All the best space missions are heists. And the latest one, courtesy of China, is a doozy. Its Chang’e-5 spacecraft, launched on November 23, was tasked with stealing volcanic treasures from the Moon’s Oceanus Procellarum, or Ocean of Storms, a frozen, silver sea of lava. It looks to have succeeded.
When it landed on the Moon at the start of December, it scooped and drilled into the ground below its metal feet, gobbling up some rock. A few days later, it rocketed up into the stars and is now flying back home. By mid-December, if all goes well, the shielded sample container will land in Inner Mongolia.
Chang’e-5’s payload is the first pristine Moon matter humanity has obtained since 1976, when the Soviet Union’s Luna 24 robotic voyager brought back 170 grams. In terms of spoils, its three successful endeavours were nothing significant compared to the crewed Apollo missions’ impressive haul of 382 kilograms. China has now obtained two kilograms of the stuff. That may not sound like much either, but for lunar detectives, quality is as important as quantity.
“This is definitely awesome,” says Paul Byrne, a planetary scientist at North Carolina State University. “These are the first samples in 44 years, and they’re from an area we haven’t sampled yet, and they’re being collected robotically. Put together, this really is a big deal.”
And it’s an even bigger deal when you understand what Chang’e-5’s payload contains. It might look like a monochrome mirror from Earth, but the Moon is actually a hole-punched volcanic crypt, a place sculpted by huge impacts and strange, epic effusions of lava. But despite visiting it a few times and scrutinising it with cutting-edge telescopes and satellites over the last few decades, we know next to nothing about the Moon. From its magmatic origins to how its molten innards and its sky-scorching eruptions changed over time, the Moon remains a mystery.
Analysing volcanic rocks collected from the Moon should go a long way to unpicking these mysteries. That makes Chang’e-5’s daylight robbery the latest chapter in the quest to answer one of planetary science’s most fundamental questions: what is going on with the Moon and its freakish volcanism?
The Moon was crafted by primeval, peculiar eruptions. It has troughs carved out by lava that anastomosed across the surface before seemingly vanishing; labyrinthine caverns once home to vast rivers of molten rock; cones and domes that once blasted lava into an atmosphere-less environment, freezing instantly into showers of glass marbles. But the real showstoppers are the big, dark patches concentrated on the Moon’s nearside, the side that always faces Earth.
They are the maria, vast seas of frozen lava, each with fantastic names like Mare Imbrium (the Sea of Rains) and Mare Tranquilitatus (Sea of Tranquillity), the latter being the site of the first Apollo landing. Many are hundreds of miles across. But these are nothing compared to the Ocean of Storms, a complex flood of lava 2,600 kilometres long that once upon a time splashed fire and brimstone along frigid shores.
They are one of the Moon’s most distinguishing features. And scientists aren’t sure how they were made. There are a few ideas. The maria often sit in giant bowls, the scars left behind by momentous impacts. Perhaps the crust cracked open so forcefully that magma below oozed out into the huge craters. The mantle, the solid but once hot and squidgy layer under the crust, used to melt when decompressed. Remove a lot of crust through an impact and you’ve suddenly got lots of magma. There are also radioactive compounds found around the Moon’s nearside. They decay as they release heat, so perhaps they are responsible for melting lots of rock which then simply poured into those convenient impact bowls.
But no-one knows which answer, or combination of answers, is correct. And that means we don’t know what made the Moon’s nearside a volcanic nirvana.
It gets stranger: based on Apollo-era samples, there appears to be gaps of several hundreds of millions of years between the impacts making a chasm and the lava gushing out. That’s like poking a hole in a water balloon as a kid but not seeing any water leak out until you’re a pensioner.
Chang’e-5’s frozen lava samples from the Ocean of Storms will provide more clues. But it won’t provide clear answers. That’s because the Ocean of Storms is an oddity. Compared to other maria, it has exotic chemistry and may not even sit in a giant impact basin.
