Alfa 177

From Memory Alpha, the free Star Trek reference.

Alfa 177 was a planet in or near Federation space. It has a nighttime temperature that reaches 120º below zero. The planet is capable of supporting life and it is also rich in a soft yellow magnetic ore with highly unusual properties.

In 2266, the USS Enterprise was on a specimen-gathering mission to this planet. While there, they brought aboard a species of dog native to the planet. Also, a member of the landing party became covered with the yellow magnetic ore, which damaged the transporters and caused the device to divide transporter signals. (TOS: "The Enemy Within")

Alfa 177 was mentioned as a small note on a very large star chart graphic created for TNG: "Conspiracy". It was the image behind the chair in the room where Dexter Remmick was killed. It appears to be located within an outlined block, which may indicate that it was surrounded or was even a part of Federation territory at the time.