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Questions and Answers
What was Aristotle's belief regarding the nature of comets?
What was Aristotle's belief regarding the nature of comets?
Which observation technique did Tycho Brahe use to determine that comets exist outside of Earth's atmosphere?
Which observation technique did Tycho Brahe use to determine that comets exist outside of Earth's atmosphere?
In what year did Isaac Newton demonstrate the parabolic orbit of a comet?
In what year did Isaac Newton demonstrate the parabolic orbit of a comet?
Which comet was identified by Edmond Halley as having similar orbital elements to two other comets?
Which comet was identified by Edmond Halley as having similar orbital elements to two other comets?
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The Great Comet of 1577 was noted for its observations that contributed to which scientific field?
The Great Comet of 1577 was noted for its observations that contributed to which scientific field?
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What are particularly bright comets referred to as?
What are particularly bright comets referred to as?
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How did Newton characterize the motion of a comet under the influence of gravity?
How did Newton characterize the motion of a comet under the influence of gravity?
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What term is used for the appearance of a comet over time?
What term is used for the appearance of a comet over time?
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What is the primary composition of a comet's nucleus?
What is the primary composition of a comet's nucleus?
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Which phenomenon occurs when a comet approaches the Sun, leading to the release of gases?
Which phenomenon occurs when a comet approaches the Sun, leading to the release of gases?
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What type of orbit do most comets have?
What type of orbit do most comets have?
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What term is used to describe the appearance of a comet when it is sufficiently bright to be seen from Earth?
What term is used to describe the appearance of a comet when it is sufficiently bright to be seen from Earth?
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What mechanism causes the tail of a comet to form and point away from the Sun?
What mechanism causes the tail of a comet to form and point away from the Sun?
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Where do short-period comets primarily originate from?
Where do short-period comets primarily originate from?
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What evidence suggests that gravitational influences can alter the orbits of comet-like bodies?
What evidence suggests that gravitational influences can alter the orbits of comet-like bodies?
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What is the term for the thin atmosphere formed around a comet when it approaches the Sun?
What is the term for the thin atmosphere formed around a comet when it approaches the Sun?
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What significant discovery related to the Kuiper belt occurred in 1992?
What significant discovery related to the Kuiper belt occurred in 1992?
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What drives near-Earth asteroids out of the asteroid belt?
What drives near-Earth asteroids out of the asteroid belt?
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Which of the following statements about the Oort cloud is true?
Which of the following statements about the Oort cloud is true?
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What is the definition of a near-Earth object (NEO)?
What is the definition of a near-Earth object (NEO)?
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What is believed to be the primary origin of long-period comets?
What is believed to be the primary origin of long-period comets?
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How far is the innermost portion of the Oort cloud estimated to be from the Sun compared to the Kuiper belt?
How far is the innermost portion of the Oort cloud estimated to be from the Sun compared to the Kuiper belt?
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What was the first near-Earth asteroid to be discovered and in what year?
What was the first near-Earth asteroid to be discovered and in what year?
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What type of bodies primarily populate the asteroid belt?
What type of bodies primarily populate the asteroid belt?
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Study Notes
Near-Earth Objects
- Near-Earth objects (NEOs) are any small Solar System bodies orbiting the Sun whose closest approach to the Sun is less than 1.3 times the Earth-Sun distance.
- This definition relates to the object's orbit, not its current position. Objects are still considered NEOs even when far from Earth.
- Scientists recognized the threat of impacts from NEOs in the 1980s.
- There is mounting evidence that the Cretaceous-Paleogene extinction event was caused by a large asteroid impact.
Comets
- The first near-Earth objects observed by humans were comets.
- The word "comet" comes from the Greek word kōmḗ, meaning "hair of the head," and was used to describe the tail of a comet.
- Comets are icy, small Solar System bodies.
- The solid core structure of a comet is called the nucleus.
- Cometary nuclei are composed of an amalgamation of rock, water ice, and frozen carbon dioxide, methane, and ammonia.
- Most comets have elongated elliptical orbits that take them close to the Sun for part of their orbit, then into the further reaches of the Solar System.
- When a comet warms as it passes close to the Sun, a process called outgassing occurs. Gases are released, forming a huge, extremely thin atmosphere around the comet called the coma.
- The force from the Sun's radiation pressure and solar wind causes a tail to form, pointing away from the Sun.
- Comets have a wide range of orbital periods; the longer the period, the more elongated the elliptical orbit.
- Short-period comets originate in the Kuiper belt or related scattered disc, beyond Neptune's orbit.
- Long-period comets originate in the Oort cloud, much farther from the Sun than the Kuiper belt (thousands of times farther).
- The appearance of a comet is called an apparition. If close enough and bright, a comet can be seen from Earth without a telescope.
Asteroids
- An asteroid is an object orbiting within the inner Solar System.
- Asteroids are typically rocky, metallic, or icy bodies.
- Most known asteroids are located between the orbits of Mars and Jupiter, in a region called the asteroid belt.
- Near-Earth asteroids are asteroids in a near-Earth orbit.
- Eros was the first near-Earth asteroid to be discovered in 1898.
- Near-Earth asteroids are driven out of the asteroid belt by gravitational interactions with Jupiter.
Cretaceous-Paleogene Extinction Event
- The Cretaceous-Paleogene (K-Pg) extinction event was a mass extinction that occurred approximately 66 million years ago.
- This event led to the extinction of all non-avian dinosaurs.
- The event is marked in the geologic record by a thin layer of sediment called the K-Pg boundary.
- This layer contains unusually high levels of iridium, a siderophile (iron-loving) element that is extremely rare in Earth's crust.
- Iridium is more common in comets and asteroids.
- The impact hypothesis, also known as the Alvarez hypothesis, suggests that the K-Pg extinction was caused by the impact of a massive asteroid.
- The impact is theorized to have created a lingering impact winter, halting photosynthesis in plants and plankton, devastating the global environment.
- The Chicxulub crater, discovered in the early 1990s, supports this theory.
Oort Cloud
- The Oort Cloud is a vast cloud of icy planetesimals thought to surround the Sun.
- The concept of the Oort cloud was proposed by Jan Oort and named in his honor.
- Telescopes have not yet detected objects in the Oort cloud.
Additional notes
- Comets have been visited by uncrewed probes.
- Newton proved comets follow parabolic orbits.
- Halley applied Newton's methods to various cometary appearances.
- Halley confidently predicted the reappearance of a particular comet, later known as Halley's Comet.
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Description
Explore the fascinating world of near-Earth objects and comets through this quiz. Learn about their definitions, orbits, and the significant impact they can have on Earth. Test your knowledge about these celestial bodies and their characteristics.
