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The K2 mission of the Kepler Space Telescope allowed the observations of light curves of small solar system bodies throughout the whole Solar system. In this paper we present the results of a collection of K2 transneptunian object observations, between Campaigns C03 (November 2014 -- February 2015) to C19 (August -- September, 2018), which includes 66 targets. Due to the faintness of our targets the detectability rate of a light curve period is $\sim$56%, notably lower than in the case of other small body populations, like Hildas or Jovian trojans. We managed to obtain light curve periods with an acceptable confidence for 37 targets; the majority of these cases are new identifications. We were able to give light curve amplitude upper limits for the other 29 targets. Several of the newly detected light curve periods are longer than $\sim$24 h, in many cases close to $\sim$80 h, i.e., these targets are slow rotators. This relative abundance of slowly rotating objects is similar to that observed among Hildas, Jovian trojans and Centaurs in the K2 mission, and also among main belt asteroids measured with the TESS Space Telescope. Transneptunian objects show notably higher light curve amplitudes at large (D $\gtrsim$ 300 km) sizes than that found among large main belt asteroids, in contrast to the general expectation that due to their lower compressive strength they reach hydrostatic equlibrium at smaller sizes than their inner solar system counterparts., Accepted for publication in ApJS

Earlier reviews of trans-Neptunian light curves reported mean rotation periods of P = 7-8 h (Duffard et al., 2009), and it was also found that the binary trans-Neptunian population rotates slower (Thirouin & Sheppard, 2014), and objects in the cold classical population have larger variability and rotate slower than the non-cold classical TNOs (Benecchi et al., 2013,Thirouin & Sheppard, 2019). While ground-based observations have obvious limitations in detecting long-period light curves the K2 mission of the Kepler Space Telescope allowed long (up to ~80 days), uninterrupted observations of many Solar system objects, including main belt asteroids, Hildas, Jovian trojans, and also the irregular satellites of giant planets. Light curves were also published for a few, selected trans-Neptunian objects based on K2 observations (see Kiss et al., 2020, for a summary). A common outcome of the studies of larger samples, across all dynamical classes, was the identification of an increased number of targets with long rotation periods compared to previous ground-based studies. A similar trend is observed among the data of nearly 10 000 main belt asteroids obtained by the TESS Space Telescope (Pál et al., 2020), and asteroids with long rotation periods were identified in other surveys like the Asteroid Terrestrial-impact Last Alert System (ATLAS), the Zwicky Transient Facility (Erasmus et al., 2021) and the All-Sky Automated Survey for Supernovae (Hanus et al., 2021). We have collected the K2 trans-Neptunian object observations between Campaigns C03 (November 2014 -- February 2015) to C19 (August -- September, 2018), which includes 67 targets. Due to the faintness of our targets the detectability rate of a light curve period is ~57 %, notably lower than in the case of other small body populations, like Hildas or Jovian trojans. We managed to obtain light curve periods with an acceptable confidence for 36 targets; the majority of these cases are new identifications. We were able to give light curve amplitude upper limits for the other 31 targets. Several of the newly detected light curve periods are longer than ~24 h, in many cases close to ~100 h, i.e., slow rotators. There is a very significant difference between the rotation rates of the LCDB and K2 TNO samples (Figs. 1 and 2). The mean LCD spin frequency is 2.71 c/d (8.8 h), while it is 0.87 c/d (27.6 h) in the K2 sample which is more similar to the K2 Hilda and Jovian Trojan spin frequency distrbutions. Thirouin & Sheppard (2019) obtained 9.48±1.53 h and 8.45±0.58 h mean rotation periods for the cold classical and the non-cold classical TNOs. Our mean values for the same dynamical groups (but using different targets) are notably longer: 1.21+1.58-0.63 c/d (19.83 h) and 0.83+1.81-0.23 c/d (P=28.91 h), respectively. The K2 mean frequency is higher than that of the K2 Jovian Trojans and Hildas, but we could not detect the very long period targets that were observed in these other K2 samples. Figure 1: frequency distribution of asteroids. The cyan, magenta, green and blue colours represent the TNOs in the LCDB and Jovian trojans, Hildas and TNOs from K2, respectively. Figure 2: Frequency as a function of absolute magnitude. Big circles with error bars mark the median values standard deviations for the different samples. The horizontal dashed lines mark the spin frequencies of fast, slow, and very slow rotators (Pravec et al., 2002). While there are only three objects with D>500 km in our sample, there are a number of objects -- both with and without detected light curve periods -- that fall in the 300≤D≤500 km transitional zone where asphericity -- hence light curve amplitude -- is expected to drop assuming a single rotating body, assuming main belt composition. Main belt asteroids are already almost extinct in this size range, and so are Centaurs -- for these bodies irregular shapes are expected in most cases. While the general trend is that larger objects have smaller light curve amplitudes among TNOs -- a trend followed both by our sample and the LCDB TNOs -- there are a considerable number of TNOs with high asphericity in the 300≤D≤500 km size range. This contradiction could be resolved if TNOs had higher-than-expected compressive strength and become spherical for sizes larger than their main belt counterparts, and remain 'irregular' in the 300≤D≤500 km range. However, their general low density and high porosity point against this scenario. A notable fraction of contact or semi-contact binary systems in which the members themselves are in hydrostatical equlibrium could produce a population of high-amplitude light curves in this size range (Lacerda et al., 2006, 2014). As some authors pointed out, contact binaries may be very frequent, especially in the plutino population (Thirouin & Sheppard, 2018,2019). The long term stability of such systems against their tidal evolution, however, should be investigated to answer the reliability of this assumption. Finally, spherical (rotationally flattened) bodies with large albedo variegations could also explain the observed amplitudes. While the general expectation in most TNO light curve studies was a double peak light curve, in our sample most light curves were found to be single-peak, after comparing the single-peak and double-peak solutions. Fgiure 3: Light curve amplitude versus the estimated size of the targets in our sample. The region between the vertical dashed lines mark the irregular-to-spherical transition size range in the main belt. Blue and red symbols mark the K2 targets and K2 upper limits, small grey symbols correspond to main belt asteroids. Large gray symbols represent the theoretical maximum light curve amplitudes the of large main belt objects if it was solely caused by the elongated shape of a body with homogeneous albedo.

