This poses challenges for mitigating solar radiation and retaining an atmosphere..
We compare these distributions to measured magnetic field signatures of 41 old impact craters on Mars larger than 300 km in diameter and calculate probabilities of their magnetization state. Gone was the warm, wet Mars of the past. Earth Science Stack Exchange is a question and answer site for those interested in the geology ... $\begingroup$ There's no good reason why an asteroid impact should generate a magnetic field.
NASA proposes a magnetic shield to protect Mars' atmosphere This week, NASA's Planetary Science Division (PSD) hosted a community workshop at their headquarters in Washington, DC. The ER map relies on tracing magnetic field lines from ~400 km to 185 km, using the following approach. The three artificial Lagrange Magnetic Fields remained in place around Mars for millennia until the year 12012 when the means of artificially restarting a planetary magnetic field was discovered. Then, the magnetic field died out roughly 4.2 billion years ago, and the Martian atmosphere as slowly stripped away over the next 500 million years.
Over the course of the next 500 million years, Mars went from being a warmer, wetter environment to the cold, uninhabitable place we know today.
The core activity is what maintains the protective magnetic field of Mars’ neighbor closer to the sun. Mars does not have an intrinsic global magnetic field, but the solar wind directly interacts with the atmosphere of Mars, leading to the formation of a magnetosphere from magnetic field tubes.
Earth's, by comparison, varies up to around 65000 nanotesla, or more than 40 times stronger than Mars'. We compare these probabilities to cratering densities and absolute model ages and in this manner arrive at a robust time history of Martian large‐crater magnetization and hence of the Martian dynamo.
I wrote an answer to a different question on the atmosphere of Mars that addresses part of this.
It would be interesting to read peer reviewed scientific papers that discuss the feasibility of "restarting Mars' core" via an asteroid impact. Mars' current magnetic field is very weak, with strengths of at most about 1500 nanotesla.
Re: Increasing Mars' atmosphere with magnetic field @ Sun-Mars L1 « Reply #37 on: 03/07/2017 08:37 pm » A charged particle encountering an axial magnetic field will be deflected around a …
Re: Re-starting the Martian core Well yes, but all it does its transport heat from the core outwards into space, reducing over time the over all energy contained in there, but at those pressures and current heat you could chuck loads of nuclear material which would help increase the temperature (thats the only way by putting more "rock" as i see it). For Mars to “restart” (actually regain, but we quibble) its magnetic field its core would have to become active or active at a higher level.
Upon the restarting of Mars' core, the four formerly extinct volcano's on Mars erupted in a magnificent display of raw power and added to the already massive height with large lava flows. A planet’s global magnetic field arises from what scientists call a dynamo: a flow of molten metal within the planet’s core that produces an electrical current. The magnetic field at the surface of Earth is of the order of 30µT which gives us a magnetic energy density in the order of $10^{-3} J/m^3$ Now we need to fill the entire volume of the planet and some surrounding space with this field in order to get some protection from the solar wind; let's assume a cube of $(20000km)^3 = 8\cdot 10^{21}m^3$.
[17] Figure 1a shows this map in orthographic projection for the hemisphere of Mars centered on 110°E, 8°N. If Mars hadn't lost its magnetic field, how quickly would its atmosphere have depleted? Mars had a global magnetic field much earlier—and much later—in the planet’s history than scientists have previously known. Solar wind-erosion of Mars' atmosphere likely took millions of years, so it's not like it'd be impossible to terraform Mars without a planetary magnetic field; it'd be a long-term concern. This is likely caused by rocks which formed when Mars was very young and still had a magnetic field. Earth's magnetic field is supported by an internal dynamo; Mars must once have had a dynamo, which would have magnetized its rocks, but then the dynamo shut down. Before I speculate on creating a magnetic field around Mars, let me just say that Mars actually does have an extremely weak magnetic field (~40 times weaker than Earth’s) but only in the southern hemisphere. Roughly 4.2 billion years ago, this planet's magnetic field suddenly disappeared, which caused Mars' atmosphere to slowly be lost to space.