Four Great Eras of Exploration (and #4 is Happening Now)

By Corey S. Powell | March 6, 2014 6:57 am

Last week’s discovery of 715 planets orbiting other stars was more than just a remarkable piece of astronomical detective work. It was also a bold confirmation that we have entered a new era of cosmic exploration. Sara Seager of MIT, one of the scientists leading the search for other Earths, beautifully expressed this sentiment to me in a recent interview: “For exoplanets, I see ourselves like the generation of Christopher Columbus. We are leaving a legacy in terms of us as a generation, and as a society.”

The multitude of worlds found by the Kepler space telescope. (Conceptual illustration by NASA.)

The multitude of worlds found by the Kepler space telescope. (Conceptual illustration by NASA.)

Often it is hard to recognize a revolution while you are right in the middle of it, but that is what I believe is happening right now. When future generations look back, as Seager suggests, I think they will recognize this time as the fourth great era of exploration, comparable to…well, let’s go back and look at the previous three great eras of exploration for context.

Era One: The discovery of boundless space. When Galileo Galilei turned his spyglass skyward in 1609, he witnessed a universe that is much messier and more complicated than anyone had realized. He observed spots on the sun and craters on the moon. He also famously delivered the death blow to the old Aristotelian idea that everything revolves around the Earth. Galileo saw that Venus has phases like the moon, something that is possible only if it orbits the sun and not the Earth. Equally significant, he observed four “stars” circling Jupiter (what we now know as the Galilean satellites: Io, Europa, Ganymede, and Callisto). Not only wasn’t Earth the center of the universe, but Earth was not even unique among the planets in having secondary bodies going around it.

A draft letter by Galileo contains, at bottom, some of his first notes on the discovery of four moons around Jupiter. (Credit: University of Michigan Special Collections Library)

A draft letter by Galileo contains, at bottom, some of his first notes on the discovery of four moons around Jupiter. (Credit: University of Michigan Special Collections Library)

If you are familiar with the history of astronomy you probably know the general outline of this. But Galileo had another,  deeper legacy. When he looked at the misty light of the Milky Way he resolved it into innumerable faint stars. In displacing Earth from the center of the universe, he set all in motion. Put the two together and Galileo finally and completely demolished another aspect of Aristotle’s cosmology: the idea that the universe was finite, tidy, and bounded, with the stars embedded in an outermost shell. Galileo’s discoveries ushered in the idea of boundless, perhaps infinite space. It created room for Isaac Newton’s theory of universal gravitation, and introduced the idea that astronomical exploration without limits.

Era Two: Bringing the heavens down to Earth. Everyone knows Galileo’s name. The second great upheaval was ushered in by two scientists who are decidedly less familiar: Robert Bunsen and Gustav Kirchoff. Today’s students recognize Bunsen’s name mainly from the Bunsen burner widely used in high school and university labs. That is an awfully modest memorial to a man who did so much to expand the range of the human intellect.

Together, Bunsen and Kirchoff established the principles of spectroscopy starting in the 1850s. They showed that each chemical element has a distinct fingerprint in the way it emits or absorbs light. Pass the light of a distant object through a prism, spread it out into a rainbow, look for a characteristic pattern of absorption lines, and you can tell what the object is made of. In 1835, the renowned French philosopher August Comte wrote that “all physical, chemical, physiological, and social researches, for which our powers fit us on our own earth, are out of the question in regard to the planets.” Less than 30 years later, Bunsen and Kirchoff proved him utterly wrong.

A detailed solar spectrum shows many dark lines--the chemical signature of elements in the sun's atmosphere. (Credit: AURA/NOAO)

A detailed solar spectrum shows many dark lines–the chemical signature of elements in the sun’s atmosphere. (Credit: AURA/NOAO)

Spectroscopy is a somewhat obscure tool, but there is nothing arcane about its importance. It proved that the rest of the universe is built from the same kinds of atoms as we are. It allowed astronomers to measure the composition of any bright object in space, whether here in our solar system or out at the edge of the visible universe. There was also an explosive corollary:  If an object is moving relative to us, that motion shifts the appearance of the lines in its spectrum. That shift makes it possible to deduce the rotations of stars, the gravitational pull of unseen planets, the movements of galaxies, even the expansion of the universe. Which brings us to:

Era Three: The discovery of the universe. Edwin Powell Hubble (no relation!) did not single-handedly discover the universe beyond our galaxy, but he sure did make the crucial breakthroughs. Up until the 1920s, nobody was sure that other galaxies existed. Astronomers knew about intriguing spirals and smears of light in the sky, and many speculated that those intriguing blurs were other galaxies like our own. But many others thought the “spiral nebulae” were gas clouds within the Milky Way, and that our galaxy was alone–that our galaxy and the universe were one and the same.

