Named after the Roman king of the gods, Jupiter is fitting of its name. With a mass of
1.90 x 1027 kg and a mean diameter of
139,822 km,
Jupiter is easily the largest and most massive planet in the Solar
System. To put this in perspective, it would take 11 Earths lined up
next to each other to stretch from one side of Jupiter to the other and
it would take 317 Earths to equal the mass of Jupiter!
What is even more provocative is the theory that Jupiter is a
failed star. Current scientific knowledge suggests that if Jupiter had,
in fact, been roughly 80 times more massive, nuclear fusion would have
taken place in its core; thus, Jupiter would have become a star, not a
planet. Regardless, it is still tempting to look at the number of
satellites orbiting Jupiter and consider it and its moons as, in many
ways, a mini solar system.
Although our scientific knowledge of Jupiter has been greatly
expanded as a result of the numerous planetary missions beginning in the
1970s, these missions are unnecessary for viewing the planet's surface
features. Instead, most of these features can be observed using
Earth-based telescopes. For example, as recently as 1994, the Hubble
Space Telescope provided stunning images of the impact of the
Shoemaker-Levy 9 comet into Jupiter.
Atmosphere
The vertical dimension (i.e., thickness) of Jupiter's atmosphere
is more difficult to define than those of the terrestrial planets. For
example, whereas the lower boundary for the atmosphere on Earth is its
solid planetary surface, there is no such equivalent on Jupiter.
Essentially, Jupiter's atmosphere transitions from a gaseous outer zone
into the planet's liquid layer. However, for practical purposes
scientists have designated the depth at which the atmospheric pressure
equals ten times the pressure at sea level on Earth as Jupiter's
"surface".
Those layers of the atmosphere visible to Earth-based telescopes
are divided into lighter and darker horizontal bands. Scientists believe
these bands to be layers of high and low pressure. As a result, storms
often develop on the boundaries between two adjacent bands. The Great
Red Spot, visible in Jupiter's southern hemisphere, is one such storm.
Amazingly, this storm has raged for centuries and is
25,000 km across—that is big enough to hold two Earths!
The composition of Jupiter's atmosphere is very interesting. At
roughly 90% hydrogen and 10% helium, Jupiter's composition is nearly the
same as the Sun's. The only difference between the two is that the Sun
is much more massive than Jupiter. This composition supports the theory
that Jupiter could have been a star.
Interior
The interior of Jupiter is believed to consist of three regions.
The first is a rocky core composed of various elements with a mass
between 12 and 45 times that of the entire Earth. The core is surrounded
by the second region, a layer of electrically conductive liquid
hydrogen. It is due to this layer, which comprises most of the planet's
mass, that Jupiter has such a strong magnetic field. The third region
consists of ordinary hydrogen with traces of helium, which transitions
into the planet's atmosphere.
A fascinating property of Jupiter is that it emits more energy
than it receives from the Sun. This is due to the planet being so
massive. As a result of such a large mass, Jupiter exerts a strong
gravitational force on itself, thus resulting in the compression of the
planet as a whole. The cumulative effect of all this inward force is the
production of a large amount of heat, which is then radiated into
space.
Orbit & Rotation
With a mean orbital distance of
7.78 x 108 km,
Jupiter is, on average, a little more than five times the distance from
the Earth to the Sun. This means that it takes about 43 minutes for
sunlight to reach Jupiter. Also, Jupiter's orbital eccentricity of
.04838 is fourth largest among the planets, giving it a perihelion of
7.41 x 108 km and an aphelion of
8.16 x 108 km. Jupiter's year is about 4,333 Earth days in length— that's about 12 times the length of one Earth year!
Jupiter's axial tilt of 3.17° is extremely small, second lowest
in the Solar System behind Mercury's. What this means is Jupiter doesn't
experience seasons at all.
Two things stand out about Jupiter's rotation. The first is its
speed. At just under 10 hours, Jupiter has the shortest rotational
period in the Solar System. (Saturn is a close second at 10.7 hours.)
This quick rotational speed causes the planet to bulge near its equator,
making it less spherical than most of the other planets. The second
stand-out characteristic of Jupiter's rotation is that different parts
rotate at different speeds. This is due to Jupiter's not being a solid
body. For example, the polar atmosphere rotates about 5 minutes more
slowly than that found at the equator.
Rings
Although the rings of Saturn are well-known, it is uncommon to
hear anything about Jupiter's rings. Nevertheless, Jupiter does have a
ring system. Jupiter's rings are lesser known than Saturn's (or even
Uranus') because they are primarily composed of dust, which makes them
difficult to see. The formation of these rings is believed to have come
about through Jupiter's gravity having captured material ejected from
its moons.
Jupiter Facts
Discovery Date: Unknown
Number of Moons:
50 Officially (64 Unofficially)
Rings: Yes
Time it takes light to reach Jupiter from the Sun:
43 min
Mass:
1.90 x 1027 kg
Mean Diameter:
139,822 km
Mean Circumference:
439,263 km
Volume:
1.43 x 1015 km3
Density:
1,326 kg/m3
Surface Gravity:
24.79 m/s2
Length of Day:
9 hours 55 minutes
Length of Year:
4,332.82 Earth Days
Orbital Eccentricity:
.04838
Mean Orbital Distance from the Sun:
7.78 x 108 km
Perihelion:
7.41 x 108 km
Aphelion:
8.16 x 108 km
Axial Tilt: 3.1°
Atmosphere:
Very Dense
Most Recent
Planetary Missions:
New Horizons, Cassini-Huygens
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