The Great Southern Comet of 1887 holds the record for getting closer to the sun than any other detected natural object, passing within 446,187 miles (718,070 km) of the solar center. While Mercury orbits at a distance of 29 million miles (47 million kilometers) at its closest point, a variety of asteroids, comets, and spacecraft routinely cross that threshold to brave the extreme heat of the inner solar system.
Mercury-Crossing Asteroids and the 2024 YL3 Record
Numerous rocks pass well inside Mercury’s orbital path. Astronomer Scott Sheppard of Carnegie Science explains that these bodies, known as Mercury-crossers, possess highly eccentric orbits. They likely originated in the main asteroid belt before gravitational scattering pushed them toward the sun. According to NASA’s Small-Body Database, the skyscraper-size asteroid 2024 YL3—measuring 463 feet (141 meters) long—currently holds the record for this category with a perihelion of 6.4 million miles (10.3 million km).
The Hypothesized Vulcanoids
Researchers have also theorized the existence of Vulcanoids, a population of asteroids thought to travel in stable, circular orbits entirely within Mercury’s path. Professor emeritus Martin Beech of the University of Regina notes that numerical models place these hypothetical orbits between 5.58 million and 23.23 million miles (8.98 million to 37.39 million km) from the sun’s center. However, astronomers have yet to confirm their existence, and a 2013 study found no trace of them.
Did you know? Asteroids that cross Mercury’s path are dynamically unstable over long timescales. Sheppard points out that they will likely collide with the sun, impact a planet, or get ejected from the solar system within a few million years.
Spacecraft Plunge Deep Into the Solar Corona
Human-made hardware has pushed past asteroid boundaries to sample the sun’s outer atmosphere. NASA’s Parker Solar Probe, launched in 2018, utilizes a carbon foam heat shield to survive blistering temperatures. During its primary mission’s final three orbits, the probe executed an eccentric path bringing it just 4.5 million miles (7.3 million km) from the sun’s center to study the corona directly.
Sungrazing and Sundiving Comets
Comets push solar proximity to even more extreme limits. A 2018 study categorizes sungrazing comets as objects that pass within 1.49 million miles (2.39 million km) of the solar center. Researcher Man-To Hui of the Shanghai Astronomical Observatory explains that small sungrazing fragments—some only 30 feet (10 meters) wide—frequently break apart due to uneven thermal rotation, while intense gravity tears larger ones apart. Despite these hazards, some survive, such as the Great Southern Comet of 1887.
Beyond sungrazers lie theoretical “sundiving” or “sunstriking” comets. While none have been officially detected yet, researchers calculate that a sundiver would require a perihelion of less than the sun’s radius—432,244 miles (695,630 km) from the center—causing it to plunge straight into the photosphere and disintegrate permanently on impact.
Frequently Asked Questions
What object has gotten closest to the sun?
The detected natural object that came closest to the sun is the Great Southern Comet of 1887, reaching a perihelion of 446,187 miles (718,070 km).
How close does Mercury get to the sun?
At its closest point, known as perihelion, Mercury comes within 29 million miles (47 million kilometers) of the sun, according to NASA.
What is a Mercury-crossing asteroid?
A Mercury-crosser is an asteroid with an eccentric orbit that crosses Mercury’s path. These rocks were scattered inward from the main asteroid belt.
Has any spacecraft touched the sun’s atmosphere?
Yes. NASA’s Parker Solar Probe has flown as close as 4.5 million miles (7.3 million km) from the solar center, plunging directly through the corona.
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