Astronomy 84 - Mercury
Overview
This lecture covers the characteristics, surface features, internal structure, atmosphere, temperature extremes, and the presence of water ice on the planet Mercury.
Mercury's Size & Surface Features
- Mercury is the smallest planet, only slightly larger than Earth's Moon.
- Its surface closely resembles the Moon, primarily dominated by craters.
- Mercury has the highest density of craters of any planet, indicating an old and geologically inactive surface.
- Volcanic activity is minimal, with only evidence of a few ancient, inactive volcanoes.
- The terrain between craters is called "intercrater plains," meaning flat land between craters.
- Mercury is overall very flat with few mountains.
Scarps (Surface Hills)
- Long, wavy hills on Mercury’s surface are called "scarps."
- Scarps formed as Mercury cooled rapidly, causing its crust to shrink, creating wrinkle-like features called "raisin wrinkles."
- Unlike Earth's hills formed by plate tectonics, Mercury's scarps result from planetary contraction.
Mercury's Internal Structure
- Mercury's core is much larger (proportionally) than those of other terrestrial planets, with a thin mantle.
- Mercury is very dense due to its high iron content.
- Leading hypothesis: Mercury was struck by a large object, losing much of its lighter material and leaving behind a dense, iron-rich core.
Atmosphere & Temperature
- Mercury has almost no atmosphere because its low gravity and high temperatures allow gases to escape into space.
- Daytime temperatures reach up to 800°F (660°F average); nighttime temperatures drop to -260°F.
- Lack of atmosphere causes extreme temperature variation—the largest in the Solar System.
- No greenhouse effect means Mercury cannot trap heat during nighttime.
Water on Mercury
- Water cannot persist on the surface due to temperature extremes and low gravity.
- Small amounts of water ice exist at Mercury's poles, inside craters that are permanently shadowed and never receive sunlight.
Key Terms & Definitions
- Crater — circular depression formed by the impact of a meteorite.
- Intercrater plains — flat regions located between impact craters.
- Scarp — long, curved cliffs or ridges on Mercury caused by contraction as the planet cooled.
- Mantle — middle layer inside a planet, between the core and crust.
- Core — central, innermost layer of a planet, typically rich in metals.
Action Items / Next Steps
- Review textbook Figure in Chapter 7 for images of Mercury’s surface features.
- Study the differences between Mercury's internal structure and other terrestrial planets.