September 13, 2019

Last week, on September 6, an up-and-coming space agency fell just short of its goal. About 1 mile (1.5 kilometers) above the moon’s surface, the India Space Research Organization (ISRO) lander Vikram deviated from its landing course and disappeared from radio contact. Vikram was to be the crowning stage of Chandrayaan-2 (Mooncraft-2), ISRO’s second lunar mission.

This artist’s depiction shows Chandrayaan-2′s lunar lander, Vikram, approaching the moon. Credit: © Raymond Cassel, Shutterstock

India was endeavoring to become the fourth country to make a soft landing (a landing that does not destroy the craft) on the surface of the moon, after the United States, the former Soviet Union, and China. Vikram would have been the first lander near the moon’s south pole, a region full of water ice and other minerals that could one day be the site of a permanent base. Vikram would have deployed a rover to explore the landing site. The Chandrayaan-2 orbiter, which had launched Vikram, located the lander on the surface of the moon a few days after its disappearance. ISRO reported that Vikram had apparently made a “hard landing,” and the lander did not respond to contact attempts.

Before the recent failure, ISRO had been riding a wave of success. In 2008, the agency deployed its first lunar satellite, Chandrayaan-1. Chandrayaan-1 mapped the moon’s surface for about a year. The satellite also released a hard lander that impacted the lunar surface. In 2013, ISRO launched the Mars Orbiter Mission, called Mangalyaan (Marscraft). The satellite overcame a minor engine failure to reach Martian orbit in September 2014.

ISRO’s failed soft landing on the moon comes on the heels of another prominent lunar failure. In April 2019, the lander Beresheet (In the Beginning), developed by the Israeli company SpaceIL, slammed into the moon when its main engine cut out unexpectedly. SpaceIL had hoped to become the first private company to place a lander on the moon’s surface. It had been one of the competitors for the Google Lunar X Prize. The contest would have awarded $20 million to the first company to achieve a soft landing on the moon. But none of the competitors attempted a landing, even after several deadline extensions, so the prize was withdrawn. The Israeli project cost about $100 million, a fraction of what a similar mission by the United States National Aeronautics and Space Administration (NASA) would have cost, but it took greater risks and ultimately failed.

The process of landing is the most dangerous phase of a lander’s mission. Many different systems must work perfectly for the lander to bring itself to a halt on the surface. Any malfunction is usually catastrophic. At other points in a mission, such as in transit to or in orbit around another body, engineers have plenty of time to identify and work around problems with a spacecraft. But this cannot be done in the time-sensitive environment of landing.

December 10, 2012

Almost the entire surface of the moon was fractured by impacts billions of years ago, according to the most detailed map of the lunar gravity field ever created. The map is based on high-resolution data collected by NASA’s twin GRAIL orbiters. (GRAIL stands for Gravity Recovery and Interior Laboratory.) The map shows many of the moon’s structures in great detail, including features in the crust, volcanic formations, and numerous other landforms. The map has also revealed that the lunar crust is marked with many holes. Scientists believe this finding indicates that the surface was battered by a heavy bombardment of meteorites and other objects early in its history. The gravity map also indicates that the crust of the moon is only about 21 to 27 miles (34 to 43 kilometers) thick, about 6 to 12 miles (10 to 20 kilometers) thinner than scientists had thought.

A gravity map of the moon reveals mountains and other higher areas (red) and craters and other lower areas (blue). (NASA/ARC/MIT)

GRAIL was designed to measure changes in the moon’s gravitation as a way to reveal structures beneath the surface. The orbiters, which were launched in September 2011, travel around the moon on opposite sides at an altitude of about 34 miles (55 kilometers). They use radio signals to precisely measure the distance between them, which changes with the density of the rock and soil below. The system is so accurate that it can measure distances less than the width of a human hair. Scientists can link the satellites’ measurements to structural differences in the moon’s surface and underlying crust. The probes were named “Ebb” and “Flow” in January 2012 by elementary students in Bozeman, Montana, in a nationwide contest. The GRAIL mission is scheduled to end later this month.

Another interesting discovery by the orbiters is collections of long, linear dikes (thin,vertical bodies of solidified magma) beneath the surface. The dikes, which extend for hundreds of miles (kilometers), crisscross the surface. Scientists think that the dikes, which are among the oldest features on the moon, likely formed as the moon’s crust expanded. Such geologic events could have occurred if the moon formed as a result of a collision known as the Giant Impact or the “Big Whack.” According to this idea, Earth collided with a planet-sized object 4.6 billion years ago. During the impact, a cloud of vaporized rock shot off Earth’s surface and went into orbit around Earth. The cloud cooled and condensed into a ring of small, solid bodies, which then gathered together, forming the moon. The rapid joining together of the small bodies released much energy as heat. Consequently, the moon melted, creating an “ocean” of magma. Over time, the magma ocean slowly cooled and solidified into rocks called basalts.

Additional World Book articles:

• Space exploration (Lunar probes)
• How the Moon Was Born (a special report)