Astronomy- Planetary Systems

Question	Answer
State the main constituents of the Solar System.	8 planets, moons, dwarf planets, asteroids, comets, centaurs, Trans-Neptunian Objects.
Name the planets in order of increasing distance from the Sun.	Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
Name three dwarf planets in the Solar System.	Pluto, Ceres, and Eris (or Haumea, Sedna, Makemake).
What is an asteroid?	A minor planet. Small solid bodies, with the majority orbiting in the Main or Asteroid Belt between the orbits of Mars and Jupiter, including Vesta (the brightest) and Pallas.
What is a comet?	Nuclei of ice, dust and rock that develop a gaseous coma and tails when close to the Sun.
What is a centaur?	Show similarities to both comets and asteroids; generally orbit the Sun between the orbits of Jupiter and Neptune, and include Chiron, Hidalgo and Asbolus.
What is a Trans-Neptunian object?	Objects orbiting the Sun beyond Neptune.
State the features that qualify an object as a 'planet'.	An object that is in orbit around the Sun, is large enough to be spherical, and has 'cleared its orbit' of other objects.
What is the ecliptic?	The projection of the Earth's orbit onto the celestial sphere; it may also be defined as the apparent yearly path of the Sun against the stars. It is inclined to the celestial equator by 23.5°.
What is the Spaced Out project?	The world's largest scale model of the Solar System (in distances), stretching across the UK from Cornwall to Shetland.
What is an astronomical unit?	1 AU is defined as 150 million km (the mean distance between the Earth and the Sun).
Describe the orbit of the planets around the Sun.	The planets orbit the Sun in slightly squashed circles or ellipses. The plane of the Earth's orbit is called the ecliptic and the planes of all the planets are inclined by only a few degrees to this.
What is the Zodiac?	A belt stretching right round the sky, 8° to either side of the ecliptic, in which the Sun, Moon, and planets (apart from Pluto) are always to be found.
What is meant by the term retrograde motion?	Orbital or rotational movement in the sense opposite to that of the Earth's movement or rotation. A planet is said to move in an apparent retrograde direction when shifting from east to west on the celestial sphere.
Define the terms: perihelion, aphelion.	Perihelion = the position of a body in the Solar System when at its closest to the Sun. Aphelion = the position of a planet or other body when at its greatest distance from the Sun.
Define the terms: greatest eastern elongation (GEE), greatest western elongation (GWE).	Mercury and Venus are best placed for observation when they are furthest from the Sun in the sky. The positions in their orbits are known as GEE and GWE and at these positions the angle between the lines planet-Earth and planet-Sun are 90°.
Define the term: conjunction.	1. A planet is in conjunction with a star or another planet when it passes by it in the sky. 2. A planet is in superior conjunction when it is on the far side of the Sun with respect to the Earth, and in inferior conjunction when passing between the Sun and the Earth.
Define the term: opposition.	The position of a planet when exactly opposite to the Sun in the sky.
Define the term: transit.	1. The passage of a celestial object across the observer's meridian. 2. The projection of Mercury or Venus against the disc of the Sun.
Define the term: occultation.	The covering-up of one celestial body by another. Strictly speaking, a solar eclipse is an occultation of the Sun by the Moon.
Describe the physical characteristics of Mercury.	Heavily cratered and contains highlands and lava- filled basins; many parts of its surface appear almost identical to the Moon.
Describe the physical properties of Venus.	Backwards-spinning, similar size to the Earth. Clouds of sulfuric acid, surface pressure 90 x greater than the Earth, surface temperature of 470°C. Dense atmosphere containing carbon dioxide.
What is the link between Venus and global warming?	Venus has a dense atmosphere containing CO2; this prevents infrared radiation leaving Venus, making the surface and lower atmosphere so hot - a 'runaway greenhouse effect'.
Describe the physical properties of Mars.	Mars has iron-rich rocks, seasonal ice caps and a 450 km-long water-carved canyon called Valles Marineris stretching east-west across its surface. It also contains the highest volcano in the Solar System - Olympus Mons - and violent dust storms rage across its surface.
Describe some of the physical characteristics of Jupiter.	Jupiter rotates on its axis in only 10 hours, producing an equatorial bulge and causing dynamic wind systems that split the atmosphere into a series of red-brown belts and yellow-white zones. The Great Red Spot (GRS) is an anticyclone weather system, larger that the planet Earth.
What are some of the physical characteristics of Saturn?	Saturn is a similar gas giant to Jupiter but it reveals less structure in its atmosphere and shows no evidence of long-term features like Jupiter's GRS. Saturn's most notable feature is its majestic rings.
What are the atmospheres of Uranus and Neptune made up of?	Both are gas giants of similar size made up of hydrogen, helium, methane and ammonia.
State some differences in the physical characteristics of Uranus and Neptune.	Uranus spins almost on its side and its surface is almost featureless; Neptune shows many surface markings (including the Great Dark Spot) with dark banded features and cirrus-like clouds of frozen methane at high altitudes.
