On the heels of the heart breaking news of the SSLV failure came a sliver of hope as ISRO’s Chandrayaan-2 delivered a scientific discovery. It has found that there is a plasma density in the moon’s ionosphere, which opens new possibilities in understanding the lunar dark side environment

It came as a heartbreak to millions as the maiden flight of ISRO’s Small Satellite Launch Vehicle (SSLV) fell short of achieving its goal. The SSLV failed to deliver two satellites into orbit rendering them unusable.

However, on the heels of the bad news came a sliver of hope as ISRO’s Chandrayaan-2 delivered a scientific discovery. Chandrayaan-2 found that there is a plasma density in the moon’s ionosphere.

Let’s understand the latest discovery made by Chandrayaan-2:

What Has Chandrayaan-2 Found?

ISRO’s indigenous spacecraft was launched into a lunar orbit in July 2019, carrying several payloads including Dual Frequency Radio Science (DFRS), which is designed to study the lunar ionosphere.

The DFRS has played a significant role in the latest discovery. Using the technology, Chandrayaan-2 has discovered that the moon’s ionosphere has a plasma density in the wake region, which is at least one order of magnitude more than what is present on the day side.

The discovery opens new possibilities in understanding the lunar dark side plasma environment.

The measurements made using DFRS have shown that the moon’s ionosphere has a plasma density of 104 per cubic centimetre in the wake region, which is at least one order of magnitude more than that present on the day side.

"In the wake region, neither the solar radiation nor the solar wind interacts directly with the available neutral particles, but still, the plasma is getting generated", ISRO said in its statement.

The DFRS uses two coherent signals in S-band (2240 MHz) and X-band (8496 MHz) of radio frequencies. These are transmitted from Chandrayaan-2 orbiter and received by the ground station at Byalalu, Bangalore, to explore lunar plasma ambiance using the radio occultation (RO) technique.

ISRO said that simultaneous measurements by two coherent radio signals helps mitigate the effect of Earth’s atmosphere and any uncertainties due to various sources during the experiments.

A total of 12 such radio occultation experiments were conducted in campaign mode on four different occasions.

The findings have been published in the journal Monthly Notices of the Royal Astronomical Society- Letter.

“These observations are unique in nature as they show post-sunset enhancements in the iEDPs compared to dayside, as reported by earlier missions. These results further confirm recent predictions from the theoretical model for the lunar ionosphere,” the paper concluded.

The experts also noted that argon and neon are the dominant ions in the wake region. These have a comparatively longer lifetime than the molecular ions of carbon dioxide and water dominant in other regions.

“Numerical simulations of the dark side of plasma environment using a 3-dimensional Lunar Ionospheric Model (3D-LIM) developed at SPL that the production of ions by charge exchange reactions may play a pivotal role in producing a significantly large plasma density in the Lunar wake region, which can sustain for a longer period,” ISRO said in a statement.