Large, Distant Comets More Common Than Previously Thought

College of Computer, Mathematical, and Natural Sciences

New study suggests there are about seven times more “long-period” comets than predictedComets that take more than 200 years to make one revolution around the sun are notoriously difficult to study. Because they spend most of their time far from our area of the solar system, many "long-period comets" will never approach the sun in a person's lifetime. In fact, those that travel inward from the Oort Cloud—a group of icy bodies beginning roughly 300 billion kilometers away from the sun—can have periods of thousands or even millions of years.
NASA's Wide-field Infrared Survey Explorer (WISE) spacecraft has delivered new insights about these distant wanderers. A team of astronomers led by James Bauer, a research professor of astronomy at the University of Maryland, found that there are about seven times more long-period comets measuring at least 1 kilometer across than previously predicted.
The researchers also found that long-period comets are, on average, nearly twice as large as "Jupiter family” comets, whose orbits are shaped by Jupiter’s gravity and have periods of less than 20 years. The findings were published July 14, 2017, in The Astronomical Journal.
"The number of comets speaks to the amount of material left over from the solar system's formation," Bauer said. "We now know that there are more relatively large chunks of ancient material coming from the Oort Cloud than we thought."
The Oort Cloud is too distant to be seen by current telescopes, but is thought to be a spherical distribution of small icy bodies at the outermost edge of the solar system. The density of comets within it is low, so the odds of comets colliding within it are low. Long-period comets that WISE observed probably got kicked out of the Oort Cloud millions of years ago. The observations were carried out in 2010 during the spacecraft's primary mission, before it was renamed NEOWISE and reactivated to target ...

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