Our solar system includes our sun at the center; four rocky planets surrounding that; an asteroid belt; four gas giants; the icy Kuiper Belt of still more rock and snow. The appearance of two similar belts of debris, one warmer and one colder, happens in at least two very near-by star systems as well. Vega and Fomalhaut, both a relatively-neighborly 25 light-years away from us. New insights into these systems, aided by observations from the Spitzer Space Telescope and Herschel Space Observatory are leaving scientists with the impression that there must also be planets around those systems. In fact, the existence of the belts may actually depend on the existence of the planets.
When star systems form, they begin with clouds of dust. Once enough of the dust has been compacted into the center of the cloud by gravity, the sudden and rapid fusion of hydrogen atoms creates a huge nuclear furnace: the star is born. The rest of the dust begins to accrete into larger and larger rocks. Dust becomes asteroid. Asteroid becomes planetesimal. And if they eat their peas and clean their rooms, planetesimals become planets. All of this happens because gravity requires them to cling together.
But the heat of the sun also plays a role. Closer to our sun, large masses of gas were not allowed to form around planets, and thus the inner most orbits are rocky. Outer worlds become gas giants like Jupiter and Neptune, playing interplanetary Dust Buster to the surrounding material. What material stretched between these two temperature zones – and everything outside the gas giants’ reach – became asteroid belts.
That similar conditions exist within these other nearby star systems suggests strongly to scientists in both NASA and the ESA (European Space Agency, whose project the Herschel SO largely is) that similar planets must also exist. What is even more compelling about the evidence is that, while the parent stars Vega and Fomalhaut are both double the size of our sun:
The gap between the inner and outer debris belts for Vega and Fomalhaut also proportionally corresponds to the distance between our sun’s asteroid and Kuiper belts. This distance works out to a ratio of about 1:10, with the outer belt 10 times farther from its host star than the inner belt.
While much of the research into extra-Solar planets has been done by observing the wobbling movement of the parent star or observing the blink of transiting planets (see this kinda weird vid for a good explainer), more new technology is on the way in the form of the James Webb Space Telescope, among other projects. How many planets will we find? How many moons?
Read More: asteroid | exoplanetology | Vega