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Monster comet discovered falling toward the sun may be biggest ever

Bigger than a normal space rock but smaller than a planet.

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2014 UN271 could be one for the ages.

NASA/JPL-Caltech

If there were any dinosaurs still around, they'd probably be having horrible flashbacks reading the news this week of a giant space rock racing toward the inner solar system from deep space.

A newfound comet heading in the direction of the sun isn't exactly a big deal. That's basically what comets do. But this one, which has been cataloged as 2014 UN271, stands out for a couple of reasons.

First, this space snowball could be around 125 miles (200 kilometers) wide, which puts it somewhere in between a giant comet and a dwarf planet. Consider that comet Hale-Bopp, one of the larger, brighter comets in recent memory, was only 24 miles (40 kilometers) across.

If the early estimates of its size hold, 2014 UN271 might even set the record for biggest comet ever spotted. But there's still quite a bit of uncertainty at this point. It could be that part of the width in early observations is actually a coma or tail and that the nucleus is far smaller than it currently appears.

That said, the pixelated images of those early observations shared by University of Pennsylvania astrophysicist Pedro Bernardinelli, who discovered the object, sure look completely tail-less.

In addition to being colossal, 2014 UN271 has a very, very long orbital path that originates 1.25 trillion miles (2 trillion kilometers) from the sun at the very edge of the solar system.

"From that distance the sun's gravity is so weak a whisper could push this thing into interstellar space," writes astronomer Phil Plait.

Astronomer T. Marshall Eubanks estimates it will make its closest pass to the sun in just under a decade, on Jan. 28, 2031. This should give observatories like the nearly complete Vera C. Rubin Observatory in Chile several years to watch the comet's approach.

The European Space Agency's Comet Interceptor mission, planned to launch in 2029, has already said it won't be able to rendezvous with 2014 UN271, but Eubanks is optimistic that "a number" of currently available rockets could intercept the comet as it approaches.

While this new comet is huge, it won't actually be coming that close to Earth, compared with other famous comets of the last few decades. Nonetheless, it may be visible with a good telescope, and astronomers are sure to provide plenty of images and new data on it in the years to come. Plan to get to know this one pretty well.

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