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Early Exploration1609 - 1965
Early Exploration
Nicolaus Copernicus Published De revolutionibus orbium coelestium (On the
Revolutions of the Celestial Spheres) in 1543
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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.
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Ptolemaic System
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Tychonian System
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Johannes KeplerAssistant to Brahe; derives first two laws of planetary
motion in 1609. 1st law derived from Brahe’s observations of Mars.
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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
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Beginning with Galileo, scientists were able to observe Mars with a new tool, the telescope.
Percival Lowell at Lowell Observatory.William Herschel’s 40ft telescope, 1789.
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.”
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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.”
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Giovanni Cassini calculated a rotational period of 24 hrs, 40 min; may have been first to report the southern polar cap in 1666.
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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.”
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In 1783, William Herschel determined Mars to have a diameter 0.55x Earth’s and an obliquity of ~28°; noted the south polar cap.
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Herschel also noted: “I have often noticed occasional changes of partial bright belts…and also a darkish one, in a pretty high latitude…
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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…”
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Herschel concluded the inhabitants of Mars “probably enjoy a situation in many respects similar to ours.”
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• 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.
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Map of Mars by Schiaparelli, 1877
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Asaph Hall of the US Naval Observatory discovered the two moons of Mars in 1877.
Deimos – 15 km (9.3 miles)
Phobos – 26.8 km (16.7 miles)
Moons
• 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)
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Lowell’s Martian canals, ca. 1900
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Let’s look at some images…
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• What observations can you make?
• How would you interpret these observations?
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.
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Mars Map by Eugène Michel Antoniadi, 1930
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.
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Image Credit: Larry Webster, Mount Wilson Observatory
NicholsonPettit
What did they find?
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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)
• What did they find?
~ 7° C at the equator
~ -68° C at the southern polar cap
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• 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
In 1947, Gerard Kuiper made the 1st positive ID of CO2 in the atmosphere of Mars.
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• 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
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*Estimates from Gérard de Vaucouleurs; also calculated an atmospheric pressure of 87 millibars (8.7% Earth’s).
• 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
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*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.
• Spinrad, Munch, & Kaplan in 1963 calculated:
• An average precipitable water amount of 14 micrometers (Earth 2.5cm); MARS IS DRY
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• 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)
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From Spinrad, Munch & Kaplan, 1963
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• 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?
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“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 of Mars revealed it to be:
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• 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
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