Comet 3I/ATLAS is expected to make its closest pass by the Sun on Oct. 30, when it will fly 130 million miles inside the orbit of Mars. It comes closest to Earth in December, when it is 170 million miles away. Because of its odd orbit, it's never coming back.

Given 3I/ATLAS' highly eccentric orbit, this will be its one and only visit to our solar system, as its trajectory does not loop back around the sun. That's why astronomers around the world are using a wide variety of telescopes to observe the comet during its brief visit, before it returns to interstellar space.