Free Astronomy Magazine September-October 2018

42 SEPTEMBER-OCTOBER 2018 PLANETOLOGY atmosphere. To stop the former, an ozone layer is needed, for the latter, a well-struc- tured ionosphere produced by a global mag- netic field. Mars is devoid of ozone and shows only a hint of ionosphere, created by relics of an ancient global magnetic field. As a result, the most energetic UV rays, small amounts of X-rays and gamma rays, and many charged particles contained in the solar wind can easily reach the ground. These problems, solvable with appropriate clothing and outdoor excursions limited in duration, are certainly not the most worrisome. In fact, the absence of a magnetosphere similar to that of Earth’s allows the solar wind to freely hit the Martian atmosphere and gradually disperse it into space, a process that has been going on for billions of years. We can, there- fore, easily understand that it would be en- tirely in vain to attempt to restore the atmosphere without first restoring a mag- netic field able to preserve it. Although it seems an extreme challenge, in the past few years various solutions have T his artist’s model shows where the landing sites are on Mars for Viking 1 & 2, Spirit, Opportunity, Phoenix, and Curiosity, in com- parison to possible locations of an early ocean which may have existed billions of years ago. In this depiction, the atmosphere is thicker than the present-day Mars atmosphere, which is only about 1% of Earth’s. The locations for the ancient ocean are based on current alti- tudes and do not reflect the actual ancient to- pography. [Created for the MAVEN mission by the Lunar and Planetary Institute] A rtist’s con- cept of a possible Mars terraforming plant. [National Geographic Channel] been proposed to address the missing mag- netic field. We only mention the last one, suggested in February 2017 by Jim Green, Planetary Science Division Director of NASA, at the Planetary Science Vision 2050 Work- shop. Green proposes to create a magnetic