UCLA

One of the Solar System's most prominent characteristics is the division of its planets into two distinct groups. The terrestrial planets have short periods, low masses, and negligible atmospheres, while the gas and ice giants have wider separations and masses 1--2 orders of magnitude larger than their inner neighbors, the majority of which is stored in prodigious atmospheres surrounding small solid cores. This feature raises the question of whether our system's architecture is the result of chance, or if Nature has a tendency to produce planetary systems like ours. Until recently, an answer to this question was beyond reach, owing to the lack of available systems hosting both planet types. In this thesis, I investigate the occurrence rate of long-period giant planets in systems known to host an inner small planet. I used the $TESS$ target pool to compile a high-purity sample of 47 Sun-like stars hosting transiting planets, which I then observed for three years to search for long-period giants. Along the way, I discovered three giant planets and developed a novel computational tool for analyzing partial orbits. I found that the occurrence rate of giant planets increases from 16\% for typical Sun-like stars to 30\% in systems with a close-in small planet, an enhancement factor of $\sim$2. This enhancement demonstrates that Solar System analogs are not rare, and that the processes which produced Earth may obtain elsewhere in the Universe.