Yup. To be a convincing find they would need to find something that doesn't exist on Earth and is proposed to not come from here.
The missing magnetic field is what allowed the sun to strip away the atmosphere, but current theory says there was an atmosphere for a long time so life could have spawned. . .or so they say.
I don't think anyone is really working on that, though I have also seen it proposed. One thing to bear in mind is that astronautical engineers love to propose stuff that would cost trillions of dollars, with no concern for who would pay for such a thing or why. I think before we were worried about how to protect an atmosphere on Mars, we'd need to provide more than there is, and have such a large population they were intent on moving out to the surface. Right now best hopes for any long term colonization are based upon the resources as exist, and still it is a pretty bleak hope.
Personally I think to justify terraforming for open planet colonization, you would need to be able to open a wormhole in Venus' atmosphere and deposit a suitable atmosphere on Mars. Then you have cause to provide a magnetic field. Wormholes first!
I think if you did a calculation for that, you'd find you need much more energy than is plausible. Even building a superconducting ring at the Lagrange point as Fluffy remarked, that is a multi-trillion dollar project. You can't do that with the kind of global economy we have right now, but you could in the future. The trick is to figure out how to make it pay.
The world's largest macro-engineering project to date is the US Interstate Highway System. It was originally sold to congress during the Cold War to supposedly make a way for civilians to flee US cities in event of a thermonuclear holocaust. Eisenhower could not have sold that to Congress or the US people except for the Cold War, and the project was not completed until after the Cold War ended. It took 50 years and half a trillion dollars to build those highways, and of course US citizens are all beneficiaries of that now. Our transport is the safest, quickest, most convenient and affordable in the world.
What you need to do to sell any space-oriented macro-engineering project, is show just exactly these kinds of positive outcomes, as well as a compelling need. That's very hard to do in space. Gerard O'Neil tried back in the 70's with his work at NASA, his book
The High Frontier, and with the first space advocacy group that endures to this day, the Space Studies Institute (you should all be members!), but even SSI can't gather funds to do simple engineering tasks like their G-Lab. If you dig space engineering, you might consider giving to SSI, as it is an even worthier cause than CIG.
http://ssi.org/category/g-lab/
