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121-454: Propagation is affected by the time of day. During the daytime the solar wind presses this layer closer to the Earth, thereby limiting how far it can reflect radio waves. Conversely, on the night ( lee ) side of the Earth, the solar wind drags the ionosphere further away, thereby greatly increasing the range which radio waves can travel by reflection. The extent of the effect is further influenced by

242-455: A = m 1 x 1 + m 2 x 2 + . . . + m N x N {\displaystyle {\overline {m}}_{a}=m_{1}x_{1}+m_{2}x_{2}+...+m_{N}x_{N}} where m 1 , m 2 , ..., m N are the atomic masses of each individual isotope, and x 1 , ..., x N are the relative abundances of these isotopes. Several applications exist that capitalize on

363-511: A chemical symbol is used, e.g. "C" for carbon, standard notation (now known as "AZE notation" because A is the mass number , Z the atomic number , and E for element ) is to indicate the mass number (number of nucleons) with a superscript at the upper left of the chemical symbol and to indicate the atomic number with a subscript at the lower left (e.g. 2 He , 2 He , 6 C , 6 C , 92 U , and 92 U ). Because

484-463: A bubble" in the interstellar medium (the rarefied hydrogen and helium gas that permeates the galaxy). The point where the solar wind's strength is no longer great enough to push back the interstellar medium is known as the heliopause and is often considered to be the outer border of the Solar System. The distance to the heliopause is not precisely known and probably depends on the current velocity of

605-491: A comet-like tail that extends to Earth's orbit. Earth itself is largely protected from the solar wind by its magnetic field , which deflects most of the charged particles; however, some of the charged particles are trapped in the Van Allen radiation belt . A smaller number of particles from the solar wind manage to travel, as though on an electromagnetic energy transmission line, to the Earth's upper atmosphere and ionosphere in

726-505: A double pairing of 2 protons and 2 neutrons prevents any nuclides containing five ( 2 He , 3 Li ) or eight ( 4 Be ) nucleons from existing long enough to serve as platforms for the buildup of heavier elements via nuclear fusion in stars (see triple alpha process ). Only five stable nuclides contain both an odd number of protons and an odd number of neutrons. The first four "odd-odd" nuclides occur in low mass nuclides, for which changing

847-400: A driver of the solar wind as a swarm of nanoflares in the form omnipresent jetting activity a.k.a. jetlets producing short-lived streams of hot plasma and Alfvén waves at the base of the solar corona. This activity could also be connected to the magnetic switchback phenomenon of the solar wind. The solar wind is observed to exist in two fundamental states, termed the slow solar wind and

968-419: A given element all have the same number of electrons and share a similar electronic structure. Because the chemical behaviour of an atom is largely determined by its electronic structure, different isotopes exhibit nearly identical chemical behaviour. The main exception to this is the kinetic isotope effect : due to their larger masses, heavier isotopes tend to react somewhat more slowly than lighter isotopes of

1089-407: A glowing patch on the plate at the point it struck. Thomson observed two separate parabolic patches of light on the photographic plate (see image), which suggested two species of nuclei with different mass-to-charge ratios. He wrote "There can, therefore, I think, be little doubt that what has been called neon is not a simple gas but a mixture of two gases, one of which has an atomic weight about 20 and

1210-456: A living person, and Parker, at age 91, was on hand to observe the launch. While early models of the solar wind relied primarily on thermal energy to accelerate the material, by the 1960s it was clear that thermal acceleration alone cannot account for the high speed of solar wind. An additional unknown acceleration mechanism is required and likely relates to magnetic fields in the solar atmosphere. The Sun's corona , or extended outer layer,

1331-468: A nonoptimal number of neutrons or protons decay by beta decay (including positron emission ), electron capture , or other less common decay modes such as spontaneous fission and cluster decay . Most stable nuclides are even-proton-even-neutron, where all numbers Z , N , and A are even. The odd- A stable nuclides are divided (roughly evenly) into odd-proton-even-neutron, and even-proton-odd-neutron nuclides. Stable odd-proton-odd-neutron nuclides are

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1452-427: A nucleus. As the number of protons increases, so does the ratio of neutrons to protons necessary to ensure a stable nucleus (see graph at right). For example, although the neutron:proton ratio of 2 He is 1:2, the neutron:proton ratio of 92 U is greater than 3:2. A number of lighter elements have stable nuclides with the ratio 1:1 ( Z = N ). The nuclide 20 Ca (calcium-40)

1573-405: A product of stellar nucleosynthesis or another type of nucleosynthesis such as cosmic ray spallation , and have persisted down to the present because their rate of decay is very slow (e.g. uranium-238 and potassium-40 ). Post-primordial isotopes were created by cosmic ray bombardment as cosmogenic nuclides (e.g., tritium , carbon-14 ), or by the decay of a radioactive primordial isotope to

1694-506: A proton to a neutron or vice versa would lead to a very lopsided proton-neutron ratio ( 1 H , 3 Li , 5 B , and 7 N ; spins 1, 1, 3, 1). The only other entirely "stable" odd-odd nuclide, 73 Ta (spin 9), is thought to be the rarest of the 251 stable nuclides, and is the only primordial nuclear isomer , which has not yet been observed to decay despite experimental attempts. Many odd-odd radionuclides (such as

1815-478: A radioactive radiogenic nuclide daughter (e.g. uranium to radium ). A few isotopes are naturally synthesized as nucleogenic nuclides, by some other natural nuclear reaction , such as when neutrons from natural nuclear fission are absorbed by another atom. As discussed above, only 80 elements have any stable isotopes, and 26 of these have only one stable isotope. Thus, about two-thirds of stable elements occur naturally on Earth in multiple stable isotopes, with

1936-513: A release of magnetic energy at the Sun. CMEs are often called "solar storms" or "space storms" in the popular media. They are sometimes, but not always, associated with solar flares , which are another manifestation of magnetic energy release at the Sun. CMEs cause shock waves in the thin plasma of the heliosphere, launching electromagnetic waves and accelerating particles (mostly protons and electrons ) to form showers of ionizing radiation that precede

