Other Members - Asteroids PDF

Other Members GILDEN MAECAH M. MIGALANG Faculty, Science and Research Department Integrated Developmental School, College of Education Mindanao State University - Iligan Institute of Technology Asteroids, sometimes called minor planets, are rocky, airless remnants left over from...

Other Members GILDEN MAECAH M. MIGALANG Faculty, Science and Research Department Integrated Developmental School, College of Education Mindanao State University - Iligan Institute of Technology Asteroids, sometimes called minor planets, are rocky, airless remnants left over from the early formation of our solar system about 4.6 billion years ago. Most asteroids can be found orbiting the Sun between Mars and Jupiter within the main asteroid belt. Asteroids range in size from Vesta – the largest at about 329 miles (530 kilometers) in diameter – to bodies that are less than 33 feet (10 meters) across. The total mass of all the asteroids combined is less than that of Earth's Moon. Sometimes, asteroids and comets are nudged into Earth's neighborhood by the gravity of nearby planets. These objects are called Near-Earth Objects, or NEOs. There are more than 35,000 NEOs, according to the Center for Near Earth Object Studies (CNEOS) at NASA's Jet Propulsion Laboratory (JPL). About 99% of NEOs are asteroids. Their closest approach to the Sun is less than 1.3 times Earth's distance from the Sun. Most asteroids are irregularly shaped, though a few are nearly spherical, and they are often pitted or cratered. As they revolve around the Sun in elliptical orbits, the asteroids also rotate, sometimes quite erratically, tumbling as they go. More than 150 asteroids are known to have a small companion moon (some have two moons). There are also binary (double) asteroids, in which two rocky bodies of roughly equal size orbit each other, as well as triple asteroid systems. Composition The three broad composition classes of asteroids are C-, S-, and M-types. The C-type (chondrite) asteroids are most common. They probably consist of clay and silicate rocks, and are dark in appearance. They are among the most ancient objects in the solar system. The S-types ("stony") are made up of silicate materials and nickel-iron. The M-types are metallic (nickel-iron). The asteroids' compositional differences are related to how far from the Sun they formed. Some experienced high temperatures after they formed and partly melted, with iron sinking to the center and forcing basaltic (volcanic) lava to the surface. The orbits of asteroids can be changed by Jupiter's massive gravity – and by occasional close encounters with Mars or other objects. These encounters can knock asteroids out of the main belt, and hurl them into space in all directions across the orbits of the other planets. Stray asteroids and asteroid fragments have slammed into Earth and the other planets in the past, playing a major role in altering the geological history of the planets and in the evolution of life on Earth. Scientists continuously monitor Earth-crossing asteroids, whose paths intersect Earth's orbit, and near-Earth asteroids that approach Earth's orbital distance to within about 28 million miles (45 million kilometers) and may pose an impact danger. Radar is a valuable tool in detecting and monitoring potential impact hazards. By reflecting transmitted signals off objects, images and other information can be derived from the echoes. Scientists can learn a great deal about an asteroid's orbit, rotation, size, shape, and metal concentration. Asteroid Classifications Main Asteroid Belt: The majority of known asteroids orbit within the asteroid belt between Mars and Jupiter, generally with not very elongated orbits. The belt is estimated to contain between 1.1 and 1.9 million asteroids larger than 1 kilometer (0.6 miles) in diameter, and millions of smaller ones. Early in the history of the solar system, the gravity of newly formed Jupiter brought an end to the formation of planetary bodies in this region and caused the small bodies to collide with one another, fragmenting them into the asteroids NASA, ESA, Joseph Olmsted (STScI) https://hubblesite.org/contents/media/images/2021/005/01EZCWR4R2ES5JTQ5F1W3WNSJM we observe today. Asteroid Classifications Trojan Asteroids - These asteroids share an orbit with a larger planet, but do not collide with it because they gather around two special places in the orbit (called the L4 and L5 Lagrangian points). There, the gravitational pull from the Sun and the planet are balanced by a trojan's tendency to otherwise fly out of orbit. The Jupiter trojans form the most significant population of trojan asteroids. It is thought that they are as numerous as the asteroids in the asteroid belt. There are Mars and Neptune trojans, and NASA announced the discovery of an https://nineplanets.org/asteroid-belt/ Earth trojan in 2011. Asteroid Classifications Near-Earth Asteroids - These objects have orbits that pass close by that of