side and one darker side — almost as if it has two different types of surfaces, Glavin said. That’s why the plan is to collect a sample from each of these two regions — on the side of Phobos that faces Mars and the opposite side facing away from the planet, said Dr. Tomohiro Usui, a scientist at the Japan Aerospace Exploration Agency, or JAXA, who has worked on the mission for 10 years.

“We’re going to choose a first landing site and then do some landing operations, and after that we’re going to lift off and get back to orbit,” Usui, professor in the department of solar system sciences at Japan’s Institute of Space and Astronautical Science, told CNN. “It takes another several months for the search of the next landing site. Landing operations are very risky.”

The MMX lander has two different ways to collect rocks and dust from Phobos. A coring sampler will drill down 0.8 inches (2 centimeters) and store the subsurface material in a tube aboard the spacecraft’s sample return capsule. A separate pneumatic sampler will use pressurized gas to kick up surface material and collect it in a tube.

After the samples have been stored aboard the MMX lander, it will lift off, make observations of Deimos and begin the journey back to Earth in 2030.

Insights gained from MMX’s tour of the Martian moons could even aid with the planning of crewed missions to Mars in the future, Usui said.

The MMX lander is like a Swiss army knife of many different components, providing scientists various ways to try to decode the mysterious origins of Phobos and Deimos.

Ahead of the samples returning to Earth, researchers will be able to get a sneak peek at initial remote-sensing data beamed back in real time from MMX instruments such as the Mars-moon Exploration with GAmma-rays and Neutrons spectrometer, or MEGANE.

MEGANE data could reveal signs of volatile elements, or chemical elements with low boiling and melting points, such as hydrogen, sodium and chlorine on Phobos and Deimos, for example. These elemental composition measurements could provide key clues that lend credibility to one origin hypothesis over another, said David Lawrence, planetary scientist at the Johns Hopkins University’s Applied Physics Laboratory and science lead for MEGANE.

“If you had a giant impact, what happens is the materials get very hot, and you will cook off these volatile elements,” Lawrence said. “In contrast, a lot of asteroids that we see have higher abundances of these volatile elements.”

Fraeman, who focused part of her doctoral thesis on Phobos’ composition, will do a combined analysis of MEGANE data and observations captured by the MMX InfraRed Spectrometer, or MIRS. The spectrometer will use near-infrared light to measure minerals, organic matter and water-related substances on Phobos.

Even though the Martian moons are mission priorities, scientists anticipate that MMX’s data will also reveal previously unknown aspects of Mars’ past.

Unmanned Exploration Laboratory and Aerospace Robotics and Mechanisms Laboratory, KAIST

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“If Phobos is made from bits of Mars that were thrown up and then recoalesced, that could give us some important new clues about the composition of the planet and what it was like when it was much younger,” Fraeman said.

Even if the rocky neighbor doesn’t contain remnants of Mars, Phobos would be equally intriguing if it’s a captured asteroid or comet — which could have transported water and other volatile elements from the edge of the solar system to Mars’ vicinity, Fraeman said.

If Phobos and Deimos were enriched with water and organics, “that could have been a seed for life on Mars,” Glavin said.

“That’s what I’m particularly interested in: the origin of life. Are we alone? Did it happen on Mars?” he added. “Studying the samples from Phobos and analyzing Deimos as well is part of that whole story.”

Glavin has worked on previous sample collection missions, like OSIRIS-REx, which returned an unexpected wealth of organic material from the near-Earth asteroid Bennu . For MMX, his team will look for amino acids, the molecules that form proteins, and other chemical building blocks of life in the Phobos samples as well.

“Amino acids seem to be literally everywhere we look in the solar system,” Glavin said. “What we’re going to be looking at is differences in the number and complexity of amino acids, but also their relative abundances, which can tell us about their origin.”

Phobos and Deimos likely have existed for billions of years, which means the moons might be witnesses of Mars’ evolution. Given its proximity, Phobos has served as a little dustpan, collecting material that has swept away from the planet’s thin atmosphere.

“There could be pieces of Mars that have landed on the surface of Phobos, much like pieces of Mars have landed on Earth,” Fraeman said. “When we bring samples back from Phobos, there could be little bits of Mars mixed in there.”

MMX is not the only craft racing toward the red planet. China’s Tianwen-3 mission, which aims to launch in 2028 and return samples directly from Mars back to Earth, is also expected to return in 2031.

“The early 2030s could really be banner years of explanation for Mars,” Glavin said.

