Science 3210 001 : Introduction to Astronomy Lecture 5 : Mars, Earth, and The Outer Planets Robert Fisher
Science 3210 001 : Introduction to Astronomy
Lecture 5 : Mars, Earth, and The Outer Planets
Robert Fisher
Items
! Tutor Akiva Bhansali has hours Monday 4 - 6 PM, Tuesday 4 - 8 PM onthe 12th floor lounge (possibly 14th floor if 12th floor is crowded.)
! Solution sets 1-3 has been posted to the website.
! Problem set number 4 has been posted to the website.
! Midterm 1 is in two weeks.
! Everything through next week’s lecture will be on the exam.
! Exam will be multiple-choice and true/false questions.
! The exam will be one hour long.
! After the exam, we’ll take a break and return to lecture.
! No homework will be due in two weeks on the day of the first midterm.
! First observational project will be distributed in two weeks, following theexam.
! Late Homeworks
Sample Midterm Question
! Which of the following inner solar system bodies is most similar to
Mercury in terms of surface properties?
! A) Venus
! B) Earth
! C) Moon
! D) Mars
Sample Midterm Question
! Which of the following statements is false?
! A) At the location of Chicago, the sun is never visible at the zenith.
! B) At the location of the North Pole, all visible stars are circumpolar
stars.
! C) At the location of the Equator, all stars are visible at some point in
the year.
! D) At the location of the South Pole, the celestial equator is at the
Meridian.
Review Week 3
! Kepler’s Three Laws
! Newton’s Three Laws
! Spectra -- Continuum, Absorption, Emission
Review Week 4
! Solar System Overview
! Sun
! Planets
! Moons/Rings
! Dwarf Planets, Asteroids, Kuiper Belt Objects, Comets, Meteors
! Mercury
! Venus
Today’s Material
! Mars, Earth
! The Outer Solar System
Mars
Mars
! The “red planet” Mars is the current focus of NASA’s unmanned
interplanetary missions, because it is believed to have once
harbored a warm, moist Earth-like phase -- possibly even life.
! There are several similarities between Earth and Mars.
! Mars orbits the sun at 1.5 AU.
! Its axis is tilted at 25 degrees.
! Its day is nearly identical to one Earth day.
A Visual Comparison of Earth and Mars
Canals on Mars??
! In 1877, Italian astronomer Giovanni Schiaparelli described
features he saw on Mars as “canali,” which is probably best
translated as “channels”.
! This phrase became mistranslated as “canals,” which suggested
to some astronomers that the features seen were artificially-
created.
! Later space missions have uncovered tons of evidence for water
on Mars, including channels like those Schiaparelli claimed to
have seen. They are, however, far too small to be visible from
Earth, even with the largest telescopes available.
Schiaparelli’s Drawing of Mars
! Although primitive photographic plates existed at that time,
Schiaparelli recorded his observations in drawings, which he
believed to be more accurate than photographic plates.
Canals on Mars??
! Other astronomers (most noteably Percival Lowell) became
fascinated with the concept, and astronomical research of Mars
has flourished since.
! Despite the body of work, it is likely that Schiaparelli’s canals
were a physiological fluke, though the explanation is still
sometimes debated today.
! These “canals” gave rise to the wealth of Martian science fiction --
from Edgar Rice Burroughs to H.G. Wells to Ray Bradbury, and
many, many more -- which in turn inspired real planetary
scientists like Carl Sagan and many others.
Early Martian Astronomy…
A Flyover Overview of Mars
Mars vs. Earth
! Mars is much smaller than the Earth, with a radius about half that of
Earth, and a mass of about a tenth the Earth’s.
! The surface temperature today is far below the freezing point of water.
! Even if one could warm water ice on Mars today, it would go directly into
a gaseous state without becoming liquid because of the thin atmosphere.
! It has two tiny moons, Phobos and Deimos, with properties radically
different than Earth’s moon.
! While tilt is similar to that of Earth today, the tilt angle oscillates wildly
over tens and hundreds of millions of years.
! It has only a weak magnetic field in its crust, and lacks a magnetic core.
Phobos and Deimos : The Moons of Mars
! Mars has two tiny moons located very near the planet’s surface --
the closest moons to any planet in the solar system.
