NASA/Johns Hopkins University Applied Physics Laboratory/Arizona State University/Carnegie Institution of Washington, Public domainMercury
The smallest planet and the fastest, scorched by day and frozen by night
Overview
Mercury is the first planet from the Sun and the smallest in the Solar System. It is a rocky planet with a trace atmosphere and a surface gravity slightly lower than that of Mars. The surface of Mercury is similar to Earth's Moon, being cratered, with an expansive rupes system generated from thrust faults, and bright ray systems, formed by ejecta. Its largest crater, Caloris Planitia, has a diameter of 1,550 km (960 mi), which is about one-third the diameter of the planet. Being the most inferior orbiting planet, it always appears close to the Sun in Earth's sky, as either a "morning star" or an "evening star". It is the planet with the highest delta-v required for travel from Earth, as well as to and from the other planets in the Solar System.
Source: Wikipedia
Why it matters
- Orbits the Sun every 88 days, yet one solar day lasts 176 Earth days because of its 3:2 spin-orbit resonance.
- Surface temperatures swing from about 430 °C in sunlight to −180 °C at night; water ice survives in permanently shadowed polar craters.
- Has an oversized iron core (about 85% of its radius) and a weak but real global magnetic field, mapped by NASA's MESSENGER.
System
- Discovered
- known since antiquity
- Star
- Sun · G2 V · 5,772 K · 1 M☉
- System
- 8 known planets
Orbit in the Solar System
| World | Period | Distance | Radius | Mass | Temp. |
|---|---|---|---|---|---|
| Mercury | 88 d | 0.387 AU | 0.38 R⊕ | 0.055 M⊕ | 440 K |
| Venus | 224.7 d | 0.723 AU | 0.95 R⊕ | 0.82 M⊕ | 737 K |
| Earth | 365.2 d | 1 AU | 1 R⊕ | 1 M⊕ | 288 K |
| Mars | 687 d | 1.52 AU | 0.53 R⊕ | 0.11 M⊕ | 208 K |
| Ceres | 4.6 yr | 2.77 AU | 0.07 R⊕ | 0.94 ×10²¹ kg | — |
| Jupiter | 11.9 yr | 5.2 AU | 1 R♃ | 1 M♃ | 163 K |
| Saturn | 29.4 yr | 9.57 AU | 0.84 R♃ | 95.11 M⊕ | 133 K |
| Uranus | 83.7 yr | 19.16 AU | 0.36 R♃ | 14.53 M⊕ | 78 K |
| Neptune | 163.7 yr | 30.18 AU | 3.88 R⊕ | 17.08 M⊕ | 73 K |
| Pluto | 247.9 yr | 39.48 AU | 0.19 R⊕ | 13 ×10²¹ kg | 48 K |
| Haumea | 282 yr | 43.1 AU | 0.12 R⊕ | — | 50 K |
| Makemake | 306.6 yr | 45.6 AU | 0.11 R⊕ | 3.1 ×10²¹ kg | — |
| Eris | 561.3 yr | 67.9 AU | 0.18 R⊕ | 17 ×10²¹ kg | 43 K |
| Sedna | 12,676.2 yr | 544 AU | 0.08 R⊕ | — | 12 K |
By the numbers
- Radius
- 0.38 R⊕2,437 km
- Mass
- 0.055 M⊕0.33 ×10²⁴ kg
- Orbital period
- 88 d0.24 yr
- Distance from Sun
- 0.387 AU58 million km
- Eccentricity
- 0.206elliptical
- Mean temperature
- 167 °C440 K
- Gravity
- 3.7 m/s²0.38 g
- Day length
- 4,222.6 h175.9 Earth days
- Moons
- 0
- Density
- 5.43 g/cm³
- Axial tilt
- 0°
Sources
Image: NASA/Johns Hopkins University Applied Physics Laboratory/Arizona State University/Carnegie Institution of Washington, Public domain · Public domain · image page
Text: Wikipedia (CC BY-SA 4.0). Taglines and highlights are editorial.