Astronomy 111: Planetary Geology, Jovian Systems, and Exoplanet Detection

Comprehensive vocabulary flashcards covering terrestrial geology, Jovian planet interiors, icy moons, and exoplanet detection techniques from Astronomy 111 lectures.

Impact Cratering

The geological process resulting from asteroids or comets colliding with a planetary surface, producing bowl-shaped depressions; the relative crater count serves as a method to estimate the age of a geological surface.

Volcanism

The geological process occurring when molten rock (magma or lava) finds a path to a planet's surface, which also expels trapped internal gases into the atmosphere through outgassing.

Tectonics

The disruption and deformation of a planetary surface driven by internal stresses, where compression forces build mountain ranges and extensional stresses pull the crust apart to form valleys and rifts.

Erosion

Any weather-driven process that breaks down or transports surface rock via the action of wind, liquid water, or ice.

Lithosphere

The outer region of cool, rigid rock encompassing a planet's crust and uppermost mantle that floats on top of warmer, softer rock below.

Lunar Maria

Smooth, dark basaltic plains on the Moon created roughly $3\,\text{billion years}$ ago when radioactive decay melted portions of the upper mantle, causing floods of lava to fill vast impact basins.

Olympus Mons

The largest volcano in the solar system, located on Mars, rising to a peak altitude of $26\,\text{km}$ above the Martian surface.

Martian "Blueberries"

Tiny mineral spheres discovered in 2004 by the Opportunity rover on Mars, composed of minerals whose formation requires a salty, liquid water environment such as a pond or lake.

Runaway Greenhouse Effect

A positive feedback process wherein higher temperatures cause increased surface liquid evaporation, and the resulting atmospheric water vapor strengthens greenhouse warming until all oceans boil away and carbonate rocks decompose into $CO_2$.

Metallic Hydrogen

A high-pressure phase of hydrogen occurring deep within giant gas planets like Jupiter and Saturn where electrons move freely among protons, allowing the liquid to conduct electricity like a metal.

Tidal Heating

A continuous interior heating process generated by friction as gravitational tidal forces periodically flex and deform a body moving along an eccentric or elliptical orbit.

Orbital Resonance

A gravitational configuration where orbiting bodies exert regular, recurring gravitational tugs on each other, such as Io, Europa, and Ganymede aligning every $7\,\text{days}$ in a $4:2:1$ orbital ratio that maintains their elliptical orbits.

Europa

A Galilean moon of Jupiter with a fractured water-ice crust and few impact craters, sustained by tidal heating and hypothesized to harbor a $100\,\text{km}$-thick liquid water ocean beneath its icy surface.

Ganymede

The largest moon in the solar system, orbiting Jupiter, showing distinct regions of grooved terrain alongside heavily cratered landscapes and evidence of a subsurface ocean heated by tidal resonance and radioactive decay.

Callisto

The outermost Galilean moon of Jupiter, characterized as a heavily cratered iceball with an ancient surface that lacks tidal heating and orbital resonance, but may still conceal a deeply buried liquid ocean.

Coronagraph

A specialized telescopic instrument designed to block out the overwhelming direct glare of a central star, allowing direct imaging and spectroscopy of faint orbiting exoplanets or debris disks.

Center of Mass

The common balance point around which two or more gravitationally bound bodies, such as a star and an orbiting planet, execute simultaneous mutual orbits on opposing sides.

Astrometric Technique

An indirect exoplanet detection method that tracks tiny, side-to-side gravitational wobble movements in a star's position on the plane of the sky relative to background stars.

Doppler Technique

An indirect exoplanet detection method that measures alternating periodic redshifts and blueshifts in a star's spectrum to deduce line-of-sight radial velocity induced by an orbiting companion.

51 Pegasi b

The first confirmed exoplanet discovered orbiting a Sun-like star (announced in 1995), found via the Doppler technique to possess a Jupiter-like mass in a close $4\,\text{day}$ orbit.

