Travelers from the Deep: Long-Period Comets Quiz

The Oort Cloud is the correct answer. Long-period comets have orbits that take thousands or millions of years to complete, which is only possible if they originate from the Oort Cloud, a vast spherical reservoir located at the very edge of the solar system.

True. Astronomers define long-period comets as those with orbital periods longer than 200 years. Short-period comets usually come from the Kuiper Belt, while long-period ones come from the much more distant Oort Cloud.

Eccentric is the correct answer. An eccentric orbit is one that is highly elongated or "stretched out." This allows the comet to spend most of its time in the freezing outer solar system before diving briefly toward the Sun.

Gravity from passing stars and galactic tidal forces are the correct answers. Because the Sun's gravity is so weak at the edge of the solar system, even tiny gravitational tugs from the rest of the galaxy can disrupt a comet's orbit.

It speeds up is the correct answer. As a comet "falls" toward the Sun, gravity pulls it faster and faster. It reaches its maximum speed at perihelion (the point closest to the Sun) before slowing down as it heads back out to the Oort Cloud.

True. Because the Oort Cloud is a sphere (unlike the flat Kuiper Belt), comets can arrive from above, below, or the sides of the planetary plane. This was the first major clue that the Oort Cloud was shaped like a ball.

Sublimation is the correct answer. In the vacuum of space, ice does not melt into liquid; instead, the Sun's heat causes it to turn directly into gas, which then carries dust away to form the visible tail.

They are ancient, frozen samples of the early solar system is the correct answer. Because they have spent billions of years in the "deep freeze" of the Oort Cloud, they preserve the original chemical ingredients that formed the planets.

Hale-Bopp and Hyakutake are the correct answers. Halley's Comet is a short-period comet (76 years), while long-period comets like Hale-Bopp take thousands of years to return to our view.

Near absolute zero is the correct answer. The Oort Cloud is so far from the Sun that temperatures are around -450°F. This extreme cold keeps the comet's ices solid and unchanged for billions of years.

True. The heat from the Sun boils away layers of ice and dust. Eventually, after many passes, the comet may lose all its ice and become a "dead" comet, which looks like a dark asteroid.

Gravity is the correct answer. The Sun's gravitational pull is the "anchor" that keeps comets in orbit, even when they are trillions of miles away at the outer edge of the Oort Cloud.

A few months to a year is the correct answer. Compared to their thousands of years in deep space, their visit to the "warm" part of the solar system is very brief. They zip in, grow a tail, and then fly back out.

The Ion and Dust tails are the correct answers. The Ion tail is made of charged gas and always points directly away from the Sun, while the Dust tail is made of solid particles and curves behind the comet's path.

False. Because they spend so much time in the distant, dark Oort Cloud, many long-period comets are "one-time visitors" that we only see when they suddenly appear in our telescopes for the first time.

100,000 is the correct answer. This massive distance means the Oort Cloud reaches nearly halfway to the next nearest star system, defining the true boundary of our solar system.

It can be torn apart by gravity or vaporized is the correct answer. These are often called "Sungrazers." The intense heat and tidal forces of the Sun can break the icy nucleus into pieces or destroy it completely.

An elliptical path and a closed loop are the correct answers. While the orbits are very stretched out, they are still loops that return to the starting point—even if that return takes millions of years.

Most are currently in the distant Oort Cloud is the correct answer. Only a tiny fraction of the trillions of objects in the Oort Cloud are ever nudged toward the Sun at any given time. Most stay in the dark, frozen outer shell of our system.

False. It is more like a "comet cemetery" or "storage locker." The objects were formed 4.5 billion years ago; they are not being "born" now, they are just being preserved from the past.