38 AUSTRALIAN SKY & TELESCOPE April 2019
Inexpensive amateur equipment is aiding astronomers
on their quest to find Kuiper Belt objects.
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 too faint to be
detected directly. 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 kilometre-size object — a missing
link between 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.
The Kuiper Belt is a sparse disk of
icy rocks extending 20 astronomical
units (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 andMakemake, 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 merging into each
other to build successively bigger bodies.
The leftovers of this process ought to
include far more smaller objects than
larger ones; indeed, monitoring stars
for occultations has turned up several
candidates less than a kilometre in
size. But until now, surveys hadn’t seen
kilometre-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 a 28-cm Celestron astrograph,
equipped with a ZWO ASI1600 MM-C
camera on a Takahashi equatorial mount.
Combined with a focal reducer, computer
and data storage, the cost of each system
came to $22,000 — relatively cheap
compared to professional equipment.
Dubbed the Organized Autotelescopes
for Serendipitous Event Survey (OASES),
the telescopes were set up on the
rooftop of the Miyako open-air schoolObjects in the Kuiper Belt, one
of which is depicted here in an
artist’s concept, are the pristine
remnants of planet formation
in our Solar System, thanks
to their dark, cold and lonely
environments.KO ARIMATSUAmateur scopes help find missing link
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,
aircraft or atmospheric turbulence.
The telescopes amassed 60 hours
under good weather 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 kilometres
across.
“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 kilometre-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 kilometre-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.DISTANT WORLDS 2 by Monica Young