In two years and 20 days, the United States will celebrate its semiquincentennial — or quarter millennial birthday — on the 250th anniversary of the adoption of the Declaration of Independence on July 4, 1776. From shore to shore, there will be grand celebrations, many for which planning is already underway. Today, however, exactly 90,560 Earth days later, is a much more obscure anniversary of this most famous day in American history. Pluto, the well-known former planet in the outer solar system, has completed one single revolution around the sun. In other words, one Pluto year has now passed so that Pluto’s location in the solar system is back to the same spot it was at on July 4, 1776, for the first time since then.
As of July 4, 1776, only five planets (excluding Earth) had been discovered, namely Mercury, Venus, Mars, Jupiter and Saturn. Pluto, approximately 1,400 miles in diameter (about half the width of the U.S.) and approximately 3.6 billion miles from the Sun, wasn’t discovered until 1930. Pluto was long classified as the ninth planet, and schoolchildren across the country and around the world were taught various acronyms to help them remember the correct order. In 2006, however, the International Astronomical Union reclassified Pluto from a planet to a dwarf planet after the discovery of many other Pluto-like objects in the Kuiper Belt. Pluto nevertheless continues its travel around the sun in the farthest reaches of the solar system and still enjoys widespread name recognition to this day.
Not only has Pluto been discovered, classified as a planet, and declassified as a planet during its most recent full 248 Earth year revolution, but much else has changed here on Earth. The U.S. has grown from the 13 original colonies (and states) to today’s 50 (plus Washington, D.C. and territories). The U.S. population has grown from approximately 250 million to over 330,000 million, and this time period has included the terms of all 46 presidents, periods of industrialization and globalization, and at least 12 recognized wars. From a global perspective, the world’s population has increased tenfold from approximately 800 million in 1776 to over 8 billion today. Empires were formed and fell, rulers were born and died, and all remaining frontiers on the planet were discovered and explored, at least on solid ground.
As to the natural world, much has also come and gone. The longest living mammal, the bowhead whale, is thought to be able to live over 200 years. Accordingly, it is likely that there is not a single mammal alive today that was around during the adoption of the Declaration of Independence. Although these are but a few of countless examples of how the U.S., the world, and human civilization have changed during Pluto’s most recent orbit, certain things remain constant. These include the values expressed in the preamble to the Declaration of Independence, specifically “that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.”
Pluto will complete its next revolution around the sun on May 25, 2272, another 90,560 Earth-days from today. Nobody knows for sure what the U.S. and the Earth will be like then, but the future is likely to include continued globalization and human migration, advances in medicine and longer human lifespans, human encroachment on Earth’s remaining wilderness, continued outer space exploration and technological developments such as artificial intelligence. Many challenges that affect humanity, as well as Earth’s natural world and its limited resources, are also certain to be presented to future generations. While no single person or generation will be able to assure what life will be like in 2272, it is not too early to start thinking about it. Here’s to the next 248 years.
Steven K. Hardy is a lawyer in Dallas, Texas, with interests in both history and astronomy.