Shuttle Discovery Head Home, Mars Lander Attempts 2nd Dirt Pickup

Space shuttle Discovery pulled away from the International Space Station on Wednesday, ending a nine-day visit highlighted by the installation of a new Japanese lab.

The shuttle and its crew of seven, including a Japanese astronaut, are due back on Earth on Saturday.

"We wish them the best with their expedition and we hope we left them a better, more capable space station than when we arrived. Sayonara," shuttle commander Mark Kelly told the space station crew before leaving.

"We wish you guys a terrific flight back, an awesome landing and look forward to seeing you on the ground," responded Gregory Chamitoff, the station's newest crew member.

Scientists troubleshooting the Phoenix lander said Monday they will try one last shake to get a scoopful of Martian dirt inside a tiny oven in hopes of jump-starting their study of Mars' north pole region.

Phoenix's first science experiment to heat the permafrost soil was delayed after it was discovered that virtually none of it passed through a screen to reach a miniature oven, one of eight aboard the spacecraft that will heat soil and sniff the resulting vapors for signs of life-friendly elements.

"This soil is very cohesive and it's very hard for it to get through the screen," said mission scientist William Boynton of the University of Arizona in Tucson, who is in charge of the oven experiment.