Comet 220P/McNaught spent years as little more than a faint point of light, barely noticeable even through telescopes. Then, in 2026, it suddenly flared to life.
The Jupiter-family comet, which orbits the Sun once every 5.5 years, had typically remained extremely dim, often around magnitude 17 or 18. But between late May and early June, its brightness surged by an extraordinary 7 to 10 magnitudes. Depending on the observations used, that represented an increase of roughly 600 to 8,000 times, with the comet briefly reaching about magnitude 8.
The outburst was not an isolated event. On Aug. 5, 220P/McNaught erupted again, rapidly brightening from around magnitude 14 to magnitude 7—an increase of more than 600 times.
For a small comet that had spent much of its orbit hidden in the darkness, two dramatic outbursts within a matter of months raise an obvious question: What is happening to 220P/McNaught?
A faint speck flares like a new star
220P/McNaught is not a newly discovered object. On May 20, 2004, the Australian astronomer Robert H. McNaught found it in CCD images taken with the Uppsala Southern Schmidt Telescope at Siding Spring Observatory in Australia. The comet then shone at magnitude 17.7, with a coma of only 8 to 10 arcseconds and no obvious central condensation. A few days later, J. Young made confirming observations at the Table Mountain Observatory in California. Observers recovered the comet in 2009, after which it received the permanent designation “220P.”
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Its orbit marks it as a short-period comet that circles the Sun once every 5.5 years. On its 2026 return, perihelion fell on June 14 at a distance of 1.56 astronomical units from the Sun. It was not expected to be one of the year’s most watched comets. Then, at the end of May, everything changed.
Between May 30 and 31, 220P/McNaught underwent a violent outburst. Analyzing data from the Zwicky Transient Facility, astronomers found that its brightness had shot up over a span of 13 and a half hours. Early analysis showed an increase of at least 600 times; other observations measured a peak of magnitude 8.2, equivalent to an 8,000-fold increase over its former faint state.
How startling is a jump of that size? An object of magnitude 17 or 18, difficult to capture even with large telescopes, suddenly became a comet that could be followed with binoculars under a dark sky, and observers quickly took notice. Images from early June showed a visibly expanding coma and tail structure around the comet, and some records captured a faint ion tail stretching 2 degrees across the sky. That was only the first act.
Why do comets suddenly erupt?
A comet looks like a small body of ice and snow, but as it approaches the Sun, violent changes can take place inside it. The nucleus of a comet is built of ice, dust, and other material. As the distance to the Sun shrinks and solar radiation grows, material at and near the surface sublimates, releasing gas and carrying large amounts of dust into the surrounding space. The gas and dust gather around the nucleus and form an enormous “coma.”
The process does not necessarily run smoothly. A comet can stay relatively calm for a long time and then abruptly release a large amount of material in a single “outburst.” Once a mass of dust and gas has been thrown out, the comet’s effective surface area and its capacity to reflect sunlight increase sharply, so that its brightness as seen from Earth can climb steeply in a very short time.
220P/McNaught is one of the extreme cases of this phenomenon. Observations in June showed a clear change in its dust production rate after the outburst. Follow-up observations with the TRAPPIST-North telescope found that C₂ appeared to have increased relative to CN in the comet’s material, and researchers proposed that a fragmentation event may have occurred. That is not the same as confirming that the nucleus broke apart, and the distinction matters.
The sudden brightening is a matter of real observation. Which physical mechanism dominated the outburst is a question that still needs more observations to settle.
The comet wakes a second time
After the first eruption, 220P/McNaught did not stay bright. By mid-June its brightness had fallen to magnitude 12, and observations at the end of June showed it back in a relatively quiet state. Had the story ended there, it would still have counted as one of the more remarkable comet outbursts of 2026. But on Aug. 5, the unexpected happened again.
220P/McNaught erupted a second time, its brightness climbing rapidly from magnitude 14 to about magnitude 7, an increase of more than 600 times. The latest observations show the coma expanding markedly once more, with some images revealing a multi-layered structure. The once-obscure comet drew attention all over again. Going from magnitude 17 or 18 to magnitude 7 or 8 is not a matter of getting “a little” brighter.
The magnitude scale used in astronomy is logarithmic: each drop of 5 magnitudes corresponds to roughly a hundredfold increase in brightness. A fall of several magnitudes within days therefore means an enormous increase in the light actually received. This is what makes comet outbursts so stunning. A point of light that was nearly invisible in the sky can, in a short time, turn into an entirely different kind of object.
A larger mystery
This is the most striking part of what Stefan Burns argued in his video. He raised a bold possibility: the timing of both of 220P/McNaught’s outbursts seems to show a coincidence worth studying with solar activity and solar energetic particle events. The idea involves an important concept called the “Parker spiral.”
The Sun does not stand still and simply radiate energy outward. The solar wind flows continuously from the Sun, and because the Sun rotates, the solar magnetic field takes on a spiral structure. That structure is the Parker spiral. If a comet happens to sit in a favorable geometric position, it can be affected by the solar wind, the magnetic field, and energetic particles.
Burns therefore proposed a hypothesis: as 220P/McNaught approached perihelion in 2026, its orbital position may have stood in a special geometric relationship to the magnetic structure of the solar wind. If energetic particles travel along the field, they could in theory interact with the gas and plasma environment already surrounding the comet.
Existing research on comets explains one thing well: drawing closer to the Sun increases the energy a comet receives, which in turn drives gas and dust activity. Proving that a specific solar proton event “triggered” the outburst of 220P/McNaught would require more direct observational evidence.
The truly astonishing thing is the comet itself
What 220P/McNaught went through in 2026 is remarkable. Its nucleus is probably only on the scale of a kilometer, yet in a short time it threw enough gas and dust into space to form a coma far larger than the nucleus itself. It is a deeply counterintuitive natural sight.
Looking at the nucleus alone, an observer might take it for a small lump of ice. Once the comet turns active, however, structures of gas, dust, and plasma on the scale of hundreds of thousands of kilometers can form around it. The most spectacular part of a comet is often not the body itself but the vast environment it leaves behind after the Sun has “woken” it.
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