Detection of CO and HCN in Pluto's atmosphere with ALMA

Detection of CO and HCN in Pluto's atmosphere with ALMA

Authors:

Lellouch et al

Abstract:

Observations of the Pluto-Charon system, acquired with the ALMA interferometer on June 12-13, 2015, have yielded a detection of the CO(3-2) and HCN(4-3) rotational transitions from Pluto, providing a strong confirmation of the presence of CO, and the first observation of HCN, in Pluto's atmosphere. The CO and HCN lines probe Pluto's atmosphere up to ~450 km and ~900 km altitude, respectively. The CO detection yields (i) a much improved determination of the CO mole fraction, as 515+/-40 ppm for a 12 ubar surface pressure (ii) clear evidence for a well-marked temperature decrease (i.e., mesosphere) above the 30-50 km stratopause and a best-determined temperature of 70+/-2 K at 300 km, in agreement with recent inferences from New Horizons / Alice solar occultation data. The HCN line shape implies a high abundance of this species in the upper atmosphere, with a mole fraction >1.5x10-5 above 450 km and a value of 4x10-5 near 800 km. The large HCN abundance and the cold upper atmosphere imply supersaturation of HCN to a degree (7-8 orders of magnitude) hitherto unseen in planetary atmospheres, probably due to the slow kinetics of condensation at the low pressure and temperature conditions of Pluto's upper atmosphere. HCN is also present in the bottom ~100 km of the atmosphere, with a 10-8 - 10-7 mole fraction; this implies either HCN saturation or undersaturation there, depending on the precise stratopause temperature. The HCN column is (1.6+/-0.4)x10^14 cm-2, suggesting a surface-referred net production rate of ~2x10^7 cm-2s-1. Although HCN rotational line cooling affects Pluto's atmosphere heat budget, the amounts determined in this study are insufficient to explain the well-marked mesosphere and upper atmosphere's ~70 K temperature. We finally report an upper limit on the HC3N column density (< 2x10^13 cm-2) and on the HC15N / HC14N ratio (< 1/125).

ALMA's Solar System Member: That's Too Fluffy or Really Dense

Tentative planetary orbital constraints of some scenarios for the possible new Solar System object recently discovered with ALMA

Authors:

Iorio

Abstract:

Some of the scenarios envisaged for the possible new Solar System object, whose discovery with the ALMA facility has been recently claimed in the literature, are preliminarily put to the test by means of the orbital motions of some planets of the Solar System. It turns out that the current ranges of admissible values for any anomalous secular precession of the perihelion of Saturn, determined in the recent past with either the EPM2011 and the INPOP10a planetary ephemerides without modeling the action of such a potential new member of the Solar System, do not rule out the existence of a putative Neptune-like pointlike perturber at about 2500 au. Instead, both a super-Earth at some hundreds of au and a Jovian-type planet up to 4000 au are strongly disfavored. An Earth-sized body at 100 au would have a density as little as ∼0.1−0.01 g cm−3, while an unusually large Centaur or (Extreme) Trans Neptunian Object with linear size of 220−880 km at 12−25 au would have density much larger than ∼1 g cm−3.

Nemesis Found? Or Gna? A TNO, SuperEarth or Cool Brown Dwarf Tracking With α Centauri System

A new submm source within a few arcseconds of α Centauri: ALMA discovers the most distant object of the solar system

Authors:

Liseau et al

Abstract:

The understanding of the formation of stellar and planetary systems requires the understanding of the structure and dynamics of their outmost regions, where large bodies are not expected to form. Serendipitous searches for Sedna-like objects allows the observation of regions that are normally not surveyed. The Atacama Large Millimeter/submillimeter Array (ALMA) is particularly sensitive to point sources and it presents currently the only means to detect Sedna-like objects far beyond their perihelia. ALMA observations 10 months apart revealed a new blackbody point source that is apparently comoving with α Cen B. We exclude that source to be a sub-/stellar member of the α Centauri system, but argue that it is either an extreme TNO, a Super-Earth or a very cool brown dwarf in the outer realm of the solar system.

oooo.  Academic bun fight:

The serendipitous discovery of a possible new solar system object with ALMA

Authors:

Vlemmings et al

Abstract:

The unprecedented sensitivity of the Atacama Large millimeter/submillimeter array (ALMA) is providing many new discoveries. Several of these are serendipitous to the original goal of the observations. We report the discovery of previously unknown continuum sources, or a single fast moving new source, in our ALMA observations. Here we aim to determine the nature of the detections. The detections, at greater than 5.8σ in the image plane and greater than 14σ in the (u,v)−plane, were made in two epochs of ALMA observations of a 25 arc second region around the asymptotic giant branch star W Aql in the continuum around 345 GHz. At a third epoch, covering 50x50 arcseconds, the source(s) were not seen. We have investigated if the detections could be spurious, if they could constitute a population of variable background sources, or if the observations revealed a fast moving single object. Based on our analysis, we conclude that a single object (with a flux of ∼3.0 mJy) exhibiting a large proper motion (∼87 arcsec/yr) is the most likely explanation. Until the nature of the source becomes clear, we have named it Gna. Unless there are yet unknown, but significant, issues with ALMA observations, we have detected a previously unknown objects in our solar system. Based on proper motion analysis we find that, if it is gravitationally bound, Gna is currently located at 12−25 AU distance and has a size of ∼220−880 km. Alternatively it is a much larger, planet-sized, object, gravitationally unbound, and located within ∼4000 AU, or beyond (out to ∼0.3~pc) if it is strongly variable. Our observations highlight the power of ALMA in detecting possible solar system objects, but also show how multiple epoch observations are crucial to identify what are otherwise probably assumed to be extra-galactic sources.