• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.2
• /
• pp.60.4-60.4
• /
• 2019

Small bodies in the solar system are pristine leftovers of planetesimals since the formation epoch (~4.6 Gyr ago). After the formation, icy planetesimals have been preserved in the distant cold place beyond 30 au (i.e., Trans-Neptunian region) until recently without any catastrophic processes but have just been injected into inner region (<~5 au from the Sun) to be observed as comets. On the contrary, asteroids are rocky primitive objects (although some of them contains icy volatiles) distributing in the mainbelt between Mars and Jupiter orbits. Because of frequent encounters in the mainbelt, asteroids have experienced a number of repeated impacts until the present day. Namely, it is important to investigate thermal alternation process of cometary volatiles and refractories in the solar radiation field, whereas collisional and subsequence phenomena of asteroidal bodies. Although recent spacecraft observations revealed the physical natures on the surfaces of comets and asteroids, their interiors still remain largely unexplored. It is likely that a sudden brightening of a comet is associated with rapid sublimation of internal CO and CO2 or phase transition of amorphous H2O. An episodic dust ejection from an asteroid is causally related to an impact among asteroids, sudden sublimation of remaining subsurficial volatiles, etc. Because these transient phenomena provide rare opportunities to investigate their interiors, immediate observations using any optical instruments are particular important. In my presentation, I will review some examples of such transient phenomena in the solar system and propose possible collaborative research using the Korean Small Telescope Network.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.1
• /
• pp.63.2-63.2
• /
• 2019

Eight hundred thousand asteroids in the solar system have been identified so far under extensive sky surveys. Kilometer to sub-km sized asteroids, however, are still waiting for discovery, and their size and orbital distribution will provide a better understanding of the collisional and dynamical evolution of the solar system. In order to study the number of asteroids which is detectable with 1.6 m telescope and their orbital distribution, we conducted a small observation campaign as a part of Deep Ecliptic Patrol of the Southern Sky (DEEP-South) project, which is an asteroid survey in the southern hemisphere with Korea Microlensing Telescope Network (KMTNet). We observed the ecliptic plane near opposition ($2^{\circ}{\times}2^{\circ}$ field of view centering on ${\alpha}=22h40m31s$, ${\delta}=-08^{\circ}22^{\prime}58^{{\prime}{\prime}}$) in August 2018, and identified 464 moving objects by visual inspection. As a result, 266 of 464 moving objects turn out to be previously unknown asteroids, and their signal to noise ratio is below two on numerous occasions. Most of the newly detected objects are main belt asteroids (MBAs), while three Hildas, one Jupiter trojan, and two Hungarias are also identified. In this meeting, we report the differences in the orbital distributions between the previously known asteroids and newly discovered ones using statistical methods. We also talk about the observational bias of this survey and suggest future works.

• Publications of The Korean Astronomical Society
• /
• v.27 no.4
• /
• pp.153-159
• /
• 2012

We constructed an unbiased asteroid catalog from the mid-infrared part of the All-Sky Survey with the Infrared Camera (IRC) on board AKARI. About 20% of the point source events recorded in the IRC All-Sky Survey observations were not used for the IRC Point Source Catalog in its production process because of a lack of multiple detection by position. Asteroids, which are moving objects on the celestial sphere, are included in these "residual events" We identified asteroids out of the residual events by matching them with the positions of known asteroids. For the identified asteroids, we calculated the size and albedo based on the Standard Thermal Model. Finally we had a new brand of asteroid catalog, which contains 5,120 objects, about twice as many as the IRAS asteroid catalog.

• Journal of The Korean Astronomical Society
• /
• v.29 no.spc1
• /
• pp.351-354
• /
• 1996

In this paper it is explained how most of asteroids can avoid very close approach to Jupiter, to the earth for earth orbit crossing asteroids, and to Neptune for Kuiper-belt asteroids by mechanisms which work also for Neptune-Pluto system. In fact the mutual distance of the planets cannot become very small as the critical argument librates around $180^{\circ}$ because of 2:3 mean motion resonance and the argument of perihelion of Pluto librates around $90^{\circ}$. And it is found that among nearly 40 Kuiper-belt asteroids discovered in recent years $40\%$ have orbits similar to Pluto. For main-belt asteroids the distribution with respect to the semi-major axes has peculiar characteristics and the author tries to explain how their peaks and gaps are created. It is also found that $30\%$ of 80 earth orbit crossing asteroids which have minimum perihelion distances less than 1.04AU have no chance to collide with the earth. Still $30\%$ of them have a few probability to collide with the earth as they have dynamical characteristics of short-periodic comets.

• The Bulletin of The Korean Astronomical Society
• /
• v.38 no.1
• /
• pp.60.1-60.1
• /
• 2013

Numerous dust particles are scattered in the interplanetary space of the solar system (Interplanetary Dust Particles; IDPs). The origin of the IDPs is one of the major questions in the solar system astronomy because IDPs are being removed from the solar system within a few million years by photon drag. Comets and asteroids were pointed out as the possible sources of IDPs. Although several dust supplying mechanisms from comets and asteroids have been revealed, amount of contribution from each sources are still not clear. Zodiacal light is sunlight scattered by IDPs. Spectra of zodiacal light can supply important observational clue to reveal the origin of the IDPs, because comets and each type of asteroids have different kind of spectra. However, reflectance spectrum of zodiacal light was not measured at the wavelength of weak atmospheric contamination. We measured the reflectance spectra of zodiacal light from $5000{\AA}$ to $7000{\AA}$. We used open data obtained by the Subaru/FOCAS instruments archived in the SMOKA database. From the longslit spectrum data, we measured spectrum of sky background and estimated flux from the sources other than the zodiacal light. We compared it with the spectra of each type of minor bodies in the solar system, and meteorites originated from these bodies.