Earth. Asteroids that actually cross Earth's orbital path are known as Earth- crossers. Figure 1: The four orbit families of Near Earth Asteroids. Image Credit: Original image courtesy of JPL Asteroid Classifications Figure 3: Illustration of the four main Near-Earth asteroid groups according to their orbits and compared with the Sun, Earth's and Mars' orbits and the Asteroid Belt NEO Risk Determination There are two scales on which astronomers determine the risk associated with an NEO: the Torino Scale and Palermo Technical Impact Hazard Scale. The Torino Scale (Morrison et al., 2009) paints a broad picture of the risk associated with a NEO. It is based on impact probability (how likely an object is to hit the Earth or its atmosphere) and kinetic energy (this depends on how fast the object moves and how massive it is). The Scale ranges from 0 to 10, where 0 indicates no hazard, and 10 indicates a certain impact with likely catastrophic global effects. While several NEAs are initially categorised as a 1 (normal) on the Torino Scale every year, as more data is taken of these objects, they are usually downgraded to a level 0 in due course. As of this writing, there is 1 NEO that rates higher than level 0 on the Torino Scale (JPL, 2023b). Credit: After Morrison, et al. (2004), Figure 16.2 NEO Risk Determination Compared to the Torino Scale, the Palermo Scale (Chelsey et al., 2002) provides more precise information about the risk associated with a NEO. The Palermo Technical Impact Hazard Scale compares information about the probability of an impact and its kinetic energy to the background frequency of similarly sized objects colliding with the Earth. This background level can be thought of as a kind of status quo of NEO impacts: it allows us to understand how entire populations of objects of a particular size will behave over long periods of time. Because there is a wide range of sizes in the overall NEO population, with a wide range of velocities, this comparison can yield a very wide range of numbers. For this reason, the Palermo Scale is most often discussed on a logarithmic scale. This scaling helps scientists notice patterns in datasets with a large range of numbers. A NEO with a Palermo Scale of -2 is 1% (or 10-2) as likely to occur as a random background event, and an NEO with a Palermo Scale of 0 is just as likely to occur as a random background event. Most often, NEOs have a Palermo Scale between -2 and 0. Positive Palermo Scale scores indicate that astronomers should proceed with some concern. As of this writing, no NEOs rank above 0 on the Palermo Scale (JPL, 2023b). Planetary Defence The International Astronomical Union (IAU) has its own NEO Working Group, composed of international experts who are highly involved in dedicated projects and institutions. Since the early 1990s, the UN Office of Space Affairs (UNOOSA) and the UN Committee on the Peaceful Uses of Outer Space (COPUOS) have convened international partners “to ensure international information sharing in discovering, monitoring and physically characterising potentially hazardous NEOs with a view to making all countries aware of potential impact threats, particularly developing countries with limited capacity in predicting and mitigating a NEO impact” (UN, 2018). From their recommendations and task forces, the International Asteroid Warning Network and the Space Mission Planning Advisory Group were formed in 2013. Every two years, the international community gets together at the Planetary Defense Conference (hosted by the UN Office for Outer Space Affairs) to present recent advances in the various activities dedicated to this topic. During this conference, an exercise is conducted during which the experts must mitigate a simulated hypothetical threat, allowing them to measure their level of readiness. International Asteroid Warning Network The International Asteroid Warning Network (IAWN) aims to coordinate the international effort to detect, observe, and characterise Near Earth Objects. An essential part of its mission is to devise comprehensive communication plans to ensure all its members have access to the most up-to-date information in the case of an emergency. They also work with governments to make policy recommendations and plan impact mitigation responses. To date, IAWN has representatives from North and South America, Europe, and Asia. Space Mission Planning Advisory Group While the IAWN focuses on observations and communications on the surface of the Earth, the Space Mission Planning Advisory Group (SMPAG) makes recommendations for research and missions in space. Part of their scope is to coordinate international efforts to produce new research and technologies on planetary defence. The IAWN and SMPAG work together to produce policy recommendations and defence strategies for governing bodies worldwide. How Asteroids Get Their Names The International Astronomical Union's (IAU's) Committee on Small Body Nomenclature is not very strict