! It is thought they were asteroids intersecting the Martian orbit
captured via drag through an early, thicker Martian atmosphere.
Phobos Deimos
Asaph Hall, Discoverer of Phobos and Deimos
From The Observatory, 1877
Phobos and Deimos
! An orbiting body at one specific radius has an orbital period equal
to the rotational period of the planet -- a geosynchronous orbit.
From the planet, the body would appear to be stationary.
Phobos
! Phobos orbits well inside Martian Geosynchronous orbit, and so
appears to rise in the west and set in the east
Deimos
Deimos orbits outside of Martian geosynchronous orbit, and remains
visible for two nights in a row.
Mars Odyssey - How to Get to Mars
Olympus Mons, The Largest Volcano in the
Solar System
! Olympus Mons is roughly three times the height of Mount
Everest, but is much broader, with shallower sides.
Digitally-Reconstructed Flythrough of Valles
Marineris from Mars Odyssey
Crevasses on Martian Polar Icecap, Revealed by
Martian Global Surveyor
What Can Cause These Variations in the Martian
Climate?
! The leading explanation for the stratification in the Martian polar
cap is the variation in the Martian rotational and orbital properties.
! All planets are “perturbed” in the orbits about the sun by
gravitational influences from the other planets, particularly Jupiter
! Mars is particularly susceptible to these perturbations because
! It is the closest planet to Jupiter
! It lacks a large moon (like Earth) to “dampen” out the effects
Variation in Martian Obliquity and Orbital
Eccentricity
! Researchers have found that both the angle of inclination of the
Martian rotation (obliquity) and the eccentricity of its orbit vary
wildly over a timescale of millions of years -- leading to alternating
epochs of warm and cold climate
Today
Earth Mars
Variation in Martian Obliquity and Orbital
Eccentricity
! Researchers have modeled the effects of the variation of Martian
obliquity and orbital eccentricity, and found that they in fact do
naturally lead to variations in the amount of power the Martian
surface receives, on the timescale of millions of years
Water on Mars
! Multiple lines of evidence compiled over many years strongly
suggest that Mars had abundant liquid water on the surface in the
distant past, and may even have frozen water just beneath the
surface today.
! One line of evidence comes from images of the surface --
suggestions that the morphology, or shapes, suggests the
presence of water.
! Another line of evidence comes from direct surface
measurements made by the Rovers sent to the surface.
! A third line of evidence comes from imaging instruments on
orbiters which detect hydrogen -- a key component of water.
Riverbeds on Mars
! Many regions on Mars show what appear to be signs of
meandering, dry riverbeds.
Evidence for Flooding on Mars
! Evidence for massive erosion from floods can be seen on the
surface of Mars today, for instance in the Ares Vallis.
Catastrophic Floods on Earth
! Similar catastrophic floods have occurred on the Earth as well, for
instance in the Washington State Scablands. These were
believed to have been formed from massive floodwaters a
thousand feet (!!) deep.
Seepage Channels
! Various craters and valleys on Mars show signs of runoff in the
recent past.
Newton Crater
Seepage Channels
! While liquid water cannot exist on the surface of Mars today, it is
possible that these runoff regions develop only after subsurface
liquid water has burst through a “dam” of frozen surface water.
! This water would be boiling away violently, and so these events
must develop suddenly and disappear rapidly.
! Similar behavior occurs in ice flows in Antarctica on the Earth.
Rock/Liquid Water Rock/Ice Side View
Where Did All That Water Go?
! Very good evidence exists that a LOT of liquid water once ran on
the surface of Mars in the past. Where did all of that water go?
! Because the atmospheric pressure is so low on Mars today, any
water on the surface of Mars today will evaporate in the first
global warming cycle
! Some water may be buried in layers of CO2 ice at the poles of
Mars
! However, the leading explanation has been that the water has
become frozen beneath the surface of Mars.
Permafrost on Earth
! The situation on Mars is analogous to permafrost on Earth, where
regions (mostly inside the arctic circles) have water frozen in the
surface year-round.
Mars Odyssey Neutron Maps
! In 2002, Mars Odyssey imaged Mars in neutrons, scanning for
hydrogen-rich material just beneath the surface.
