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The Pioneer missions were the first spacecraft to take close up pictures of Jupiter and its moons. Five years later, the two Voyager spacecraft discovered over 20 new moons. They captured photo evidence of lightning on the night side of Jupiter.
The Ulysses probe was sent to study the Sun. It only went to Jupiter after it had finished its main mission. Ulysses had no cameras so it took no photographs.
In 2006, the Cassini spacecraft, on its way to Saturn, took some very good, very clear pictures of the planet. Cassini also found a moon and took a picture of it but it was too far away to show the details.
The Galileo mission in 1995 was the first spacecraft to go into orbit around Jupiter. It flew around the planet for seven years and studied the four biggest moons. It launched a probe into the planet to get information about Jupiter's atmosphere. The probe travelled to a depth of about 150 km before it was crushed by the weight of all the gas above it. This is called pressure. The Galileo spacecraft was also crushed in 2003 when NASA steered the craft into the planet. They did this so that the craft could not crash into Europa, a moon which scientists think might have life.
NASA have sent another spacecraft to Jupiter called Juno. It was launched on August 5, 2011 and arrived at Jupiter on July 4, 2016. NASA published some results from the Juno mission in March 2018. Several other missions have been planned to send spacecraft to Jupiter's moons Europa and Callisto. One called JIMO (Jupiter Icy Moons Orbiter) was cancelled in 2006 because it cost too much money.
Jupiter has 79 known moons. The four largest were seen by Galileo with his primitive telescope, and nine more can be seen from Earth with modern telescopes. The rest of the moons have been identified by spacecraft. The smallest moon (S/2003 J 12) is only one kilometre across. The largest, Ganymede, has a diameter of 5,262 kilometres. It is bigger than the planet Mercury. The other three Galilean moons are Io, Europa and Callisto. Because of the way they orbit Jupiter, gravity affects three of these moons greatly. The friction caused by the gravity of Europa and Ganymede pulling on Io makes it the most volcanic object in the Solar System. It has over 400 volcanoes, more than three times as many as Earth.
Jupiter's large gravity has had an effect on the Solar System. Jupiter protects the inner planets from comets by pulling them towards itself. Because of this, Jupiter has the most comet impacts in the Solar System.
Two groups of asteroids, called Trojan asteroids, have settled into Jupiter's orbit round the Sun. One group is called the "Trojans" and the other group is called the "Greeks". They go around the Sun at the same time as Jupiter.
Notes
King
A king is a man who rules a country, because of inheritance. A king usually comes to power when the previous monarch dies, who is usually a family member of his. Sometimes a person may become king due to the previous monarch's abdication, for example George VI. For most of history, most countries were ruled in this way, especially in Europe. Some countries, such as France, are no longer monarchies. Some, such as the United Kingdom, still have a royal family. In some countries, people chose a new king from other people to decide from.
The wife of a king is called a queen. A woman who becomes a ruler because of inheritance is also called a queen.
If a country has a king or a queen, that means it is a monarchy. A country which a king or queen rules is called a kingdom.
In the Muslim world a King would be known as Malik or Sultan.
Knowledge
Knowledge means the things which are true, as opposed to opinion. Information which is correct is knowledge. Knowledge can always be supported by evidence. If a statement is not supported by evidence, then it is not knowledge. The evidence makes it justified; .
Knowledge can refer to a theoretical or practical understanding of a subject. This was the point of Ryle's distinction between "knowing that" and "knowing how". It can be implicit (as with practical skill or expertise) or explicit (as with the theoretical understanding of a subject); it can be more or less formal or systematic. In philosophy, the study of knowledge is called epistemology. The philosopher Plato defined knowledge as "justified true belief". This definition is the subject of the Gettier problems.
All knowledge is a claim to be true, but the claim can be incorrect. The only claims (propositions) which are certainly true are circular, based on how we use words or terms. We can correctly claim that there are 360 degrees in a circle, since that is part of how circles are defined. The point of Aristotle's syllogism was to show that this kind of reasoning had a machine-like form:
But actually, in the real world, not all swans are white.
The most widely accepted way to find reliable knowledge is the scientific method. Yet one thing all philosophers of science agree is that scientific knowledge is just the best we can do at any one time. All scientific knowledge is provisional, not a claim of absolute truth.