Here we present an improved algorithm to model the serpentinization process in planetesimals in the early Solar system. Although it is hypothesized that serpentinization-like reactions played an important role in the thermal evolution of planetesimals, few and restricted models are available in this topic. These processes may be important as the materials involved were abundant in these objects. Our model is based on the model by (Gobi & Kereszturi 2017), and contains improvements in the consideration of heat capacities and lithospheric pressure, and in the calculation of the amount of interfacial water. Comparison of our results with previous calculations shows that there are significant differences in the e.g. the serpentinization time -- the time necessary to consume most of the reactants at specific initial conditions -- or the amount of heat produced by this process. In a simple application we show that in icy bodies, under some realistic conditions, below the melting point of water ice, serpentinization reaction using interfacial water may be able to proceed and eventually push the local temperature above the melting point to start a 'runaway' serpentinization. According to our calculations in objects with radii R $\gtrsim$ 200 km serpentinization might have quickly reformed nearly the whole interior of these bodies in the early Solar system., Accepted for publication in the Planetary Science Journal

Despite that they are the brightest representatives of trans-Neptunian objects, many dwarf planets still miss a well-determined light curve and hence rotation period, in many cases due to the biases and aliases of ground-based observations. As it was previously shown in the case of e.g. Gonggong (2007 OR10), one of the largest Kuiper belt objects known, a well determined rotation period can be deduced from light curve data obtained by space surveys with original goals very different from the observations of Solar system objects (Pál et al., 2016; Kiss et al., 2017). In the case of Gonggong the observations were taken in the framework of the K2 mission of the Kepler Space Telescope (Howell et al., 2014) which was initially dedicated to measure exoplanet transits. However, in its K2 mission the telescope was pointed to the ecliptic, and allowed the long, in some cases up to ~80 day measurements of small solar system bodies, resulting in a previously undetected overabundance of long rotation periods in many of the small body populations, including the Hildas, Jovian Trojans, Centaurs, as well as trans-Neptunian objects (Kalup et al., 2021; Kiss et al., 2020; Marton et al., 2020; Szabó et al., 2017, 2020). The Transiting Exoplanet Survey Satellite (TESS, Ricker et al., 2015) was also designed originally to find exoplanets and avoid the vicinity of the ecliptic. However, it was still able to observe many asteroid at intermediate ecliptic latitudes. While the maximum length of the TESS observations are shorter than those in the K2 mission (28 days vs. 80 days) these are still much longer than that a typical long observing campaign can provide from the ground. Recently, a large number of main belt asteroid light curves was obtained by TESS, leading to the discovery of a previously undetected group of slow rotators (Pál et al., 2020). Due to the smaller light collecting area most trans-Neptunian objects are too faint to be observed with TESS, but the largest ones -- the dwarf planets -- are bright enough to provide a meaningful light curve. In this presentation we show results from the analysis of TESS light curves of the Kuiper belt dwarf planets Eris, Makemake and Orcus. These data are, in some cases, combined with ground-based data, and also with thermal emission measurements to constrain the spin axis orientation and determine how the light curve can be caused by surface features. As all the three targets have companions, the rotational information can also be incorporated into tidal evolution models and can be used to constrain the formation scenarios of the system, and, in some cases, give hints on the internal structure and material properties. Figure 1: Right panels: The apparent path of Eris during the first year of the TESS observations just in between the boundaries of TESS Sectors #3 (red) and #4 (blue). During its retrograde motion, Eris just misses Camera #1, CCD #3 of Sector #3. The thin line shows the full path of Eris while the thick red