In Liu Cixin’s “The Three-Body Problem,” the alien civilization is known as the Trisolarans. They originate on the planet Trisolaris, a world whose chaotic orbit around three suns produces repeated eras of stability, extreme climate, destruction, and recovery.
Because their home planet is so unstable, the Trisolarans seek a more reliable place to live. The civilization becomes aware of Earth after astronomer Ye Wenjie uses the Sun as an amplifier to send a message into space. Her decision to reveal Earth’s location changes the future of both worlds and helps trigger the central conflict of the trilogy.
The Trisolarans are technologically far ahead of humanity. Their sophons—protons unfolded and engineered into advanced devices—can monitor Earth and interfere with particle-physics experiments. Their invasion fleet is expected to take centuries to reach the Solar System, giving humanity time to organize a response while also creating fear, political division, and scientific uncertainty.
“Trisolarans” refers to the inhabitants or civilization, not simply the planet. “Trisolaris” is the world they inhabit, while the three-body problem describes the orbital difficulty caused by its three suns. Martians, Zerg, and Alpha Centaurians belong to other fictional settings or concepts and are not Liu’s canonical term.