At https://phys.org/print410429403.html … sent in by William, an unusual story concerning the orbit of Mars and some mini planets (known as Trojans). These are really asteroids and they all share a common ancestry we are told in what had once been a single body. In other words they are the remains of a mini planet – rather than a succession of mini planets in themselves. Their origin is millions, if not billions, of years ago – we are also told. The reason they have been targeted as all belonging to a single cosmic object is their make -up, displaying heavy signs of olivine. The mineral is supposed to be prominent in the mantle of the Earth and there is speculation the asteroids come from the missing mantle of Mars.
…the same story is at www.dailymail.co.uk/sciencetech/article-4378550/Remains-ancient-planet-s… (sent in by Gary).