Page 3 - Reading Success B9

Astronomers have discovered an extra solar planet having the largest solid

core of any known planet. Extra solar planets, also known as exoplanets, are
mainly giant planets that exist beyond the Solar System. The extra solar planet
scientists recently found has approximately the same mass as Saturn, but has a

significantly smaller diameter. Compared to Earth, the mass of its solid core is

about 70 times that of our planet.

Scientists are excited with the new findings, which provide strong support to the
core accretion theory, one of two competing theories about planet formation. The

more recent theory called the core accretion theory proposes that planets start as
small cores of rock and ice that grow as they gravitationally acquire additional

mass. Upon reaching a certain critical mass , the core begins to collect a gas
envelope around it. On the other hand, the earlier view known as the gravitational

instability theory holds that planets form when the disk of dust swirling around a
star, collapses and merges through gravity. The pieces come together to form

small clusters that attract other clusters to form bigger ones, with the process
continuing for a few million years. A rough analogy provided about this theory is

the way dust left under the bed for a long time will clump together to form a ball of
dust.

However, the newly found extra solar planet is said to be the first observational
evidence that proves the core accretion theory. Scientists believe that the large,

rocky core of this planet could not have been formed by mere cloud collapse.
They think that it must have grown a core first, and then acquired gas over time.

According to them, this discovery does not only confirm the core accretion theory
for planet formations but also provides evidence that a great number of planets of

this kind do exist.

Main Idea

What is the main idea of this story?

a. the faults of core accretion theory
b. two competing theories on planet formation

c. the discovery of a new planet
d. the gravitational instability theory of planet formation

6_Reading Success B 9