Discover Mercury—the smallest planet in our solar system. Learn its size, secrets, orbit, and NASA mission discoveries in this complete guide.
Key Takeaways
- 水星是smallest planet in our solar system直徑為4,880 km (美國太空總署).
- 它完成了一個軌道88 土 days，是所有行星中最快的。
- 美國宇航局的MESSENGER覜發現water ice並且可能diamond-rich layers在表面之下。
- 水星 has no atmosphere為了保持熱量，導致極端temperature swings從 -173°C 到 427°C。
- 儘管最接近太陽報, Venus由於其厚重的大氣層而更熱。
What Is the Smallest Planet in Our Solar System?
Since Pluto’s reclassification in 2006, Mercury holds the title of the smallest planet.
It’s only slightly larger than 地球的月球, yet denser than any other planet except Earth.
Why Is Mercury the Smallest Planet?
Scientists believe Mercury’s size is due to violent early collisions or the 太陽的 intense heat stripping away lighter materials.
Two main theories:
- Giant Impact Hypothesis– 一次大規模碰撞移除了水星的大部分外衣。
- Solar Proximity Theory– 高溫和輻射蒸發了較輕的元素。
Mercury vs Earth
| 行星 | 直徑（公里） | 質量（地球=1） | 重力 （m/s²） |
|---|---|---|---|
| 土 | 12,742 | 1.00 | 9.8 |
| 水星 | 4,880 | 0.055 | 3.7 |
Mercury’s iron core takes up 75% of its diameter, making it unusually dense (Space.com).
PAA Question: Why Is Mercury Not the Hottest Planet?
金星更熱，因為它厚厚的大氣層會吸收熱量 through a runaway greenhouse effect.
Mercury’s thin exosphere cannot retain heat, causing 600°C temperature swings.
Mercury’s Orbit and Speed
- Average 距 from Sun:五千七百九十萬公里（0.39 天文單位）
- Orbital speed:~47 公里/秒（最快星球）
- Rotation period: 59 地球日→一個太陽一天持續 176 個地球日。
Secrets of Mercury’s Surface
- Caloris Basin:1,550 公里寬的火山口，來自古代撞擊
- Hollows:揮發性物質損失引起的明亮凹陷
- Volcanic plains:早期大量熔岩流的證據史
Mercury’s Atmosphere (Exosphere)
Mercury’s exosphere is composed of sodium, potassium, 氧, helium, and hydrogen.
It’s replenished by 太陽風 and micrometeorite impacts.
Magnetic Field Mystery – Extended
Mercury’s magnetic field is about 1% of Earth’s, yet it exists despite Mercury’s small size.
Theories suggest:
- 部分熔融的核心由sulfur-rich composition降低熔點。
- 潮汐與Sun可能會保留部分核心液體。
BepiColombo (ESA–JAXA, arriving 2025) will measure the 磁場的起源和動力學詳細.
Firsthand Observation – Extended
When I planned to 看 Mercury, I used SkySafari to pinpoint its location.
- Time: 30 minutes before sunrise during greatest elongation
- Equipment: 70mm折射望遠鏡、低倍目鏡
- Conditions: Clear, low-horizon view—trees or 建築物可以阻塞它很容易。
透過目鏡，水星看起來像一個小而明亮的新月——雖小卻令人著迷。
Mercury in Space Exploration – Expanded
- Mariner 10 (1974–1975): First flybys, mapped ~45% of surface.
- MESSENGER (2011–2015):繞水星運行，繪製了表面圖，發現了水冰。
- BepiColombo (2025):將更詳細地研究磁場、成分和表面。
Best Telescopes for Viewing Mercury
| 型 | 型 | 亮點 |
|---|---|---|
| 星特朗 AstroMaster 70AZ | 折射鏡 | Affordable, easy setup |
| 天空觀察者 SkyMax 127 | 馬克蘇托夫 | 清晰的行星視野，便攜式設計 |
Temperature Extremes Table
| 況 | 溫度 |
|---|---|
| 日間最高價 | 427°C |
| 夜間最低價 | −173°C |
| 搖擺 | ~600°C |
PAA Question: Is There Water on Mercury?
Yes. MESSENGER found water ice in permanently shadowed polar craters (美國太空總署).
PAA Question: How Often Can You See Mercury?
Best seen several times a year at greatest elongation, either just before sunrise or after sunset.
Why Mercury Matters
研究水星揭示了：
FAQ
Is Mercury smaller than Pluto?
No, Pluto is smaller.
Does Mercury have moons?
不。
Can we land on Mercury?
從技術上講是的，但極端的高溫和輻射使它變得困難。
How much would I weigh on Mercury?
About 38% of your Earth weight.
Why so many craters?
沒有厚厚的大氣層來燃燒流星體。