Knowledge in religion is different in that it depends on faith, belief and the authority of religious leaders, not on evidence of a scientific or legal kind. There are differing views on whether religious statements should be regarded as knowledge.
In many expressions of Christianity, such as Catholicism and Anglicanism, knowledge is one of the seven gifts of the Holy Spirit.
In the Garden of Eden knowledge is the factor that made humans greedy and treacherous. But in the Book of Proverbs it states: 'to be wise you must first obey the LORD' (9:10).
In Islam, knowledge has great significance. "The All-Knowing" ("al-ʿAlīm") is one of the Names of God, reflecting distinct properties of God in Islam. The Qur'an asserts that knowledge comes from God () and various "hadith" encourage getting knowledge. Muhammad is reported to have said "Seek knowledge from the cradle to the grave" and "Verily the men of knowledge are the inheritors of the prophets". Islamic scholars, theologians and jurists are often given the title "alim", meaning 'knowledgeable'.
Kauai
Kauai (Kaua'i in Hawaiian) is the second oldest (after Ni'ihau) and fourth largest of the main Hawaiian Islands, in the United States. Known also as the "Garden Isle", Kaua'i lies 73 miles (117 kilometers) across the Kauai Channel, northwest of Honolulu on Oahu. It is of volcanic origin. The highest point on the island is Kawaikini. It is located above sea level. The wettest spot on Earth, with average rainfall of a year, is just east of Mount Waialeale. The high yearly rainfall has eroded deep valleys and canyons in the central mountain. The waterfalls that have been created by erosion in canyons are now popular tourist spots.
The city of Lihue, on the island's southeast side, is the seat of Kauai County. It has a population of around 6,500, and is the main city on the island. Waimea, which is located on the island's southwest side and the first capital of Kauai, was the first place visited by Englishexplorer Captain James Cook in 1778. It was also the first capital of Kauai. The city is at the head of one of the most beautiful canyons in the world, Waimea Canyon, whose gorge is 900 meters (3,000 feet) deep.
The island of Kauai was featured in Disney's 2002 animated feature film "Lilo & Stitch".
Kahoolawe
Kahoolawe is the smallest of the eight main volcanic islands of Hawaii. It is west of Maui and south of Lanai. It is roughly 11 miles long by across (). The highest point, Lua Makika, is above sea level. The island is dry because its low elevation does not cause much rain (orographic precipitation) to fall from the northeastern trade winds.
Kahoolawe was used as a gunfire and bombing target by the United States military during World War II. It was a defense training area by the United States Navy from around 1941 until May 1994. Popular opinion in the state against this practice brought the end to this use. Navy has since been trying to cleanup unexploded ordnance (bombs and explosive shells) from the island. Ordnance is still buried or lying on the ground. Other items have washed down gullies and still other unexploded ordnance is underwater offshore. In 1981, the entire island was included on the National Register of Historic Places.
The island is planned to be given back to the Hawaiian people. In 1993, the U.S. Congress passed a law that "recognized the cultural importance of the island, required the Navy to return the island to the State, and directed the Navy to do an unexploded ordnance (UXO) cleanup and environmental restoration" . The turnover officially occurred on November 11, 2003, but the cleanup has not yet been completed. The U.S. Navy was given $400 million and 10 years to complete the large cleanup task, but this work has gone much slower than planned.
In 1993, the Hawaii State Legislature established the Kahoolawe Island Reserve. It is made up of the whole island and waters out to from shore. By State Law, Kahoolawe and its waters can only be used for Native Hawaiian cultural, spiritual, and subsistence purposes; fishing; environmental restoration; historic preservation; and education. Commercial uses are not allowed. The Legislature also created the Kahoolawe Island Reserve Commission (KIRC) to manage the Reserve while it is held in trust for a "future Native Hawaiian Sovereignty entity" .
After the cleanup is finished, the restoration of Kahoolawe will need ways to control erosion, restore the plant life, recharge the water table, and slowly replace alien plants with native ones. Plans will include methods for damming gullies and reducing rainwater runoff. Non-natives will temporarily stabilize some areas before the permanent planting of native plants.
Killing
Killing a living thing is when someone or something ends that life and makes the living thing die. It means causing a death. When a human being kills another human being, it is called murder or homicide, such as manslaughter.
