Periodic comets of different dynamical groups with orbits at 2 - 5 AU still occasionally active. The observed dust activity of such objects can be connected with processes of water ice sublimation (MBCs) or crystallization of amorphous water ice (QHCs) as well as with external causes. No connections of cometary flares with cyclic variations of solar activity indexes were found. But some individual solar flares can affect the brightness of comets. Cometary objects in the main asteroid belt have a lower statistic of flares than comets at orbits like quasi-Hilda objects.
Brightness and Orbital Motion Peculiarities of Comet C/2012 S1 (ISON): Comparison with Two Very Different Comets
为了更深入地了解彗星C/2012 S1的物理行为即将发生的演变，将其光变曲线和轨道特性与C/1962 C1（Seki-Lines）和C/2002 O 4（Hoenig）进行了比较。这三颗彗星都可能是奥尔特云彗星。C/1962 C1在距离太阳不到7朗日的地方与太阳相遇后幸存下来，而C/2002 O 4则在距离太阳0.78天文单位的近日点附近解体。距离近日点2.7朗日不到两个月，C/2012 S1的光变曲线更接近C/1962 C1，而不是C/2002 O 4。它的运动是否受到非引力摄动的影响还有待观察。随着关于C/2012 S1的新数据不断出现，它与两颗彗星的持续比较将通过更新和调整其状态来提供有关其健康状况的信息。最终将评估这种方法在未来潜在应用中的优点和缺点。
Comets are made of volatile and refractory material and naturally experience various degrees of sublimation as they orbit around the Sun. This gas release, accompanied by dust, represents what is traditionally described as activity. Although the basic principles are well established, most details remain elusive, especially regarding the mechanisms by which dust is detached from the surface and subsequently accelerated by the gas flows surrounding the nucleus. During its 2 years rendez-vous with comet 67P/Churyumov-Gerasimenko, ESA's Rosetta has observed cometary activity with unprecedented det…
Jupiter-family comet (JFC) P/2021 HS (PANSTARRS) only exhibits a coma within a few weeks of its perihelion passage at 0.8~au, which is atypical for a comet. Here we present an investigation into the underlying cause using serendipitous survey detections as well as targeted observations. We find that the detection of the activity is caused by an extremely faint coma being enhanced by forward scattering effect due to the comet reaching a phase angle of $\sim140^\circ$. The coma morphology is consistent with sustained, sublimation-driven activity produced by a small active area, $\sim700~\mathrm{…
The gas-driven dust activity of comets is still an unresolved question in cometary science. In the past, it was believed that comets are dirty snowballs and that the dust is ejected when the ice retreats. However, thanks to the various space missions to comets, it has become evident that comets have a much higher dust-to-ice ratio than previously thought and that most of the dust mass is ejected in large particles. Here we report on new comet-simulation experiments dedicated to the study of the ejection of dust aggregates caused by the sublimation of solid water ice. We find that dust ejection…
Recent observations show activity in long-period comet C/2017 K2 at heliocentric distances beyond the orbit of Uranus. With this as motivation, we constructed a simple model that takes a detailed account of gas transport modes and simulates the time-dependent sublimation of super-volatile ice from beneath a porous mantle on an incoming cometary nucleus. The model reveals a localized increase in carbon monoxide (CO) sublimation close to heliocentric distance rH = 150 AU (local blackbody temperature around 23 K), followed by a plateau and then a slow increase in activity towards smaller distance…
In 2017, 2018 and 2019, comets 46P/Wirtanen, 45P/Honda-Mrkos-Pajdusakova, and 41P/Tuttle-Giacobini-Kresak all had perihelion passages. Their hydrogen comae were observed by the Solar Wind ANisotropies (SWAN) all-sky hydrogen Lyman-alpha Camera on the SOlar and Heliospheric Observer (SOHO) satellite: comet 46P for the fourth time and comets 45P and 41P for the third time each since 1997. Comet 46P/Wirtanen is one of a small class of so-called hyperactive comets whose gas production rates belie their small size. This comet was the original target comet of the Rosetta mission. The Solar Wind ANis…
