The duration of the dip discloses its orbital inclination. Thus we can calculate the size, mass, and even the average density of the planet unambiguously. Many are extremely close to their parent star, and those farther out have highly elliptical orbits. Terrestrial planets, composed of less volatile materials, are expected to form close to the star, while gas giants, comprised of more volatile materials, should only be able to form in the colder regions much farther from the star. Though there is still much debate, current theory and computer modeling suggests the following scenario.
Gas giants do form farther out.
But spiral density waves in the remaining protoplanetary disk material, through which these planets orbit, creates a torque that causes them to migrate in toward the star. Some suggest that they actually do, with many cycles of planets forming and crashing into the star. Only those forming toward the end, when very little protoplanetary material remains, survive and don't spiral into their stars. However, protoplanetary disks are thought to last for only 10-100 million years. Under current models, there is simply not enough time for these multiple cycles of planetary formation to occur.