An Age of Wonders

We live in an unprecedented age of wonders. When Merck was born, the only way to gather data about the planets was remotely, and at wavelengths of the electro-magnetic spectrum that could penetrate Earth's atmosphere. Today we have access to:

The purpose of this lecture is to outline:

Major information sources:

Tycho Brahe at his mural quadrant from Wikipedia.
Naked-eye observations of motion: For all but the last 400 years, the only way to observe the planets. Practiced rigorously by many ancient civilizations. Reached its zenith with the accurate measurements by Tycho Brahe (right - 1546 - 1601) that enabled subsequent researchers like Johannes Kepler to formulate the laws of orbital mechanics (1609).

Of course, these observations said little about the nature of Solar System objects. They were mostly good for describing their locations and motion.

Replica of Galileo's telescope from Write Science.
Visible-light telescopy: Starting in 1609, telescopic observations added two new classes of information:

Enduring discoveries included:

And perhaps coming soon:

Such information could be frustratingly vague. Around the turn of the twentieth century, debate raged over the reality and origin of Martian "canals," linear features that might be natural or, as advocated by the astronomer Percival Lowell, the product of an advanced civilization.

Sir William Herschel from Cool Cosmos.
Spectroscopy: Since antiquity, prisms were long known to break white light into a spectrum of colors. In 1800, Sir William Herschel discovered that the spectrum also included light that the eye could not see - infrared radiation. Soon, the full electromagnetic spectrum was revealed. In the ensuing early years of the 19th century, astronomers realized that spectra - the varying intensities of light at different wave lengths (both visible and not) contained useful information about: that could be studied by passing light through a prism. Thus, it became possible to describe these attributes without having a physical sample.

Replica of Karl Jansky's dipole array - 1931 from Wikipedia.
Radio astronomy: Alas, Earth's atmosphere is opaque to most wavelengths of the electro-magnetic spectrum other than visible light. One exception is radio, which penetrates both Earth's atmosphere and clouds of interstellar gas and dust. Karl Jansky's dipole array, the first radio telescope began operating in 1931. During the mid-twentieth century, radio astronomy began to provide information on the temperature and magnetic fields of the giant planets, especially Jupiter, and revealed unseen processes in other celestial bodies.

The far side of the Moon seen for the first time by Luna 3 - 1959
from NASA.

The space age:

Robot spacecraft fly-by: Beginning with images of the moon's far side from Luna 3 (USSR) in 1959 (right), robot spacecraft began returning close-range data from other planetary bodies. The volume of planetary information they have revealed greatly outclasses previous remote-sensing efforts. Often, they have quickly cleared up long standing debates while raising new questions. Mariner 4's (1965) ground breaking images of a cratered, moon-like Mars, for instance, quickly silenced the debate about Martian canals. As of July 17, 2015, all of the traditional planets of the Solar System and their major moons have been visited by fly-by or orbital missions.

Lunar orbiter image - 1967 Wikipedia.
Orbiters: Spacecraft began studying planetary bodies from orbit with the NASA Lunar Orbiter series of 1967. Within five years, robot spacecraft were orbiting Mars (1971) and Venus (1983). Orbiters are technically more difficult than fly-by or impactor missions because they must carry and successfully use extra engines and fuel to execute precise maneuvers to place them in orbit. To date, spacecraft have surveyed the following worlds from orbit:

Mars in visible and infrared
from Magnus Galfalk.
Orbiting observatories: When it became possible to orbit telescopes above the atmosphere, it became possible to view the heavens in wavelengths that don't make it to Earth's surface, allowing the description of the planets in infrared (E.G. Mars, right) and ultraviolet light.

Luna 9 - 1966 from NASA.
Landers and rovers: In 1966, Luna 9 (USSR - right) made the first soft landing on another planetary body - the moon. It was followed by a volley of NASA and Soviet landers of the Luna and Surveyor series, and, in 1970, was followed by the deployment of the Lunokhod 1 rover. At this point, proper on the spot geologic data on other planetary bodies became available. The first images from the surface of another planet was a single image transmitted from Venera 9 (USSR) in 1975. To date, have been visited by landers or rovers designed to return data from the surface.

Neil Armstrong on the Moon - Apollo 11 - 1969 from Wikipedia.
  • Sample return missions: In 1969, Apollo 11 landed human astronauts on the moon, whose primary scientific mission was the return of 22 kg of lunar material to Earth for study. In 1970, the somewhat less expensive robotic Luna 16 (USSR) landed on the moon, collected samples of lunar material (0.101 kg), and returned them to Earth in a sample return module. For the first time, geologists had samples of another planetary body whose exact origin was absolutely known.

    But sample-return missions are diabolically complex and expensive - a large part of the lander's mass consists of a return vehicle that must launch and return to Earth. Only three objects have been sampled in this way:

    Today, robotic exploration of the solar system, including the deployment of orbiters, landers, and a few sample return missions is ongoing. Indeed, the miniaturization of electronic components and increasing power of computers makes it possible, relatively inexpensively, to send robot probes to the planets that would have been unimaginably powerful to the pioneers of the 1960s. Recent or ongoing missions to explore the Solar System include the following:

    The Players - Active space agencies with the means to explore the planets:

    Alas, there are more milestones in planetary exploration than we can address in one lecture. GEOL212 will make frequent reference to the following milestones:

    Current Frontiers in Planetary Exploration

    The Moon

    Chang'e-3 mission's Yutu rover from NASA.