Name five general techniques by unmanned probes to investigate planets and other Solar System bodies.	Flyby, orbit, landing, impact collision, collecting and returning.
State some of the problems associated with manned exploration of the Solar System.	Space Adaption Syndrome, problems associated with living in a zero-gravity environment (brittle bones, muscle fatigue, reduced red blood cell counts), communication delays, radiation risk, psychological problems.
What are the names of the two moons of Mars?	Phobos (Fear) and Deimos (Terror).
What is the believed origins of the moons of Mars?	Captured bodies from the Asteroid Belt.
What are the names of the 4 Galilean moons of Jupiter?	Io, Ganymede, Callisto, Europa.
Which is the only moon in the Solar System which has a dense atmosphere?	Saturn's moon Titan, which has an atmosphere that extends 600 km from the moon's surface, consisting of 95% nitrogen and methane and other hydrocarbons, which creates a pressure of 1.5 x that of the Earth's atmosphere.
What is unusual about the orbit of Triton around Neptune?	Its orbit is highly-inclined and revolves around Neptune in the opposite sense to that in which Neptune spins (the only large moon in the Solar System to do so).
What is the proposed origin of Neptune's moon Triton?	Probably a captured body, but because of its size and mass, Triton's capture might have been a result of a collision with Neptune or another of its moons. Some of Neptune's small inner moons. An alternative is that Triton was once part of binary system, but only Triton was captured, hence its unusual orbit.
How were some of Neptune's small inner moons formed?	Some of Neptune's small inner moons may have been formed from left-over debris from collisions.
What is the proposed origin of Neptune's moon Proteus?	As Proteus orbits in the plane of Neptune's equator and in the same sense as the planet's spin, it is suggested that Proteus formed at the same time as Neptune.
What is unusual about the orbit of Neptune's moon Nereid?	It is the most highly eccentric orbit of any moon or planet in the Solar System; it takes 360 days to orbit Neptune. It is most likely a captured Kuiper Belt object.
What is the Kuiper Belt?	Frozen objects (mainly methane, ammonia and water) that lie mostly beyond Neptune. Thought to be the source of comets.
What is the Oort Cloud?	The outermost region of the Solar System (at a distance of 1.5 light years from the Sun). Consists of billions of small lumps of rock and ice. The objects of the Oort cloud are too faint to be seen using visible light.
What is the ring system?	Billions of individual particles of ice, rock and dust that range from a few micrometres to several meters in size. The exact composition varies from planet to planet.
What are the possible origins of ring system?	Debris left over after the formation of the planet; large impacts between moons; a moon that was torn apart through tidal gravitational forces; from material ejected from the surfaces of moons by the meteoric impacts.
What is a comet?	Balls of rock and ice that form tails in the course of their highly-elliptical orbits around the Sun.
What are the two classes of comet?	Short-period comets (periods of less than 200 years) and long-period comets (periods of greater than 200 years).
Where do the two classes of comet originate?	Short-period comets originate from the Kuiper belt (30-50 AU from the Sun), long-period comets originate from the Oort cloud (about 50,000 AU from the Sun).
Is the Halley Comet a short-period or a long-period comet? What is its period?	Short-period, with a period of 76 years.
What is the difference between the nucleus and the coma of a comet?	Nucleus = the core of rock and ice. Coma = extremely rarefied sphere of gas and dust surrounding the nucleus (100,000 km across) formed as the temperature rises as a comet approaches the Sun.
Explain the two types of tail on a comet.	Blue-coloured, straight ion tail consisting of atoms and molecules of gas (mostly carbon monoxide) that have been ionised by the solar wind (when they de-excite, atoms emit light by fluorescence). Lighter-coloured, shorter, broader and slightly curved dust tails are produced by radiation pressure that pushes particles out of the nucleus; this tail shines by reflecting sunlight and its curvature is due to the individual dust particles following their own independant solar orbit.
Define the terms; meteoroid, meteor, meteorite.	Meteoroid = small rocky irregular lumps of debris in the solar system. Meteor = when meteoroids enter the Earth's atmosphere, friction causes the meteoroid and surrounding air to heat up producing a short streak of incandescent light. Meteorite = if part of a meteoroid survives its passage through the atmosphere, it lands on the Earth's surface and is called a meteorite.
What is a fireball?	A meteor with a magnitude of 3 or brighter.
Name four annual meteor showers.	Perseids (August), Quandrantids (January), Leonids (November), Geminids (December).
What is a radiant?	The point in the sky from which meteors of any particular shower appears to radiate.
What is a Near Earth Object (NEO)?	Any asteroid or comet with an orbit that brings them close to Earth (closer than 0.3 AU); in 10/08 about 5600 NEOs were known.
What is a Potentially Hazardous Object (PHO)?	A NEO whose orbit brings it within 0.05 AU of Earth; in 10/08 about 1000 were known.
