A rocket has been developed that could get a spaceprobe to the moon on just 100g of fuel
Some tasks can only be done by a large satellite, but there are many others which can be done as well if not better with several smaller ones. Any measurement which requires measuring something in more than one place, like magnetic field, solar wind or gravity, is much better done with more small probes, as could be exploring a planet where 20 small rovers can cover more ground than one big one.
These nanosats have been gaining in popularity, but so far they have had no way of moving, chemical rockets need a lot of heavy fuel, because the exhaust gasses move out of the back of the rocket relatively slowly so each gram of fuel only gives a limited push. Electric ion thrusters, throw xenon gas out of the back of the rocket 10 times faster than a chemical rocket so use a tenth of the fuel, but they are complex, involving piping gas about, valves and other devices which don't miniaturise easily.
However the Dutch company EFPL has managed to build an ion thruster which could weigh as little as 200g including the fuel. They have simplified the design by instead of using a gas as the fuel, using an ionic liquid, this is a liquid made up of positive and negative ions, a bit like molten salt, but which will stay liquid in the cold of space, and won't evaporate. They move this liquid from the tank to the thruster which is made using similar processes to a computer chip using capillary action, and then accelerate the ions out of the back using an alternating high voltage, first pushing out the positive then the negative ions out of the back producing thrust. This thrust is minute equivalent to the weight of a square cm of paper on earth, but in space there is no friction, and the rocket can keep firing for years, allowing it to move a long way.
The first use they want to make of this rocket is on a satellite called clean space 1, which aims to launch in 3-5 years time and is designed to tidy up old defunct satellites and other space junk by capturing them and dragging them into the atmosphere. Though the same rocket design could be used for small cheap satellites in earth's orbit which need to maintain their position, or for missions to the moon, which would only take 100g of fuel for a 1kg probe, or even further into the solar system, opening up the possibility of cheaply reaching the moon or even further out into the solar system, opening up all sorts of interesting scientific possibilities.