    A host of recent missions including:


    Curiosity in front of Mt. Sharp from

    Mars Science Laboratory: The powerful next-generation NASA Mars rover, Curiosity, landed in Gale Crater on 8/6/12. The size of a small car and powered by an internal nuclear source, it is faster and expected to travel farther than any previous rover.

    Opportunity at Meridiani from KCRW.

    Mars Exploration Rovers: Two NASA rovers, Spirit and Opportunity, have functioned since 2004. Opportunity arrived at the 14 mi. wide Endeavor Crater in August 2011 and is functioning well. Spirit ceased functioning in 2010.

    MAVEN from NASA.
    MAVEN (Mars Atmospheric And Volitile EvolutioN): NASA's next Mars orbiter mission, arrived in September 2014, studies the interaction of Mars' upper atmosphere and interplanetary space.

    Mars InSight from Wikipedia.
    Mars InSight The Mars geophysics probe. On its way to a Nov. 26, 2018 arrival. A lander featuring a drill with which to bore over a meter beneath the surface in order to measure seismic waves and heat flow.

    The Asteroids and Comets

    Asteroid Ryugu Wikipedia.

    Hayabusa 2: JAXA's (Japan) ambitious sample return mission to the small near-Earth asteroid Ryugu. Hayabusa 2 entered orbit around Ryugu in July, 2018. It aims to deploy small rovers to the surface, capture a surface sample, and return it to Earth in 2020.

    Vesta as seen by Dawn. Click image for Ceres.

    Dawn: NASA's mission to study the asteroids/dwarf planets? Vesta (right) and Ceres. Groundbreaking study of a class of objects that has never been observed up close, and demonstration of ion propulsion systems. Entered Vesta orbit in July 2011, left Vesta orbit in July 2012, and entered Ceres orbit in February 2015.

    OSIRIS-REx at Asteroid Bennu NASA.

    OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer): NASA sample return mission to near-Earth Asteroid Bennu. Launched in 2016, planned return of samples, 2023.

    The Outer Solar System

    Juno from CNN.

    Juno: NASA Jupiter orbiter to probe chemistry and physics of Jupiter's interior. Launched in August 2011 and arrived July 4, 2016.

    Voyager trajectories from Wikipedia.

    Voyager 1 and 2: NASA's grand tour of the outer solar system, launched in 1977 (Merck was college senior and the Radio Shack TRS 80 personal computer offered 4 KB of RAM) are still returning useful data. Voyager I encountered Jupiter in 1979 and Saturn in 1980. In September 2013 NASA announced that Voyager 1 had finally crossed the heliopause, the point at which the solar wind gives way to the galactic wind of the interstellar medium. Voyager 2 encountered Jupiter in 1979, Saturn in 1981, Uranus in 1986, and Neptune in 1989. It is the only spacecraft to have visited these outer planets. Voyager 2 continues to function despite some technical glitches. In principle, the Voygers could continue to return data until their power source runs out in 2025.

    Pluto as seen by New Horizons from NASA.
    Trans-Neptunian Objects

    New Horizons: NASA's outer Solar System probe flew through the Pluto system in 2015 and is now on its way to a 2019 encounter with the farther Kuiper Belt object (486958) 2014 MU69.

    The Future - Funded

    Europa Clipper Wikipedia.

    Europa Clipper: NASA's concept for a Jupiter orbiter that would perform a series of fly-bys of Europa, assessing surface composition and topography, and thickness of the icy crust. Launch date in between 2022 and 2025.

    JUICE Wikipedia.

    JUpiter ICy moons Explorer (JUICE): ESA's concept for a Jupiter orbiter that would perform a series of fly-bys of Europa, Ganymede, and Callisto, eventually settling into orbit around Ganymede. Launch date in 2022, reaching Jupiter system in 2030 and settling into Ganymede orbit in 2033.

    The Future - imagined

    Titan atmospheric probe from NASA.

    Titan Saturn System Explorer: A three-part orbiter, atmospheric balloon "rover" and lander to unlock the mysteries of Titan's physical geology and atmospheric and lake chemistry. Video.

    Venus landerfrom NASA-JPL.

    Venus Flagship: An orbiter, atmospheric balloons, and landers in a coordinated campaign against the most hostile planetary environment in the solar system.

    Neptune mission from SpaceToday.

    The Ice Giants: And for future generations, orbiter missions to the Uranus and Neptune systems on the scale of Cassini and Galileo. (Sigh.)

    Key concepts and vocabulary. Understand these or you're toast:

  • Tycho Brahe (1546 - 1601)
  • Galileo Galilei (1564 - 1642)
  • Sir William Herschel (1738 - 1822)
  • Percival Lowell

  • Information sources:

  • Active space agencies:
  • Important robot spacecraft missions: