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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

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