Pluto Discovered 96 Years Ago Today

 

Today is International Pluto Day, marking the discovery of planet Pluto by Clyde Tombaugh at the Lowell Observatory 96 years ago, on February 18, 1930.

It is a day to celebrate all things Pluto, a planet whose understanding has eluded people for nearly a century.

When first discovered, Pluto’s planethood was questioned because telescopes of the time could not resolve it into a disk. Later, when it was revealed to be spherical, meaning rounded by its own gravity, many planetary scientists assumed it to be a dead world with no active geology or planetary processes.

The New Horizons flyby proved that wrong, revealing Pluto to be a surprisingly active world with complex processes, some of which are seen elsewhere in the solar system only on Earth and Mars.

Incorrect assumptions have often been made about Pluto because it is so small and so far away, making it a challenge to study and understand.

One of those incorrect assumptions, also a premature one, was the controversial decision by four percent of the IAU to label Pluto before the first reconnaissance of this world. Had the IAU waited for the New Horizons flyby, it would have become clear that Pluto, though small, has the same geology and processes seen on larger planets.

While Pluto was discovered in 1930, one could legitimately say people have been “discovering” its true nature for close to 100 years now, as Pluto continues to surprise us.

At last summer’s conference, “Progress in Understanding the Pluto System: Ten Years After Flyby,” possible next steps in the discovery of Pluto’s nature, namely hypothetical orbiter missions, were presented and discussed. As of now, there are no formal plans for any of these missions, but they are still worth being given serious consideration.

Planetary scientist Carly Howett, in her presentation titled, “Persephone: A Pluto System Orbiter and Kuiper Belt Explorer,” outlined a NASA-funded concept study involving returning to the Pluto system with an orbiter.

Orbiters are generally the next step in planetary exploration after the first reconnaissance of a world in a flyby, like that New Horizons did at Pluto in 2015.

The goal of the Persephone mission would be understanding Pluto’s composition, including its possible subsurface ocean, determining how Pluto’s surfaces and atmosphere evolved, and studying the diversity of the Kuiper Belt.

According to the proposal, the spacecraft would orbit Pluto for 1.3 years, then leave on an extended mission to explore the Kuiper Belt.

The proposal recommends a payload of 11 science instruments and notes that ice-penetrating radar would have to be powered by a radioisotope thermoelectric generator (RTG), the nuclear battery that powers New Horizons.

The spacecraft would conduct high and low flybys of Pluto, use Charon to change its orbit, and image all of Pluto at high resolution.

Drawbacks include the $3 billion cost, excluding launch vehicles, and the fact that travel time from Earth to Pluto would take 27.3 years.

Another proposal, “The Gold Standard: A Combined Pluto Orbiter and KBO Explorer Mission” was presented by Alan Stern. This spacecraft would be powered by an electric propulsion system using RTGs but have a smaller payload than Persephone.

The spacecraft would orbit Pluto for two years, then go on to visit other KBOs.

Stern noted that braking the spacecraft to enter Pluto orbit would double the travel time to the planetary system.

Including launch vehicles, this mission would cost $2.7 billion. Using three RTGs, existing launch systems could launch this spacecraft with current technology.

Returning to Pluto is a worthwhile endeavor for many reasons. Pluto joins a growing number of ocean worlds like Europa and Enceladus, which could potentially host microbial life in their subsurface oceans.

Embarking on such a mission would also give humanity another chance to study the Kuiper Belt in situ rather than from a great distance.

Discovery is an ongoing process not limited to one person or one time period. When Clyde Tombaugh first found Pluto, no one really understood what it was. Today, New Horizons has given us more knowledge and understanding of this small world than ever, but that is only a beginning.

We do know that Pluto is both a small planet and a Kuiper Belt Object. Neither of these categories precludes the other. The first tells us what it is while the second tells us where it is.

One legacy of Tombaugh’s find is not just that there are more planets out there than previously thought, but there are more types of planets out there than we recognize, even today.

Exploring the frontiers of our solar system is just a first step in looking even further beyond to the amazing variety of worlds and phenomena waiting to be discovered.