Making Mars more massive

One problem of Mars is that due to its low mass it cannot hold an atmosphere well. Therefore I now got the idea to start the terraforming process by increasing its mass to Earth mass, or at least close.

The idea is to send asteroids from the asteroid belt onto a collision course on Mars, and continue to do so until Mars is massive enough to hold an atmosphere. The asteroids would be sent to that trajectory by detonating well-placed nuclear or thermonuclear bombs on them.

My question is now: Could this strategy work? In particular:

• Are there actually enough asteroids in the asteroid belt to sufficiently increase Mars' mass?
• Would it be practically possible to send those asteroids to Mars using bombs?
• Would be be able to build sufficiently many bombs for this task?

You may assume that if we can build the bombs, we also can transport them to the asteroid belt, so space ships are no bottleneck. Also time plays no major role; lets say anything up to about 300 years is acceptable.

• See other questions about adding atmosphere to the moon. It works on a human time scale. So it would be fine on Mars too! The premise of your question is challenged. Easier to add air every few thousand years. Commented Aug 6, 2016 at 14:29
• ,,,or build domes. Commented Aug 6, 2016 at 17:46

There isn't remotely enough mass in the asteroid belt for the job. The total mass of the main belt is about 1/2000 of Earth's mass. That's enough to increase Mars' mass by about 0.5%.

The idea that the asteroids are a planet's worth of matter just isn't true. The Wikipedia article on the asteroid belt explains why the "Planetesimals" in the region didn't accrete into a planet, and why most of them were ejected from the region, and in most cases, the inner solar system.

Even if there was enough mass in the asteroid belt to raise the mass of the planet Mars using thermonuclear bombs as the technique to send them on a collision course with Mars wouldn't work.

At least, it wouldn't work well. Too many asteroids are structurally fragile. Detonate a thermonuclear bomb on one and it will mainly scatter fragments of asteroid around the solar system. Eventually adding to the mass of the other planets in solar system.

Mass drivers and the various solar radiation pressure techniques would be far more reliable. But this still runs up against the lack of mass in the asteroid belt. Of course, an alternative solution would be moving one or more Jovian moons to add mass to planet Mars.

• Sadly, Jupiter's four large moons total only about 6.6% of a Earth mass. Hauling them out of Jupiter's gravity well would also be challenging. Moving Venus would do the job, but terraforming it would probably be easier. Commented Aug 6, 2016 at 13:58
• @JohnDallman A sad total indeed. I guessed Jovian gravity would be a tough challenge. Moving Venus to Mars' orbit would be a better solution and easier to terraform there too. I like it. Commented Aug 7, 2016 at 3:26
• Would the Venus atmosphere have an effect on Mars, and would it be a positive or negative effect? Commented Sep 12, 2018 at 17:48
• @TrevorD Moving Venus is intended to be an alternative to making Mars more massive. Venus is Mars orbit could then be terraformed. Mars would probably need to be moved from its present orbit to avoid any unnecessary collision. Commented Sep 13, 2018 at 4:19
• @a4android Oh I thought you meant to crash Venus into Mars. Your plan makes much more sense Commented Sep 17, 2018 at 12:53