IN THE LAST DECADE NASA'S KEPLER MISSION HAS REVOLUTIONIZED THE FIELD OF (EXO-)PLANETARY SCIENCE BY DISCOVERING MORE THAN 4000 PLANETARY CANDIDATES. ONE OF KEPLER'S KEY FINDINGS IS THAT THE MOST ABUNDANT PLANETS IN OUR GALAXY OBSERVED TO DATE ARE LARGER THAN EARTH BUT SMALLER THAN NEPTUNE. INTRIGUINGLY FURTHER OBSERVATIONS HAVE REVEALED A 'RADIUS VALLEY" IN THE DISTRIBUTION OF SUCH SMALL EXOPLANETS WITH PERIODS LESS THAN 100 DAYS