We have detected a sample of the reddest, and likely youngest, protostars in the Orion molecular clouds using PACS observations from the Herschel Space Observatory as part of the Herschel Orion Protostar Survey (HOPS). We find 19 sources (12 of which are Herschel-only detections) that have extremely red 24 μm to 70 μm colors (Figure 1). We refer to these sources as the "PACS Bright Red sources", or PBRS. Stutz et al. (2013) concluded that the red colors of the PBRS (Figure 1) are best explained

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... by high envelope densities, the highest Class 0 envelope densities of all the observed protostars in Orion. To further characterize these the PBRS, we have now obtained follow-up CARMA 2.9 mm continuum and CO (J=1-0) maps toward 14/19 PBRS, in addition to Herschel PACS spectroscopy toward 8/19 PBRS. Figure 1: Plots showing the extreme characteristics of the PBRS compared to other Orion protostars and well studied protostars in other clouds. Both panels show the sample of HOPS protostars detected at 70 μm; the green symbols show the PBRS (and other'newother'new' sources) and the black diamonds are well known protostars from other clouds. The left panel shows the color selection criteria of the PBRS. The right panel shows that PBRS appear to be extreme Class 0 objects, with similar luminosities but systematically colder T bol. The rarity of the PBRS suggest they have lifetimes of only ~25,000 years, 5% of the protostellar lifetime (Stutz et al. 2013).