Our Solar System: Facts, Formation and Discovery

Solar System – Overview

Structure
At the heart of the solar system is our sun. The four planets nearest it are rocky, terrestrial worlds — Mercury, Venus, Earth and Mars. After that are four gas giants — Jupiter, Saturn, Uranus and Neptune. Between the orbits of Mars and Jupiter lies the asteroid belt, which includes the dwarf planet Ceres. Beyond the orbit of Neptune one finds the disk-shaped Kuiper belt, in which dwarf planet Pluto resides, and far beyond that is the giant, spherical Oort Cloud and the teardrop-shaped heliopause.

Discovery
For millennia, astronomers have followed points of light that seemed to move among the stars. The ancient Greeks named these planets, meaning wanderers. Mercury, Venus, Mars, Jupiter and Saturn were known in antiquity, and the invention of the telescope added the asteroid belt, Uranus and Neptune, Pluto and many of these worlds' moons. The dawn of the space age saw dozens of probes launched to explore our system, an adventure that continues today. The discovery of Eris kicked off a rash of new discoveries of dwarf planets, and more than 100 could remain to be found.

This artist's conception shows the relative size of a hypothetical brown dwarf-planetary system — assuming planets someday form around OTS 44 — compared to our own solar system (top).

Sun

The sun is by far the largest object in our solar system, containing 99.8 percent of the solar system's mass. It sheds most of the heat and light that makes life possible on Earth and possibly elsewhere. Planets orbit the sun in oval-shaped paths called ellipses, and the sun is slightly off to the side of the center of each ellipse.

Inner Solar System

• Inner Planets

The inner four planets — Mercury, Venus, Earth and Mars — are made up mostly of iron and rock. They are known as terrestrial or earthlike planets because of their similar size and composition.

• Asteroid belt

Asteroids are minor planets, most of which circle the sun in a region known as the asteroid belt, between the orbits of Mars and Jupiter. Scientists estimate that there are more than 750,000 asteroids in the belt with diameters larger than three-fifths of a mile (1 kilometer), and there are millions of smaller asteroids. A number have orbits that take them closer into the solar system that sometimes lead them to collide with Earth or the other inner planets.

Outer Solar System

• Outer Planets

The outer planets are giant worlds with thick outer layers of gas. Nearly all their mass is made up of  hydrogen and helium, giving them compositions like that of the sun. Beneath these outer layers, they have no solid surfaces — the pressure from their thick atmospheres liquefy their insides, although they might have rocky cores. Rings of dust, rock, and ice encircle all these giants, with Saturn's being the most famous.

• Comets

Comets are often known as dirty snowballs, and consist mainly of ice and rock. When a comet's orbit takes it close to the sun, some of the ice in its central nucleus turns into gas that shoots out of the comet's sunlit side, which the solar wind carries outward to form into a long tail. Short-period comets that complete their orbits in less than 200 years are thought to originate from the the disk-shaped Kuiper belt, while long-period comets that take more than 200 years to return are thought to come from the spherical Oort cloud.

Formation

Many scientists think our solar system formed from a giant, rotating cloud of gas and dust known as the solar nebula. As the nebula collapsed because of its gravity, it spun faster and flattened into a disk. Most of the material was pulled toward the center to form the sun. Other particles within the disk collided and stuck together to form asteroid-sized objects named as planetesimals, some of which combined to become the asteroids, comets, moons and planets. The solar wind from the sun was so powerful that it swept away most of the lighter elements, such as hydrogen and helium, from the innermost planets, leaving behind mostly small, rocky worlds. The solar wind was much weaker in the outer regions, however, resulting in gas giants made up mostly of hydrogen and helium.

Trans-Neptunian Region

Astronomers had long suspected that a band of icy material known as the Kuiper belt existed past the orbit of Neptune extending from about 30 to 55 times the distance of Earth to the sun, and from the last decade of the 20th century up to now, they have found more than a thousand of such objects. Scientists estimate the Kuiper belt is likely home to hundreds of thousands of icy bodies larger than 60 miles (100 km) wide, as well as an estimated trillion or more comets.

