Astronomy Chapter 24

C-type asteroids have albedos less than ____________ and would look very ___________ to human eyes. They are probably made of ____________-rich material similar to that in carbonaceous chondrite meteorites. C-type asteroids are more common in the ______________ asteroid belt.

0.06; Dark; Carbon; Outer

S-type asteroids have albedos of _________ to ________, so they would look ___________________ and also ________________ than C-types; S-types may be composed of _____________ material.

0.1; 0.2; Brighter; Redder; Rocky

1.) Asteroids can be classified by their ______________, ______________, and ______________ to reveal clues to their compositions. This also allows them to be compared to meteorites in labs on Earth. 2.) What are the main classes identified by this method?

1.) Albedos; Colors; Spectra 2.) C-type, S-type, and M-type asteroids

Short-period comets usually follow orbits that lie within __________ degrees of the plane of the Solar System, and most revolve around the Sun in the __________________ direction.

30; Prograde

Sporadic Meteors

A meteor not part of a meteor shower

Falls

A meteorite seen to fall

Finds

A meteorite that is found but was not seen to fall

Chondrites

A stony meteorite that contains chondrules

M-Type Asteroids

A type of asteroid with relatively high reflectivity and grayish color, probably composed primarily of metal

Some ______________________ seem like pieces of lava flows, whereas _____________-_____________ and _____________ meteorites apparently were once deep inside the molten interiors of differentiated objects, and __________________________ _______________________ seem to be unaltered lumps of condensed solar nebula.

Achondrites; Stony-Iron; Iron; Carbonaceous Chondrites

Studies of the motions of comets' jets as the nucleus rotates reveal that they originate from small _____________ ________________ that may be similar to volcanic faults or vents.

Active Regions

__________ objects follow orbits that cross the orbit of Mars but don't reach the orbit of Earth, whereas ______________ objects have Earth-crossing orbits.

Amor; Apollo

Near Earth Objects (NEOs)

An asteroid or comet in an orbit that passes near or intersects Earth's orbit that could potentially collide with Earth

Meteor Showers

An event lasting for hours or days in which the number of meteors entering Earth's atmosphere suddenly increases; The meteors in a shower have a common origin and are traveling through space on nearly parallel paths

Centaurs

An outer Solar System body with an orbit entirely within the region of the Jovian planets (for example Chiron, that orbits between Saturn and Uranus)

Where is the best place(s) to study meteorites and why?

Antarctica and the Sahara desert, they are easier to recognize (stick out in the snow/sand; earth rocks would be under the ice/sand)

_______________-_____________ ___________________ are asteroids with orbits that carry them into the inner Solar System.

Apollo-Amor Objects

Apollo-Amor Objects

Asteroid whose orbit crosses that of Earth (Apollo) and Mars (Amor)

Evidence from meteorites shows that the ________________________ are the last remains of the population of rocky planetesimals from which the Terrestrial planets were built 4.6 billion years ago.

Asteroids

_______________________ are distant objects too small to study in detail with Earth-based telescopes.

Asteroids

Astronomers have evidence that the __________________ are the remains of material lying 2 to 4 AU from the Sun that was prevented from assembling into a planet because of the gravitational influence of ______________, the next planet outward.

Asteroids; Jupiter

Widmanstätten Patterns

Bands in iron meteorites large crystals of nickel-iron alloys

Comets most often _________________ ___________ as they pass close to the Sun or close to a massive planet like Jupiter.

Break Up

M-type asteroids are also _______________ but not as ______________ as the S-types; they seem to be ____________ rich and may be fragments from ____________ cores of differentiated asteroids.

Bright; Red; Metal; Iron

________-type asteroids are as dark as lumps of sooty coal and are probably carbonaceous.

C

CAIs

Calcium-aluminum-rich inclusions found in some meteorites

__________________________ ___________________ are rare stony meteorites that are rich in carbon, making them very dark.

Carbonaceous Chondrites

Objects such as Chiron with orbits between, or crossing, orbits of the Jovian planets are called ___________________

Centaurs

Do chondrites or achrondrites look like dark gray, granular rocks?

Chondrites

The differences in details between the compositions of various __________________ are thought to result from some locations in the solar nebula receiving material transported and mixed in from other locations.

Chondrites (Basically, meteorites provide evidence that the young Solar System was a complicated place)

What are the two types of stony meteorites?

Chondrites and Achondrites

To be glassy rather than crystalline, the __________________ must have cooled from a molten state quickly, within a few hours.

