A model of Chandrayaan-2 rover undergoing tests to prepare for moon’s anemic gravity landing

by Pallava Bagla

BANGALORE—Sometime this summer, a spacecraft orbiting over the moon's far side, out of contact with controllers on Earth, will release a lander. The craft will ease to a soft landing just after lunar sunrise on an ancient, table-flat plain about 600 kilometers from the south pole. There, it will unleash a rover into territory never before explored at the surface; all previous lunar craft have set down near the equator.

That's the ambitious vision for India's second voyage to the moon in a decade, due to launch in the coming weeks. If Chandrayaan-2 is successful, it will pave the way for even more ambitious Indian missions, such as landings on Mars and an asteroid, as well a Venus probe, says Kailasavadivoo Sivan, chairman of the Indian Space Research Organisation (ISRO) here. Chandrayaan-2, he says, is meant to show that India has the technological prowess "to soft land on other heavenly bodies."

But lunar scientists have much at stake, too. "There has been a rebirth of lunar exploration across the globe, and India can't be left behind," says Mylswamy Annadurai, director of the ISRO Satellite Centre. Instruments aboard the lander and rover will collect data on the moon's thin envelope of plasma, as well as isotopes such as helium-3, a potential fuel for future fusion energy reactors. The orbiter itself will follow up on a stunning discovery by India's first lunar foray, the Chandrayaan-1 orbiter, which found water molecules on the moon in 2009. Before that, "It was kind of a kooky science to think that you'd find water" there, says James Greenwood, a cosmochemist at Wesleyan University in Middletown, Connecticut. "Now, we're arguing about how much water, and not whether it has water or not." Cameras and a spectrometer aboard the Chandrayaan-2 orbiter could help settle that question.

The $150 million mission was originally meant to fly 3 years ago, but Russia failed to deliver a promised lander, prompting India to go it alone. Final preparations are underway on the Chandrayaan-2 spacecraft, which will launch from the Sriharikota spaceport on the Bay of Bengal aboard India's Geosynchronous Satellite Launch Vehicle.

A landing so far from the lunar equator is especially tricky. "It is a difficult and complicated mission," says Wu Ji, director of the National Space Science Center in Beijing. Less sunlight reaches the poles, which means the lander and rover must be parsimonious with power. The plan is to set down in a high plain between two craters, Manzinus C and Simpelius N, at a latitude of about 70° south.

The lander will pack as much science as it can into its first lunar day—14 Earth days—as controllers may not be able to revive it after the long lunar night. The craft has a Langmuir probe to measure the moon's plasma—a wispy layer of charged ions that may explain why the lunar regolith, or dust, has a tendency to float in the thin atmosphere. It also has a seismometer for recording moonquakes. Its seismic measurements would supplement those from the Apollo landings, because readings from high latitudes would be sensitive to signals passing through different parts of the moon. And if the seismometer is lucky enough to record a sizable quake during its operational lifetime, it might offer new evidence in a long-running debate over what the moon's core is composed of, and whether it's solid. "We just need more data to understand the lunar interior," says David Kring, a planetary geologist at the Lunar and Planetary Institute in Houston, Texas, who is not involved in the mission.

The briefcase-size rover, weighing just 25 kilograms, will also carry two spectrometers for probing the lunar surface's elemental composition. The area is enticing, as it is thought to be made up of rocks more than 4 billion years old that solidified from the magma ocean that covered the newly formed moon. The data would be compared with those from Apollo-era missions that landed in other ancient highlands closer to the equator.

For some scientists, the most anticipated data will come from the orbiter's water mapper. Protons in the solar wind generate hydroxyl ions when they strike oxides in the regolith. The ions drift to the poles, where they are trapped in craters as water ice, which the orbiter will inventory. Shedding light on the moon's water circulation "is a worthwhile endeavor," says Carle Pieters, a lunar scientist at Brown University. Locating substantial water, adds Muthayya Vanitha, Chandrayaan-2's project director at ISRO, "could pave the way for the future habitation of the moon," as water is a limiting factor for operating a base.

Regardless of whether Chandrayaan-2 breaks new scientific ground, a successful soft landing near the south pole will be a technical accomplishment for India, as well as a proud moment for the country. It may even benefit other countries' moon programs. "One of NASA's main priorities is to go [to the south pole] on a sample return mission," Greenwood says, "so this could help us also later down the road as they give us more information as to what's there."