They had moved across the galaxy at half the speed of light, covering the 17.6 light-years from their planet in the orbit of Ehseaplus to the Sol system in a couple of hundred days and now they had slowed down their inter-constellation craft to manoeuvre prior to landing on the planet Sol III.  They were looking for a blue planet but they had found two reddish planets orbiting the star, Sol adjacent to an asteroid belt.  Their expedition had been launched after an alien object had been detected and recovered as it passed about two light-years from their planet, Ehseaplus VI.  The recovered object, which at some point appeared to have had an atomic energy source, carried on its exterior surface a gold-plated disc with primitive representations of various lifeforms and a map that appeared to suggest that the object had come from a planet orbiting the star, Sol.  Although, they had not been able to detect any artificial signals from that part of the Milky Way, their mission was to make contact with the lifeforms.  However, it appeared that Sol III was no longer blue but had become a cold, dark planet like its neighbour, Sol IV.  As they orbited Sol III, their sensor systems told them that most of the planet was covered by a thick ice-sheet with a dusting of volcanic ash, which they presumed was from volcanoes that dotted its surface – they counted about fifty of them erupting as they orbited the planet.  Their sensors also informed them that the atmosphere contained some water crystals and large amounts of carbon dioxide and sulphur dioxide.  Their explorations of the galaxy had not revealed any lifeforms capable of surviving in such an atmosphere so they were beginning to think that they had had a wasted journey.  They discussed their findings with mission control and concluded that the lifeforms responsible for the representations on the gold disc must have become extinct.  A catastrophic climate change had probably led to a mass extinction though they could not deduce whether the catastrophe had occurred due to an asteroid strike or the activities of the lifeform causing the planet’s climate to reach a tipping point.  The navigation system of their craft was weaving a gently curving path through what appeared to be tens of thousands of artificial objects in orbit around Sol III.  So, they launched one of the crafts’s autonomous probes to recover some of the objects and perform some tests which revealed that a crude carbon-based system had been used to push the objects into orbit about 40,000 Sol III years ago.  Maybe the high levels of carbon dioxide they had detected in the atmosphere of Soll III originated from these carbon-based energy systems and excessive use of them had taken the planet’s climate to a tipping point?  They gave up on finding life on Sol III and set course for home.

Footnotes:

1. I was inspired to write this short story after reading ‘The NASA Archives: from Project Mercury to the Mars rovers’ by Piers Bizony, Andrew Chiakin and Roger Launius (Taschen GmbH, 2022).
2. The NASA space probe, Voyager 1 was launched in 1977 and is travelling through space at 10 miles per second carrying a gold-plated metal disc with messages from humanity and images of life on Earth. It will pass close to a star, AC+79 3888 in the Ursa Minor constellation in 40,272 AD.
3. The atmosphere of Mars, the fourth planet from the Sun, is very thin, cold and composed mainly of carbon dioxide. About one-third of the surface of Mars is covered by a very thick layer of ice that is only a spade’s depth beneath the red soil that gives our neighbouring plant its reddish tint when seen from Earth.
4. Image: NASA snowball planet from https://news.climate.columbia.edu/2018/05/04/snowball-earth-frozen-solid/