First Detection of Negative Ions on the Moon

First Detection of Negative Ions on the Moon
by Erica Marchand
Paris, France (SPX) Jun 07, 2024

The first ESA instrument on the Moon has detected negative ions on the lunar surface produced through interactions with the solar wind.

The European team with the Negative Ions at the Lunar Surface (NILS) instrument confirmed the success of this mission aboard the Chang"e-6 spacecraft.

The discovery of a new component of plasma at the Moon"s surface opens new avenues for space physics and lunar exploration.

Mission of Firsts
The negative ion detector on the Moon collected over three hours of data, exceeding the mission"s requirements. This marked the first time ESA produced scientific data on the lunar surface.

"This was ESA"s first activity on the surface of the Moon, a world-first scientifically, and a first lunar cooperation with China. We have collected an amount and quality of data far beyond our expectations," says Neil Melville, ESA"s technical officer for the experiment built by the Swedish Institute of Space Physics (IRF).

Negative Ions - The Missing Piece
The solar wind is a constant flow of radiation and particles from the Sun. Unlike Earth, the Moon has no magnetic field and a very tenuous atmosphere, called the exosphere. When the solar wind hits the Moon, the surface reacts by releasing secondary particles.

These particles can be positively or negatively charged or neutral. While positively charged particles have been measured from orbit before, measuring negative particles was challenging.

Negative ions are short-lived and cannot reach orbit. This necessitated operating the instrument close to the lunar surface, a first for a particle detector.

"These observations on the Moon will help us better understand the surface environment and act as a pathfinder to explore negative ion populations in other airless bodies in the Solar System, from planets to asteroids and other moons," explains Martin Wieser, NILS principal investigator at IRF.

The science team is already working on research publications to share their findings. These measurements and the instrumentation used may aid further lunar environment investigations.

Two Days on the Moon for a European Experiment
Chang"e-6 landed in the South Pole-Aitken Basin on the Moon"s far side on 1 June 2024 at 23:23 BST (2 June 00:23 CEST).

The NILS team analyzed the landing parameters and activated the instrument about four hours after touchdown.

NILS started collecting data 280 minutes after landing. The first data collection lasted 23 minutes, followed by more rounds between communications blackouts and reboots.

"We were alternating between short bursts of full-power and long cooling-off periods because the instrument was heating up. The fact that it stayed within its thermal design limits and managed to recover under extremely hot conditions is a testament to the quality of the work done by the Swedish Institute of Space Physics," says Neil.

NILS was switched off at 15:20 BST/16:20 CEST on 3 June 2024.

Tracking from Earth
European ground stations are supporting the Chang"e-6 mission. Shortly after launch from China on 3 May 2024, ESA"s Kourou station in French Guiana tracked the spacecraft for several hours to confirm its orbit.

Around 25 June, ESA will catch signals from the spacecraft as it returns to Earth with lunar samples using the Maspalomas station, operated by the Instituto Nacional de Tecnica Aerospacial (INTA) in Gran Canaria, Spain.