when it comes to naming asteroids. Asteroids are also named for places and a variety of other things. Asteroids are also given a number, for example (99942) Apophis. The Minor Planet Center keeps a list of asteroid names. Asteroids Named After Filipinos In December 2016 the United Nations General Assembly adopted resolution A/RES/71/90, declaring 30 June International Asteroid Day in order to "observe each year at the international level the anniversary of the Tunguska impact over Siberia, Russian Federation, on 30 June 1908, and to raise public awareness about the asteroid impact hazard." International Asteroid Day aims to raise public awareness about the asteroid impact hazard and to inform the public about the crisis communication actions to be taken at the global level in case of a credible near-Earth object threat. Here the asteroids named after Filipinos: Asteroids Named After Filipinos Asteroids Named After Filipinos Asteroids Named After Filipinos Asteroids Named After Filipinos Asteroids Named After Filipinos International Asteroid Day The UN General Assembly adopted resolution A/RES/71/90 on December 2016, declaring June 30 as International Asteroid Day. It is a day to raise public awareness about the asteroid impact hazard. International Asteroid Day Near-Earth objects (NEOs) pose grave risks to our planet. When a near-Earth objects orbit, such as those of asteroids, reaches within 0.05 AU of the Earth's orbit and its estimated diameter is bigger than 140 m, the asteroid is considered to be potentially hazardous. An impact from one of these objects may cause wind blast, overpressure shock, thermal radiation, cratering, seismic shaking, ejecta deposition, and tsunami. Asteroid Impact that killed Dinosaurs In 1980, Nobel Prize-winning physicist Luis Walter Alvarez and his geologist son Walter published a theory that a historic layer of iridium-rich clay was caused by a large asteroid colliding with Earth. The instantaneous devastation in the immediate vicinity and the widespread secondary effects of an asteroid impact were considered to be why the dinosaurs died out so suddenly. Luis Walter Alvarez (left) and his son Walter (right) Photo from Natura History Museum Page Asteroid Impact that killed Dinosaurs The impact site, known as the Chicxulub crater, is centred on the Yucatán Peninsula in Mexico. The asteroid is thought to have been between 10 and 15 kilometers wide, but the velocity of its collision caused the creation of a much larger crater, 150 kilometers in diameter. It's the second-largest crater on the planet. Rocks in this area were found to exactly the same age as the extinction of the non-bird dinosaurs. Asteroid Impact that killed Dinosaurs The Chicxulub crater was formed around 66 million years ago, when a large asteroid (10km in diameter) struck the Earth. Many scientists think that this event was the cause of the the Cretaceous-Paleogene extinction. The Chicxulub crater is not visible at the Earth's surface like the famous Meteor Crater of Arizona. There are, however, two surface expressions of the crater. Radar measurements captured from one of NASA's space shuttles detected a subtle depression in the sediments that bury the crater. It's now largely buried on the seafloor off the coast of Mexico. It is exactly the same age as the extinction of the non-bird #dinosaurs, which can be tracked in the rock record all around the world. ' The impact site, known as the Chicxulub crater, is centred on the Yucatán Peninsula in Mexico. Meteoroids, Meteors and Meteorites Meteors, and meteorites are often called “shooting stars” - bright lights streaking across the sky. But we call the same objects by different names, depending on where they are located. Meteoroids: These rocks still are in space. Meteoroids range in size from dust grains to small asteroids. Meteors: When meteoroids enter Earth’s atmosphere (or that of another planet, like Mars) at high speed and burn up, the fireballs or “shooting stars” are called meteors. Meteorites: When a meteoroid survives a trip through the atmosphere and hits the ground, it’s called a meteorite. Meteoroids, Meteors and Meteorites Diagram illustrating the difference between a Meteoroid (a small body in the solar system that could collide with Earth), a Meteor (a small extraterrestrial body falling through Earth's atmosphere), and a Meteorite (a small extraterrestrial body that has landed on Earth). Edwards, 2024 Classification of Meteorites There are three main types of meteorites: iron meteorites: which are almost completely made of metal stony-iron meteorites: which have nearly equal amounts of metal and silicate crystals stony meteorites: which mostly have silicate minerals Iron Meteorites Most iron meteorites are thought to be the cores of asteroids that melted early in their history. They consist mainly of iron-nickel metal with small amounts of sulphide and carbide minerals. During the decay of radioactive elements in the early history of the