January 27, 2020 : Some Researchers Have Suggested At The 235th Meeting Of The American Astronomical Society That The Haze Of Pluto May Resemble The Haze Of Titan
A group of researchers has revealed, during a presentation on January 8, 2020 at the 235th meeting of the American Astronomical Society taking place in Honolulu in the state of Hawaii, that the haze identified in the atmosphere of the Dwarf Planet Pluto may look like the haze of Saturn's largest moon Titan. Researchers had collected a huge amount of data regarding Titan's atmosphere during the Cassini-Huygens mission in the Saturn System from 2004 to 2017. On July 14, 2015, the New Horizons spacecraft performed the first flyby of Pluto and Charon revealing a remarkably complex world with a varied landscape and with a thin atmosphere composed of several layers. In fact, researchers were in a position to determine that Pluto's atmosphere is a blue atmosphere like the atmosphere of our planet and that a haze evolves in that exotic gas blanket. The team involving Bonnie Buratti who is a planetary scientist at NASA's Jet Propulsion Laboratory in California advanced that the haze of Pluto is rich in organics like the haze of Titan. The atmosphere of Pluto is particularly thin like the atmosphere of Neptune's largest moon Triton but the haze of Pluto may be closer to the haze of Titan in terms of composition.
Pluto and Triton represent small worlds whose size is roughly similar. Those planetary bodies appear to be remarkably active in terms of geology. In spite of their relatively low gravity, they contain a thin atmosphere dominated by nitrogen. Most moons or icy bodies in the Solar System are devoid of any atmosphere but Titan, Triton and Pluto unveil an atmosphere. There is apparently the right combination of environmental temperature and gravity on each planetary body to allow the presence of an atmosphere. The atmosphere of Titan is reminiscent of the atmosphere of the Early Earth and of the Earth today because that gas layer is mostly composed of molecular nitrogen. Unlike the atmosphere of Pluto and Triton, the atmosphere of the Orange Moon appears completely opaque from outer space in the visible spectrum. The global haze of Saturn's largest moon prevents us from discerning surface features from outer space. The atmosphere of Pluto appears more optically thick than the atmosphere of the strange moon of Neptune Triton. The difference may be related to a carbon-rich haze in the environment of Pluto. The reddish areas observed on Pluto imply the potential presence of tholins, a type of mud or sludge rich in organics and hydrocarbons.
Prior to the historic flyby of Pluto and Charon performed by the New Horizons spacecraft at a particularly high speed, planetologists knew that there was a sharp contrast between red areas and bright areas and they believed that Pluto may resemble Triton in terms of geology or meteorology. However, the images obtained from the New Horizons spacecraft have unveiled a complex and active world with topographic or geologic features we had never seen before beyond the Earth. We realize that the worlds of the Outer Solar System which evolve in an extremely cold environment can unveil a cryovolcanic activity. Two worlds whose size and albedo are relatively similar can be, in fact, very different in terms of geology or topography. The bright heart-shaped area of Pluto known as Tombaugh Regio is not located in one of its polar regions and implies a relatively strong geologic activity. That bright area which is rich in nitrogen and carbon monoxide may represent a major reservoir of the thin atmosphere of the Dwarf Planet. We have identified potential clouds as well as multiple haze layers on the former ninth planet of the Solar System.
In order to characterize the optical depth and the surface properties of the Dwarf Planet Pluto and of the largest moon of Neptune Triton whose diameter is much higher than 2000 km and slightly higher than that of Pluto, the team of Bonnie Buratti resorted to a radiative transfer model based on Chandrasekhar's « Planetary Problem » of an atmosphere and used a surface of arbitrary single scattering albedo as well as a single particle phase function. The model of the planetologists also allows us to quantify the forward-scattering properties of the haze. The researchers studied the data related to optical imaging regarding Triton and Pluto. Regarding the Opaque Moon Titan, they resorted to published data on that world as well as new Visual Infrared Mapping Spectrometer (VIMS) data acquired from the Cassini spacecraft. That instrument can see in the wavelength range between 0.35 and 5.2 microns and contains several channels in the mid-infrared where the atmosphere appears transparent with a relatively low opacity. Thus, the atmosphere that is opaque in the visible spectrum can appear optically thin in certain wavelengths.
