Named after the Roman god of sky and thunder, Jupiter is by far the largest planet in the Solar system, having 2.5 times more mass than all other planets combined. This means mass of 318 Earths or about one thousandth of the Sun’s mass. It may not sound a lot compared to the Sun, but it’s enough to place its barycentre with the Sun above our stars surface.
Barycentre is the point around which two objects orbit. For all other planets, this point is inside the Sun’s volume, but the heavier the second object, the further away from the first object’s centre lies this point.
Jupiter’s radius is 11 times that of Earth and one tenth the radius of the Sun. Its volume is so great, you could fit 1321 Earths inside it. Jupiter is so massive, unit “Jupiter mass” is used for describing masses of extra-solar planets and brown dwarf stars. It is the third brightest object in the night sky, after the Moon and Venus.
Interestingly, if Jupiter had more mass, it would shrink under increased pressure. So, yeah, Jupiter is massive. Let’s move on!
Jupiter orbits the Sun at the average distance 5.2 times the Earth, or 5.2 astronomical units (AUs) and it needs 11.86 years to circle our star. This is exactly two fifths the time it takes Saturn for a full revolution around the Sun, which means the two planets have 5:2 orbital resonance. Since Jupiter’s axis is tilted by only 3 degrees, on it’s way around the Sun it doesn’t experience seasonal changes like we on Earth do.
Around its own axis, Jupiter rotates once every 9 hours and 50 minutes, with different points in higher atmosphere rotating at different speeds, like in all gas giants. This is the fastest rotation among all planets, causing Jupiter to flatten at the poles and have a bulge at the equator i.e. it is oblate spheroid with diameter between poles is shorter than diameter across the equator.
In composition, Jupiter is similar to Saturn, but a lot remains unknown because we haven’t been able to send a probe which would survive more than a minute before being crushed by the pressure. Hydrogen (75%) and helium (24%) make up most of planet’s mass. Models suggest Jupiter has a solid core, surrounded by liquid-metallic hydrogen. This layer is enriched with helium droplets falling toward centre of the planet, leaving upper atmosphere relatively depleted of helium. Above this layer, where pressures are less extreme, there is a transparent layer of gassy hydrogen.
Jupiter has the largest atmosphere of all planets in the Solar system. It is covered with orange and brown clouds composed of ammonia crystals with phosphorus, sulfur and hydrocarbons giving the atmosphere its colour. The clouds are divided into belts with distinctive features and circulation patterns, interaction between them causing storms and turbulence. The best known storm is the giant Great Red Spot, a anticyclonic storm that possibly exists for at least 350 years. It is larger than Earth itself and could be planet’s permanent feature.
Jupiter, like all other gas giants, has a faint ring system made of three segments. They are made of dust, unlike Saturn’s icy rings. Jupiter has 67 moons, mostly less than 10 kilometres in diameter, but four Galilean moons make up for it, Ganymede being the largest in the Solar system and others all making top 6 by diameter.
Jupiter and its gravity have played a significant role in forming the Solar system. Orbits of most planets lie closer to its orbital plane than the Sun’s equatorial plane i.e. orbits of other planets are more in line with Jupiter’s orbit than the line extending from the Sun’s equator. Furthermore, Jupiter has been called the Solar system’s vacuum cleaner, attracting the most frequent bombardment by comets. If this helps keeping inner planets safer or not is a much discussed topic, since some argue that Jupiter’s gravity is also responsible for attracting new comets from Kuiper belt toward Earth. Jupiter also has a great impact on the asteroid belt between it and Mars. Very interesting are the two groups of asteroids, Greeks and Trojans, preceding and following Jupiter, respectively, on its orbit around the Sun, settled in planets Lagrangian points L4 and L5.
All images credited to NASA