The Nozomi orbiter was to reach Mars orbit in 1999 but sputtered during a slingshot maneuver around Earth. Nozomi, also known as Planet-B, guzzled so much fuel during a course correction that it must wait four additional years. It will focus its instruments on the upper atmosphere, a study that could shed light on how Mars lost water over time. Scientists have long thought Mars' surface coursed with water billions of years ago, based on evidence of liquid erosion and signs of ancient channels and seas. But the water all but disappeared as the planet cooled and its atmosphere thinned.
Water exists today as ice in the northern polar cap and as vapor in faint clouds.
But until last week's announcement, few scientists held out hope that the cold, arid planet could possibly have retained liquid water into the recent geologic past. Given that European and Japanese spacecraft should reach the martian system in 2003, the United States might feel pressured to join the exploration party, one NASA scientist acknowledged. But scientists dismiss suggestions of a serious rivalry among government space agencies. The world community should have plenty of time to cooperate on the search for martian water. No one will know exactly what the theoretical wet spots hold until probes study them directly, scientists said.