Mars air mostly CO2, rover finds
The Curiosity rover has tasted Mars' air: It's made mostly of carbon dioxide with hints of other gases. The measurements closely match what the twin Viking landers detected in the late 1970s and what scientists have gleaned from Martian meteorites. Mars' atmosphere is overwhelmingly dominated by carbon dioxide, unlike Earth's air, which is a mix of nitrogen and oxygen. There was a small surprise: Viking found nitrogen to be the second most abundant gas in the Martian air, but Curiosity's measurements revealed a nearly equal abundance of nitrogen and argon, a stable noble gas. Mission scientists suspect it might have to do with the different tools used.
U.S. heat wave stuck in reverse
The sweltering weather in the Northeast has surprised meteorologists: It's moving backward across America, which rarely happens. U.S. weather systems normally move west to east. The western Atlantic high pressure system behind the hot weather started moving east to west last week and by Tuesday was centered over lower Michigan, the National Weather Service said. Forecasters say the high pressure is about to return eastward, extending the Northeast's heat wave a day or two. Thursday the heat index, which factors in humidity, hit 106 degrees in Washington, Baltimore and Philadelphia.
Find may be Civil War cannonball
Atlanta police say a construction crew on Thursday unearthed what appears to be a cannonball near Centennial Olympic Park. Police spokesman John Chafee says bomb technicians said the artifact may be from the Civil War era, but it has not yet been examined by an expert. When federal troops besieged Atlanta in 1864, they fired thousands of cannon shells into the downtown area that now includes the park.