New Horizons Spacecraft to Encounter Pluto

June 2015  :  Dave Huestis

See most recent Pluto encountere images here:
http://pluto.jhuapl.edu/soc/Pluto-Encounter/

Pluto as seen from New Horizons a few hours before closest approach.

Basic astronomical knowledge seems to be lacking among the general population these days. However it has been my experience that almost everyone knows that Pluto, an icy world out in the depths of our solar system, was kicked out of the planet club. The International Astronomical Union (IAU) that governs such things decided to modify the definition for a planet, and Pluto no longer qualified as one. A new term, dwarf planet, was introduced. This reclassification became official on August 24, 2006.

Interestingly enough, just seven months prior, on January 19, NASA launched the New Horizons spacecraft to explore the planet Pluto and its five known moons. Pluto has an eccentric orbit that varies from 2.7 billion miles out to 4.6 billion miles from the Sun, so it is understandable that the journey takes a long time. And that journey is almost completed. On July 14, at around 7:50 a.m. EDT, this small piano-sized craft will cruise by Pluto, passing approximately 7,800 miles above the surface at about 31,000 miles per hour. At the time of close encounter, the Earth will be a distant three billion miles away. New Horizons’ radio signal, travelling at 186,282 miles per second, will take almost four and a half hours to reach mission control.

Not only will New Horizons obtain detailed images of Pluto and its moon Charon, but also it will map features of the other four moons as well. Instruments will record a wide-range of data, including Pluto’s surface and atmospheric composition and temperature. Charon’s surface will be analyzed, and instruments will determine if it has an atmosphere. The astronomical community will learn more about Pluto during this mission than they have since its discovery in 1930. It will be an exciting time in (dwarf) planetary exploration.

As historian for Skyscrapers, Inc, the Amateur Astronomical Society of Rhode Island, I am privileged to share a special Rhode Island connection to Pluto with you of which only a few people are aware.

First, let’s briefly examine the history of Pluto’s discovery. A wealthy Boston astronomer, Percival Lowell, started a search for “Planet X” in 1905 using his observatory out in Flagstaff, Arizona. Why the search for an unknown object? Because of small perturbations in Neptune’s orbit, it was suggested another “Trans-Neptunian planet” existed. Lowell, with his mathematics background, and with the help of colleagues, tried to derive a possible orbit. They even took photographic plates in 1906 of an area of sky where they thought planet “X” might be located, but with no results.

During my research on the life of Frank Evans Seagrave (1860-1934), the original owner of Seagrave Memorial Observatory in North Scituate, I uncovered many unique and fascinating details about this Rhode Island astronomer. Seagrave was a frequent visitor to Harvard College Observatory (HCO) in Cambridge, Massachusetts during the first decade of the 1900s. And though Lowell spent most of his time out at Flagstaff, he did have an office in Boston. My research revealed that Seagrave and Lowell not only corresponded, but also they became good friends. They both had a flair for mathematics, and both loved astronomy.

Seagrave was very well known up at HCO, having sent many letters to Director E.C. Pickering containing computations for the orbits of comets (including Halley’s Comet in 1910) and asteroids. And Seagrave contributed these same calculations to many of the astronomical journals of the time.

I do not know when Lowell and Seagrave first met, but from 1915 – 1917, when Seagrave was “working” as an assistant at HCO, it is apparent they had become fast friends. I have copies of a couple of postcards between them in January and February 1915. Seagrave was trying to compute a new asteroid’s orbit. He wrote, “My Dear Friend. Well how do you do. Hope you arrived safe at Flagstaff. I am at work on that asteroid orbit and will send figures to you when finished. Thank you very much for all you have done and are doing for me. Let us hear from you. Hope you will find X.”

Seems it wasn’t an asteroid but a comet, for Lowell sent a response to Seagrave on March 3, 1915 saying, “So the Harvard ‘harvest on their plates’ have made an asteroid into a comet! That’s going some. And I am told The Herald tried to credit us with the transformation. No! No! we are only astronomers, not astro-misnomers. I wish this definition, which I just dropped off the end of my obliging pen, had occurred to me yesterday when I wired a modest denial of such ultra-heavenly powers with a ‘please correct’ to the Herald.”

Lowell died at age 61 on November 12, 1916. The search for “Planet X” ended. Seagrave continued his correspondence with Dr. Slipher, the new Director of Lowell Observatory. On April 23, 1917, Seagrave wrote to Slipher, “Have you taken any observations of Mellish’s latest Comet? I want some positions. The computed orbit is away off, and I wanted to see what I could make out of it. Three positions, say a week apart. How are you getting along these days since Dr. Lowell died? I do miss him so. I am yours.”

