We have grown quite accustomed to what has been taught during our school days that Pluto is the ninth and the last planet of the solar system. Discovered in 1930, Pluto had been considered as a planet ever since. That is, until the International Astronomical Union (IAU) crossed out Pluto as a planet in 2006, downgrading it instead to a dwarf planet. Officials argued that although Pluto orbits around the sun and has a spherical shape, it’s not otherwise not large enough to qualify as a “true” planet.
But eight years later, Pluto became a hot topic again. It’s because Pluto may have a good chance to reclaim its old status as a planet. In July 2015 a NASA space probe New Horizon flew by Pluto to take detailed images and measurements of the dwarf planet.
Scientists think of the possibility of Pluto having its own ring system, but it hasn’t been confirmed yet. A research team recently came out with a discussion regarding the impact of Pluto’s two of five rings — Nix and Hydra — and how the resulting debris from that collision could form a ring around Pluto.
When the New Horizon spacecraft reaches Pluto this July (as of this writing), it will undertake one of its intriguing missions: to look for a potential ring system around Pluto, and its moons.
The dwarf planet has five known moons: Charon (the largest, whose diameter is just over half of Pluto’s), Styx, Nix, Kerberos and Hydra.
Pluto is also almost as old as Earth as well — about 4.54 or 4.6 billion years old.
Although Pluto and Neptune’s moon Triton have distinct histories, these two bodies have something more in common. Both Pluto and Triton have the same retrograde orbit, the faint nitrogen atmosphere, as well as the similar composition of rock and ice.
For so long, we think of Pluto as the farthest from the Sun. In reality though, Pluto has the most eccentric orbit of all the planets in the solar system. Its orbit takes it to 39.5 astronomical units (AU). In its closest point, called “perihelion,” it can get as close as 29.7 AU (about over 4 billion kilometers) and in its farthest point, known as “aphelion,” the dwarf planet can get as far as 49.7 AU from the Sun. It means that Pluto’s orbit runs within that of Neptune, making it look like the eighth rather than the ninth planet for about 20 years at a time. From 1979 to 1999, Pluto was actually ahead of Neptune, making the latter planet the ninth and last planet!
To keep the tradition of naming newly discovered or created elements after the planets, American chemist Glenn T. Seaborg named a newly created element, plutonium, after Pluto. Other previously discovered or created elements like uranium and neptunium were named after the planets, Uranus and Neptune, respectively.
Pluto is currently over 5 billion kilometers away from Earth and 6 billion kilometers away from the Sun. The sunlight travels to Pluto at 30,000 kilometers per second — about a billion kilometers per hour. So it means that for a light to reach to Pluto, it will take about 5 1/2 to 6 hours to arrive from the sun.
It’s because Pluto completes one rotation in about six Earth days, so it means the sun rises and sets in Pluto almost once every Earth week.
Contrary to what’s commonly thought, Pluto actually has an atmosphere. Like Mercury and the moon, it has a very thin atmosphere called exosphere which is composed of mostly nitrogen and methane. As Pluto moves farther from the Sun, its atmosphere freezes out onto the surface.
Pluto’s biggest moon, Charon, might have had an subsurface ocean. Scientists think that Charon’s icy surface is cracked which, in turn, means that beneath that surface could lie a warmer interior, warm enough to hold an ocean. When the New Horizons reaches Pluto this coming July, it could help researchers figure out if Charon indeed harbors an underground ocean consisting of liquid water.
Charon, Pluto’s largest satellite, is over half the size of the dwarf planet. There are many theories regarding Charon’s formation. Some astronomers think that Charon’s formation began when a large object collided with Pluto, possibly a virtual twin planet. Some scientists think that Pluto and Charon could have formed together at the same time, while other scientists aren’t quite sure about it.
In 2006 the International Astronomical Union demoted Pluto from “planet” to “dwarf planet.” However, leader of the New Horizon mission Alan Stern strongly disagrees with the definition. At the time when the IAU voted out Pluto as a planet, he said that IAU’s definition of a planet does not hold true for any other celestial body. For instance, he pointed out that the Earth (as well as Mars, Jupiter and Neptune) has not cleared the neighborhood around its orbit, as it has asteroids as neighbors.