Solar System Facts A Guide to Things Orbiting Our Sun | Exploring Nature Solar System Facts A Guide to Things Orbiting Our Sun The solar system is made up ...
Solar System Facts A Guide to Things Orbiting
The solar system is made up of the sun and
everything that orbits around it, including
planets, moons, asteroids, comets and meteoroids.
It extends from the sun, called Sol by the
ancient Romans, and goes past the four inner
planets, through the Asteroid Belt to the
four gas giants and on to the disk-shaped
Kuiper Belt and far beyond to the giant, spherical
Oort Cloud and the teardrop-shaped heliopause.
Scientists estimate that the edge of the solar
system is about 9 billion miles (15 billion
kilometers) from the sun.
For millennia, astronomers have followed points
of light that seemed to move among the stars.
The ancient Greeks named these planets, meaning
Mercury, Venus, Mars, Jupiter and Saturn were
known in antiquity, and the invention of the
telescope added the Asteroid Belt, Uranus,
Neptune, Pluto and many of these worlds' moons.
The dawn of the space age saw dozens of probes
launched to explore our system, an adventure
that continues today.
The discovery of Eris kicked off a rash of
new discoveries of dwarf planets.
Astronomers are now hunting for another planet
in our solar system, a true ninth planet,
after evidence of its existence was unveiled
on Jan. 20, 2016.
The so-called "Planet Nine," as scientists
are calling it, is about 10 times the mass
of Earth and 5,000 times the mass of Pluto.
Many scientists think our solar system formed
from a giant, rotating cloud of gas and dust
known as the solar nebula.
As the nebula collapsed because of its gravity,
it spun faster and flattened into a disk.
Most of the material was pulled toward the
center to form the sun.
Other particles within the disk collided and
stuck together to form asteroid-sized objects
named as planetesimals, some of which combined
to become the asteroids, comets, moons and
The solar wind from the sun was so powerful
that it swept away most of the lighter elements,
such as hydrogen and helium, from the innermost
planets, leaving behind mostly small, rocky
The solar wind was much weaker in the outer
regions, however, resulting in gas giants
made up mostly of hydrogen and helium.
The sun is by far the largest object in our
solar system, containing 99.8 percent of the
solar system's mass.
It sheds most of the heat and light that makes
life possible on Earth and possibly elsewhere.
Planets orbit the sun in oval-shaped paths
called ellipses, with the sun slightly off-center
of each ellipse.
Inner solar system
The four inner four planets — Mercury, Venus,
Earth and Mars — are made up mostly of iron
They are known as terrestrial or earthlike
planets because of their similar size and
Earth has one natural satellite — the moon—
and Mars has two moons — Deimos and Phobos.
Between Mars and Jupiter lies the Asteroid
Asteroids are minor planets, and scientists
estimate there are more than 750,000 of them
with diameters larger than three-fifths of
a mile (1 km) and millions of smaller asteroids.
The dwarf planet Ceres, about 590 miles (950
km) in diameter, resides here.
A number of asteroids have orbits that take
them closer into the solar system that sometimes
lead them to collide with Earth or the other
Outer solar system
The outer planets — Jupiter, Saturn, Uranus
and Neptune — are giant worlds with thick
outer layers of gas.
Nearly all their mass is made up of hydrogen
and helium, giving them compositions like
that of the sun.
Beneath these outer layers, they have no solid
surfaces — the pressure from their thick
atmospheres liquefy their insides, although
they might have rocky cores.
Rings of dust, rock, and ice encircle all
these giants, with Saturn's being the most
Comets are often known as dirty snowballs,
and consist mainly of ice and rock.
When a comet's orbit takes it close to the
sun, some of the ice in its central nucleus
turns into gas that shoots out of the comet's
sunlit side, which the solar wind carries
outward to form into a long tail.
Short-period comets that complete their orbits
in less than 200 years are thought to originate
from the disk-shaped Kuiper Belt, while long-period
comets that take more than 200 years to return
are thought to come from the spherical Oort
Astronomers had long suspected that a band
of icy material known as the Kuiper Belt existed
past the orbit of Neptune extending from about
30 to 55 times the distance of Earth to the
sun, and from the last decade of the 20th
century up to now, they have found more than
a thousand of such objects.
Scientists estimate the Kuiper Belt is likely
home to hundreds of thousands of icy bodies
larger than 60 miles (100 km) wide, as well
as an estimated trillion or more comets.
Pluto, now considered a dwarf planet, dwells
in the Kuiper Belt.
It is not alone — recent additions include
Makemake, Haumea and Eris.
Another Kuiper Belt object dubbed Quaoar is
probably massive enough to be considered a
dwarf planet, but it has not been classified
as such yet.
Sedna, which is about three-fourths the size
of Pluto, is the first dwarf planet discovered
in the Oort Cloud.
NASA's New Horizons mission performed history's
first flyby of the Pluto system on July 14,
2015, and continues to explore the Kuiper
The Oort Cloud lies well past the Kuiper Belt,
and theoretically extends from 5,000 to 100,000
times the distance of Earth to the sun, and
is home to up to 2 trillion icy bodies, according
Past the Oort Cloud is the very edge of the
solar system, the heliosphere, a vast, teardrop-shaped
region of space containing electrically charged
particles given off by the sun.
Many astronomers think that the limit of the
heliosphere, known as the heliopause, is about
9 billion miles (15 billion km) from the sun.