2057-418: A similar suggestion at a Royal Institution address the previous year, in which he had postulated that the ejected material consisted of electrons, whereas in his study of Comet Morehouse he had supposed them to be ions . The idea that the ejected material consisted of both ions and electrons was first suggested by Norwegian scientist Kristian Birkeland . His geomagnetic surveys showed that auroral activity

2178-424: A single stable isotope (of these, 19 are so-called mononuclidic elements , having a single primordial stable isotope that dominates and fixes the atomic weight of the natural element to high precision; 3 radioactive mononuclidic elements occur as well). In total, there are 251 nuclides that have not been observed to decay. For the 80 elements that have one or more stable isotopes, the average number of stable isotopes

2299-510: A somewhat common, and possibly constant, instrument for the entrance of solar wind into terrestrial magnetospheres under various IMF orientations. The solar wind affects other incoming cosmic rays interacting with planetary atmospheres. Moreover, planets with a weak or non-existent magnetosphere are subject to atmospheric stripping by the solar wind. Venus , the nearest and most similar planet to Earth, has 100 times denser atmosphere, with little or no geo-magnetic field. Space probes discovered

2420-492: A stable (non-radioactive) element was found by J. J. Thomson in 1912 as part of his exploration into the composition of canal rays (positive ions). Thomson channelled streams of neon ions through parallel magnetic and electric fields, measured their deflection by placing a photographic plate in their path, and computed their mass to charge ratio using a method that became known as the Thomson's parabola method. Each stream created

2541-622: A total 30 + 2(9) = 48 stable odd-even isotopes. There are also five primordial long-lived radioactive odd-even isotopes, 37 Rb , 49 In , 75 Re , 63 Eu , and 83 Bi . The last two were only recently found to decay, with half-lives greater than 10 years. Actinides with odd neutron number are generally fissile (with thermal neutrons ), whereas those with even neutron number are generally not, though they are fissionable with fast neutrons . All observationally stable odd-odd nuclides have nonzero integer spin. This

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2662-431: A total solar eclipse ). Later spectroscopic work confirmed this extraordinary temperature to be the case. In the mid-1950s, British mathematician Sydney Chapman calculated the properties of a gas at such a temperature and determined that the corona being such a superb conductor of heat, it must extend way out into space, beyond the orbit of Earth. Also in the 1950s, German astronomer Ludwig Biermann became interested in

2783-681: Is aluminium-26 , which is not naturally found on Earth but is found in abundance on an astronomical scale. The tabulated atomic masses of elements are averages that account for the presence of multiple isotopes with different masses. Before the discovery of isotopes, empirically determined noninteger values of atomic mass confounded scientists. For example, a sample of chlorine contains 75.8% chlorine-35 and 24.2% chlorine-37 , giving an average atomic mass of 35.5 atomic mass units . According to generally accepted cosmology theory , only isotopes of hydrogen and helium, traces of some isotopes of lithium and beryllium, and perhaps some boron, were created at

2904-547: Is 251/80 ≈ 3.14 isotopes per element. The proton:neutron ratio is not the only factor affecting nuclear stability. It depends also on evenness or oddness of its atomic number Z , neutron number N and, consequently, of their sum, the mass number A . Oddness of both Z and N tends to lower the nuclear binding energy , making odd nuclei, generally, less stable. This remarkable difference of nuclear binding energy between neighbouring nuclei, especially of odd- A isobars , has important consequences: unstable isotopes with

3025-635: Is a radioactive form of carbon, whereas C and C are stable isotopes. There are about 339 naturally occurring nuclides on Earth, of which 286 are primordial nuclides , meaning that they have existed since the Solar System 's formation. Primordial nuclides include 35 nuclides with very long half-lives (over 100 million years) and 251 that are formally considered as " stable nuclides ", because they have not been observed to decay. In most cases, for obvious reasons, if an element has stable isotopes, those isotopes predominate in

3146-415: Is a region of plasma that is heated to over a megakelvin . As a result of thermal collisions, the particles within the inner corona have a range and distribution of speeds described by a Maxwellian distribution . The mean velocity of these particles is about 145 km/s , which is well below the solar escape velocity of 618 km/s . However, a few of the particles achieve energies sufficient to reach

3267-495: Is about (2–3) × 10 solar masses , or about 1.3–1.9 million tonnes per second. This is equivalent to losing a mass equal to the Earth every 150 million years. However, since the Sun's formation, only about 0.01% of its initial mass has been lost through the solar wind. Other stars have much stronger stellar winds that result in significantly higher mass-loss rates. In March 2023 solar extreme ultraviolet observations have shown that small-scale magnetic reconnection could be

3388-663: Is because the single unpaired neutron and unpaired proton have a larger nuclear force attraction to each other if their spins are aligned (producing a total spin of at least 1 unit), instead of anti-aligned. See deuterium for the simplest case of this nuclear behavior. Only 78 Pt , 4 Be , and 7 N have odd neutron number and are the most naturally abundant isotope of their element. Elements are composed either of one nuclide ( mononuclidic elements ), or of more than one naturally occurring isotopes. The unstable (radioactive) isotopes are either primordial or postprimordial. Primordial isotopes were

3509-484: Is called the Alfvén surface . At a distance of more than a few solar radii from the Sun, the solar wind reaches speeds of 250–750  km/s and is supersonic, meaning it moves faster than the speed of fast magnetosonic waves . The flow of the solar wind is no longer supersonic at the termination shock . Other related phenomena include the aurora (northern and southern lights), comet tails that always point away from

3630-435: Is denoted with symbols "u" (for unified atomic mass unit) or "Da" (for dalton ). The atomic masses of naturally occurring isotopes of an element determine the standard atomic weight of the element. When the element contains N isotopes, the expression below is applied for the average atomic mass m ¯ a {\displaystyle {\overline {m}}_{a}} : m ¯

