10/23/2012 05:38 pm ET Updated Dec 23, 2012

The Search for Martians Finds Pluto... And a Lot More

In 1877, Earth passed very close to Mars, affording the best view of the red planet for a generation. The repercussions from a mistranslated map of Mars made in that year still resonates today -- and it led to the discovery of many new members of the Solar System.

Pioneering telescope astronomers, Giovanni Cassini and Christiaan Huygens had reported that Mars had ice caps at the poles and dark regions on its surface. William Herschel then used the largest telescope ever built to date to reveal that the ice caps shrunk and grew each year just as on Earth. The dark regions also grew in size -- Herschel suggested that meltwater from the poles was flooding the surface. Others thought that the color changes, which developed over a matter of weeks, were patches of vegetation sprouting in the Martian spring.

We know now that the dark areas are bare rock exposed by huge storms blowing away paler dust, but in 1877 the world's astronomers peered through the scopes with a wider set of possibilities in mind. The Italian Giovanni Schiaparelli saw what could be rivers connecting the dark "oceans." He marked them as canali, meaning channels, on a detailed map, but that was translated into English as canals -- entirely artificial waterways. And so was seeded the idea that Mars was home to aliens, and aliens who appeared industrious. Perhaps Martians were belligerent, too? H.G. Wells certainly thought so when he wrote The War of the Worlds 20 years later.

Giovanni Schiaparelli's 1877 map of Mars showing what he described as its canali. More recent surveys of the surface have revealed that there are many erosional features, probably formed by a shallow water ocean that covered the now-dry planet in its early history.

Mars watching became a rich-man's hobby and many amateur astronomers began to report more canals. They included Percival Lowell, a wealthy American businessman. He built an entire observatory at Flagstaff, Arizona, with the express intention of searching for signs of Martian life. Of course, the Lowell Observatory failed in its primary mission--even if Mars once harbored life is it utterly dead today. However, Lowell's legacy came back into the spotlight in 1930 when it began looking for Planet X.

Perturbations in the orbit of Neptune suggested there was something else beyond. The Lowell Observatory began to survey the ecliptic (the areas of the sky where the planets roam) for Planet X in 1906. In 1916, Percival Lowell died and his observatory began a dispute over funds with his widow Constance. That put a halt to the project until 1929. Clyde Tombaugh, a 23-year-old researcher, was then given the job of searching. He spent a year taking images of the sky every two weeks and comparing them to see if anything had moved. His discovery of a wandering object in 1930 made world headlines, and suggested names for the new planet flooded in. Constance Lowell proposed either Percival or Constance, but in the end the ninth planet was named Pluto, the god of the underworld, after an 11-year-old English schoolgirl suggested it was very cold that far from the Sun.

Clyde Tombaugh used a blink comparator to switch back and forth between photos -- in the blink of an eye -- and so show up any object moving position.

However, 76 years later, the Solar System's lost its ninth planet. Pluto was demoted to the status of dwarf planet, deemed to tiny to be a proper planet after all. It also appeared that Pluto was by no means the biggest little object beyond Neptune.

In 1978, the mass that had been thought to be Pluto alone -- estimated back then as little more than that of Mercury's -- turned out to be shared between Pluto and a very large moon. That satellite was named Charon (for the boatman who took souls to Pluto's underworld); it was about a third of the size of its "planet." Some suggested that Pluto-Charon should be regarded as a binary planet, still out there in ninth place. However as the sheer extent of the other objects in this zone of space -- named the Kuiper Belt (pronounced wiper) -- became established, a rethink was needed.

Following the discovery of Eris, a KBO (Kuiper Belt Object) that was slightly larger than Pluto in 2005, the International Astronomical Union decided to act. The following year, Pluto, Eris, two other KBOs, Haumea and Makemake, and the largest asteroid Ceres were to be re-termed dwarf planets. What set them apart was that firstly these objects, like planets, were large enough for their gravity to pull them into a sphere (although Haumea is more like an egg). Secondly, and unlike a planet, they were not large enough to clear their orbit of other objects. As the regular planets formed they drew all nearby material to them, perturbing any other objects so that they crashed into the young planet. As a result, planets orbit in empty space. Not so the dwarfs, with Ceres surrounded by asteroids and the others in the crowded Kuiper Belt. So far there are just five dwarf planets on the list but many more are being considered. Within a few decades there will be dozens of dwarf planets on the books, all needing names. These newest member of the Solar System are still named after deities as tradition dictates, just not the Greco-Roman ones relied on previously.

No one suggests that the dwarf planets harbor life -- and the threat from Martians is no longer a mainstream concern. However, a simple mistranslation in the 1870s did much to ignite an interest in space, science fiction, and planetary exploration that still burns strongly today.

Once Charon was on the scene it became apparent that Pluto -- pictured here with Charon between Earth and our Moon -- was not quite the body everyone had been imagining since 1930. In 2005, Pluto was found to have two other tiny moons named Nix and Hydra, plus a fourth, as yet unnamed, was spotted in 2011.

The article was inspired by The Universe: An Illustrated History of Astronomy, part of the Ponderables TM Series from Shelter Harbor Press.