In a follow-up letter in an obvious response to Slipher’s answer, Seagrave wrote, “Thank you so much for your letter that I received Sunday morning. If you should at anytime find any conspicuous object that you think is “X” please send me some positions. Dr. Lowell many times promised me that I should be the first one to work on its orbit when discovered.”

The search for Planet “X” resumed in 1929. Finally, on February 18, 1930, Clyde Tombaugh discovered Lowell’s distant world by “blinking” photographic glass plates he had meticulously exposed. As Clyde told Skyscraper members when he visited Seagrave Observatory for Astro Assembly in 1987, until he informed his colleague Dr. C. O. Lampland across the hall from his office and then his boss V.M. Slipher, for 45 minutes he was the only person in the world who knew of the new planet’s existence.

This monumental discovery was announced to the world on March 13, 1930. Seagrave, now 70 years-old, hadn’t been asked to compute Pluto’s orbit as had been promised. In a letter to Dr. Slipher in Flagstaff on March 14, 1930, Seagrave wrote, “Can you send me some positions of planet X, the newly discovered one beyond the planet Neptune. Many years ago (say from 1912 to 1915) the late Dr. Lowell promised me that if the Lowell Observatory ever found X that he would let me be one of the first to compute its orbit ... Thank you in advance for anything you can send me in relation to this most interesting planet. I am yours. Frank E. Seagrave.”

Well, Seagrave didn’t immediately receive an answer to his query. One month later, on April 15, 1930, an impatient Seagrave sent another letter to Dr. Slipher at Lowell Observatory in Flagstaff. He wrote. “About the middle of March I sent you a letter asking for some photographic positions of the outer Neptunian planet, or the new Asteroid, or the new Comet, whatever it proves to be. Up to date I have never heard from you. I am wondering why as the newspapers all mention positions secured during January and February. The last time I was with Dr. Percival Lowell was late in September 1916. At that time he was getting ready to leave Boston (I was at the Lowell Observatory Office, 53 State St, Boston with him.) for Flagstaff, and was to stop at three or four places on the way to lecture. He showed me his computations in relation to the outer Neptunian planet, and said to me, ‘Seagrave, if the Lowell Observatory is the Observatory that will first find this planet, you will be the first one to compute its orbit.’ No writing to this effect. Only a verbal statement. I am wondering why you did not send me some positions as you seem to have sent some to Dr. Miller of Sproul. Dr. Van Biesbroeck of Yerkes Observatory sent me four positions. From two of these positions one of March 16 and one of March 20, I have computed approximate circular elements as per enclosed sheet. The enclosed look ‘OK’ and all check ‘OK’. Here Seagrave supplies some formulas and provides the sheet of elements. In closing, Seagrave writes, “I shall hope to hear from you soon, and tell me the very latest. Is it ‘X,’ an Asteroid of enormous size, or a Comet great in size and nearly 40 units from the Sun. I am yours. Frank E. Seagrave.”

Slipher finally responded to Seagrave on April 19. “It was my aim to get off to you yesterday some of the early positions of Lowell’s Transneptunian object, apparently planet X, but the day was not long enough. In fact, as you can imagine the days have for weeks all been too short for us to get done what should have been done, and we, in consequence have had to appear unfriendly or discourteous to many good people like yourself. And just now your second letter has come to hand with your orbit, for which we thank you.”

Slipher went on to say that “it seemed to me that we here should determine for it a preliminary orbit. This because it seemed best for Lowell Observatory to find it out and make it known if the object were thus shown to be less important than it had appeared. Dr. Lowell and the Observatory had put so much into the problem as to appear to justify this policy.” He went on to say, “The enclosed positions are being mailed to you in advance of any other person (this is, of course, in confidence). And I hope you will feel that we have tried to be fair. We of course realized at the outset that you who compute orbits were better equipped to do such work, but the reasons given above decided our course. We hope that you will get from these early places and other more recent ones an improved orbit, and needless to say we shall be greatly obliged to you for letting us know what results you get. With best wishes. V.M. Slipher”

As the months went by and more observations were made, Seagrave continued to receive new positions to compute a more refined orbit for Lowell’s “Planet X.” Only a few individuals know of Seagrave’s Lowell and Pluto connection. I hope to remedy that oversight when I publish Seagrave’s biography.

So as the New Horizons spacecraft explores this distant world, think about Frank Seagrave’s contributions in calculating Pluto’s orbit by hand 85 years ago. This Rhode Island astronomer helped to pave the way for our quest for knowledge in the far reaches of the solar system.

While Pluto is merely a tiny speck as seen through the largest of the telescopes in Rhode Island, there are many other more prominent celestial objects to view that will impress you with their beauty. Let the volunteers at all the Rhode Island observatories (http://www.theskyscrapers.org/free-public-observing-at-seagrave-memorial-observatory) help you explore the heavens during free public open nights.

Keep your eyes to the skies.

Celebrate the Pluto Encounter with us