Second Week of Class, Wherein I Get Distracted by a Picture of the Earth

Earthrise from the Lunar Reconnaissance Orbiter

I can't help it. I get to the end of another lecture, one I've done dozens of times over the years, and it dawns on me what an extraordinary time we live in. We were talking today about the origin of our planet, and the evidence that has accumulated regarding the formation of planets in general. I presented a PowerPoint that ended with the picture above. I dismissed the class, but left the picture on the screen as I gathered up my things. This picture amazes me, in much the same way as the earth rise picture from the Apollo Mission in 1968. From the perspective of teaching for more than thirty years, I stand in awe at the wonders revealed by our exploration of the cosmos.

When I started teaching, the origin of Earth and Solar System was reasonably well-understood, but direct visual evidence was somewhat lacking. Quantitative measurements and laboratory simulations shed a great deal of light on the process of planetary formation, but visual evidence provides an emotional charge to understanding. Emotion is not a prerequisite to learning, but it can inspire the desire to learn.

When I started teaching all those years ago, I had slides, images that were shone by a piece of technology called a "slide projector". They mostly described the origin of the Solar System with a series of paintings, depicting what we thought the process would have looked like. I didn't scan them all, but one of them looked like this:

Credit: William K. Hartmann, Planetary Science Institute, Tucson, Arizona

As the years passed, our ability to look farther into the Universe improved, and striking images appeared in the media. One by one, the paintings disappeared from my presentations, to be replaced by actual scenes of planetary formation taking place outside our own Solar System. The first was a fuzzy image of dust clouds around Beta Pictoris, a star about 65 light years away from Earth. It was the first time such clouds were imaged.

Then, in the early 1990s the Hubble Space Telescope transformed our view of the Universe. Spectacular images arrived, including those of the Orion Nebula, showing numerous planetary disks in the stellar nursery. More paintings disappeared from my class presentations.

Hubble image of planetary disks (proplyds)

Most recently, in 2014, it was the stunning image of a newly forming star with gaps in the dust cloud, showing where new planets were clearing space in the planetary disk. We aren't quite to the point of seeing the individual planets or their features, so the last painting in my presentation will probably remain, but who knows? The new James Webb space telescope is set to launch in 2018. It will represent 30 years of technological improvements over the Hubble Telescope, and it will be bigger. Who knows what wonders we will see next?

ALMA image of the young star HL Tau and its protoplanetary disk.  Credit: ALMA (NRAO/ESO/NAOJ); C. Brogan, B. Saxton (NRAO/AUI/NSF)

But we always come back in my lectures to the home planet, our Earth. It's our home and will be for the conceivable future. Images of the pale blue dot in space illustrate both our isolation, but also our hope. Knowing it's all we have, one can hope that our students and our society will chose to care for, rather than exploit our fragile planet. The most distant picture of our planet was photographed by the Voyager Spacecraft in 1990 after it left the Solar System for an unknown future in interstellar space. The Earth was a single pixel at that distance.

If you've never heard or read Carl Sagan's comments about the Pale Blue Dot, here they are. I certainly could never have said it better:

We succeeded in taking that picture, and, if you look at it, you see a dot. That's here. That's home. That's us. On it, everyone you ever heard of, every human being who ever lived, lived out their lives. The aggregate of all our joys and sufferings, thousands of confident religions, ideologies and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilizations, every king and peasant, every young couple in love, every hopeful child, every mother and father, every inventor and explorer, every teacher of morals, every corrupt politician, every superstar, every supreme leader, every saint and sinner in the history of our species, lived there – on a mote of dust, suspended in a sunbeam.

The Earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors so that in glory and in triumph they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of the dot on scarcely distinguishable inhabitants of some other corner of the dot. How frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds. Our posturings, our imagined self-importance, the delusion that we have some privileged position in the universe, are challenged by this point of pale light.

[...] To my mind, there is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly and compassionately with one another and to preserve and cherish that pale blue dot, the only home we've ever known.