How our understanding of Pluto has evolved over the years is fascinating. From being a only a dot visible to us, to a dot that bulges (hmm, maybe a moon there), to a clear color picture of the (dwarf) planet. Let us take you through its history visually.
Discovery in 1905-1930
The ninth planet (as known then) was almost discovered by Percival Lowell in 1905 from his personal observatory. But, he is not really credited with the discovery. Lowell was a rich Bostonian and had setup his own observatory. Lowell initially kept it a secret so as to protect his pet project. He announced his "Planet X" only in 1908. Lowell predicted it to be much larger and the one to effect Neptune's orbit. His search continued to 1915, but Pluto appeared only twice in the set of plates and was much dimmer than expected. During his time, these two images were not convincing enough to be instated as a 9th planet.
Credit: Percival Lowell, via Wikipedia
Credit: Venetia Burney Phair, via the BBC
After Lowell's death in 1916, not much moved till Clyde Tombaugh joined the Lowell observatory in 1929. He used a blink comparator to compare photographs and detect any movement which would betray the existence of a planet. On 18th February 1930, he was comparing two plates when he saw a star shifting position. Fainter than expected, he knew that he had finally found Lowell's planet. It was finally announced on 13 March 1930, on Lowells birthday.
Pluto shot to fame instantly all over the world. Lowell Observatory had the naming rights and received scores of suggestions for the name. After much drama, it was an 11-year old girl named Venetia Burney who suggested the name Pluto, which won the unanimous vote of the members of the observatory.
Credit: Lowell Observatory
Not Much Visual Action in 40 years
Pluto was discovered to be within 6 degrees of position predicted by Lowell, but he pegged the size at being 6.6x of Earth. In 1955, it was determined by measuring brightness that Pluto has a period of rotation measuring 6.4 Earth days. In 1950, Gerard Kuiper used a 200-inch telescope to measure Pluto's diameter to be 5,900km (Earth is 12,756km).
In 1976, Kitt Peak Observatory made near-infra red measurements that showed that Pluto was covered with frozen methane which is highly reflective. But, with that fact, the planet should appear much brighter. It was clear that Pluto was probably smaller than earlier assumed. Frozen methane had never been detected on any planet as to stay frozen it requires immensely cold temperatures of -373 degrees F. The existence of methane ice on Pluto suggested that the sun has never shone enough on Pluto to boil off the methane.
In 1988, Pluto passed in front of a star which was its first occulation. Occulation is an event when the planet passes in front of a distant star. Such events can help us learn a lot about the planet like pressure density and temperature. In the case of Pluto, The star did not wink out, it gradually disappeared and reappeard which meant that Pluto had an atmosphere.
Pluto is not alone
Many of Pluto's photographs were elongated, which were believed to be defective. But, astronomer James Christy saw that the bulge moved around the planet. Christy was not even tasked to look at Pluto, he had requested images of the moons of Neptune and Uranus for a project, but just extended the request to Pluto because he could. The images were marked as defective due to the bump on Pluto, but Christy studied the other stars in the images and found no defect. So, he concluded that what seemed like a defect in Pluto was actually its property. Further, he showed that the bump progressed around Pluto in a 6-day period which established the satellite theory. The moon was named Charon.
Credit: US Naval Observatory
Pluto becomes clearer - 1996 onward
In the late 90's, the Hubble telescope became operational. Now, astronomers could see Pluto without the interference of the Earth's atmosphere. In 1996, first details of Pluto's surface were revealed by Alan Stern and Marc Buie. Images of entire Pluto's surface were taken by the Hubble over its 6.4 day rotation period. This revealed that Pluto's surface was interesting. It had the high large-scale contrast which is only true for one other planet - Earth. The features on the surface of Pluto were caused by complex distribution of frost which migrate across the surface with orbital cycles.
By 2006, Hubble also revealed that Charon was not the only moon. Pluto had two more companions named Nix and Hydra. And then, it spotted two more moons in 2011 and 2012 called Kerberos and Styx. Pluto was now a family.
The New Horizons Era - 2006 to 2015
Johns Hopkins APL took on an ambitious project. They engineered the New Horizons interplanetary space probe which was launched in 2006 with the primary mission to fly-by Pluto. It cruised passed Asteroids and Jupiter to reach Pluto Jan 2015. A total of 9 years taken to reach its destination. T
The Surface Appears
After a scary software glitch, the spacecraft had its closest approach of the Pluto system on 14 July 2015, but the first data did not get to Earth till the next day. Download of the complete data set took 15 months though. That event gave us the breathtaking images of Pluto, its icy surface and its moons. Enjoy.
If you found this post interesting, I am sure you are a Space geek and would love to wear a t-shirt that represents 110 years of works of so many scientists on Pluto. The surface of this planet is truly fascinating and so is its history. To celebrate this fascination, we've created high quality Pluto themed t-shirts. They are all-over print t-shirt which will give you the feel of wearing the planet on your skin.