Scavenging the Early Sun: Oort Cloud Formation Quiz

Closer to the Sun, near the giant planets is the correct answer. The icy objects, or planetesimals, originally formed in the same disk as the planets. They were later ejected outward by the intense gravity of the growing gas giants.

True. The formation of the Oort Cloud was a byproduct of the planet-building process. As the giant planets moved and settled into their orbits, they cleared out the surrounding debris, creating the cloud we see today.

Jupiter is the correct answer. Being the most massive planet, Jupiter’s gravitational pull was strong enough to act as a slingshot, flinging billions of icy bodies into the far-flung orbits of the Oort Cloud.

Sun's weak gravity, passing stars, and galactic tides are the correct answers. While objects were kicked out in a flat plane, external forces from the rest of the galaxy "puffed" the cloud into a spherical shape over billions of years.

They were lost to interstellar space is the correct answer. If a planet's "slingshot" effect was too strong, the object reached escape velocity and left our solar system forever, becoming "rogue" comets between the stars.

True. The frost line is the distance from the Sun where it is cold enough for volatile compounds like water and methane to freeze. Because Oort Cloud objects are mostly ice, they must have formed at or beyond this line.

Planetesimals is the correct answer. These are the "building blocks" of planets. The ones that didn't get incorporated into planets like Neptune or Saturn were either destroyed or tossed into the Oort Cloud.

They reached a balance with galactic gravity is the correct answer. At a distance of about 50,000 to 100,000 AU, the inward pull of the Sun and the outward pull of the rest of the galaxy reach a balance, allowing the objects to stay in stable, distant orbits.

Jupiter, Saturn, Uranus, and Neptune are the correct answers. All four gas and ice giants had sufficient mass to gravitationally interact with and scatter the surrounding icy debris during the solar system's chaotic youth.

The migration of giant planets is the correct answer. The Nice Model suggests the giant planets moved their positions early on, which would have triggered a massive wave of object scattering, populating the Oort Cloud and Kuiper Belt.

False. It is estimated that 90% to 99% of the original icy planetesimals were ejected into interstellar space entirely. The Oort Cloud contains only the small fraction that remained gravitationally bound to the Sun.

Hills is the correct answer. Also known as the Inner Oort Cloud, the Hills Cloud is a massive reservoir of objects that likely formed closer to the planetary disk than the outer spherical shell.

It would be a flat disk is the correct answer. Without the gravitational "perturbations" from passing stars and the galactic disk to pull orbits in all directions, the scattered objects would have stayed in the flat plane they were ejected from.

Violent/chaotic history, planet migration, and leftover ice are the correct answers. The Oort Cloud is a "fossil" record of the gravitational scattering that occurred while the planets were finding their permanent homes.

True. Just like scraps of wood left over from building a house, the Oort Cloud is made of the material that wasn't used to make the large planets or their moons.

Gravity is the correct answer. Even though the Sun is a tiny dot from that distance, its mass is so great that it can hold onto these trillions of objects across trillions of miles.

It would not exist is the correct answer. Without the massive gravity of the gas giants to "kick" objects out to great distances, the icy material would have likely stayed in the outer solar system as a much thicker version of the Kuiper Belt.

Timeline, visibility, and lack of samples are the correct answers. Because we can't see the Oort Cloud, scientists must rely on computer simulations and the study of comets that occasionally visit from that region.

About 5 to 100 times Earth's mass is the correct answer. While individual objects are small, there are so many of them that their combined mass is significant, though still much less than the mass of a planet like Jupiter.

False. The "clearing out" of the solar system ended billions of years ago. While a few objects might occasionally be added, the Oort Cloud is a stable structure that was largely finished during the first few hundred million years of the solar system.