Edwin Hubble's original diagram establishing the expansion of the universe. (Credit: NASA)

Edwin Hubble’s original diagram establishing the expansion of the universe. (Credit: NASA)

Late in 1923, Hubble found a specific type of star, called a Cepheid variable, in what was then known as the Andromeda Nebula. The star’s pattern of variation allowed Hubble to derive its distance and prove that it, and the “nebula” around it, was far beyond the edge of the Milky Way. Overnight, the Andromeda Nebula became the Andromeda Galaxy, and our home galaxy became just one of a multitude. A scant 6 years later, Hubble measured the motions of those other galaxies and discovered that they were systematically moving away from us, with their speed directly proportional to their distance. This was the discovery of the expanding universe, which led to the idea of the Big Bang, galaxy evolution, dark energy, and all the other wild concepts of modern cosmology.

I still find it mind-boggling that less than a century ago nobody even knew whether other galaxies existed. The pace of astronomical discovery is truly shocking when you step back and look at it.

Era Four: The discovery of endless worlds. That brings us to the present era, and the discovery of planets around other stars. It is a different kind of breakthrough than the others. Smaller, in one sense, since it does not fundamentally shift the scale of our cosmic perception. But greater, in another sense, because it is the most personal of the four astronomical revolutions. If life exists anywhere else in the universe, it almost surely sits on the surface of a planet. Those are the safe havens in space; those are the places where complex chemistry can happen, where biology can take hold, where–in at least one instance–inert molecules can come together to create consciousness, intellect, and passion.

Just as Galileo brought us other stars and Hubble brought us other galaxies, people like Seager and Geoff Marcy and Bill Borucki are bringing us other worlds. And again, the pace of discovery is hard to fathom until you take a couple steps back. Until 1992, astronomers did not know of a single planet outside our solar system–not one. Every idea, every discussion, lived in the realm of speculation and science fiction. Now we have charts containing thousands of planets.

As has happened so many times before, scientists are finding that their imaginations paled in comparison to the creativity of Nature. The diversity of worlds out there is far richer than anyone envisioned. If we find alien life, it too may well turn out to be something entirely unexpected. Now at last we are securely on the path to finding out.

Follow me on Twitter: @coreyspowell

  • Uncle Al

    Nobody goes Columbus until the lightspeed limit of information and material transfer is finessed. This would violate causality. Humanity will do no more than window shop until it is clever. Cleverer.

    Greeks and Muslims both knew Earth is a ball. They also knew its size (e.g., Eratosthenes of Cyrene, ~240 BC; 75 Roman miles/meridian degree). Columbus was a closet Freemason. Sailing west was a quantitated risk. The Spanish crown won either way.

    • coreyspowell

      I would argue that detecting and studying new worlds from afar is still a very real form of exploration. Galileo did not visit the moons of Jupiter, Kirchoff did not visit the sun, and Hubble did not cruise to the Andromeda galaxy, yet each of them made huge advances to cosmic exploration as well.

      What Sara Seager is expressing is that Columbus discovered parts of the Earth that were previously unknown, and in so doing gave the Europeans a totally new perspective on their place in the world. Finding other planets–and eventually finding inhabited ones, I hope–is now similarly altering humanity’s perspective on our place in the universe.

      And far in the future…who knows? It may be possible to achieve the kinds of speeds that will reach other planetary systems within a human lifetime. There may even be physical processes that let us beat the speed of light without violating causality. I hold out hope, but I do not rest any part of my argument on such far-off dreams.

      • Uncle Al

        The Alcubierre drive and such – aside from reduction to practice, ah, challenges – are supercavitating torpedo analogues. Rules can be bent if there is no bridge to communicate the violation. By definition, one cannot navigate en route or know when to stop en route. That puts a lot of faith in the launch and the internal stopwatch. Bring marshmalllows, for the Unruh effect may be operative at superluminal launch.