Pesticides and herbicides are poisons for killing bad wild small animals or plants, respectively.
When a soldier kills another in war, it is called "combat". When the state kills a convict sentenced to capital punishment, it is called execution. When someone kills a powerful person it is called assassination. When a person who wants to die kills himself it is suicide, or euthanasia if killed by another. When people kill other people to eat them, it is called cannibalism.
Kilometre
The kilometre is a common unit used for longer distances on Earth. The international unit for measuring distances is the metre and a kilometre is 1000 metres. It is used in some countries for measuring road and sea distances. In the UK and the USA, the mile is used more than kilometres for road distances and the nautical mile for sea distances.
It is often used to measure the speed of cars, planes and boats by saying how many kilometres it can travel in an hour. This is shown as km/h.
It is also spelled kilometer. This spelling is used in American English.
One kilometre is 0.6214 miles (3280.84 feet). This means that one mile is 1.6093 kilometres.
One kilometre is the approximate distance a healthy adult human being can walk in ten minutes.
Language
Language is the normal way humans communicate. Only humans use language, though other animals communicate through other means. The study of language is called linguistics.
Human language has syntax, a set of rules for connecting words together to make statements and questions. Language can also be changed, by adding new words, for example, to describe new things. Other animals may inherit a set of calls which have pee-set functions.
Language may be done by speech or by writing or by moving the hands to make signs. It follows that language is "not" just any way of communicating. Even some human communication is not language: see non-verbal communication. Humans also use language for thinking.
When people use the word "language", they can also mean:
UNESCO says that 2,500 languages are at risk of becoming extinct.
All languages share certain things which separate them from all other kinds of communication.
There are many more things in common between languages.
The capacity to learn and use language is inherited. Normally, all humans are born with this capability. "Which" language is learned by a child depends on which language is spoken by the child's community. The "capacity" is inherited, but the particular language is learned.
Children have a special period, from about 18 months to about four years, which is critical for learning the language. If this is seriously disrupted, then their language skills will be damaged. Older people learn differently, so they seldom learn a second language as well as they learn their native language.
Mathematics and computer science use created languages called formal languages (like computer programming languages), but these may or may not be 'true' languages. Mathematics itself is seen as a language by many. Some people consider musical notation to be a way of writing the musical language.
Chinese is the language with the most native speakers in the world, but Chinese is not really a language. It is a close family of dialects, some of which are as different as Romance languages are from one another.
English is often called "the international language", or lingua franca. It is the main second language of the world and the international language of science, travel, technology, business, diplomacy, and entertainment. French had a similar status until the 20th century, and other languages had it at other times.
Some languages are made up so that a lot of people around the world can learn them, without the new languages being tied to any specific country or place. These are called constructed languages. One of the most popular of these languages is Esperanto, which is sometimes called "La Internacia Lingvo," or "The International Language." Another of these languages is called Volapük, which was popular about a hundred years ago but is much less popular now. It has mostly been replaced by languages like Esperanto, Interlingua, and Ido. Dialects are basically other versions of a language. For example Hoffish is a dialect of swedish.
Part of the reason that Volapük became unpopular is that some sounds are hard to say for people who speak Spanish or English, two of the most widely spoken languages in the world.
Leisure
Leisure (or free time) is when a person can choose what to do. During a person's leisure time, they do not have an obligation to be at school or work at a job. During leisure time, people can do fun activities, family activities, or other non-work activity, such as hobbies.
Common forms of recreation or leisure are:
A vacation or holiday is the setting aside of time specifically for leisure. During their vacation, some people travel to a different region or country, and stay at a hotel so that they can do things they could not do near home. Other people prefer to spend their vacation time at home in their own community.
In rich industrialized countries such as the US and Canada, as well as in most European countries, workers are allowed to stay home on the weekend (usually Saturday and Sunday), and use it as leisure time. People in poorer developing countries usually have less leisure time, as they have to work longer hours and more days per year.
Live
Live can be a verb. It rhymes with "give". "To live" means "to be alive" (and not dead). If you live, then you have life.
It can be used in a general way:
Live can be an adjective. It rhymes with "five".
Life
Life is a concept in biology. It is about the characteristics, state, or mode that separates a living thing from dead matter.
