History of solar system exploration: Mercury

In this series I’ll give a brief history of humanity’s modern exploration attempts of the various worlds (gravitationally-rounded objects) of the solar system with a little projection in the future when warranted.

The innermost terrestrial planet was seen to move across the sky faster than any other “wander,” and so the ancient Romans named it after their fleet-footed god of trade, Mercury. Because it is an inferior planet with respect to the Earth (has a closer orbit), it is observed from Earth always near the Sun, which made it difficult to study by conventional means and so has been one of the least-studied planets. Because of its relative proximity to the Sun, it’s very difficult to send do robotic missions as well since any naive attempts to go straight to the planet would get accelerated by the Sun’s gravitation and rocket passed Mercury. Instead, complicated maneuvers must be conducted to safely reach the innermost planet while leaving sufficient fuel reserves to do actual science. An analogy is trying to reach a spot on a steep hill from higher up. Attempting to slide directly to to spot would likely result in failure and a tumble. The best bet is to make slower headway by crisscrossing back and forth and getting closer each pass.

Modern Exploration of Mercury:

  • Mariner 10 (1974) – NASA mission that achieved three close flybys of Mercury and partially mapped (40 – 45%) its surface before running out of fuel. Discovered a tenuous helium atmosphere and an unexpected magnetic field.
  • MESSENGER (2011) – NASA mission that entered a Mercurian orbit rather than just doing flybys (though due to the complexity of celestial maneuvers nearer the gravity well of the Sun it had done three flybys of Mercury prior to orbital insertion). Carried a broad suite of instruments and will map the entirety of the planet’s surface with high resolution. Ongoing.
  • BepiColombo (2019?) – Proposed joint ESA-JAXA mission. Planned to map the surface in several wavelengths and conduct precision tests of general relativity.
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