Jupiter, the fifth planet from the sun in our solar system, is the largest planet. It derives its name from the Roman god Jove and has a significant size, being 318 times more massive than Earth. It accounts for two-thirds of the total planetary mass in our solar system. Unlike Earth, Jupiter’s surface is gaseous rather than solid, primarily composed of hydrogen (90%) and helium (10%). Additionally, it contains traces of methane, ammonia, water, and rock. Its interior resembles that of the Sun but with a lower temperature.
Some scientists speculate that Jupiter may have a core consisting of liquid metallic hydrogen; however, this theory remains uncertain due to requiring pressures exceeding 4 million bars. Interestingly enough, Jupiter emits more energy into space than it receives from the sun.
This enormous planet orbits beyond the asteroid belt at an average distance of approximately 483 million miles (773 million kilometers) from the sun. It completes one revolution every 11.86 years.
Amongst the Jovian planets – Jupiter, Saturn, Uranus, and Neptune – Jupiter stands out due to its large diameter measuring 88,679 miles (142,800 kilometers). This diameter is over eleven times larger than that of Earth’s diameter.
In addition to its size advantage,
the mass of Jupiter surpasses that of Earth by a factor of 318 and exceeds combined mass
of all other planets by more than two and a half times.
The determination of Jupiter’s flattening involved measuring its diameter from Earth and finding it slightly larger than previous measurements. Measurements were taken at a pressure of 800 mbar near the planet’s cloud tops. During the occultation of the spacecraft by Jupiter, observations revealed that the polar diameter is 133,540 km (82,980 miles), and the equatorial diameter is 142,796 kilometers (88,732 miles). The greater flattening compared to Earth is primarily due to Jupiter’s non-solid state and faster rotation. Calculations based on mass and volume confirmed an average density of 1.33 gm/cm^3 for Jupiter, while water has a density of 1.
Jupiter’s atmosphere is mostly made up of hydrogen, helium, methane, and ammonia. It is divided into bands that run parallel to the equator and contains a notable feature called the Great Red Spot in its southern hemisphere. This massive storm has been present for over 300 years and rotates counterclockwise as a high-pressure system with winds that can reach speeds of around 270 mph. The Great Red Spot holds the record for being the largest known storm in our Solar System, measuring 15,400 miles in diameter which is almost twice as big as Earth and about one-sixth the size of Jupiter itself. Robert Hooke first observed it in 1664. Unlike hurricanes found in the Caribbean region, storms on Jupiter rotate counterclockwise because it doesn’t have a solid surface. Instead, its atmosphere transitions from outer ammonia clouds to frozen gases and eventually to a liquid or solid hydrogen mantle. These unique atmospheric features like the Great Red Spot provide evidence of Jupiter’s fast rotation period lasting approximately 9 hours and 55 minutes, causing polar flattening that exceeds 6%. (Source: Columbia University)
Jupiter’s temperature range varies from approximately -190°F (-124°C) on its visible atmospheric surface to 9°F (-13°C) at lower cloud levels. In specific equatorial regions, temperatures can reach up to 40°F (4°C) at lower cloud levels. Interestingly, Jupiter emits about four times more heat energy than it receives from the sun, suggesting the presence of internal heat sources. This is believed to be partially caused by the gradual contraction of the planet.
Moreover, Jupiter is well-known for its intense non-thermal radio emission in the 15-m range. Moving on to its ring system, it consists of three components: an inner halo, a main ring, and a Gossamer ring. Initially observed by the Voyager spacecraft as a single ring, imagery captured by the Galileo spacecraft revealed that Gossamer actually comprises two nested rings with one embedded within the other.
These rings surrounding Jupiter are incredibly thin and mainly composed of dust particles formed when interplanetary meteoroids collide with its four inner moons: Metis, Adrastea, Thebe, and Amalthea. The innermost halo ring has a toroidal shape and extends radially from around 92,000 kilometers (57,000 miles) to approximately 122,500 kilometers (76,000 miles) from Jupiter’s center. Starting from the inner boundary of the main ring, fine dust particles disperse outward while falling towards the planet.The brightest ring, known as the main ring, starts from the halo boundary and reaches a distance of approximately 128,940 kilometers (80,000 miles). This places it just inside Adrastea’s orbit. As we approach Metis’ orbit, the brightness of the main ring diminishes. The two faint Gossamer rings share similar characteristics. The innermost Gossamer ring called Amalthea stretches from Adrastea’s orbit to Amalthea’s orbit at a distance of about 181,000 kilometers (112,000 miles) from Jupiter’s center. The other Gossamer ring named Thebe extends from Amalthea’s orbit to roughly 221,000 kilometers (136,000 miles) away at around Thebe’s orbit.