The word itself may refer to a living being or to the processes of which living things are a part. It may refer to the period when a living thing is functional (as between birth and death).
The study of life is called biology: people who study life are called biologists. A lifespan is the average length of life in a species. Most life on Earth is powered by solar energy: the only known exceptions are the chemosynthetic bacteria living around the hydrothermal vents on the ocean floor. All life on Earth is based on the chemistry of carbon compounds, specifically involving long-chain molecules such as proteins and nucleic acid. With water, which all life needs, the long molecules are wrapped inside membranes as cells. This may or may not be true of all possible forms of life in the Universe: it is true of all life on Earth today.
Living things, or organisms, can be explained as open systems. They are always changing, because they exchange materials and information with their environment. They undergo metabolism, maintain homeostasis, possess a capacity to grow, respond to stimuli and reproduce.
Through natural selection, they adapt to their environment in successive generations. More complex living organisms can communicate through various means. Many life forms can be found on Earth. The properties common to these organisms—plants, animals, fungi, protists, archaea, and bacteria—are a carbon and water-based cellular form with complex organization and heritable genetic information.
The systems that make up life have many levels of organization. From smallest to biggest, they are: molecule, cell, tissue (group of cells with a common purpose), organ (part of the body with a purpose), organ system (group of organs that work together), organism, population (group of organisms of the same species), community (all of the organisms that interact in an area), ecosystem (all of the organisms in an area and the non-living surroundings), and biosphere (all parts of the Earth that have life).
At present, the Earth is the only planet humans have detailed information about. The question of whether life exists elsewhere in the Universe is open. There have been a number of claims of life elsewhere in the Universe. None of these have been confirmed so far. The best evidence of life outside of Earth is are nucleic acids that have been found in certain types of meteorites.
One explanation of life is called the cell theory. The cell theory has three basic points: all living things are made up of cells. The cell is the smallest living thing that can do all the things needed for life. All cells must come from pre-existing cells.
Something is often said to be alive if it:
However, not all living things fit every point on this list.
They do, however, fit the biochemical definitions: they are made of the same kind of chemicals.
The thermodynamic definition of life is any system which can keep its entropy levels below maximum (usually through adaptation and mutations).
A modern definition was given by Humberto Maturana and Francisco Varela in 1980, to which they gave the name "autopoiesis":
Roth commented that "In short, organisms are self-reproducing and self-maintaining, or 'autopoietic', systems". This approach makes use of molecular biology ideas and systems science ideas.
Life on Earth is made from organic compounds — molecules that contain carbon. Four types of long-chain molecules (macromolecules) are important: carbohydrates, lipids, proteins, and nucleic acids.
Almost all living things need the chemical elements carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus, to build these macromolecules. Living things also need small amounts of other elements, called "trace elements". Water is a very important part of all living things. For example, humans are about two-thirds water. Water is a solvent that lets molecules mix and react with other molecules.
All living things need energy to survive, move, grow, and reproduce. Some can get energy from the environment without help from other living things: these are called producers, or autotrophs. Plants, algae, and some bacteria, a group of producers called photoautotrophs, use the sun's light for energy. When producers use light to make and store organic compounds, this is called photosynthesis. Some other producers, called chemoautotrophs, get energy from chemicals that come out of the ocean floor in hydrothermal vents. Other living things get their energy from organic compounds: these are called consumers, or heterotrophs. Animals, fungi, most bacteria, and most protists are consumers. Consumers can eat other living things or dead material.
Both producers and consumers need to break down organic compounds to free energy. The best way to do this is aerobic respiration, which frees the most energy, but living things can only do aerobic respiration if they have oxygen (O2). They can also break down these compounds without oxygen, using anaerobic respiration or fermentation.
All living things have cells. Every cell has a cell membrane on the outside, and a jelly-like material that fills the inside, called cytoplasm. The membrane is important because it separates the chemicals inside and outside. Some molecules can pass through the membrane, but others cannot. Living cells have genes, made of DNA. Genes say to the cell what to do, like a language. One DNA molecule, with many genes, is called a chromosome. Cells can copy themselves to make two new cells.
