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The Arecibo Observatory (AO) is a multidisciplinary research and education facility that is recognized worldwide as a leading facility in astronomy, planetary, and atmospheric and space sciences. AO's cornerstone research instrument was the 305-m William E. Gordon telescope. On December 1, 2020, the 305-m telescope collapsed and was irreparably damaged. In the three weeks following the collapse, AO's scientific and engineering staff and the AO users community initiated extensive discussions on the future of the observatory. The community is in overwhelming agreement that there is a need to build an enhanced, next-generation radar-radio telescope at the AO site. From these discussions, we established the set of science requirements the new facility should enable. These requirements can be summarized briefly as: 5 MW of continuous wave transmitter power at 2 - 6 GHz, 10 MW of peak transmitter power at 430 MHz (also at 220MHz under consideration), zenith angle coverage 0 to 48 deg, frequency coverage 0.2 to 30 GHz and increased Field-of-View. These requirements determine the unique specifications of the proposed new instrument. The telescope design concept we suggest consists of a compact array of fixed dishes on a tiltable, plate-like structure with a collecting area equivalent to a 300m dish. This concept, referred to as the Next Generation Arecibo Telescope (NGAT), meets all of the desired specifications and provides significant new science capabilities to all three research groups at AO. This whitepaper presents a sample of the wide variety of the science that can be achieved with the NGAT, the details of the telescope design concept and the need for the new telescope to be located at the AO site. We also discuss other AO science activities that interlock with the NGAT in the white paper.

Context. The existence of comets with heliocentric orbital periods close to that of Jupiter (i.e., co-orbitals) has been known for some time. Comet 295P/LINEAR (2002 AR2) is a well-known quasi-satellite of Jupiter. However, their orbits are not long-term stable, and they may eventually experience flybys with Jupiter at very close range, close enough to trigger tidal disruptions like the one suffered by comet Shoemaker-Levy 9 in 1992. Aims. Our aim was to study the observed activity and the dynamical evolution of the Jupiter transient co-orbital comet P/2019 LD2 (ATLAS) and its dynamical evolution. Methods. We present results of an observational study of P/2019 LD2 carried out with the 10.4 m Gran Telescopio Canarias (GTC) that includes image analyses using a Monte Carlo dust tail fitting code to characterize its level of cometary activity, and spectroscopic studies to search for gas emission. We also present N-body simulations to explore its past, present, and future orbital evolution. Results. Images of P/2019 LD2 obtained on May 16, 2020, show a conspicuous coma and tail, but the spectrum obtained on May 17, 2020, does not exhibit any evidence of CN, C2, or C3 emission. The comet brightness in a 2.6′′ aperture diameter is r′ = 19.34 ± 0.02 mag, with colors (g′- r′) = 0.78 ± 0.03, (r′- i′) = 0.31 ± 0.03, and (i′- z′) = 0.26 ± 0.03. The temporal dependence of the dust loss rate of P/2019 LD2 can be parameterized by a Gaussian function having a full width at half maximum of 350 days, with a maximum dust mass loss rate of 60 kg s-1 reached on August 15, 2019. The total dust loss rate from the beginning of activity until the GTC observation date (May 16, 2020) is estimated at 1.9 × 109 kg. Comet P/2019 LD2 is now an ephemeral co-orbital of Jupiter, following what looks like a short arc of a quasi-satellite cycle that started in 2017 and will end in 2028. On January 23, 2063, it will experience a very close encounter with Jupiter at perhaps 0.016 au; its probability of

Jupiter Trojan asteroids are minor bodies that share Jupiter's orbit around the Sun. Although not yet well understood in origin and composition, they have surface properties that, besides being comparable with other populations of small bodies in the Solar System, hold information that may restrict models of planetary formation. Because of this, there has been a significant increase in the interest in studying this population. In this context arises the NASA Mission Lucy, with a planned launch in 2021. The Lucy Mission will be the first one to address a group of six objects (five Jupiter Trojans and one main belt asteroid) with the aim of investigating, in detail, their nature. In order to provide valuable information for mission planning and maximize the scientific return, we carried out ground based observations of four targets of the mission. Aimed at looking for variabilities on the spectra of (3548) Eurybates, (15094) Polymele and (21900) Orus, we performed rotationally resolved visible spectroscopy of them at SOAR Telescope. We also analyzed the first visible spectrum obtained for the main belt asteroid (52246) Donaldjohanson at Gran Telescopio Canarias. The spectra of (21900) Orus and (15094) Polymele present here are the first ones in the visible range and show rather homogeneous characteristics along the surfaces. Their taxa correspond with those of the two dominant Trojan populations, the P- and the D-type group of objects. Spectroscopy of (3548) Eurybates, on the other side, suggests that some variation on the characteristics of the reflectance of this body. Donaldjohanson shows hints of hydrated materials in its visible spectrum. The Lucy mission will investigate the surface composition of these targets and will shed light on their connections with other populations of minor bodies and on their role in the evolution of the Solar System. ©2020

Makemake is one of the brightest known trans-Neptunian objects, as such, it has been widely observed. Nevertheless, its visibility to near-infrared spectrum has not been completely observed in medium-resolving power, aimed at studying in detail the absorption features of CH4 ice. In this paper, we present the spectrum of Makemake observed with X-Shooter at the Very Large Telescope (Chile). We analyse the detected features, measuring their location and depth. Furthermore, we compare Makemake's spectrum with that of Eris, obtained with the same instrument and similar setup, to conclude that the bands of the CH4 ice in both objects show similar shifts. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society

