In reference to several commentators WRT to the energy you need to command to get to another star system, as I recall Eric Drexler in Engines of Creation posited this approach:
Use lasers pumped by your sun to accelerate a solar sail probe to a good fraction of c. Once that's done, the probe reassembles itself into a linear accelerator. As it flashes through the target system, the accelerator deaccelerates tiny probes, which make their way to planets. Those probes of course have nanotech which they use to assemble ... stuff (maybe even copies of the aliens).
Any one of a number of science fiction stories continue the plot from there.
Note that this approach will result in a signature the target system can see, as described in Niven and Pournelle's The Mote in God's Eye.
In reference to several commentators WRT to the energy you need to command to get to another star system, as I recall Eric Drexler in Engines of Creation posited this approach:
Use lasers pumped by your sun to accelerate a solar sail probe to a good fraction of c. Once that's done, the probe reassembles itself into a linear accelerator. As it flashes through the target system, the accelerator deaccelerates tiny probes, which make their way to planets. Those probes of course have nanotech which they use to assemble ... stuff (maybe even copies of the aliens).
Any one of a number of science fiction stories continue the plot from there.
Note that this approach will result in a signature the target system can see, as described in Niven and Pournelle's The Mote in God's Eye.