The Vikram lander on the Moon, as photographed by the Pragyan spacecraft.Source: Indian Space Research Organization via AP/Alamy
The Vikram moon lander and the Indian Space Research Organization (ISRO) robotic rover Pragyan have now been told to go to sleep. ISRO hopes to wake them up at lunar dawn on September 22nd.
But during their two-week stay around the moon’s south pole, they provided insights that puzzled planetary scientists. Here are some of the first great results.
A thin soup of ions and electrons swirls near the lunar pole
A probe aboard Vikram made the first measurements of the density and temperature of the moon’s ionosphere. ISRO notes that there is a “relatively sparse” mixture of ions and electrons in the 100-kilometre-thick layer of electrically charged plasma that surrounds the lunar surface near the south pole.
Initial measurements of the plasma indicate a density of about 5 million to 30 million electrons per cubic meter. The intensity appears to vary as the lunar day progresses, said the ISRO scientist who analyzes data for 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 navigation and communication systems if humans inhabited the moon. The denser the electrons, the longer it would take for radio signals to travel through the ionosphere. The scientist says the sparse plasma means the potential delay will be “minimal” and will not pose a problem for transmission.
Temperature differences with depth
Understanding lunar soil, including its temperature and conductivity, will be important when considering lunar settlement. Soil is important Active “This product is a resource for building,” says Anil Bhardwaj, director of ISRO’s Physics Research Laboratory in Ahmedabad.
The lander is equipped with a temperature probe that has 10 sensors and is capable of reaching a depth of 10 centimeters below the lunar surface. 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, says planetary scientist Paul Hein of the University of Colorado Boulder, because heat does not travel down from the warm, sunlit surface. “This is similar to the effect one feels when visiting the beach on a hot day – just dig in a few centimeters and the sand is much cooler,” he says.
Hein adds that measurements made so far have found the surface temperature to be much warmer than what was recorded by NASA’s Lunar Reconnaissance Orbiter in 2009.
Temperatures are “far too warm for water ice to be stable,” Hein says, explaining that water changes from a solid to a gaseous state at a very low temperature in the vacuum of space, at about minus 160 degrees Celsius. Chandrayaan-3 data indicate temperatures warmer than -10 °C at all sampled depths. “We expect temperatures to drop to close to the average surface temperature of about -80 degrees Celsius,” Hein says.
Suspected lunar earthquake
Among the many vibrations recorded by the lander’s seismograph, one in particular caught the scientists’ attention. Planetary chemist Mark Norman of the Australian National University in Canberra says the instrument “appears to have recorded a very small seismic event, receding into the background at about 4 seconds”. ISRO scientists suspect it was a small earthquake or the impact of a small meteorite.
Such disturbances are expected on the moon. “Small influences and local tectonic adjustments related to tidal forces are common on the Moon, but we really need a global seismic network on the Moon and long-term observations to understand the significance of any particular event,” says Norman.
Sulfur confirmed
Tests conducted by the rover unequivocally confirm the presence of sulfur on the lunar surface near the south pole, ISRO reports. It also found aluminum, silicon, calcium and iron, among other elements.
“Sulfur is generally not expected to be present, as it is a volatile substance,” Bhardwaj explains. Scientists say confirmation of its existence is really important. Sulfur is an essential element of molten rock, and researchers believe that the primordial moon was covered with a thick layer of hot molten rock, which crystallized to form the lunar surface. The ISRO scientist says measurements of sulfur concentrations can provide insight into this process. However, it is also possible that the sulfur may have come from asteroids bombarding the lunar surface. The ISRO scientist says they hope to add their findings to those of the US Apollo missions to better understand the geochemistry of the moon.