NAKHLA METEORITE - Achondrite that exploded over the Egyptian town of El-Nakhla, on June. 28, 1911. The Nakhla meteorite broke into ~40 fragments, one of which allegedly (though this has never been proved) killed a dog. The meteorite was later identified as belonging to an exclusive group of objects, known as SNC meteorites, which are believed to have come from the surface of Mars.
NAKHLITE (NAK) - One of the SNC meteorites believed to have come from Mars. Nakhlites probably formed as lava flows with unusual compositions. The nakhlites consist mainly of green augite crystals with some olivine in a very fine-grained matrix of plagioclase, feldspar, clinopyroxene, Fe-Ti oxide, sulfide, and phosphate. There are traces of pre-terrestrial aqueous alteration products in the form of hydrated minerals, including clay minerals and carbonates. Nakhlites have relatively young ages (1.3-1.4 Ga) and, based on the age of clay found inside the specimens examined, are thought to have been exposed to water at ~600 Ma.
NEAR EARTH ASTEROID RENDEZVOUS (NEAR SHOEMAKER) - First mission to orbit an asteroid (see http://near.jhuapl.edu/). The spacecraft carried six instruments: a multi-Spectral Imager (MSI) to image Eros in multiple spectral bands to determine its shape and surface features, and mineral distributions; a Near Infrared Spectrometer (NIS) to measure the near-infrared spectrum to determine distribution and abundance of surface minerals like olivine and pyroxene; a NEAR Laser Rangefinder (NLR), a laser altimeter that measures the range to the surface to build up high resolution topographic profiles; an X-ray/Gamma-ray Spectrometer (XGRS) to detect X-ray fluorescence and γ-rays from elements on the asteroid surface excited by solar x-rays, cosmic rays and natural radioactivity in the asteroid; and a Magnetometer (MAG) to search for and map any intrinsic magnetic field around Eros. The NEAR spacecraft passed within 1225 km of the asteroid 253 Mathilde, a C-type carbon-rich asteroid, on its trip to Eros and acquired images and determined its mass to an accuracy of ~5%. After a year of orbiting Eros, the spacecraft touched down on asteroid's surface, after transmitting close-up images of the surface during its final descent.
NEUTRALINO - Candidate for non-baryonic dark matter particle. Supersymmetry, a hypothetical symmetry relating bosons to fermions, predicts the existence of hitherto undetected "partners" for each type of particle in the Standard Model of particle physics. Under certain assumptions, the lightest such partner particle would be stable, and if it is neutral (a "neutralino"), would make a good dark matter candidate. Reasonable neutralino masses range from 30 GeV to 10 TeV. If they make up the dark matter of the Milky Way, then they should have nonrelativistic velocities and hence their annihilation would give rise to gamma rays with unique energies.
NEUTRINO (ν) - One of three electrically neutral leptons that experience only the weak nuclear force and gravitional force, and pass easily through matter. Three types of neutrinos are known and there is strong experimental evidence that no additional types of neutrinos exist. Each type or "flavor" of neutrino is related to a charged particle (which gives the corresponding neutrino its name):
| Neutrino | νe | νμ | ντ |
|---|---|---|---|
| Charger Partner | electron (e-) | muon (μ) | tau (τ) |
Electron neutrinos (νe) are generated in the interior of the Sun and similar stars during hydrogen burning. normous numbers of neutrinos are formed during supernova explosions as electrons are squeezed into protons, producing a neutron core. The potential energy liberated by such a collapse is radiated mainly in a burst of neutrinos. Such a neutrino burst was first observed of the supernova of 1987.
Recent solar and atmospheric neutrino experiments have established that at least some neutrinos have mass and that they mix (oscillate) between themselves. Based on these experiments, it appears that the cosmic density of massive neutrinos is at least as large as that of luminous matter. Neutrino experiments as well as the large-scale clustering of galaxies indicate that light stable neutrinos have a mass less than a few electron volts. Best mass estimates as of 2006 are that the heaviest neutrino must be at least 0.05 eV, but no more than 0.18 eV.
In addition to neutrinos produced in nuclear reactions, a large number of "relic" neutrinos originated in the Big Bang. These should have a local present density of ~110 per nerutrino species per cm3. However, no viable method of direct detection exists.
NEUTRON (n) - Charge-neutral hadron with a mass of 1.6748 x 10-27 kg, equivalent to 939.573 MeV, and an intrinsic angular momentum, or spin, of ½ (in units of h/2π). The neutron is a nucleon, one of the two basic constituents of all atomic nuclei (apart from 1H, which consists of a single proton). The total number of protons and neutrons in an atomic nucleus defines its mass number, A. Neutrons are stable within the nucleus, but unstable in isolation (t½ = 886±2 s), decay being mediated by a W boson:
NEUTRON CAPTURE - Primary mechanisms by which very massive nuclei are formed in stars and supernova explosions, principally, the s-process and r- process. Instead of fusion of like nuclei, heavy elements are created by the addition of more and more neutrons to existing nuclei.
