India’s Chandrayaan-2 orbiter – up and operating.
Credit: ISRO

India’s Chandrayaan-2 orbiter is chalking up scientific findings as it circles the Moon, making use of eight state-of-the-art scientific instruments.

Schematic of the origin and dynamics of 40Ar in lunar exosphere.
As part of its early operation, India’s Moon orbiter has detected 40Ar in the lunar exosphere from an altitude of roughly 62 miles (100 kilometers), capturing the day-night variations of concentration. 40Ar being a condensable gas at the temperatures and pressures that prevail on the lunar surface, condenses during lunar night. After lunar dawn, the 40Ar starts getting released to the lunar exosphere (blue shaded region in figure).
Credit: ISRO

The orbiter’s Chandra Atmospheric Composition Explorer-2 (CHACE-2) payload has detected Argon-40 in the tenuous lunar exosphere – so thin that gas atoms very rarely collide with each other.

Argon-40 (40Ar), which is one of the isotopes of the noble gas Argon, is an important constituent of the lunar exosphere. The radioactive 40K nuclide, which is present deep below the lunar surface, disintegrates to 40Ar, which, in turn, diffuses through the intergranular space and makes its way up to the lunar exosphere through seepages and faults on the Moon’s landscape.

Chandrayaan-2’s Dual-Frequency Synthetic Aperture Radar (DF-SAR) payload can help unambiguously identify and quantitatively estimate lunar polar water-ice in permanently shadowed regions.
Credit: ISRO

Radar remote sensing

The Chandrayaan-2 orbiter has also made initial images and observations by its Dual-Frequency Synthetic Aperture Radar (DF-SAR).



SAR is a powerful remote sensing instrument for studying planetary surfaces and subsurface due to the ability of the radar signal to penetrate the surface. It is also sensitive to the roughness, structure and composition of the surface material and the buried terrain.


The main scientific objectives of this SAR payload are:

— High-resolution lunar mapping in the polar regions

— Quantitative estimation of water-ice in the polar regions

— Estimation of regolith thickness and its distribution

Pre-launch photo shows India’s Pragyan rover mounted on the ramp projecting from out of the sides of Vikram lunar lander. Vikram and the rover were scheduled on September 6 to land on near the Moon’s south polar region – but crashed onto the lunar surface.
Credit: ISRO

Lander lost

Chandrayaan-2 was launched by the Indian Space Research Organization (ISRO) on July 22, 2019. The craft entered lunar orbit on August 20, 2019.  

At liftoff, this spacecraft mission consisted of a lunar orbiter, the Vikram Moon lander, and the Pragyan lunar rover. Vikram and the rover were scheduled on September 6 to land on near the Moon’s south polar region – but crashed onto the lunar surface.

Meanwhile, the orbiter experiments are to be operational for 7 years, according to ISRO.

A Chandrayaan-2 data users meeting was held on October 22, 2019 in New Delhi.

Chandrayaan-2 data users meeting.
Credit: ISRO

One Response to “India’s Moon Orbiter: Scientific Sleuthing”

  • Doug Jones says:

    The very low density and long mean free path of the lunar atmosphere imply that any volatiles arriving at the polar cold traps do so individually. Dust particles are also levitated by solar UV and hop around until they are discharged or reach a cold trap.

    It’s not surprising in retrospect that there was a substantial amount of mercury detected; every atom of Hg that has arrived on the moon over billions of years has been mobilized by sunlight every day and bounced about until reaching the cold traps. In a way the traps are like the oceans of Earth, catching every solute washed downhill.

    Putting that all together, the polar traps are likely to have pitch-black (due to the porous fractal shape) fairy castles of dust grains cemented together by frost, filling the basins up to the sunlight line. Any rover sent into the darkness may simply submerge in a Fall of Moondust. Arthur Clarke was prescient.

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