solar system, many asteroids melted and the iron they contained, being dense, sank to the centre to form a metallic core. Meteorites from melted asteroids are also known as differentiated meteorites, as they have experienced major chemical or physical changes, solidifying from a molten state. Sometimes they have an iron core and concentric layers, surrounded by a silicate mantle and crust. This type of structure is very similar to terrestrial planets (Mercury, Venus, Mars and Earth), which also have metallic cores. Iron meteorites can tell us a great deal about how the metallic cores of planets formed. Iron Meteorites Iron meteorites are mainly made of an iron-nickel alloy with a distinctive crystalline structure known as a Widmanstätten texture. Bands are formed by varying levels of nickel. There can be wide variation in the texture and mix of minerals present within iron meteorites, which will produce many groups and subtypes. Stony-iron meteorites Stony-iron meteorites consist of almost equal parts iron-nickel metal and silicate minerals including precious and semi-precious gemstones. They are considered some of the most beautiful meteorites. There are two different types of stony-iron meteorites: pallasite and mesosiderite. Stony-iron meteorites Mesosiderite meteorites are breccias, a variety of rock composed of broken fragments of minerals or rock cemented together by a finer material. The fragments are roughly centimetre- sized and contain a mix of igneous (solidified) silicate and metal clasts (rocks made of pieces of older rocks). Mesosiderites form when debris from a collision between two asteroids is mixed together. In the crash, molten metal mixes together with solid fragments of silicate rocks. Mesosiderites can therefore both record the history of both meteorites and reveal a snapshot of the conditions required for asteroids to melt and form iron cores. Stony meteorites The majority of meteorite finds are stony meteorites, consisting mostly of silicate minerals. There are two main types of stony meteorite: chondrites (some of the oldest materials in the solar system) and achondrites (including meteorites from asteroids, Mars and the Moon). Both chondrites and achondrites have many subgroups based on their compositions, structures and the minerals they contain. At over 4.5 billion years old, chondrites are some of the most primitive and pristine rocks in the solar system and have never been melted. Chondrites have a distinctive appearance, made from droplets of silicate minerals mixed with small grains of sulphides and iron-nickel metal. Their millimetre-sized granules give chondrites their name, from the Greek 'chondres' meaning sand grains. There are many varieties of chondrite, with differences in mineralogy relating to the type of asteroid the meteorite came from. Chondrites are the material from which the solar system formed. They have been little changed compared with rocks from larger planets, which have been subjected to geological activity. Chondrites can tell us a lot about how the solar system formed. Stony meteorites Achondrites include meteorites from asteroids, Mars and the Moon. They are igneous, meaning at some point they were melted into magma. When magma cools and crystallises, it creates a concentric layered structure. This process is known as igneous differentiation. The rocky planets Mercury, Venus, Earth and Mars were formed in this way, giving them planetary crusts, mantles and cores. Achondrites can tell us a lot about the internal structure and formation of the planets, including our own. Meteorites One mineral's name — elaliite — derives from the space object itself, which is called the “El Ali” meteorite since it was found near the town of El Ali in central Somalia. Herd named the second one elkinstantonite after Lindy Elkins- Tanton, vice president of Arizona State University's Interplanetary A sample of the El Ali meteorite (this sample now Initiative. housed in the UCLA Meteorite Collection) contains two minerals never before seen on Earth. (Photo: Nick Gessler/Duke University) Tektites Tektites (from the Greek tektos, meaning “molten”) are rare natural glass that were created from rocks and soil that have been vaporized by hypervelocity impact of meteorites. The force melted these earthy materials at the site of impact and splashed them up into our atmosphere, where they cool into these small, jet-black glassy objects before falling back to Earth. Tektites vary in size, shape, and surface sculpture. Dumbbell-shaped tektites are formed when the molten mass rapidly spins in flight, forcing the material to both ends. If this mass splits, two teardrop-shaped tektites are formed. Spheroidal tektites, on the other hand, are from non-spinning glassy blobs. Sometimes, air will force the forwardmost portion of the molten mass back around the outer edges, creating rivet head-shaped or lens- like tektites. Types of Tektites Four principal types have been distinguished. The