ISRO: Chandrayaan-2 orbiter detects Argon-40 on Lunar exosphere

The Chandra’s Atmospheric Composition Explorer-2 (CHACE-2) payload aboard the Chandrayaan-2 orbiter has detected Argon-40 from an altitude of approximately 100 km said ISRO on Thursday. Planetary scientists prefer to call the thin gaseous envelope around the Moon as the ‘Lunar exosphere’ since it is so tenuous that the gas atoms very rarely collide with each other. ISRO also released a schematic of how Argon-40 is formed.

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An important constituent of the lunar exosphere

Argon-40 (⁴⁰Ar), which is one of the isotopes of the noble gas Argon, is an important constituent of the lunar exosphere. It originates from the radioactive disintegration of Potassium-40 (⁴⁰K), which has a half-life of ~1.2 X 10⁹ years. 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 way up to the lunar exosphere through seepages and faults.

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CHACE-2 is a neutral mass spectrometer

The Chandra’s Atmospheric Composition Explorer-2 (CHACE-2) payload aboard the Chandrayaan-2 orbiter, is a neutral mass spectrometer-based payload which can detect constituents in the lunar neutral exosphere in the range of 1-300 amu (atomic mass unit). As part of its early operation, it has detected ⁴⁰Ar in the lunar exosphere from an altitude of ~100 km, 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.

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Impact craters on the south polar region of the moon

On October 22, ISRO released the pictures of the impact craters on the south polar region of the moon clicked by the orbiter of Chandrayaan 2. These pictures show the observations made by the Synthetic Aperture Radar on the lunar surface. Moon’s surface has a lot of impact craters owing to the continuous bombardment of celestial bodies, these craters are usually studied by a powerful remote sensing instrument to know more about the moon’s surface. 

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