In this work, we present the results of an observational study of 2I/Borisov carried out with the 10.4-m Gran Telescopio Canarias (GTC) and the 3.6-m Telescopio Nazionale Galileo (TNG), both telescopes located at the Roque de Los Muchachos Observatory, in the island of La Palma (Spain). The study includes images in the visible and near-infrared, as well as visible spectra in the 3600-9200 Å wavelength range. N-body simulations were also performed to explore its orbital evolution and Galactic kinematic context. The comet's dust continuum and near-infrared colours are compatible with those observed for Solar system comets. From its visible spectrum on the nights of 2019 September 24 and 26, we measured CN gas production rates Q(CN) = (2.3 ± 0.4) × 1024 mol s-1 and Q(CN) = (9.5 ± 0.2) × 1024 mol s-1, respectively, in agreement with measurements reported by other authors on similar nights. We also obtained an upper limit for the C2 production rate of Q(C2) < (4.5 ± 0.1) × 1024 mol s-1. Dust modelling results indicate a moderate dust production rate of ∼50 kg s-1 at heliocentric distance rh = 2.6 au, with a differential power-law dust size distribution of index ∼-3.4, within the range reported for many comet comae. Our simulations show that the Galactic velocity of 2I/Borisov matches well that of known stars in the solar neighbourhood and also those of more distant regions of the Galactic disc. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society

From CCD observations carried out with different telescopes, we present short-term photometric measurements of the large trans-Neptunian object Varuna in 10 epochs, spanning around 19 years. We observe that the amplitude of the rotational light curve has changed considerably during this period of time from 0.41 to 0.55 mag. In order to explain this variation, we constructed a model in which Varuna has a simple triaxial shape, assuming that the main effect comes from the change of the aspect angle as seen from Earth, due to Varuna's orbital motion in the 19 year time span. The best fits to the data correspond to a family of solutions with axial ratios b/a between 0.56 and 0.60. This constrains the pole orientation in two different ranges of solutions presented here as maps. Apart from the remarkable variation of the amplitude, we have detected changes in the overall shape of the rotational light curve over shorter timescales. After the analysis of the periodogram of the residuals to a 6.343572 hr double-peaked rotational light-curve fit, we find a clear additional periodicity. We propose that these changes in the rotational light-curve shape are due to a large and close-in satellite whose rotation induces the additional periodicity. The peak-to-valley amplitude of this oscillation is in the order of 0.04 mag. We estimate that the satellite orbits Varuna with a period of 11.9819 hr (or 23.9638 hr), assuming that the satellite is tidally locked, at a distance of ∼1300 km (or ∼2000 km) from Varuna, outside the Roche limit.© 2019. The American Astronomical Society..

2012 DR is one of the known solar system objects with the largest aphelion distance, exceeding 2200 au, on a high inclination orbit (i =78). It has been recognized to be either a borderline representative of high inclination, high perihelion distance (HiHq) objects, or even a new class of bodies, similar to HiHq objects for orbit but with an aphelion in the inner Oort Cloud. Here, we present photometry using long-term data from 2000 to 2013 taken by the SDSS sky survey, ESO MPG 2.2 m and McDonald 2.1 m telescopes, and a visual+near-infrared spectrum taken with the Southern Astrophysical Research Telescope and Magellan telescopes, providing insights into the surface composition of this body. Our best fit suggests that the surface contains 60% of complex organics (30% of Titan and 30% of Triton tholins) with a significant fraction of ice (30%, including pure water and water with inclusions of complex organics) and 10% silicates. The models also suggest a low limit of amorphous carbons, and hence the fragmentation of long-chained complex organics is slower than their rate of generation. 2012 DR30 just recently passed the perihelion, and the long-term photometry of the object suggested ambiguous signs of activity, since the long-term photometric scatter well exceeded the supposed measurement errors and the expected brightness variation related to rotation. Photometric colors put 2012 DR30 exactly between dark neutral and red objects, thus it either can be in a transition phase between the two classes or have differing surface properties from these populated classes.© 2018. The American Astronomical Society. All rights reserved.

Accurate measurements of diameters of trans-Neptunian objects (TNOs) are extremely difficult to obtain. Thermal modeling can provide good results, but accurate absolute magnitudes are needed to constrain the thermal models and derive diameters and geometric albedos. The absolute magnitude, H, is defined as the magnitude of the object reduced to unit helio-and geocentric distances and a zero solar phase angle and is determined using phase curves. Phase coefficients can also be obtained from phase curves. These are related to surface properties, but only few are known. Aims. Our objective is to measure accurate V-band absolute magnitudes and phase coefficients for a sample of TNOs, many of which have been observed and modeled within the program >TNOs are cool>, which is one of the Herschel Space Observatory key projects. Methods. We observed 56 objects using the V and R filters. These data, along with those available in the literature, were used to obtain phase curves and measure V-band absolute magnitudes and phase coefficients by assuming a linear trend of the phase curves and considering a magnitude variability that is due to the rotational light-curve. Results. We obtained 237 new magnitudes for the 56 objects, six of which were without previously reported measurements. Including the data from the literature, we report a total of 110 absolute magnitudes with their respective phase coefficients. The average value of H is 6.39, bracketed by a minimum of 14.60 and a maximum of-1.12. For the phase coefficients we report a median value of 0.10 mag per degree and a very large dispersion, ranging from-0.88 up to 1.35 mag per degree. © 2016 ESO.