Kuiper Belts around other Stars
The green light signal arrived from New Horizons earlier today as it traverses the Kuiper Belt. It tells the NH team that the spacecraft (while mostly asleep) is still safely on its way to the next object on its itinerary. That’s another tiny step in the exploration of the outer solar system.
While this study of our own trans-Neptunian region is underway, keep in mind that it’s probably not the only such region in the galaxy. Other stars that have dusty disks around them are pretty likely to have their own versions of this collection of objects. These “extrasolar” disks and belts could be populated with many of the same types of object that we see in ours.
Why Study these Regions?
A number of stars have dusty planet-forming disks around them. Studying those distant Kuiper Belts helps us understand the region where Pluto, Quaoar, Makemake, and Haumea now orbit. Most are pretty young. These “baby” disks are likely a bit narrower and flatter than the older ones, and their materials are still sorting themselves out. Planets form in the disk, some closer to the star than others. The icy “leftovers” eventually migrate to the outer regions where they won’t be destroyed by the heat of the star.
Without going into gory details about disk dynamics, that’s more or less how our planets got sorted out in the early solar system. The rocky bodies formed close to the Sun. The gas giants may well have formed closer to the Sun than where they are now. However, through the disk’s evolution, they made their way out to cooler regions where their gases and ices could exist. The cometary bodies and dwarf planets (icy or ice-covered bodies for the most part) also settled out in the deep freeze.
Plumbing the Depths of our Own Kuiper Belt
Astronomers use many tools to study the regions beyond Neptune. Joining Hubble Space Telescope in the hunt for worlds “out there” is a myriad of observers using ground-based telescopes such as the Palomar Observatory in California, the European Southern Observatory in Chile, the Keck telescopes in Hawai’i, and orbiting observatories such as the Spitzer Space Telescope (which is sensitive to infrared light). Using infrared telescopes helps astronomers detect the “warmth” of these objects as they orbit in the much-colder outer solar system. Even cold bodies such as Pluto can glow in the infrared, giving off clues about them. Granted, they’re very distant and small. So, even with well-equipped facilities, they can and will continue to be difficult to find.
What tales will they tell us about themselves and maybe our own Kuiper Belt? For one thing, studying them long-term will allow astronomers to watch them evolve (slowly but surely). Look at their structures can reveal gaps where giant planets form. As those worlds coalesce, they can nudge smaller objects out to alien Kuiper Belts. That helps astronomers understand how own Belt and Oort Cloud formed billions of years ago. Finally, studies of the distant regions of those disks may reveal water ice and other frozen constituents of outer-system worlds. They could be very similar to what we see at Pluto and beyond. On the flip side, our own Kuiper Belt can tell astronomers what to look for at other circumstellar disks. It’s win-win all the way around.