3751-441: Is easier for the solar wind to infiltrate the magnetosphere than previously believed. A group of scientists directly observed the existence of certain waves in the solar wind that were not expected. A recent study shows that these waves enable incoming charged particles of solar wind to breach the magnetopause. This suggests that the magnetic bubble forms more as a filter than a continuous barrier. This latest discovery occurred through

Kennelly–Heaviside layer - Misplaced Pages Continue

3872-652: Is gas caught in bubbles of the magnetic field, which are ripped off by the solar wind. In 2015 the NASA Mars Atmosphere and Volatile Evolution ( MAVEN ) mission measured the rate of atmospheric stripping caused by the magnetic field carried by the solar wind as it flows past Mars, which generates an electric field, much as a turbine on Earth can be used to generate electricity. This electric field accelerates electrically charged gas atoms, called ions, in Mars's upper atmosphere and shoots them into space. The MAVEN mission measured

3993-628: Is observationally the heaviest stable nuclide with the same number of neutrons and protons. All stable nuclides heavier than calcium-40 contain more neutrons than protons. Of the 80 elements with a stable isotope, the largest number of stable isotopes observed for any element is ten (for the element tin ). No element has nine or eight stable isotopes. Five elements have seven stable isotopes, eight have six stable isotopes, ten have five stable isotopes, nine have four stable isotopes, five have three stable isotopes, 16 have two stable isotopes (counting 73 Ta as stable), and 26 elements have only

4114-538: Is roughly shaped like a hemisphere on the side facing the Sun, then is drawn out in a long wake on the opposite side. The boundary of this region is called the magnetopause , and some of the particles are able to penetrate the magnetosphere through this region by partial reconnection of the magnetic field lines. The solar wind is responsible for the overall shape of Earth's magnetosphere. Fluctuations in its speed, density, direction, and entrained magnetic field strongly affect Earth's local space environment. For example,

4235-428: Is still very hot at large distances from the Sun. As solar gravity weakens with increasing distance from the Sun, the outer coronal atmosphere is able to escape supersonically into interstellar space. Parker was also the first person to notice that the weakening influence of the Sun's gravity has the same effect on hydrodynamic flow as a de Laval nozzle , inciting a transition from subsonic to supersonic flow. There

4356-677: The Ulysses probe was launched to study the solar wind from high solar latitudes. All prior observations had been made at or near the Solar System's ecliptic plane. In the late 1990s, the Ultraviolet Coronal Spectrometer (UVCS) instrument on board the SOHO spacecraft observed the acceleration region of the fast solar wind emanating from the poles of the Sun and found that the wind accelerates much faster than can be accounted for by thermodynamic expansion alone. Parker's model predicted that

4477-424: The phase velocity and the group velocity . The phase velocity can in fact be greater than c , but the group velocity, being capable of transmitting information, cannot, by special relativity , be greater than c . The phase velocity for radio waves in the ionosphere is indeed greater than c , and that makes total internal reflection possible, and so the ionosphere can reflect radio waves. The geometric mean of

4598-469: The Big Bang , while all other nuclides were synthesized later, in stars and supernovae, and in interactions between energetic particles such as cosmic rays, and previously produced nuclides. (See nucleosynthesis for details of the various processes thought responsible for isotope production.) The respective abundances of isotopes on Earth result from the quantities formed by these processes, their spread through

4719-444: The CNO cycle . The nuclides 3 Li and 5 B are minority isotopes of elements that are themselves rare compared to other light elements, whereas the other six isotopes make up only a tiny percentage of the natural abundance of their elements. 53 stable nuclides have an even number of protons and an odd number of neutrons. They are a minority in comparison to

4840-494: The aurora . CMEs are not the only cause of space weather . Different patches on the Sun are known to give rise to slightly different speeds and densities of wind depending on local conditions. In isolation, each of these different wind streams would form a spiral with a slightly different angle, with fast-moving streams moving out more directly and slow-moving streams wrapping more around the Sun. Fast-moving streams tend to overtake slower streams that originate westward of them on

4961-410: The binding energy of the nucleus (see mass defect ), the slight difference in mass between proton and neutron, and the mass of the electrons associated with the atom, the latter because the electron:nucleon ratio differs among isotopes. The mass number is a dimensionless quantity . The atomic mass, on the other hand, is measured using the atomic mass unit based on the mass of the carbon-12 atom. It

Kennelly–Heaviside layer - Misplaced Pages Continue

5082-465: The fissile 92 U . Because of their odd neutron numbers, the even-odd nuclides tend to have large neutron capture cross-sections, due to the energy that results from neutron-pairing effects. These stable even-proton odd-neutron nuclides tend to be uncommon by abundance in nature, generally because, to form and enter into primordial abundance, they must have escaped capturing neutrons to form yet other stable even-even isotopes, during both

5203-425: The isotope concept (grouping all atoms of each element) emphasizes chemical over nuclear. The neutron number greatly affects nuclear properties, but its effect on chemical properties is negligible for most elements. Even for the lightest elements, whose ratio of neutron number to atomic number varies the most between isotopes, it usually has only a small effect although it matters in some circumstances (for hydrogen,

5324-490: The periodic table (and hence belong to the same chemical element), but different nucleon numbers ( mass numbers ) due to different numbers of neutrons in their nuclei. While all isotopes of a given element have similar chemical properties, they have different atomic masses and physical properties. The term isotope is derived from the Greek roots isos ( ἴσος "equal") and topos ( τόπος "place"), meaning "the same place"; thus,

5445-436: The residual strong force . Because protons are positively charged, they repel each other. Neutrons, which are electrically neutral, stabilize the nucleus in two ways. Their copresence pushes protons slightly apart, reducing the electrostatic repulsion between the protons, and they exert an attractive nuclear force on each other and on protons. For this reason, one or more neutrons are necessary for two or more protons to bind into