and blue sections correspond to the observing runs of Sectors #3 and #4, respectively. Left panels: The same plot for Orcus and for TESS Sectors #8 (red) and #9 (blue). Orcus has been observed during Sector #9 by CCD #1 of Camera #1, pretty close to the CCD edges. Bottom panel: The apparent track of Orcus within the field of view of TESS Camera #1 CCD #1, section [44:144]x[1675:1705]. The semi-transparent green curve shows the full track where observations were available while the thin red curve shows the track from which data points were involved in the photometric analysis. The direction of this section with respect to the sky is mirrored (east is nearly to the right and north points nearly to up): Orcus moved from the left to right due to its retrograde motion at its opposition. References: - Howell, S.B., et al., 2014, PASP, 126, 398- Kalup, C., et al., 2021, ApJS, 254, 7- Kiss C., et al., 2017, ApJL, 838, L1- Kiss, C., et al., 2020, EPSC2020-536 - Marton, G., et al., 2020, Icarus, 345, 113721- Pál, A., et al., 2020, ApJS, 247, 26- Ricker, G.R., et al. 2015, J. Astron. Telesc. Instrum. Syst. Vol. 1,id. 014003- Szabó et al., 2017, A&A, 599, 44- Szabó et al., 2020, ApJS, 247, 26

The satellite of (225088) 2007 OR10 was discovered on archival Hubble Space Telescope images and along with new observations with the WFC3 camera in late 2017 we have been able to determine the orbit. The orbit's notable eccentricity, e$\approx$0.3, may be a consequence of an intrinsically eccentric orbit and slow tidal evolution, but may also be caused by the Kozai mechanism. Dynamical considerations also suggest that the moon is small, D$_{eff}$ $, Comment: Accepted for publication in Icarus

V555 Ori is a T Tauri star, whose 1.5 mag brightening was published as a Gaia science alert in 2017. We carried out optical and near-infrared photometric, and optical spectroscopic observations to understand the light variations. The light curves show that V555 Ori was faint before 2017, entered a high state for about a year, and returned to the faint state by mid-2018. In addition to the long-term flux evolution, quasi-periodic brightness oscillations were also evident, with a period of about 5 days. At optical wavelengths both the long-term and short-term variations exhibited colourless changes, while in the near-infrared they were consistent with changing extinction. We explain the brightness variations as the consequence of changing extinction. The object has a low accretion rate whose variation in itself would not be enough to reproduce the optical flux changes. This behaviour makes V555 Ori similar to the pre-main sequence star AA Tau, where the light changes are interpreted as periodic eclipses of the star by a rotating inner disc warp. The brightness maximum of V555 Ori was a moderately obscured ($A_V$=2.3 mag) state, while the extinction in the low state was $A_V$=6.4 mag. We found that while the Gaia alert hinted at an accretion burst, V555 Ori is a standard dipper, similar to the prototype AA Tau. However, unlike in AA Tau, the periodic behaviour was also detectable in the faint phase, implying that the inner disc warp remained stable in both the high and low states of the system., Accepted to MNRAS

The Herschel Space Observatory had two imaging instruments, working in the far-infrared and submillimetre regimes: the PACS cameras at 70/100 and 160 μm and the SPIRE photometers at 250, 350 and 500 μm. Small solar system bodies, especially main belt asteroids were serendipitously present in the field of view mainly in large scan maps. We identified these objects with the original aim to mark the affected sources in the Herschel PACS and SPIRE Point Source Catalogues. In our present study we extracted flux densities in the PACS bands for asteroids above the detection limit, either using existing standard data products from the Herschel Science Archive, or re-reducing the PACS maps in the co-moving frame of the target. We obtained ~600 new flux density values for 270 asteroids, a significant increase in the number of Herschel asteroid observations. These new flux densities will be included in the Small Bodies: Near and Far (SBNAF) Infrared Database (Szakáts et al., 2020). The fluxes obtained from Herschel are excellent for radiometric studies to get the object's size, albedo and maybe also thermal properties, when combined with other measurements (Alí-Lagoa et al., 2020).

