Chandrayaan-2's CHACE-2 makes first-ever observation of a solar CME's effect on the Moon's exosphere
On 18 October 2025, in India, ISRO announced that the CHACE-2 instrument on the Chandrayaan-2 orbiter had made the first-ever observation of the effect of the Sun's coronal mass ejection (CME) on the Moon's exosphere.
Summary
On 18 October 2025, in India, the Indian Space Research Organisation (ISRO) announced that Chandra's Atmospheric Composition Explorer-2 (CHACE-2) on the Chandrayaan-2 lunar orbiter had made the first-ever observation of the effects of a solar coronal mass ejection (CME) on the Moon. When a series of CMEs struck the Moon on 10 May 2024, CHACE-2 recorded a rise in the total pressure of the dayside lunar exosphere, and the derived total number density increased by more than an order of magnitude, as earlier theoretical models had predicted. ISRO said the Moon is an airless body without a global magnetic field, so such solar events affect it strongly, which also points to challenges for building scientific bases on the Moon. The study was published in Geophysical Research Letters on 16 August 2025.
Key facts
- Announced
- 18 Oct 2025, ISRO
- Instrument
- CHACE-2 (Chandra's Atmospheric Composition Explorer-2), Chandrayaan-2 orbiter
- First
- First-ever observation of a CME's effect on the lunar exosphere
- CME event
- 10 May 2024
- Finding
- Dayside exosphere pressure rose; number density up by more than an order of magnitude
- Moon's exosphere
- A 'surface boundary exosphere'
- CMEs
- Mostly helium and hydrogen ions
- Paper
- Geophysical Research Letters, 16 Aug 2025
Practice MCQs 3 questions
Which instrument on the Chandrayaan-2 orbiter made the first-ever observation of a solar CME's effect on the lunar exosphere, as announced by ISRO on 18 October 2025?
Show answer
Correct answer: D — CHACE-2
ISRO (18 Oct 2025): the observation was made by Chandra's Atmospheric Composition Explorer-2 (CHACE-2) on board the Chandrayaan-2 orbiter.
On which date did the series of coronal mass ejections occur whose impact on the Moon was observed by Chandrayaan-2's CHACE-2?
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Correct answer: B — 10 May 2024
ISRO (18 Oct 2025): the opportunity came in a rare occurrence on 10 May 2024, when a series of CMEs were hurled by the Sun.
Consider the following statements, as stated by ISRO in October 2025: 1. The Moon's exosphere falls under the category of a 'surface boundary exosphere'. 2. Coronal mass ejections comprise mostly helium and hydrogen ions. Which of the above is/are correct?
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Correct answer: C — Both 1 and 2
ISRO (18 Oct 2025): the Moon's exosphere is a 'surface boundary exosphere', and CMEs comprise mostly helium and hydrogen ions, so both statements are correct.