Jupiter
Jupiter is the fifth planet from the Sun and the largest planet in the Solar System. It is a gas giant composed mainly of hydrogen and helium, without a solid surface like Earth's. Its visible disk consists of clouds arranged in light and dark bands. Among them lies the Great Red Spot, an enormous long-lived atmospheric vortex.[2]
Size and physical characteristics
Jupiter's mean diameter is approximately 139,822 km, almost eleven times the diameter of Earth. It has about 1,321 times Earth's volume and 318 times its mass. Its mean density is only 1.33 g/cm³, roughly one quarter of Earth's.[5][1]
The planet is visibly flattened at the poles. Its equatorial diameter is approximately 142,984 km, while the polar diameter is 133,708 km, a difference of more than 9,200 km. This shape results from Jupiter's rapid rotation.[1][2]
Jupiter contains more than twice the mass of all the other planets combined. It remains far less massive than the Sun, which has about one thousand times the mass of the gas giant.[2][6]
Orbit and rotation
Jupiter completes one orbit around the Sun in approximately 11.86 Earth years. Its distance from the Sun changes from about 741 million km to 816 million km. The mean orbital speed is 13.1 km/s, so the planet travels almost 800 kilometres in one minute.[1]
Jupiter rotates in less than 10 hours, the shortest day of any planet in the Solar System. Equatorial clouds and clouds at other latitudes move at different speeds. The axial tilt is only about 3°, so seasonal changes in sunlight are weaker than on Earth.[2]
Atmosphere and cloud bands
The atmosphere consists primarily of hydrogen and helium. Ammonia and other compounds occur in the upper cloud layers, while water clouds form deeper down. Pressure and temperature rise with depth: the temperature is approximately −108 °C at the 1-bar level and about −161 °C at 0.1 bar higher in the atmosphere.[1][2]
Dark belts and bright zones encircle the planet parallel to the equator. Jet streams flowing mainly eastward or westward separate them. Juno measurements show that these flows extend approximately 3,000 km below the cloud tops; the striped appearance is therefore connected with motion deep inside the atmosphere.[7]
Stable groups of cyclones surround the poles. Juno observed eight vortices around a central northern cyclone and five around the southern one. Repeated measurements showed that these systems retained their general arrangement for several years.[8]
Great Red Spot
The Great Red Spot is a giant anticyclone in Jupiter's southern hemisphere. Its east-to-west span exceeds Earth's diameter. Its dimensions and shape change with time; Hubble observations from December 2023 to March 2024 revealed oscillations in its outline over a cycle of roughly 90 days.[9]
The earliest observations reliably identified with the modern spot date from 1831. By 2026, its documented history therefore spans about 195 years, although the vortex may have formed earlier. An uninterrupted sequence of annual observations began in 1878. Telescopic drawings have since been supplemented by photography, digital imaging and spacecraft measurements.[10]
In 1665, Giovanni Domenico Cassini described another long-lived oval at a similar latitude, later known as the Permanent Spot. It was observed until 1713, followed by a gap of more than a century. Analysis of historical drawings and vortex dynamics published in 2024 indicates that Cassini's spot and the modern Great Red Spot were most likely separate formations. The age of the present vortex therefore cannot be securely traced back to the seventeenth century.[11]
The spot has contracted substantially during the period of observation. Its long axis was estimated at about 41,000 km in the late nineteenth century; Voyager measured about 23,300 km in 1979, and Hubble measured roughly 16,500 km in 2014. The contraction has been accompanied by changes in shape, colour and circulation.[12][10]
The vortex extends far below the visible cloud layer. Juno gravity measurements constrain its depth to roughly 500 km.[8]
There is no reliable forecast for how long the Great Red Spot will survive. Its observed contraction does not establish a disappearance date: the vortex may continue shrinking, stabilise at a smaller size or break apart. Historical measurements also show that the changes have not been uniform; its area temporarily increased during the 1920s.[10]
Internal structure
With increasing depth, hydrogen becomes a dense liquid and, under still greater pressure, enters a metallic state in which it conducts electricity efficiently. Jupiter has no sharp boundary between its atmosphere and a solid surface.[2]
