Context

The Imaging Infrared Spectrometer (IIRS) instrument on Chandrayaan-2 lunar orbiter has confirmed the presence of hydroxyl ions (OH) and water molecules (H2O) on the surface of the moon.

Background

About Chandrayaan-2 mission

• Chandrayaan-2 is an Indian lunar mission to explore the uncharted south pole of the celestial body by landing a rover.
• Aim: To enhance understanding of the Moon, stimulate the advancement of technology, promote global alliances and inspire a future generation of explorers and scientists.
• Mission coverage: This is a unique mission that aims at studying not just one area of the Moon but all the areas combining the exosphere, the surface as well as the sub-surface of the moon in a single mission.
• The GSLV Mk-III is India's most powerful launcher to date, and has been completely designed and fabricated from within the country.

Components:

• This highly complex mission brought together an Orbiter, Lander and Rover with the goal of exploring the South Pole of the Moon.
• Orbiter: The Orbiter will observe the lunar surface and relay communication between Earth and Chandrayaan 2”s Lander — Vikram.
• Vikram Lander: The lander was designed to execute India's first soft landing on the lunar surface.
• Pragyan Rover: The rover was a 6-wheeled, AI-powered vehicle named Pragyan, which translates to “wisdom”in Sanskrit.

Why the South Pole was chosen? The Lunar South pole is especially interesting because the lunar surface area that remains in shadow is much larger than that at the North Pole. There could be a possibility of presence of water in permanently shadowed areas around it. In addition, the South Pole region has craters that are cold traps and contain a fossil record of the early Solar System.

Key-Findings: 

• The new infrared spectrometer IIRS was designed to operate in the 0.8 to 5 μm range and mapped the lunar surface from a circular orbit of 100km from the Moon’s surface.
• It has quantified the amount of water molecules present on the lunar surface regions and distinguished parts of the moon which are water-rich and scant in hydration.
• Earlier detection: Water was originally discovered by the Chandrayaan-1 mission, in 2008, but the low resolution of its mapper could not quantify between the OH and water molecules readings.
• Two instruments-M3 instrument and MIP instrument on CHACE instrument, confirmed the presence of water.

Source of water

• Location of water: The data confirmed that hydration exists on sunlit portions, permanently shadowed craters, and Polar regions.
  • The silicate rocks called plagioclase absorbed more water, while older highland rocks that rise above the surface showed weak signatures of hydration.

Proposed Theories regarding presence of water on MoonA number of theories have been proposed for the source of hydration on the moon, including-

• Origins from within the Moon’s internal mantle processes of the past.
• Water or ice-bearing comets could have crashed into the Moon millions of years ago, depositing water molecules.
• The findings of water within olivine melt inclusions or small crystallised bits of magma on the Moon also back this origin.
• The initial data analysis from Indian Institute of Remote Sensing  (IIRS) clearly demonstrates the presence of widespread lunar hydration and unambiguous detection of OH and H2O signatures between 29 degrees north and 62 degrees north latitude.
• Space weathering

What is Space Weathering?

• The most likely and widespread source of water is the interaction of the solar wind or charged solar particles with the surface of the Moon, in the absence of a protective atmosphere or magnetic field.
• This process is called space weathering.
• This process is similar to weathering processes on Earth, there are weathering effects on atmosphere-less bodies exposed to the vacuum of space.
• It can also alter reflection and spectral readings and the optical properties of surfaces, sometimes resulting in incorrectly interpreted data.