Quiescia

Quiescia was a planet with made of nothing but jagged blue rocks and pebbles. It had a breathable atmosphere that seemed to soak up noise. It was in the furthest system of Earth's galaxy, (PROSE: Alien Bodies) almost on the opposite side of Mutter's Spiral from Dust. (PROSE: Interference) Its sun was huge, red, cold, and slow, and it tinted the blue rocks with a violent light. (PROSE: Alien Bodies)

The Third Doctor and Sarah Jane Smith buried Laika on a hill on Quiescia. The Doctor chose the location because time wasn't an issue there. He marked the grave with a blue tombstone, which he burned the word "LAIKA" into with his sonic screwdriver. Upon noticing that Quiescia had no native life-forms despite its breathable atmosphere, Sarah Jane Smith speculated that the whole world had been built by the Doctor purely for the purposes of burying Laika.

One hundred million nights later, the Eighth Doctor returned to the planet, finding it completely unchanged since his absence. He buried the Relic next to Laika, then destroyed the grave site with a thermosystron bomb. The explosion turned the hill into a ten-foot-wide, carefully-contained neutron star. After the Doctor left, another hundred million nights passed on Quiescia without anyone else coming or anything changing. (PROSE: Alien Bodies)

Bernice Summerfield searched for the Doctor's remains on the planet, but she found nothing. (PROSE: The Shape of the Hole)