Well past the Kuiper belt is the Oort cloud, which theoretically extends from 5,000 to 100,000 times the distance of Earth to the sun, and is home to up to two trillion icy bodies. Past that is the very edge of the solar system, the heliosphere, a vast, teardrop-shaped region of space containing electrically charged particles given off by the sun. Many astronomers think that the limit of the heliosphere, known as the heliopause, is about 9 billion miles (15 billion kilometers) from the sun.

Pluto is now considered a dwarf planet dwelling in the Kuiper belt. It is not alone — recent additions include Makemake, Haumea and Eris. Another object dubbed Sedna, which is about three-fourths the size of Pluto, might be the first dwarf planet discovered in the Oort cloud.

All About Fish - Part 3

Fish Behavior Behavior is the action of a fish in response to its environment including other animals.  The most interesting and sometimes the most obvious behaviors involve interactions with other individuals. Migration: Many species of fish migrate during their life cycle.  It is well known that salmon make long migrations to spawn.  Other fish migrate in response to changing environmental conditions, such as temperature or abundance of food. Schooling:Many fish congregate in groups called schools.  A school is a group of similarly-sized fish of the same species aligned and swimming in the same direction.   Sight seems to be the primary means of maintaining the school.  The lateral line may also be used. Aggression:Aggressive behavior is an interaction between two fish of the same species (intraspecific) or different species (interspecific).  It is usually associated with reproduction or the defense of feeding territory.  It includes posturing, direct attacks and displays such as fin flaring and changes of color. Resting:Some fish spend a good portion of their day resting.  Resting reduces competition, provides protection from predators and may help in energy conservation. Communication:Senses play an important part in fish communication.  Visual communication is important to most fish.  Body movements, postures, colors and color patterns are the primary means of visual communication.  Sound is also used for communication.   Sounds are produced by grinding teeth, flexing or contracting muscles and vibrating the swim bladder.  Fish also communicate by releasing chemicals called pheromones.  These are chemical signals produced by an animal that, when released, influence the behavior of others of the same species.  The sense of smell is important for this form of communication. Cleaning: Some tropical fish are cleaners.  They pick parasites from other fish.  Cleaning fish, such as wrasses, are brightly colored.  They establish cleaning stations that other fish approach in order to be cleaned.  Body posturing, a form of visual communication, is used to initiate cleaning. Color Red: Red is a common color in fish.  You might think that red fish would be very easy for a predator to find.  However, most fish that have this coloration live in dark or deep water, or are nocturnal (active at night).  In deep water, red light is filtered out quickly so red is a good camouflage.  At night, red-colored objects appear gray. Countershading:Many fish are dark on top and light on the bottom.  When seen from above they "disappear" by blending in with the dark color of the depths of the bottom.   Seen from below, the light belly blends into the sky above.

Disruptive Coloration: This is a form of camouflage.  The patterns and lines break up the outline of the fish and help it to blend into the background.  This confuses predators since the fish shape is not easily identifiable. Eye Spots:Eye spots are a form of mimicry.  They eye spot, usually found near the tail, may be used to draw attention away from the real eye which is a target that a predator might strike. Warning Coloration:Many fish use bright colors to "advertise" the presence of venomous spines or some other defensive mechanism. Camouflage:Many fish have colors or patterns that match their backgrounds.  Some fish can even change color to match different backgrounds either to hide from prey (if an ambush is planned!) or to hide from a predator. Food (Preferences, Resources and Digestion) As a group, bony fishes have a diverse range of food preferences.  They may be herbivores (plant-eaters), carnivores (meat-eaters), omnivores (plant- and meat-eaters) or detritivores (animals that eat decomposing plants and animals).  Some of the animals common in the diets of bony fishes include worms, marine snails, mussels, clams, squids, crustaceans, insects, birds, amphibians, small mammals and other fishes. The amount of food a bony fish eats is directly related to its size, its metabolic rate and the temperature of its environment.  Warmwater fishes, such as tropical fish, generally have higher metabolic rates and require more food than coldwater species of the same size. The esophagus in bony fishes is short, expandable and layered with muscles so that large objects can be swallowed.  Most species of bony fishes have a stomach with gastric glands that release substances that break down the food to prepare it for digestion.  The intestine is where the majority of food absorption takes place and the digestive system terminates at the anus. Reproduction in Fish In most species of bony fishes, sperm and eggs develop in separate male and female individuals.  Fertilization is predominately external and, in some instances, internal.  Males and females may look similar, or they may look very different.  Male/female characteristics may include size, coloration, external reproductive organs, head characteristics and body shape.  While reproduction in bony fishes is generally cyclic, various factors may influence bony fish breeding such as changes in the duration of sunlight, temperature changes, moon stages and presence of spawning areas. Bony fishes show at least three types of embryonic development:  egg layers (oviparous), egg retainers (ovoviviparous) and live bearing (viviparous).  Depending on the species, fish parents (male and/or female) may scatter, hide, guard or brood eggs.  There is great variation in the development stage at which offspring are released from the parent fish.  The number of offspring is inversely related to the chance a single egg has to reach maturity and reproduce; in general, species whose eggs have little chance to reach maturity lay the most eggs.  For the most part, many species give no care to their eggs or young.