Chondrules

Comets can also fragment far from planets, perhaps because of the ______________ of cavities within the icy nucleus.

Collapse

Some asteroids are double objects or have small moons in orbit around them. This is further evidence that asteroids have suffered _______________________.

Collisions

The ____________ of a comet is the cloud of gas and dust that surrounds the nucleus. It can be more than 1,000,000 km in diameter, as large as the Sun.

Coma

Meteors in a shower are debris left behind as a ____________________ _____________ __________________ vaporizes.

Comet's Icy Nucleus

________________ are ancient samples of the gases and dust from which the outer planets formed.

Comets

Meteors come from two different sources. What are they?

Comets and Asteroid Belt

The distinction between _____________ and ___________________ is not sharply defined.

Comets; Asteroids

The nuclei of comets appear to have a ___________ of rocky dust left behind as the ices vaporize. Breaks in this can expose ices to sunlight, and ____________ can occur in those regions

Crust; Vents

Asteroid Toutatis is revealed to be a _______________ _________________.

Double Object (two objects orbiting close to each other or actually in contact)

Some comet ________________ is crystalline and must have formed originally in warm locations near the Sun but then somehow was included in comet ________________ in the cold outer Solar System.

Dust; Nuclei

What is the largest object in the asteroid belt?

Dwarf Planet Ceres

The spectrum of a gas tail is an _________________ spectrum.

Emission

True or False: There is a selection effect that causes stony meteorites to be found more often.

False (This is true for iron meteorites; Stony are the most often to be found among falls (not finds))

True or False: A comet can survive long in an orbit that brings it into the inner Solar System.

False (it cannot)

Hirayama Families

Family of asteroids with or bits of similar size, shape, and orientation; thought to be fragments of larger bodies

Modern observations show that the asteroids in a ______________ typically share similar _______________________ characteristics. Apparently, each family was produced by a _____________________ collision that broke a single asteroid into fragments that continue traveling along similar orbits around the Sun.

Family; Spectroscopic; Catastrophic

Most Sun grazers belong to one of ___________ groups, the comets in each group having similar orbits.

Four

It seems that the _________________________ of asteroids is a continuing process.

Fragmentation

Occasional collisions among the asteroids release _______________________, and Jupiter's gravity scatters them into the inner Solar System as a continuous supply of ________________.

Fragments; Meteors

A few asteroids show signs of _______________________ _________________ that probably happened on their surfaces when those asteroids were young.

Geological Activity

Gas and dust released by a comet's icy nucleus produce a ____________ or ____________ and are then blown outward, away from the Sun, responding differently to solar wind and solar radiation pressures to form a separate gas _____________ and dust ____________.

Head; Coma; Tail; Tail

Most comet nuclei must be fluffy mixtures of __________ and __________ with significant amounts of ________________ __________________.

Ices; Dust; Empty Space

Material from the _____________ solar nebula was mixed outward and became part of the forming _____________ in the outer Solar System.

Inner; Comets

The fact that long-period comets are observed to fall ______________ from all directions is explained by their _______________ _________________ reservoir being approximately spherically symmetric around the Sun and inner Solar System.

Inward; Oort Cloud

What is the most common meteorite among finds?

Iron

_______________ meteorites are easy to recognize because they are heavy, dense lumps of metal—a magnet will stick to them.

Iron

Meteorites can be divided into three broad composition categories. What are they?

Iron meteorites, stony-iron meteorites, and stony meteorites

The distribution of asteroids in the belt is strongly affected by ___________________ _________________________.

Jupiter's Gravitation

_____________________ ____________ are regions like cosmic sinkholes where gravitational effects of the two larger bodies combine to trap small bodies

Lagrange Points

The Jupiter ____________________-____________ ________________ are called Trojan asteroids because individual asteroids have been named after the heroes of the Trojan War.

Lagrange-Point Objects

Are comets more or less dense than ice?

Less (much less)

The ____________-_________________ _______________ orbits are randomly inclined to the plane of the Solar System, so those comets approach the inner Solar System from all directions.

Long-Period Comet

Most comets have long, elliptical orbits with periods greater than 200 years and are known as _____________-_________________ ________________.

Long-Period Comets

_________-type asteroids are not too dark but are also not very red. They may be mostly ____________-________________ alloys.

M; Iron-Nickel

The presence of chondrule particles inside chondrite meteorites indicates that those rocks have not __________________ since they formed because ___________________ would have destroyed the chondrules.

