Using data from the WISE space telescope, astronomers have found that there are more comets lurking in the far reaches of the solar system than they had predicted.
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.
These are comets whose orbits never allow them to come close to the inner solar system, which allows them to remain puffy and large.