Mars and science fiction
The Moon and Mars figure prominently
in science fiction, starting
in the 19th century.
link to basic Mars data:
http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html
Overview
The 4th planet
from the sun at 1.52 AU
–The 3rd largest rocky (terrestrial)
planet in the solar system with an equatorial radius of 3402 km
(3000 km smaller than Earth)
–1/3rd Earth’s surface gravity
–Eccentric orbit (0.09 compared to
0.01 for Earth) is as important as the planet’s tilt in causing
seasons
–2 small captured asteroid ‘moons’
Phobos and Deimos
–Distinctive reddish color from
‘rusted’ iron compounds
–Geologically very active in the past
– home of the solar system’s largest volcano (Olympus Mons) and
largest canyon (Valles Marineris)
–Possesses surface water in polar ice
caps which may have flowed in ancient times
–The most clement body in the solar
system (after the Earth) for supporting life as we know it
Mars
through history
Visible to the naked eye
and known to early astronomers
–Red color earned it the title of
‘god of war’ for the Greeks (Ares) and Romans (Mars)
–Mars' red surface color actually
comes from a coating of oxidized iron-bearing rock and dust
particles (like rust).
Helped Kepler derive his
laws of planetary motion in 1609
–The large eccentricity could not be
reconciled with circular orbits
By the late 1800s
telescopes were powerful enough to observe surface features
–They claimed they saw evidence for
Martian life and civilization
The ‘Canals’ and ‘Oases’ of Mars
A large greenish bluish triangular
feature (Syrtis Major) thought to be plant life
–Not all astronomers could
distinguish or agree on what was being seen
The
"Canals":
A fanciful "canal scape":
from “The Decline and
Fall of the Martian Empire” by Kevin Zahnle (2001) in Nature
(http://www.nature.com/nature/journal/v412/n6843/full/412209a0.html
)
The great
English science fiction author H. G. Wells
wrote the classic "War
of the Worlds",
and other authors such as Edgar
Rice Burroughs and Ray Bradbury
described an inhabited Mars.
In reality
there are no canals and there is no vegetation -- these were just
optical illusions due to the difficulties of observing Mars
through the Earth's atmosphere.
View of Mars
from the Mariner 4 spacecraft flyby (1965). The first close-up
photographs of Mars were from spacecraft, and they indicated a
bleak, cratered, lunar-like landscape.
Hope of
ancient civilizations on Mars were dashed
View of Mars
from the Hubble Space Telescope, showing the north polar cap and
high clouds over the Tharsis volcanoes:
Before we had such data,
Mars remained largely a mystery until the robotic exploration of
the 1960s and 1970s.
Mars Exploration
Mars has been a hard target to
explore. Here is a scorecard:
http://www.bio.aps.anl.gov/~dgore/fun/PSL/marsscorecard.html
Some successful (and unsuccessful)
landing sites:
The latest Mars mission is the
Curiosity rover, landed in 94-km diameter Gale Crater last
summer:
Curiosity's landing zone has been
named Bradbury Landing, in honor of Ray Bradbury:
Mars'
greatest
similarity to Earth: polar caps and seasons
Mars has subsurface water at high latitudes and ice caps at both
poles. Like the Earth's ice caps, Mars' ice caps change
with the seasons:
The ice caps are
composed of water ice overlain at times by "dry ice" (carbon
dioxide ice)
–Northern cap is much larger than the
southern cap
–Both caps are dissected by spiral
troughs
Not well understood what causes the
spiral pattern
Thought to be some kind of interplay
between sun and sublimation of ice
Troughs are composed of layers
Each cap has a permanent and seasonal component
–Permanent cap is water ice
–Seasonal cap is frozen carbon
dioxide ("dry ice")
There is a great deal of
ice off the cap, especially in the Northern Lowlands
–detected by Mars Odyssey
This ice is frozen
throughout the martian year leading to a condition in the soil
known as permafrost
–Leads to the formation of Ice Wedge
Polygons:
Contracting ice cracks
Cracks infill with more water (or
dust)
Crack location from the previous year
is a weak spot and re-cracks the next year
The process repeats
Here is a view of the polygonal
terrain from orbit:
And here is a closeup view from the
UA Phoenix Lander, which is situated in the martian arctic in
just such an ice-polygon region:
An image of the underside of the
Phoenix lander, where the landing thrusters have blown aside a
thin surface layer of dust to reveal solid ice.
Mars is both Earthlike and Moonlike