  • Gary Childers

    If electrons can be entangled and rendered oblivious to time and space (Care to enforce speed limits without them?) then we have much more to learn. The drill is still observe, record, and finally make sense of it. I can hardly wait!

  • Vassilis Papadolias

    I’d prefer a more historical approach actually, relating to colonization… 1st era would in that sence be the ancient greek colonization of the Mediterranean. The 2nd era the european colonization of Africa, India Australia and America from 15th to 19th century and the 3rd era would be colonization of space…

    • coreyspowell

      That’s an interesting perspective, but very different than the one I’m talking about in this post. I’m focused on the intellectual side of exploration. That’s more relevant when talking about cosmic distances (since we barely know how to get humans to Mars, much less to the nearest exoplanet), and it also avoids ambiguous cultural perspectives. For instance–did the colonization of the Americas happen in the 16th century, or did it happen 15,000 years ago?

      • Vassilis Papadolias

        Hm,.in that sense why not put Aristotle and Aristarchos as the first stage of exploration and start with Galilei? I mean there is always an assumption somewhere, a pivoting idea. Und usually it is culture-centered.

        • coreyspowell

          Absolutely, I am making some specific rules to define the four eras. I’m talking about exploration that goes beyond the Earth; that is based on empirical evidence; and that goes beyond the unaided human senses. Note that all 4 of these advances are not culture specific. Galileo was the first in the world to observe the moons of Jupiter. Nobody knew about spectroscopy before the 1850s…and so on.

          I don’t mean to dismiss the incredible efforts of the pre-telescopic thinkers and their insights into the working of heaven & Earth. But once you go down that path, it becomes hard to decide where to draw the line. Do you go back to the Ancient Egyptian astronomers To Mesopotamian astronomers? To Stonehenge and other aligned megaliths? You see what I mean.

          • Vassilis Papadolias

            Well in that case including the arab astrologers who were using the astrolabe might be a good idea. In any case my point is that looking back to history we create a specific abstraction which talks more about ourselves rather than our ancestors. Galilei is praised for example for being a science hero against the church, whereas his motive to observe the sky was purely philosophic. Being a follower of the neoplatonic view of the world as much as kepler tried to prove that aristotle’s view of an physical centered and thus geocentric world was wrong. The center of the world had to be above earth because the origin of the world had to be Logos, or the world of ideas, the Sun. Unlike believed he only tried to prove his mystical beliefs being right, he didn’t start with observing and then hypothesizing like any descent scientist would do. He already had the belief (today we would say the preconception) and all he cared about was proving it right. Lucky for him, we got it all right.

          • coreyspowell

            By all means, the Islamic astrologers would fit in with the pre-telescopic thinkers, but not with the scheme in my post. And the relevant point is not Galieo’s philosophical preconceptions, but his skills as an observer and as an interpreter of his findings.

            In the annals of philosophy trumping observation, few things beat Aristotile’s notorious declaration that “Males have more teeth than females in the case of men, sheep, goats,
            and swine.” Apparently he never bothered to look into his wife’s mouth to check.

          • Vassilis Papadolias

            And yet he was considered the first actual empirical observer. This if not anything shows how later abstractions redefine actual history. But i don’t want to take anymore of your time. Thank you for explaining your thoughts in such detail..

  • David

    Awesome, you found some useless rocks billions of miles away. What a discovery!!!!!!

    • coreyspowell

      On a practical level: Every new stage of inquiry and exploration has ended up bringing major material improvements in the way we live (from ocean navigation to electricity to GPS and cell phones).

      On a philosophical level: Of course you could live your life without curiosity and without any interest regarding your place in the universe. But why would you want to?

      • David

        So how does this make our lives better? It doesn’t.

        • coreyspowell

          I think you missed my point. You could rewind and ask the same question about almost any earlier scientific discovery. What was the immediate utility of figuring out that Earth goes around the sun, or that electricity can be stored in a battery, or that DNA has a double helix structure? For that matter, did the discovery of the New World immediately improve the lives of people living in Europe?

          If you judge the world according to the immediate ways that things “make our lives better,” not much makes the list. Or you can look at things the other way around: Almost every improvement in the way we live has ultimately resulted from open, scientific inquiry into the workings of the world. And to my mind, the great discoveries about our place in the universe bring far more meaning and satisfaction than, say, a big-budget movie or video game.

  • bgrnathan

    HAVING THE RIGHT CONDITIONS AND RAW MATERIALS FOR LIFE doesn’t mean that life can originate by chance.

    Proteins can’t come into existence unless there’s life first! Miller, in his famous experiment in 1953, showed that individual amino acids (the building blocks of life) could come into existence by chance. But, it’s not enough just to have amino acids. The various amino acids that make-up life must link together in a precise sequence, just like the letters in a sentence, to form functioning protein molecules. If they’re not in the right sequence the protein molecules won’t work. It has never been shown that various amino acids can bind together into a sequence by chance to form protein molecules. Even the simplest cell is made up of many millions of various protein molecules.

    The probability of just an average size protein molecule arising by chance is 10 to the 65th power. Mathematicians have said any event in the universe with odds of 10 to 50th power or greater is impossible! The late great British scientist Sir Frederick Hoyle calculated that the the odds of even the simplest cell coming into existence by chance is 10 to the 40,000th power! How large is this? Consider that the total number of atoms in our universe is 10 to the 82 power.

    Also, what many don’t realize is that Miller had a laboratory apparatus that shielded and protected the individual amino acids the moment they were formed, otherwise the amino acids would have quickly disintegrated and been destroyed in the mix of random energy and forces involved in Miller’s experiment.

    There is no innate chemical tendency for the various amino acids to bond with one another in a sequence. Any one amino acid can just as easily bond with any other. The only reason at all for why the various amino acids bond with one another in a precise sequence in the cells of our bodies is because they’re directed to do so by an already existing sequence of molecules found in our genetic code.

    Of course, once you have a complete and living cell then the genetic code and biological machinery exist to direct the formation of more cells, but how could life or the cell have naturally originated when no directing code and mechanisms existed in nature? Read my Internet article: HOW FORENSIC SCIENCE REFUTES ATHEISM.

    A partially evolved cell would quickly disintegrate under the effects of random forces of the environment, especially without the protection of a complete and fully functioning cell membrane. A partially evolved cell cannot wait millions of years for chance to make it complete and living! In fact, it couldn’t have even reached the partially evolved state.

    Please read my popular Internet articles listed below:


    Visit my newest Internet site: THE SCIENCE SUPPORTING CREATION

    Babu G. Ranganathan*
    (B.A. theology/biology)


    * I have had the privilege of being recognized in the 24th edition of Marquis “Who’s Who In The East” for my writings on religion and science, and I have given successful lectures (with question and answer time afterwards) defending creation from science before evolutionist science faculty and students at various colleges and universities.

  • John Paily

    Two fact stand between us and
    knowing reality;
    1] Galileo, Newton and Einstein failed when they failed to observe their role in their work. The ball would not have gone to the top of the table unless Galileo lifted it up doing work proportional to the weight of the ball. The world would have been different had Newton observed the tree growing and the seed in the apple sprouting and Einstein had blown the spider instead of the Globe in his imagination to develop relativity theory. Life has inner space that transforms gravity into
    anti-gravity. This is conscious and intelligent field that has creative and
    sustaining potential. It is the field on which universe exist and it can be
    traced to a single being, single cell, single atom and single God Particle which carries maximum energy and can communicate through the inner space and recreates and restores everything to new order when it is endangered.

    2] They failed to perceive a principle and design governing the particle and whole system. They failed to perceive the picture of light and atom and differentiate them – the fallowing and extensions bring a new thinking that can put all developments in science in order in a sensible way


Out There

Notes from the far edge of space, astronomy, and physics.

About Corey S. Powell

Corey S. Powell is DISCOVER's Editor at Large and former Editor in Chief. Previously he has sat on the board of editors of Scientific American, taught science journalism at NYU, and been fired from NASA. Corey is the author of "20 Ways the World Could End," one of the first doomsday manuals, and "God in the Equation," an examination of the spiritual impulse in modern cosmology. He lives in Brooklyn, under nearly starless skies.


See More


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

Collapse bottom bar