Page 88 - Grasp English C1+ (Workbook)

9 Cosmology

In 1930, Pluto was discovered and added to the map of our solar system. However, in 2006, it lost its
standing as a planet and became relegated to the status of a dwarf planet. Why did this happen
and what implications did it have for the future of our solar system?
At the time of Pluto’s discovery, telescopic equipment was still fairly rudimentary. The telescope
Clyde Tombaugh used in the Arizona-based Lowell Observatory had a camera attached which
would take two images of the night sky on different days. Tombaugh then analysed the photos
using a device called a blink compactor, which allowed him to see differences between the two
images. Whilst distant objects would remain in the same position, anything closer would change
position between the two photos.
However, in the next seventy-five years, huge advances were made in the equipment used to study
the sky above us. During that time, astronomers learned much more about our universe and other
large celestial bodies around the solar system, such as Ceres, an object in the asteroid belt between
Mars and Jupiter, which had been discovered at the start of the 19 century. Although Pluto is
th
larger than Ceres, it raised the question of what defined a planet, and in 2006, the International
Astronomical Union agreed on firm criteria.

Pluto meets the first two of the criteria, namely that it is in orbit around the sun and, because of the
forces of gravity, maintains a nearly round shape. Nonetheless, because it is found in the Kuiper
Belt along with other celestial bodies of a similar mass, it did not meet the third criterion of existing
in a clear “neighbourhood”. This redefining of planetary status means that our solar system is now
limited to eight planets as, at the time of deciding the criteria, one of the IAU’s leading scientists
joked that otherwise “by the end of the decade, we would have had 100 planets.”

Although there were many opposed to Pluto’s demotion and challenges to the wording of the IAU’s
criteria, Pluto is unlikely to regain planetary status. The unmanned New Horizons mission launched
in 2006 and, taking almost 10 years to reach Pluto, has since sent back images and data about the
dwarf planet. Scientists say the probe will teach us more about the origins of our solar system and
how it has evolved.

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