How big is Jupiter?
Sen—With a diameter of about 140,000 kilometres, or 36 per cent of the distance between the Earth and Moon, Jupiter is the largest planet in our Solar System.
Jupiter, like the Sun, is composed almost entirely of hydrogen and helium gas. As Jupiter is by far the most massive planet in the Solar System—containing an astonishing 2.5 times the mass of all the other planets put together—it can easily hold on to these gases. On Earth, hydrogen and helium would escape into space. But how did it get to the size it is?
Scientists think that when the Solar System formed 4.5 billion years ago, the young Jupiter was able to 'grab' a lot of hydrogen and helium before the Sun started to shine. That way the giant planet's immense gravity could maintain this bulk, gassy mass. Planets closer to the Sun however, such as Mercury, Venus, Earth and Mars, lost any hydrogen and helium to the nascent Sun itself. Then, when it started to shine, the smaller, closer planets didn't have enough mass for their gravity to hold on to any remaining gas. The now-shining Sun 'evaporated' it away.
As Jupiter is a gas planet (unlike Earth, which is rocky and solid) and rotates so rapidly that its day is under 10 hours long, it actually bulges outwards a little. That means that its diameter as measured pole to pole is different for its equator. Jupiter's polar diameter is 133,708 kilometres and its equatorial diameter is larger, at 142,984 kilometres. And these figures can vary by a few kilometres. Amateur astronomers can even measure this bulging property—called 'oblateness'—with a good telescope and a micrometer eyepiece.
Interesting to note is that whilst Jupiter is nearly 11 times the diameter of Earth—which has a width of 12,742 kilometres, it's also one-tenth the diameter of the Sun—1,392,684 kilometres. That puts Jupiter virtually in the middle of the Sun and the Earth in terms of size.