He married fellow astronomer Ingrid Groeneveld (who became Ingrid van Houten-Groeneveld) and together they became interested in asteroids. They had a son, Karel.
In a jointly-credited trio with Tom Gehrels and Ingrid, he was an extremely prolific discoverer of many thousands of asteroids. Gehrels did a sky survey using the 48-inch Schmidt telescope at Palomar Observatory and shipped the plates to the van Houtens at Leiden Observatory, who analyzed them for new asteroids. The trio are jointly credited with several thousand discoveries.
From the statistical properties uncovered it became clear that asteroids fall into certain "families".