Subaru Telescope has been collaborating with the NASA’s first Pluto-Kuiper Belt mission called “New Horizons.” This article introduces the mission features and research contents.

Solar system exploration by spacecraft has been very active. After the 1960’s, the USA and the Soviet Union (present day Russia) have sent spacecraft one after another to Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune. On the other hand, Japan has also obtained remarkable results from space missions for small objects such as asteroids and comets; particularly the “Hayabusa” (“falcon” in Japanese) mission of rendezvousing and observing an asteroid “Itokawa” is still fresh in our memory.

Pluto, the farthest planet in the solar system with an average distance of about 6 billion kilometers (3.8 billion miles) from Earth, is the only planet which no spacecraft has approached. NASA has selected a Pluto-Kuiper Belt mission “New Horizons” as the first project of an open competition “New Frontiers Program.” The New Horizons spacecraft, similar to the size of a car, has 7 science instruments including cameras and spectroscopes to observe the atmosphere and surface of objects.

The New Horizons spacecraft is going to be launched with an Atlas V rocket from Cape Canaveral Air Force Station in Florida on January 17, 2006. It will cut across the moon’s orbit in just about 9 hours after the launch, pass near Jupiter in February 2007, and get through and observe Pluto and its satellite Charon at 14 kilometers a second in 2015 (Fig. 2). After this exploration, the spacecraft will keep sailing farther and approach Kuiper Belt Objects (KBOs; or Edgeworth-Kuiper Belt Objects) spreading over the outer solar system through 2016 to 2020 (Fig. 3).

The existence of KBOs, which were not able to finish becoming planets, was predicted by two astronomers about 50 years ago. The first KBO was found in 1992, and the total number of discovered KBOs is about 1,000 so far. The range of the KBOs’ diameters is from about 100 kilometers (about 60 miles) to about 1,000 kilometers (about 600 miles), and their surfaces are thought to be composed of ice and dust. The details are still unrevealed, because it is very difficult to observe from Earth due to the long-distance.

However, no KBO approachable by the New Horizons spacecraft has been discovered yet. The mission team PI Alan Stern noticed that the 8-m Subaru Telescope and a wide-field camera “Suprime-Cam” is the best combination to search KBOs for the mission, and proposed collaboration to the Director of Subaru Telescope Hiroshi Karoji.

Subaru has used about 20 nights of Director’s discretionary time for New Horizons since April of 2004 (Fig. 4). The observations led to some terabytes of data. The Japanese research team[*] and New Horizons team are currently analyzing Subaru’s data to find approachable KBOs. Once such a KBO is discovered, the spacecraft’s orbit will be maneuvered after the Pluto passage.

Pluto and KBOs have never seen by an approaching spacecraft, and they are thought to retain conditions from when the solar system was formed. Researchers expect that we will be able to obtain new knowledge on planetary formation and the history of the solar system from the detailed explorations by the New Horizons spacecraft.

“When the spacecraft approach the objects discovered by Subaru, the children of today will be adults. I want to see the launch of the spacecraft which will be traveling through the solar system for more than 10 years,” said Tetsuharu Fuse, Subaru Telescope, who conducted the Subaru observations and also attended New Horizons’ science team meetings (Fig. 5).

[*] Japanese research team: H. Karoji, T. Fuse, S. Miyazaki, H. Furusawa (Subaru Telescope, NAOJ), T. Yanagisawa (JAXA), F. Yoshida (NAOJ), D. Kinoshita (NCU, Taiwan)


* New Horizons mission web site

* NASA’s New Horizons web site


[Fig.1:] Pluto (left) and its satellite Charon observed with Subaru

[Fig.2:] An illustration of the spacecraft passing by Pluto (left) and Charon. (JHU/APL)

[Fig.3:] An illustration of the spacecraft approaching a KBO. (JHU/APL)

[Fig.4: (11KB)] Scene of KBO observations with Subaru

[Fig.5: (161KB)] New Horizons team group picture