5566-421: The s-process and r-process of neutron capture, during nucleosynthesis in stars . For this reason, only 78 Pt and 4 Be are the most naturally abundant isotopes of their element. 48 stable odd-proton-even-neutron nuclides, stabilized by their paired neutrons, form most of the stable isotopes of the odd-numbered elements; the very few odd-proton-odd-neutron nuclides comprise

5687-553: The season , and the amount of sunspot activity. Existence of a reflective layer was predicted in 1902 independently and almost simultaneously by the American electrical engineer Arthur Edwin Kennelly (1861–1939) and the British polymath Oliver Heaviside (1850–1925), as an explanation for the propagation of radio waves beyond the horizon observed by Guglielmo Marconi in 1901. However, it

5808-435: The 1970s. Around 1910, William Eccles proposed the name "Heaviside Layer" for the radio-wave reflecting layer in the upper atmosphere, and the name has subsequently been widely adopted. The name Kennelly–Heaviside layer was proposed in 1925 to give credit to the work of Kennelly, which predated the proposal by Heaviside by several months. Solar wind The solar wind is a stream of charged particles released from

5929-460: The Alfvén critical surface of the Sun lay. Based on remote images of the corona, estimates had put it somewhere between 10 and 20 solar radii from the surface of the Sun. On April 28, 2021, during its eighth flyby of the Sun, NASA's Parker Solar Probe encountered the specific magnetic and particle conditions at 18.8 solar radii that indicated that it penetrated the Alfvén surface. The solar wind "blows

6050-533: The CME. When a CME impacts the Earth's magnetosphere, it temporarily deforms the Earth's magnetic field , changing the direction of compass needles and inducing large electrical ground currents in Earth itself; this is called a geomagnetic storm and it is a global phenomenon. CME impacts can induce magnetic reconnection in Earth's magnetotail (the midnight side of the magnetosphere); this launches protons and electrons downward toward Earth's atmosphere, where they form

6171-453: The Earth's magnetosphere and on various space weather phenomena, such as the behavior of Van Allen radiation belts . Magnetic switchbacks are sudden reversals in the magnetic field of the solar wind. They can also be described as traveling disturbances in the solar wind that caused the magnetic field to bend back on itself. They were first observed by the NASA–ESA mission Ulysses ,

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6292-439: The Earth's magnetosphere . Irish academic George FitzGerald later suggested that matter was being regularly accelerated away from the Sun, reaching the Earth after several days. In 1910, British astrophysicist Arthur Eddington essentially suggested the existence of the solar wind, without naming it, in a footnote to an article on Comet Morehouse . Eddington's proposition was never fully embraced, even though he had also made

6413-638: The Earth's orbit at 1 astronomical unit (AU) the plasma flows at speeds ranging from 250 to 750 km/s with a density ranging between 3 and 10 particles per cubic centimeter and temperature ranging from 10 to 10 kelvin . On average, the plasma density decreases with the square of the distance from the Sun, while the velocity decreases and flattens out at 1 AU. Voyager 1 and Voyager 2 reported plasma density n between 0.001 and 0.005 particles/cm at distances of 80 to 120 AU, increasing rapidly beyond 120 AU at heliopause to between 0.05 and 0.2 particles/cm . At 1  AU ,

6534-456: The Earth, through an effect called interplanetary scintillation . Where the solar wind intersects with a planet that has a well-developed magnetic field (such as Earth, Jupiter or Saturn), the particles are deflected by the Lorentz force . This region, known as the magnetosphere , causes the particles to travel around the planet rather than bombarding the atmosphere or surface. The magnetosphere

6655-584: The Sun to flow to Earth in narrow beams known as " strahl ", which caused a highly unusual "polar rain" event, in which a visible aurora appeared over the North Pole. In addition, Earth's magnetosphere increased to between 5 and 6 times its normal size. The STEREO mission was launched in 2006 to study coronal mass ejections and the solar corona, using stereoscopy from two widely separated imaging systems. Each STEREO spacecraft carried two heliospheric imagers: highly sensitive wide-field cameras capable of imaging

6776-448: The Sun's magnetic field . Such open lines are particularly prevalent around the Sun's magnetic poles. The plasma source is small magnetic fields created by convection cells in the solar atmosphere. These fields confine the plasma and transport it into the narrow necks of the coronal funnels, which are located only 20,000 km above the photosphere. The plasma is released into the funnel when these magnetic field lines reconnect. Near

6897-492: The Sun's gravitational influence is matched by other stars. The maximum extent of that influence has been estimated at between 50,000 AU and 2 light-years, compared to the heliopause (the outer boundary of the heliosphere), which has been detected at about 120 AU by the Voyager 1 spacecraft. The Voyager 2 spacecraft crossed the termination shock more than five times between August 30 and December 10, 2007. Voyager 2 crossed

7018-625: The Sun's outermost atmospheric layer, the corona . This plasma mostly consists of electrons , protons and alpha particles with kinetic energy between 0.5 and 10  keV . The composition of the solar wind plasma also includes a mixture of particle species found in the solar plasma: trace amounts of heavy ions and atomic nuclei of elements such as carbon , nitrogen , oxygen , neon , magnesium , silicon , sulfur , and iron . There are also rarer traces of some other nuclei and isotopes such as phosphorus , titanium , chromium , and nickel 's isotopes Ni, Ni, and Ni. Superimposed with

7139-507: The Sun, and geomagnetic storms that can change the direction of magnetic field lines. The existence of particles flowing outward from the Sun to the Earth was first suggested by British astronomer Richard C. Carrington . In 1859, Carrington and Richard Hodgson independently made the first observations of what would later be called a solar flare . This is a sudden, localised increase in brightness on

