Phobos

• Phobos is the larger and innermost of the two natural moons of Mars. The other moon is Deimos.
• Origin: Its origin is not fully established; scientists have proposed that it may be a captured asteroid or formed from debris following a major impact on Mars.
• Orbit: It orbits very close to Mars and completes one revolution in approximately 7 hours and 39 minutes.
• Orbital movement: Phobos orbits Mars faster than Mars rotates, so it rises in the west and sets in the east.
• Surface: It is irregularly shaped and heavily cratered, with Stickney being its largest crater.
• Future: Phobos is gradually moving closer to Mars and may eventually break apart or collide with the planet.

• Discovery: Discovered by astronomer Asaph Hall in August 1877.
• Gravity: Phobos has extremely weak gravity, about one-thousandth of Earth’s gravity.
• Atmosphere: It has no atmosphere.
• Current affairs — MMX Mission: Japan’s JAXA launched the Martian Moons eXploration (MMX) spacecraft on 19 October 2026. The mission aims to study Phobos and Deimos and return samples from Phobos to Earth in 2031.

UPSC Prelims Practice Questions

Q1. Consider the following statements about Phobos:

1. It is a natural satellite of Mars.
2. It is larger than Deimos.
3. It is gradually moving away from Mars.
4. It has a prominent crater named Stickney.

Which of the statements given above are correct?

A. 1 and 2 only

B. 1, 2 and 4 only

C. 1, 3 and 4 only

D. 1, 2, 3 and 4

The correct answer is B.

Explanation: Phobos is larger than Deimos and has the Stickney crater. It is moving closer to Mars, not away from it.

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