• The Bulletin of The Korean Astronomical Society
• /
• v.45 no.1
• /
• pp.46.2-46.2
• /
• 2020

Dust ejection activities have been discovered from a few tens of asteroids since the first confirmation in 2006. Those objects are known as active asteroids. They provide good observational chances to study ongoing phenomena in the solar system such as sublimation of icy volatiles, mutual collisions among asteroids, rotational disintegrations, thermal fatigue, etc. Although dust ejection mechanisms of individual cases have been investigated through observations, the frequencies of the events and their connection to the overall evolutionary budget of the solar system have not yet been studied thoroughly, mainly because previous studies were based on serendipitous discoveries without any systematic surveys of these objects. In this work, we made wide-field monitoring observations of asteroids using Korea Microlensing Telescope Network (KMTNet) during the 2018/2019 winter season. Among 3,644 asteroids in the field-of-view, we detected nine candidates of brightness enhancements which we suspect as possible activities. It is still possible that some of those brightness increases have caused by long-term rotations. However, our observed frequency and brightness enhancements size-frequency distribution agrees with the expectations from impacts with decimeter sized objects, when the main belt objects size-frequency distribution observed down to decameter sized bodies are extrapolated to decimeter size.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.1
• /
• pp.83.1-83.1
• /
• 2019

Identifying asteroid families, which are groups of asteroids with similar orbital properties, is important for understanding the formation and evolution of the solar system, and probing the origins of Near-Earth Objects (NEOs). Although asteroid taxonomy can be used to identify and refine asteroid families, there are numerous asteroids which are not taxonomically classified yet. Korea Microlensing Telescope Network (KMTNet) can be useful to investigate types of that asteroids, because the telescope can observe a number of asteroids at once by its large field of view. Using KMTNet data, we confirmed that the taxonomic classification of the asteroids is possible by plotting color-color diagram. There is a clear division between C-type and S-type, but ambiguous division between C-type and X-type. In the future, we will observe and classify asteroids which are not classified yet and utilize the data to identify and refine asteroid families.

• The Bulletin of The Korean Astronomical Society
• /
• v.46 no.2
• /
• pp.57.2-57.2
• /
• 2021

An asteroid is important for understanding the condition of our solar system in early-stage because an asteroid, considered as a building block of the solar system, preserves the information when our solar system was formed. It has been continuously flowing into the near-Earth space, and then some asteroids have a probability of impacting Earth. Some asteroids have valuable minerals and volatiles for future resources in space activity. Korean government clarified, in the 3rd promotion plan for space activity, an asteroid sample return mission by the mid-2030s. However, it is almost impossible to do so based on only a single experience of an exploration mission to the Moon, Korea Pathfinder Lunar Orbiter, which will be launched in mid-2022. We propose a Rendezvous Mission to Apophis(RMA), beneficial in terms of science, impact hazardous, resource, and technical readiness for the space exploration of Korea.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.1
• /
• pp.63.1-63.1
• /
• 2019

Solar system small bodies are unusual objects in astronomical survey data in that they are moving on the celestial sphere. In addition, even in a normal status, their magnitudes are changing over time, firstly because their relative positions with respect to the Sun and Earth are continually changing, secondly because they are rotating bodies with non-spherical shapes. Furthermore, some of them might exhibit unexpected activities, which could be caused by mass ejection or disintegration. Detections and observations of such activities are challenging due to their abrupt nature. Therefore, continuous monitoring observations of large number of Solar system small bodies are required to systematically obtain detailed/transient information about them. Since 2018/2019 winter, we have launched a new project using Korea Microlensing Telescope Network (KMTNet) for detecting such transient phenomena of Solar system objects. Our main goal is to monitor the magnitudes and detect sudden brightness changes. We also plan to discover interesting new objects, and monitor rotational brightness oscillations of asteroids. We intend to monitor the magnitudes of ~ 20,000 known Solar system small bodies per night, and acquire lightcurves of ~ 1,000 asteroids.

• The Bulletin of The Korean Astronomical Society
• /
• v.39 no.2
• /
• pp.96.1-96.1
• /
• 2014

The rotation of asteroids can help reveal not only the fundamental characteristics of asteroids but also the origin and evolution of our Solar System. From the photometric observations for NEA 162173 (1999 JU3) and Maria family asteroids using 0.5 m- to 2 m- class telescopes at 10 observatories in the northern hemisphere, I obtained a total of 260 lightcurves for 97 asteroids and derived synodic rotational periods for 51 objects, including newly obtained periods of 34 asteroids. For the sake of efficiency, I developed an observation scheduler, SMART (Scheduler for Measuring Asteroid RoTation) and a photometric analysis software subsystem, ASAP (Asteroid Spin Analysis Package). Based on the lightcurve analysis of NEA 162173 (1999 JU3) and Maria family asteroids, 1) I present the rotational and observational characteristics of 1999 JU3 and provided the Hayabusa-2 Science team with the information on pole orientations, 2) I investigated correlations among rotational periods, amplitudes of lightcurves, and sizes, and conclude that the rotational properties of old-type family asteroids have been changed considerably by the YORP effect. 3) Finally, I found the Yarkovsky footprints on the Maria asteroid family and estimated that approximately 37 to 75 Maria family asteroids larger than 1 km have entered the near-Earth space every 100 Myr. This study should reveal the collisional history and transport route of the members from the resonance region to the near Earth space, for the first time.