# Internet of Spacecraft for Multi-Planetary Defense and Prosperity
## 2 Extra-Terrestrialization: Make Life Multi-Planetary
### Terraforming  
After setting the first foundation or even the first self-sustaining city with its own relatively comprehensive industry, agriculture, and services, terraforming, which is the hypothetical process of deliberately modifying the atmosphere, temperature, surface topography, or ecology of a celestial body to make it more similar or habitable to the environment of Earth, should commence. It can be a very long procedure but will benefit mankind and even Earth's animals and plants for the multi-planetary transition in the long term as depicted in Figure 9.  
In contrast to the controversy on terraforming Earth's Moon due to its higher difficulty [46, 47], Mars is the most likely candidate to be terraformed. For example, it is believed that Mars used to be a warmer and wetter planet [37, 38], with a thicker atmosphere but lost it during a course of hundreds of millions of years due to reasons still unclear [48]. Some likely mechanisms behind it could be related to the planetary surface absorption of greenhouse gases such as carbon dioxide, the lack of powerful magnetosphere around Mars due to the ceased dynamo function [49], or asteroid impacts that ejected the ancient Martian atmosphere into deep space [50]. However, there is evidence from the NASA MAVEN  
Figure 8: Illustration of foundation of: (**a**) Mars city; (**b**) Moon base with massive connected spaceships.  
Figure 9: Illustration of Mars before and after terraforming.  
mission that the Mars atmosphere was removed due mainly to coronal mass ejection events, but Mars still retains a level of magnetosphere covering approximately 40% of the surface rather than uniformly covering and protecting the atmosphere from solar wind [51].  
Theoretically, terraforming Mars is the reverse procedure of how it lost the atmosphere and water. Among many proposals, including exploding nuclear devices on Mars [52], several are particularly worth mentioning. Greenhouse gases such as carbon dioxide can be generated on Mars through heating [53], to form CO\({}_{2}\) clouds to scatter infrared radiation and thus trap the incoming solar radiation [54]. Subsequently, the raised temperature can add more greenhouse gases to the atmosphere, and the two processes will augment each other and form a positive loop. Moreover, authors in [55] have demonstrated a 2-3 cm-thick layer of silica aerogel which will simultaneously transmit sufficient visible light for photosynthesis, block hazardous ultraviolet radiation and raise temperatures underneath it permanently to above the melting point of water without the need for any internal heat source. All experiments and modeling were under Martian environmental conditions. On the other hand, as motivated by the microorganisms' diverse roles in sustaining life on Earth, authors in [56] have proposed a framework for a new discussion based on the scientific implications of future terraforming such as avoiding accidentally distributing Earth's harmful microorganisms and genes to extraterrestrial areas and letting life stretch as a continuum connecting certain planetary bodies, with microbes doing the work of pioneer habitat conditioning. However, it requires many rigorous systematic, and controlled experimental studies with an ethical platform developed on Earth in advance.  
Several other celestial bodies, such as Venus, and Mercury, have also been studied for terraforming. Still, Mars may be the most feasible one within mankind's technological capabilities, although the economic resources required can call for an enormous global joint effort in various aspects.