Mars has two small moons, Phobos and Deimos, respectively 11 and 6 km in diameter. Our Moon of 3476 km in diameter is huge compared to those two potatoshaped rocks. Phobos and Deimos are asteroids captured in Mars’ gravity field. When the Mars Terraforming Effort succeeds Mars will have a thicker atmosphere but most of all an ocean, an ocean without tides. For that you need a bigger Moon. Scientists agree the best candidate is 932 km in diameter: Ceres, the largest asteroid in the asteroid belt.

How do you get an object that large from it’s present day orbit into an orbit around Mars without accidents? Accidents are an understatement here, celestrial objects fly with such large speeds around the sun that Ceres could become a planetary sized bullet inflicting serious damage to a planet like Mars, possibly even destroying it. Because that isn’t desirable a simple but affective method has to be devised to transport Ceres to Mars.

A new article in Nature describes how to park Ceres in a Mars orbit. First of all Ceres needs to be made fully controllable. That is realized by putting a grid full of rockets on the surface, allowing the planetoid to accelerate, slow down and change direction. Ceres has to be slowed down from it's current orbit around the sun in such a way that is follows an elliptic path toward Mars, which is closer to the sun in orbit. At Mars it will enter a large elliptic orbit. Now only finetuning the orbit remains.

In this new situation Phobos and Deimos can stay functioning as spacestations or they could be moved to other places in the solar system where they are more needed. Ceres could be colonized, mined and cities and stations could be build on it's surface.