Some meteorite samples show that in addition to heat from accretion and radioactive decay, there may have been chemical processes that, at least at some point in the history of the Solar System, could significantly alter the lithological characteristics of the objects and contributed notably to internal heat production. We constructed a model considering the chemical process of serpentinization. Serpentine is a hydrous magnesium phyllosilicate mineral, resulting from the hydration of olivine and/or pyroxene, in an exothermic reaction that takes place in the presence of liquid water. 2Mg2SiO4 + 3H2O -> Mg3Si2O5(OH)4 + Mg(OH)2Mg2SiO4 + MgSiO3 + 2H2O -> Mg3Si2O5(OH)4 Our model is based on earlier models (Cohen et al., 2000; Góbi et al., 2017) which estimated the serpentinization time scale and examined the effect of interfacial liquid water below the melting point of ice and calculated the necessary initial temperature and the amount of heat produced. We take into account several effects that have previously been neglected. Our results show a significant difference compared with previous outcomes, under the same initial conditions: the reaction time scale increased significantly especially in cases where the initial temperature was below the melting point of water -- in these cases, the difference in the characteristic length of the process was longer by two orders of magnitude. Another significant difference was the extent of the effect of interfacial water, as previous studies found that the process takes place at a similar rate below the freezing point of water as above. Our results show that although the process works below the freezing point it slows down significantly. We also examined whether these chemical processes could take place under the different conditions in the outer Solar System and influence significantly the evolution of the objects there.

This is an open access article distributed under the terms of the Creative Commons CC-BY license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited., Here we present the results of visible range light curve observations of ten Centaurs using the Kepler Space Telescope in the framework of the K2 mission. Well defined periodic light curves are obtained in six cases allowing us to derive rotational periods, a notable increase in the number of Centaurs with known rotational properties. The low amplitude light curves of (471931) 2013 PH44 and (250112) 2002 KY14 can be explained either by albedo variegations, binarity or elongated shape. (353222) 2009 YD7 and (514312) 2016 AE193 could be rotating elongated objects, while 2017 CX33 and 2012 VU85 are the most promising binary candidates due to their slow rotations and higher light curve amplitudes. (463368) 2012 VU85 has the longest rotation period, P = 56.2 h observed among Centaurs. The P > 20 h rotation periods obtained for the two potential binaries underlines the importance of long, uninterrupted time series photometry of solar system targets that can suitably be performed only from spacecraft, like the Kepler in the K2 mission, and the currently running TESS mission. © 2020 The Authors, The research leading to these results has received funding from the European Union 's Horizon 2020 Research and Innovation Programme, under Grant Agreement No. 687378 ; from the K-125015 , PD-116175 , PD-128360 , and GINOP-2.3.2-15-2016-00003 grants of the National Research Development and Innovation Office (NKFIH, Hungary); and from the LP2012-31 and LP2018-7/2019 Lendület grants of the Hungarian Academy of Sciences . L. M. was supported by the Premium Postdoctoral Research Program of the Hungarian Academy of Sciences . The research leading to these results have been supported by the ÚNKP-19-2 New National Excellence Program of the Ministry of Human Capacities , Hungary. Funding for the Kepler and K2 missions are provided by the NASA Science Mission Directorate. The data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555 . Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. The authors thank the hospitality of the Veszprém Regional Centre of the Hungarian Academy of Sciences (MTA VEAB), where part of this project was carried out. We also indebted to S. Benecchi and an anonymous reviewer for their comments which have helped to improve the paper.

