Key Takeaways

• Average distance: 57,910,000 km (0.387 AU) from the Sun.
• Closest approach (perihelion): approximately 46,001,000 km.
• Farthest point (aphelion): approximately 69,817,000 km.
• Orbital period: Mercury completes one orbit every 88 Earth days.
• Light travel time: sunlight takes roughly 3 minutes and 1 second to reach Mercury on average.
• Distance variation: Mercury's orbit is the most elliptical of any planet, causing a 52% swing between perihelion and aphelion.

What Is Mercury's Distance from the Sun in KM?

Mercury, the innermost planet in our solar system, orbits at an average distance of 57,910,000 kilometers (km) from the Sun. To put that into perspective, that is roughly 39% of the Earth–Sun distance (1 AU), making Mercury the planet closest to our star by a significant margin.

However, Mercury does not maintain a constant distance. Because it travels in a highly elliptical (oval-shaped) orbit, its distance from the Sun varies dramatically throughout its 88-day year. This orbital eccentricity is the highest of all eight planets, with an eccentricity value of 0.2056.

Detailed Mercury Distance Breakdown

Average Orbital Distance

The mean (average) distance from Mercury to the Sun is 57,910,000 km, which equals 0.387 astronomical units (AU). One AU is defined as the average Earth–Sun distance of approximately 149,597,871 km. Astronomers use this average as the standard reference point for comparing planetary distances.

Perihelion – Closest Approach

At perihelion, Mercury comes within roughly 46,001,000 km of the Sun. This is the point in its orbit where solar radiation and gravitational pull are at their strongest. Temperatures on Mercury's surface can reach as high as 430°C (800°F) at this proximity, making it the hottest planet despite Venus being closer to the Sun in terms of average orbital radius.

Aphelion – Farthest Point

At aphelion, Mercury recedes to approximately 69,817,000 km from the Sun. Despite being farther away, Mercury remains the hottest planet because it lacks a substantial atmosphere to retain or redistribute heat. The dramatic temperature swings between its day and night sides—reaching down to −180°C (−290°F)—are partly a consequence of this extreme orbital variation.

Why Does Mercury's Distance Variation Matter?

Mercury's extreme orbital eccentricity has several important implications for both science and exploration:

• Solar energy intensity: At perihelion, Mercury receives roughly 2.3 times more solar radiation than at aphelion. This affects surface temperatures, space weather modeling, and spacecraft thermal design.
• Space mission planning: NASA's MESSENGER and BepiColombo missions had to account for these distance variations when planning orbital insertions and flybys. Closer approach trajectories require greater thermal shielding.
• Visibility from Earth: Mercury's changing distance influences its apparent brightness and elongation angles, affecting when and how well it can be observed from Earth.
• Orbital resonance: The elliptical orbit contributes to Mercury's unique 3:2 spin–orbit resonance, where the planet rotates exactly three times on its axis for every two orbits around the Sun.

Mercury Compared to Other Planets: Distance from the Sun

Understanding Mercury's distance is easier when compared to the rest of the solar system. The table below ranks all eight planets by their average distance from the Sun.