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| solarsystem.nasa.gov |
When NASA’s space
probe, New Horizons, headed for space in January 2006, it’s destination was Pluto. And we knew it would arrive mid July 2015 – nine and half years
later. The aim of the mission was to take photographs of Pluto as the space craft flew
close to it – a flyby.
In 2006, America’s
National Aeronautics and Space Administration (NASA) admitted that scientists
knew very little about Pluto. What was known ‘could fit on a postcard.’ That’s
not true anymore. Pluto was a planet in 2006. But it was demoted from planet to
dwarf planet on August 24, 2006, because scientists said it wasn’t big enough
to be a planet. Other scientists said it was unfair to demote Pluto because it
had a crust and a core (the attributes of a planet), and atmospheres and moons
(the attributes of a planet), and seasons too (also the attributes of a
planet).
The International
Astronomical Union (IAU) voted to demote Pluto. When American Clyde W. Tombaugh
first discovered Pluto in 1930 he declared it a planet and gave it its name. In
1978 scientists determined that its mass and size (2,400 kilometres or 1,500
miles across) was a bit smaller than planet Mercury (4,880 kilometres or 3,032
miles across). But it was in the Kuiper Belt where, in 2005, scientists found another object the same size as Pluto,
called UB313, but now called Eris (2,600 kilometres or 1,600 miles across with
25% more mass than Pluto).
So at the IAU
conference in 2006, scientists debated the definition of a planet. Some said
Pluto, Eris, and the asteroid Ceres were planets. IAU concluded that a planet
was defined as: (1) an object in orbit around the Sun; (2) having sufficient gravity
to hold its spherical shape; and (3) having ‘cleared the neighbourhood’ of its
orbit. Big objects in space push away smaller objects in their own orbits. For
example, Earth has 1.7 million times the mass of other objects in its own orbit
and therefore it can push them away. But Pluto is only 0.7 times the mass of
other objects in its orbit and therefore is not very strong. Hence IAU voted
that Pluto did not conform to the third requirement, and was therefore not a
planet. Strength, not size, was its downfall.
The flyby was the
first time a craft had flown so close to Pluto - as close as 12,500
kilometres (7,750 miles) at a speed of 14 kilometres per second (31,000 miles
per hour).
The photographs of Pluto have
provided NASA with a lot of information – such as its size. Pluto is 2,370
kilometres across, which is about two-thirds the size of our moon. From the
photographs, scientists also learned that it is comprised of more ice than
previously thought, and confirmed the presence of its five moons.
New Horizons had a
ten-year mission, but it will continue flying into the Kuiper Belt beyond the
planets. Expect more information on its findings in 2019.
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