Astronomy: Mercury

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Across
  1. 4. The largest and most well-known impact crater on Mercury, spanning over 900 miles (1,500 km).
  2. 8. The innermost and smallest planet in the Solar System.
  3. 9. A NASA spacecraft (2011-2015) that was the first to orbit Mercury, mapping its entire surface.
  4. 10. Describes Mercury's surface, which is covered in impact craters similar to Earth's Moon, indicating a long history of bombardment.
  5. 11. Mercury doesn't have a true atmosphere, but rather a thin "exosphere" composed of atoms blasted off its surface by radiation and solar wind.
  6. 12. The time from one sunrise to the next on Mercury, which is exceptionally long (about 176 Earth days).
  7. 14. Mercury has an unusually large and dense metallic core (primarily iron) that is thought to make up about 85% of the planet's radius.
  8. 15. Mercury is named after the Roman messenger god (Mercurius), known for his speed, fitting for the planet with the fastest orbit.
  9. 16. An event where Mercury passes directly between the Sun and Earth, appearing as a tiny black dot crossing the Sun's disk.
  10. 18. Mercury experiences the most drastic temperature range in the Solar System, from scorching hot (800°F / 430°C) to freezing cold (-290°F / -180°C).
Down
  1. 1. A characteristic of Mercury; it lacks any natural satellites.
  2. 2. Deposits of this have been confirmed to exist in permanently shadowed craters near Mercury's poles, protected from the Sun's heat.
  3. 3. The first NASA space probe to visit Mercury, conducting three flybys in 1974 and 1975.
  4. 5. Long, curving, steep cliffs (rupes) on Mercury's surface, believed to have formed as the planet's iron core cooled and contracted.
  5. 6. A nickname for Mercury because it has the fastest orbit in the Solar System, completing a revolution in 88 days.
  6. 7. A current joint mission by ESA and JAXA (European and Japanese space agencies) to study Mercury, which arrived in 2025.
  7. 13. The time it takes Mercury to rotate once on its axis (about 59 Earth days). Mercury's unique orbital dynamic, where it rotates exactly three times on its axis for every two orbits it completes around the Sun.
  8. 17. The tenuous, atmosphere-like layer surrounding Mercury, composed of atoms like sodium, potassium, and calcium.