Vikram lunar lander, photographed by the Pragyan rover. Source: Indian Space Research Organization via AP/Alamy
The Vikram lunar lander and the Indian Space Research Organization (ISRO) robotic rover, Prajyan, have been ordered to sleep. ISRO hopes to wake them up at dawn on September 22.
But during their two-week stay around the moon’s south pole, they provided information that puzzled planetary scientists. Here are some fascinating early finds.
A fine soup of ions and electrons orbits near the lunar pole
A probe aboard Vikram took the first measurements of the density and temperature of the Moon’s ionosphere. ISRO reported a “relatively sparse” mixture of ions and electrons in the 100-kilometre-thick layer of electrically charged plasma surrounding the moon’s surface near the south pole.
Early measurements of plasma suggested a density of about 5 to 30 million electrons per cubic metre. The density appears to vary as the lunar day progresses, said an ISRO scientist analyzing data from the Chandrayaan-3 mission. nature. The maximum density of a similar layer in the Earth’s upper atmosphere is one million electrons per cubic centimeter.
The density of the ionosphere would affect lunar communications and navigation systems if humans inhabited the Moon: the higher the electron density, the longer it would take radio signals to cross the ionosphere. The scientist says the scattered plasma means potential delays will be “minimal” and will not pose a problem with transmission.
Temperature differences with depth
Understanding lunar soil, including its temperature and conductivity, will be important when considering a site on the moon. Soil is “an important component of the region’s building resource,” says Anil Bhardwaj, director of ISRO’s Physical Research Laboratory in Ahmedabad.
The lander is equipped with a temperature probe containing 10 sensors and capable of reaching a depth of 10 centimeters below the surface of the moon. Its preliminary data indicate that the temperature at a depth of 8 cm during the day is about 60 degrees Celsius lower than the temperature at the surface.
A sharp drop in temperature is expected during the lunar day, as heat does not flow down from the warm, sunlit surface, says planetary scientist Paul Hein of the University of Colorado in Boulder. “It’s similar to the effect one gets when visiting the beach on a hot day: just dig a few inches and you’ll find the sand is much cooler,” he says.
Hein adds that measurements so far have revealed that the surface temperature is much warmer than that recorded by NASA’s Lunar Reconnaissance Orbiter in 2009.
The temperatures are “much too hot for water ice to be stable,” says Hein, explaining that water changes from solid to gas at very low temperatures in the vacuum of space, around -160 degrees Celsius. Chandrayaan-3 data indicate temperatures above -10 °C at all sampling depths. Further down, “we expect temperatures to stabilize near the average surface temperature of around -80°C,” says Hein.
Suspected lunar earthquake
Among the many vibrations recorded by the lander’s seismograph, one in particular caught scientists’ attention. “The instrument appears to have recorded a very small seismic event that decayed in about 4 seconds,” says planetary chemist Mark Norman of the Australian National University in Canberra. ISRO scientists suspect it was a small earthquake or small meteorite impact.
Such disturbances are expected to occur on the moon. “Small impacts and local tectonic modifications associated with tidal forces are common on the Moon, but we really need a global lunar seismic network and long-term observations to understand the significance of a special event,” Norman says.
Confirmed sulfur
Tests conducted by the rover unambiguously confirm the presence of sulfur on the moon’s surface near the south pole, ISRO reports. Aluminum, silicon, calcium, and iron have also been found, among other elements.
“Sulphur, as it is a volatile substance, is not generally expected to be present,” says Bhardwaj. Scientists say that confirming its existence is very important. Sulfur is a major component of molten rock, and researchers believe the early Moon was covered in a thick layer of hot molten rock, which crystallized to form the moon’s surface. Measurements of sulfur concentrations could provide insight into this process, says the ISRO scientist. However, it is also possible that the sulfur comes from asteroids bombarding the moon’s surface. The ISRO scientist hopes to add his findings to those of the US Apollo missions to better understand the moon’s geochemistry.
