A surprisingly inexpensive setup of amateur equipment is helping astronomers on their quest to find Kuiper Belt objects of every size to better understand how planets formed in our solar system.
Blink and you’ll miss it.
Every now and then a star appears to flicker out for a fraction of a second, its light blocked when a small object in the outer solar system passes in front of it. While some of these objects are large enough to be seen by the sunlight they reflect, most are far too small and thus too faint to be detected directly. So-called stellar occultations, where the light of a background star briefly winks out, are one of the only ways to know these objects exist.
Now, astronomers using amateur equipment to monitor some 2,000 stars have discovered what appears to be a kilometer-size object — a missing link between the size of the dwarf planets and the many, much smaller objects in the far-out Kuiper Belt. Its mere existence points to a great many more where it came from and promises to shed light on how planets formed in the solar system.
A Belt of Ancient Remnants
The Kuiper Belt is a sparse disk of icy rocks extending 20 a.u. beyond Neptune’s orbit. These objects are the building blocks leftover from our solar system’s planet formation. Thanks to their cold, dark and lonely environment, they’ve remained largely unchanged over the past 4.5 billion years or so. The largest and more famous representatives are the three dwarf planets Pluto, Haumea, and Makemake, which span 2,400 km, 1,600 km, and 1,400 km, respectively. But the disk probably contains hundreds of thousands of smaller objects, too.
Planets are thought to have formed by accretion, pieces glomming onto each other to build successively bigger bodies. The leftovers of this process ought to include a good deal more smaller objects than larger ones; indeed, monitoring stars for occultations has turned up several candidates less than a kilometer in size. But until now, surveys hadn’t seen kilometer-size objects.
To extend the search toward the rarer, larger Kuiper Belt objects, Ko Arimatsu (National Astronomical Observatory of Japan) led a team in setting up two identical observing systems using off-the-shelf equipment. The two setups each included an 11-inch Celestron astrograph, equipped with a ZWO ASI1600 MM-C CMOS camera, on a Takahashi equatorial mount. Combined with a focal reducer, control computer, and data storage, the total cost of each system came to $16,000 — relatively cheap compared to most professional equipment.
Dubbed the Organized Autotelescopes for Serendipitous Event Survey (OASES), the telescopes were set up on the rooftop of the Miyako open-air school on Miyako Island, Japan. Having two identical systems helped the astronomers correct for other objects that might block or alter a star’s light, such as birds, airplanes, or atmospheric turbulence.
A Kilometer-size Kuiper Belt Object
Observing for a little over a year, the telescopes amassed 60 hours under good weather conditions over the course of about 13 months. Put in terms of observing hours per star in the field of view, OASES captured the equivalent of 60,500 “star hours.” Out of all of this data — which amounts to 50 terabytes — Arimatsu and colleagues found a single blip that marked a candidate Kuiper Belt object between 1.2 and 2.1 kilometers in radius. The discovery appeared in Nature Astronomy on January 28th.
“This is a real victory for little projects,” Arimatsu says. “Our team had less than 0.3% of the budget of large international projects. We didn’t even have enough money to build a second dome to protect our second telescope! Yet we still managed to make a discovery that is impossible for the big projects.”
Granted, the scientists only have a single kilometer-size detection in hand, but even that one event is more than they expected based on the number of smaller Kuiper Belt objects. The fact that they were able to detect even a single kilometer-size object suggests an abundance of icy rocks of this size, perhaps indicating that this was the typical size of protoplanetary bodies in the primordial solar system.
For the researchers, the event marks a proof of concept: “Now that we know our system works, we will investigate the Kuiper Belt in more detail,” Arimatsu says.