Early Exploration

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 st 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.” Early Exploration

Giovanni Cassini calculated a rotational period of 24 hrs, 40 min; may have been first to report the southern polar cap in 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.

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…

Early Exploration 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. Early Exploration Image Credit: Larry Webster, Mount Wilson Observatory Nicholson Pettit

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 (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 - CO 2 ? Freezing temperature of -100° C

In 1947, Gerard Kuiper made the 1 st positive ID of CO 2 in the atmosphere of Mars. Early Exploration

In 1950, the best guess* for the composition of the Martian atmosphere was: % N - 1.2% Ar % CO 2 - <0.1% O Early Exploration *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% N 2 25% CO 2 2% Ar < 0.5% O 2 Trace amounts of H 2 O 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

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 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 Early Exploration