Pluto atmosphere on infrared view

Pluto Atmosphere Wraps Loose – Of Fascinating Blue Hazes

Scientific Importance of Pluto Atmosphere

What makes Pluto Atmosphere that significant?

From the discovery of Pluto in 1930 till the end of 2010’s, a long way is crossed about understanding her. This has been of huge importance for astronomy in last decades because understanding Pluto also means understanding the big rocky and icy objects beyond Neptune. And there are dozens of them in Kuiper Belt.

Although scientists believe there should be quite many objects beyond Neptune, they were not sure till 1990’s. With 1990’s, lots of rocky objects in various sizes were in line for discovery. And 2000’s were the time for discovery of bigger planets like Eris. However this was a bad news for Pluto. Because as a consequence, Pluto was kicked out of planetness.

// Thanks a lot to our readers for their attention and comments about sizes of Pluto and Eris. Here are the up-to-date numbers for both planets:

Despite above, planet Pluto is still the best option to focus and further analyse as a great prototype. One of the basic reasons for this is: Pluto is the only known Kuiper Belt Object with atmosphere.

Pluto, behind Sun
A Pluto picture in black from New Horizons spacecraft. She is located in between Sun and the spacecraft. Source: NASA

This was one of the biggest motivations of the ambitious New Horizons Mission for deducting useful information from Pluto.

You might think that the New Horizons flyby is the pioneer for discovery of Pluto’s atmosphere and revealing more Pluto facts. However, that’s not completely true.

How Was Pluto Atmosphere Detected?

There is one very important method to analyze a planets’ atmosphere: Stellar Occultation. It works when a bright star is exactly behind the source of interest, while your observatory is on Earth. This method has been very useful in last decades for analysing such atmospheric data or ring systems of gas giants.

For this method of atmospheric data detection; instead of observing reflected sunlight (which is not sufficient to analyze) from Pluto atmosphere, you need to detect the starlight sourced from a proper background star. This simply fades in the details of tiny particles from Pluto atmosphere. And our spectrometers on Earth grabs&processes that information.

Kuiper Airborne Observatory was a flying telescopic plane in Earth’s atmosphere, which was working in coordination with ground stations . In 1988, it was the primal source for detecting signs of haze layers of Pluto atmosphere via stellar occultation. What is more, similar observations were performed in different times. In this way, existence of Pluto atmosphere was strongly proved. It was also understood that the breadth of the atmosphere was dramatically varying in years.

Kuiper Airborne Observatory
KAO, hosting first device ever to observe Pluto atmosphere. Source: here, Credit: Credit: NASA/Ames Research Center.

After above, spectroscopic detections in 1993 and 1994 resulted with diagnosis of nitrogen, carbon monoxide and methane on Pluto atmosphere. Afterwards, as New Horizons Mission revealed more and verificative data together with Pluto’s surface and even mapped Pluto features, we still know those are the same materials existing on Pluto atmosphere and the surface.

Reaching to New Horizons

New Horizons Spacecraft – Atmospheric Composition

It was a milestone to send New Horizons Spacecraft away and sense Pluto atmosphere from only tens of thousands of kilometers proximity.

If you think that amount of sunlight is not enough for such measurements out there.. You don’t need to! OK, a sunny day means like dawn on planet Pluto surface. But don’t worry: It is sufficient enough for our spectrometers.

And stellar occultation is still the best method for any atmospheric analysis. What is more, New Horizons’ way of using occultation is the most efficient one within the solar system: Sun occultation!

Considering previous atmospheric knowledge about Pluto System, resulting headlines of NH information was not surprising at all: Pluto had an atmosphere consisting mostly of predicted materials. And Charon together with other Pluto moons (Kerberos, Nix, Styx, Hydra) didn’t.

However, what team saw while observing the atmosphere was extraordinary. There were quite a lot of haze layers yielding Pluto atmosphere!

Haze layers of Pluto atmosphere
Atmospheric hazes of the south pole. Source: NASA

Following further analysis of atmosphere; up to 20 different haze layers were detected. What’s more; acetylene, etylene and ethane molecules were pointed within those layers in addition to nitrogen, methane and carbon monoxide. Previous stellar occultations were verified by New Horizons as the dominant molecules in the atmosphere belong to nitrogen.

New Horizons Spacecraft – More Atmospheric Features

The average atmospheric pressure is about 100.000 times less than Earth’s. This seems to be varying in time as previous occultations suggest.

Average temperature of the atmosphere lays between -230 and -210ºC.

The measurements indicate that the thickness of the atmosphere is about 160km. However the recent simulations and calculations still result the thickness can easily vary in different seasons.

Pluto atmosphere on infrared view
Pluto atmosphere on infrared view. Source: NASA

This is one important thing to know about Pluto atmosphere. It’s variable and uncertain. That’s mainly because of the orbital eccentricity. It is so high that the distance between Pluto and Sun increases 0.6 times from the perihelion to aphelion.

Although the surface temperature and lower atmospheric temperature is always below -200ºC, minor temperature changes can easily cause gaseous materials in the atmosphere turn into solid form. This will substantially cause an atmospherical decay. And the reason for that is simple: Pluto atmosphere consists mostly of nitrogen, while nitrogen condensates in -210ºC .

Above seems to be proof of a condensating atmosphere. However, it might still not be the case. Because there are too many parameters to calculate and take into account. That’s why, best way would be to wait until the aphelion day is closer. It’s only half a century time after all!

Blue Pluto Skies

While New Horizons Spacecraft was hiding from the Sun on the far side of Pluto, below Pluto image was captured:

Pluto atmosphere view
Beautiful blue layers of Pluto atmosphere, as seen by New Horizons Spacecraft. Source: NASA, JHU APL, SWrI

It was quite fantastic to observe an Earth-like atmospheric view over there in 2015. But the truth is, for a planetary object with a stable atmosphere, this is what you’d mostly see!

The source of blue colored atmosphere is mostly the interaction of floating tholins with the solar radiation in the atmosphere. While that’s the case, same tholins reflect sort of brownish color while existing on the surface.

Would you see a blue sky on a sunny Pluto afternoon than? Unfortunately that would be a dream only. The amount of sunlight is not enough and atmosphere is not dense enough over there. That’s why, it will mostly be a black one.

Pluto clouds
Pluto Clouds. Source/Credit: NASA

Future About Pluto Atmosphere Exploration

New Horizons Mission opened a broad page for atmospheric analysis of Pluto. And several scientists are still working on those data from New Horizons.

On the other hand, there are other plans for future Pluto missions, where a landing mission is also on the table. Such long term missions can always reveal more details about Pluto atmosphere. However, New Horizons is a giant step about understanding Pluto atmosphere and it truely did its duty properly.

We wish all Plutopician fellows open & black skies!


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  1. Mike Wrathell September 26, 2019
    • Plutopic September 27, 2019
  2. Laurel E. Kornfeld September 2, 2019
    • Plutopic September 2, 2019
  3. Mike Wrathell July 26, 2019
    • Plutopic July 28, 2019
      • Laurel E. Kornfeld September 27, 2019
        • Plutopic September 27, 2019

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