solar system
the sun and all of the planets and other bodies that travel around it; consists of the sun, planets, dwarf planets, and all of the other bodies that revolve around the sun
planets
the primary bodies that orbit the sun; a celestial body that orbits the sun, is round because of its own gravity, and has cleared the neighborhood around its orbital path
nebular hypothesis
hypothesis that states that the sun and the planets condensed at about the same time out of a nebula; created in 1796 by the French mathematician Pierre-Simon, marquis de Laplace
nebula
a rotating cloud of gas and dust
solar nebula
the rotating cloud of dust and gas from which the sun and planets formed; also any nebula from which stars and exoplanets may form
planetesimal
a small body from which a planet originated in the early stages of formation/development of the solar system
protoplanets
larger bodies than planetesimals; formed when planetesimals join together through collisions and through the force of gravity; eventually became large enough to form planets and moons
moons
the smaller bodies that orbit the planets; planets and _____ are smaller and denser than the protoplanets
inner planets
planets close to the sun; Mercury, Venus, Earth, and Mars
gas giants
huge planets that are composed of mostly gases, have low density; a planet that has a deep, massive atmosphere, such as Jupiter, Saturn, Uranus, or Neptune (the outer planets)
outer planets
the four planets farthest from the sun which are Jupiter, Saturn, Uranus, and Neptune; formed in colder regions of the solar nebula far away from the sun
ice giants
Uranus and Neptune are different from Jupiter and Saturn and are sometimes called ___ ______ because they have more frozen gases
dwarf planets
any object that orbits the sun, is round because of its own gravity, has not cleared the region around its orbit, and is not a satellite of another planet; Pluto is best described as an ice ball made of frozen gases and rock and has a very tilted orbit. M
differentiation
process during a planets developing stages; denser materials sink to the center and less dense materials are forced to the outer layers; caused Earth to form three distinct layers
core
dense center layer of Earth composed of mostly iron and nickel
mantle
very thick layer of Earth around the core composed of iron and magnesium-rich rock
crust
the outermost layer of Earth composed of less dense, silica-rich rock
outgassing
formed a new atmosphere; process of volcanic eruptions releasing large amounts of gases, mainly water vapor, carbon dioxide, nitrogen, methane, sulfur dioxide, and ammonia
ozone
a molecule that contains three oxygen atoms; collected in a high atmospheric layer around Earth and shielded Earth's surface from the harmful ultraviolet radiation of the sun
geocentric
Earth-centered or __________ model of the solar system; suggested by the Greek philosopher Aristotle; in this model the sun, the stars, and the planets revolved around Earth
retrograde motion
a pattern of planets that sometimes appeared to move backwards in the sky relative to the stars
epicycles
Claudius Ptolemy, a Greek astronomer, suggested in 150 CE that planets moved in small circles called _________ as they revolved in larger circles around Earth
heliocentric
sun-centered or ____________ model of the solar system suggested by a Polish astronomer named Nicolaus Copernicus in 1543 CE; in this model the planets revolved around the sun in the same direction but at different speeds and distances from the sun; fast
law of ellipses
Kepler's first law; states that each planet orbits the sun in a path called an ellipse, not a circle
ellipse
a closed curve whose shape is determined by two points, or foci, within an _______; the shape of the planet's orbits
eccentricity
the degree of elongation of an elliptical orbit (symbol, e); determined by dividing the distance between the foci of the ellipse by the length of the major axis
parabolic orbit
the eccentricity of this type of extremely elongated orbit is e=1
law of equal areas
Kepler's second law; describes the speed at which objects travel at different points in their orbits; states that equal areas are covered in equal amounts of time as an object orbits the sun; Kepler calculated that a line from the center of the sun to the
law of periods
Kepler's third law; describes the relationship between the average distance of a planet from the sun and the orbital period of the planet; the cube of the average distance (a) of a planet from the sun is always proportional to the square of the period (p)
orbital period
the time required for a body to complete a single orbit
inertia
the tendency of an object to resist a change in motion unless an outside force acts on the object; Isaac Newton hypothesized that a moving body will remain in motion and resist a change in speed or direction until an outside force acts on it
gravity
an outside force that causes a planet's orbit to curve; this attractive force exists between any two objects in the universe; named by Newton
terrestrial planets
the inner planets are also called ___________ _______ because they are similar to Earth; highly dense planets nearest to the sun; Mercury, Venus, Mars, and Earth; consist mostly of solid rock and have metallic cores; number of moons per planet varies from
impact craters
bowl-shaped depressions that occur on the surfaces of inner planets; caused by collisions of the planets with other space objects
greenhouse effect
type of heating; occurs when the high concentration of carbon dioxide in the atmosphere blocks most of the infrared radiation from escaping; on Earth, it warms Earth enough for organisms to live on the planet
runaway greenhouse effect
phenomenon that makes Venus' surface temperature the highest known in the solar system (464degC)
evening star or morning star
what Venus is called because it is usually visible in the early morning or evening; Venus has sulfur dioxide droplets in its upper atmosphere, which forms a cloud layer that reflects light so strongly that from Earth, Venus appears to be near the sun and
Magellan
satellite that orbited Venus for four years in the 1990s before the satellite was steered into the planet to collect atmospheric data; bounced radio waves off Venus to produce radar images of Venus' surface, which found landforms such as mountains, volcan
Venus Express
European Space Agency's spacecraft that orbited Venus between April 2006 and May 2009
Viking
landing craft that detected two geological events that produced seismic waves on Mars
marsquakes
geological events on Mars that produced seismic waves; may indicate that volcanoes on Mars are more active
Spirit and Opportunity
mars rovers which landed on Mars in 2004; found liquid evidence that water did exist on Mars' surface in the past
Phoenix
lander that confirmed in 2008 that water also exists as ice just below the Martian surface of Mars
asteroid belt
a ring of debris that separates the inner planets from the outer planets
Great Red Spot
Jupiter's most distinctive feature; a giant rotating storm, similar to a hurricane of Earth, that has been raging for at least several hundred years
Galileo
spacecraft that dropped a probe on Jupiter which measured wind speeds of up to 540 km/h on Jupiter
Cassini
scientist are learning more about Saturn and its moons from this spacecraft which reached Saturn in 2004
Huygens
carried by Cassini, this probe landed on Titan, Saturn's largest moon
Hubble Space Telescope
has taken images that show changes in Uranus' atmosphere; images taken has also indicated that Neptune has an active weather system
Voyager 2
space probe that passed by Uranus and helped in the discovery of the rotation rate of Uranus; data from this probe indicate that Neptune's atmosphere is made up of mostly hydrogen, helium, and methane; images taken by this probe indicate that Neptune has
Great Dark Spot
a storm the size of Earth that appeared and disappeared on Neptune's surface
trans-Neptunian objects
(TNOs) hundreds of objects in our solar system beyond Neptune's orbit; some are similar to Pluto in size and composition, but most are simply small chunks of ice; scientists think that these bodies are the remnants of material that formed the early solar
Kuiper Belt
the region beyond Neptune's orbit where TNOs exist; a region of the solar system that starts just beyond the orbit of Neptune and that contains dwarf planets and other small bodies made mostly of ice
plutoids
trans-Neptunian dwarf planets such as Eris, Makemake, and Haumea
exoplanets
several hundred planetlike objects that circle stars other than Earth's sun; most known __________ circle stars like the Earth's sun therefore, the existence of __________ leads some scientists to wonder if life could exists in another solar system; most