We report VLT spectroscopy of the interstellar comet 3I/ATLAS (C/2025 N1) from $r_{\rm h}\!\simeq\!4.4$ to $2.85$ au using X-shooter (300-550 nm, $R\!\simeq\!3000$) and UVES (optical, $R\!\simeq\!35k-80k$). The coma is dust-dominated with a fairly constant red optical continuum slope ($\sim$21-22\%/1000Γ ). At $r_{\rm h}\!\simeq\!3.17$ au we derive $3Ο$ limits of $Q({\rm OH})<7.76\times10^{23}\ {\rm s^{-1}}$, but find no indications for [O I], C$_2$, C$_3$ or NH$_2$. We report detection of CN emission and also detect numerous Ni I lines while Fe I remains undetected, potentially implying efficiently released gas-phase Ni. From our latest X-shooter measurements conducted on 2025-08-21 ($r_{\rm h} = 2.85$\,au) we measure production rates of $\log~Q(\mathrm{CN}) = 23.61\pm 0.05$ molecules s$^{-1}$ and $\log~Q$(Ni) $= 22.67\pm0.07$ atoms s$^{-1}$, and characterize their evolution as the comet approaches perihelion. We observe a steep heliocentric-distance scaling for the production rates $Q(\mathrm{Ni}) \propto r_h^{-8.43 \pm 0.79}$ and for $Q(\mathrm{CN}) \propto r_h^{-9.38 \pm 1.2}$, and predict a Ni-CO$_{(2)}$ correlation if the Ni I emission is driven by the carbonyl formation channel. Energetic considerations of activation barriers show that this behavior is inconsistent with direct sublimation of canonical metal/sulfide phases and instead favors low-activation-energy release from dust, e.g. photon-stimulated desorption or mild thermolysis of metalated organics or Ni-rich nanophases, possibly including Ni-carbonyl-like complexes. These hypotheses are testable with future coordinated ground-based and space-based monitoring as 3I becomes more active during its continued passage through the solar system.
Grand #cosmicfireworks
#Sprites are an extremely rare phenomenon of #atmosphericluminescence that appear like fireworks.
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3i/Atlas
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Peter Riley