 Dust is the base material for planet formation. The dust grains run into each other and stick, forming larger and larger grains, mixing compounds and eventually forming mineral-rich pebble-sized objects that grow to boulder size. The near-Earth asteroid 2015 TC-25 is an example of an object this size. With a 4 meter diameter, that's 13 feet, it's one of the smallest asteroids ever detected. The process continues to grow the rocks into rubble heaps, large enough for a little gravity to hold them together. Ryugu is an example of an object this size. It's one kilometer wide and weighs in at just under a half a trillion kilograms. Japan landed rovers on this asteroid in 2018. You can see the rubble nature of the object with this picture, taken from the surface. By the time enough matter has accumulated into objects like these, we have what astronomers call planetesimals. These can extend from several to hundreds of kilometers in diameter. Object 67P, visited by the Rosetta mission in 2014, is thought to be a combination of two planetesimals that bound together in a slow-speed collision. Their combined mass is just under 10 trillion kilograms. This is a roacoth. It was discovered in 2014 out in the Kuiper Belt by the New Horizons search team using the Hubble Space Telescope. This object is 36 kilometers across. It's 22 miles. It's considered a minor planet like Pluto. Like P67, it has two lobes that collided slowly. A close examination of the surface shows lighter lines separating sections of the lobe. These indicate that a roacoth was built piece by piece by the coalescing of over a dozen smaller planetesimals. By the time this collide-and-merge process creates objects with enough mass to produce a gravitational strength that exceeds the structural strength of the rocks, the object is forced into a spherical shape. Series is a good example of this. And once the mass reaches around 14 billion trillion kilograms, solid mass convection activates. The temperatures and pressures inside the object liquefy matter, and the core becomes molten. Mercury, our smallest planet, is a good example of this. The star, Formelhout, is a good example of this process. Its circumstellar disc morphed into a protoplanetary disc with at least one object large enough to be considered a planet. Formelhout B. Some approximate measurements. My. You. Me. You. You. Me. I. I'm. Me. Me. I'm. Me. Me. Me. Me. Me. Me. Me. Me. Me. Me. Me. Me.