microtektites have a diameter of less than 2 millimeters and are nearly spherical, although some are shaped like teardrops, rods and dumbbells. The Muong-Nong type, named after the site in Vietnam where they were first found, are often chunky or platy in external form. The splash-form tektites are similar to microtektite in shape but are million times larger. Lastly, the Australites and related forms have a characteristic lens- like form. Tektites Tektites are found only in certain areas of the Earth’s surface, scattered over large areas called strewn fields. Those found in the Philippines are called philippinites. They are sometimes referred to as rizalites after the province of Rizal where the first tektite in the country was reported. Locally, they are known as “Tae ng Bituin.” They are part of the Australasian strewnfield, the youngest and largest of the tektite strewnfields. Like all Australasian tektites, philippinites were produced during an impact event roughly 788 thousand years ago. You can find philippinites along plains all over the country, particularly in Cagayan Valley, Pangasinan, Rizal, Bicol, Iloilo and Agusan. In prehistoric Philippines, tektites are used as charm-stone or amulets while others used it as tools and for decorative purposes. In Cagayan Valley and Cabatuan, Iloilo, they were found in Pleistocene sediments containing fossils of elephants and stegodons and stone tools. Meteorites in the Philippines Classified as an H3-4 chondrite, this space rock is one of the first solid materials to form from the earliest days of our solar system, about 4.6 billion years ago. The Orconuma meteorite is the FIRST EVER meteorite specimen to be included in the National Geological and Paleontological Collections. The donated specimen is a complete slice weighing 160.17 grams and has a dimension of 149x108x3 mm. It is a portion of the 7.8 kg meteorite that fell on March 7, 2011, in Orconuma, Bongabong, Oriental Mindoro. It was found in the field by three farmers namely Fredo Manzano, Edgar Francisco, Sr., and Enrico Camacho, Jr., who hid and stored the specimen for 9 years. The main mass was described as a single ellipsoidal, dense stone with a regmaglypted exterior coated by a dark fusion crust. - National Museum of the Philippines Meteorites in the Philippines Meteorites in the Philippines Philippine Meteorites Bondoc Meteorite (Iron Nodules) These nodules are part of the 888-kilogram stony- iron meteorite that fell around 2.5 million years ago in Bondoc Peninsula, Quezon Province. The main mass was accidentally found by a local huntsman in 1956. Its recovery was initiated in 1957 by Dr. Harvey H. Nininger, the Father of Modern Meteoritics. The Bondoc Meteorite is the largest and oldest known meteorite found in the Philippines. Philippine Meteorites Brenham Meteorite (Part Slice) This rare stony-iron meteorite is classified as a pallasite, representing less than 1% of all known meteorites. Based on studies, it originated from the mantle-core boundary of a celestial body. Pieces of the Brenham Meteorite were first found in Kansas, U.S.A. in 1882. This specimen displays metal embedded with translucent "space gems" called olivine crystals. Philippine Meteorites Muonionalusta Meteorite (Full Slice) This etched slice of iron meteorite from Kiruna, Norrbotten, Sweden exhibits an out-of-this-world octahedral crystalline structure known as the Widmanstätten pattern. Based on studies, its parent meteoroid entered our atmosphere and created a meteorite shower around 1 million years ago. However, the first Muonionalusta specimen was found in 1906. Philippine Meteorites Sahara 99753 Meteorite (Large Fragment) This crusted stony meteorite was recovered from the Sahara Desert in 1999 by the Labenne Family —a well-known family of French meteorite hunters. It carries a unique field number, where "99" denotes that this specimen was from the 1999 Labenne Sahara Expedition, while the "753" identifies it as the 753rd stone of interest found during that expedition. What is a Meteor Shower? Scientists estimate that about 48.5 tons (44 tonnes or 44,000 kilograms) of meteoritic material falls on Earth each day. Almost all the material is vaporized in Earth's atmosphere, leaving a bright trail fondly called "shooting stars." Several meteors per hour can usually be seen on any given night. Sometimes the number increases dramatically—these events are called meteor showers. Meteor showers occur annually or at regular intervals as the Earth passes through the trail of dusty debris left by a comet. Meteor showers are usually named after a star or constellation that is close to where the meteors appear in the sky. Perhaps the most famous are the Perseids, which peak in August every year. Every Perseid meteor is a tiny piece of the comet Swift-Tuttle, which swings by the Sun every 135 years. Meteor Crater Natural Landmark Northern Arizona, United States. meteorcrater.com/info/ Comets are frozen leftovers from the formation