A Giant Icy Shell: Oort Cloud Structure Quiz

A giant spherical shell is the correct answer. While the inner solar system is flat like a pancake, the Oort Cloud is so far from the Sun that it forms a massive "bubble" that surrounds the Sun and all the planets from every direction.

True. Astronomers divide the Oort Cloud into the "Inner Hills Cloud" (which is shaped like a thick donut) and the "Outer Oort Cloud" (which is a vast sphere). Both parts contain icy debris, but they have slightly different shapes and locations.

Hills is the correct answer. This region is known as the "Hills Cloud." It serves as a transition zone between the flat Kuiper Belt and the massive outer sphere, holding a huge amount of icy material that can eventually move into the outer cloud.

Water, methane, and ammonia ices are the correct answers. Because the Oort Cloud is trillions of miles from the Sun, it is far too cold for liquid water or gas. The objects are "dirty snowballs" made of different types of frozen chemicals and dust.

Gravity from passing stars "puffs" it out is the correct answer. In the deep outer solar system, the Sun's gravity is very weak. The tiny tugs from other stars in our galaxy pull the objects in different directions, turning a flat disk into a round cloud over billions of years.

False. The Oort Cloud is mostly empty space. Even though there are trillions of icy objects, they are separated by millions of miles. If you were standing on an Oort Cloud object, the next nearest object would be invisible to your eyes because it is so far away.

Dirty is the correct answer. This term is used because comets and Oort Cloud objects are a mixture of frozen ices and rocky dust. When these "dirty snowballs" get close to the Sun, the ice turns to gas and releases the dust, creating the comet's tail.

They were kicked out by giant planets is the correct answer. Most Oort Cloud objects actually formed much closer to the Sun. Long ago, the gravity of giant planets like Jupiter and Saturn acted like a "slingshot," throwing these icy leftovers into the far reaches of space.

The Inner Hills Cloud and Outer Spherical Cloud are the correct answers. These two layers make up the entire Oort Cloud. The Asteroid Belt and Kuiper Belt are separate regions located much closer to the Sun.

Trillions is the correct answer. While we can't see them all, the sheer size of the Oort Cloud suggests it contains billions or trillions of individual icy rocks. This provides a nearly endless supply of comets that can visit the inner solar system over billions of years.

True. The Oort Cloud is significantly larger than the region where the planets live. It reaches nearly a light-year away from the Sun, making the rest of the solar system (the planets and the Kuiper Belt) look like a tiny dot in the middle of a giant bubble.

Hills is the correct answer. The Hills Cloud is the "bridge" between the inner and outer parts of the deep solar system. It is much thicker than the Kuiper Belt but not yet a perfect sphere like the outermost layer of the Oort Cloud.

The Sun's gravity is the correct answer. Even though the Sun is very far away, its massive gravity still reaches out to the Oort Cloud. This keeps the icy objects in orbit, preventing them from floating away into the empty space between stars.

Mostly empty space and huge distances are the correct answers. Unlike the clouds in our atmosphere, the Oort Cloud is not a thick mist. It is a collection of solid objects that are so far apart that space travel through it is very safe and easy.

True. Because the Oort Cloud is a sphere (surrounding us on all sides), comets can appear from the "top," "bottom," or "sides" of the solar system. This is one of the main ways scientists proved the Oort Cloud must be a sphere and not a flat ring.

Reservoir is the correct answer. Because it is so far away and cold, the Oort Cloud preserves the original materials that built the planets 4.5 billion years ago. It is like a cosmic "time capsule" or storage tank for the early solar system.

Near absolute zero is the correct answer. At trillions of miles from the Sun, there is almost no heat. The temperature is roughly -450 degrees Fahrenheit (-270 Celsius). This extreme cold is what allows the objects to remain frozen as solid ice for billions of years.

Cannot see it directly, too far to visit, and to predict comets are the correct answers. Because the Oort Cloud is invisible to our current technology, scientists use math and the behavior of comets to build a "model" or a map of what it must look like.

The Kuiper Belt is the correct answer. The Kuiper Belt is located just past Neptune (about 30-50 AU), while the Oort Cloud doesn't even begin until at least 2,000 AU. The Kuiper Belt is the "neighbor" to the planets, while the Oort Cloud is the "frontier."

True. The outer edge of the Oort Cloud is the boundary where the Sun's gravity finally stops being the boss. Beyond this point, you are officially in the space between stars, where the gravity of other stars in the Milky Way becomes more important than our Sun.