NEUTRON DECAY - Nuclear decay by emission of a neutron (decreasing A by 1).
NEUTRON DEGENERACY PRESSURE - Pressure produced by quantum mechanic constrains on neutron packing. Quantum mechanics restricts the number of neutrons that can have low energy. Each neutron must occupy its own energy state. When neutrons are packed together, the number of available low energy states is too small and many neutrons are forced into high energy states that produce pressure. Because the pressure arises from a quantum mechanical effect, it is insensitive to temperature (pressure doesn't go down as the star cools). Similar to electron degeneracy pressure but, because neutrons are much more massive than electrons, neutron degeneracy pressure is much larger and can support stars more massive than the Chandrasekhar mass limit.
NEUTRON STAR - Dense ball of neutrons that remains at the core of a star after a supernova e8;plosion has destroyed the rest of a star with mass 8-18 (?) Msun. A neutron star has mass ~2-3 Msun, density ~1014 g/cm3, and is supported byneutron degeneracy pressure. Typical neutron stars are 10-20 km across and have escape velocities ~70% speed of light. The interior of a neutron star contains exotic matter such as superfluid neutrons, superconducting protons, and stranger subatomic particles (e.g., π condensates, λ hyperons, Δ isobars, and quark-gluon plasmas). Rapidly rotating neutron stars are called pulsars.
NEWMAN LINES - Fine striations seen in some high-Ni iron meteorites.
NEWTON'S LAWS - Isaac Newton's theory of mechanics, describing the motions of objects, and the law of gravitation. First Law: An object in a state of uniform motion will remain in that state unless acted upon by an external force. Second Law: Net applied force on an object produces acceleration in proportion to the mass:
Third Law: If A exerts a force on B, then B will exert an equal and oppositely directed force on A. For every action, there is an equal and opposite reaction.
NITROGEN (N) - Principal constituent of the Earth's atmosphere (78.08 vol. % at ground level). Nitrogen is the fifth most abundant element in the universe by atom abundance. Nitrogen comprises only 3.5 vol. % of the atmosphere of Venus and 2.7 vol. % of Mars's atmosphere. Nitrogen has two isotopes: 14N (99.632 %) and 15N (0.368 %). Nitrogen isotopic variations are reported as δ15N in parts per thousand (‰) deviations from the nitrogen isotopic composition of Earth's atmosphere (15N/14N = 0.003676). Large N isotopic variations are observed in the solar system from -250 ‰ (lowest values in lunar soils) to 1600 ‰ (CB chondrites - bencubinites). Comets Hale-Bopp and LINEAR have essentially identical δ15N values of ~940 ‰.
Values of δ15N in the lunar regolith show a very large range from ~100 ‰ to -250 ‰ with ratios appearing to vary with age. The lunar results can be explained by secular variation in δ15N of the solar wind over time, although this hypothesis conflicts with the apparent stability of ratios in other solar wind volatile elements. Alternatively, the variation could result from mixing in a non-solar wind component (meteorite or comet material deposited on the moon during impacts). Extreme δ15N variations have been documented in organic material from meteorites (image of insoluble organic matter extracted from the CR chondrite EET 92042).
NOBLE GASES - Element occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive.
NORITE - Igneous rock found in the lunar highlands composed of plagioclase and pyroxene.
NOVA - Star that, over a period of a few days, becomes 103-104 times brighter than it was previously. Novae are observed ~10-15 times per year in the Milky Way.
NUCLEAR FORCES - Two of the fundamental forces, or interactions, the strong interaction and the weak interaction. These are not necessarily confined to the nucleus, despite the name. The strong interaction not only holds nucleons together in the nucleus, but also binds quarks into hadrons. The weak interaction is involved in some nuclear processes such as radioactivity, but also causes free neutrons to decay.
NUCLEON - Either of the two baryons, the proton and the neutron, which form the nuclei of atoms.
NUCLEOSYNTHESIS - Process by which nuclear reactions produce the various elements of the periodic table. H and He were largely created in the Big Bang; most of the heavier elements were formed inside stars and during supernova explosions by the r-process and s-process.
NUCLEOTIDE - Subunits of nucleic acids and the fundamental structural unit of the nucleic acid group of organic macromolecules. Nucleotides are composed of a phosphate, a sugar such as ribose, and a nitrogen-containing base such as adenine. Nucleotides are involved in information storage (as nucleotides in DNA), protein synthesis (as nucleotides in RNA), and energy transfers (e.g. as single nucleotide ATP).
NUCLEUS - Core of an atom, where most mass and all positive charge is concentrated. It consists of protons and neutrons.
NUMBER DENSITY - Number of a particular type of object found in each unit volume. For example, if 2500 garnets are fairly uniformly spread through a volume of 100 cm3, the number density of garnets is 25/cm3.