What evidence is there for collisions between astronomical bodies?	Craters on the Moon, asteroids and other planets; the unusual rotations of Venus and Uranus; evidence for the Giant Impact Hypothesis; direct observation of the collision between Jupiter and Shoemaker-Levy in 1994; evidence of PHO impact craters on Earth (Barringer, Chicxulub, Tunguska).
What scale is used to categorise impact hazards and potential risks?	The Torino Scale.
What are the names of the two models of the Solar System?	Geocentric and Heliocentric.
What was Copernicus' contribution to the geocentric vs. heliocentric argument?	Proposed a heliocentric model in order to explain the occasional retrograde motion of Mars, Jupiter and Saturn.
What was Tycho's contribution to the geocentric vs. heliocentric argument?	Undertook meticulous observations of the skies with precision using his purpose-built observatory on the island of Hven, near Copenhagen.
What is Kepler's first law of planetary motion?	Planets move in elliptical orbit around the Sun, with the Sun at one focus of each ellipse.
What is Kepler's second law planetary motion?	An imaginary line from a planet to the Sun sweeps out equal areas in equal intervals of time.
(Mathematically) What is Kepler's third law of planetary motion?	T³ = r², where T is the orbital period of a planet in years, and r is its mean distance from the Sun in AU.
What were Galileo's three major astronomical discoveries relating to the Solar System?	Phases and apparent size of Venus; relief features of the Moon; principal satellites of Jupiter (Ganymede, Io, Callisto, Europa).
Who discovered Uranus and how?	William Herschel in 1781. He had been carrying out a 'review of heavens' with a home-made telescope from the garden of his house in Bath, with particular emphasis in faint naked-eye stars. He found one such disc that he at first mistook for a comet, but subsequent observations allowed him to determine an orbit from which he deduced the object to be a planet.
Who discovered Ceres and how?	Guiseppe Piazzi in 1801. Several astronomers had predicted that an undiscovered planet lay in the obvious gap between the orbits of Mars and Jupiter. He observed the skies at the Palermo Observatory and noted a faint star had moved in position on several successive nights.
Who discovered Neptune and how?	Johann Galle and Heinrich d'Arret in 1846. Discovered first night of telescopic observation based on the predictions of Urbain le Verrier, who predicted the existence of Neptune to explain perturbations in the motion of Uranus.
Who discovered Pluto and how?	Clyde Tombaugh, an American student, in 1930. Located by photographic techniques.
What is gravitation?	The force of attraction that exists between all particles of matter in the Universe.
(Mathematically) What is Newton's law of gravitation?	Image: 92e82c9c-e2d5-4770-b3b1-27890d2d8110 (image/png)
What is meant by an inverse square law?	As the distance between two objects doubles, the force between them in one quarter of its previous value.
What are the three main techniques for detecting or inferring the presence of exoplanets?	Astrometry, transit method, radial-velocity method (using Doppler shifts).
What are the difficulties with detecting individual planets?	Current methods do not allow the discovery of small, rocky exoplanets similar to Earth because atmospheric turbulence and the fact that planets with a relatively small mass have less significant effect on their host star.
What do scientists think are the two essential chemical ingredients for life?	Carbon and liquid water.
What are the two principle theories for the origin of water on Earth?	Out-gassing of hydrogen and oxygen from volcanoes that combined to produce steam that condensed into water; deposited by comets (containing ice) striking Earth.
What methods have astronomers used to determine the origin of water on Earth?	I 2004, ESA's Rosetta space probe set off on a 10-year journey to comet 67p/Churyumov-Cerasimenko where, on arrival, it will drop a small ladder onto the surface of the nucleus. One of the scientific instruments, Ptolemy, will analyse the comet's water content and examine whether it has the same relative abundances of isotopes as water on Earth. The results will help to determine the likelihood of substantial amounts of our water being ''delivered' by comets.
What factors are included in the Drake equation for assessing the likelihood of life existing elsewhere in our galaxy?	Number of stars in our galaxy; fraction of stars with a planetary system; number of planets capable of sustaining life; fraction of life-forms that are intelligent; fraction of these that can and wish to communicate; fraction of a planet's lifetime for which such civilisations can live.
What is meant the term 'habitable zone'?	A narrow range of distances from the star in which the temperature allows liquid water to exist (sometimes called the Goldilocks Zone because it is 'neither too hot nor too cold').
Name two other bodies in our Solar System that are candidates for micro-organisms to exist.	Mars, Jupiter's moon Europa.
State some methods astronomers use to search for signs of life on other planets?	Space probes, spectral analysis of planetary atmospheres above rocky exoplanets to search for gases such as oxygen and methane that are produced by living organisms; analysis of radio waves from space to try to detect signals that have originated from ET intelligent forms of life in our galaxy.
What are the benefits and advantages of discovering ET life?	Would it be wise to transfer organisms from one environment into a totally different one in which they might become extinct or adapt too well and flourish? We know nothing of the intent or capabilities of possible alien life-forms - could continued life on Earth be threatened? Do we really want to discover that we are not alone in the Universe?

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