Educational Resources – Glossary

Educational Resources – Glossary

This glossary defines terms used in Europlanet educational resources (The Icy Moons Collection, The Mars Collection, etc) that may be unfamiliar.

Abiogenesis – The original evolution of life from non-living matter, for example simple organic compounds. 

Archaea – A domain of single-celled organisms. They lack cell nuclei (therefore are prokaryotic) and are evolutionarily distinct from bacteria. 

Converted by impact – When asteroids impact planetary bodies, they transfer large amounts of energy. The energy from the impacts can modify the surfaces of the impacted bodies, with the potential to induce chemical reactions, changing the composition of the surface. 

Cryovolcanism – Cold volcanism. A type of volcanic activity that occurs in environments with extremely low temperatures. A cryovolcano erupts liquids and gases through an overlaying crust of ice. 

Differentiated – When a planetary interior is separated into distinct compositional layers. 

Enceladus – Enceladus is the sixth largest moon to orbit Saturn. Below its icy surface appears to be a vast ocean that encircles the entire core, heated through tidal deformation. Plumes of water are ejected through cracks in the crust at Enceladus’s south pole, due to cryovolcanism.

Europa – Europa is the smallest of the four largest (Galilean) moons of Jupiter. It has the smoothest surface of any known object in our Solar System. The internal structure of Europa is thought to be a metallic core, surrounded by silicate rock, covered by a global, liquid water ocean, beneath a thick icy crust. Despite its unusual smoothness, the surface ice of Europa is marked with long, thin, parallel cracks, referred to as lineae. Material seeping through the lineae gives clues to the ocean’s composition and density. 

Extremophiles – Microorganisms that live in extreme conditions, for example extreme temperature, pressure, pH, radiation, or chemical concentration. 

Fissures – A long, narrow opening in a planetary body formed because of cracking or breaking.

Ganymede – Jupiter’s moon, Ganymede, is the largest known moon in our Solar System.  With a diameter of 5268 kilometres, it’s almost 10% bigger than Mercury. Ganymede has an icy crust covering a very deep subsurface ocean (around 100 kilometres deep). Ganymede is the only known moon with a magnetic field.

Galilean – Related to or discovered by the famous astronomer, Galileo Galilei. The four innermost moons of Jupiter are referred to as the ‘Galilean Moons’ as they were discovered by Galileo in 1610.

Hydrological – The water cycle. The motion of water from the ground to the atmosphere and back again. 

Hydrothermal vents – Cracks on the seafloor from which geothermally heated water is expelled. One of the places hypothesised to be where life originated on Earth, because of the rich chemistry. This is due to chemical reactions between sea water and the minerals in the rocks of the vents. On Earth, hydrothermal vents are host to complex ecosystems, fuelled by the chemicals dissolved in the vent fluids. 

Io Jupiter’s volcanic moon and the fourth largest moon in the Solar System. Because of the huge amount of heat generated by being constantly pulled through its orbit (tidal heating), Io is the most volcanically active body in our solar system. It has hundreds of volcanoes, and lakes of molten silicate lava on its surface. Its volcanoes are so powerful that they can be seen with large telescopes on Earth.

Kuiper belt – A region of space containing icy objects and dwarf planets such as Pluto. It is located just beyond the orbit of Neptune. Short-period comets generally originate in the Kuiper belt, and there may be trillions of comets which reside here.  

Magnetometer – An instrument used to measure magnetic forces, for example their direction, strength, or relative change in magnetic field at a particular location. On the Galileo spacecraft, it was used to map the magnetic field (or magnetosphere) of Jupiter, measure any fluctuations in this, determine whether any of the moons had intrinsic magnetic fields (e.g., Ganymede), and investigate how the magnetic field of Jupiter interacted with its moons. 

Natural Satellites – Another word for moon. An astronomical body which orbits a planet, dwarf planet, or other small body. 

Nitrogen isotope ratio – How much 14N/15N is present, used to evaluate how the atmosphere has changed over time.  In Titan, this is an ‘evolved ratio’, which means it has changed as the moon has formed and developed its atmosphere. ‘Primordial ratios’, such as those seen in comets, are thought to be a record of the original isotope ratio of the parent body when it formed in the early stages of the Solar System. 

Oort cloud – A spherical layer of icy objects surrounding our Solar System. The icy objects that form the cloud range in size, and the Oort cloud is expected to contain billions, or even trillions of objects. This is probably the source of most long-period comets we see and is also known as a cometary reservoir. No missions have been sent to the Oort cloud because it is so far away.  

Orbital period – how long a body takes to complete an orbit.

Orbital resonance – Occurs if the orbital periods of two bodies (e.g. moons) can be expressed as a ratio of two integers. This happens when two bodies exert a regular, periodic, gravitational influence on each other. 

Primordial soup – A theory of the origin of life, whereby organic molecules were mixed in ancient bodies of water, assembling to form living organisms. Today scientists are still working on this theory.

Retrograde orbit – When an object spins in the opposite direction to its orbit. For moons, this is when the moon revolves in its orbit in the opposite direction from that in which the planet rotates about its axis.

Striated – Marked with long, thin, parallel streaks or stripes.

Synchronous rotations – The same as being tidally locked. It describes the rotation of a body which has equal rotational and orbital periods, showing the same face to the object it is orbiting all year round. 

Tholin haze – Tholins are complex organic molecules. They are formed by irradiation via solar or cosmic rays of simple molecules such as methane, ethane, or carbon dioxide, often in combination with water or nitrogen. The tholin haze is the orange atmosphere around Titan, which shields its surface from view in visible wavelengths. 

Tidal deformation – This describes how much a body is deformed, or changes shape, because of gravitational effects. Tidal forces occur when objects exert a gravitational pull on each other, for example our Earth and the moon (causing the tides). This arises because the gravitational pull of an object as it orbits a parent body is different across its parts; the side closest to the parent body is more gravitationally attracted than the side furthest away, causing it to be stretched. In space, tidal forces can be so great that they generate enough heat to maintain volcanic activity, for example on Jupiter’s volcanic moon Io. These forces result in some of the diverse geology we see on many of the icy moons, for example the large cracks in Enceladus’ surface which are home to the plumes.

Tidal forces – A force due to the gravitational attraction between two bodies. It stretches a body, deforming the shape of it and generating heat in the body’s interior. See image below, which shows how the Earth is deformed due to the gravitational pull of the moon, causing our tides. 
Ocean Motion : Background : Tide-Generating Forces

Tidally Locked – When a body has the same rotational period as its orbital period. This means the time taken to rotate around its own axis (a day for Earth), is equal to the time taken to rotate around its parent body (a year for Earth). By having equal years and days, the orbiting body shows the same face to the parent body. For example, we only see one side of the moon because it is tidally locked.  

Volatile – A substance which easily evaporates to be a gas. Volatile substances have high vapour pressures and low boiling points. 

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