Imagine you’re going to meet a friend’s extended family for the first time. Everyone is dressed sombrely – except for one person. “There’s this one cousin who’s wearing a flamenco outfit,” says Tracy Gregg, an expert on planetary volcanology at the University at Buffalo College of Arts and Sciences. “You’re going to want to talk to the person in the flamenco outfit.” That’s the Ocean of Storms: an extreme outlier. “We will learn something really cool about the strangest lunar maria,” says Gregg. “But it is not necessarily going to be representative of all the other maria.”
So why did China go there? “It’s what people always do, right?” she says. If you want to understand Earth’s mountains, going to the top of Mount Everest may not be an ideal first choice, because Mount Everest is not necessarily representative of typical mountains on Earth. “And yet, because it’s so cool, it draws the eye.” It’s the same with the Ocean of Storms: it’s too flamboyant to ignore.
It also contains some of the Moon’s youngest volcanism. “All the Apollo samples we have are older than three billion years,” says Dan Moriarty, a lunar geologist at Nasa’s Goddard Space Flight Center in Greenbelt, Maryland. Some of the frozen lava (a rock called basalt) in Oceanus Procellarum are estimated to be 1.2 billion years old. And that doesn’t make a lick of sense.
You need trapped heat to make magma. The Moon has two internal heat sources: radioactive decay, and the leftover heat from its fiery formation. The Moon is also tiny. You could fit 50 of them inside Earth. The heat produced by both should have escaped into space not long after the Moon was born 4.5 billion years ago. To still be erupting a billion years ago – or, as one other locale suggests, 100 million years ago – seems impossible.
No-one’s expecting a new lunar eruption, but the Moon’s crust may not be completely magma-free today. “We can’t even say that most basic thing,” says Gregg. “Is the Moon volcanologically dead?”
The decay of various radioactive elements within volcanic rocks happens at known rates, which makes said elements atomic hourglasses. Getting samples from the Ocean of Storms that appear to be 1.2 billion years old would let scientists accurately date them. If they do happen to be as youthful as their appearances suggested, then the chemistry of the rocks may help tell us how the Moon could keep on cooking lava long after it should have cooled down.
These samples won’t merely move us closer to understanding the Moon. It’s suspected that a Mars-sized proto-planet slammed into the infant Earth about 4.5 billion years ago, and the material that was flung around coalesced and made the Moon. Both worlds lost a lot of their water during that momentous event, some of which continued boiling off into space while the planet-wide magma oceans cooled off.
And yet Earth has oceans and rain. The Moon has no atmosphere, so it can’t have liquid water at the surface. But studies of its volcanic glass beads reveal its underbelly is still soggy. Water is vital for life as we know it, so it’s in our interests to determine its provenance. Damp asteroids and comets slamming into the Moon would have hydrated it after its violent birth. “Every impact delivers volatiles to the Moon,” says Gregg. “There’s nothing that hits the Moon that’s totally dry.”
Earth’s story is fuzzier. It may have been able to hold on to more water after the Moon-forming mega-impact than first thought; belching volcanoes later threw lots of it onto the surface. Alternatively, a bombardment of watery space rocks may have rehydrated it, just like the Moon. Scientific studies looking at the chemical fingerprints of Earth’s water and comparing it to what we know about the water in asteroids and comets, lend support to both ideas. Perhaps both played a role, along with other astronomic actors.
Either way, the Moon and Earth are something of a dyad. What happens to one happens to the other. Understanding how the Moon got its water will help explain why Earth is brimming with life. And Chang’e-5 is likely to have scooped up some hydrated volcanic minerals and glasses that will aid both quests.
If the touchdown works out, this sample return mission will be the latest success story in China’s lunar exploration program, one that (like all space programs) has political and economic goals, as well as scientific rewards. But whatever your perspective, the Chang’e-5 mission should be celebrated.
“If this kind of approach, with a robotic lander using hazard avoidance and other advanced navigation techniques, is shown to be successful, then we may very well see a new era of relatively inexpensive, robotic missions to the lunar surface in support of both scientific and human exploration efforts,” says Byrne. Other space agencies may need to take heed as they engage in their own missions to the Moon.
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