Official 38 - lecture 4

Listen to part of a lecture in an astronomy class.

Last week, we discussed the formation of Earth and the other rocky planets, of planets in the inner solar system.

the overall figure of solar system.

what about the gas giants?

Jupiter, Saturn, Uranus and Neptune.

well there are two theories.

But first, let's recap.

we believe our solar system began as a huge spinning cloud of dust and gas, which flattened and eventually collapsed in on itself.

the matter it's centered condensed into a ball of hot gas and dust, eventually becoming our sun.

and what happened to the remaining could?

to the disk encircling the sun when it was a young star.

the rocky planets were born.

dust, little grains of rocks and metal within the disk collided with each other and stuck together, and this process sort of snowballed over millions of years until the chunks grew into mini-planets, proto-planets.

this process is called accretion.

and we call the disk an accretion disk.

now, think of it as two parts: an inner accretion disk, and an outer accretion disk.

in the inner part, once an object gets large enough, that object's gravitational field gets stronger, which speeds up the accretion process.

You know, larger objects attract smaller ones and sort of gobble them up.

gobble: to swallow or eat greedily, to take eagerly: grab usually used with up.

And eventually, you get a full-sized planet in its own orbit.

Okay. That's how the inner rocky planets probably formed by accretion.

But what about those gas planets in the outer solar system, in the outer accretion disk?

Well, the first theory says the accretion process was similar to the one that formed the rocky planets, with some key differences.

Remember, the gas giants are farther from the sun, where temperatures are much colder.

So, in the outer accretion disk, compounds like water and ammonia exist in frozen form.

ammonia: Ammonia is a colorless, poisonous gas with a familiar noxious odor.