of the solar system composed of dust, rock, and ices. They range from a few miles to tens of miles wide, but as they orbit closer to the Sun, they heat up and spew gases and dust into a glowing head that can be larger than a planet. This material forms a tail that stretches millions of miles. Comets are cosmic snowballs of frozen gases, rock, and dust that orbit the Sun. When frozen, they are the size of a small town. When a comet's orbit brings it close to the Sun, it heats up and spews dust and gases into a giant glowing head larger than most planets. The dust and gases form a tail that stretches away from the Sun for millions of miles. There are likely billions of comets orbiting our Sun in the Kuiper Belt and even more distant Oort Cloud. Where do comets come from? Comets are mostly found way out in the solar system. Some exist in a wide disk beyond the orbit of Neptune called the Kuiper Belt. We call these short-period comets. They take less than 200 years to orbit the Sun. Other comets live in the Oort Cloud, the sphere-shaped, outer edge of the solar system that is about 50 times farther away from the Sun than the Kuiper Belt. These are called long-period comets because they take much longer to orbit the Sun. The comet with the longest known orbit takes more than 250,000 years to make just one trip around the Sun!  This illustration shows that the Kuiper Belt is shaped like a disk [see inset diagram] and resides within the shell-like structure of the Oort Cloud. Located on the outskirts of the solar system, the Kuiper Belt is a "junkyard" of countless icy bodies left over from the solar system's formation. The Oort Cloud is a vast shell of billions of comets. The inset diagram compares Pluto's orbit with a Kuiper Belt binary object called 1998 WW31. The Kuiper Belt [the fuzzy disk] extends from inside Pluto's orbit to the edge of the solar system. https://esahubble.org/images/opo0204i/ Credit: NASA/ESA and A. Feild (Space Telescope Science Institute) What are the parts of a comet? Comet Neowise streaks through the night sky above the forests of Girona, Spain, leaving behind a glowing trail of gas and dust. Humans have long had a fascination with comets and asteroids—both beautiful and menacing as they hurtle past Earth. ​ Photograph by JUAN CARLOS CASADO, SCIENCE PHOTO LIBRARY What are the parts of a comet? Nucleus - It is the central solid part of the comet. The nucleus occupies the central position, also known as the core. It consists mostly of ice, gases, and dust particles covered with dark organic matter. The nucleus is often frozen, consisting of carbon dioxide, ammonia, carbon monoxide, and methane. It is sometimes composed of rocks. Coma - The coma is the most visible portion of the comet surrounding the nucleus. Along with the nucleus, they form the comet’s head. It is a spherical envelope of evaporated gases such as water vapor, ammonia, carbon dioxide, and dust particles. The coma forms when dust and gases sublimate from the nucleus, bypassing the intermediate liquid phase. Ion Tail - It is made of electrically charged molecules of carbon dioxide, nitrogen, and water. The ion tail is also called the plasma or gas tail. It forms when the charged molecules are pushed away from the solar wind’s nucleus, converting some gases into ions. It is not as enormous as the dust tail, but accelerates faster than them, moving in a straight line opposite to the comet and the Sun. Dust Tail - It is the layer away from the Sun. The dust tail is made of small dust particles that evaporate from the nucleus, pushing them away from the comet due to sunlight pressure. It is often curved due to the comet’s motion in fixed orbit at the same speed at which the dust moves away, much in the same way as water leaves the nozzle of a moving hose. This acceleration is relatively slow. Why do comets have tails? Some Identified Comets Halley's Comet Comet Hale–Bopp appears every 72–80 years. a long-period comet that was one of the most widely observed of the 20th century and one of the brightest seen for many decades.  Some Identified Comets Comet ISON C/2022 E3 (ZTF) Comet ISON, formally known as C/2012 S1, was a sungrazing comet from C/2022 E3 (ZTF) is a non-periodic comet from the Oort cloud that was the Oort cloud which was discovered on 21 September 2012 by Vitaly discovered by the Zwicky Transient Facility (ZTF) on 2 March 2022. The Nevsky and Artyom Novichonok. comet has a bright green glow around its nucleus, due to the effect of sunlight on diatomic carbon and cyanogen.  