All About Fish - Part 2

Mouths The position of a fish's mouth gives a general indication of where it feeds in the water column.  In an aquarium, fish with up-pointing mouths like hatchetfish primarily feed on the food flakes that float or hang near the water surface.  Some fish with mouths on the underside of their head, like the catfish, feed on the bottom.  A catfish would be very beneficial to the Aquademics™ aquarium because, as a bottom-feeder, it helps eliminate unused food buildup by eating the food particles that sink to the lower levels of the tank. The shape and size of a fish's mouth can also tell you what it eats.   Since tropical fish in an aquarium have small mouths, Tetra has developed a variety of small fish food flakes, granules and tablets for daily feedings. Breathing Underwater Fish, like most organisms, need oxygen to survive.  The oxygen that fish "breathe" is dissolved in the water.  The oxygen enters the water surface by diffusion or in the water from plants as a byproduct of photosynthesis.   Water enters the fish's mouth, moves across the gills and passes out the gill slits or operculum.  The gills are made up of a bony or cartilaginous arch supporting a large number of paired gill filaments.  Numerous small projections with very thin membranes on each filament are the sites of gas exchange (oxygen to carbon dioxide).   Beneath the thin membrane is a network of blood vessels.  Oxygen diffuses from the water through the membrane into the blood and carbon dioxide diffuses outward. Senses Sight:Most fish have well-developed eyes on the sides of their heads.  This placement allows them to see in all directions.  The structure of the eye is very similar to that of other vertebrates.  In fish, focusing on near and distant objects is achieved by moving the lens backward and forward by muscular action.  Fish that are colorful can probably see in color.  Bony fish that are active at night have large eyes that help them see in the dark.

Smell: Fish can smell odors in the water with receptors inside blind sacs, called nares, located on the head.  Nares are similar to our nostrils, but fish do not use them to breathe.  The sense of smell is well developed and is useful in detecting distant odors. Taste:For fish, taste is more of a close range sense.  Taste buds, which can be found on different parts of the fish, are used in the identification of food.  Taste buds are located in and around the mouth, and, on some fish, on the skin and even on the fins.  Barbels, whisker-like structures near the mouth of fish such as catfish, are covered with taste buds and are used in locating food. Hearing: Fish have ears but they do not open to the outside and cannot be seen.   Hearing in fish is well developed, however.  Water carries sound much better than air and the sound waves are picked up through the fish's body. Lateral Line:A line of holes runs along both sides of a fish from the head to the tail.   The holes have nerve connections that are sensitive to vibrations.  The lateral line is used form schooling, avoiding obstacles and detecting prey and predators. Electroreception:Some bony fish can detect weak electrical fields through pit organs on their heads and faces.  This ability is used for locating prey (all living things give off weak electrical fields), avoiding obstacles in murky water and in migrating. Buoyancy Neutral buoyancy, the ability to remain motionless in the water without rising or sinking, is of great importance to a fish.  It allows a fish to spend energy feeding, escaping predators or mating that would otherwise be needed to maintain its position in the water.  Several strategies help achieve neutral buoyancy.   Most bony fish have a structure called a swim bladder, which is a balloon-like organ in the body cavity.  Gases from the blood are added or removed to control buoyancy at different depths.

