Since Pluto was first discovered back in 1930, what we know about its size, color, structure and overall appearance has changed dramatically.
Originally believed to be the ninth and furthest planet from the Sun, it was thought to be of a dirty brown color. However, this was based on the findings of what little access scientists had to study the then-planet.
Its brown, earthy appearance was based solely on what astronomers could see using Earth-based telescopes and before the possibility of attaining high-resolution images like we do now.
Early space technology only allowed us to see Pluto from a great distance which is why it appeared to have this ‘ruddy’ appearance.
This all changed after ‘New Horizons’ mission which took place in 2015. The mission was able to provide astronomers with the first close-up images of Pluto.
So, as technology has improved and further research has been carried out, we know that the color of Pluto is much more complex and varies from deep reds to light blues and many other shades in between.
The 2015 ‘New Horizons’ mission
In 2015, a mission to capture close-up, high resolution images, called the New Horizons mission, took place. Since the mission, much has been learned about Pluto’s appearance.
The mission was highly successful and managed to take a series of breathtaking images which showed a clear picture of the dwarf planet, from a range of 22,025 miles!
The images were able to produce as close to natural colors as possible, using a specially designed Multi-spectral Visible Imaging Camera.
Because of this new technology, astronomers were able to create images that were closely matched to how the human eye would perceive color, showing us the truest possible color of the dwarf planet.
What the images taught us is that the dwarf planet is actually much more complex than they initially thought and is made up of a variety of colors and surface features.
Noe we know that its surface has several dark, reddish areas. These are the result of the presence of ‘tholins’, which are compounds created by ultraviolet and other charged particles from the Sun. There are also patches of orange and yellow.
In addition to this range of colors, there are also smaller sections that consist of much paler colors, such as dirty white and light blue.
These are due to Pluto’s visual apparent magnitude, or brightness, which is around 13.65 at perihelion (the point in the orbit when the dwarf planet is closest to the sun) and can reach up to 15.1.
As a result of these findings, Pluto can no longer be described in just one color. These high-resolution images reveal the full complexity of the once-planet’s appearance.
In addition to information about its surface features and color, the New Horizons mission also uncovered more information on its composition and tenuous atmosphere.
Others aspects of Pluto’s appearance
The new images show Pluto’s features extremely clearly, and found that one patch of the dwarf planet, the ‘Sputnik Planitia’ as it has since been named, can be described as the ‘heart’ of the dwarf planet.
The icy surface has been descried as the heart due to its heart-like shape.
That’s not the only interesting aspect of its appearance. In fact, Pluto’s surface is quite varied and differs greatly in color and brightness in different areas of the dwarf planet.
It is thought to have lots of large craters, with some on the dayside (the side closest to the sun) measuring about 162 miles in diameter!
Its structural features include escarpment, or steep cliffs in its surface, and lower, trough-like dips, some measuring up to 370 miles in length.
Pluto’s chemical make-up is a mixture of rocky core and icy mantle. Its surface is made up of 98% nitrogen ice with small traces of carbon monoxide and methane.
Scientists also predict the internal make-up of Pluto is a combination of a rocky material which has congealed into a concentrated core that is surrounded by a layer of ice.
How hot or cold is Pluto?
When Pluto was still considered a planet, it was labelled the coldest planet in the solar system. These days, Pluto is described as a dwarf planet which makes its freezing temperature less extraordinary. Now, Uranus is considered the coldest planet in our solar system.
In order to understand just how cold Pluto is, we need to look at how temperature is measured in space and compare it to the temperatures on Earth.
So, room temperature on our planet is around 70 degrees Fahrenheit and the freezing point of water is 32 degrees Fahrenheit. But, temperatures in space get so cold that they are measured using ‘Kelvin’.
The average surface temperature on Pluto is 44 Kelvin or -380.2 Fahrenheit. This is extremely cold.
To put it into perspective, zero Kelvin relates to the ‘absolute zero’ temperature i.e. the absolute minimum point at which energy can be obtained from a system. Zero Kelvin would equal to -459.4 degrees Fahrenheit!
Being such a huge distance from the Sun, Pluto is incredibly cold. But, the temperature can go up and down, resulting in the changing of its appearance.
The surface of Pluto can vary between a maximum low temperature of 33 Kelvin or -400 degrees Fahrenheit and a maximum high temperature of 55 Kelvin or -360 degrees Fahrenheit.
Its thin icy atmosphere consists of traces of methane and carbon monoxide, and a larger percentage of nitrogen. Pluto’s temperature changes can affect how its atmosphere appears and where it is located around it.
When the dwarf planet reaches its closest point to the Sun, it is able to heat up enough to sublimate its nitrogen atmosphere which turns into a diffuse cloud, changing the appearance of the planet.
But, at its furthest point from the Sun, Pluto can get so cold that its nitrogen atmosphere freezes to the point that it falls to the dwarf planet’s surface, a bit like snow.