V582 Aur is an FU Ori-type young eruptive star in outburst since $\sim$1985. The eruption is currently in a relatively constant plateau phase, with photometric and spectroscopic variability superimposed. Here we will characterize the progenitor of the outbursting object, explore its environment, and analyse the temporal evolution of the eruption. We are particularly interested in the physical origin of the two deep photometric dips, one occurred in 2012, and one is ongoing since 2016. We collected archival photographic plates, and carried out new optical, infrared, and millimeter wave photometric and spectroscopic observations between 2010 and 2017, with high sampling rate during the current minimum. Beside analysing the color changes during fading, we compiled multiepoch spectral energy distributions, and fitted them with a simple accretion disk model. Based on pre-outburst data and a millimeter continuum measurement, we suggest that the progenitor of the V582 Aur outburst is a low-mass T Tauri star with average properties. The mass of an unresolved circumstellar structure, probably a disk, is 0.04 M$_{\odot}$. The optical and near-infrared spectra demonstrate the presence of hydrogen and metallic lines, show the CO bandhead in absorption, and exhibit a variable H$\alpha$ profile. The color variations strongly indicate that both the $\sim$1 year long brightness dip in 2012, and the current minimum since 2016 are caused by increased extinction along the line of sight. According to our accretion disk models, the reddening changed from $A_V$=4.5 mag to 12.5 mag, while the accretion rate remained practically constant. Similarly to the models of the UXor phenomenon of intermediate and low-mass young stars, orbiting disk structures could be responsible for the eclipses., Comment: 20 pages, 11 figures, accepted for publication in ApJ

In this paper we present visible range light curves of the irregular Uranian satellites Sycorax, Caliban, Prospero, Ferdinand and Setebos taken with Kepler Space Telescope in the course of the K2 mission. Thermal emission measurements obtained with the Herschel/PACS and Spitzer/MIPS instruments of Sycorax and Caliban were also analysed and used to determine size, albedo and surface characteristics of these bodies. We compare these properties with the rotational and surface characteristics of irregular satellites in other giant planet systems and also with those of main belt and Trojan asteroids and trans-Neptunian objects. Our results indicate that the Uranian irregular satellite system likely went through a more intense collisional evolution than the irregular satellites of Jupiter and Saturn. Surface characteristics of Uranian irregular satellites seems to resemble the Centaurs and trans-Neptunian objects more than irregular satellites around other giant planets, suggesting the existence of a compositional discontinuity in the young Solar system inside the orbit of Uranus., Accepted for publication in the Astronomical Journal

2007 OR10 is currently the third largest known dwarf planet in the trans-Neptunian region, with an effective radiometric diameter of ∼1535 km. It has a slow rotation period of ∼45 hr that was suspected to be caused by tidal interactions with a satellite undetected at that time. Here, we report on the discovery of a likely moon of 2007 OR10, identified on archival Hubble Space Telescope WFC3/UVIS system images. Although the satellite is detected at two epochs, this does not allow an unambiguous determination of the orbit and the orbital period. A feasible 1.5-5.8 • 1021 kg estimate for the system mass leads to a likely 35-100 day orbital period. The moon is about 4.2 fainter than 2007 OR10 in HST images that corresponds to a diameter of 237 km assuming equal albedos with the primary. Due to the relatively small size of the moon, the previous size and albedo estimates for the primary remains unchanged. With this discovery all trans-Neptunian objects larger than 1000 km are now known to harbor satellites, an important constraint for moon formation theories in the young solar system. © 2017. The American Astronomical Society. All rights reserved., The research leading to these results has received funding from the European Unions Horizon 2020 Research and Innovation Programme, under Grant Agreement No. 687378; from the GINOP-2.3.2-15-2016-00003 grant of the National Research, Development and Innovation Office (Hungary); and from the LP2012-31 grant of the Hungarian Academy of Sciences. Funding from Spanish grant AYA-2014-56637-C21-P is acknowledged, as is the Proyecto de Excelencia de la Junta de Andaluca, J.A. 2012-FQM1776.

In this paper we present the "Small Bodies: Near and Far" Infrared Database, an easy-to-use tool intended to facilitate the modeling of thermal emission of small Solar System bodies. Our database collects thermal emission measurements of small Solar Systems targets that are otherwise available in scattered sources and gives a complete description of the data, with all information necessary to perform direct scientific analyses and without the need to access additional, external resources. This public database contains representative data of asteroid observations of large surveys (e.g. AKARI, IRAS and WISE) as well as a collection of small body observations of infrared space telescopes (e.g. the Herschel Space Observatory) and provides a web interface to access this data (https://ird.konkoly.hu). We also provide an example for the direct application of the database and show how it can be used to estimate the thermal inertia of specific populations, e.g. asteroids within a given size range. We show how different scalings of thermal inertia with heliocentric distance (i.e. temperature) may affect our interpretation of the data and discuss why the widely-used radiative conductivity exponent ($\alpha$=-3/4) might not be adequate in general, as hinted by previous studies., Comment: 16 pages, 8 figures, 2 tables