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Speaker 1: Welcome to brain Stuff production of I Heart Radio, Hey

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Speaker 1: brain Stuff Lauren vogebom Here. Earth has only one moon,

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Speaker 1: but dozens of natural satellites revolve around Jupiter, the biggest

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Speaker 1: planet in our Solar System, and new members in the

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Speaker 1: Jupiter posse are still being discovered. In July, a team

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Speaker 1: of astronomers announced that they found twelve previously unknown moons

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Speaker 1: around Jupiter. Scott S. Shepherd of the Carnegie Institute for

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Speaker 1: Sciences was leading a search for new objects in the

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Speaker 1: distant Kuiper Belt, an enormous ring of debris that lies

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Speaker 1: beyond Neptune. Shepherd and his colleagues decided to take a

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Speaker 1: break from their primary research goal and observed Jupiter for

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Speaker 1: a while. That's how they wound up standing on Galileo's shoulders.

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Speaker 1: In sixteen ten, the great astronomer Galileo Galilei noticed four

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Speaker 1: heavenly bodies that appeared to revolve around Jupiter, named Io, Europa, Ganymede,

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Speaker 1: and Callisto. These are Jupiter's biggest moons by far, and

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Speaker 1: they were the first to be discovered. As stargazing technology

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Speaker 1: grew more sophisticated, it became clear that the quartet had

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Speaker 1: lots of company. Shepherd's team just brought the total number

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Speaker 1: of identified Jovian moons, that is, moons that revolve around Jupiter,

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Speaker 1: up to seventy nine. No other planet in the Solar

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Speaker 1: System comes close to that figure. Saturn is the runner

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Speaker 1: up with its sixty two verified moons, while Urinas boasts

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Speaker 1: twenty seven and Neptune has fourteen. Mars, our beloved next

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Speaker 1: door neighbor, possesses two satellites, Demos and Phobos. And if

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Speaker 1: that's making you feel insecure about Earth's lonely single moon,

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Speaker 1: at least you could take solace in the fact that

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Speaker 1: Mercury and Venus are totally moonless. According to the astronomer

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Speaker 1: Neil F. Corman's, if planet Earth had two moons instead

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Speaker 1: of one, our knights would get brighter because there would

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Speaker 1: be twice as much sunlight reflecting off of lunar surfaces.

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Speaker 1: Also would see significantly higher tides, rendering many coastal areas uninhabitable.

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Speaker 1: There's a reason why Jupiter has so many satellites while

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Speaker 1: other planets, Ours, for instance, have so few, or a

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Speaker 1: few reasons really, but it all comes down to gravity.

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Speaker 1: Astronomers divide the planets within our Solar System into two categories. Mercury, venous,

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Speaker 1: Earth and Mars are so called terrestrial or inner planets,

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Speaker 1: while Jupiter, Saturn, Uranus, and Neptune have been classified as

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Speaker 1: gas giants, also known as outer planets. The size gap

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Speaker 1: between those factions is quite considerable. Although Uranus is the

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Speaker 1: smallest outer planet, it's still fifteen times more massive than Earth,

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Speaker 1: which is the largest of the inner planets. But none

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Speaker 1: of the other planets can compete with Jupiter in terms

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Speaker 1: of sheer bulk. You'd need more than three hundred duplicates

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Speaker 1: of our puny home world to equal Jupiter's colossal mass. Now,

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Speaker 1: as Isaac Newton observed, there's a positive correlation between the

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Speaker 1: mass of an object and the strength of its gravitational field.

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Speaker 1: Because the gas giants are so massive, they're able to

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Speaker 1: attract more satellites. That's not the only reason why planets

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Speaker 1: like Jupiter have such large moon collections. Our Solar systems

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Speaker 1: gas giants are relatively far away from the Sun. In contrast,

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Speaker 1: some stars have massive Jupiter like planets called hot jupiters. Basically,

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Speaker 1: these are gas giants that orbit in close proximity to

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Speaker 1: their stars. Imagine if Saturn switched places with mercury. A

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Speaker 1: twenty ten paper by French astronomer effect He in the

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Speaker 1: Money argues that hot jupiters have few, if any moons.

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Speaker 1: These planets are thought to originate in distant parts of

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Speaker 1: their solar systems, and then migrate inwards. Along the way,

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Speaker 1: their moons get caught in a game of celestial tug

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Speaker 1: of war. Gas Giants may be big, but stars are

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Speaker 1: much bigger. As such, they've got far stronger gravitational fields,

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Speaker 1: so when a hot jupiter gets too close to its star,

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Speaker 1: the star will eventually steal its moons. Distance offsets this ability.

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Speaker 1: The further you travel from the Sun, the weaker its

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Speaker 1: gravitational pull on you becomes. Are For, if Naumali is correct,

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Speaker 1: then our Jupiter has seventy nine moons and counting. Because

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Speaker 1: it's a ridiculously massive planet that's far enough away from

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Speaker 1: the Sun to avoid lunar theft. Jupiter's moons are hardly

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Speaker 1: a monolithic family. A few of them have quirks that

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Speaker 1: are well known to astronomy enthusiasts. Io is loaded with

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Speaker 1: active volcanoes, there's a hidden ocean on Europa that might

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Speaker 1: harbor alien life, and at two thirds the size of Mars.

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Speaker 1: Ganymede is the biggest satellite in the entire Solar System.

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Speaker 1: These three moons, along with Kalisto, probably formed in tandem

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Speaker 1: with Jupiter itself. The big planet likely started out as

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Speaker 1: a disc of gases and dust that eventually became the

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Speaker 1: gas giant we know today. While Jupiter took shape, some

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Speaker 1: of the materials swirling around it coalesced into the four moons.

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Speaker 1: Galileo spied in sixteen Saturn may have helped move the

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Speaker 1: process along. It's also been hypothesized that early Jupiter had

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Speaker 1: a number of failed moons that were pulled into and

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Speaker 1: absorbed by the huge planet. It's other satellites weren't necessarily homegrown.

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Speaker 1: Scientists think that many of Jupiter's moons started out as

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Speaker 1: drifting chunks of rock that became ensnared by the planet's

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Speaker 1: gravitational pull, And we also have to talk about lunar behavior.

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Speaker 1: Many of the Jovian moons orbit in the same direction

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Speaker 1: in which Jupiter spins, but there are those that go

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Speaker 1: the opposite way, including nine of the new moons discovered

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Speaker 1: by Shepherd and his colleagues. With so many bodies revolving

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Speaker 1: in different directions. Collisions are inevitable. Moons that crash into

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Speaker 1: one another might well be destroyed in the process. Just

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Speaker 1: as Jupiter acquires new moons, it's finding ways to lose

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Speaker 1: some of the older ones. Today's episode was written by

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Speaker 1: Mark Mancini and produced by Tyler Clang. Brain Stuff is

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Speaker 1: production of I Heart Radio's How Stuff Works. For more

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Speaker 1: on this and lots of other far from monolithic topics,

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Speaker 1: visit our home planet, how stuff Works dot com. And

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