WASHINGTON, April 16 (UPI) -- Opportunity's phenomenal luck continues. Not only did NASA's rover land smack-dab in the middle of a neatly excavated and navigable crater on Mars, where it promptly uncovered persuasive evidence that water once flowed across the red planet, and not only has it been performing nearly flawlessly since it touched down on Jan. 24. Now, it also, essentially, has stubbed its toe on a rock whose discovery portends cosmic implications. A few days ago, on its slow roll across the Martian terrain at its landing site at Meridiani Planum, an iron-oxide-rich area near the planet's equator,...