New Horizons and Current Science
As the 1940s approached, the initial excitement following Pluto’s discovery faded from public interest. War, industrial growth, and international developments all emerged at the forefront of the nation’s mind, leaving Pluto in the shadows once more. The limitations of technology also contributed to the lull in Pluto research between the late 1930s and the 1950s. Scientists had not yet developed machinery powerful enough to endure the long trip from Earth to Pluto, which restricted astronomers to making observations through telescopes and theorizing about the planet’s characteristics. Much like Percival Lowell’s search in the early 1900s, Pluto research during this period was slow and produced little results, but astronomer Gerard Kuiper was eager to learn more about the distant planet. In the late 1940s and 50s, Dr. Kuiper from the Department of Planetary Sciences at the University of Arizona collaborated with fellow astronomer Milton Humason to begin measuring Pluto’s size. They utilized the largest telescope in the world at that time, the Palomar two hundred inch, to observe Pluto by eye. The astronomers soon realized that the planet’s diameter was much smaller than anticipated. Select astronomers across the country began their own observations to validate what Kuiper and Humason proposed and ultimately agreed that Pluto was, indeed, not nearly the size of Earth as Percival Lowell had predicted.
Evidence of Pluto’s new size influenced another small wave of interest in the scientific community throughout the 1960s and 70s. Researchers began studying Pluto’s surface using photoelectric photometry, which measures the brightness of celestial objects such as stars. Other astronomers, like Jim Christy, worked on refining the calculations of Pluto’s orbit around the sun and found much more surprising results. In the spring of 1978, Christy requested images of Pluto from the Naval Observatory Flagstaff Station (NOFS) and on April 13 and May 12 of that year, astronomer Anthony Hewitt took the requested photographs on glass plates before sending them to Christy in Washington, D.C. Christy began studying the plates on June 22, 1978 and found an abnormal bulge that seemed to protrude from Pluto. After studying images of Pluto and the movement of that abnormality, Christy realized that the image had captured Pluto’s moon. In the upper left corner, the discovery plate of Pluto’s moon is featured. The left panel shows an elongated Pluto, not quite circular because its moon is peeking over the top of the planet. The right panel shows a perfectly circular Pluto lined up with its moon. With assistance from a colleague, Christy began calculating the orbit of the moon and determining its name. He took his wife’s nickname, “Char,” and added “-on” like the ending of “proton” and “electron,” but he feared that using the name “Charon” would not follow the trend of naming celestial objects after characters from mythology. To his surprise, Christy found that the name “Charon” was also the name of the ferryman in Roman mythology who transported souls across the River Styx into the underworld, which is ruled by the god Pluto. Below the plate image is an artist’s rendering of Pluto and its moon, Charon.
The discovery of Charon raised even more questions and inspired further interest in Pluto research. Researchers continued to study images of Pluto and Charon, but technological developments in the 1990s propelled Pluto studies further than it had ever gone. Astronomers Alan Stern and Marc Buie were especially interested in using the newly developed Hubble Space telescope to further explore Pluto’s surface. Hubble technology confirmed several theories about the Pluto system, including the fact that Charon is tidally locked meaning that it only shows one face as it rotates about Pluto. Thanks to Hubble, astronomers were also able to study the Pluto system’s surface and atmosphere using infrared wavelengths, which showed them the various gasses found on both Pluto and Charon.
In the early 2000s, Alan Stern and other astronomers like Will Grundy began devising plans for potential missions to Pluto. Technology was quickly advancing and for the first time since its discovery, astronomers believed that Pluto wasn’t destined to remain in the darkness forever. Stern and fellow astronomers joined NASA’s proposed Pluto mission, the Pluto Kuiper Express, in early 2000, but it was quickly canceled by NASA. The team led by Stern joined with researchers from Johns Hopkins University’s Applied Physics department in 2001 to propose a new mission to Pluto called New Horizons. Above is an article written by Will Grundy in a 2002 copy of Lowell Observatory’s quarterly newsletter, The Lowell Observer, that discusses the plans for the New Horizons mission. The project received much support from local Arizonans who sent thousands of letters to Congress voicing their optimism about the outcome of the mission. Public encouragement proved to be crucial to the mission, and in 2006, NASA approved the New Horizons mission. It launched from Kennedy Space Center in Florida on January 19, 2006, but it took several more years before astronomers saw Pluto up close. Above is another article by Will Grundy from the spring 2006 edition of The Lowell Observer providing an update on the New Horizons mission a couple weeks after the launch.
On July 13, 2015 the New Horizons mission transmitted the first color images of Pluto and Charon back to the research team on Earth. The image above is one of those enhanced images produced by NASA to highlight the different color regions on Pluto invisible to the naked eye. The New Horizons team then prepared to share the images with the public and scheduled several press conferences to take place over the next couple of days. The image above captures the New Horizons team during one of those press conferences as they shared the newest images of Pluto and other scientific findings. The New Horizons flyby gathered valuable data that astronomers are still grappling with today. Astronomer Will Grundy talks about the current scholarship and future projects involving Pluto in the audio clip below. According to Dr. Grundy, New Horizons changed perceptions about the planet and challenged the assumption that it was inactive due to its far distance from the sun. Planetary researchers continue to study Pluto and are eager to learn more about its relationship to other objects in the Kuiper belt. Click on the audio below to hear more about the research that astronomers at Lowell Observatory and across the world are conducting on Pluto.