Marnaltharke is the first planet of Archas. It was originally a barren world, similar to Mercury before terraforming, but it was a turned into hellish world similar to pre-terraformed Venus after a catastrophic accident, a few thousand years before its destruction.
Marnaltharke was a relatively large world, around 3900 km in radius. Before terraforming, it had vast, deep crater fields covering its surface, and a thick ice cap on the night side. However, after terraforming, the atmosphere thickened at an alarming pace, reaching over two hundred atmospheric pressures. Its brightness in the sky of Angertharke increased drastically due to the high albedo of its new cloud layer.
After this, the extreme atmospheric pressure rapidly eroded away most surface features, making the planet very flat. The surface remained like this until the planet's demise in the Great Lareas War.
Marnaltharke was originally discovered in prehistory by the Ornali, the main species of its sister planet Angertharke. It was later the first terraforming attempt by that species, which worked initially. This prompted the colonization of the world, who's population grew to over five billion before the Marnaltharke Incident, which flooded the atmosphere with noxious gases including Carbon Dioxide, killing the majority of the population.
Soon afterwards, the Great Lareas War started, between the Ornali's nation, the Republic of the Spider Nebula, and two other nations: The Kormin Empire and the Union of Narenna. The Kormin Empire launched an attack designed to strike fear into the hearts of the civilians on Angertharke and test their new long-range weaponry. They sneakily arranged some mirrors around Alnert A, a wolf-rayet star near the system, and focused all of the star's energy into a beam, which was aimed into a wormhole. The other end of the wormhole was near the edge of the Archas System, and positioned to make the beam impact Marnaltharke when it is at its maximum distance from Archas as for the maximum fear factor. The beam impacted and destroyed the entire planet in a huge explosion, creating a vast asteroid belt at its original orbit.