When I was in grade school, I designed a crewed mission to Pluto and dubbed it Hercules, obviously taking a cue from the then recent Apollo program. The ship itself was armed with laser banks. Not sure what exactly I was expecting to run into out there, perhaps just Cold War paranoia. The crew was also top heavy in security personnel. As anyone who watches Star Trek can tell you, just like pitchers in baseball, you can’t have enough redshirts on a space mission. The mission was planned to go in the year 2002.
It’s really funny to see the ideas one can conjure when you do not have to worry about budgets, research, and politics. The people at NASA who do have to worry about that stuff are unable to send humans that far, but have pulled off a most excellent mission in New Horizons that will flyby Pluto with its closest approach on July 14th. An added bonus, with the advent of social media, we will get to see the images from this mission almost in real-time.
This particular mission has a personal tie to me in that it was launched on January 19, 2006, the very same week I started my first class teaching astronomy. Next fall, in my 10th year of teaching, I will finally be able to discuss the New Horizon’s images of Pluto rather as something to look forward to. An animation of New Horizon’s voyage to Pluto is below. You’ll note that New Horizons performed a flyby of Jupiter to receive a gravity boost towards Pluto.
The gravity boost from Jupiter in 2007 shortened the journey to Pluto by three years. The flyby of Jupiter provided a test run for New Horizon’s imaging equipment and the results were impressive. The video below shows New Horizon’s look at the rotation of Jupiter.
New Horizons also took this shot of a volcanic plume on Io, which is the most volcanically active body in the Solar System. This activity is generated by gravitational flexing of Io as it is stretched back and forth by Jupiter, Europa, and Ganymede. This is similar to the heat caused by stretching a putty ball back and forth.
The image above of Io was taken from 1.5 million miles away. While Pluto is only 60% the size of Io, New Horizons will approach much closer at 6,200 miles and should provide exceptional image quality.
A lot has happened to Pluto itself over the past decade. Not so much Pluto, but rather our perception of it. Of course, when New Horizons was first proposed in 2001, Pluto was still classified as a planet. It is now referred to as a dwarf planet. Over time, as memory of Pluto as a planet fades, I suspect this will eventually be changed to simply a Kuiper Belt object (KBO).
The reclassification was portrayed in the popular media as a demotion for Pluto. It really was not so much a demotion as it was an expansion of our understanding of the nature of Pluto and the Solar System. For those of us who went to grade school before the reclassification, we were introduced to the planets with a diagram such as this:
An updated version of this diagram looks like this:
The yellow line is the path of the New Horizons probe. The yellow dots? Those are Kuiper Belt objects of which Pluto is one of.
Pluto’s classification as a planet was shaky from the start. Pluto’s orbit is inclined much more than the other eight planets and its composition is unlike the four gas giants which occupy the outer Solar System. Questions about Pluto’s planet classification were raised only a few months after its discovery by Clyde Tombaugh of the Lowell Observatory, as this New York Times article from April of 1930 indicates.
However, Pluto’s size was thought to be much larger at the time than it actually is and that caused the planetary classification to stick. Gerard Kuiper himself, as late as 1950, calculated Pluto to be about the same size as Earth. In fact, it was this overestimate of Pluto’s size that caused Kuiper to predict the following year there would not be what we now call the Kuiper Belt. It’s a bit ironic that the Kuiper Belt is named after the astronomer who predicted its non-existence, as Kuiper felt Pluto would have cleared out that region of the Solar System during its formation.
Nonetheless, Kuiper had a distinguished career that included the discovery of Titan’s atmosphere, carbon dioxide in Mars’ atmosphere, and the Uranus satellite Miranda. Kuiper played a key role as mentor to Carl Sagan during the 1950’s as well. Unlike most astronomers at the time, Kuiper felt there was an abundance of planets outside the Solar System. In turn, this inspired Sagan to explore that along with the possibility of life beyond Earth. This was mentioned prominently during Ann Druyan’s remarks at the recent inauguration of the Carl Sagan Institute at Cornell University.
The Kuiper Belt is a region of the Solar System past the orbit of Neptune that is thought to contain thousands of small celestial bodies composed of water ice, methane, and ammonia. Short period comets originate from this region. An excellent overview on the Kuiper Belt can be found here.
The first Kuiper Belt object discovered besides Pluto came in 1992. Since then, some 1,300 Kuiper Belt objects have been observed. This, along with more precise measurements of Pluto’s mass, which have come in at 0.002% of Earth’s, have resulted in the reclassification of Pluto to its present dwarf-planet designation. Pluto is simply too small to be considered a planet and its placement in the Solar System puts it among other Kuiper Belt objects.
Does this reclassification affect Clyde Tombaugh’s legacy as the discoverer of Pluto? I think not. Consider this, Tombaugh discovered a Kuiper Belt object 62 years ahead of the next observation of another such object. Tombaugh also discovered Pluto six years before earning his bachelors degree at University of Kansas. Keep in mind, the discovery of Pluto would have been a suitable topic for a Ph.D thesis. Tombaugh’s legacy is quite safe. In fact, a portion of Tombaugh’s ashes are aboard the New Horizons probe and will flyby Pluto along with the spacecraft.
The flyby of Pluto next July may very well represent a once in a lifetime opportunity to observe Pluto this close. No other missions are in the proposal stage at this time and given the travel time to Pluto, it will be at the very least, 15-20 years before another mission arrives in that part of the Solar System. NASA has just released the first color image of Pluto and its moon Charon (below). I consider myself very fortunate to be able to witness the culmination of this 15 year effort .
*Image on top of post is the Pluto discovery plates. Credit: Lowell Observatory Archives.