Jupiter’s magnetosphere, a magnetic environment extending 3 to 7 million kilometers towards the Sun and spanning a distance of 750 million kilometers, contains harsh radiation belts filled with electrons and ions (Seeds). This powerful magnetic field, stronger than Earth’s, generates phenomena such as intense lightning and an aurora similar to Earth’s aurora borealis. Due to Jupiter’s rapid rotation, its magnetosphere is flattened and not perfectly spherical. Unlike Earth, Jupiter has three distinct weather-producing zones known as tropospheres that may contain ammonia ice, ammonium hydrosulfide, water ice crystals, and liquid ammonia-water droplets. The uppermost atmosphere of Jupiter experiences temperatures around 150 degrees Kelvin where ammonia ice crystals thrive (A.U.R.A.). Astronomers speculate that the next atmospheric layer consists primarily of ammonium hydrosulfide crystals. Preceding the layer of liquid metallic hydrogen is believed to be a layer composed of liquid ammonia and water droplets. Additionally, high-speed winds in wide bands occur in Jupiter’s atmosphere. These opposing winds along the latitude result in colorful bands due to chemical reactions and variations.The distinct lighter bands, referred to as zones, and the darker bands, known as belts, are a prominent characteristic of Jupiter’s atmosphere. The longevity of these bands over the past eighty years has left uncertainty about their permanence. A suggested theory is that the jet streams found at the borders between belts and zones might be linked to deep circulation patterns within Jupiter’s liquid interior (Seeds).
Jupiter has at least sixteen natural satellites, with twelve being relatively small and likely captured rather than formed in Jupiter’s orbit. These moons are categorized into three groups. The four largest satellites – Io, Europa, Ganymede, and Callisto – were initially discovered by Galileo in 1610 after the invention of the telescope. They are collectively referred to as the Galilean satellites. It is believed that these sizable moons formed through accretion, a process where dust and gas accumulate to form larger bodies.
Ganymede holds two distinctions: it is both the largest satellite in the solar system and bigger than Mercury itself, measuring 3,268 miles (5,262 kilometers) in diameter. In 1979, Voyager I and II observed Io during a flyby and witnessed its numerous active erupting volcanoes.
Io, the innermost of the Galilean satellites, is similar in size and density to our Moon but has the highest density among them. During its flyby in December 1995, the Galileo spacecraft detected an iron inner core on Io and also observed a high-altitude ionosphere. The Voyager spacecraft discovered erupting volcanoes on Io in 1979 while passing through the Jovian system. It was found that Io is more volcanically active than Earth, making it the most volcanically active planet in our solar system. This volcanic activity is caused by internal heat generated by tidal forces between Jupiter, Europa, and Ganymede. Pele, which is the largest volcano on Io, was first identified during this time and had an active eruption with a plume measuring 300 km high. In total, Voyager recorded eleven active volcanoes and hundreds of volcanic calderas during its flyby.
Io, one of Jupiter’s moons, is thought to have a surface younger than a million years old and lacks impact craters. It is continuously refreshed by volcanic activity, showcasing vibrant red, yellow, white, and orange-black markings. The primary composition of Io’s surface is sulfur with deposits of frozen sulfur dioxide. While it mainly consists of flat plains under 1 km in height, there are also observed mountain ranges that can reach up to 9 km. Alongside this, there exists a torus made up of sodium gas and sulfur ions spread throughout Io’s orbit.
Europa, another moon of Jupiter, stands out due to its distinct appearance and numerous intersecting features. Unlike Callisto and Ganymede, Europa has minimal vertical relief on its crust with very few craters present. Some scientists describe its features as if they were drawn using a felt marker. Europa may potentially experience internal activity caused by tidal heating but on a much smaller scale compared to Io. Scientists have developed models suggesting that beneath Europa’s thin crust measuring around 5 km in thickness lies vast oceans reaching depths exceeding 50 km or more: “The visible markings observed on Europa may be a consequence of a global expansion process in which the crust potentially fractured became filled with water and subsequently froze.”
