{"group":"place","pic":"living/pics/plain-city.webp","question":"Why build the first city here?","answer":"Arcadia is smooth, flat and wide open, and a sheet of ancient ice lies just under its soil. Ships land safely, and the water is right under your boots.","play":{"label":"Walk the plain","href":"play/?era=city&light=day"},"rules":{"title":"Passing the landing rules","line":"SpaceX and NASA scientists tested {ap_sites} sites in Arcadia against every one of these. The city's site came out the safest.","items":[{"id":"flat","name":"Nearly flat","text":"Slopes under {slope}° across every {slope_len} m."},{"id":"rocks","name":"Almost no rocks","text":"Less than a {rock_pct}% chance of a rock over {rock_h} m: about knee high."},{"id":"firm","name":"Firm ground","text":"Ground that holds the day's heat, so it is not deep, loose dust."},{"id":"radar","name":"A radar echo","text":"Ground that reflects radar, so a landing ship can measure its height."},{"id":"sun","name":"Sun and warmth","text":"Within {sun_lim}° of the equator, for sunlight and milder nights."},{"id":"ice","name":"Ice below","text":"Thick, fairly pure ice under the plain, from {ice_top} m down."}],"pass":"Passed"},"gives_title":"What the plain gives the city","gives":[{"icon":"house","name":"Soft ground to dig","text":"Fine soil with few rocks is easy to move: every home lies under {cover} m of it."},{"icon":"spark","name":"Room to grow","text":"Flat ground runs to the skyline in every direction, with space for dome after dome."},{"icon":"drop","name":"Ice under every step","text":"Wherever a well goes down it meets ice, from {ice_top} m to about {ice_base} m deep."},{"icon":"rocket","name":"Smooth ground to land on","text":"Ships touch down on slopes under {slope}°, with almost no rocks to hit."}],"band":{"title":"Between sunshine and ice","line":"Nearer the equator means more sun and warmth. Further north means ice. The city sits where the two meet.","sun":"Within {sun_lim}° of the equator","ice":"Buried ice from {ice_lat}°N","you":"Arcadia City, {lat}°N","text":"SpaceX keeps its landing sites within {sun_lim}° of the equator, and clean buried ice reaches south to about {ice_lat}°N. At {lat}°N the city has both. At noon the Sun climbs {sum_noon}° high in summer and {win_noon}° in winter.","equator":"Equator","pole":"North pole","rays":"Sunlight"},"crater":{"title":"How we know the ice is there","line":"Small craters in Arcadia have steps in their walls where a weak, icy layer sits on stronger ground. Radar from orbit sees where the ice ends.","soil":"Dry soil","ice":"Ice-rich ground","rock":"Stronger ground","steps":"Steps at {bad1} and {bad2} m","radar":"Radar sees the base, {sh_mode} m","text":"One crater, nicknamed Badger, steps at {bad1} and {bad2} m. Radar sees the bottom of the ice most often {sh_mode} m down, under at least {sh_area} km² of the plain."},"earth_mars":{"earth":{"head":"Ice hides under the tundra"},"mars":{"head":"Ice hides under the plain"},"pics":{"earth":"living/pics/em-plain-earth.webp","mars":"living/pics/em-plain-mars.webp"},"rows":[{"label":"Cracked ground","icon":"layers","earth":"Winter frost splits the frozen ground into polygons you can see from the air.","mars":"The same polygons, about {poly_m} m across: {poly_n} of them mapped around the city's site."},{"label":"Under your boots","icon":"drop","earth":"Permafrost: ground that stays frozen all year round.","mars":"Ice-rich ground from {ice_top} m down to about {ice_base} m, up to {ice_pct}% ice."},{"label":"The skyline","icon":"globe","earth":"Flat tundra to the horizon, threaded with lakes and rivers.","mars":"Flat all the way round, with no hill above it, so the city shows from far off."