NASA has successfully landed five robots on Mars over the past three decades. Its latest spacecraft, Phoenix Mars, will touch down in the Martian arctic region Sunday. Here’s why NASA is going again.

How is the Phoenix lander different from the Mars rovers that went up four years ago?

Phoenix is a lander, which means it will stay in place after touchdown unlike the rovers, which explored. Phoenix will dig down into the soil; the rovers drilled into surface rocks. Also, Phoenix is half as expensive as the rovers, costing $420 million to develop and launch.

Where will Phoenix land?

Phoenix will touch down on Mars’ high northern latitudes – similar in location to Earth’s Greenland or northern Alaska. Scientists chose that site because it’s flat and relatively rock-free.

What are the main goals of the Phoenix mission?

To find out whether the landing site has an environment suitable for life to emerge. Phoenix will study whether there was once water at the site and sample the soil for traces of organic compounds, two essential ingredients for life. However, Phoenix is not equipped to detect past or present life.

What’s the next step if Phoenix finds out there are ingredients for life?

The Martian arctic region would suddenly be an attractive site for future exploration. It will likely spur interest in revisiting the area with a more capable robotic probe designed to find life. NASA currently does not have plans to go back to Phoenix’s landing site.

How does the Phoenix landing compare to past Mars touchdowns?

Unlike the rovers, which used airbags to cushion their landing, Phoenix will attempt a soft landing. It will use a parachute to slow down, then fire its thrusters to land.

If successful, it will be the first time since the twin Viking missions of 1976 that a spacecraft has done a powered landing on Mars.