7260-489: The Sun, forming turbulent co-rotating interaction regions that give rise to wave motions and accelerated particles, and that affect Earth's magnetosphere in the same way as, but more gently than, CMEs. CMEs have a complex internal structure, with a highly turbulent region of hot and compressed plasma (known as sheath) preceding an arrival of relatively cold and strongly magnetized plasma region (known as magnetic cloud or ejecta). Sheath and ejecta have very different impact on

7381-429: The almost integral masses for the two isotopes Cl and Cl. After the discovery of the neutron by James Chadwick in 1932, the ultimate root cause for the existence of isotopes was clarified, that is, the nuclei of different isotopes for a given element have different numbers of neutrons, albeit having the same number of protons. A neutral atom has the same number of electrons as protons. Thus different isotopes of

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7502-463: The atomic number is given by the element symbol, it is common to state only the mass number in the superscript and leave out the atomic number subscript (e.g. He , He , C , C , U , and U ). The letter m (for metastable) is sometimes appended after the mass number to indicate a nuclear isomer , a metastable or energetically excited nuclear state (as opposed to

7623-399: The auroral zones. The only time the solar wind is observable on the Earth is when it is strong enough to produce phenomena such as the aurora and geomagnetic storms . Bright auroras strongly heat the ionosphere, causing its plasma to expand into the magnetosphere, increasing the size of the plasma geosphere and injecting atmospheric matter into the solar wind. Geomagnetic storms result when

7744-635: The beta decay of actinium-230 forms thorium-230. The term "isotope", Greek for "at the same place", was suggested to Soddy by Margaret Todd , a Scottish physician and family friend, during a conversation in which he explained his ideas to her. He received the 1921 Nobel Prize in Chemistry in part for his work on isotopes. In 1914 T. W. Richards found variations between the atomic weight of lead from different mineral sources, attributable to variations in isotopic composition due to different radioactive origins. The first evidence for multiple isotopes of

7865-525: The comet Whipple–Fedke (1942g). American astrophysicist Eugene Parker realised that heat flowing from the Sun in Chapman's model, and the comet tail blowing away from the Sun in Biermann's hypothesis, had to be the result of the same phenomenon which he termed the "solar wind". In 1957, Parker showed that although the Sun's corona is strongly attracted by solar gravity, it is such a good conductor of heat that it

7986-452: The composition of the Sun's photosphere . The slow solar wind is twice as dense and more variable in nature than the fast solar wind. The slow solar wind appears to originate from a region around the Sun's equatorial belt that is known as the "streamer belt", where coronal streamers are produced by magnetic flux open to the heliosphere draping over closed magnetic loops. The exact coronal structures involved in slow solar wind formation and

8107-486: The distinctive arrangement of the four identical Cluster spacecraft, which fly in a controlled configuration through near-Earth space. As they sweep from the magnetosphere into interplanetary space and back again, the fleet provides exceptional three-dimensional insights on the phenomena that connect the sun to Earth. The research characterised variances in formation of the interplanetary magnetic field (IMF) largely influenced by Kelvin–Helmholtz instability (which occur at

8228-510: The element carbon with mass numbers 12, 13, and 14, respectively. The atomic number of carbon is 6, which means that every carbon atom has 6 protons so that the neutron numbers of these isotopes are 6, 7, and 8 respectively. A nuclide is a species of an atom with a specific number of protons and neutrons in the nucleus, for example, carbon-13 with 6 protons and 7 neutrons. The nuclide concept (referring to individual nuclear species) emphasizes nuclear properties over chemical properties, whereas

8349-439: The elemental abundance found on Earth and in the Solar System. However, in the cases of three elements ( tellurium , indium , and rhenium ) the most abundant isotope found in nature is actually one (or two) extremely long-lived radioisotope(s) of the element, despite these elements having one or more stable isotopes. Theory predicts that many apparently "stable" nuclides are radioactive, with extremely long half-lives (discounting

8470-410: The even-even isotopes, which are about 3 times as numerous. Among the 41 even- Z elements that have a stable nuclide, only two elements (argon and cerium) have no even-odd stable nuclides. One element (tin) has three. There are 24 elements that have one even-odd nuclide and 13 that have two odd-even nuclides. Of 35 primordial radionuclides there exist four even-odd nuclides (see table at right), including

8591-422: The fact that the tail of a comet always points away from the Sun, regardless of the direction in which the comet is travelling. Biermann postulated that this happens because the Sun emits a steady stream of particles that pushes the comet's tail away. German astronomer Paul Ahnert is credited (by Wilfried Schröder) as being the first to relate solar wind to the direction of a comet's tail based on observations of

8712-411: The fast solar wind, though their differences extend well beyond their speeds. In near-Earth space, the slow solar wind is observed to have a velocity of 300–500 km/s , a temperature of ~ 100  kilokelvin and a composition that is a close match to the corona . By contrast, the fast solar wind has a typical velocity of 750 km/s , a temperature of 800 kilokelvin and it nearly matches

8833-489: The fast wind is still not understood and cannot be fully explained by Parker's theory. However, the gravitational and electromagnetic explanation for this acceleration is detailed in an earlier paper by 1970 Nobel laureate in Physics , Hannes Alfvén . From May 10 to May 12, 1999, NASA's Advanced Composition Explorer (ACE) and WIND spacecraft observed a 98% decrease of solar wind density. This allowed energetic electrons from

8954-432: The first spacecraft to fly over the Sun 's poles. Parker Solar Probe observed first switchbacks in 2018. Over the Sun's lifetime, the interaction of its surface layers with the escaping solar wind has significantly decreased its surface rotation rate. The wind is considered responsible for comets' tails, along with the Sun's radiation. The solar wind contributes to fluctuations in celestial radio waves observed on

9075-486: The galaxy, and the rates of decay for isotopes that are unstable. After the initial coalescence of the Solar System , isotopes were redistributed according to mass, and the isotopic composition of elements varies slightly from planet to planet. This sometimes makes it possible to trace the origin of meteorites . The atomic mass ( m r ) of an isotope (nuclide) is determined mainly by its mass number (i.e. number of nucleons in its nucleus). Small corrections are due to

