Petroleum in space? Ain’t that a gas! – Part 4

Neptune, the smallest and farthest out of the giant planets, receives very little solar energy, which is radiated from four and a half billion km away—roughly 30 times the distance between Earth and Sun.

In fact, astronomers have found that this beautiful blue world emits 2.7 times more heat than the Sun imparts to it. The source of its energy, they believe, is atmospheric methane.

Being a greenhouse gas, methane has prevented Neptune from cooling down, as rapidly as neighbouring Uranus—thus storing up the energy that powers Neptune’s turbulent wind-system.

“It appears,” surmises the University of Oregon’s Department of Astronomy, “that Neptune is …efficient at trapping leftover formation heat due to the fact that methane is highly abundant”.

The methane in Neptune’s atmosphere is “an excellent insulator (i.e. the greenhouse effect)”, they note, and is thus trapping heat that “should have been radiated [away] billions of years ago”.

Orbiting the Sun beyond Neptune is the Pluto/Charon system, in which two minor planets revolve around each other. The surface of Pluto, in particular, is thought to be covered with methane ice.

Actually, Pluto is merely the nearest and most visually accessible of a vast, disc-shaped belt of icy bodies revolving beyond Neptune. At least 70,000 of these have diameters of 100 or more km.

Investigators believe most of these “Trans-Neptunian” or, more commonly, Kuiper Belt Objects; contain varying amounts of primordial methane.

Writing in the journal Astrobiology last year, O. Mousis, and ten others, from Aix Marseille Université Marseille, France, traced the origin of the solar system’s methane to the period of formation.

“Methane,” they explain, “was formed in the interstellar medium prior to having been embedded in the proto-solar nebula [the molecular cloud from which the Sun and its planets materialized]…”

“Interstellar medium” (ISM) refers to the space between the stars, where atoms, molecules and dust-grains coalesce and accrete into new stars, which, in many instances, evolve into planetary systems.

The ISM is especially rich in hydrogen and carbon. The former is the most abundant element in the universe, while the latter ranks fourth. They make up the methane molecule (CH4).

“This molecule,” the scientists continue, “was…trapped in…crystalline water ice during the cooling of the disk and incorporated… into the building blocks of comets, icy bodies, and giant planets”.

As explained on the “Astronomy Stack Exchange.Com website,” tiny silicate particles (“cosmic dust”) are crucially important in to the formation of methane and other ISM molecules:

“Often for molecules to form… dust is…a catalyst. …an atom can stick to a dust grain and wait… until other atoms stick. The atoms slowly “crawl” around on the surface…eventually meet and make bonds.”

When the outer solar system was taking shape, on the fringes of the disk-like solar nebula, these methane molecules were frozen into icy lattices called “clathrate structures”.

But while this largely accounts for the existence of methane in the composition of the giant planets and Kuiper Belt Objects, hydrocarbon molecule can form via other processes.

The liberation of hydrocarbons from clathrates alone, cannot account for the presence of methane, in varying quantities, on all the planets and most of the moons of the solar system.

Wikipedia reports that even the tenuous atmospheres of Mercury and our Moon contain traces of natural gas, while Venus harbours huge amounts of methane, from 60 km up down to its surface.

In conditions on Earth, methane is known to form through three processes. One is “serpentinization”—changes in basalt rocks, induced when hot fluid circulates through them.

*To be continued.