|Why isn't Pluto a planet? I think that it was a
star but people think that it was a planet and
that you guys saw a real planet, is it true or no?
I am not in school summer break.|
|Question Date: 2015-06-16|
Pluto, probably the most favorite planet among
kids from the 90s (because of Pluto, the cartoon
character maybe?), is one of the many thousands
of objects found in the "Kuiper belt" that orbit
the sun farther than the planet Neptune. These
are called trans-neptunian objects.
Pluto was recognized as a dwarf planet, after
the discoveries of many more trans-neptunian
objects. Slowly, planetariums started leaving out
Pluto and made models of the solar system with
only 8 planets leading to controversies. In
2006 or so, after much debate, Pluto was demoted
to a "dwarf planet". Neil deGrasse Tyson,
director of the Hayden planetarium, was very
involved in this.
The reason for its demotion was that, it did
not satisfy the one of the three conditions that
defined a planet, according to IAU (Internation
Astronomical Union): a planet should have cleared
A star is something that produces energy
(light and heat) due to a mechanism called nuclear
fusion, which is what makes our sun shine
everyday. Hydrogen in a star fuses together to
form other elements in the periodic table and in
the process releases a lot of energy in the form
of heat and light.
Pluto is not a star.
Different people argue about what makes a
planet or not. Pluto is large enough that its
gravity makes it round, and it probably has
different layers of material inside of it. These
things are planet-like. Pluto has not swept the
other things in its orbit away, though, which is a
different meaning of the word "planet". As a
result, people argue about whether Pluto is a
planet or not.
Ultimately, whether something is a planet or
not is something we call it. Pluto is what it is,
and it doesn't matter whether we call it a planet,
a dwarf planet, a comet, or something else.
Nothing about Pluto has changed but it is no
longer considered a planet because we changed how
we define a planet. We changed the definition of
planet so that it would be more useful for
scientists to tell different objects in space
Planets are now defined as large round
objects that orbit around stars in a predictable
way, and they need to clear the area around
their path of other objects. Our solar system has
eight planets but there are many other objects
around that don’t count as planets. For example,
the asteroid belt contains lots of big rocks but
never condensed into a single planet.
The Kuiper belt, past the orbit of
Neptune, contains many large objects that might
count as planets if they weren’t so close
together. Pluto is one of these objects. It was
first object in the Kuiper belt that we saw and it
has a regular (but strange) orbit. We called it a
planet until 2006. As our telescopes and sensors
advanced, we found many more “planets” near Pluto
and one of them is even bigger (Eris). Since Pluto
doesn’t clear the space around it as it orbits, we
no longer consider Pluto a planet – instead, it is
considered part of the Kuiper belt.
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