Planet Pluto Discovered 93 Years Ago Today, February 18, 1930

 

On February 18, 1930, exactly 93 years ago today, 24-year-old Clyde Tombaugh discovered Planet Pluto while blinking between two photographic plates of the same part of the sky taken six days apart at the Lowell Observatory in Flagstaff, Arizona.

He found a tiny dot that moved against the background stars from one plate to the next and thus succeeded just over a year after arriving at Lowell Observatory to take up the search for a new outer solar system planet, begun many years earlier by observatory founder Percival Lowell.

Now close to 130 years old, the Lowell Observatory is today holding its annual “I Heart Pluto” celebration to commemorate the discovery. The 13-inch Lawrence Lowell telescope Tombaugh used to take the photographic plates, recently restored, still sits within its original dome and is viewed by visitors every day.

Discoveries are not always well understood at the time they are made. In Pluto’s case, the new planet was too small to be resolved into a disk, leading some scientists to speculate that it might be a moon of a not-yet discovered larger parent planet.

Eventually, telescopes became powerful enough to resolve Pluto into a disk, but even Hubble images taken during the 1990s were fuzzy. The real revelation of Pluto in all its glory happened in 2015, when the New Horizons spacecraft flew by that world, imaged its varied terrains, and returned data that is still being studied and analyzed today.

Tombaugh and his fellow astronomers in 1930 had no way of knowing that they had found the first of many small planets in what is now known as the solar system’s third zone. They certainly had no inkling that the newly discovered world was one of many solar system objects that has a subsurface ocean possibly capable of hosting microbial life.

With the recent renewed interest in UFOs, it is important to remember that as of today, we have not even determined whether any other place in our own solar system harbors life. What we have discovered is that small planets Pluto and Ceres, as well as various moons of the gas and ice giants, likely have oceans beneath their surfaces that could potentially host microbes. Among that growing list of worlds are Jupiter’s moons Europa, Ganymede, and Callisto; Saturn’s moons Enceladus, Titan, and possibly even Mimas; Neptune’s moon Triton, and possibly Pluto’s binary companion Charon.

Distant planets like Eris and Sedna could also potentially host such oceans, but we won’t know until we send probes to study them up close.

On February 18, 1930, Clyde Tombaugh had no way of knowing that he had not only unlocked a third zone of the solar system, but also discovered a new class of ocean worlds that could be the prime locations for life taking hold beyond the Earth.

While it is clear that any extraterrestrial life in our solar system is limited to microbes, finding evidence of such life on any world would be one of the most significant scientific discoveries in history, as it would confirm life got started on worlds other than Earth.

Tombaugh also could not have known that the world he discovered was not a dead rock, but a geologically active planet that appears to have an internal heat source. No one expected something like this so far from the Sun. Today, the discovery of Pluto’s complexity and activity raises the possibility that other, even more distant worlds, could also be active planets.

Our technology is not yet at the level of being able to discover Pluto-sized planets in other solar systems, but the ability to do so is likely just a matter of time. While his search was for a gas giant planet, Tombaugh discovered the first in a new subclass of planets, the dwarf or small planets, largely but not solely present in the outer solar system. It is reasonable to hypothesize that other solar systems could also have regions like this, with scattered small planets that might be hiding subsurface oceans.

Some in the astronomy community did not give Tombaugh sufficient credit for his discovery back in 1930. His name was not even mentioned in Lowell Observatory’s press release announcing the discovery. Some astronomers of the day even looked down on him because he was a 24-year-old with just a high school education, not an astronomy PhD.

Yet even here, Tombaugh set a new trend though it would not become a “thing” until many decades later. This trend is that of astronomical and planetary discoveries being made by ordinary citizens, amateur astronomers, and even kids, who don’t have PhDs, but are passionate about the universe. Internet and telescope technology have opened the discovery process to interested citizens around the world, who have discovered exoplanets, brown dwarfs, supernovae, etc.

In so many ways, Tombaugh was far ahead of his time. This is also true of his staunch support of Pluto’s planethood. Doubts about that began not in 2005 but in 1930, soon after its discovery. Yet Tombaugh never wavered in his position even though he did not live to see the New Horizons flyby. Today, we know that Pluto is actually part of a binary system with Charon, meaning it is not one but two planets! The system’s four smaller moons orbit not Pluto itself but the center of gravity between Pluto and Charon.

This is a day to celebrate Planet Pluto and its opening of new frontiers in solar system and planetary studies. I personally wish I could be at Lowell Observatory’s I Heart Pluto celebration and hope to to be there for the centennial in 2030.

This year’s celebration will conclude with two talks that will be livestreamed online. The first, “The Future of New Horizons,” will be presented by Alan Stern on Sunday, February 19, at 7 PM Mountain Standard Time, which is 9 PM Eastern time. The second, “New Horizons: NASA’s Mission to Pluto and the Kuiper Belt,” by New Horizons engineer and mission operations manager Alice Bowman, will be presented on Monday, February 20, at 7 PM Mountain time/9 pm Eastern time.

Happy Discovery Day, Planet Pluto!