Curiosity, the largest and most advanced spacecraft ever sent to another planet, appears to have landed on Mars to begin its pioneering, two-year hunt for the building blocks of life — signs that Earth’s creatures may not be alone in the universe.

The craft was scheduled to land at 10:31 p.m. Pacific time in an ancient geological feature known as Gale Crater.

The landing site was 154 million miles from home, enough distance that the spacecraft’s elaborate landing sequence had to be automated. The Earth also “set” below the Mars horizon shortly before landing, making even delayed direct communication with mission control impossible — and confirmation of Curiosity’s fate tricky.

PHOTOS: Preparing for Martian landing

Engineers were waiting for a passing satellite, Odyssey, to relay a series of three messages from Curiosity. One would indicate the robot’s rough position and how hard it had landed; another would indicate that it was no longer moving; and a third would indicate that the spacecraft was emitting a continuous stream of communication.

If Curiosity’s success is confirmed, it would be a moment of triumph for NASA and the Jet Propulsion Laboratory in La Cañada Flintridge, which is managing the $2.5-billion mission.

Shortly after 10:31 p.m., engineers inside mission control appeared to indicate that they were receiving at least some of those messages, indicating that Curiosity had survived its elaborate landing sequence.

INTERACTIVE: Curiosity, from liftoff to landing

Curiosity is expected to revolutionize the understanding of Mars, gathering evidence that Mars is or was capable of fostering life, probably in microbial form.

The spacecraft is also expected to pave the way for important leaps in deep-space exploration, including bringing Martian rock or soil back to Earth for detailed analysis and, eventually, human exploration.

President Obama has established a goal of sending astronauts to Mars in the 2030’s, and John Grunsfeld, NASA’s associate administrator, said on Sunday that humans might one day live there too.

“Curiosity has captured the imagination of the world,” Grunsfeld said before the landing. “We’re about to do something that I think is just huge for humankind.”

PHOTOS: History of Mars exploration