Mercury looks unremarkable at first glance ? a gray, cratered world baked by the sun and seemingly devoid of life or water. Yet this small, scorched planet has become one of the solar system’s greatest puzzles, defying long-held ideas about how planets form and evolve.
The mystery begins with Mercury’s size and composition. Only slightly more than a third the width of Earth, it is nonetheless the solar system’s second-densest planet. That surprising weight comes from an enormous metallic core that accounts for about 85% of the planet’s radius, leaving only a thin rocky mantle and crust above it. No current model of planet formation easily explains how such a structure could arise, particularly so close to the sun.
Spacecraft visits have only deepened the conundrum. NASA’s Mariner 10 flybys in the 1970s first hinted at Mercury’s oversized core. Decades later, the Messenger mission uncovered even more surprises. Among the most startling discoveries was that, despite extreme surface temperatures reaching up to 430 degrees Celsius and plunging as low as minus 180 degrees, Mercury holds volatile elements that should have evaporated long ago, along with water ice hidden in permanently shadowed polar craters. Together, these findings suggest Mercury may not have formed where it now orbits. Several theories attempt to explain the planet’s origins. One leading idea proposes that Mercury was once much larger and lost a significant portion of its outer layers in a colossal collision early in its history, leaving behind a dense, iron-rich remnant. Others argue it formed from unusually metal-rich material near the young sun, or that it migrated inward after forming elsewhere. Each scenario resolves some questions while creating others.
Fresh clues may arrive soon. The European-Japanese BepiColombo mission, launched in 2018, is set to enter orbit around Mercury in late 2026. Its instruments will map the planet’s surface, gravity, and magnetic field in unprecedented detail, helping scientists piece together its history.
Yesel Kang Copy Editor teen/1770600610/1613367750
1. What metallic core accounts for eighty-five percent of Mercury's radius?
2. Who hinted that Mercury has an oversized core in the seventies?
3. When will the BepiColombo mission enter orbit around the small planet?
4. Why does Mercury hold volatile elements despite its extreme surface heat?
1. Why should humans explore planets that cannot support any life?
2. How does scientific discovery change our long-held ideas about space?
3. Would you travel to Mercury if it was safe to visit?
4. What is the most mysterious planet in our solar system?
Mercury looks unremarkable at first glance ? a gray, cratered world baked by the sun and seemingly devoid of life or water. Yet this small, scorched planet has become one of the solar system’s greatest puzzles, defying long-held ideas about how planets form and evolve.
