In 1993 the astronomers Carolyn and Gene Shoemaker and David Levy discovered the fragments of a comet. The comet, thereafter christened comet Shoemaker-Levy 9, had been torn apart by Jupiter’s gravitational field, and it was calculated that its approximately 21 fragments, the largest of which was half a mile wide, were headed on a collision course with the planet.
In the year 1994, between July 16 and July 22, astronomers pointed every available piece of technology at Jupiter and recorded in awe as multiple titanic explosions, each with the force of hundreds of times the nuclear arsenal of the world, generated colossal fireballs and plumes of smoke that rose nearly two thousand miles over the Jovian clouds and heated the atmosphere to temperatures of tens of thousands of degrees Fahrenheit. The explosions left dark spots on the surface of the planet the size of the Earth which would fade away over several months and provide astronomers with important information about the nature of Jupiter’s atmosphere. The event and its aftermath are described in the video below.
This event and other considerations led to the creation of the Planetary Defense Coordination Office which has as a goal to identify and track potentially hazardous objects that may come close to Earth’s orbit.
As another year comes to a close during which we have again experienced the joys and the nightmares of who/what we are as a species, it is apt to remember the vision of the Pale Blue Dot.
In 1990 NASA instructed the Voyager 1 space probe, then 3.7 billion miles away from Earth, to take a picture of our world. The picture shows our planet as a minute speck (arrow) in the middle of one of several bands caused by the interaction of sunlight with the camera.
The late astronomer Carl Sagan used this picture and its title "Pale Blue Dot" to write an eponymous book in which he put forward one of the greatest calls to reason that have ever been written. It takes an astronomer to look at things from the outside, and remind us of how petty and insignificant our quarrels are, and how tenuous our foothold in the universe is. Below you can see a video and /or read the passage from the book.
From this distant vantage point, the Earth might not seem of any particular interest. But for us, it's different. Consider again that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, 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 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 this pixel on the scarcely distinguishable inhabitants of some other corner. 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. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity – in all this vastness – there is no hint that help will come from elsewhere to save us from ourselves. The Earth is the only world known, so far, to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment, the Earth is where we make our stand. It has been said that astronomy is a humbling and character-building experience. 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 with one another and to preserve and cherish the pale blue dot, the only home we've ever known.
Carl Sagan (1934-1996)