If visitors to our solar system are on a similar scale of a few grams we're unlikely to detect them soon. If they can fit von Neumann constructors in those and

If visitors to our solar system are on a similar scale of a few grams we're unlikely to detect them soon. If they can fit von Neumann constructors in those and make them to survive planet fall we may be their offspring. If we could reach and seed potentially habitable planets that we wouldn't we? Shouldn't we?