A Solar System research
team from the National Astronomical Observatory of Japan
(NAOJ), the Graduate University for Advanced Studies, and
the Science University of Tokyo have discovered small objects
extended within the outer solar system using Subaru Telescope.
Although more than 350 such objects are now known, these
are the first discovered by Japanese astronomers.
Around 1950, Edgeworth and Kuiper independently proposed
that there should be many small objects in the outer solar
system that never became planets. We call them "Edgeworth-Kuiper
Belt Objects (EKBOs)." Since we believe that they are
composed of the materials of the early Solar System in their
original state, EKBOs should be very useful objects for
teaching us about how the Solar System formed. EKBOs may
also be the source of the short-period comets, according
to computer simulations.
The first EKBO was discovered with the University of Hawaii's
24" telescope at the summit of Mauna Kea in August
1992. In the nine years since the discovery of this EKBO
(named 1992 QB1), more than 350 EKBOs have now been observed.
On UT February 21 and 24, 2001, the Japanese team of astronomers
discovered nine candidates for new EKBOs using the Subaru
prime-focus camera (Suprime-Cam). Since two of the nine
objects have observations on both days and their initial
orbits have been determined, the International Astronomical
Union has classified them as EKBOs and given them provisional
designations "2001 DR106" and "2001 DS106."
The distance between the objects and the earth is approximately
6.3 billion kilometers and their brightness is approximately
25th magnitude, a value about forty million times fainter
than what can be seen with the unaided human eye (sixth
magnitude). The objects are estimated to be approximately
100 kilometers in diameter, about 10% the size of the largest
asteroid Ceres (910 kilometers). These observations show
that the projected surface density of objects the size of
these two EKBOs is approximately 10 per square degree along
the plane of the ecliptic, consistent with previous results.
Compared to the asteroids which exist between the orbits
of Mars and Jupiter, the motion of EKBOs against the stellar
background is very slow because they are much further from
the sun. Mr. Daisuke Kinoshita (Grad. Univ. for Advanced
Studies) and Mr. Naotaka Yamamoto (Science Univ. of Tokyo)
have developed an auto-detection program for slow moving
EKBOs. They comment, "I tremendously realized the great
performance of Subaru and Suprime-Cam"; "it's
impossible to describe the impression when I look at the
results of the program." According to Dr. Jun-ichi
Watanabe (NAOJ), the team leader, "Subaru's wide-field
and big mirror offers the highest performance in the world
for this type of work, and I fully expect more discoveries
to be made." This is just the starting point for Subaru's
EKBO studies.
The results are reported in Minor Planets Electric Circular
MPEC 2001-J33
(
http://cfa-www.harvard.edu/mpec/K01/K01J33.html)
issued on May 15, 2001.
