Alien asteroid

At the end of last year, a rock from far away in our galaxy happened to fall almost centrally through our solar system, and then out; I wrote more than I expected to about this first-known interstellar visitor, as well as about the Hawaiian name that was given to it,’Oumuamua.

Now another and larger rock has been found that apparently originated from outside the solar system, but has been inside it for billions of years, a permanent immigrant.

It is an asteroid with the preliminary designation 2015 BZ509, which means that it was recorded in the second half of January 2015, and it later got the number 514107; it is estimated to be about 3 kilometers wide.

What is unusual about it, and invited investigation, is that its orbit is both so similar to Jupiter’s and so different.  Its average distance from the Sun (5.14 astronomical units or Sun-Earth distances) is close to Jupiter’s, but the orbit is quite strongly elliptical (eccentricity 0.38) and inclined: 163°, which means it is retrograde.  That is, it moves around the Sun in the opposite direction from all the planets and most of the asteroids.

This remarkable orbit has the property of being almost resonant with that of Jupiter, and changes in it will tend to self-correct, making the orbit very stable.  There are some asteroids of the outer solar system whose orbits are retrograde, but not tied to Jupiter and probably not stable for long.

It looks as if 2015 BZ509 was captured by Jupiter’s gravity, and a mlllionfold computer simulation by the investigating scientists (Fathi Namouni and Helena Morais) suggested that this happened soon after the formation of the planets, 4.5 billion years ago.  And since it had been moving in a direction opposite to all the matter circulating around the Sun, it surely cam in from outside.

If this is an example of matter introduced into our solar system from the systems of other stars, there could be others, and there could be particles of them in our bodies.