Melted; Melting

What are shooting stars?

Meteors vaporizing as they enter our atmosphere (although they can survive and reach Earth's surface)

Can comets only fragment near planets?

No

Are all of our Solar System's asteroids in the asteroid belt?

No (many lie in the inner Solar System)

Are meteoroids visible through telescopes?

No, they are too small

Evidence shows that comet ______________ are fragile and can break into pieces easily.

Nuclei

What is the source of most comets?

Oort Cloud

Meteors in meteor showers travel along __________________ paths.

Parallel (Although perception makes it look like they are coming from one point - think of train tracks)

The largest asteroids astronomers see today may be nearly unbroken examples of original _______________________, but the smaller asteroids are ___________________ produced by 4.6 billion years of collisions.

Planetesimals; Fragments

Kirkwood Gaps

Regions in the asteroid belt in which there are very few asteroids; caused by orbital resonances with Jupiter

Chondrules

Round, glassy body in some stony meteorites; thought to have solidified very quickly from molten drops of silicate material

Chondrite meteorites are in fact fragments of ________-type asteroids.

S (common type of asteroid nearest Earth is the source of the most common type of meteorite that hits Earth; bombardment by micrometeorites and solar wind particles can redden and darken rocky materials until they have the colors and albedos of S-type asteroids)

_________-type asteroids have high albedos and tend to be reddish. They are the most common kind of asteroid and appear to be the source of the most common __________________ meteorites.

S; Chondrite

Trojan Asteroids

Small, rocky body caught in Jupiter's orbit at the Lagrange points, 60 degrees ahead of and behind the planet

What is the most common meteorite among falls?

Stony

Carbonaceous chondrites are a special type of ____________ ___________________.

Stony Meteorite

Achrondrites

Stony meteorite containing no chondrules or volatiles

Carbonaceous Chondrites

Stony meteorite that contains both chondrules and volatiles. These may be the least altered remains of the solar nebula still present in the Solar System

________________-_____________ meteorites apparently come from boundaries between stony mantles and iron cores. _____________ meteorites that have been strongly heated evidently come from the mantles or surfaces of such bodies. Many __________________ are probably fragments of smaller bodies that never melted, and ___________________________ ____________________ may be from unaltered bodies that formed especially far from the Sun.

Stony-Iron; Stony; Chondrites; Carbonaceous Chondrites (Iron comes from cores)

Oort Cloud

The cloud of icy bodies (extending from the outer part of our Solar System out to roughly 100,000 from the Sun) that acts as the source of most comets

Radiant

The point in the sky from which meteors in a shower seem to come

Do comets whiz across the sky or is their motion hardly apparent?

Their motion is hardly apparent

Do long-period comets orbit prograde or retrograde?

They orbit both ways in about equal numbers

As many as ______________ small comets per week plunge into the Sun and are destroyed.

Three

Comets subjected to ___________ ________________ from Jupiter or the Sun come apart very easily.

Tidal Stresses

Some astronomers speculate that there may be as many ______________ _______________________ as asteroids in the main belt.

Trojan Asteroids

True or False: Dust released from a comet's nucleus into the dust tail eventually spreads throughout the Solar System. Some of those comet dust particles later encounter the Earth and are seen as shower meteors and sporadic meteors.

True

True or False: Many meteorites are fragments of parent bodies that were large enough to grow hot from radioactive decay or other processes.

True

True or False: There must be a continuous supply of new comets.

True (Astronomers calculate that even before a comet completely vaporizes from solar heating, it can't survive more than about half a million years crossing the orbits of the planets, especially Jupiter, without having its path rerouted into the Sun, out of the Solar System, or into collision with one of the planets; Therefore, comets visible in our skies now can't have survived in their present orbits for 4.6 billion years since the formation of the Solar System)

True or False: If you were standing on an asteroid, it would be many months or years between sightings of other asteroids.

True (Movies displaying dodging of asteroids has lead to a common misconception)

It also seems that some comets have large pockets of __________________ below the crust. When one of those pockets is exposed and begins to _______________, the comet can suffer a dramatic outburst

Volatiles; Vaporize

Spectra of comet comae (plural of coma) and tails indicate the nuclei must contain ices of ____________ and other _______________ compounds such as carbon dioxide, carbon monoxide, methane, ammonia, and so on.

Water; Volatile

Do stars pass close enough to affect the Oort Cloud?

Yes

Does Ceres have an atmosphere?

Yes, it is very thin and composed of water vapor