From Molecular Cores to Planet Forming Disks (c2d)

Since the 1990s, astronomers have identified thousands of exoplanets, indicating that the Milky Way alone could be host to hundreds of billions of planets. However, we are still learning how these planets formed in the first place, crucial information in understanding the variety of systems researchers have cataloged. To fill in those gaps, astronomers from the Center for Astrophysics | Harvard & Smithsonian collaborated with others from around the world on the project named “From Molecular Cores to Planet Forming Disks” (c2d). This program used NASA’s Spitzer Infrared Space Telescope to observe star-forming systems and the protoplanetary disks where future planets are born. The c2d program ended its observational phase in the mid-2000s, but maintains a catalog of these systems that continues to be used by astronomers studying star formation.

This artist's concept shows a young star surrounded by a dusty protoplanetary disk. This disk contains the raw material that can form planets as the star system matures.

Credit: NASA/JPL-Caltech/R. Hurt (SSC/Caltech)

Studying Planetary Nurseries

Stars and planets are born in dense, cold interstellar clouds of gas and dust. These regions of space are opaque to visible light, but infrared light reveals a wealth of details. The c2d program exploited that using the Spitzer telescope to observe inside the dark blobs known as molecular cores, where stars and planets form.

Spitzer’s original three instruments — Infrared Array Camera (IRAC), Infrared Spectrograph (IRS), and Imaging Photometer for Spitzer (MIPS) — made it uniquely able to observe star-forming regions in a wide range of infrared wavelengths. The c2d project used Spitzer to look at five of the nearest large molecular clouds for protostars, protoplanetary disks, and other signs of newborn stars. Astronomers identified nearly 100 molecular cores and protostellar objects, which are cataloged on the c2d website.

Today, only the IRAC instrument on Spitzer is still operational, but the c2d project paved the way to later observing campaigns, such as the CfA-led COordinated Molecular Probe Line Extinction Thermal Emission (COMPLETE) Survey of Star Forming Regions.