Sky Tonight — May 31, 2026
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Current Viewing Status
Mercury reached superior solar conjunction on May 14 and is now reappearing low in the western sky after sunset. Best views coming after June 15 (greatest eastern elongation). Look 45 minutes after sunset, just above Venus. Magnitude −0.4 — bright but low on the horizon.
Mercury is the smallest and innermost planet — a world of brutal extremes. With virtually no atmosphere to moderate temperature, its surface swings from −180°C in shadowed polar craters to +430°C on the sun-baked dayside — the largest temperature range of any planet.
Despite being closest to the Sun, Mercury is NOT the hottest planet (Venus holds that title due to its thick greenhouse atmosphere). Mercury's day is extraordinarily long at 176 Earth days — longer than its year of 88 days — meaning one Mercurian day covers two full trips around the Sun.
Mercury's surface looks remarkably like the Moon — heavily cratered, ancient, and geologically inactive. NASA's MESSENGER orbited Mercury from 2011–2015, revealing a surprisingly large iron core, water ice in permanently shadowed polar craters, and a global magnetic field. The ESA/JAXA BepiColombo mission arrives for orbital insertion in November 2026.
Type
Rocky terrestrial planet
Distance from Sun
57.9M km · 0.39 AU
Diameter
4,879 km (38% of Earth)
Temp range
−180°C to +430°C
Surface gravity
3.7 m/s² (38% Earth)
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Caloris Basin
1,550 km wide impact crater — one of the largest in the Solar System. The impact was so powerful it created chaotic terrain on the exact opposite side of the planet.
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Polar Ice
Permanently shadowed polar craters contain water ice deposited by comets — ice on the planet closest to the Sun! Confirmed by MESSENGER radar in 2012.
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Large Iron Core
Mercury's core makes up ~85% of its radius — proportionally the largest in the Solar System. Scientists believe it generates the planet's weak but real global magnetic field.
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Scarps (Rupes)
Giant cliffs stretching thousands of km. As Mercury's core cooled and shrank, the crust buckled inward, creating these wrinkle ridges unique to Mercury.
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NASA
MESSENGER (2011–2015)
Orbited Mercury for 4 years. First detailed maps, confirmed polar ice, revealed the giant core. Intentionally crashed into the surface in 2015.
✓ HistoricalESA·JAXA
BepiColombo
Two-spacecraft mission en route — ESA's MPO plus JAXA's MMO. Arrives for orbital insertion November 2026 after 7 years and 9 gravity-assist flybys. Will study the magnetic field, geology, and interior in unprecedented detail.
🔭 Planned
