What would happen if you brought a mercury barometer to Earth, the Moon, Mercury, Venus, and Mars?
Here, we assume that the mercury barometer has a U-shaped tube: one side is open, and the other side is sealed and kept in a vacuum.
🌍 Earth
- It works normally.
- Earth’s atmosphere (about 1 atm) pushes the mercury upward, maintaining a mercury column height of about 760 mmHg.
- The space above the mercury in the sealed tube becomes a vacuum (Torricelli’s vacuum).
🌙 Moon
- The Moon essentially has no atmosphere—it is almost a vacuum.
- Therefore, there is no atmospheric pressure to push the mercury upward.
- No mercury column is formed, and the entire barometer (except for the mercury itself) remains in a near-vacuum state.
- The height difference of the mercury column becomes 0.
☿ Mercury
- Mercury has an extremely thin atmosphere with practically zero pressure.
- Thus, the barometer does not function, and the mercury column does not rise.
- Also, due to the extremely high daytime temperatures, some mercury may even evaporate.
♀ Venus
- The atmospheric pressure on Venus is about 90 atm.
- This enormous pressure would push the mercury up very strongly. However, the resulting column height would be so large that it would be nearly impossible to measure with a real barometer.
- Because the mercury column height is proportional to atmospheric pressure:
→ 760 mm × 90 = 68,400 mm ≈ 68.4 meters - Therefore, to measure Venus’s atmospheric pressure with a mercury barometer, you would need a glass tube about 68 meters tall.
- Such equipment would likely break, overflow, or fail structurally.
♂ Mars
- Mars’s surface pressure is about 0.6% of Earth’s (≈ 0.006 atm).
- A mercury barometer on Mars would show:
→ 760 mmHg × 0.006 ≈ 4.5 mmHg - In other words, the mercury level would rise only a few millimeters, very close to the bottom.
- This is so small that accurate measurement becomes difficult.