13: Aiming at Pluto’s Heart — Part 1

New Horizons — $700 Million

Abhinav Yadav
4 min readOct 21, 2023
Pluto in true color as seen by New Horizons spacecraft (credit)

This is a story about an elusive Planet ‘X’, that shot to fame overnight and became the ‘god of the underworld’, only to then be demoted to dwarf-status. But it turned out to have a planet-sized heart. It’s also a story about human perseverance, ingenuity and curiosity about the unknown. Both these stories play out through the billion mile journey of an unlikely hero that continues to be our workhorse.

Discovery

After the discovery of Uranus and Neptune, Percival Lowell speculated the existence of a 9th planet. He founded the Lowell Observatory and began searching the night sky for ‘Planet X’. Unfortunately, he could not find it before his death in 1916. His widow, Constance Lowell, had to fight a 10-year legal battle over the observatory before the search could begin again.

Clyde Tombaugh, in Kansas & the Pluto discovery plates (credit)

Pluto was eventually discovered by a 23 year old astronomer named Clyde Tombaugh in 1930 at the Lowell observatory. He used a blink comparator to meticulously compare changes in images of the night sky. Nearer objects, like those within our solar system, appear to move over time compared to distant stars that appear to be fixed. The name Pluto, submitted by Venetia Burney, was chosen because among other things ‘PL’ were the initials of Percival Lowell.

The 9th planet’s discovery caught the public’s attention. Walt Disney named Mickey Mouse’s canine companion Pluto (as did we with our family dog). Then, in keeping with traditions, a newly discovered element was named Plutonium after Pluto, like uranium was named after Uranus, and neptunium after Neptune.

What makes Pluto interesting?

The Kuiper belt is a doughnut-shaped ring in the outer Solar System, extending beyond Neptune’s orbit. It’s similar to the asteroid belt, which exists between Mars and Jupiter’s orbit, but is more massive and much further out. It’s also composed of mostly icy objects and is home to many dwarf-planets like Pluto.

Kuiper Belt with Sun and the four gas giants (Credit).

Like other Kuiper Belt Objects (KBOs), Pluto is also an early remnant of our Solar System’s creation. A 4.5 billion year old relic that is preserved perfectly in the cold storage of space. Planetary scientists understood that Pluto could tell us a lot about how our world was created!

With a distance of about 3 billion miles from Earth, a mission to Pluto was going to require a lot of patience and perseverance. But as Voyager missions have shown us, it’s a frontier of science.

Unknowns

Computer-generated rotating image of Pluto based on observations by the Hubble. (NASA)

Being so dim compared to the background starlight means that even our most powerful telescopes, including the Hubble, could only give us a fuzzy image. We expected it to be an icy world, but could only guess about any geological or chemical activity on it.

Animation of Pluto’s orbit from 1850 to 2097 with Sun, Saturn, Uranus, Neptune and then Pluto. Credit

We knew that like other trans-Neptune objects, Pluto’s orbit is eccentric. For one its moderately inclined and elliptical. It’s also in a 2:3 orbital resonance with Neptune, which means that Pluto completes two orbits in the time it takes Neptune to complete three. In fact, its eccentric orbit brings Pluto closer to the Sun than Neptune. It also takes Pluto 248 years to complete one orbit around the sun. Which means Pluto has not completed one orbit since its discovery.

An oblique view of the Pluto–Charon system showing that Pluto orbits a point outside itself. The two bodies are mutually tidally locked (credit)

We also knew it had a moon named Charon, which has mass sufficient to cause the barycenter of the Pluto–Charon system to be outside of Pluto. Beyond that, we didn’t know what other natural satellites or rings might be around Pluto.

Purse

Of all the obstacles and uncertainty facing a mission to Pluto, perhaps getting it funded was the biggest one. With the successes of Voyager missions, there was more scientific interest in exploring four gas giants and their moons in closer detail.

So for various reasons, no missions to Pluto materialized. Not to give up, Alan Stern & team eventually lobbied the Planetary Science Decadal Survey; a prioritized “wish list”, compiled by the National Research Council, that reflects the priorities of the scientific community. In the 2003–2013 decadal survey, New Horizons mission topped that list and removed any remaining doubts.

These delays in approval put immense pressure on teams developing the spacecraft. It also reduced our chance of taking advantage of Planetary alignment to shorten spacecraft journey time. This meant we almost missed our once-in-lifetime opportunity to study & marvel at this amazing world!

We’ll dive deeper into those stories next. To be continued…

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Abhinav Yadav

Engineer. Optimist. Top Writer in Space 🚀 🔭🌌