Planet Pluto Discovered 90 Years Ago Today

Today, February 18, 2020, marks the 90^th anniversary of Pluto’s discovery by 24-year-old Clyde Tombaugh at the Lowell Observatory in 1930. The little planet that could has now been a part of our science, history, and culture for nine decades!

The Lowell Observatory is hosting an “I Heart Pluto” event complete with talks by leading planetary scientists, including Alan Stern; Charon discoverer James Christy; astronomer Larry Wasserman, Lowell astronomer Will Grundy, Lowell historian Kevin Schindler, and Tombaugh’s son Alden Tombaugh.

Pluto-themed art is on display for the event, and participants are being treated to tours of the renovated telescope, known as an astrograph, that Tombaugh used to take the photographic plates of the sky from which he discovered Pluto. Attendees also have the opportunity to see the blink comparator Tombaugh used to “blink” or move back and forth between two pictures of the same part of the sky taken several days apart to search for something that moved against the background stars.

On February 18, 1930, 24-year-old Tombaugh found that tiny dot that moved against the same field of stars taken on January 23 and January 29 of that year.

To commemorate the occasion, Mother Road Brewing Company, together with Lowell astronomers, has created a special “Pluto Porter” brew. Celebrants will dine today at Flagstaff’s Karma Sushi Bar and Grill, which was The Black Cat Café in 1930, where Clyde Tombaugh dined on the afternoon of the day he found Pluto.

Karma Sushi Bar and Grill has even created a special “Pluto Roll” for the occasion.

This time around, Tombaugh is getting far more recognition and accolades than he did upon making his discovery. Back in 1930, the Lowell Observatory credited the late Percival Lowell, founder of the observatory, who had died in 1916 after devoting his life to searching for a planet beyond Neptune. Tombaugh’s name was not even mentioned in a circular released by the Observatory announcing the discovery. Instead, he was referred to as a “junior astronomer.”

Personally, I deeply regret not being able to attend this Pluto-lovers’ celebration at the Lowell Observatory, much as I regret never having met Clyde Tombaugh.

If he were here, Tombaugh would have a lot to celebrate. Over the past five years, and especially within the last year, consensus among both scientists and members of the public that Pluto is a planet and that the IAU got it wrong in 2006 has been steadily growing. Even the media has picked up on this, with some coverage acknowledging the many problems inherent in the 2006 vote by just four percent of the IAU’s members.

What has played the largest role in turning the tide in favor of Pluto’s planethood is without question the New Horizons flyby data. One simply has to look at the varied terrains on Pluto’s surface to see what is obviously a planet. Before the flyby, many scientists expected Pluto to be a dead rock. Instead, the spacecraft and its science instruments revealed a geologically active world with weather, a hazy atmosphere, interaction between atmosphere and surface, floating glaciers, windswept dunes, water ice mountains, cryovolcanism, and very likely a subsurface ocean.

The latter adds Pluto to a growing list of ocean worlds that could potentially host microbial life. Solar system worlds known or suspected to harbor subsurface oceans include Ceres, Jupiter’s moon Europa, Saturn’s moons Titan and Enceladus, Neptune’s moon Triton, and now Pluto.

From the time of its discovery until today, Pluto has had a hold on people, has fascinated so many to the point that both scientists and journalists are often puzzled. What is it about this world that is so compelling? Those supporters who claimed that children who learn an eight-planet solar system will not share this excitement over Pluto have largely been wrong. Children as young as three, four, and five have gotten media coverage for rejecting the notion that Pluto is not a planet! Many school age children refuse to see Pluto as anything but a planet.

Continued opposition to the IAU demotion is not limited to children. More and more scientists are gradually coming on board the Pluto-is-a-planet train. After a debate last April between Alan Stern and Ron Ekers of the IAU, audience members voted overwhelmingly in favor of Pluto’s planet status.

Just last week, an article was published in a North Jersey newspaper about the 90^th anniversary of Pluto’s discovery, in which an astronomer who gave a talk about Pluto last April was interviewed. He reported that after three people approached him following his talk and made the case for Pluto’s planet status, he spent a lot of time considering their points and finally came to agree with them. While he doesn’t mention any names, I was at that event with a friend, and it is clear that two of those three people were my friend and me!

In 2015, as the Pluto flyby approached, I had fears that even though New Horizons’ findings would excite and fascinate people, they would not be enough to change people’s minds. What if the reactions of scientists, reporters, and members of the public were, yes Pluto is fascinating and beautiful, but it is still not a planet? Some did react that way, but over time, the New Horizons data and images are working their magic.

Just this month, a paper by planetary scientist and astrophysicst Tanguy Bertrand of the NASA Ames Research Center was published in the Journal of Geophysical Research: Planets noting that Pluto’s iconic heart feature, which definitely made people fall in love with the small planet, actually behaves like a “beating heart” in controlling Pluto’s winds and possibly even shaping its surface features.

Pluto has weather, and understanding that weather, which is based on a hydrologic cycle involving nitrogen, could actually help scientists better understand Earth’s atmosphere, Bertrand stated. And it has geological processes seen elsewhere in the solar system only on Earth and Mars! Alan Stern once described Pluto as the most Earth-like solar system planet other than Earth itself!

In 90 years, we have gone from a tiny dot that could not be resolved into a disk by the world’s largest telescopes to a gorgeous planet, complete with a beating heart! If only Tombaugh could have seen and known the full nature of his discovery!

Every day, that discovery is defying the IAU and mainstream media in revealing itself as a planet. As New Horizons planetary scientist Cathy Olkin noted, “I naturally refer to Pluto as a planet because that seems like the right moniker. It has an atmosphere; it has interesting geology; it orbits the sun; it has moons. 'Planet' just seems right to me.”

Let’s raise a toast to celebrate the discovery of this iconic, unforgettable planet and 90 years of it inspiring people of all ages, backgrounds, and walks of life. And then, let’s get to work on sending an orbiter to unravel even more of Pluto and its system’s mysteries.