1. The Solar System only has 8
planets
That’s right, only 8 planets. Not
the 9 planets you grew up with.
That’s because the International
Astronomical Union reclassified
Pluto as a dwarf planet in 2006.
Why is Pluto not a planet? To
qualify as a planet, an object
needs to orbit the Sun, have
enough mass to pull itself into a
spherical shape, and have cleared
out its orbit of other material. It’s
this third requirement that Pluto
hasn’t fulfilled; it’s just a fraction
of the mass in its orbit while the
other planets are millions of
times more massive than
everything else in their orbits.
2. But the Solar System has 4
dwarf planets
Pluto has been downgraded, but
there are now 4 dwarf planets in
the Solar System: Ceres, Pluto, Eris
and Makemake. Dwarf planets
are objects that orbit the Sun and
have enough mass to form a
sphere, but they share
their orbit with other objects.
And as telescopes improve,more
dwarf planets will be discovered.
There might eventually be more
dwarf planets than planets. See
how much you already know
about our Solar System?
3. The influence of the Solar
System extends out for almost
2 light-years
The theoretical size of the Solar
System goes out as far as the the
Sun’s gravity overpowers
anything else in the region; and
this is almost 2 light-years away,
nearly halfway to the nearest
star. It’s thought that the Oort
Cloud – a region where the long-
period comets come from –
extends out to 100,000
astronomical units from the Sun
(1 astronomical unit, or AU, is the
average distance from the Earth
to the Sun).
4. Most of the mass of the Solar
System is the Sun
In fact, the Sun contains 99.86%
of the mass in the Solar System.
And the Sun is 73% hydrogen, so
most of the matter in the Solar
System is hydrogen, with the
remaining amount being mostly
helium, oxygen and carbon.
Everything else, like the metals
and rocks is just a tiny fraction of
a fraction of the mass in the Solar
System.
5. The Solar System is 4.6 billion
years old
Since the Earth is constantly
resurfacing itself, we can’t find
out how old it is, but there’s
another way to find
out.Meteorites, which date back
to the formation of the Solar
System, have been raining down
on Earth for millions of years.
Scientists have sampled
meteorites and learned that
they’re all 4.6 billion years old.
That means that everything in
the Solar System formed around
the same time – give or take a
few million years.
6. Everything orbits in the same
direction
All the objects in the Solar System
orbit the Sun in a counter-
clockwise direction. This matches
the theory that the Solar System
formed all at once from a cool
cloud of hydrogen. As the gas
came together, it began to spin,
so that the Sun collected in the
middle, surrounded by an
accretion disk of gas and dust. All
the planets and other material in
the Solar System formed within
this rotating disk. There are a
few exceptions, however, like
Halley’s Comet.
7. The Sun is just one star in
200 billion in the
Milky Way
Doesn’t that give you
perspective? Our whole world is
just one planet orbiting one star
in a galaxy of 200 billion stars.
OMG..
8. But they’re really far apart
There are only a few stars within
10 light-years of the Sun. The
closest system is the Alpha
Centauri system, 4.4 light-years
away. Barnard’s Star is 5.9 light-
years away, and then Wolf 359
(7.8 light-years), Lalande 21185
(8.3 light-years), Sirius (8.6 light-
years), Luyten 726-8 (8.7 light-
years), and finally Ross 154 at 9.7
light-years away.Interstellar travel
will be difficult when you’re
dealing with these distances.
9. Astronomers used to think
the Earth was the center
You take it for granted that the
Sun is the center of the Solar
System, but astronomers used to
think that the Earth was the
center of the entire Universe. It
wasn’t until the 17th century,
when Nicolaus Copernicus first
presented the concept, and
showed how it accurately
predicts the positions of the
planets.
10. Humans have sent
spacecraft almost everywhere
Spacecraft from Earth have
visited or orbited every planet in
the Solar System, and more are
on their way to visit some of the
dwarf planets. We’ve explored
the Sun,the Moon, and many
asteroids. And now some of the
oldest spacecraft still active –
NASA’s Voyager spacecraft – have
almost reached the Sun’s
heliosphere;the point where the
solar wind slows down as it
bumps against the interstellar
wind.
www.universetoday.com/15959/interesting-facts-about-the-solar-
system/
