Milkyway nannites

From laboratory work on presolar particles incorporated into meteorites, we know that small particles ejected by radiation pressure from stars, and spread across the galaxy in dust clouds, make it to the surface of planets in new solar systems. That means that we can similarly launch particles, sufficiently small to be ejected by our sun's radiation pressure, out into the interstellar medium for later emergence on planetary surfaces in new star systems. This would emphatically not happen quickly (we're likely talking >10^8 year time lines) but it would be limited not so much by money as my our cleverness in particle design. Think of it as the low-budget long-term approach to taking over the galaxy.

Footnotes

• Maria Lugaro (2005) Stardust from Meteorites: An Introduction to Presolar Grains (World Scientific, NY) 209 pp., ISBN 9812560998, 9789812560995 preview
• Imperial College London's astrophysicist David L. Clements Sailors of the Second Sun in Analog Jul 2019 discusses "life in the atmosphere of brown dwarfs" expanding to other brown dwarfs using radiation pressure in this way.