Neptunian Descent

        "The faint glow of a far-off sun struggles through the gloom. An icy sleet of methane rain envelopes the probe as distant lightning illuminates the swirling and billowing cloud tops." 

Decades from now a small atmospheric probe plummets through the sapphire clouds of the distant planet, Neptune. In a little over an hour its harrowing journey across the Solar System will come to an end as its main parachute fails, casting it down into the crushing depths of the planet's interior. Until that moment the probe drifts downward through the layers of Neptune's frigid atmosphere as it relays telemetry of its surroundings to a waiting orbiter.

Here we see the probe as it breaks through the hydrocarbon haze (probably ethane and ethyne) which enshrouds the planet, finally reaching the main deck of methane (CH₄) clouds below. During its nearly 50 km descent through the haze layer the probe has rocked and swayed beneath its parachute canopy, gently jostled to and fro as its swept up by a strong eastward wind travelling at a blistering 300 m/s (1,080 km/hr or 671 miles/hr). Despite these fearsome wind speed measurements, thus far the descent has been surprisingly smooth. But how can this be? How can the most distant giant planet boast the fastest winds in the Solar System? And how can our space probe survive plunging through this vicious, supersonic wind? Far from the warmth of the Sun, these ancient winds are generated by primordial heat welling-up from the interior of Neptune and spun up over billions of years, without a solid surface to slow it down. As a result, some models of Neptune's atmosphere suggest that the flow of gases may be somewhat laminar in nature, with individual particles flowing relatively smooth and layered paths. This smooth flow is characterised by very low turbulence. 

Having taken regular measurements during the descent, onboard thermometers register a sudden and rapid increase in atmospheric temperatures. Previously, the trip through the haze layers had seen temperatures fall with altitude, now they are rising quickly. Upon reaching the methane cloud layer, temperatures have increased to roughly 150 K (-123°C/-190°F).

SCIENTIFIC CONSIDERATIONS:

For the sake of clarity and visibility, the ambient lighting conditions presented in this piece has been boosted significantly. At roughly 30 AU from the Sun (4.5 billion km/2.8 billion miles) Neptune receives roughly 1/900th (0.111%) the solar energy the Earth receives from the Sun. Thus the noon-day sun at the top of the atmosphere on Neptune would be comparable to the illumination experienced at sunrise or sunset on Earth. 

PAINTER's COMMENTARY
This is the first new(ish) piece I've uploaded to DeviantART since July or August. Its not really a full-on feature piece like Saturnian Dream was. Instead in's more of a digital painting study, and a rather quick one at that. I probably should have left out the probe, but without its just a rather naked cloudscape.

In the future, I would like to paint a series of images based on the future atmospheric exploration of Neptune. The series would cover the probe from planet approach, atmospheric entry, parachute deployment, scientific measurement at the different cloud layers and finally its ultimate destruction at depth.

I. Seventh Planet as Viewed From Miranda ► SUBJECT: Uranus/Miranda
II. Saturnian Dream: Moonlet Requiem ► SUBJECT: Saturn

IV. Fall of Icarus: A Sungrazer Strays Too Close ► SUBJECT: Sun