The comet that came nearest to the sun without escaping its hold was not the planet closest to it; that title goes to Mercury.
Asteroids, comets and spacecraft have occasionally come closer to the Sun than Mercury’s perihelion, the point where a planet or orbiting body sits nearest to the star. That distance alone does not settle the question of which object gets closest to the Sun. Survival matters too. Some bodies make it through the passage intact. Others do not.
Mercury’s Perihelion
NASA says Mercury gets as close as 29 million miles from the sun at a point known as perihelion.
That is the benchmark. Anything closer counts as closer than Mercury.
Mercury-crossing asteroids exist too. A number of known objects cross Mercury’s orbit, which is why astronomers give them that name. Their paths are highly eccentric, so they did not form where they now travel. Rather, they were thrown from the main asteroid belt toward the Sun.
Scott Sheppard, an astronomer at Carnegie Science in Washington, D.C., told Live Science that the scattering is the likely explanation. “They did not form in this location but were likely scattered from the main asteroid belt towards the Sun,” he said.
A review of NASA’s Small-Body Database finds that 2024 YL3 holds the title for the largest known object that crosses Mercury’s orbit. The skyscraper-sized rock measures 463 feet long and comes within 6.4 million miles of the Sun at its closest approach.
The Hypothetical Vulcanoids
A set of objects has been suggested that might surpass 2024 YL3, though none of them have turned up so far. They are the proposed asteroids that sit inside Mercury’s path, named Vulcanoids for Vulcan, a supposed world once thought to exist in this very spot.
A professor emeritus of physics at the University of Regina in Canada named Martin Beech spoke with Live Science about the matter. His numerical models indicate that such asteroids could maintain stable orbits between 5.58 million and 23.23 million miles from the sun’s center. This suggests some Vulcanoids might actually come closer to the sun than Mercury-crossers do.
The catch is that Vulcanoids have not been shown to exist. A 2013 study found no trace of them.
Spacecraft That Came Closer
Spacecraft have come much, much closer than any known asteroid. NASA’s Parker Solar Probe, which launched in 2018, studied the sun’s outer atmosphere, or corona. For the primary mission’s final three orbits, the probe took an eccentric path with a perihelion of merely 4.5 million miles from the sun’s center.
The probe passed through the corona at that distance, and a carbon foam shield was there to guard it against the intense heat.
The Sungrazers
A second kind of natural object comes even nearer to the sun. These are the sungrazing comets, which approach within 1.49 million miles of its center. One 2018 investigation described these bodies.
Live Science reported that Man-To Hui, a researcher at the Shanghai Astronomical Observatory, said smaller sungrazers, some of which measure just 30 feet across, come apart as they spin due to uneven heating. Larger sungrazers are pulled apart by the sun’s powerful gravity.
A few escape without harm. The nearest one seen to date was the Great Southern Comet of 1887, which approached to a mere 446,187 miles from the sun.
The Sundivers
The true beneficiaries are the comets that dive toward the sun. These objects traverse the sun’s visible surface, known as its photosphere, before plunging into the star itself. Scientists believe such comets were plentiful when the solar system was young, yet they are uncommon today.
A 2018 study noted that a comet would need a perihelion less than the sun’s radius, or 432,244 miles from the sun’s center, to count as a sundiver. There are no second passes — all sundiving comets are destroyed within the sun.
A comet that comes close enough to the Sun to be called a sundiver has never been recorded. Should such an object be seen, it would set a new mark, surpassing the distance of the Great Southern Comet by 13,943 miles.
The Numbers That Matter
Here is the hard count:
- Mercury’s perihelion: 29 million miles (47 million kilometers)
- 2024 YL3’s perihelion: 6.4 million miles (10.3 million kilometers)
- Parker Solar Probe’s closest approach: 4.5 million miles (7.3 million kilometers)
- Great Southern Comet of 1887: 446,187 miles (718,070 kilometers)
- Sundiver threshold: 432,244 miles (695,630 kilometers)
The Order of Approaches
| Object | Type | Distance |
|---|---|---|
| Mercury | Planet | 29 million miles |
| 2024 YL3 | Asteroid | 6.4 million miles |
| Parker Solar Probe | Spacecraft | 4.5 million miles |
| Great Southern Comet | Comet | 446,187 miles |
| Sundiver threshold | Comet | 432,244 miles |
What We Make Of It
What comes nearest to the sun tells a tale of things that endure and things that perish. Some objects hold firm within orbits that keep them safe, while others fall apart after coming close, and still others vanish entirely without surviving the approach.
The comet that came nearest to the sun was the Great Southern Comet of 1887. Should any sundiver be sighted, it would take over as the new record-holder.
The closest object to the sun is a moving target. A sundiver, if it appears, will take the title. Until then, the Great Southern Comet of 1887 holds it.
The tale begins with Mercury-crosser asteroids and works its way toward the imagined Vulcanoids, then turns to sungrazing comets before closing with the doomed sundivers. Every step brings a different kind of object closer to the sun, and every step asks anew whether any of these objects can survive.
A survivor sits nearest to the sun. A phantom exists at the closest possible distance. And a comet that will not live to tell the tale might be detected as the closest object of all.
The tale is one of nearness and endurance, of objects that hold their place and those that do not. It moves from the known to the unknown, from the real to the imagined, and from the enduring to the destroyed.
Source material: “What is the closest any object has gotten to the sun?,” Live Science.
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