A comet is an object that travels through space. It is composed of a solid core with a long "tail." Its core, or nucleus, consists of rock, dust, and ice. Its tail is a trailing cloud of dust and gas. In 1993, astronomers identified a previously unknown comet, which was given the name
Shoemaker-Levy 9. They calculated its orbit and realized that the comet would soon collide with the planet Jupiter. In the summer of 1994, they
prepared to observe the impact.
Shoemaker-Levy 9 was not a typical comet. Astronomers determined that previously, most likely in about 1929, the comet had come close
to Jupiter. The tremendous pull of the planet's gravity shattered the comet's nucleus into about 21 pieces, permanently changing the comet's
appearance. Unlike most comets, which have a nucleus that looks like a single point of light, Shoemaker-Levy 9 had a nucleus that resembled a
string of glowing beads.
In 1994, these fragments slammed into Jupiter's atmosphere when the comet's orbit again brought it near the planet. The collision occurred
on a side of Jupiter that was out of view of Earth-based telescopes. However, within a few hours, the planet had rotated so that astronomers could
observe the impact sites. The sites looked like dark patches on the planet. The dark patches were actually clouds composed of comet dust and
gases, which remained visible for months.
Choose the two central ideas developed in the passage.
U 1. Shoemaker-Levy 9 was an unusual comet.
2. Shoemaker-Levy 9 collided with Jupiter in 1994.
03. Shoemaker-Levy 9 was not discovered until 1993.
4. Astronomers were able to calculate the orbit of Shoemaker-Levy 9.
O 5. Astronomers had to wait to observe the impact sites of Shoemaker-Levy 9.