No signal from Mars Polar Lander

Just as NASA was about to abandon efforts to contact the Mars Polar Lander spacecraft, which vanished last Dec. 3, a radio signal Jan. 4 buoyed hopes that the craft was still alive on the Red Planet. The changing pitch of the signal, the radio equivalent of a whistle, indicated it could have been sent by the craft’s transmitter as it was warming up (SN: 2/19/00, p.