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Meet our Solar System – Pluto

How well do you know your astronomical neighborhood? Let’s go on a trip through our solar system and explore the weird, the wild, and the beautiful all around us. Today, we are learning all about Pluto.

Where is it?

Pluto is a complex world of ice mountains and frozen plains. Once considered the ninth planet, Pluto is the largest member of the Kuiper Belt and the best known of a new class of worlds called dwarf planets.

Pluto orbits the Sun about 3.6 billion miles (5.8 billion km) away on average, about 40 times as far as Earth.


What’s up with the name?

Pluto is the only world (so far) named by an 11-year-old girl. In 1930, Venetia Burney of Oxford, England, suggested to her grandfather that the new discovery be named for the Roman god of the underworld. He forwarded the name to the Lowell Observatory and it was selected.

Pluto, or Hades, is the god of the underworld. He rules over the afterlife and helps usher souls across the River Styx. The brother of Jupiter, or Zeus, Pluto was also the god of wealth because diamonds and other jewels come from underground.

In his Roman and Greek mythology, Pluto stole away the daughter of the goddess of the earth and tricked her to residing with him three months a year. These months were then why the earth goddess was inconsolable with grief, thus the earth itself is cold and icy. In other words, the mythologies used this story to explain the seasons and why winter exists.

Ploutos with the horn of abundance, in the company of Dionysos (4th century BC)

Who “discovered” it?

Pluto was discovered on Feb. 18, 1930 at the Lowell Observatory in Flagstaff, Arizona, by astronomer Clyde W. Tombaugh, with contributions from William H. Pickering. This period in astronomy was one of intense planet hunting, and Pickering was a prolific planet predictor.

In 1906, Percival Lowell, a wealthy Bostonian who had founded the Lowell Observatory in Flagstaff, Arizona in 1894, started an extensive project in search of a possible ninth planet, which he termed “Planet X.” By 1909, Lowell and Pickering had suggested several possible celestial coordinates for such a planet.

The search for Planet X did not resume until 1929, when the job was handed to Clyde Tombaugh, a 23-year-old Kansan who had just arrived at the Lowell Observatory. Tombaugh’s task was to systematically image the night sky in pairs of photographs taken two weeks apart, then examine each pair and determine whether any objects had shifted position.

Using a machine called a blink comparator, he rapidly shifted back and forth between views of each of the plates to create the illusion of movement of any objects that had changed position or appearance between photographs.

On Feb. 18, after nearly a year of searching, Tombaugh discovered a possible moving object on photographic plates taken on Jan. 23 and Jan. 29.

Pluto officially became Pluto on March 24, 1930, when Burney’s suggestion was adopted and announced to the world.

What’s it made of?

Pluto is about two-thirds the diameter of Earth’s Moon and probably has a rocky core surrounded by a mantle of water ice. Interesting ices like methane and nitrogen frost coat the surface. Due to its lower density, Pluto’s mass is about one-sixth that of Earth’s Moon.

Pluto’s surface is characterized by mountains, valleys, plains, and craters. The temperature on Pluto can be as cold as -375 to -400 degrees Fahrenheit (-226 to -240 degrees Celsius).

Pluto has a thin, tenuous atmosphere that expands when it comes closer to the Sun and collapses as it moves farther away – similar to a comet. The main constituent is molecular nitrogen, though molecules of methane and carbon monoxide have also been detected.

When Pluto is close to the Sun, its surface ices sublimate (changing directly from solid to gas) and rise to temporarily form a thin atmosphere. Pluto’s low gravity (about 6% of Earth’s) causes the atmosphere to be much more extended in altitude than our planet’s atmosphere. Pluto becomes much colder during the part of each year when it is traveling far away from the Sun. During this time, the bulk of the planet’s atmosphere may freeze and fall as snow to the surface.

Can we live there?

You won’t find many places in our solar system less hospitable to life than Pluto. The surface of Pluto is extremely cold, so it seems unlikely that life could exist there. At such cold temperatures, water, which is vital for life as we know it, is essentially rock-like. Pluto’s interior is warmer, however, and some think there could even be an ocean deep inside.

Living and working on Pluto might be similar to being on the Moon, but the temperature extremes are so much worse, since it’s further from the Sun.

How long is a year there? What about a day?

Pluto’s orbit around the Sun is unusual compared to the planets: it’s both elliptical and tilted, like a comet. It takes Pluto about 248 years to orbit the Sun once.

One day on Pluto takes about 153 hours. Its axis of rotation is tilted 57 degrees, so it spins almost on its side. Pluto also rotates from east to west like Venus and Uranus.


Has NASA sent any missions there?

Pluto is so far away, it takes a very long time for spacecraft to reach it. That’s why it took a while for missions to first explore Pluto.

The most extensive mission sent to the dwarf planet was New Horizons.

New Horizons launched on Jan. 19, 2006; it swung past Jupiter for a gravity boost and scientific studies in February 2007, and conducted a six-month-long reconnaissance flyby study of Pluto and its moons in summer 2015, culminating with Pluto closest approach on July 14, 2015.

The spacecraft provided the first close-up images of Pluto and its moons and collecting other data that has transformed our understanding of these mysterious worlds on the solar system’s outer frontier.

In the years since that groundbreaking flyby, nearly every conjecture about Pluto possibly being an inert ball of ice has been thrown out the window or flipped on its head.

New Horizons at Pluto Artist Concept

Can I see it from here?

Not really. To catch a glimpse of the dwarf planet, you’ll need a telescope with at least an 8-inch diameter mirror, according to Sky and Telescope. Even at its brightest, Pluto is not visible to the naked eye and is about 27 million times fainter than Venus.

Are there any pretty pictures of it?

Of course! We recently got so many good shots of Pluto from the New Horizons mission.

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