Understanding planet formation with ALMA and EVLA

目前已知的太阳系外行星超过450颗，最近在两颗恒星周围直接拍摄到了行星的图像。虽然我们知道行星一定是在恒星周围由气体和固体组成的原行星盘中形成的，但行星在圆盘中形成的实际过程尚不清楚。两个高分辨率望远镜阵列——位于智利北部的ALMA（阿塔卡马大型毫米-亚毫米阵列）和位于新墨西哥州的EVLA（扩展超大阵列）——的建成，将使我们能够首次通过对原行星盘内部详细结构的高分辨率研究，对行星形成过程进行成像。这些仪器的组合对于追踪行星形成的开始是理想的，当微米大小的颗粒开始聚集成更大的鹅卵石时。我们将寻找这些鹅卵石的证据，以确定行星形成的开始时间和地点。我们的观察将揭示是否需要特殊的条件来开始鹅卵石的形成，或者这个过程是否稳健并发生在整个磁盘上。比较不同区域的圆盘将揭示恒星形成的环境是否会影响其周围行星的形成。我们还将观察到更老的圆盘，到那时行星质量体一定已经形成了。在形成的最后阶段的行星可以直接在圆盘内成像，并且由于行星与圆盘中的物质相互作用而形成的间隙和洞将揭示更多。在我们发现行星证据的地方，我们将对气体含量进行详细观察，以了解形成行星的大气可能包含什么。有了这些数据，我们很快就能更好地了解太阳系、地球甚至生命本身的形成。

Over 450 extrasolar planets are now known, and planets have recently been directly imaged around two stars. Although we know that planets must form in protoplanetary disks of gas and solids around forming stars, the actual process by which planets are built up in disks is not yet known. The completion of two high-resolution telescope arrays, ALMA (Atacama Large Millimeter-submillimeter Array) in northern Chile and the EVLA (Expanded Very Large Array) in New Mexico will enable us to image the process of planet formation for the first time using high-resolution studies of the detailed structures within protoplanetary disks. The combination of these instruments is ideal for tracing the onset of planet formation, when micron-sized particles start to agglomerate into larger pebbles. We will search for evidence of these pebbles to determine when and where the onset of planet formation occurs. Our observations will reveal whether special conditions are needed to start the build up of pebbles or whether the process is robust and occurs throughout the disks. Comparison of disks in different regions will reveal whether the environment in which stars forms impacts the formation of planets around them. We will also observe older disks by which time planetary mass bodies must have formed. Planets in the final stages of formation could be directly imaged within disks, and many more will be revealed by the gaps and holes that form due to the interaction of the planet with material in the disk. Where we find evidence of planets, we will take detailed observations of the gas content to learn what the atmospheres of forming planets could contain. With all these data in hand, we will soon better understand the formation of our own Solar System, the Earth and perhaps even life itself.