Stellar Radial Velocity Proportionality

The mathematical relationship determining the amplitude of a star's reflex Doppler shift, which is proportional to $\frac{m_{\text{planet}}}{\sqrt{M_{\text{star}} \times d}}$, making planets with high masses orbiting close to low-mass stars the easiest to detect.

Transit Method

An indirect exoplanet detection technique that monitors the apparent brightness of a star to observe the slight, periodic dip in light caused when a planet passes directly across the stellar disk along the observer's line of sight.

Light Curve

A graph tracking the observed brightness of an astronomical object over time, used in transit observations to reveal an exoplanet's presence, size, and orbital period.

Transit Dip Depth

The fractional reduction in a star's observed brightness during a transit, which directly relates to the physical cross-sectional area and radius of the transiting planet relative to the host star.

Transit Dip Width

The duration of time an exoplanet takes to transit the disk of its host star, which is determined by the planet's orbital speed and period.

Kepler Mission

A NASA space telescope operational from 2009 to 2018 that monitored over $150{,}000$ stars using the transit method, discovering approximately $2{,}600$ confirmed exoplanets and over $5{,}000$ candidates.

Exoplanet Density Determination

The calculation of an exoplanet's mean bulk density, made possible when a planet is observed by both the Doppler technique (yielding mass) and the transit method (yielding physical radius and volume).

Hot Jupiters

Gas giant exoplanets with masses similar to or greater than Jupiter that orbit exceptionally close to their parent stars (with distances as small as 0.03 AU0.03AU and orbital periods of only a few days), indicating that planetary migration occurred after formation.

Gravitational Equilibrium

The stable physical balance within a star where the inward gravitational pull of overlying mass is exactly countered by the outward thermal gas pressure generated by nuclear reactions.

Energy Balance

The steady state maintained inside a star where the rate of thermal energy generated by fusion in the core equals the rate of radiative power emitted from the stellar surface into space.

Strong Force

The short-range fundamental interaction that overcomes electrostatic repulsion to bind positively charged protons and neutrons together once stellar core temperatures give particles sufficient kinetic energy.

Proton-Proton Chain

The primary nuclear fusion pathway operating in low-mass stars like the Sun, in which four hydrogen nuclei (protons) fuse to produce one helium-4 nucleus, releasing energy in the form of gamma-ray photons, positrons, and neutrinos.

Solar Thermostat

The self-regulating feedback mechanism in a star's core: an increase in core temperature causes the core to expand and cool back down, whereas a drop in temperature causes contraction and heating.

Inverse Square Law for Light

he geometric principle stating that the apparent brightness of an astronomical body decreases with the square of the distance from the observer, expressed mathematically as Brightness=Luminosity4πd2Brightness=4πd2Luminosity​.

Stellar Parallax

The apparent annual shift in a nearby star's position against background stars viewed over a six-month baseline, yielding distance in parsecs via the formula d=p/1​, where p is the parallax angle in arcseconds.

Parsec

A standard astronomical unit of distance defined as the distance to an object with a parallax angle of one arcsecond, equivalent to approximately 3.26 light-years3.26light-years or 3.09×1013 km3.09×1013km.

Spectral Types

A temperature sequence of stellar classifications determined by absorption line patterns, ordered from hottest to coolest as O, B, A, F, G, K, and M, with each letter subdivided numerically from 0 to 9

Newtons Version of Keplers Third Law

The fundamental gravitational relationship used to calculate the total mass of stars in a binary system from their orbital period and separation: M1+M2=4π2a3GP2M1​+M2​=GP24π2a3​.

Main Sequence

The primary diagonal strip on the H-R diagram where stars stably convert hydrogen into helium in their cores, with the star's initial mass dictating its position, surface temperature, luminosity, and lifetime

Luminosity Classes

Designations using Roman numerals (such as I for supergiants, III for giants, and V for main-sequence stars) that establish a star's location on the H-R diagram and reflect its physical radius.