Free Astronomy Magazine January-February 2015

JANUARY-FEBRUARY 2015 PLANETOLOGY of that dust (and the low temperature characterizing it) hides to white-light telescopes every detail, whereas infrared telescopes only allow to perceive mostly indistinct scenarios. Today, however, ALMA offers research opportunities previously unthought of, and this for two good reasons. One relates to the reachable wave- lengths, that are more compatible with colder environments than those reachable with more traditional telescopes; and protoplane- tary disks are indeed cold environments (a few tens of kelvin). The other good reason refers to the high angular resolution of the images obtainable with ALMA using the interferometry principles, according to which the more distant from each other the individual elements of an array of telescopes and radio telescopes, the higher the resulting resolving power (and more difficult it will be to con- structively overlay the different signals acquired). The 66 ALMA antennas can be spaced out over an area as wide as 16 km, that with regard to resolution is equivalent to using a single antenna with such diameter. For comparison, it has to be kept in mind that other similar facilities operating at millimeter wavelengths have an- tennas that can be spaced apart by a couple of kilometres at most. Last September ALMA began a test cycle with images acquisition over a baseline of 15 km, hence close to the maximum permitted, and the results were not long in coming. The space observatory in T he above illustration gives an idea of how the accretion of solids bod- ies inside protoplanetary disks occurs: from simple conglomerates of tiny grains similar to sand, to planetary size objects. Right, the great nebular region of the constellation Taurus in which less than 1 million years ago the star HL Tauri (shown by the arrow) was born with its pro- toplanetary disk. [Alan Brandon/Nature, ESO/Digitized Sky Survey 2]