You can slow down - just that the probe won't remain intact. But perhaps that isn't necessary for the probe to be useful. We can also use these space probes to do geological and atmospheric surveys of the planet when they arrive.
Simply: we slam the probe into the planet, a few milliseconds after it transmits the final images. One gram going at 20% of the speed of light has kinetic energy that bears comparison to the Hiroshima bomb.
At a steep angle of entry, the huge entry glow will give a reading of the atmospheric molecular makeup. And if we can ionize some of the crust, massive space telescopes can get a spectroscopic measurement of the composition, four light years away.
now that's a way to say Hi to a foreign species! there isn't high chance this wouldn't be considered as an act of hostility, and if they would check our history of our current world, they would probably just decide to erase this dangerous species from the face of the universe for greater common good.
Could they carry mini solar sails to slow down? Solar parachutes if you will.
Or if we sent them in single file several seconds apart they could each relay what they see to the ones behind them and then back to us. Effective oh giving us a long exposure.
if even a tiny fraction of those 1000 tiny probes hit that planet at 20% of speed of light, could that pose a problem? it sounds like a shotgun approach, not so figuratively, using pellets loaded with plutonium.
The probes would each be only a few grams, so they'd have about 10^13 J of relativistic kinetic energy, or a half kilotons of TNT equivalent. This can be compared with the 15 kilotons for the (small, by modern standard) Little Boy atomic bomb. So it's probably noticeable for any inhabitants in the area, depending on how the energy is dissipated in the atmosphere, but still quite small on the scale of a planet.
It should be noted that meteors explode with Hiroshima-like force fairly regularly within Earth's atmosphere, on the order of once a decade or so. It happens high up enough that nobody notices beyond an occasional light show. The meteor explosion which hurt a bunch of people in Chelyabinsk a few years back was about 500 kilotons.
Indeed, that's pretty much what "duck and cover" was all about. There was even a school teacher in Chelyabinsk who apparently remembered her Cold War drills and had her students take cover, saving them from injury.
cool, good to know that raining down a bunch of probes in this manner would most likely be a pretty light show. still i wonder about the plutonium aspect of this?
it might be prudent to first consult with the legal experts and diplomats of the Galactic Council, to clear this type of activity with them first, minimize interpretation of this probing as a hostile interstellar act.
I don't think the plutonium would be enough to have any real effect, although it might irritate the inhabitants if there are any. Certainly, we've put far more plutonium into Earth's atmosphere by blowing up thousands of nuclear bombs in it, and we survived.
Clearing it with the Galactic Council definitely sounds like a good idea. Do you have their phone number handy? I seem to have deleted their contact info by accident.
>>So it's probably noticeable for any inhabitants in the area
An intelligent civilization with a 1000 year head start whose presence was just proven by device that arrived at 10% the speed of light would pretty much scare any government on earth.
I would assume it would scare the aliens there too.