Going through a phase: What accounts for our current obsession with the moon?

Major missions have focused on Mars and the Sun; so has popular culture. The earth’s core has had more of a starring role in Hollywood than our steadfast satellite.

But for the scientific community, the promise that the moon holds has never been greater. This naked rock devoid of atmosphere, rotating in time with Earth, about 1.3 light seconds away, is a vital stepping stone for interplanetary exploration. It also holds rare minerals and elements, including stores of titanium and helium-3 that could be used to power nuclear fusion plants. And it holds frozen water.

The new space race is a more quiet but equally frenetic one focused on who can first figure out how to get at these precious resources, and transport them home, or find ways to build around them on the lunar surface.

“We explore space because we are curious beings,” says Anil Bhardwaj, astrophysicist, planetary scientist, and director of the Physical Research Laboratory, Ahmedabad, a unit of the government’s Department of Space and a national space research institute. “We also explore as an insurance policy for humanity, which can be wiped out at any second if a large enough asteroid collides with Earth, as happened with the dinosaurs. We explore because everyone else is exploring and it’s important for us to make our mark. But we also explore because ultimately it all boils down to economics. Whoever manages to bring back these elements, it could generate billions of dollars for them.”

This year, accordingly, will be a very busy one on the moon. At least five missions aim to land there in 2023. Japanese startup ispace aims to have a lander on the moon in April. In June, India is scheduled to launch Chandrayaan-3, equipped with a lander and rover. The private American aerospace companies Intuitive Machines and Astrobotic Technology each aim to place a lander there. And Russia’s lander mission Luna 25 (its first such mission since Luna 24 in 1976) is scheduled for launch in July.

Humans are headed back there too. The Artemis programme of the US National Aeronautics and Space Administration (NASA) plans to send a crewed craft to the moon by 2025. China’s National Space Administration aims to do this by 2030.

A lot of the attention is now focused on the permanently shadowed regions of the moon’s south pole, where temperatures stand below -200 degrees Celsius, and India is part of the reason for this. In 2008, NASA instruments aboard the Indian Space Research Organisation’s first moon mission, the Chandrayaan-1 orbiter, definitively confirmed the presence of water ice on the moon.

“At first we weren’t convinced about the data we were receiving,” says Bhardwaj. “No one expected water to show up like that, so prominent and evident.” Amid tremendous excitement, NASA turned the lenses on its Deep Impact and Cassini spacecraft towards the moon for a closer look, and confirmed the findings.

Water is a dramatic game-changer, of course. It indicates potential for life, for research stations or settlements, perhaps even crops. Already lunar soil has been used to germinate plants on Earth.

With the diameter of the moon being about one-fourth that of Earth, that’s a lot of potential.

If Chandrayaan-3 succeeds, India could become only the fourth country in the world to place a lander on the moon. After the US and Russia, China’s Chang-e missions have placed landers and rovers there, three times between 2013 and 2020. As Chandrayaan-3 readies to study thermal conductivity and seismic activity, among other things, lingering mysteries remain: Why is there rust on the moon, even though it has no ambient oxygen; and why exactly is the moon’s crust 20 km thicker on the far side?

Some leaps of discovery have recently been made from here on Earth. Read on for a closer look.

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NEW VIEWS OF THE MOON

Boots on the ground

The 25-day trip was a test drive. Orion is part of the Artemis mission (named after Apollo’s divine twin, the Greek goddess of the hunt) to put American boots back on the moon. Its journey was meant to demonstrate re-entry, descent, splashdown and recovery capabilities, before the first flight crew heads out on the Artemis II next year.

First, a manned test flight will orbit the moon, followed by the manned landing. The hope is to finally have a woman and a person of colour step onto the lunar surface. The eventual goal: to lay the ground for a long-term human presence on the satellite.

Incidentally, while there are UN treaties in place that state that no country may lay claim to extraterrestrial territories, these are non-binding agreements that have not been signed by major players such as the US, Russia and China.

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Extreme close-ups via an Indian vessel

India’s second mission went less well. Chandrayaan-2 was meant to land on the surface in 2019, but lost contact shortly before touchdown and was later found to have crashed. Its accompanying orbiter, meant to relay data back for a year, has been a stunning success, however. It’s still sending images back.

In August 2019, ISRO released Chandrayaan-2’s first image of the far side of the moon (above), taken by the lander before it lost contact. Other rare photographs taken as part of that mission include very-high-resolution images of tiny craters with diameters of less than 5 metres, and boulders as small as 1 to 2 metres in height.

India’s Chandrayaan 3, with a new and improved lander and rover, is due for launch in June.

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Who’s there?

The radar system has been built by Raytheon Intelligence & Space in collaboration with the US’s National Radio Astronomy Observatory (NRAO) network and the Green Bank Observatory (GBO), to detect and track potentially harmful objects that may be on a collision course with Earth. The aim is to spot even small celestial bodies, when they’re still far away.

