[LINK] On two serendipitous discoveries of objects in deep space

[rfmcdonald]

Two posts yesterday at The Dragon's Gaze, here and here pointing to the serendipitous discovery of two very distant objects. Centauri Dreams set things up.

Two papers have appeared on the arXiv server suggesting hitherto undiscovered objects in the outer Solar System (thanks to Centauri Dreams reader Stevo Darkly for the pointer). Both papers use data harvested by the Atacama Large millimeter/submillimeter array (ALMA), an interferometer of radio telescopes in Chile’s northern high desert. Here some 66 12-meter and 7-meter radio telescopes work the sky at millimeter and submillimeter wavelengths, with targets that have ranged from galactic dust in the early universe to magnetic fields near a supermassive black hole.

ALMA’s uses closer to home are made clear in the new papers, which demonstrate that this array can be a major tool in helping us probe the outer system well into the Oort Cloud. In the first paper, the researchers draw on three periods of observation with ALMA to detect point-like emissions at different positions in two of the periods. The two emissions are thought to be the same source, considering what the authors call “the negligible probability of having identified two independent highly variable background sources.” Assuming a single source, the team dubs the object Gna, noting that it was not visible in the third observing period 42 days later.

So what exactly do we have here? If gravitationally bound, the object would be at a distance between 12 and 25 AU, most likely a Centaur with a semi-major axis between Jupiter and Neptune, though a large one, in the range of 220-800 kilometers depending on distance and albedo. The authors note that the location of the field of view (close to the galactic plane toward the star W Aquilae) may explain why the object was not seen sooner despite its size.

But there is another possibility, that Gna is unbound. “In that case,” write the authors, “the most exciting possibility is that we have observed a planetary body or brown dwarf in the outer reaches of the Oort cloud.” Which leads to recent WISE studies that found no evidence of a Saturn-class object out as far as 28000 AU, or of a Jupiter out to 82000 AU, while a Jupiter-sized brown dwarf could be excluded out to 26000 AU at the locations previously suggested by John Matese and Daniel Whitmire. The latter have argued that a large planetary body in the Oort would explain the seemingly clustered orbits of many comets.

Other blogs, including D-Brief, noted this was very early yet.