There are two main kinds of cells: prokaryotic and eukaryotic. Prokaryotic cells have only a few parts. Their DNA is the shape of a circle, inside the cytoplasm, and they have no membranes inside the cell. Eukaryotic cells are more complex, and they have a cell nucleus. The DNA is inside the nucleus, and a membrane is around the nucleus. Eukaryotic cells also have other parts, called organelles. Some of these other organelles also have membranes.
Taxonomy is how lifeforms are put into groups. The smaller groups are more closely related, but the larger classes are more distantly related. The levels, or ranks, of taxonomy are domain, kingdom, phylum, class, order, family, genus, and species. There are many ideas for the meaning of species. One idea, called the biological species concept, is as follows. A species is a group of living things that can mate with each other, and whose children can make their own children.
Taxonomy aims to group together living things with a common ancestor. This can now be done by comparing their DNA. Originally, it was done by comparing their anatomy.
The three domains of life are Bacteria, Archaea, and Eukarya. Bacteria and archaea are prokaryotic and have only one cell. Bacteria range in size from 0.15 cubic micrometres ("Mycoplasma") to 200,000,000 cubic micrometres ("Thiomargarita namibiensis"). Bacteria have shapes which are useful in classification, such as round, long and thin, and spiral. Some bacteria cause diseases. Bacteria in our intestines are part of our gut flora. They break down some of our food. Both bacteria and archaea may live where larger forms of life cannot. Bacteria have a molecule called peptidoglycan in their cell wall, but archaea do not. Archaea have a molecule called isoprene in their cell membrane, but bacteria do not.
Eukarya are living things with eukaryotic cells, and they can have one cell or many cells. Most eukaryotes use sexual reproduction to make new copies of themselves. In sexual reproduction, two sex cells, one from each parent, join together to make a new living thing.
Plants are eukaryotes that use the Sun's light for energy. They include algae, which live in water, and land plants. All land plants have two forms during their life cycle, called alternation of generations. One form is diploid, where the cells have two copies of their chromosomes, and the other form is haploid, where the cells have one copy of their chromosomes. In land plants, both diploid and haploid forms have many cells. Two kinds of land plants are vascular plants and bryophytes. Vascular plants have long tissues that stretch from end to end of the plant. These tissues carry water and food. Most plants have roots and leaves.
Animals are eukaryotes with many cells, which have no rigid cell walls. All animals are consumers: they survive by eating other organic material. Almost all animals have neurons, a signalling system. They usually have muscles, which make the body move. Many animals have a head and legs. Most animals are either male or female. They need a mate of the opposite sex to make offspring. Sex cells from the male and female can meet inside or outside the body.
Fungi are eukaryotes which may have one cell, like yeasts, or many cells, like mushrooms. They are saprophytes. Fungi break down living or dead material, so they are decomposers. Only fungi, and a few bacteria, can break down lignin and cellulose, two parts of wood. Some fungi are mycorrhiza. They live under ground and give nutrients to plants, like nitrogen and phosphorus. Eukaryotes that are not plants, animals, or fungi are called protists. Most protists live in water.
Over thousands or millions of years, living things can change, through the process of evolution. One kind of evolution is when a species changes over time, such as giraffes growing longer necks. Most of the time, the species because better suited to its environment, a process called adaptation. Evolution can also cause one group of living things to split into two groups. This is called speciation if it makes a new species. An example is mockingbirds on the Galapagos Islands — one species of mockingbird lives on each island, but all the species split from a shared ancestor species. Groups that are bigger than species can also split from a shared ancestor — for example, reptiles and mammals. A group of living things and their shared ancestor is called a clade.
Living things can evolve to be quite different from their ancestors. As a result, parts of the body can also change. The same bone structure became the hands of humans, the hooves of horses, and the wings of birds. Different body parts that evolved from the same thing are called homologous.
Extinction is when all members of a species die. About 99.9% of all species that have ever lived are extinct. Extinction can happen at any time, but it is more common in certain time periods called extinction events. The most recent was 65 million years ago, when the dinosaurs went extinct.
By comparing fossils and DNA, we know that all life on Earth today had a shared ancestor, called the last universal common ancestor (LUCA). Other living things may have been alive at the same time as the LUCA, but they died out. A study from 2018 suggests that the LUCA is about 4.5 billion (4,500,000,000) years old, nearly as old as the Earth. The oldest fossil evidence of life is about 3.5 billion years old.