[Chiba Institute of Technology] The structure of the outer solar system is being revealed
*Chiba Institute of Technology*
Press release: September 5, 2024
**
The structure of the outer solar system is being revealed
*- 20 years of challenges between Subaru Telescope and New Horizons -* Figure 1: Subaru Telescope (left) and New Horizons spacecraft (right). (Credit: National Astronomical Observatory of Japan/Southwest Research Institute)
Explorations using the Subaru Telescope’s ultra-wide-field prime focus camera have shown that there may be a group of celestial bodies that we don’t know about yet beyond the Kuiper belt. This research result, which is important for understanding the origins of the solar system, was obtained through international cooperation between the New Horizons spacecraft and the Subaru telescope, which are traveling through the outer reaches of the solar system.
The National Aeronautics and Space Administration (NASA)’s New Horizons spacecraft was launched in 2006 with the important mission of observing the surface of an outer solar system object up close for the first time in human history. In 2015, we successfully completed a flyby of the Pluto system, and in 2019 we conducted a flyby of Arrokoth, a Kuiper belt object (Note 1). There have been five spacecraft that have flown beyond the solar system, but New Horizons is the only spacecraft that has flown through the Kuiper Belt while observing Kuiper Belt objects.
When observing Kuiper belt objects from the ground, they can only be observed at a small solar phase angle (the angle between the sun, the object, and the observer). On the other hand, when a Kuiper belt object is observed from a spacecraft in the Kuiper belt, the surface state of the object can be estimated by observing the same object at various phase angles and examining its reflection characteristics. This is something only New Horizons can do.
However, the narrow field of view of the camera mounted on the spacecraft makes it impossible for the spacecraft to discover Kuiper belt objects by itself. This is where the Subaru Telescope comes in handy. The Subaru Telescope will use its wide-field camera to find many Kuiper Belt objects, and from among them, we will narrow down the objects that the spacecraft can flyby and those that can be observed from the spacecraft. This cooperation between New Horizons and the Subaru telescope began in 2004.
When observations were made with the Subaru Telescope’s prime focus camera, Suprime-Cam, from 2004 to 2005, due to the spacecraft’s orbit, the field of view for searching for Kuiper belt objects was toward the center of the Milky Way Galaxy. . It was extremely difficult to search for celestial objects in the presence of many background stars, but we were able to discover 24 Kuiper belt objects.
Unfortunately, the Kuiper Belt object discovered during this observation was not a candidate for flyby due to the spacecraft’s fuel limitations, but if it is a new object that is further away, it may be possible to reach it using New Horizons’ remaining fuel. I don’t know. From 2020, Subaru Telescope’s ultra-wide-field prime focus camera Hyper
Suprime* -Cam*
Deeper observations using the Hyper Supreme Cam (HSC) have begun, and 239 Kuiper Belt objects have been discovered through observations up to 2023.
“Before this discovery, a new machine learning technology was developed to search for celestial objects from the images observed, as well as observations with the Subaru Telescope. In order to verify this, each team member had to visually check thousands to tens of thousands of astronomical images, but their efforts paid off and we were able to achieve great results.” Team member Dr. Ryo Ishimaru (Chiba Institute of Technology Planetary Exploration Research Center) says:
“The most exciting thing about the HSC observations was that we discovered 11 celestial objects that are located at distances beyond the known Kuiper belt,” said research team member Dr. Fumi Yoshida (University of Occupational and Industrial Medicine; Chiba Institute of Technology Planetary Exploration). research center) speaks.
Many of the objects discovered by HSC are 30-55 meters from the Sun. It is located at a distance of 1 astronomical unit (au; 1 astronomical unit is equivalent to the distance between the Sun and the Earth) and is thought to be within the known Kuiper belt. On the other hand, what the research team did not expect was that 70-90
There seems to be a group of celestial objects around AU, and 55 AU and 70 The thing is that there appears to be a valley (with few celestial bodies) between the au. Such a valley has not been reported in other observations.
Figure 2: Distance distribution of Kuiper belt objects discovered by HSC. The horizontal axis is the distance from the sun to the celestial body, measured in units of Earth-sun distance (1 astronomical unit; au). The vertical axis is the number of celestial objects. (Credit: Wesley
Fraser)
“70-90
There may be a new group of celestial objects in au. If this is true, it would be a great discovery. “This means that the proto-solar nebula is much larger than previously believed, and this may have
implications for research into the solar system’s planet formation process,” says Dr. Yoshida.
Dr. Ishimaru also said, “Conventionally, the Kuiper belt in our solar system was thought to be extremely compact compared to the planetary disk outside our solar system. The results of this study, which suggest the existence of a Kuiper belt that extends far into the distance, will be important in understanding how the solar system is positioned among the many different planetary systems in the universe.”
Dr Alan Stern, leader of the New Horizons mission, said: “This groundbreaking discovery has revealed the existence of something unexpected, unknown and exciting in a remote region of the solar system. Without that ability, it would not have been possible.”
The research team is continuing observations using HSC to determine the exact orbits of the objects discovered in this study. “Discovering distant celestial bodies and clarifying their orbital distribution is an important clue to unraveling part of the history of the formation of the solar system. This research aims to learn about the formation history of the solar system, compare it with exoplanet systems, and explore the universal I think this is an important stepping stone to understanding planet formation,” says Dr. Yoshida, explaining its significance.
New Horizons is currently 60 degrees from the sun.
It is flying further outward from the au area. There are still many undiscovered distant objects. The research team is looking forward to seeing what the Subaru Telescope and New Horizons spacecraft will discover beyond the Kuiper Belt.
The results of this research will be published as two academic papers in the American scientific journal Planetary Science Journal. (1) Buie et al. 2024 “The New Horizons Extended Mission Target: Arrokoth Search and Discovery”
Preprint available here
National Astronomical Observatory of Japan September 5, 2024 Press Release
National Astronomical Observatory Astronomical Simulation Project September 5, 2024 News
Is the Kuiper belt unexpectedly vast? -Subaru Telescope cooperates with “New Horizons” with ultra-wide field observation- (June 26, 2024)