Jupiter, by far the largest planet in the Solar System, itself composed of two-thirds of all planetary mass available, is so heavy, so radiomagnetic, so geothermal that it is almost a star. Jupiter is a gas giant, being in size 1,318 times larger than the Earth but weighing only 318 times more, so it is mostly atmosphere, with a "small" solid core only slightly larger than the Earth.

But such an atmosphere! Mostly hydrogen, helium, methane & ammonia; a swirl of gasses under such extreme conditions of temperture variation and gravitational pressure that it resembles an eternally boiling soup--lateral bands of dark & light clouds swirl across the face of Jupiter (winds of 150 meters per second!), constantly changing place and size and color, except for that huge vortex known as the Great Red Spot, which defies all explanation. And that huge atmosphere is so ponderously heavy that as it is pressed down upon itself by the intense gravity it becomes denser, thicker, until it is liquid hydrogen, jellifying, and still deeper until it becomes liquid metal.

And yet, for all that, Jupiter is considered the one other place in our Solar System where the probability for Life is considered highest: because it generates heat, because the atmosphere resembles an ocean, and because it is so mysterious and full of extremes and surprises.
Diameter/equator:  12,391 km      142,857 km        
Mass:              1              318.4             
Gravity:           1 g            2.64 g            
Rotation Day:      24h            9h 50m 30s        
Orbital Year:      365 days       11.86y (4,332.59 days)    
Distance from sun: 147/152 m km   740.9/815.7 million km    
Moons:             1              17 (or more)