All About Fish - Part 1

Classification of Fish Fish are classified according to the material which makes up their skeletons.  For example, sharks, skates and rays belong to a group called cartilaginous fish because their skeletons are composed entirely of cartilage.   Tropical fish, which are members of the fish group that are represented in the Aquademics™ aquarium, are called bony fish (scientific name Osteichthyes) because they have skeletons made of bone.  All of the facts and information for the Aquademics™ program, as well as the material in the Aquademics™ Parent and Teacher's Guide, will focus on the bony fish group. Skin The skin of most bony fish is covered with bony scales that look like shingles on a roof.  Bony fish scales are waterproof and help protect the fish.   Glands in the skin in which the scales are embedded secrete a layer of mucus that covers the entire body.  Mucus helps protect fish from infection.  Handling fish removes this mucus coating and can be harmful to the fish. Gills Oxygen enters the bloodstream and carbon dioxide diffuses out at the gills, which are feathery structures found along the sides of the head.  The gills of a healthy fish are bright red due to the high level of oxygen in the blood that is very close to the surface of the gills. (Without oxygen, the gills would be brown.) In bony fish, the gills are covered by a bony place called an operculum. Shape The shape of a fish's body tells a lot about its lifestyle.  Fish with fusiform, or streamlined, bodies are usually fast swimming predators that may swim at high speeds much of the time or are capable of great bursts of speed. Many tropical fish are laterally compressed (flattened from side to side).  Fish with this shape are not very streamlined but they do not rely on speed for catching food or escaping from predators.  Their body shape is perfectly adapted for hiding in the cracks and crevices of rocks and reef.  They can move into these areas to hide, to escape predators or to get at food that cannot be reached by other fish.  Fish with this body shape, like angelfish, are very maneuverable and capable of short bursts of speed.   They are often camouflaged with disruptive coloration. Other fish are flattened from top to bottom.  Fish with this body shape spend most of their time at the bottom.  They are usually camouflaged or can change color to match the bottom.

Fins Fins are used for swimming and sometimes for protection.  Some fins are paired and others unpaired.  The paired fins are the pectoral and pelvic fins.   The unpaired fins are the dorsal, caudal (tail) and anal fins.  The way the fins are used varies among different groups of fish.  Most fish use their tails to move through the water and their other fins to steer with.  Fins are most bony fish are flexible and supported by visible spines and rays.  The shape, location and size of a fish's fins are closely linked with its way of life. See more about fins. Pectoral Fins:The paired pectoral fins are usually responsible for turning, although they can be used for other functions such as tasting, touching, support and as a source of power for swimming. Pelvic Fins:Paired pelvic fins add stability and are used for slowing some bony fishes. Dorsal Fin:This may be a single fin or be separated into several fins.  In most bony fishes, the dorsal fin is used for sudden direction changes and acts as a "keel" to keep the fish stable in the water. Caudal (or tail) fin:This is responsible for propulsion in most bony fishes. Anal Fin:The anal fin adds stability. Tails:The shape of the tail can be an indicator of how fast a fish usually swims. Crescent-shaped: Fish with crescent-shaped tails are fast swimmers and constantly on the move. Forked: Fish with forked tails are also fast swimmers, though they may not swim fast all of the time.  The deeper the fork, the faster the fish can swim. Rounded: Fish with a rounded or flattened tail are generally slow moving, but are capable of short, accurate bursts of speed. Eyes Fish are visual predators.  Many nocturnal fish have large eyes to help them feed at night.  Fish such as sharks have pupils that dilate and constrict, and some sharks also have an eyelid that closes from the bottom upward.  Bony fish eyes lack both of these characteristics.

North American Beaver

The North American Beaver, most commonly known only as the Beaver, is one of the national symbols of Canada. They are often considered pests.

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Description

Description

Latin Name: Castor canadensis Conservation Status: Least Concern Distribution: Canada, USA, Northern Mexico

The North American Beaver is a rodent native to North America. They are semi-aquatic, but spend most of their day in the water. They are slow moving on land, and are easily scared. They are excellent swimmers, and their bodies are well adapted for water. Their tails are large, flat, and paddle-like, while their feet are webbed. The North American Beaver can stay under water for up to 15 minutes at a time. These pesky rodents are well known for creating dams in waterways, often resulting in the flooding of the surrounding areas.