}]},"living":"Step outside and the whole sky meets a flat, unbroken skyline. On winter mornings frost draws the polygons in fine white lines, and on summer afternoons dust devils wander far off to the south.","fact":"In June 2008 NASA's Phoenix lander scraped up dice-sized crumbs of bright ice on the northern plains. Within {phx_days} days they had turned to vapour and vanished. 'It must be ice,' said its lead scientist, Peter Smith.","later":{"pics":{"city":"living/pics/plain-city.webp","far":"living/pics/plain-far.webp"},"city":{"tag":"One city on the plain","text":"Arcadia City stands alone on the plain: its buried rows, its first dome, the wells and the port, joined by graded tracks."},"far":{"tag":"Domes to the skyline","text":"Three great domes, wide solar fields and roads running out across the plain to the towns beyond the skyline."}},"pin":[0.86,0.5],"scene":{"pic":"living/pics/scene-plain.webp","look":"02-05","shot":"city_plain","focus":"50% 45%","spots":[{"at":[0.12,0.43]},{"at":[0.28,0.34]},{"at":[0.55,0.39],"zoom":2.6},{"at":[0.89,0.27],"side":"left"}]},"proof":{"pic":"living/people/plain-proof.webp","place":"Phoenix lander, the northern plains of Mars","when":"June 2008","head":"Ice that vanished in {phx_days} days","credit":"Photo: NASA/JPL-Caltech/University of Arizona/Texas A&M University (public domain)"},"quiz":[{"q":"How deep does the ice reach under the plain?","a":["About {ice_base} m","About 2 m","More than a kilometre"],"why":"Ice-rich ground runs from {ice_top} m down to about {ice_base} m, and it is up to {ice_pct}% ice.","more":"Radar from orbit traces the bottom of the ice under at least {sh_area} km² of Arcadia, and perhaps up to {sh_max} km².","cite":"02-05 SU-02, SU-03, F-09","from":"problem","fig":0,"icon":"drop"},{"q":"What does a landing ship need from the ground?","a":["Smooth, nearly flat ground with almost no rocks","Soft, deep dust to cushion it","A hill to shelter behind"],"why":"The rules ask for slopes under {slope}° and less than a {rock_pct}% chance of a rock over {rock_h} m.","more":"The nearby site with the thickest ice lost out because it looked slightly rocky and rough. The safest ground and the best ice are a long day's walk apart.","cite":"02-05 F-01, F-02","from":"problem","fig":1,"icon":"target"},{"q":"Why does the city stand at {lat}°N?","a":["South enough for sun, north enough for ice","It is the warmest place on Mars","It sits right on the equator"],"why":"Landing sites stay within {sun_lim}° of the equator for sun and warmth, and clean buried ice reaches south to about {ice_lat}°N.","more":"Arcadia Planitia was named by Giovanni Schiaparelli in {named}, after the Arcadia region of ancient Greece.","cite":"02-03 F-33, 02-05 F-03, F-11","from":"why","fig":0,"icon":"globe"}],"notes":[{"beat":"fix","text":"Viking Lander 2, on a northern plain much like this one, watched weather fronts sweep past about every {front} days, just like highs and lows on Earth.","cite":"02-05 F-15"}],"from":"From the edge of the plain","everyday":{"title":"A day on the plain","items":[{"time":"07:10","head":"The frost net","text":"On a clear winter morning frost draws every polygon in fine white lines. By mid-morning the Sun has wiped them away.","tag":"{poly_m} m polygons","pic":"living/pics/em-plain-mars.webp","pos":"50% 75%"},{"time":"12:40","head":"Dust devils to the south","text":"Around midday tall whirls of dust wander the southern skyline, so tall they show from tens of kilometres away.","tag":"{bk_h1}:00 to {bk_h2}:00","pic":"living/pics/em-dangers-mars.webp","pos":"12% 45%"},{"time":"18:30","head":"Home along the tracks","text":"Rovers roll home across the polygons, their ruts running straight and flat towards the glow of the town.","tag":"Slopes under {slope}°","pic":"living/pics/scene-plain.webp","pos":"70% 70%"}]}}