PTYS_411_511_1_gravity_topography

PTYS_411_511_1_gravity_topography - Planetary Gravity and...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon
PTYS 411/511 Geology and Geophysics of the Solar System Shane Byrne – [email protected] Background is from Lamb and Könemann 1998 Planetary Gravity and Topography
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
PYTS 411/511 – Planetary Gravity and Topography 2 Planetary wide gravity Planetary shapes Moments of inertia Gravitational potential Defining the reference surface Geoids Measurements from space Flybys vs. orbiters Correcting gravity observations Interpreting gravity anomalies Compensated? Crustal thickness Planetary gravity Lunar gravity Martian gravity Planetary comparisons In this lecture
Background image of page 2
PYTS 411/511 – Planetary Gravity and Topography 3 Pythagoras (~550 BC) Speculation that the Earth was a sphere Eratosthenes (~250 BC) Calculation of Earth’s size Shadows at Syene vs. none at Alexandria Angular separation and distance converted to radius Estimate of 7360km – only ~15% too high Invention of the telescope Jean Picard (1671) – length of 1° of meridian arc Radius of 6372 Km – only 1km off! Length of 1° changes with latitude Controversy of prolate vs. oblate spheroids Pierre Louis Maupertuis - Survey 1736-1737 Equatorial degrees are smaller Earth is an oblate spheroid Quick History – The Shape of the World
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
PYTS 411/511 – Planetary Gravity and Topography 4 Galileo Galilei (~1600 AD) Accurately determined g All objects fall at the same rate 1 gal = 1 cm s -1 , g = 981 gals Quick History – Gravity Isaac Newton (1687) Universal law of gravitation Derived to explain Kepler’s third law Led to the discovery of Neptune 2 r GMm F = Henry Cavendish (1798) Attempt to measure the Earth’s density Measured G as a by-product Found ρ Earth ~5500 kg/m 3 > ρ rocks Density must increase with Depth Nineteenth century Everest and Bouguer both find mountains cause deflections in gravity field Deflections less than expected Airy and Pratt propose isostasy via different mechanisms
Background image of page 4
PYTS 411/511 – Planetary Gravity and Topography 5 Planets are flattened by rotation Hydrostatic approximation Gravity at equator adjusted by centrifugal acceleration: Gravity at pole unaffected by rotation Planetary flattening described by: f for a perfectly fluid Earth 1/299.5 Difference due to internal strength Perhaps a relict of previously faster spin f for Mars ~ 1/170 – much more flattened Planets are represented by ellipsoids i.e. a = b ≠ c Triaxial ellipsoids can be used: a ≠ b ≠ c ..but only for a few irregular bodies Planetary Shape 257 . 298 1 10 352 . 3 3 = × = - = - a c a f g p g e ( 29 latitude a cos 2 ϖ
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
PYTS 411/511 – Planetary Gravity and Topography 6 Analogous to mass for linear systems Moment of Inertia Linear Rotational Momentum P = m v L = I ω Energy E = ½ m v 2 E = ½ I ω 2 Response to force t v m F δ = t I δϖ τ = ‘I’ can be integrated over entire bodies, usually I = k MR
Background image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/01/2011 for the course PTYS/ASTR 411/511 taught by Professor Shanebyrne during the Spring '08 term at Arizona.

Page1 / 28

PTYS_411_511_1_gravity_topography - Planetary Gravity and...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online