Weird Jupiter

Jupiter is more than twice as massive as all the other planets in the Solar System combined

Jupiter was the first planet in our Solar System, and it's also the most massive. In fact, it's actually 2.5 times the mass of the other planets in our Solar System combined.

All of that mass is squeezed into a sphere just under 140,000 kilometers (around 87,000 miles) across, giving it huge gravitational pull that likely shaped the orbit of Earth and the rest of the planets in our neighborhood. The gargantuan planet takes about 12 Earth years to complete its orbit, yet its atmosphere rotates at an incredible rate, completing an average 'day' in just under 10 hours.

The gas giant doesn't have a surface

There is no sharp distinction between the gases making up Jupiter's atmosphere and its dense, liquid hydrogen core. For convenience, astronomers might use the point at which pressure passes one bar, or one atmosphere of pressure at sea level on Earth, as a way to mark where the atmosphere ends and the core begins. Below this line, matter slowly compresses into strange states. Above it, layers of red and white clouds containing ammonia, ammonium hydrosulfide, and water rise in warming zones and fall in cooling bands, tumbling over one another as winds push and shove them around in violent storms.

Its famous Great Red Spot is shrinking

One such storm, called the Great Red Spot, has been swirling for nearly two centuries, if not more. Though once big enough to swallow three Earths with room to spare, its girth has shrunk in recent years, prompting astronomers to wonder if it was growing weaker. More recent assessments make any imminent end to the large hurricane unlikely. Interestingly, Hubble data have recently shown that the winds around the Great Red Spot appear to be speeding up.

Jupiter emits more energy than it receives

At five times the distance from the Sun as Earth, it receives just a few percent of the sunlight. Much of its energy instead comes from deep within, as gravity pulls its gases into a dense liquid state as high as a hundred million atmospheres at the core, generating temperatures of tens of thousands of degrees Celsius. This means Jupiter emits around 1.6 times the energy it receives from the Sun, whipping its thick atmosphere into intense weather systems as it rises from below.

The gas giant is sometimes called a 'failed star'

At the very core of this hot, dense ball, hydrogen is thought to transform into a metallic state that physicists are still working to understand. While Jupiter is larger than some stars, it's sometimes referred to as a 'failed star' because it doesn't have anywhere near enough mass to fuse hydrogen into helium. The planet is actually not a true failed star – this title belongs to brown dwarfs, which fill the gap between gas giants and true stars.