Last year, scientists announced that they had discovered a colossal comet lingering just inside Neptune’s orbit. They estimated its icy core to be between 62 and 125 miles long, based on its brightness. If the estimates were accurate, this would be the largest comet ever discovered.

But scientists wanted to be certain that the superlative stuck, so in January they pointed the Hubble Space Telescope at the comet and measured its nucleus with precision. As reported this week in The Astrophysical Journal Letters, the comet’s core could be up to 85 miles across, making it more than twice the width of the state of Rhode Island. It also has a mass of 500 trillion tons, equivalent to roughly 2,800 Mount Everests.

“It’s 100 times bigger than the typical comets we’ve been studying for all these years,” said David Jewitt, an astronomer and planetary scientist at the University of California, Los Angeles, and an author of the new study.

Despite its impressive dimensions, this comet — named C/2014 UN271 (Bernardinelli-Bernstein) after its two discoverers — will be visible to the naked eye for only a brief time. It is barreling toward the sun at 22,000 miles per hour. But at its closest approach, in 2031, it will get only within a billion miles of the sun — just behind Saturn’s orbit — where it will appear as a faint glow in the night sky before boomeranging back out into the shadows.