Ganymede holds the title for being both the largest moon of Jupiter and the largest known moon in our Solar System; it surpasses even the size of planet Mercury with its diameter measuring at 5,260 km/3,270 mi.Ganymede, a moon of Jupiter, completes an orbit around the planet every 7.2 days at a distance of 1.1 million km/700,000 mi. Its surface showcases both cratered and grooved terrain. Furthermore, in 1994, molecular oxygen was discovered on Ganymede’s surface (Ganymede;Helicon).
In 1996, the space probe Galileo observed a magnetic field surrounding Ganymede, implicating the possibility of a molten core (Hamilton). Galileo captured images of Ganymede from a distance of 7,448 km/4,628 mi. These photos were significantly clearer than those taken by Voyager 2 in 1979 and revealed a heavily cratered and ridged surface, likely influenced by similar forces that shape mountains on Earth. Furthermore, Galileo detected the presence of carbon and nitrogen molecules on Ganymede’s surface in March 1997, which could suggest the potential existence of life in the past (Hamilton).
Callisto, Jupiter’s eighth known satellite and the second largest, was discovered by Galileo and Marius in 1610. Unlike Ganymede, Callisto appears to possess limited internal structure. However, recent data from Galileo indicates that the interior materials have settled to some extent, with an increasing concentration of rock towards the center. It is estimated that Callisto consists of approximately 40% ice and 60% rock/iron (Callisto;Helicon). The entire surface of Callisto is covered in craters (Hamilton).
Callisto, like the Moon and Mars, is renowned for its ancient and heavily cratered surface. It has remained largely unchanged over a span of 4 billion years, except for occasional impacts. The largest craters on Callisto exhibit concentric rings that resemble cracks but have been smoothed out by ice movement over time. Valhalla, an example of a multi-ring basin formed by a massive impact, holds the distinction as the largest crater with a diameter of 4000 km.
In terms of mass comparison to Earth’s Moon, Jupiter’s Galilean satellites can be ranked as follows: Io – 1.21; Europa – 0.65; Ganymede – 2.02; and Callisto – 1.46. However, researchers discovered during the Pioneer odyssey mission that Io’s mass was actually 23% greater than previously estimated. As distance from Jupiter increases, satellite density decreases.
The densities of the four satellites are as follows: Io – 3.52 gm/cm^3; Europa – 3.28 gm/cm^3; Ganymede – 1.95 gm/cm^3; and Callisto – 1.63 gm/cm^3 due to their low density characteristics.All four satellites experience average daylight surface temperatures around -140 C (-220 F).
There is another group consisting of innermost satellites such as Metis, Adrastea, Amalthea, and Thebe.Barnard discovered Amalthea in1892.It measures approximately168 mi(270 km)in length and possesses an elongated shapeMetis and Adrastea, while orbiting near Jupiter’s thin ring system, play a role in providing material to sustain it. The last group of satellites consists of eight moons with a diameter of about 110 mi (180 km). Among these outer satellites, four are positioned at distances ranging from 14 million to 16 million mi (22 million-26 million km) and move in a retrograde motion contrary to the planet’s rotation. Conversely, the other four satellites have a direct orbit. Some theories suggest that these eight satellites might be asteroids captured by Jupiter.
When it is nighttime, Jupiter is often the brightest “star” in the sky (it is second only to Venus, which is seldom visible in a dark sky). The four Galilean moons can easily be seen with binoculars, and a few bands and the Great Red Spot are visible on Jupiter. Jupiter is gradually slowing down due to the tidal drag produced by the Galilean satellites. This slowdown is also affecting the orbits of the moons, slowly pushing them farther away from Jupiter. The fate of Jupiter and its moons can only be determined with more data and advancements in technology. Until then, we can only speculate about its eventual state as a Jovian planet.
Bibliography
- The Columbia Encyclopedia, Fifth Edition. Copyright ©1993, Columbia University Press. Licensed from Lernout & Hauspie Speech Products USA, Inc.
- Pioneer: First to Jupiter, Saturn, and Beyond: Chapter 6A Results At The New Frontier; Fimmel, Richard O.; Van Allen, James; Burgess, Eric; 09-01-1990