9196-401: The ground state of tantalum-180) with comparatively short half-lives are known. Usually, they beta-decay to their nearby even-even isobars that have paired protons and paired neutrons. Of the nine primordial odd-odd nuclides (five stable and four radioactive with long half-lives), only 7 N is the most common isotope of a common element. This is the case because it is a part of

9317-409: The integers 20 and 22 and that neither is equal to the known molar mass (20.2) of neon gas. This is an example of Aston's whole number rule for isotopic masses, which states that large deviations of elemental molar masses from integers are primarily due to the fact that the element is a mixture of isotopes. Aston similarly showed in 1920 that the molar mass of chlorine (35.45) is a weighted average of

9438-777: The interface of two fluids) as a result of differences in thickness and numerous other characteristics of the boundary layer. Experts believe that this was the first occasion that the appearance of Kelvin–Helmholtz waves at the magnetopause had been displayed at high latitude downward orientation of the IMF. These waves are being seen in unforeseen places under solar wind conditions that were formerly believed to be undesired for their generation. These discoveries show how Earth's magnetosphere can be penetrated by solar particles under specific IMF circumstances. The findings are also relevant to studies of magnetospheric progressions around other planetary bodies. This study suggests that Kelvin–Helmholtz waves can be

9559-464: The largest number of stable isotopes for an element being ten, for tin ( 50 Sn ). There are about 94 elements found naturally on Earth (up to plutonium inclusive), though some are detected only in very tiny amounts, such as plutonium-244 . Scientists estimate that the elements that occur naturally on Earth (some only as radioisotopes) occur as 339 isotopes ( nuclides ) in total. Only 251 of these naturally occurring nuclides are stable, in

9680-527: The latter speed is essentially the same as the speed of light in vacuum ( c ), scientists were unwilling to believe the speed in the ionosphere could be higher. Nevertheless, Marconi had received signals in Newfoundland that were broadcast in England, so clearly there must be some mechanism allowing the transmission to reach that far. The paradox was resolved by the discovery that there were two velocities of light,

9801-482: The least common. The 146 even-proton, even-neutron (EE) nuclides comprise ~58% of all stable nuclides and all have spin 0 because of pairing. There are also 24 primordial long-lived even-even nuclides. As a result, each of the 41 even-numbered elements from 2 to 82 has at least one stable isotope , and most of these elements have several primordial isotopes. Half of these even-numbered elements have six or more stable isotopes. The extreme stability of helium-4 due to

9922-508: The levels of ionizing radiation and radio interference can vary by factors of hundreds to thousands; and the shape and location of the magnetopause and bow shock wave upstream of it can change by several Earth radii, exposing geosynchronous satellites to the direct solar wind. These phenomena are collectively called space weather . From the European Space Agency 's Cluster mission, a new study has taken place that proposes that it

10043-517: The lightest element, the isotope effect is large enough to affect biology strongly). The term isotopes (originally also isotopic elements , now sometimes isotopic nuclides ) is intended to imply comparison (like synonyms or isomers ). For example, the nuclides 6 C , 6 C , 6 C are isotopes (nuclides with the same atomic number but different mass numbers ), but 18 Ar , 19 K , 20 Ca are isobars (nuclides with

10164-402: The longest-lived isotope), and thorium X ( Ra) are impossible to separate. Attempts to place the radioelements in the periodic table led Soddy and Kazimierz Fajans independently to propose their radioactive displacement law in 1913, to the effect that alpha decay produced an element two places to the left in the periodic table, whereas beta decay emission produced an element one place to

10285-696: The lowest-energy ground state ), for example 73 Ta ( tantalum-180m ). The common pronunciation of the AZE notation is different from how it is written: 2 He is commonly pronounced as helium-four instead of four-two-helium, and 92 U as uranium two-thirty-five (American English) or uranium-two-three-five (British) instead of 235-92-uranium. Some isotopes/nuclides are radioactive , and are therefore referred to as radioisotopes or radionuclides , whereas others have never been observed to decay radioactively and are referred to as stable isotopes or stable nuclides . For example, C

10406-402: The meaning behind the name is that different isotopes of a single element occupy the same position on the periodic table . It was coined by Scottish doctor and writer Margaret Todd in a 1913 suggestion to the British chemist Frederick Soddy , who popularized the term. The number of protons within the atom's nucleus is called its atomic number and is equal to the number of electrons in

10527-509: The method by which the material is released is still under debate. Observations of the Sun between 1996 and 2001 showed that emission of the slow solar wind occurred at latitudes up to 30–35° during the solar minimum (the period of lowest solar activity), then expanded toward the poles as the solar cycle approached maximum. At solar maximum , the poles were also emitting a slow solar wind. The fast solar wind originates from coronal holes , which are funnel-like regions of open field lines in

10648-421: The neutral (non-ionized) atom. Each atomic number identifies a specific element, but not the isotope; an atom of a given element may have a wide range in its number of neutrons . The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number , and each isotope of a given element has a different mass number. For example, carbon-12 , carbon-13 , and carbon-14 are three isotopes of

10769-417: The other about 22. The parabola due to the heavier gas is always much fainter than that due to the lighter, so that probably the heavier gas forms only a small percentage of the mixture." F. W. Aston subsequently discovered multiple stable isotopes for numerous elements using a mass spectrograph . In 1919 Aston studied neon with sufficient resolution to show that the two isotopic masses are very close to

10890-689: The other naturally occurring nuclides are radioactive but occur on Earth due to their relatively long half-lives, or else due to other means of ongoing natural production. These include the afore-mentioned cosmogenic nuclides , the nucleogenic nuclides, and any radiogenic nuclides formed by ongoing decay of a primordial radioactive nuclide, such as radon and radium from uranium. An additional ~3000 radioactive nuclides not found in nature have been created in nuclear reactors and in particle accelerators. Many short-lived nuclides not found naturally on Earth have also been observed by spectroscopic analysis, being naturally created in stars or supernovae . An example

