<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>TTPrograms</author><text>For people asking about the amount of energy we&amp;#x27;re talking about, the energy density of a magnetic field is |B|^2 &amp;#x2F;(2mu_0). It appears that the described structure has something on the order of the cross section of Mars, and I&amp;#x27;ll assume that it&amp;#x27;s depth is in that ballpark as well. For a fictitious uniform field that would require on the order of 1.6e19 J, which is roughly 1.2 times the total electrical energy output of the US in 2001:&lt;p&gt;&lt;a href=&quot;http:&amp;#x2F;&amp;#x2F;www.wolframalpha.com&amp;#x2F;input&amp;#x2F;?i=4%2F3+pi+*+(radius+of+mars)%5E3+*+(500,000+nT)%5E2+%2F+(2*mu_0)&quot; rel=&quot;nofollow&quot;&gt;http:&amp;#x2F;&amp;#x2F;www.wolframalpha.com&amp;#x2F;input&amp;#x2F;?i=4%2F3+pi+*+(radius+of+m...&lt;/a&gt;&lt;p&gt;&lt;a href=&quot;http:&amp;#x2F;&amp;#x2F;www.wolframalpha.com&amp;#x2F;input&amp;#x2F;?i=1.617%C3%9710%5E19+joules&amp;amp;lk=1&amp;amp;rawformassumption=%22ClashPrefs%22+-%3E+%22ClashPrefs%22&quot; rel=&quot;nofollow&quot;&gt;http:&amp;#x2F;&amp;#x2F;www.wolframalpha.com&amp;#x2F;input&amp;#x2F;?i=1.617%C3%9710%5E19+joul...&lt;/a&gt;&lt;p&gt;Assuming you had no losses, so say ideal superconducting coils, that&amp;#x27;s how much energy you have to dump into magnetic field. You can do this as slow as you like, so with 1&amp;#x2F;10 the US electrical energy production it would take 10 years to build up that magnetic field. Hypothetically, if you had thin-film plastic PV cells (like cellophane thin to be reasonable to build and get into space) with 100% efficiency covering the footprint of this system (Mars) you could generate enough power to charge up this field in 471 seconds:&lt;p&gt;&lt;a href=&quot;http:&amp;#x2F;&amp;#x2F;www.wolframalpha.com&amp;#x2F;input&amp;#x2F;?i=1e19+J+%2F+((solar+power+output*pi*(radius+of+mars%5E2))%2F(4*pi*radius+of+mars+orbit%5E2)&quot; rel=&quot;nofollow&quot;&gt;http:&amp;#x2F;&amp;#x2F;www.wolframalpha.com&amp;#x2F;input&amp;#x2F;?i=1e19+J+%2F+((solar+powe...&lt;/a&gt;)&lt;p&gt;Of course the big story here is that efficient thin film solar in space could generate obscene amounts of power.&lt;p&gt;I&amp;#x27;m not sure on the depth of the field volume required, so that might make it easier, too.</text><parent_chain><item><author>thatcherc</author><text>This is incredibly exciting but a few important details are missing.&lt;p&gt;The first is how big does the structure need to be? I can buy a 1 Tesla magnet online right now but that&amp;#x27;s probably not what they&amp;#x27;re thinking of. Would we need a city-sized coil or something like that?&lt;p&gt;The second is the time scale. They say that the temperature could rise by 4 Celsius and trigger a greenhouse effect, but is that an immediate effect (10 years or so) or century-scale effect? I&amp;#x27;m hoping the scientists put out a paper because I&amp;#x27;d love to learn more about the specifics of their proposal.</text></item></parent_chain></comment><story><title>NASA proposes a magnetic shield to protect Mars&apos; atmosphere</title><url>https://phys.org/news/2017-03-nasa-magnetic-shield-mars-atmosphere.html</url></story>
<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>fenollp</author><text>Less than 700 million years apparently.&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;twitter.com&amp;#x2F;humansareawesme&amp;#x2F;status&amp;#x2F;836961705745858560&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;twitter.com&amp;#x2F;humansareawesme&amp;#x2F;status&amp;#x2F;83696170574585856...&lt;/a&gt;</text><parent_chain><item><author>thatcherc</author><text>This is incredibly exciting but a few important details are missing.&lt;p&gt;The first is how big does the structure need to be? I can buy a 1 Tesla magnet online right now but that&amp;#x27;s probably not what they&amp;#x27;re thinking of. Would we need a city-sized coil or something like that?&lt;p&gt;The second is the time scale. They say that the temperature could rise by 4 Celsius and trigger a greenhouse effect, but is that an immediate effect (10 years or so) or century-scale effect? I&amp;#x27;m hoping the scientists put out a paper because I&amp;#x27;d love to learn more about the specifics of their proposal.</text></item></parent_chain></comment><story><title>NASA proposes a magnetic shield to protect Mars&apos; atmosphere</title><url>https://phys.org/news/2017-03-nasa-magnetic-shield-mars-atmosphere.html</url></story>