In the Solar System, there are a few Terrestrial worlds or icy worlds which contain a relatively significant atmosphere. Among those worlds, Venus is covered in the thickest atmosphere. At first sight, We could advance that Venus which looks like the Earth in terms of size should contain a thinner atmosphere than that of the Earth because its gravity is lower and because the environment in which it evolves is warmer than that of the Earth. But that is far from being the case. The atmospheric pressure on Titan's surface is higher than that of the Earth at sea level even if the gravity of Titan is much lower than that of the Earth. Triton and Pluto which are much smaller than Titan are covered in a thin atmosphere whereas a world like Ganymede which is bigger than Titan is devoid of any atmosphere. Planetologists can analyze the atmosphere of a few Terrestrial or icy worlds in order to deduce the general dynamics of the atmosphere of worlds located beyond the Earth, in the Outer Solar System or around other stars. The team of Bonnie Buratti has been in a position to determine that Pluto's atmosphere is more optically thick than Triton's gas blanket.
A contrast can be observed between the composition of Triton's haze layer and Titan's haze layer. The haze of Triton is rich in water ice whereas the haze of Titan is rich in organics or hydrocarbons. The haze of Pluto unveils a bluish color. The atmosphere of Titan is completely opaque and appears orange from outer space but its upper boundaries are composed of blue or purple haze layers. In the impressive images of Pluto's surface obtained during the historic flyby of the New Horizons spacecraft, planetologists have clearly noticed the presence of areas unveiling a reddish tint. Those areas may contain tholins or a deposit of haze. That's a configuration which may look like the configuration of Titan where there are complex interactions between the crust, the soil and the atmosphere. UV light from the Sun must play a key role in the formation or development of organics or hydrocarbons in the atmosphere and on the surface of those Outer Solar System worlds. The team of Bonnie Buratti strongly believes that the haze of Pluto may be similar to the haze of Titan which is rich in carbon-made molecules.
The outcome of the new research work is in line with the idea that Titan and Pluto represent « factories » for the production of organics in the Outer Solar System. Those molecules rich in carbon are similar to the molecules which have been sent by comets and asteroids into the Inner Solar System and which may represent prebiotic molecules or molecules which may have led to the formation and the development of life on Earth billions of years ago. The haze layer of Titan or Pluto can tell us a lot regarding the chemistry of hydrocarbons and organics. Researchers are fascinated by what they see and they are encouraged to continue their studies regarding fascinating worlds like Pluto, Triton or Titan. Some individuals regard Pluto as a new Mars but it may be closer to Titan in terms of chemistry. Pluto and Titan unveil dunes, mountains, hills, red or dark regions as well as bright regions. Titan is the only extraterrestrial world known to harbor lakes, seas and rivers. The pools of liquids on Titan are dominated by hydrocarbons. They are rich in methane or ethane which represent molecules that can appear in their liquid form on Titan's surface. Planetary scientists believe that the linear and parallel dunes of Saturn's largest moon are composed of sand generated by the photochemical haze present in its atmosphere.
The team of Bonnie Buratti tries to determine the potential relationship between the haze of Pluto and its soil or crust. Are there snowfall events of organics or hydrocarbons engendering dunes ? The first goal of the group was to determine the potential composition of Pluto's haze. The collaborators managed to conclude that the haze of the three planetary bodies studied is made up of icy particles. However, the nature of the haze on Triton may be radically different from that of the haze of Pluto and Titan. The haze of the captivating moon of Neptune may be dominated by water ice. The team of Bonnie Buratti notes a reddish tinge to the light signature of Pluto's haze implying the potential presence of organics. That's why the haze of Pluto is believed to be closer to that of Titan than that of Triton. Pluto, Triton and Titan represent a small sample of the potential worlds one can encounter beyond the Earth but they allow us to imagine or to anticipate the potential environments found on other worlds in the Outer Solar System, in the Kuiper Belt or on exoplanets or planets orbiting other stars of the cosmos.
The image above reveals a portion of Titan in the lower part of the view as well as a portion of Pluto in the upper part of the view. The original view of Titan was obtained on January 30, 2012 from the Cassini spacecraft. The original view of Pluto was obtained on July 14, 2015 from the New Horizons spacecraft. The views of Titan and Pluto are at scale. Each side of the image represents about 1000 km. One can notice, in particular, a multitude of layers in Pluto's atmosphere and a detached haze layer in Titan's atmosphere. A parallel can be drawn between the haze on Titan and the haze on Pluto. Credit for the original view of Titan: NASA/JPL-Caltech/Space Science Institute. Credit for the original view of Pluto: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute. Credit for the montage: Marc Lafferre, 2020.
- To get further information on that news, go to: https://aas.org/meetings/aas235 and https://www.space.com/pluto-hazy-organics-surprise-scientists.html.