We investigated three comets, which are active at large heliocentric distances, using observations obtained at the 6-m BTA telescope (SAO RAS, Russia) in the photometric mode of the focal reducer SCORPIO. The three comets, 29P/Schwassmann-Wachmann 1, C/2003 WT42 (LINEAR), and C/2002 VQ94 (LINEAR), were observed after their perihelion passages at heliocentric distances between 5.5 and 7.08 AU. The dust production rates in terms of Afrho was measured for these comets. Using the retrieved values, an average dust production rate was derived under different model assumptions. A tentative calculatio…
We carried out photometric and spectroscopic observations of comet 29P/Schwassmann-Wachmann 1 at the 6-m BTA telescope (SAO RAS, Russia) and the 1.6-m telescope of the National Laboratory for Astro-physics (LNA, Brazil) on February 20, 2012, and on May 31, 2011, respectively. The spectra revealed the presence of CO+ and N2+ emissions in the cometary coma at a distance of 5.25 AU from the Sun. The ratio [N2+]/[CO+] within the projected slit is 0.013. The images obtained through BVR filters showed a bright, dust coma, indicating a high level of activity. We estimated a colour index and a colour …
Aims. Understanding the activity is vital for deciphering the structure, formation, and evolution of comets. We investigate models of cometary activity by comparing them to the dynamics of 67P/Churyumov-Gerasimenko. Methods. We matched simple thermal models of water activity to the combined Rosetta datasets by fitting to the total outgassing rate and four components of the outgassing induced non-gravitational force and torque, with a final manual adjustment of the model parameters to additionally match the other two torque components. We parametrised the thermal model in terms of a distributio…
Comets formed in solar-nebula instabilities! -- An experimental and modeling attempt to relate the activity of comets to their formation process (corrigendum included)
Rapid temperature changes and the early activity on comet 67P/Churyumov-Gerasimenko
彗星67 P/Churyumov-Gerasimenko的所谓“早期活动”被观察到主要起源于其两个叶之间的凹区或“颈部”。由于活动是由挥发物的升华驱动的，因此这是一个令人困惑的结果，因为该区域暴露在太阳下的时间较少，因此预计平均温度会更低（Sierks等人。2015）。我们使用了一个热物理模型，考虑到热惯性，全球自热，阴影，计算地面温度的彗星。我们发现，对于2014年8月至12月期间的每次旋转，颈部区域的某些部分经历了彗星表面最快的温度变化，因为它们被周围的地形所遮蔽。我们的工作表明，这些快速的温度变化与彗星的早期活动有关，我们提出了这样的假设，即由于这些快速的温度变化，与热裂纹有关的侵蚀在颈部区域以很高的速度运行。这可以解释为什么颈部含有一些冰-与表面的大多数其他部分相反（Capaccioni et al. 2015）-以及为什么它是彗星早期活动的主要来源（Sierks et al. 2015）。在更广泛的背景下，这些结果表明，热裂解可以在具有显著凹陷的无大气物体上比目前可用的估计值更快地进行（Delbo等人，2014年）。
Comet 2I/Borisov, the first unambiguous interstellar comet ever found, was discovered in August 2019 at $\sim3$ au from the Sun on its inbound leg. No pre-discovery detection beyond 3 au has yet been reported, mostly due to the comet's proximity to the Sun as seen from the Earth. Here we present a search for pre-discovery detections of comet Borisov using images taken by the Catalina Sky Survey (CSS), Pan-STARRS and Zwicky Transient Facility (ZTF), with a further comprehensive follow-up campaign being presented in \citet{Bolin2019}. We identified comet Borisov in ZTF images taken in May 2019 a…
In 1985 Comet 21P/Giacobini-Zinner was the first comet visited by a spacecraft, the International Cometary Explorer (ICE) satellite, several months before the armada of Halley spacecraft had their encounters in 1986. ICE was originally the ISEE-3 satellite, designed for magnetospheric measurements near the Earth, and was diverted via a lunar gravity assist to pass through the plasma tail of the comet. The comet has been observed by the all-sky hydrogen Lyman-alpha Solar Wind Anisotropies (SWAN) camera on the SOlar and Heliospheric Observatory satellite during its last four apparitions in 1998,…
Water-ice driven activity on Main-Belt Comet P/2010 A2 (LINEAR) ?