火星上那些鲜为人知的卫星即将成为人们关注的焦点，一项史无前例的任务即将启程。

这颗红色星球还有许多未解之谜，但由日本主导的火星卫星探测计划将专注于两颗环绕火星运行的最令人好奇的天体——火卫一和火卫二。长期以来，科学家们一直对这两颗体积小、表面凹凸不平的卫星感到困惑，他们试图从中寻找火星早期历史的线索。

NASA/JPL-加州理工学院/亚利桑那州立大学/MSSS

NASA或许已经掌握了其他星球曾经存在生命的证据。科学家们或许永远也无法找到答案。

“这有点像是太阳系形成过程中尚未解开的主要谜团之一，即火卫一和火卫二的起源，所以我们确实需要像 MMX 这样的任务来弄清楚这个问题，”美国宇航局戈达德太空飞行中心（位于马里兰州格林贝尔特）的高级科学家、MMX 任务的参与科学家丹尼尔·格拉文博士说。

以往的火星探测任务都会在条件允许的情况下观测这对奇特的天体。多年来，环绕火星运行的轨道探测器拍摄了这对岩质天体的照片，而“好奇号”和“毅力号”等火星车则在火卫一运行到火星和太阳之间时，捕捉到了一些奇妙的“咕噜眼”日食景象。但即便经过数十年的观测，科学家们仍然不知道火卫一和火卫二是如何形成的。

NASA/JPL-加州理工学院/亚利桑那州立大学/MSSS/SSI

“这些太空小土豆是什么？我们现在还无法解释火卫一（福波斯）和火卫二（戴莫斯）的存在。它们本不应该存在，但它们确实存在，”美国宇航局喷气推进实验室（位于加利福尼亚州帕萨迪纳）的研究科学家阿比盖尔·弗雷曼博士说。“它们非常奇特，非常小，而且非常令人费解。”

MMX 将于美国东部时间周一下午 3:41（日本标准时间周二凌晨 4:41）从日本西南部鹿儿岛县日本宇宙航空研究开发机构种子岛宇宙中心的吉信发射场搭乘 H3 火箭升空。

这项风险极高的机器人任务是一项国际合作项目，其中包括来自美国宇航局、欧洲航天局、法国国家空间研究中心和德国航空航天中心的科学仪器，其目标是从火卫一（福波斯）采集超过 0.4 盎司（10 克）的物质，并于 2031 年返回地球。

MMX探测器采集的详细观测数据和样本或许能揭示火卫一和火卫二起源故事中缺失的部分，甚至可能揭开火星本身的秘密。如果样本中包含火星物质，MMX有望成为首个成功将火星物质带回地球供科学家使用的火星探测任务，与中国展开竞争。

美国天文学家阿萨夫·霍尔于 1877 年发现了火星的奇特卫星。他以罗马神话中战神玛尔斯的两个儿子的名字命名了它们：福波斯（Phobos），意为恐惧；戴莫斯（Deimos），意为恐惧。

火卫一（福波斯）是一颗注定毁灭的卫星，它每100年就会向火星靠近1.8米（6英尺）。科学家预计，这颗凹凸不平的岩石将在大约5000万年后撞击火星，或者分裂成一个继续绕火星运行的岩石环。火卫一最显著的特征是斯蒂克尼陨石坑——一个巨大的凹陷，直径约9.7公里（6英里）​​，占据了这颗小型卫星表面近一半的面积。随着时间的推移，数千颗陨石撞击也给火卫一留下了伤痕。

HiRISE/MRO/LPL（美国亚利桑那州）/NASA

与此同时，距离更远、体积更小的火卫二（戴莫斯）正缓慢地螺旋式远离火星。这颗卫星的表面比火卫一（福波斯）光滑，但仍然布满坑洼，并覆盖着数量惊人的尘埃。

科学家们正在权衡两种关于这两颗奇特卫星如何围绕火星运行的主要假说。格拉文表示，一种假说认为，一个大型天体撞击了火星，抛射出的岩石物质凝聚成了火卫一和火卫二。另一种假说则认为，这两颗卫星是小行星，它们过于接近火星，最终被火星引力吸引而来。

“我们的数据都无法完全符合任何一种假设，”弗雷曼说道，他也是MMX项目的参与科学家之一。弗雷曼补充说，日本对这些神秘卫星的探测可能会发现新的数据，从而支持现有的某种假设，或者揭示一个完全不同的形成背景。

此次任务将主要集中于侦察和访问火卫一（距离火星两颗卫星中较大且较近的一颗），但在此过程中，它还将拍摄火卫二的图像，以帮助科学家更好地了解这两颗卫星之间的异同。

MMX 航天器由三个模块组成，分别用于推进、探索和返回地球，它将携带名为 Idefix 的小型火星车，花费大约一年时间前往火星，然后绕火卫一运行大约三年。

探测器着陆器（即探测舱）上搭载的一系列仪器将使科学家能够收集各种数据，包括地形、矿物、化学元素和太空辐射的测量数据。两台超高清摄像机将以 4K 和 8K 分辨率拍摄火星及其卫星的最高分辨率图像。

该航天器将于 2029 年初首先部署由德国航空航天中心和法国国家空间研究中心开发的 Idefix 火星探测车。这款机器人探测器将进行初步观测，以帮助任务科学家和工程师确定 MMX 四足着陆器直接在火卫一上采集样本的地点。

探测车将从大约 40 到 100 米（131 到 328 英尺）的高度落到火卫一表面；这颗小型卫星的微弱引力应该可以缓冲它的下落，使探测车在着陆前能够弹跳一下。

德国航空航天中心/DLR

在自主释放轮子和太阳能电池板并调整至直立位置后，Idefix 将开始为期 100 天的任务。火卫一的重力非常弱，因此重约 55 磅（25 公斤）的 Idefix 在表面作业时重量仅约为 0.5 盎司（15 克）。

