The European Space Agency's Rosetta spacecraft has been trying to reach out to Philae, the lander sitting on a comet hurtling through space.
After a journey of more than 10 years, Rosetta in November released Philae so the probe could land on the comet 67P/Churyumov-Gerasimenko. After bouncing around a bit on the comet's surface, Philae landed safely and worked continuously for 54 hours, using its 10 scientific instruments and sending data and images back to Earth.
Then, as expected, the lander's battery ran out.
Philae ended up in a more shaded area than scientists had planned and hope it can absorb enough solar power to kick itself back on. The scientists are anxiously waiting to see if the lander will be able to generate 19 watts of power so it can relay messages to Earth through Rosetta.
By studying comets, scientists say they may get critical clues about the origins of the sun and planets, as well as to how water arrived on Earth. Primitive comets are believed to be the building blocks of the solar system.
Earlier this month, ESA scientists had Rosetta, which has been orbiting the comet, send signals to Philae and listen for a response. So far, there has been no responding signal from the lander.
"It was a very early attempt; we will repeat this process until we receive a response from Philae," said Project Manager Stephan Ulamec of the ESA. "We have to be patient."
Scientists reported on the ESA website that the lander could be too cold or in too much shadow to charge up enough power to send a signal.
Scientists plan to try to communicate with Philae again in April, when the spacecraft is closer to the comet and Philae is exposed to more sunlight to generate power to receive and send signals.
"These conditions must last for at least 45 minutes, because Philae only operates its receiver every 30 minutes after awakening," said Koen Geurts, a member of the control room team, in a statement.
Unlike the March attempt, engineers will send commands to Philae to focus its energy solely on heating and communications. That should increase the odds of the lander having enough power to communicate with Rosetta.
"We are sure that the communication unit on the orbiter worked, but whether Philae has received the new commands, we do not yet know," said Geurts. It could be that the lander is already awake but doesn't have enough power to transmit a response. In that case, Philae could still receive the commands and execute them.
Scientists are hopeful that by summer, when the comet and Philae are much closer to the sun, that it will have enough power to come back to life and resume its work for a time.
"Philae is configured in an optimal way for on-comet survival," Geurts noted.