海角大神

NASA has whittled to four the number of potential landing sites for its 2016 mission to Mars. All of the 鈥渟emifinalists,鈥� as the agency puts it, are un-interesting, featureless plots.

NASA鈥檚 next mission to Mars is scheduled to land on the planet in August 2016, six months after its launch from Earth. Called the Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport lander 鈥� or, more succinctly, InSight 鈥� the to investigate the Red Planet鈥檚 interior and its formation some 4.6 billion years ago. Scientists hope that plumbing beneath Mars鈥檚 surface will help in explaining the processes that formed Earth, as well as the exoplanets popping up in new portraits of the universe.

Choosing a landing ground for InSight is much simpler than choosing one for a Mars rover, said Matthew Golombek, a geologist at NASA鈥檚 Jet Propulsion Laboratory. Rovers must be put down near the features they鈥檝e been outfitted to research, which means that the crafts have been deposited next to interesting plains or mountains. But InSight is designed to research Mars鈥檚 interior, which, conveniently, is accessible all over the planet, as long as the surface is soft enough to penetrate.

鈥淲hen you land a rover, it鈥檚 designed to measure certain things, so you have to make sure those things are available,鈥� says Dr. Golombek. 鈥淗ere, there are no real scientific requirements. That makes the job dramatically easier.鈥�

Still, there are some conditions that a plausible landing spot must meet. The four landing-site candidates, selected from an initial roster of 22 potential plots of real estate, are all in Mars鈥檚 Elysium Planitia, an equatorial plain named for the ancient Greeks鈥� heroic afterlife.

That region, about 500 miles southward from Curiosity鈥檚 touchdown spot, is near enough to the equator to protect landers from the cold closer to the poles, as well as primed to power the InSight鈥檚 solar array throughout the year. The region is also low enough in elevation to have the requisite atmosphere to decelerate the craft and, NASA hopes, land it without incident.

And though InSight is less hampered with the demands of science, it is perhaps more hampered with cost restrains than previous rover missions. InSight鈥檚 budget is capped at $425 million, not including rocket costs, as per the conditions of NASA鈥檚 , the competition through which the project won funding in August 2012. That means that the lander is reliant on cost-effective but imprecise landing gear 鈥� the same design that ferried to Mars' surface in 2008.

To cope with the imprecision, each of the four possible landing sites is an ellipse measuring 81 miles from east to west and 17 miles from north to south. That gives the lander a wide berth within which the craft has a 99 percent chance of landing. In comparison, the Curiosity rover 鈥� for which totaled about $2.5 billion 鈥� 聽could steer itself as it slipped through the atmosphere and about 12 miles by 16 miles wide.

鈥淭he less complex your landing system is, the bigger your uncertainty,鈥� says Bruce Banerdt, InSight principal investigator at the Jet Propulsion Laboratory.

Since it鈥檚 not possible to predict just where in that giant ellipse InSight will touch down, NASA scientists plan to next use images to make careful reviews of the four sites' potentially hazardous rocks and slopes, looking for the 鈥渇lattest and safest鈥� of the choices, says Dr. Banerdt.

In July of next year, the scientists will present the two choices believed to have the fewest number of obstacles within their borders. Then, a year after that, the scientists will choose just one site. That final site will also have to go through another review process before the lander is launched that spring 鈥� no stone will be left unturned, so to speak.

If the landing goes well, InSight will hammer a probe nine to 15 feet into the ground to monitor heat coming from the planet's interior. It will also use a seismometer to measure Martian earthquakes, as well as radio equipment to gauge the planet鈥檚 rotation pull.

Mars鈥� interior is believed to have changed little over the last four billion years or so, even as its surface, once warm and wet before the planet morphed into a 鈥淩ed鈥� one, has changed, says Banerdt, That鈥檚 because, so far as scientists know, Mars has not been subject to plate tectonics, the eraser-like process that has melted down all record of Earth鈥檚 own earliest years.

鈥淭hat evidence has been obliterated on the Earth,鈥� says Banerdt. 鈥淭o understand how planets formed, we need to go to a planet that hasn鈥檛 gone through a plate tectonic phase.鈥