Juno gravity measurements support models of a dilute core. Heavy elements are concentrated toward the centre but spread through a substantial volume and mixed with hydrogen and helium. This structure differs from a simple model containing a small, sharply bounded dense core.[13]
Magnetic field and auroras
Jupiter has the strongest intrinsic magnetic field of any planet in the Solar System. Electric currents in its conductive interior generate the field. The magnetosphere traps charged particles and forms intense radiation belts.[14]
The volcanoes of Io are an important source of magnetospheric material. Ejected gas becomes ionised, and the charged particles interact with Jupiter's magnetic field. Particles entering the upper atmosphere produce powerful auroras, observed at ultraviolet and X-ray wavelengths among others.[15]
Moons
NASA's October 2026 summary lists 115 Jovian moons recognised by the International Astronomical Union. The four largest—Io, Europa, Ganymede and Callisto—were discovered by Galileo Galilei in 1610 and are known as the Galilean moons.[3][2]
Io is the most volcanically active body in the Solar System. Its interior is heated by tidal deformation caused by Jupiter's gravity and orbital interactions with the other large moons.[16]
Europa is covered by an icy crust beneath which strong evidence indicates a liquid-water ocean. Ganymede is the largest moon in the Solar System and exceeds Mercury in diameter. Callisto has an ancient surface densely covered with impact craters.[3]
Rings
Jupiter has a faint ring system, discovered by Voyager 1 in 1979. Unlike Saturn's bright rings, Jupiter's rings consist mostly of fine dust and are difficult to see in ordinary reflected light.[2]
Galileo data link the dust to impacts of interplanetary particles on small inner moons. Ejected material spreads along their orbits and replenishes the rings. The principal sources are Metis, Adrastea, Amalthea and Thebe.[4]
Spacecraft exploration
Pioneer 10 became the first spacecraft to fly past Jupiter in December 1973. Pioneer 11 and the Voyager probes followed. Their observations revealed the structure of the cloud belts, characteristics of the magnetosphere and the diversity of the moons.[17]
In 1995, Galileo became the first spacecraft to orbit Jupiter. A probe released from the spacecraft entered the atmosphere and returned direct measurements of its properties. The orbiter studied Jupiter and its moons until 2003.[18]
Juno entered orbit in 2016. Measurements of gravity, the magnetic field and microwave radiation have revealed deep atmospheric flows, internal structure and the polar atmosphere.[7]
Two newer missions are travelling to the Jovian system. NASA's Europa Clipper, launched on 14 October 2024, is scheduled to arrive in 2030 and investigate Europa during repeated close flybys from an orbit around Jupiter.[19] ESA's Juice launched on 14 April 2023 and is scheduled to arrive in 2031. Its principal targets are Jupiter and the icy moons, especially Ganymede, Callisto and Europa.[20]
See also
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 Jupiter Fact Sheet // NASA, National Space Science Data Center.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 Jupiter Facts // NASA Science.
- ↑ 3.0 3.1 3.2 Jupiter Moons // NASA Science.
- ↑ 4.0 4.1 Galileo Finds Jupiter's Rings Formed by Dust Blasted Off Small Moons // NASA Jet Propulsion Laboratory. 1998.
- ↑ Planetary Fact Sheet — Metric // NASA, National Space Science Data Center.
- ↑ Sun Fact Sheet // NASA, National Space Science Data Center.
- ↑ 7.0 7.1 Juno // NASA Science.
- ↑ 8.0 8.1 NASA's Juno: Science Results Offer First 3D View of Jupiter Atmosphere // NASA Jet Propulsion Laboratory. 28 October 2021.
- ↑ NASA's Hubble Watches Jupiter's Great Red Spot Behave Like a Stress Ball // NASA Science. 2024.
- ↑ 10.0 10.1 10.2 Jupiter's Great Red Spot Getting Taller as it Shrinks, NASA Team Finds // NASA. 13 March 2018.
- ↑ Sánchez-Lavega A. et al. The Origin of Jupiter's Great Red Spot // Geophysical Research Letters. 2024. Vol. 51. e2024GL108993.
- ↑ NASA's Hubble Shows Jupiter's Great Red Spot is Smaller than Ever Measured // NASA. 15 May 2014.
- ↑ Wahl S. M. et al. Comparing Jupiter interior structure models to Juno gravity measurements and the role of a dilute core // Geophysical Research Letters. 2017.
- ↑ NASA Investigates Invisible Magnetic Bubbles in Outer Solar System // NASA. 2017.
- ↑ High-Energy X-rays Detected From Jupiter's Auroras // NASA Science.
- ↑ Io Facts // NASA Science.
- ↑ Jupiter Exploration // NASA Science.
- ↑ Galileo Jupiter Atmospheric Probe // NASA Science.
- ↑ Europa Clipper // NASA Science.
- ↑ Juice // European Space Agency.