Mercury Takes 176 Earth Days to Reach Sunrise Again as 3:2 Resonance Locks Its 88-Day Year
Updated
Updated · spacedaily.com · Jun 12
Mercury Takes 176 Earth Days to Reach Sunrise Again as 3:2 Resonance Locks Its 88-Day Year
1 articles · Updated · spacedaily.com · Jun 12
Summary
176 Earth days pass between sunrises on Mercury, meaning one solar day lasts just over two of the planet’s 88-day years.
NASA says the mismatch comes from Mercury’s 3:2 spin-orbit resonance: it rotates once every 59 Earth days while circling the Sun every 88, so the spin must catch up to the fast orbit.
1965 radar observations from Arecibo overturned the old belief that Mercury kept one face toward the Sun, showing instead a stable three-rotations-for-two-orbits rhythm.
That rhythm, combined with Mercury’s highly eccentric orbit, can make the Sun appear to rise, stop, reverse and rise again from some parts of the surface.
The months-long day and near-airless surface drive extreme temperatures, with highs near 800°F and lows around -290°F.