Early Exploration1609 - 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

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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.

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.

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.”

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.”

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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.”

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

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.

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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)

Early Exploration

Lowell’s Martian canals, ca. 1900

Early Exploration

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.

Early Exploration

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

Early Exploration

• 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.

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

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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

Early Exploration

*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

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)

Early Exploration

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?

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 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

Early Exploration