NEOWISE: Large, Distant Comets More Common Than Previously Thought

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NEOWISE: Large, Distant Comets More Common Than Previously Thought

Post by bystander » Tue Jul 25, 2017 6:56 pm

Large, Distant Comets More Common Than Previously Thought
NASA | JPL-Caltech | NEOWISE | 2017 Jul 25
[img3="This illustration shows how scientists used data from NASA's WISE spacecraft to determine the nucleus sizes of comets. They subtracted a model of how dust and gas behave in comets in order to obtain the core size. Credit: NASA/JPL-Caltech"]https://www.nasa.gov/sites/default/file ... t-nasa.jpg[/img3][hr][/hr]
Comets 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 186 billion miles (300 billion kilometers) away from the Sun -- can have periods of thousands or even millions of years.

NASA's WISE spacecraft, scanning the entire sky at infrared wavelengths, has delivered new insights about these distant wanderers. Scientists found that there are about seven times more long-period comets measuring at least 0.6 miles (1 kilometer) across than had been predicted previously. They also found that long-period comets are on average up to twice as large as "Jupiter family comets," whose orbits are shaped by Jupiter's gravity and have periods of less than 20 years.

Researchers also observed that in eight months, three to five times as many long-period comets passed by the Sun than had been predicted. ...

Debiasing the NEOWISE Cryogenic Mission Comet Populations - James M. Bauer et al
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