CAPE CANAVERAL, Fla.—A NASA rover streaked toward a landing on Mars on Thursday in the riskiest step yet in an epic quest to bring back rocks that could answer whether life ever existed on the red planet. Ground controllers at the space agency’s Jet Propulsion Laboratory in Pasadena, California, settled in nervously for the descent of Perseverance to the surface of Mars, long a deathtrap for incoming spacecraft. It takes a nail-biting 11 1/2 minutes for a signal that would confirm success to reach Earth. The landing of the six-wheeled vehicle would mark the third visit to Mars in just over a week. Two spacecraft from the United Arab Emirates and China swung into orbit around the planet on successive days last week. All three missions lifted off in July to take advantage of the close alignment of Earth and Mars, traveling some 300 million miles in nearly seven months. …