这辆饮料箱大小的探测车将勘察具有科学价值的区域和潜在的安全着陆点。任务团队随后将选择两个不同的地点供MMX着陆器着陆。

格拉文表示，目前轨道飞行器拍摄的图像显示，火卫一似乎有一面较亮，一面较暗——几乎就像它拥有两种不同类型的表面。日本宇宙航空研究开发机构（JAXA）的科学家臼井智宏博士解释说，这就是为什么计划要从火卫一面向火星的一侧和背对火星的一侧分别采集样本的原因。臼井博士参与这项任务已有10年之久。

“我们将首先选择一个着陆点，然后进行着陆操作，之后我们将再次发射升空，返回轨道，”日本宇宙航空研究开发机构太阳系科学系教授臼井告诉CNN。“寻找下一个着陆点还需要几个月的时间。着陆操作风险非常高。”

MMX着陆器有两种不同的方式从火卫一（福波斯）采集岩石和尘埃。一种是取芯采样器，它会钻入地下0.8英寸（2厘米）深处，并将地下物质储存在航天器返回舱的管子中。另一种是气动采样器，它会利用加压气体吹起表面物质，并将其收集在管子中。

样本被储存在 MMX 着陆器上后，它将升空，对火卫二进行观测，并于 2030 年开始返回地球的旅程。

臼井表示，MMX 对火星卫星的探测所获得的经验甚至可以帮助规划未来载人火星任务。

MMX着陆器就像一把瑞士军刀，由许多不同的组件构成，为科学家们提供了各种方法来尝试破解火卫一和火卫二神秘的起源。

在样本返回地球之前，研究人员将能够先睹为快，实时查看从火星-月球伽马射线和中子探测光谱仪（MEGANE）等 MMX 仪器传回的初始遥感数据。

MEGANE 的数据可以揭示易挥发元素或低沸点和熔点化学元素的迹象，例如火卫一和火卫二上的氢、钠和氯。约翰·霍普金斯大学应用物理实验室的行星科学家、MEGANE 项目科学负责人大卫·劳伦斯表示，这些元素组成测量结果可以提供关键线索，使某种起源假说比其他假说更具可信度。

劳伦斯说：“如果发生巨大的撞击，物质会变得非常热，这些易挥发元素就会被蒸发掉。相比之下，我们观测到的许多小行星都含有较高丰度的这些易挥发元素。”

弗雷曼的博士论文部分内容集中研究火卫一的成分，她将对MEGANE卫星数据和MMX红外光谱仪（MIRS）的观测数据进行综合分析。该光谱仪将利用近红外光测量火卫一上的矿物质、有机物和水相关物质。

尽管火星卫星是任务的重点，但科学家们预计 MMX 的数据也将揭示火星过去不为人知的方面。

韩国科学技术院（KAIST）无人探索实验室和航空航天机器人与机构实验室

这些受折纸艺术启发而设计的探测车轮子或许能帮助探索月球上的熔岩管。

“如果火卫一是由火星碎片抛射出去后又重新聚合而成的，那么这或许能为我们提供一些关于火卫一组成成分以及它年轻时的样子的重要新线索，”弗雷曼说。

弗雷曼说，即使这颗岩石邻居不包含火星的残余物，但如果火卫一是被捕获的小行星或彗星，它也同样令人着迷——它可能将水和其他挥发性元素从太阳系边缘输送到火星附近。

格拉文说，如果火卫一和火卫二富含水和有机物，“那可能就是火星生命诞生的种子”。

“我特别感兴趣的是生命的起源。我们是宇宙中唯一的生命吗？生命起源于火星吗？”他补充道，“研究火卫一（福波斯）的样本，以及分析火卫二（戴莫斯）的样本，都是揭开这个谜团的一部分。”

格拉文曾参与过多次样本采集任务，例如OSIRIS-REx探测器，该探测器从近地小行星贝努带回了数量惊人的有机物质。在MMX任务中，他的团队也将从火卫一的样本中寻找氨基酸（构成蛋白质的分子）以及其他生命的基本化学成分。

格拉文说：“在太阳系中，我们似乎到处都能看到氨基酸。我们将研究氨基酸的数量和复杂性差异，以及它们的相对丰度，这可以告诉我们它们的起源。”

火卫一和火卫二可能已经存在了数十亿年，这意味着这两颗卫星或许见证了火星的演化历程。由于距离火星很近，火卫一就像一个小簸箕，收集着从火星稀薄大气层中飘散出来的物质。

弗雷曼说：“可能有一些火星碎片落在了火卫一表面，就像火星碎片落在地球上一样。当我们从火卫一带回样本时，里面可能混杂着一些火星碎片。”

MMX并非唯一一个奔赴火星的探测器。中国的“天问三号”任务计划于2028年发射，并将直接从火星采集的样本带回地球，预计于2031年返回地球。

格拉文说：“2030年代初期可能是火星研究取得重大突破的几年。”