The Great Southern Comet came within 446,000 miles of the Sun — scientists explain how close an object can get and survive

Mercury is often described as the planet living closest to the Sun. But when it comes to getting dangerously close to our star, the planet is nowhere near the limit.

Asteroids, comets and even spacecraft have ventured millions of miles inside Mercury’s orbit. Some have survived the encounter and continued their journeys through space. Others have been torn apart, evaporated or plunged directly into the Sun.

Also Read | Why your next close friendship may start with something surprisingly ordinary: Scientists reveal how small everyday interactions can turn casual connections into lasting friendships


One of the closest known natural objects to make it through such an encounter was the Great Southern Comet of 1887, which passed just 446,187 miles (718,070 kilometres) from the Sun’s centre.

That distance is extraordinarily small on a solar-system scale. But somehow, the comet managed to survive.

The account poses an intriguingly straightforward question: How near to the Sun can an object come before it becomes impossible to sustain?

Also Read | In 1884, a ship disappeared near Nantucket after a powerful winter storm. More than a century later, another major storm has brought part of the shipwreck back to the surface

Based on the opinion of astronomers from Live Science, there is no one particular answer to this question.

An object's size, composition, orbit and exposure to solar heat and gravity all affect what happens during a close solar encounter.

Mercury is not even close to the solar danger zone

While Mercury could be the planet closest to the Sun, there are asteroids and comets that take trajectories further from the planet’s orbit.

The closest approach of Mercury brings the planet at around 29 million miles or 47 million kilometres away from the Sun. This distance is approximately 65 times the Great Southern Comet’s nearest recorded approach distance.

There are also asteroids that go much closer to the inner solar system.

According to Scott Sheppard, an astronomer at Carnegie Science, asteroids that cross Mercury’s orbit are called Mercury crossers. These objects' highly elliptical orbits indicate that their birthplace could have been somewhere else, as they were possibly influenced by gravitational forces and thrown out of their previous orbits.

The 2024 YL3 is the currently known record holder among the Mercury crossers identified in the NASA Small-Body Database. It is approximately 463 feet or 141 meters long and has the potential to get within 6.4 million miles or 10.3 million kilometres of the Sun.

That is still more than nine times farther from the Sun than the Great Southern Comet got.

There may also be objects that travel even closer — although astronomers have not confirmed that they exist.

These hypothetical asteroids are known as Vulcanoids. Models suggest that if such objects exist, some could maintain stable orbits between about 5.58 million and 23.23 million miles (8.98 million to 37.39 million kilometres) from the Sun's centre. Searches, however, have failed to find convincing evidence of a Vulcanoid population.

Some comets get so close that the Sun tears them apart

Comets represent another form of problem. While asteroids are rocky, comets consist of ice and volatile matter. Upon approaching the Sun, they heat up because of increased radiation and start sublimating ice.

That material can form the glowing coma and tail associated with comets.

With increasing closeness to the object, the conditions become harsher.

There is a category of comets called “sungrazers” which regularly approach very close to the Sun. As noted by Live Science in a 2018 study, “sungrazers” are comets that approach the Sun up to the distance of approximately 1.49 million miles (2.39 million kilometres) from its centre. However, proximity alone does not guarantee survival for a comet.

Man-To Hui of the Shanghai Astronomical Observatory told Live Science that smaller sungrazers can break apart because uneven heating causes them to rotate and fragment. Larger bodies can also be subjected to intense tidal forces from the Sun's gravity.

Yet some comets make it through.

The Great Southern Comet of 1887 is one of the closest observed examples. It passed only about 718,070 kilometres from the Sun's centre and survived its solar encounter, making it the closest detected natural object known to have approached the Sun and escaped.

Its survival is especially striking because the distance is only slightly greater than the Sun's radius.

The closest spacecraft has gone even deeper

Natural objects are not the only things capable of getting close to the Sun.

Human beings have now launched a probe into a region of space that has proved more hostile even than the planet Mercury.

Launched in 2018, NASA's Parker Solar Probe was expressly built to explore the upper layers of the atmosphere of the Sun. In its closest orbits around the star, Parker Solar Probe has approached within approximately 4.5 million miles (7.3 million kilometres) of the centre of the Sun.

That is a little further out than the Great Southern Comet's record approach, although the Parker Solar Probe has something that the comet does not: engineering design.

Thanks to a special heat shield made of carbon composite material, the Parker Solar Probe can explore regions of space too hostile for other probes.

This difference highlights why "closest" does not necessarily mean "most extreme."

A comet has to endure the Sun's heat and gravitational forces with its natural structure. Parker Solar Probe was built specifically to withstand the encounter.

One type of comet would have no chance of coming back

There is an even more extreme category: sundiving, or sunstriking, comets.

Unlike sungrazers that pass close to the Sun, a sundiving comet would actually cross the Sun's visible surface, known as the photosphere.

No such comet has yet been directly detected making that final plunge, according to Live Science. But orbital calculations show what would be required: its perihelion would have to be less than the Sun's radius, about 432,244 miles (695,630 kilometres) from the Sun's centre.

There would be no second encounter.

A comet that enters the Sun would be destroyed rather than completing an orbit and returning to space.

That creates a useful dividing line in the story of solar visitors. Objects can approach remarkably close and survive, but there is a point where "close encounter" becomes "one-way trip."

The Great Southern Comet of 1887 sits just outside that extreme boundary. It survived an approach of 446,187 miles, while a hypothetical sundiver would travel less than the Sun's radius from its centre and be consumed.

For now, that makes the 1887 comet the closest detected natural object known to have approached the Sun and lived to continue its journey.

But the record may not be permanent.

If astronomers eventually identify a genuine sundiving comet, it would technically pass closer to the Sun than the Great Southern Comet — by about 13,943 miles (22,439 kilometres).

What is interesting is that the point of greatest closeness is not always the point of destruction. There have been objects that have managed to remain intact despite being incredibly close to the Sun, although that would be possible only if they possess a particular size and shape