WEBVTT - How Can Jupiter Have 79 Moons While Other Planets Have None?

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<v Speaker 1>Welcome to brain Stuff production of I Heart Radio, Hey

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<v Speaker 1>brain Stuff Lauren vogebom Here. Earth has only one moon,

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<v Speaker 1>but dozens of natural satellites revolve around Jupiter, the biggest

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<v Speaker 1>planet in our Solar System, and new members in the

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<v Speaker 1>Jupiter posse are still being discovered. In July, a team

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<v Speaker 1>of astronomers announced that they found twelve previously unknown moons

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<v Speaker 1>around Jupiter. Scott S. Shepherd of the Carnegie Institute for

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<v Speaker 1>Sciences was leading a search for new objects in the

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<v Speaker 1>distant Kuiper Belt, an enormous ring of debris that lies

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<v Speaker 1>beyond Neptune. Shepherd and his colleagues decided to take a

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<v Speaker 1>break from their primary research goal and observed Jupiter for

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

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<v Speaker 1>In sixteen ten, the great astronomer Galileo Galilei noticed four

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<v Speaker 1>heavenly bodies that appeared to revolve around Jupiter, named Io, Europa, Ganymede,

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<v Speaker 1>and Callisto. These are Jupiter's biggest moons by far, and

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<v Speaker 1>they were the first to be discovered. As stargazing technology

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<v Speaker 1>grew more sophisticated, it became clear that the quartet had

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<v Speaker 1>lots of company. Shepherd's team just brought the total number

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<v Speaker 1>of identified Jovian moons, that is, moons that revolve around Jupiter,

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<v Speaker 1>up to seventy nine. No other planet in the Solar

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<v Speaker 1>System comes close to that figure. Saturn is the runner

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<v Speaker 1>up with its sixty two verified moons, while Urinas boasts

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<v Speaker 1>twenty seven and Neptune has fourteen. Mars, our beloved next

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<v Speaker 1>door neighbor, possesses two satellites, Demos and Phobos. And if

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<v Speaker 1>that's making you feel insecure about Earth's lonely single moon,

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<v Speaker 1>at least you could take solace in the fact that

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<v Speaker 1>Mercury and Venus are totally moonless. According to the astronomer

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

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<v Speaker 1>of one, our knights would get brighter because there would

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<v Speaker 1>be twice as much sunlight reflecting off of lunar surfaces.

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<v Speaker 1>Also would see significantly higher tides, rendering many coastal areas uninhabitable.

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<v Speaker 1>There's a reason why Jupiter has so many satellites while

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<v Speaker 1>other planets, Ours, for instance, have so few, or a

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<v Speaker 1>few reasons really, but it all comes down to gravity.

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

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<v Speaker 1>Earth and Mars are so called terrestrial or inner planets,

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<v Speaker 1>while Jupiter, Saturn, Uranus, and Neptune have been classified as

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<v Speaker 1>gas giants, also known as outer planets. The size gap

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<v Speaker 1>between those factions is quite considerable. Although Uranus is the

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

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<v Speaker 1>which is the largest of the inner planets. But none

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<v Speaker 1>of the other planets can compete with Jupiter in terms

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<v Speaker 1>of sheer bulk. You'd need more than three hundred duplicates

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

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<v Speaker 1>as Isaac Newton observed, there's a positive correlation between the

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<v Speaker 1>mass of an object and the strength of its gravitational field.

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<v Speaker 1>Because the gas giants are so massive, they're able to

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<v Speaker 1>attract more satellites. That's not the only reason why planets

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<v Speaker 1>like Jupiter have such large moon collections. Our Solar systems

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<v Speaker 1>gas giants are relatively far away from the Sun. In contrast,

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<v Speaker 1>some stars have massive Jupiter like planets called hot jupiters. Basically,

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<v Speaker 1>these are gas giants that orbit in close proximity to

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<v Speaker 1>their stars. Imagine if Saturn switched places with mercury. A

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<v Speaker 1>twenty ten paper by French astronomer effect He in the

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<v Speaker 1>Money argues that hot jupiters have few, if any moons.

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<v Speaker 1>These planets are thought to originate in distant parts of

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<v Speaker 1>their solar systems, and then migrate inwards. Along the way,

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<v Speaker 1>their moons get caught in a game of celestial tug

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<v Speaker 1>of war. Gas Giants may be big, but stars are

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

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<v Speaker 1>so when a hot jupiter gets too close to its star,

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<v Speaker 1>the star will eventually steal its moons. Distance offsets this ability.

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<v Speaker 1>The further you travel from the Sun, the weaker its

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<v Speaker 1>gravitational pull on you becomes. Are For, if Naumali is correct,

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<v Speaker 1>then our Jupiter has seventy nine moons and counting. Because

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<v Speaker 1>it's a ridiculously massive planet that's far enough away from

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<v Speaker 1>the Sun to avoid lunar theft. Jupiter's moons are hardly

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<v Speaker 1>a monolithic family. A few of them have quirks that

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<v Speaker 1>are well known to astronomy enthusiasts. Io is loaded with

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<v Speaker 1>active volcanoes, there's a hidden ocean on Europa that might

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<v Speaker 1>harbor alien life, and at two thirds the size of Mars.

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<v Speaker 1>Ganymede is the biggest satellite in the entire Solar System.

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<v Speaker 1>These three moons, along with Kalisto, probably formed in tandem

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<v Speaker 1>with Jupiter itself. The big planet likely started out as

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<v Speaker 1>a disc of gases and dust that eventually became the

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<v Speaker 1>gas giant we know today. While Jupiter took shape, some

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<v Speaker 1>of the materials swirling around it coalesced into the four moons.

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<v Speaker 1>Galileo spied in sixteen Saturn may have helped move the

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<v Speaker 1>process along. It's also been hypothesized that early Jupiter had

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<v Speaker 1>a number of failed moons that were pulled into and

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

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<v Speaker 1>Scientists think that many of Jupiter's moons started out as

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<v Speaker 1>drifting chunks of rock that became ensnared by the planet's

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<v Speaker 1>gravitational pull, And we also have to talk about lunar behavior.

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<v Speaker 1>Many of the Jovian moons orbit in the same direction

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<v Speaker 1>in which Jupiter spins, but there are those that go

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<v Speaker 1>the opposite way, including nine of the new moons discovered

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<v Speaker 1>by Shepherd and his colleagues. With so many bodies revolving

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<v Speaker 1>in different directions. Collisions are inevitable. Moons that crash into

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<v Speaker 1>one another might well be destroyed in the process. Just

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<v Speaker 1>as Jupiter acquires new moons, it's finding ways to lose

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<v Speaker 1>some of the older ones. Today's episode was written by

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<v Speaker 1>Mark Mancini and produced by Tyler Clang. Brain Stuff is

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<v Speaker 1>production of I Heart Radio's How Stuff Works. For more

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<v Speaker 1>on this and lots of other far from monolithic topics,

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<v Speaker 1>visit our home planet, how stuff Works dot com. And

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