Odyssey’s Hydrogen Map of Mars
! Odyssey found bands of hydrogen-rich material around both the
north and south poles of Mars -- possibly due to frozen water.
Surface Water on Mars
! In the very distant past -- billions of years ago -- Mars appears to
have had abundant surface liquid water. It is possible that the
lowest-lying areas on the surface, particularly in the Northern
hemisphere, were submerged in a giant ocean.
! Mars’ climate eventually became unsuited to liquid water at the
surface, and most of it was probably lost over time to atmospheric
evaporation.
! The remaining water became frozen into the surface in a kind of
permafrost, similar to that on arctic regions on Earth.
Life on Mars?
! Because there is excellent evidence suggesting that large
amounts of surface water existed in the past on Mars, it is natural
to think that life may have existed on Mars as well.
! One of the biggest questions that one can ask today is whether
life existed on Mars in the past, and may possibly even exist
today.
! The pioneering Viking 2 lander, launched by NASA in the 1970s,
tested directly for the existence of life on the surface of Mars.
Question
! How would you construct a test for life on another planet?
Viking 2 Lander Model
Viking 2 Lander on Surface of Mars
Viking 2 Tests for Life
! The Viking 2 mission to Mars contained a highly-sophisticated
scientific package with four experiments designed to detect the
presence of life in the Martian surface soil.
Where’s the Carbon?
! One experiment, the gas chromatograph - mass spectrometer -
took a scoop of Martian soil, vaporized the soil and analyzed the
composition of the resulting chemicals.
! The idea was to test for the presence of carbon-bearing
compounds, which are the hallmark of organic chemistry and life
on Earth.
! The result was a stunning negative - there is even less organic
material on Mars than in the lunar regolith.
The Labeled Release Experiment
! Perhaps the most clever of the Viking experiments was the
labeled release experiment, which put a drop of liquid nutrient
bearing seven organic molecules metabolized by microorganisms
on Earth.
! The trick was to tag each of the carbon molecules using a very
rare isotope of radioactive carbon 14.
! Amazingly, this test produced a measurable response.
How to Reconcile the Viking Measurements?
! How can one reconcile the two Viking measurements?
The Earth
“We shall not cease from exploration,
and at the end of all our exploring
will be to arrive where we started
and know the place for the first time.”
-- T.S. Eliot, Little Gidding
Earth
! Earth is superficially similar in many respects to both Venus andMars, in terms of its composition, size, and so on.
! The primary features which distinguish Earth is
! Existence of a major moon.
! Relatively strong magnetic field.
! Abundant surface water.
! Life.
Greenhouse Effect Demo
Coriolis Demo (2/2)
Circulation Demo
Greenhouse Effect
! Molecules in the atmosphere are transparent to visible light, but
absorb radiation in the infrared.
! Fundamentally, this is because individual atoms in molecules can
rotate and vibrate at energies much lower than electrons in
atoms.
! These lower-energy transitions typically occur in the infrared
portion of the spectrum.
Diatomic Molecule
Coriolis Demo (1/2)
Long-Term Stability of Earth’s Climate
! Physicists and other scientists will often characterize a system by
its equilibrium and stability.
! For instance, a ball may be instantaneously in balance -- in
equilibrium -- but that balance may be either stable or unstable.
Unstable Stable
Earth’s Climate
! Up until now, Earth’s climate has been stable…
Earth’s Climate
! The trend of global warming has been pronounced in the last one
hundred and fifty years.
Carbon Dioxide Emissions
! The trend of heating is correlated with increased greenhouse gas
emissions.
Astronomical Context
! We have seen that Earth is unique in the solar system.
! Runaway greenhouse heating resulted in the hellish world of
Venus.
! Insufficient greenhouse heating resulted in the frigid world of
Mars.
! Has mankind upset the delicate climate equilibrium on Earth?
Outer Planets
Gas Giant Planet Interiors
! Each of the gas giants is thought to have a rocky core interior
about the size of the Earth or greater, overlaid by thick gaseous
atmospheres.
Next Week -- Midterm!
! We will begin to cover the Outer Planets.
! First midterm next week!