11011-726: The others. There are 41 odd-numbered elements with Z = 1 through 81, of which 39 have stable isotopes ( technetium ( 43 Tc ) and promethium ( 61 Pm ) have no stable isotopes). Of these 39 odd Z elements, 30 elements (including hydrogen-1 where 0 neutrons is even ) have one stable odd-even isotope, and nine elements: chlorine ( 17 Cl ), potassium ( 19 K ), copper ( 29 Cu ), gallium ( 31 Ga ), bromine ( 35 Br ), silver ( 47 Ag ), antimony ( 51 Sb ), iridium ( 77 Ir ), and thallium ( 81 Tl ), have two odd-even stable isotopes each. This makes

11132-593: The phase velocity and the group velocity cannot exceed c , so when the phase velocity goes above c , the group velocity must go below it. In 1925, Americans Gregory Breit and Merle A. Tuve first mapped the Heaviside layer's variations in altitude. The ITU standard model of absorption and reflection of radio waves by the Heaviside Layer was developed by the British Ionospheric physicist Louis Muggleton in

11253-415: The possibility of proton decay , which would make all nuclides ultimately unstable). Some stable nuclides are in theory energetically susceptible to other known forms of decay, such as alpha decay or double beta decay, but no decay products have yet been observed, and so these isotopes are said to be "observationally stable". The predicted half-lives for these nuclides often greatly exceed the estimated age of

11374-415: The pressure of plasmas contained inside the magnetosphere is sufficiently large to inflate and thereby distort the geomagnetic field. Although Mars is larger than Mercury and four times farther from the Sun, it is thought that the solar wind has stripped away up to a third of its original atmosphere, leaving a layer 1/100th as dense as the Earth's. It is believed the mechanism for this atmospheric stripping

11495-432: The primary exceptions). The vibrational modes of a molecule are determined by its shape and by the masses of its constituent atoms; so different isotopologues have different sets of vibrational modes. Because vibrational modes allow a molecule to absorb photons of corresponding energies, isotopologues have different optical properties in the infrared range. Atomic nuclei consist of protons and neutrons bound together by

11616-457: The properties of the various isotopes of a given element. Isotope separation is a significant technological challenge, particularly with heavy elements such as uranium or plutonium. Lighter elements such as lithium, carbon, nitrogen, and oxygen are commonly separated by gas diffusion of their compounds such as CO and NO. The separation of hydrogen and deuterium is unusual because it is based on chemical rather than physical properties, for example in

11737-410: The rate of atmospheric stripping at about 100 grams (≈1/4 lb) per second. Mercury , the nearest planet to the Sun, bears the full brunt of the solar wind, and since its atmosphere is vestigial and transient, its surface is bathed in radiation. Mercury has an intrinsic magnetic field, so under normal solar wind conditions, the solar wind cannot penetrate its magnetosphere and particles only reach

11858-586: The relative mass difference between isotopes is much less so that the mass-difference effects on chemistry are usually negligible. (Heavy elements also have relatively more neutrons than lighter elements, so the ratio of the nuclear mass to the collective electronic mass is slightly greater.) There is also an equilibrium isotope effect . Similarly, two molecules that differ only in the isotopes of their atoms ( isotopologues ) have identical electronic structures, and therefore almost indistinguishable physical and chemical properties (again with deuterium and tritium being

11979-451: The right. Soddy recognized that emission of an alpha particle followed by two beta particles led to the formation of an element chemically identical to the initial element but with a mass four units lighter and with different radioactive properties. Soddy proposed that several types of atoms (differing in radioactive properties) could occupy the same place in the table. For example, the alpha-decay of uranium-235 forms thorium-231, whereas

12100-441: The same element. This is most pronounced by far for protium ( H ), deuterium ( H ), and tritium ( H ), because deuterium has twice the mass of protium and tritium has three times the mass of protium. These mass differences also affect the behavior of their respective chemical bonds, by changing the center of gravity ( reduced mass ) of the atomic systems. However, for heavier elements,

12221-489: The same mass number ). However, isotope is the older term and so is better known than nuclide and is still sometimes used in contexts in which nuclide might be more appropriate, such as nuclear technology and nuclear medicine . An isotope and/or nuclide is specified by the name of the particular element (this indicates the atomic number) followed by a hyphen and the mass number (e.g. helium-3 , helium-4 , carbon-12 , carbon-14 , uranium-235 and uranium-239 ). When

12342-406: The sense of never having been observed to decay as of the present time. An additional 35 primordial nuclides (to a total of 286 primordial nuclides), are radioactive with known half-lives, but have half-lives longer than 100 million years, allowing them to exist from the beginning of the Solar System. See list of nuclides for details. All the known stable nuclides occur naturally on Earth;

12463-449: The shock about a Tm closer to the Sun than the 13.5 Tm distance where Voyager 1 came upon the termination shock. The spacecraft moved outward through the termination shock into the heliosheath and onward toward the interstellar medium . Isotopes Isotopes are distinct nuclear species (or nuclides ) of the same chemical element . They have the same atomic number (number of protons in their nuclei ) and position in

12584-449: The solar disc, which is now known to often occur in conjunction with an episodic ejection of material and magnetic flux from the Sun's atmosphere, known as a coronal mass ejection . The following day, a powerful geomagnetic storm was observed, and Carrington suspected that there might be a connection; the geomagnetic storm is now attributed to the arrival of the coronal mass ejection in near-Earth space and its subsequent interaction with

12705-580: The solar wind and the local density of the interstellar medium, but it is far outside Pluto 's orbit. Scientists hope to gain perspective on the heliopause from data acquired through the Interstellar Boundary Explorer (IBEX) mission, launched in October 2008. The heliopause is noted as one of the ways of defining the extent of the Solar System, along with the Kuiper Belt and the radius at which