Some Identified Comets Comet Ikeya–Seki Comet Hyakutake There are two comets named Ikeya–Seki: C/1965 S1, and C/1967 Y1, a.k.a. Comet Hyakutake is a comet discovered on 31 January 1996. It was 1968 I, 1967n. Comet Ikeya–Seki, formally designated C/1965 S1, 1965 VIII, dubbed the Great Comet of 1996; its passage to within 0.1 AU of the and 1965f, was a long-period comet discovered independently by Kaoru Earth on 25 March was one of the closest cometary approaches of the Ikeya and Tsutomu Seki. previous 200 years. Some Identified Comets Comet C/2023 A3 Tsuchinshan-ATLAS returns to the inner solar system once every 80,000 years. Our Sun is a 4.5 billion-year-old yellow dwarf star – a hot glowing ball of hydrogen and helium – at the center of our solar system. It’s about 93 million miles (150 million kilometers) from Earth and it’s our solar system’s only star. The Sun orbits the center of the Milky Way, bringing with it the planets, asteroids, comets, and other objects in our solar system. Our solar system is moving with an average velocity of 450,000 miles per hour (720,000 kilometers per hour). But even at this speed, it takes about 230 million years for the Sun to make one complete trip around the Milky Way. The Sun rotates on its axis as it revolves around the galaxy. Its spin has a tilt of 7.25 degrees with respect to the plane of the planets’ orbits. Since the Sun is not solid, different parts rotate at different rates. At the equator, the Sun spins around once about every 25 Earth days, but at its poles, the Sun rotates once on its axis every 36 Earth days. Sun Rings Sun Structure The Sun would have been surrounded by a disk of gas and dust early in its history when the solar system was first forming, about 4.6 billion years ago. Some of that dust is still around today, in several dust rings that circle the Sun. They trace the orbits of planets, whose gravity tugs dust into place around the Sun. The Sun’s Internal Structure and Atmosphere The solar interior, from the inside out, is made up of the core, radiative zone and convective zone. The sun and its atmosphere consist of several zones or layers. From the inside out, the solar interior consists of: the Core (the central region where nuclear reactions consume hydrogen to form helium. These reactions release the energy that ultimately leaves the surface as visible light. ), the Radiative Zone (extends outward from the outer edge of the core to base of the convection zone, characterized by the method of energy transport – radiation), and the Convection Zone (the outer-most layer of the solar interior extending from a depth of about 200,000 km to the visible surface where its motion is seen as granules and supergranules. ). Credit: NASA/Goddard  The Sun’s Internal Structure and Atmosphere The solar atmosphere above that consists of the photosphere, chromosphere, and the corona (solar wind is an outflow of gas from the corona). The solar atmosphere is made up of: the Photosphere (the visible surface of the Sun), the Chromosphere (an irregular layer above the photosphere where the temperature rises from 6000°C to about 20,000°C), a Transition Region (a thin and very irregular layer of the Sun’s atmosphere that separates the hot corona from the much cooler chromosphere), and the Corona (the Sun’s outer atmosphere.). Beyond the corona is the solar wind, which is actually an outward flow of coronal gas. The sun’s magnetic fields rise through the convection zone and erupt through the photosphere into the chromosphere and corona. The eruptions lead to solar activity, which includes such phenomena as sunspots, flares, Credit: NASA/Goddard prominences, and coronal mass ejections. Sun Features Sun Features Sun Features Sun Features Sun Features Sun Features Low- and Medium-mass stars A star's life cycle is determined by its mass. The larger its mass, the shorter its life cycle. A star's mass is determined by the amount of matter that is available in its nebula, the giant cloud of gas and dust from which it was born. Over time, the hydrogen gas in the nebula is pulled together by gravity and it begins to spin. As the gas spins faster, it heats up and becomes as a protostar. Eventually the temperature reaches 15,000,000 degrees and nuclear fusion occurs in the cloud's core. The cloud begins to glow brightly, contracts a little, and becomes stable. It is now a main sequence star and will remain in this stage, shining for millions to billions of years to come. This is the stage our Sun is at right now. Low- and Medium-mass stars As the main sequence star glows, hydrogen in its core is converted into helium by nuclear fusion. When the hydrogen supply in the core begins to run out, and the star is no longer generating heat by nuclear fusion, the core becomes unstable and contracts. The outer shell of the star, which is still mostly hydrogen, starts to expand. As it expands, it cools and glows red. The star has now reached the red giant phase. It is red because it is cooler than it was in the main sequence star stage and it is a giant because the outer shell has expanded outward. In the core of the red giant, helium fuses into carbon. All stars evolve the same way up to the red giant phase. The amount of mass a star has determines which of the following life cycle paths it will take from there. Low- and Medium-mass stars As the core collapses, the outer layers of the star are expelled. A planetary nebula