On 15th September 1998, the rings around the
planet Jupiter were declared to be made of dust from the impacts of cosmic
bodies that crashed into Jupiter's moons. The idea came from studies of the
rings made by scientists at several institutions.
Jupiter is the fifth planet from the Sun and the largest
planet in the Solar System. It is a giant planet with a mass one-thousandth
that of the Sun, but is two and a half times that of all the other planets in
the Solar System combined. Jupiter is a gas giant, along with Saturn (Uranus
and Neptune are ice giants).
Jupiter was known to astronomers of ancient times.
The Romans named it after their god Jupiter. When viewed from Earth, Jupiter
can reach an apparent magnitude of −2.94, bright enough to cast shadows, and
making it on average the third-brightest object in the night sky after the Moon
and Venus.
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| A portrait of Jupiter. Source: NASA |
Jupiter is primarily composed of hydrogen with a quarter of
its mass being helium, although helium only comprises about a tenth of the
number of molecules. It may also have a rocky core of heavier elements, but
like the other giant planets, Jupiter lacks a well-defined solid surface.
Because of its rapid rotation, the planet's shape is that of an oblate spheroid
(it has a slight but noticeable bulge around the equator).
The outer atmosphere
is visibly segregated into several bands at different latitudes, resulting in
turbulence and storms along their interacting boundaries. A prominent result is
the Great Red Spot, a giant storm that is known to have existed since at least
the 17th century when it was first seen by telescope.
Surrounding Jupiter is a
faint planetary ring system and a powerful magnetosphere. Jupiter has at least
67 moons, including the four large Galilean moons discovered by Galileo Galilei
in 1610. Ganymede, the largest of these, has a diameter greater than that of
the planet Mercury.
Jupiter has been explored on several occasions by robotic
spacecraft, most notably during the early Pioneer and Voyager flyby missions
and later by the Galileo orbiter. The most recent probe to visit Jupiter was
the New Horizons spacecraft in late February 2007 en route to Pluto, using the
gravity from Jupiter to increase its speed and bend its trajectory. Future
targets for exploration in the Jovian system include the possible ice-covered
liquid ocean on the moon Europa.
The Galileo orbiter, which went into orbit around Jupiter on
December 7, 1995 orbited the planet for over seven years, conducting multiple
flybys of all the Galilean moons and Amalthea. The spacecraft also witnessed
the impact of Comet Shoemaker–Levy 9 as it approached Jupiter in 1994, giving a
unique vantage point for the event. While the information gained about the
Jovian system from Galileo was extensive, its originally designed capacity was
limited by the failed deployment of its high-gain radio transmitting antenna.
A 340-kilogram titanium atmospheric probe was released from
the spacecraft in July 1995, entering Jupiter's atmosphere on December 7. It
parachuted through 150 km (93 mi) of the atmosphere at speed of about 2,575
km/h (1600 mph)[28] and collected data for 57.6 minutes before it was crushed
by the pressure of about 23 atmospheres at a temperature of 153 °C. It would
have melted thereafter, and possibly vaporized. The Galileo orbiter itself
experienced a more rapid version of the same fate when it was deliberately
steered into the planet on September 21, 2003, at a speed of over 50 km/s, to
avoid any possibility of it crashing into and possibly contaminating Europa—a
moon which has been hypothesized to have the possibility of harboring life.
Data from this mission revealed that hydrogen composes up to
90% of Jupiter's atmosphere. The temperatures data recorded was more than 300
°C (>570 °F) and the windspeed measured more than 644 kmph (>400 mph)
before the probes vapourised.
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