astronomer: A scientist who works in the field of research that deals with celestial objects, space and the physical universe.

carbon dioxide: (or CO₂) A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). On Earth, carbon dioxide acts as a greenhouse gas, trapping heat in the planet’s atmosphere.

chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H₂O.

core: Something — usually round-shaped — in the center of an object. (in geology) the innermost layer of a planet, such as Earth.

crust: (in planetary science) the outermost surface of rocky planets, dwarf planets and natural satellites.

entrails: The intestines or internal organs of some animal, or the inner materials from some nonliving thing. The term is usually applied when these tissues have been taken from the body or exposed to onlookers.

exoplanet: Short for extrasolar planet, it’s a planet that orbits a star outside our solar system.

gut: An informal term for the gastrointestinal tract, especially the intestines.

host: The act of providing a home or environment for something. A website, for instance, could host photos, news or other types of information.

innards: Slang term for internal organs, such as the stomach and intestines.

iron: A metallic element that is common within minerals in Earth’s crust and in its hot core. This metal also is found in cosmic dust and in many meteorites.

light-year: The distance light travels in one year, about 9.46 trillion kilometers (almost 6 trillion miles). To get some idea of this length, imagine a rope long enough to wrap around the Earth. It would be a little over 40,000 kilometers (24,900 miles) long. Lay it out straight. Now lay another 236 million more that are the same length, end-to-end, right after the first. The total distance they now span would equal one light-year.

link: A connection between two people or things.

magma: The molten rock that resides under Earth’s crust. When it erupts from a volcano, this material is referred to as lava.

magnesium: A metallic element that is number 12 on the periodic table. It burns with a white light and is the eighth most abundant element in Earth’s crust.

mantle: (in geology) The thick layer of the outer crust or Earth or so some other non-gaseous planet. Earth’s mantle is semi-solid and generally divided into an upper and lower mantle.

mineral: Crystal-forming substances that make up rock, such as quartz, apatite or various carbonates. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in regular three-dimensional patterns).

nitric oxide: A chemical (NO) involved in many biological functions, including helping blood vessels relax to increase blood flow. Also a potentially toxic pollutant released by the combustion of fossil fuels or generated by lightning. NO can play a role in the formation of smog ozone, a potent lung irritant.

opaque: Unable to see through, blocking light.

orbit: The curved path of a celestial object or spacecraft around a galaxy, star, planet or moon. One complete circuit around a celestial body.

oxide: A compound made by combining one or more elements with oxygen. Rust is an oxide; so is water.

peer review: (in research) A process in which experts in a field carefully read and critique the work of their peers before it is published in a research journal. Peer review helps to prevent sloppy science and bad mistakes from being published.

planet: A large celestial object that orbits a star but unlike a star does not generate any visible light.

preliminary: An early step or stage that precedes something more important.

silicon: A nonmetal, semiconducting element used in making electronic circuits. Pure silicon exists in a shiny, dark-gray crystalline form and as a shapeless powder.

spectrometer: An instrument that measures a spectrum, such as light, energy, or atomic mass. Typically, chemists use these instruments to measure and report the wavelengths of light that it observes. The collection of data using this instrument, a process is known as spectrometry, can help identify the elements or molecules present in an unknown sample.

star: The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become hot enough, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.

telescope: Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.

unique: Something that is unlike anything else; the only one of its kind.

wavelength: The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It’s also one of the “yardsticks” used to measure radiation.