Early Exploration
1609 - 1965
Early Exploration
Nicolaus Copernicus
 Published De revolutionibus orbium coelestium (On the
Revolutions of the Celestial Spheres) in 1543
Early Exploration
Tycho Brahe
 Observations of Mars in 1583 showed Mars could move
closer to Earth than it did to the Sun; possible in a
heliocentric universe, but not geocentric.
Early Exploration
Ptolemaic System
Early Exploration
Tychonian System
Early Exploration
Johannes Kepler
 Assistant to Brahe; derives first two laws of planetary
motion in 1609. 1st law derived from Brahe’s
observations of Mars.
Early Exploration
 Though these early observations helped scientists
accurately describe the motion of Mars in the sky, nothing
about the planet itself was known.
Mars retrograde motion. Image Credit: Tunç Tezel
Early Exploration
 Beginning with Galileo, scientists were able to observe
Mars with a new tool, the telescope.
William Herschel’s 40ft telescope, 1789.
Percival Lowell at Lowell Observatory.
Early Exploration
Galileo Galilei observed Mars in 1610
and wrote: “…unless I am deceiving
myself, I believe that I have already
seen that it is not perfectly round.”
Early Exploration
Christiaan Huygens made the first (known)
sketch of Mars in 1659; determined a
rotational period for Mars:
“The Rotation of Mars, like that of the Earth,
seems to have a period of 24 hours.”
Early Exploration
Giovanni Cassini calculated a rotational period
of 24 hrs, 40 min; may have been first to report
the southern polar cap in 1666.
Early Exploration
French author Bernard le Bovier de Fontenelle
wrote about Mars in 1686:
“Mars has nothing curious that I know of; its
days are not quite an hour longer than ours
and its year’s the value of two of ours. It’s
smaller than the Earth, it sees the Sun a little
less large and bright than we see it; in sum,
Mars isn’t worth the trouble stopping there.”
Early Exploration
In 1783, William Herschel determined
Mars to have a diameter 0.55x Earth’s
and an obliquity of ~28°; noted the
south polar cap.
Early Exploration
Herschel also noted:
“I have often noticed occasional changes of
partial bright belts…and also a darkish one,
in a pretty high latitude…
Early Exploration
Herschel also noted:
“I have often noticed occasional changes of
partial bright belts…and also a darkish one,
in a pretty high latitude… And these
alterations we can hardly ascribe to any other
cause than the variable disposition of clouds
and vapors…”
Early Exploration
Herschel concluded the inhabitants of
Mars “probably enjoy a situation in many
respects similar to ours.”
Early Exploration
• Giovanni Schiaparelli popularized the straight
lines he called canali (can mean “channels” or
“canals”). He also used fiume or “river.”
• Started a new nomenclature for Martian
features.
Early Exploration
Map of Mars by Schiaparelli, 1877
Early Exploration
Asaph Hall of the US Naval Observatory
discovered the two moons of Mars in 1877.
Moons
Deimos – 15 km (9.3 miles)
Phobos – 26.8 km (16.7 miles)
Early Exploration
• Percival Lowell misinterpreted “canali” to mean canals
(artificial); mapped 437 “canals” in 917 sketches; took the
idea of artificial canals to the grave.
• Calculated an atmospheric pressure of 85 millibars (8.5%
of Earth’s)
Lowell’s Martian canals, ca. 1900
Early Exploration
Let’s look at some images…
Early Exploration
• What observations can you make?
• How would you interpret these
observations?
Early Exploration
Setting aside the argument of whether or not the canals were real, astronomers
knew with certainty that the surface of Mars changed - dark and light patterns did
not remain the same over time.
Mars Map by Eugène Michel Antoniadi, 1930
Early Exploration
In 1924, Edison Pettit and Seth B. Nicholson used a thermocouple
affixed to the 100 in. telescope at Mt. Wilson (CA) to determine surface
temperatures on Mars.
Pettit
Image Credit: Larry Webster, Mount Wilson
Observatory
Nicholson
Early Exploration
What did they find?
Early Exploration
What did they find?
Pettit, E. & Nicholson, S.B. (1924). Measurements of the radiation
from the planet Mars, Popular Astronomy, Vol. 32, p. 601. (Table 2 on
page 606)
Early Exploration
• What did they find?
~ 7° C at the equator
~ -68° C at the southern polar cap
• As telescopes improved, astronomers became confident that Mars
had a polar cap. The question remained, what was it made of?
- Water? Freezing temperature of 0° C
- CO2? Freezing temperature of -100° C
Early Exploration
In 1947, Gerard Kuiper made the 1st positive ID of CO2 in the
atmosphere of Mars.
Early Exploration
• In 1950, the best guess* for the composition of the Martian
atmosphere was:
- 98.5% N
- 1.2% Ar
- 0.25% CO2
- <0.1% O
*Estimates from Gérard de Vaucouleurs; also calculated an atmospheric pressure of
87 millibars (8.7% Earth’s).
Early Exploration
• In 1963*, the “probable composition of the Martian
atmosphere” was believed to be:
• 72% N2
• 25% CO2
• 2% Ar
• < 0.5% O2
• Trace amounts of H2O
*Estimates from NASA Technical Document NASA-TM-X-56223, 1963; presented at the
Symposium on Extraterrestrial Biology and Organic Chemistry, Warsaw, June 3-12, 1963.
Early Exploration
• Spinrad, Munch, & Kaplan in 1963 calculated:
• An average precipitable water amount of 14 micrometers
(Earth 2.5cm); MARS IS DRY
Early Exploration
• Spinrad, Munch, & Kaplan in 1963 calculated:
• An average precipitable water amount of 14 micrometers
(Earth 2.5cm); MARS IS DRY
• An atmospheric pressure of 25 millibars (2.5% Earth’s)
From Spinrad, Munch & Kaplan, 1963
Early Exploration
• What can you say we know about Mars at
this point? How certain are you?
• What questions would you ask about Mars?
• How would you attempt to answer these
questions?
• What are the ground-based telescope’s
limitations?
Early Exploration
“A third presence on Mars indicates a living world: vegetation. The
evidence is in the blue-green areas and the changes in their
appearance. Vegetation would present exactly the appearance
shown…. The seasonal change that sweeps over them is
metabolic; that is, it shows both growth and decay….”
- Earl C. Slipher, 1962
Image Credit: Lowell Observatory
Early Exploration
• Early exploration of Mars revealed it to be:
Early Exploration
• Early exploration of Mars revealed it to be:
• Cold; temperatures at freezing or well below freezing
• Dynamic, at least regarding patterns on the surface;
dust, vegetation, or both?
• Low atmospheric pressure; clouds
• Unsure about the atmospheric composition
• Arid
• Polar cap – What is it made of?
• No canals/intelligent life