12826-416: The solar wind consists of both negative electrons and positive ions. Three years later, in 1919, British physicist Frederick Lindemann also suggested that the Sun ejects particles of both polarities: protons as well as electrons. Around the 1930s, scientists had concluded that the temperature of the solar corona must be a million degrees Celsius because of the way it extended into space (as seen during

12947-400: The solar wind itself, via Thomson scattering of sunlight off of free electrons. Movies from STEREO revealed the solar wind near the ecliptic, as a large-scale turbulent flow. On December 13, 2010, Voyager 1 determined that the velocity of the solar wind, at its location 10.8 billion miles (17.4 billion kilometres) from Earth had slowed to zero. "We have gotten to the point where

13068-442: The solar wind, and lunar soil returned for study confirmed that the lunar regolith is enriched in atomic nuclei deposited from the solar wind. These elements may prove useful resources for future lunar expeditions. The Alfvén surface is the boundary separating the corona from the solar wind defined as where the coronal plasma's Alfvén speed and the large-scale solar wind speed are equal. Researchers were unsure exactly where

13189-412: The solar-wind plasma is the interplanetary magnetic field . The solar wind varies in density , temperature and speed over time and over solar latitude and longitude . Its particles can escape the Sun's gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field. The boundary separating the corona from the solar wind

13310-417: The structure and dynamics of the solar corona, in an attempt to understand the mechanisms that cause particles to be heated and accelerated as solar wind. During its seven-year mission, the probe will make twenty-four orbits of the Sun, passing further into the corona with each orbit's perihelion , ultimately passing within 0.04 astronomical units of the Sun's surface. It is the first NASA spacecraft named for

13431-457: The surface in the cusp regions. During coronal mass ejections, however, the magnetopause may get pressed into the surface of the planet, and under these conditions, the solar wind may interact freely with the planetary surface. The Earth's Moon has no atmosphere or intrinsic magnetic field , and consequently its surface is bombarded with the full solar wind. The Project Apollo missions deployed passive aluminum collectors in an attempt to sample

13552-400: The terminal velocity of 400 km/s , which allows them to feed the solar wind. At the same temperature, electrons, due to their much smaller mass, reach escape velocity and build up an electric field that further accelerates ions away from the Sun. The total number of particles carried away from the Sun by the solar wind is about 1.3 × 10 per second. Thus, the total mass loss each year

13673-420: The universe, and in fact, there are also 31 known radionuclides (see primordial nuclide ) with half-lives longer than the age of the universe. Adding in the radioactive nuclides that have been created artificially, there are 3,339 currently known nuclides . These include 905 nuclides that are either stable or have half-lives longer than 60 minutes. See list of nuclides for details. The existence of isotopes

13794-580: The wind exerts a pressure typically in the range of 1–6 nPa ( (1–6) × 10  N/m ), although it can readily vary outside that range. The ram pressure is a function of wind speed and density. The formula is where m p is the proton mass, pressure P is in Pa (pascals), n is the density in particles/cm and V is the speed in km/s of the solar wind. Both the fast and slow solar wind can be interrupted by large, fast-moving bursts of plasma called coronal mass ejections , or CMEs. CMEs are caused by

13915-466: The wind from the Sun, which until now has always had an outward motion, is no longer moving outward; it is only moving sideways so that it can end up going down the tail of the heliosphere, which is a comet-shaped-like object", said Voyager project scientist Edward Stone. In 2018, NASA launched the Parker Solar Probe , named in honor of American astrophysicist Eugene Parker, on a mission to study

14036-414: The wind should make the transition to supersonic flow at an altitude of about four solar radii (approx. 3,000,000 km) from the photosphere (surface); but the transition (or "sonic point") now appears to be much lower, perhaps only one solar radius (approx. 700,000 km) above the photosphere, suggesting that some additional mechanism accelerates the solar wind away from the Sun. The acceleration of

14157-416: Was almost uninterrupted. As these displays and other geomagnetic activity were being produced by particles from the Sun, he concluded that the Earth was being continually bombarded by "rays of electric corpuscles emitted by the Sun". He proposed in 1916 that, "From a physical point of view it is most probable that solar rays are neither exclusively negative nor positive rays, but of both kinds"; in other words,

14278-513: Was first suggested in 1913 by the radiochemist Frederick Soddy , based on studies of radioactive decay chains that indicated about 40 different species referred to as radioelements (i.e. radioactive elements) between uranium and lead, although the periodic table only allowed for 11 elements between lead and uranium inclusive. Several attempts to separate these new radioelements chemically had failed. For example, Soddy had shown in 1910 that mesothorium (later shown to be Ra), radium ( Ra,

14399-400: Was not until 1924 that its existence was shown by British scientist Edward V. Appleton , for which he received the 1947 Nobel Prize in Physics . Physicists resisted the idea of the reflecting layer for one very good reason; it would require total internal reflection , which in turn would require that the speed of light in the ionosphere would be greater than in the atmosphere below it. Since

14520-548: Was strong opposition to Parker's hypothesis on the solar wind; the paper he submitted to The Astrophysical Journal in 1958 was rejected by two reviewers, before being accepted by the editor Subrahmanyan Chandrasekhar . In January 1959, the Soviet spacecraft Luna 1 first directly observed the solar wind and measured its strength, using hemispherical ion traps. The discovery, made by Konstantin Gringauz  [ ru ] ,

14641-615: Was verified by Luna 2 , Luna 3 , and the more distant measurements of Venera 1 . Three years later, a similar measurement was performed by American geophysicist Marcia Neugebauer and collaborators using the Mariner ;2 spacecraft. The first numerical simulation of the solar wind in the solar corona, including closed and open field lines , was performed by Pneuman and Kopp in 1971. The magnetohydrodynamics equations in steady state were solved iteratively starting with an initial dipolar configuration. In 1990,

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