Narrator: Every
5.4 years, comet 41P swings around the Sun
and puts on a show for observers on Earth.
Between March and April 2017, as the comet made its closest approach
to Earth, astronomers caught it doing something never before seen.
41P is an icy body from the Kuiper Belt,
the cold storage zone beyond Neptune.
Neptune's gravity first sent it hurtling toward the sun, and Jupiter trapped
it in its current orbit. As it nears the Sun,
the comet's icy areas warm up and turn to gas.
This forms jets that blast gas and dust into space.
This material becomes an extended atmosphere around the comet and makes up its
tail. To better understand how comets work,
astronomers study how these jets change as a comet approaches and
departs the inner solar system. From this, astronomers can measure
how fast the comet rotates.
When 41P approached, in March 2017, astronomers found
it to be rotating about once every 20 hours. But when
NASA's Swift studied the comet in May, 41P's rotation
period had more than doubled. This is the largest, most
abrupt rotational change ever seen on a comet.
Comet 41P is a small object, smaller than most of the
so-called Jupiter Family Comets, and very active.
Astronomers think a particularly strong active area produced jets that
lined up in just the right way to suddenly put the brakes on the comet's spin.
Extrapolating from the Swift measurements,
41P could have continued to slow in the following months,
spinning less than once every four days by summer.
This spin is too slow to keep the comet stable, so even
small jets can set it wobbling like a top, or tumbling,
and ultimately rotating around a different axis.
Such changes affect which parts of the comet are exposed to sunlight.
Perhaps, this will drive new levels of activity that will further change
the comet's spin. Scientists have never before
observed this phase of comet evolution, and they look forward to
41P's next visit in 2022.
[Beeping]