The Comet That Flared Twenty Thousand-Fold
Comet 220P/McNaught was supposed to need a telescope. Two unexplained outbursts have made it about 20,000 times brighter than usual — and nobody yet knows what cracked the switch.
The Outburst
Periodic comet 220P/McNaught has erupted twice this year, becoming roughly 20,000 times brighter than usual. A comet normally reserved for telescopes can now be picked up with binoculars and long-exposure cameras.
NASA's Astronomy Picture of the Day documented the transformation on 24 August. The featured observation shows a bright green coma and a short dust tail as 220P continues its orbit between Mars and Jupiter.
What Makes It Strange
Comets brighten as solar heating releases gas and dust, but the trigger for these two enormous jumps has not been identified. NASA lists two possibilities rather than a verdict:
- built-up gas may have escaped from below the surface;
- a fracture or comet quake may have exposed fresh volatile material;
- the separate outbursts may have involved more than one process.
Something inside a dark, routine comet abruptly turned the lights on.
The Implications
An outburst is a glimpse beneath a comet's processed exterior. The expelled material may carry clues about hidden ice, internal stress and the structure of a small body that has repeatedly crossed the inner Solar System.
The gas-release and quake explanations remain hypotheses. NASA's account does not identify a measured cause, so the spectacle is real while the mechanism is still open.
What Happens Next
220P follows an orbit lasting more than five years and is due to pass about one astronomical unit from Earth in October. That is approximately the average Earth-Sun distance, not a close-approach warning.
Astronomers now have a suddenly accessible target and a fading clock. As the comet turns back toward the outer part of its orbit, its unexpected brightness is expected to disappear with it.