In order to test the prototype, in January, a team of scientists from NRAO, GBO and Raytheon, which is part of an American defence and aerospace conglomerate, pointed the radar system towards the moon. The result is extremely-high-resolution imagery of features such as the 85-km-wide Tycho Crater (above).

To compile the image, the Green Bank Telescope in West Virginia was fitted with a radar (RAdio Detection And Ranging) transmitter that uses less power than the average microwave oven. The system sent out a signal to the moon, which bounced back and was received by NRAO’s collection of radio telescopes across the US.

In the test run, the scientists also spotted a 1-km-long asteroid a mere 2.1 million km away. It is not, they confirmed, on a collision course with Earth.

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Light on the dark side

The photographs revealed a dramatically different landscape. For one thing, the far side has a crust that is thicker by almost 20 km. It is also a more densely pockmarked hemisphere, with millions more asteroids and comets having crashed into it over billions of years. And, perhaps most remarkably, it has almost none of the characteristic dark splotches (they’re actually less-reflective, volcanic basalt plains) that we see on the near side.

The lack of basalt plains baffled scientists for decades. Now, researchers have a possible explanation. In a study published in the journal Science Advances in 2022, scientists from Brown, Purdue and Stanford universities and NASA’s Jet Propulsion Laboratory attribute the dichotomy to a massive asteroid that collided with the far side some 4.3 billion years ago.

It created one of the largest known craters in the solar system, the 2,600-km-wide South Pole-Aitken Basin, on the far side. The impact was so powerful that it disrupted convection in the Moon’s interior, and caused massive volcanic eruptions on the near side of the satellite. These, the researchers say, are the massive volcanic plains we see today.

As for the crust, one theory holds that the far side likely cooled much faster than the near side in the early years of the moon’s formation, because the near side was exposed to Earth’s super-hot all-lava phase. And so the far side formed a thicker crust.

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A lunar salad?

Lunar soil – called regolith – contains a number of familiar elements such as iron, silicon, potassium, manganese and magnesium. But it doesn’t contain organic matter, microbes or insects. It’s also hydrophobic (it repels rather than absorbs water). And with no atmosphere on the moon, regolith has been exposed to extremely unhealthy amounts of solar radiation.

So when scientists at the University of Florida planted three seeds of a type of mustard in three regolith samples, they weren’t sure what to expect. They added a nutrient solution and water, and waited.

“After two days, they started to sprout!” lead scientist Anna-Lisa Paul of the University of Florida said in a press release. “Everything sprouted. I can’t tell you how astonished we were! Every plant – whether in a lunar sample or in a control – looked the same up until about day six.”

On Day 6, it was clear that the lunar plants weren’t doing as well as the control group planted in volcanic ash. They were growing slower, had stunted roots and leaves, and developed mysterious red spots.

On Day 20, the plants were harvested for genetic analysis. RNA studies showed that they were stressed, with too much exposure to salt or heavy metals. More-drought-resistant plants would likely fare better; introducing microbes to the regolith might help too, researchers say.

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A mystery rogue rocket

First, it’s not entirely clear who the booster belongs to. It was initially identified as a part of the SpaceX 2015 Falcon rocket, but further analysis pointed to a 2014 Chinese mission. China denies this is its booster.

This is now the first manmade object to end up on the moon by accident.

Meanwhile, the number of craters makes this an even-more-unusual event. A spent rocket body typically consists of one mass of fuel, which explodes to cause a single crater. All previous crashes have resulted in single craters. The double crater could indicate large fuel masses on both ends of the rocket shell, an unusual and heavy-duty design.

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The icy poles

But for decades, no one knew where to look for proof. In 1996, the NASA lunar orbiter Clementine sent home the first hints: data indicating the signature of water ice at the lunar poles. Radio signals beamed at the poles indicated the presence of icy material; then came images, via NASA’s Lunar Prospector, in 1998.

There was still no definitive proof. That came in 2008, via Chandrayaan-1. India’s first moon mission, an orbiter, took off carrying, among other things, two instruments provided by NASA for the express purpose of surveying the poles for water ice. The instruments – the Moon Mineralogical Mapper (M3), an infrared spectrometer; and the MiniSAR (Miniature Synthetic Aperture Radar) – found the signatures they were looking for, in more than 40 craters. There was no longer any doubt; wherever the water may have come from, it’s there now.

“More water is likely concentrated in the craters at the poles because they don’t receive any sunlight,” says Anil Bhardwaj, astrophysicist and director of the Physical Research Laboratory, Ahmedabad, a national space research institute. Elsewhere on the low-pressure moon, where daytime temperatures reach 120 degrees Celsius, water would be vapourised.

How much water is there? “That question remains,” Bhardwaj says. And it recently became more complicated.

In 2020, data from NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) found the first evidence of water in a sunlit spot, indicating that these precious molecules are more widely distributed than previously thought.

“Without a thick atmosphere, water on the sunlit lunar surface should just be lost to space,” Casey Honniball, a postdoctoral fellow at NASA’s Goddard Space Flight Center, said in a press release. “Yet somehow we’re seeing it. Something is generating the water, and something must be trapping it there.”