Thanksgiving invader

There is some excitement about comet 3I/ATLAS, discovered in 2025 July 1.

In this space view, the dashed line is the vernal equinox direction, longitude 0. The viewpoint is 6 AU (astronomical unit, Sun-Earth distances, about 150 million kilometers or 93 million miles) from the Sun, and at latitude 15° north of the ecliptic plane. The paths of the planes are shown in November; the trajectory of the comet is shown in the last three months of 2025, with stalks to the ecliptic plane at the beginning of each month.

In the comet’s designation, ATLAS means that it was found by the team operating the Asteroidal Terrestrial-impact Last Alert System’s robotic telescope. And 3I means that it is the third known to be interstellar: calculations show that it was not formerly in a long orbit around the Sun, like others with huge and very eccentric orbits, but has entered the our star’s gravitational domain from outside. (Its eccentricity is given as 6.13, where 0 is a circle and 1 is a parabola.)

So, is it a spaceship bringing invaders from an alien civilization?

Probably not. Unlike the alien invaders for whose arrival the natives of America did not give thanks in 1621.

The interstellar traveler was, if my calculations are correct, at opposition on June 25; at perihelion on October 29; and will be nearest to Earth on December 19 – a safely distant 1.8 AU.

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