At www.astronomy.com/2018/05/the-first-interstellar-immigrant#.WwkdtRo80vA…. … (link provided by Jovan). In a study published in the Monthly Notices of the Royal Astronomical Society; Letter, astronomers announced the discovery of the first interstellar object known to have taken up permanent residence in the solar system, an asteroid. It has a peculiar yet stable orbit. It is almost in perfect resonance with Jupiter yet travels in the opposite direction. It is theorised that if the asteroid was native to our own solar system it should have the the same rotational direction as the other planets and asteroids (assuming they were born in a cloud of gas). The protoplanetary disc spins in the same driection as the star spins – hence the planets rotate the same way (and all other space objects should do likewise, including comets and asteroids). However, they can travel on contrary orbits if kicked out by a larger object, such as Jupiter (for example) but rotating in opposite direction appears to be something different. The researchers argue that because it does not rotate in the right direction this asteroid must be an interloper.
The same story is at www.scientificamerican.com/article/astronomers-spot-potential-interstell… … where an interesting addition is included. If the solar system is home to objects born in different star systems matter carried by these alien objects may have influenced life on earth. In addition, it would add complications to the mainstream scenario, and the construct we are all familiar with. It may affect the timing and mechanics of planet construction and the delivery of water and molecules to the surface of the earth, and the genesis of life itself. If the latter hitch hiked a ride on an alien asteroid after forming elsewhere in the galaxy – the whole carefully constructed story of the solar system and how it came about may be all hot air. Mind you, it might be hot air anyhow.