Astronomers using data from the Atacama Large Millimeter/submillimeter Array (ALMA) have found a distant object in the direction of Alpha Centauri. The object appears to be in the outer region of our solar system, and depending on its distance could be a hypothesized ”super-Earth.”
ALMA is capable of precise observations at short microwave wavelengths, typically emitted by cold gas and dust. But objects on the edge of our solar system also emit light in this range, and would be too cool and distant to be observed by infrared telescopes. In 2014, ALMA found a faint object in the direction of Alpha Centauri A and B. The object was again observed in May of this year, this time more clearly the object is most likely part of the solar system, in prograde motion, albeit at a distance too far to be detectable at other wavelengths,
* an ETNO [Extreme Trans Neptunian Object] (≫ 100 AU)
* a hypothesized Super-Earth (∼ 300 AU)
* a super-cool brown dwarf (∼ 20 000 AU).
It doesn’t seem to be part of the Alpha Centauri system, it must be closer and correspondingly smaller. With just two observations it isn’t possible to determine the object’s orbit, so we can only guess at its distance and size. One possibility (and the one I think most likely) is that it’s an extreme trans-Neptunian object about 100 astronomical units away from the Sun, which is further than Sedna at 86 AU. This would make it the most distant known object in the solar system, but likely smaller than Pluto.
Another possibility (which seems more likely to the object’s discoverers) is that it is about 300 AU away and about 1.5 times the size of Earth, making it the first “super-Earth” found in our solar system. Observations of trans-Neptunian objects have led to some speculation that one or two super-Earth’s could lurk in the outer solar system, so it’s not out of the question. There’s reason to be cautious of this idea, however, because of its location. Alpha Centauri is about 42 degrees away from the ecliptic. Most large solar system lay within a few degrees of the ecliptic, and even Sedna’s orbit is only inclined about 12 degrees from it.
A third possibility is that the object is a cool brown dwarf about 20,000 AU away. Such an object should also be visible in the infrared, so there would still be the question as to why it wasn’t discovered by earlier infrared sky surveys. Its proximity to Alpha Centauri would seem to make such an object easy to find.
The only way to know for sure is to gather more observations.
It will take a lot of work to learn more about the new ALMA objects, but we’re finding out how the array can fine-tune our capabilities in probing out into the Oort Cloud. If such perturbers exist, we’re going to turn them up sooner or later as we continue to map the system’s farthest depths.
The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical interferometer of radio telescopes in the Atacama desert of northern Chile. Since a high and dry site is crucial to millimeter wavelength operations, the array has been constructed on the Chajnantor plateau at 5,000 meters altitude, near Llano de Chajnantor Observatory and Atacama Pathfinder Experiment. Consisting of 66 12-meter (39 ft), and 7-meter (23 ft) diameter radio telescopes observing at millimeter and submillimeter wavelengths, ALMA is expected to provide insight on star birth during the early universe and detailed imaging of local star and planet formation.
ALMA is an international partnership among Europe, the United States, Canada, several countries from East Asia and the Republic of Chile. Costing about US$1.4 billion, it is the most expensive ground-based telescope in operation
Abstract – A new submm source within a few arcseconds of α Centauri: ALMA discovers the most distant object of the solar system
We recently announced the detection of an unknown submillimeter source in our ALMA observations of alpha Cen AB. The source was detected in two epochs, a strong detection at 445~GHz and one at lower significance at 343.5~GHz. After valuable feedback of the community, it turns out that the detection at 343.5~GHz could not be reproduced with a different reduction software nor with fitting within the (u,v)-plane. The detection at 445~GHz has been further confirmed with modeling of the (u,v)-data and was shown to be robust at >12σ, confirming our detection of this unknown source. However, based on only one epoch, further analysis and preferably new data are needed, before publication of an article in which the nature of the new source can be discussed. The analysis has indicated the importance of both (u,v)-plane fitting and alternative data reduction when dealing with low signal to noise source detections.
Abstract – The serendipitous discovery of a possible new solar system object with ALMA
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 over 5.8σ in the image plane and over 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 50×50 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.