主带彗星P/2010 A2（LINEAR）的尘埃喷出物已经在西班牙La Palma的Observatorio del Roque de los Muchachos的几个望远镜中观测到。应用逆尘埃尾蒙特卡罗方法从对象的尘埃喷出物的图像表明，一个持续的，可能是水冰驱动，活动超过约八个月的机制，负责形成所观察到的尾巴。释放的尘埃总量估计为5E 7千克，约占核质量的0.3%。虽然该事件可能是由碰撞触发的，但根据目前可用的数据无法确定。
Cometary activity may be driven by ices with very low sublimation temperatures, such as carbon monoxide ice, which can sublimate at distances well beyond 20 au. This point is emphasized by the discovery of Oort cloud comet C/2014 UN$_{271}$ (Bernardinelli-Bernstein), and its observed activity out to $\sim$26 au. Through observations of this comet's optical brightness and behavior, we can potentially discern the drivers of activity in the outer solar system. We present a study of the activity of comet Bernardinelli-Bernstein with broad-band optical photometry taken at 19-20 au from the Sun (202…
Dust, gas activity and morphology of comet 12P/Pons-Brooks at heliocentric distances beyond 1.1 au
Astronomical Institute of the Slovak Academy of Sciences（斯洛伐克科学院天文研究所）；Institute of Astrophysics, National Academy of Sciences of Tajikistan（塔吉克斯坦国家科学院天体物理研究所）；Institut für Geophysik und Extraterrestrische Physik, Technische Universität Braunschweig（布伦瑞克工业大学地球物理学与外层空间物理研究所）；Space Sciences, Technologies & Astrophysics Research (STAR) Institute, University of Liège（列日大学空间科学与技术天体物理研究（STAR）研究所）；M. P. Birla Institute of Fundamental Research（M.P.比尔拉基础研究所）；UNEX EuroMoonMars EuroSpaceHub（UNEX 欧洲月球火星欧洲太空中心）；Astronomical Observatory of Taras Shevchenko National University of Kyiv（基辅塔拉斯舍甫琴科国立大学天文台）；Main Astronomical Observatory on the National Academy of Sciences of Ukraine（乌克兰国家科学院主天文台）
Using the Secular Light Curve (SLC) formalism (Ferrín, 2010a, PSS, 58, 365-391), we searched for cometary activity of six NEAS: 2201 Oljato. The SLC exhibits significant cometary activity and evidence of an eclipse. 3200 Phaethon. Is the parent of the Geminid meteor stream and exhibited a faint tail at perihelion in several oppositions. The SLC fails to show cometary activity using a 1995 to 2017 data set, suggesting that we are in the presence of a dormant cometary nucleus. 99942 Apophis. This SLC does not shows evidence of cometary activity, however it shows evidence of an eclipse. The evide…
Sublimative outgassing of comets produces torques that alter the rotation state of their nuclei. Recently, parameterized sublimative torque models have been developed to study rotation state changes of individual comet nuclei and populations of cometary bodies. However, these models simplify the interactions between the escaping gas and cometary surface into only a few parameters that hide the details of these complex interactions. Here we directly compare the X-parameter model (Samarasinha & Mueller, 2013) with the SYORP model (Steckloff & Jacobson, 2016) to tease out insights into the detail…
The Alice ultraviolet spectrograph on board the \textit{Rosetta} orbiter provided the first near-nucleus ultraviolet observations of a cometary coma from arrival at comet 67P/Churyumov-Gerasimenko in 2014 August through 2016 September. The characterization of atomic and molecular emissions in the coma revealed the unexpected contribution of dissociative electron impact emission at large heliocentric distances and during some outbursts. This mechanism also proved useful for compositional analysis, and Alice observed many cases that suggested elevated levels of the supervolatile \ce{O2}, identif…
Hyperactive comets are a small group of comets whose activity are higher than expected. They seem to emit more water than they should based on the size of their nucleus and comet 46P/Wirtanen is one of them. Investigating its activity and composition evolution could provide clues about its origins and formation region in the Solar nebulae. Given the exceptional close approach in 2018 of comet 46P to the Earth, we aim to study the evolution of its activity and composition as a function of heliocentric distances before and after perihelion. We used both TRAPPIST telescopes to monitor the comet f…
