What Really Happens When a Comet Falls Into the Sun: Evaporation, Impact, and Solar Science

The SOHO spacecraft has tracked more than 4,000 comets diving toward the sun since it launched in 1995. Nearly all of them vanish. Not in a collision, the sun has no hard surface to strike, but in something slower and stranger: they dissolve. A comet approaching the sun is mostly ice, dust, and rock. At about 40 million kilometres out, the heat becomes intense enough to sublimate the ice directly into gas, skipping the liquid phase entirely. The comet's tail, the bright streamer we see in photographs, is this escaping material, pushed away from the sun by solar wind and radiation pressure. The tail always points away from the sun, regardless of which direction the comet is moving.
What makes a sungrazer different is the orbit. These comets don't just pass near the sun, they pass through or extremely close to the corona, the sun's outer atmosphere, which extends millions of kilometres into space and burns at temperatures above a million degrees Celsius. The corona is hotter than the sun's visible surface, a fact that still doesn't have a fully settled explanation in solar physics. A comet flying through it is flying through a furnace that operates by rules the sun's own surface doesn't follow.The process of destruction has a precise sequence. First, solar radiation heats the comet's surface, driving off volatile ices, water, carbon dioxide, carbon monoxide. This outgassing forms the coma, the fuzzy cloud around the nucleus. As the comet gets closer, tidal forces from the sun's gravity begin pulling on the nucleus itself. A comet that is loosely held together, and most are, essentially rubble piles bound by weak gravity, can break apart under this tidal stress before the heat even finishes the job. Comet Shoemaker-Levy 9 broke into 21 fragments from Jupiter's tidal forces in 1992 before crashing into that planet in 1994. The sun's tidal forces are considerably stronger.
If the nucleus survives tidal disruption, the corona finishes it. At perihelion, the closest point of approach, temperatures and radiation fluxes are extreme enough to sublimate rock. Not just ice. Rock. Silicate material, the stuff of stone, vaporises. The comet doesn't impact the sun's surface; it simply ceases to exist as a solid object. What's left is a cloud of ionised gas and dust that gets swept into the solar wind and dispersed across the inner solar system. The whole process, from first corona contact to complete evaporation, can take minutes.Most sungrazers belong to a family called the Kreutz group, named after German astronomer Heinrich Kreutz, who established in the late 19th century that several bright comets shared nearly identical orbits. The current understanding is that they are fragments of a single massive comet that broke apart, probably more than a thousand years ago. Each fragment follows a similar path, swinging to within a few hundred thousand kilometres of the sun's surface. Most are small, a few metres to tens of metres across, and they evaporate completely.
Comet Lovejoy, discovered by Australian amateur astronomer Terry Lovejoy, was a Kreutz sungrazer that passed through the corona in December 2011. It was expected to disintegrate. Instead, it emerged on the other side. NASA's Solar Dynamics Observatory captured the event in detail. Lovejoy survived because its nucleus was large enough, estimated at around 200 metres, to lose enormous amounts of material and still retain a core. It was visibly smaller after perihelion. It had left a trail of debris along its orbit path, a comet in the process of dying across multiple passes rather than one.A comet entering the solar corona is an unintentional probe. As it disintegrates, its material mixes with the solar wind and creates measurable disturbances. The Parker Solar Probe, launched by NASA in 2018, has been making increasingly close passes to the sun, in December 2024 it reached within about 6.1 million kilometres of the solar surface, the closest any spacecraft has ever come. Its instruments are designed to measure exactly the kinds of plasma and magnetic field interactions that a disintegrating comet produces at scale.

India's Aditya-L1 mission, launched by ISRO from Sriharikota in September 2023, reached its observation point at the L1 Lagrange point, about 1.5 million kilometres from Earth, in the direction of the sun, and carries instruments to study the solar corona and solar wind. The data Aditya-L1 collects on coronal behaviour directly informs how scientists model what happens to material entering that region, whether it's a comet, a spacecraft, or charged particles heading toward Earth. The comet and the satellite are studying the same zone from opposite directions.
Comet impacts on the sun also produce seismic-like waves in the corona, detectable as disturbances in the magnetic field. These are brief but measurable, and they've helped researchers map coronal density in ways that purely observational instruments can't. A comet that dies in the corona is, in that sense, doing science on the way out.Of the 4,000-plus comets SOHO has catalogued diving toward the sun, the overwhelming majority were discovered not by professional astronomers but by volunteers examining SOHO's publicly available imagery through a citizen science programme called Sungrazer Project. Amateurs sitting at computers in Mumbai, Bengaluru, and cities across the world have found comets in these images that no automated system flagged. Several Indian contributors have confirmed sungrazers in the SOHO archive.

A comet that formed in the outer solar system four billion years ago, made of the same primordial material as the planets, travels for millions of years on an orbit that eventually bends it inward. It crosses the orbit of Jupiter, then Mars, then Earth, then Venus. It enters the corona and evaporates in minutes. The whole sequence, billions of years of cold storage, minutes of dissolution, is one of the more extreme contrasts in planetary science. What the sun takes in, it doesn't give back whole. It gives back data.