is formed by the outer layers. The core remains as a white dwarf and eventually cools to become a black dwarf. High-mass stars Once stars that are 5 times or more massive than our Sun reach the red giant phase, their core temperature increases as carbon atoms are formed from the fusion of helium atoms. Gravity continues to pull carbon atoms together as the temperature increases and additional fusion processes proceed, forming oxygen, nitrogen, and eventually iron. High-mass stars When the core contains essentially just iron, fusion in the core ceases. This is because iron is the most compact and stable of all the elements. It takes more energy to break up the iron nucleus than that of any other element. Creating heavier elements through fusing of iron thus requires an input of energy rather than the release of energy. High-mass stars Since energy is no longer being radiated from the core, in less than a second, the star begins the final phase of gravitational collapse. The core temperature rises to over 100 billion degrees as the iron atoms are crushed together. The repulsive force between the nuclei overcomes the force of gravity, and the core recoils out from the heart of the star in a shock wave, which we see as a supernova explosion. High-mass stars Like low-mass stars, high-mass stars are born in nebulae and evolve and live in the Main Sequence. However, their life cycles start to differ after the red giant phase. A massive star will undergo a supernova explosion. If the remnant of the explosion is 1.4 to about 3 times as massive as our Sun, it will become a neutron star. The core of a massive star that has more than roughly 3 times the mass of our Sun after the explosion will do something quite different. The force of gravity overcomes the nuclear forces which keep protons and neutrons from combining. The core is thus swallowed by its own gravity. It has now become a black hole which readily attracts any matter and energy that comes near it. As the shock encounters material in the star's outer layers, the material is heated, fusing to form new elements and radioactive isotopes. While many of the more common elements are made through nuclear fusion in the cores of stars, it takes the unstable conditions of the supernova explosion to form many of the heavier elements. The shock wave propels this material out into space. The material that is exploded away from the star is now known as a supernova remnant. The hot material, the radioactive isotopes, as well as the leftover core of the exploded star, produce X-rays and gamma-rays. The Hertzsprung-Russell diagram (HR diagram) is one of the most important tools in the study of stellar evolution. Developed independently in the early 1900s by Ejnar Hertzsprung and Henry Norris Russell, it plots the temperature of stars against their luminosity (the theoretical HR diagram), or the colour of stars (or spectral type) against their absolute magnitude (the observational HR diagram, also known as a colour- magnitude diagram). Depending on its initial mass, every star goes through specific evolutionary stages dictated by its internal structure and how it produces energy. Each of these stages corresponds to a change in the temperature and luminosity of the star, which can be seen to move to different regions on the HR diagram as it evolves. This reveals the true power of the HR diagram – astronomers can know a star’s internal structure and evolutionary stage simply by determining its position in the diagram. This Hertzsprung-Russell diagram shows a group of stars in various stages of their evolution. By far the most prominent feature is the main sequence, which runs from the upper left (hot, luminous stars) to the bottom right (cool, faint stars) of the diagram. The giant branch is also well populated and there are many white dwarfs. Also plotted are the Morgan-Keenan luminosity classes that distinguish between stars of the same temperature but different luminosity. There are 3 main regions (or evolutionary stages) of the HR diagram: 1. The main sequence stretching from the upper left (hot, luminous stars) to the bottom right (cool, faint stars) dominates the HR diagram. It is here that stars spend about 90% of their lives burning hydrogen into helium in their cores. Main sequence stars have a Morgan-Keenan luminosity class labelled V. 2. red giant and supergiant stars (luminosity classes I through III) occupy the region above the main sequence. They have low surface temperatures and high luminosities which, according to the Stefan- Boltzmann law, means they also have large radii. Stars enter this evolutionary stage once they have exhausted the hydrogen fuel in their cores and have started to burn helium and other heavier elements. 3. white dwarf stars (luminosity class D) are the final evolutionary stage of low to intermediate mass stars, and are found in the bottom left of the HR diagram. These stars are very hot but have low luminosities due to their small size.