Comet 49P/Arend-Rigaux is a well known low-activity Jupiter Family comet. Despite the low activity, we have witnessed outgassing activity in 1992, 2004, and 2012. In 2012 a broad tail-like feature (PA$\sim270^\circ, \sim2.3\times10^5$ km) and a narrow jet-like feature (PA$\sim180^\circ, \sim9.3\times10^4$ km) were seen simultaneously. Using Finson-Probstein (FP) dust dynamical models we determine: grain sizes released in each event; duration of activity; when activity peaked; and velocity of the dust particles, allowing us to make comparisons between the events. We find that the tail feature i…
Asteroid pairs are genetically related asteroids that recently separated ($<$few million years), but still reside on similar heliocentric orbits. A few hundred of these systems have been identified, primarily in the asteroid main-belt. Here we studied a newly discovered pair of near-Earth objects (NEOs): 2019 PR2 and 2019 QR6. Based on broad-band photometry, we found these asteroids to be spectrally similar to D-types, a type rare amongst NEOs. We recovered astrometric observations for both asteroids from the Catalina Sky Survey from 2005, which significantly improved their fitted orbits. With…
We report on photometry and imaging of the Jupiter Family Comets 41P/Tuttle-Giacobini-Kresak and 45P/Honda-Mrkos-Pajdusakova with the TRAPPIST-North telescope. We observed 41P on 34 nights from February 16, 2017 to July 27, 2017 pre- and post-perihelion (r$_h$=1.04 au), while we collected data for comet 45P from February 10 to March 30 after perihelion (r$_h$=0.53 au). We computed the production rates of the daughter species OH, NH, CN, C$_3$ and C$_2$ and we measured the dust proxy, Af$ρ$, for both comets. The peak of water production rate of 41P was (3.46$\pm$0.20)$\times$10$^{27}$ molecules…
Comet 2I/Borisov is the first true interstellar comet discovered. Here we present results from observational programs at two Indian observatories, 2 m Himalayan Chandra Telescope at the Indian Astronomical Observatory, Hanle (HCT) and 1.2 m telescope at the Mount Abu Infrared Observatory (MIRO). Two epochs of imaging and spectroscopy were carried out at the HCT and three epochs of imaging at MIRO. We found CN to be the dominant molecular emission on both epochs, 31/11/2019 and 22/12/2019, at distances of r$_H$ = 2.013 and 2.031 AU respectively. The comet was inferred to be relatively depleted …
We study the development of activity in the incoming long-period comet C/2017 K2 over the heliocentric distance range 9 < r_H < 16 AU. The comet continues to be characterized by a coma of sub-millimeter and larger particles ejected at low velocity. In a fixed co-moving volume around the nucleus we find that the scattering cross-section of the coma is related to the heliocentric distance by a power law with heliocentric index $s = 1.14\pm0.05$. This dependence is significantly weaker than the inverse square variation of the insolation as a result of two effects. These are, first, the heliocentr…
Beginning of activity in 67P/Churyumov-Gerasimenko and predictions for 2014/5
彗星67P/Churyumov-Gerasimenko于2003年被选为罗塞塔任务的新目标。从那时起，它一直是一个详细的观察运动的主题，以确定其核心和活动。在这里，我们提出了以前未发表的数据，在2007/8年彗星活动开始时，在其最后一次近日点通过之前。我们限制了活动开始的时间，并将其与整个彗星轨道上的其他数据相结合，以预测罗塞塔运行期间2014/5年可能的行为。在过去的几年里，观测67P的一个相当大的困难是它的位置在很长一段时间里都是朝向银河系中心的拥挤的区域。这里提供的2007/8年数据特别困难，2014/5年这颗彗星将再次处于地球观测的不利位置。我们利用差分图像分析（DIA）技术，这是常用的变星和系外行星的研究，以消除背景源和提取图像的彗星。此外，我们重新处理了大量的档案图像的67P覆盖其整个轨道，以产生一个日心光变曲线。通过使用一致的减少，测量和校准技术，我们产生了一个非常干净的光曲线，它可以用来测量亮度距离的关系，并预测彗星的未来亮度。我们确定这颗彗星在2007年11月左右活跃，距离太阳的近日点距离为4.3 AU。这颗彗星将到达这个距离，并可能在2014年3月再次活跃。我们发现尘埃亮度在近日点前和近日点后分别可以用Δ f ρ \propto r ^-3.2和r ^-3.4来描述，并且彗星的尘气比高于平均值。一个模型拟合的光度数据表明，只有一小部分（1.4%）的表面是活跃的。
In 2010 Jewitt and Li published a paper examining the behavior of comet-asteroid transition object 3200 Phaethon, arguing it was asteroid-like in its behavior throughout most of its orbit, but that near its perihelion, at a distance of only 0.165 AU from the sun, its dayside temperatures would be hot enough to vaporize rock (>1000 K, Hanus et al. 2016). Thus it would act like a "rock comet" as gases produced from evaporating rock were released from the body, in a manner similar to the more familiar sublimation of water ice into vacuum seen for comets coming within ~3 AU of the Sun. In this Not…
