In 2004, NASA launched the MESSENGER spacecraft primarily to study which planet in our solar system?

Introduction / Context:
This question is about space exploration and planetary science. It asks which planet NASA aimed to study with the MESSENGER spacecraft launched in 2004. Knowing the targets of major missions helps you connect space technology with discoveries about different planets in our solar system.

Given Data / Assumptions:

• The mission name MESSENGER is given, and the launch year is 2004.
• Options include Saturn, Jupiter, Pluto, and Mercury.
• Basic awareness of well known planetary missions is assumed.

Concept / Approach:
MESSENGER was a NASA mission specifically designed to study Mercury, the smallest and innermost planet in the solar system. The name MESSENGER is an acronym and also recalls the Roman god Mercury, who was a messenger, which hints at the mission target. The spacecraft orbited Mercury and collected data on its surface, gravity field, magnetic field, and thin atmosphere. Other planets in the options were studied by different missions: Saturn by Cassini, Jupiter by Galileo and Juno, and Pluto by New Horizons, not by MESSENGER.

Step-by-Step Solution:

Verification / Alternative check:
Space mission summaries from NASA and educational sources clearly state that MESSENGER was the first spacecraft to orbit Mercury. They highlight discoveries such as Mercury unusual core size, magnetic field, and surface composition. Mission timelines show a 2004 launch, a long journey with multiple flybys, and final insertion into Mercury orbit. These independent details confirm that Mercury and MESSENGER are linked, while the other planets were explored by different missions.

Why Other Options Are Wrong:

Saturn, the ringed gas giant, is incorrect because Saturn was studied in detail by the Cassini mission rather than by MESSENGER.

Jupiter, the largest planet, is wrong because missions like Galileo and Juno focused on Jupiter, not MESSENGER.

Pluto, a distant dwarf planet, is incorrect because it was visited by the New Horizons mission many years after MESSENGER was launched.

Common Pitfalls:
Students sometimes mix up mission names due to the large number of space probes and similar sounding acronyms. Another pitfall is to assume that any prominent mission must have gone to the biggest or most famous planet, such as Jupiter or Saturn. However, exam questions often use the mission name itself as a clue, as in this case where MESSENGER points toward Mercury. Paying attention to these hints and cross linking them with known missions helps avoid confusion.

Final Answer:
The MESSENGER spacecraft launched in 2004 was sent to study Mercury, the innermost planet closest to the Sun.