The next twenty years promises to be an exciting time for studying the ISM. Each of the following telescopes is described in detail on a separate wordpress page (click on the acronym) and on their official websites (click the full name).
ALMA will begin early science observations with Cycle 0 in September, 2011 and should be completed in 2013. The high spatial resolution of ALMA will allow astronomers to image young planets embedded in disks around nearby
JWST is an exciting space-based infrared observatory that promises to acquire a wealth of photometric and spectroscopic information. For studies of the ISM, JWST will be particularly useful for mapping the distribution of dust and for observing obscured systems such as young stellar objects and circumstellar disks (see Gardner et al. 2006).
TMT will conduct near-UV, optical, and near-infrared observations of young stellar objects, protoplanetary disks, and hot, young Jovian planets. The large primary mirror of the telescope and the adaptive optics system will allow TMT to produce high-resolution images of star and planet formation that include small-scale details that are unobservable with current telescopes.
GMT has the same strong science case as TMT, but will be a ~25m telescope in the southern hemisphere. The main differences between GMT and TMT are shown in the table below.
The Astro2010 Decadel Survey identified U.S. participation in a Giant Segmented Mirror Telescope (either GMT, TMT, or E-ELT) as Priority 3 for large, ground-based missions (after the Large Synoptic Survey Telescope and a Mid-Scale Innovations Program). As part of the process, the National Academy of Sciences conducted an independent cost estimates for the telescopes optics and instruments for GMT and TMT. The resulting estimates at 70% confidence are $1.1 billion for GMT construction and $1.4 billion for TMT construction. These cost estimates assume that the telescopes will begin science operations with adaptive optics and three instruments in spring 2024 for GMT and between 2025 and 2030 for TMT. Although both the TMT website and the GMT website indicate science observation start dates in 2018, the Decadal Survey estimates are probably more realistic.