NRAO | ALMA | 2015 Apr 07
A series of images made with the Atacama Large Millimeter/submillimeter Array (ALMA) provides an unprecedented view of the surface of Juno, one of the largest members of our solar system's main asteroid belt. Linked together into a brief animation, these high-resolution images show the asteroid rotating through space as it shines in millimeter-wavelength light. ...
The complete ALMA observation, which includes 10 separate images, documents about 60 percent of one rotation of the asteroid. It was conducted over the course of four hours on 19 October 2014 when Juno was approximately 295 million kilometers from Earth. In these images, the asteroid's axis of rotation is tilted away from the Earth, revealing its southern hemisphere most prominently.
For this observation, ALMA achieved a resolution of 40 milliarcseconds, meaning that each "pixel" in the images is about 60 kilometers across, covering approximately one fourth of the surface of Juno. This resolution is a vast improvement over earlier observations made at similar wavelengths and is enough to clearly resolve the shape of the asteroid and potentially tease out prominent surface features.
Juno will make its next close approach to Earth in November 2018. Since the asteroid will be much closer than it was in the most recent observations, ALMA will be able to double its resolution, potentially revealing new details about this intriguing object. At approximately 240 kilometers across, Juno is among the largest members of the solar system’s main asteroid belt, but it is still only a few percent the mass of this region’s largest inhabitant: the dwarf planet Ceres, which is now playing host to NASA’s Dawn spacecraft. ...
ALMA Observations of Asteroid 3 Juno at 60 Kilometer Resolution - ALMA Partnership, T. R. Hunter et al
- arXiv.org > astro-ph > arXiv:1503.02650 > 09 Mar 2015 (v1), 06 Apr 2015 (v2)