Understanding planet formation with ALMA and EVLA

现在已知的太阳系外行星超过450颗，最近还直接拍摄到了围绕两颗恒星的行星。 虽然我们知道行星一定是在围绕恒星形成的气体和固体的原行星盘中形成的，但行星在盘中形成的实际过程还不清楚。 智利北方的阿塔卡马大型毫米-亚毫米阵列（阿尔马）和新墨西哥州的扩展甚大阵列（EVLA）这两个高分辨率望远镜阵列的建成，将使我们能够利用对原行星盘内详细结构的高分辨率研究，首次对行星形成过程进行成像。 这些仪器的组合非常适合追踪行星形成的开始，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建立卵石或是否该过程是强大的，并发生在整个磁盘。比较不同区域的盘将揭示恒星形成的环境是否会影响其周围行星的形成。我们还将观察到更古老的圆盘，那时行星质量体一定已经形成。 处于形成最后阶段的行星可以直接在盘中成像，并且由于行星与盘中物质的相互作用而形成的间隙和孔将揭示更多。 当我们发现行星的证据时，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。有了所有这些数据，我们很快就会更好地了解我们自己的太阳系，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.