Free Astronomy Magazine May-June 2016

29 MAY-JUNE 2016 SPACE CHRONICLES tres from the central star, sim- ilar to the average distances from the Sun to Uranus and Pluto in the Solar System. They too are likely to be the results of particles that came together to form planets, which then swept their orbits clear of dust and gas and shepherded the remaining material into well- defined bands. For the new TW Hydrae observations, astronomers imaged the faint radio emission from millimetre-sized dust grains in the disc, revealing details on the order of the distance between the Earth and the Sun (about 150 mil- lion kilometres). These detailed observations were made possible with ALMA’s high-resolution, long- baseline configuration. When AL- MA's dishes are at their maximum I n the background, ALMA image of the planet-forming disc around the young, Sun-like star TW Hydrae. The inset image (left) zooms in on the gap nearest to the star, which is at the same distance as the Earth is from the Sun, suggesting an infant version of our home planet could be emerging from the dust and gas. The additional concentric light and dark features represent other planet- forming regions farther out in the disc. [S. Andrews (Harvard-Smithsonian CfA), ALMA (ESO/NAOJ/NRAO)] n disc with features that strongly suggest planets are beginning to coalesce," said Sean Andrews with the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, USA and lead au- thor of the study. "The new ALMA images show the disc in unprecedented detail, re- vealing a series of concentric dusty bright rings and dark gaps, includ- ing intriguing features that may in- dicate that a planet with an Earth- like orbit is forming there." Other pronounced gaps that show up in the new images are located three billion and six billion kilome- separation, up to 15 kilometres apart, the telescope is able to re- solve finer details. "This is the high- est spatial resolution image ever of a protoplanetary disc from ALMA, and that won't be easily beaten in the future!" said Andrews. (The an- gular resolution of the images of HL Tauri was similar to these new observations, but as TW Hydrae is much closer to Earth, finer details can be seen.) "TW Hydrae is quite special. It is the nearest known protoplanetary disc to Earth and it may closely resem-ble the Solar System when it was only 10 million years old," adds co-author David Wilner, also with the Harvard-Smithsonian Cen- ter for Astrophysics. Earlier ALMA observations of an- other system, HL Tauri, show that even younger protoplanetary discs — a mere 1 million years old — can display similar signatures of planet formation. By studying the older TW Hydrae disc, astronomers hope to better understand the evolution of our own planet and the pros- pects for similar systems through- out the Milky Way. The astronomers now want to find out how common these kinds of features are in discs around other young stars and how they might change with time or environment.