Simons Observatory in a nutshell

The Simons Observatory (SO) is a ground-based cosmic microwave background (CMB) experiment situated on Cerrro Toco, 5300 m (17,000 feet) above the Atacama Desert in Chile. It will make precise and detailed observations of the CMB, the heat left over from the hot, early days of the history of the Universe.  These SO observations promise to provide breakthrough discoveries in fundamental physics, cosmology and astrophysics. For a detailed list, jump to:

The SO experiment in its currently funded form (which we call “SO-Nominal”) consists of three 0.4 m (16 inch) Small Aperture Telescopes (SATs) and one 6 m (20 feet) Large Aperture Telescope (LAT).  Both operate over a range of microwave to submillimeter wavelengths.  Optimized to keep systematic errors small in polarization measurements at large angular scale, the SATs will perform a deep, degree-scale survey of 10% of the sky to search for the imprint of primordial gravitational waves on the CMB.  The LAT will survey nearly 1/2 of the sky with arcminute resolution.  When combined, the SO observations will measure (or put limits on) the sum of masses of the three species of neutrinos, allow a search for other light elementary particles, track the behavior of dark energy, and refine our understanding of the intergalactic medium, clusters of galaxies and the role of feedback in galaxy formation.

With up to ten times the sensitivity and five times the angular resolution of the Planck satellite, and roughly an order of magnitude increase in survey speed over other, currently operating, CMB experiments, SO will measure both temperature and polarization fluctuations in the CMB to exquisite precision at several frequencies.  Accompanying SO measurements will allow us to map and remove competing emission from the Milky Way Galaxy.

Fig. 1 The survey areas of the Small- and Large-Aperture telescopes (top panel) and the forecast power spectrum of the Simons Observatory (bottom panel).

Each oval in the top portion of the figure shows the whole sky, with the extent of the two SO surveys indicated, the smaller SAT survey on the left, and the larger area LAT survey on the right.  The bright red band in each oval traces the plane of our Milky Way Galaxy; to map the CMB we need to measure and remove this foreground emission.  The LAT survey, on purpose, overlaps several other surveys of the sky made at other wavelength (DESI and LSST, for instance).  The lower panel shows the expected level of  CMB fluctuations of various sorts as a function of their angular size (with angular size decreasing to the right).  The top curve is for fluctuations in temperature; the lower two for polarized fluctuations.  For all three, current results from Planck and BICEP2/Keck, and projected errors for LiteBIRD 0.4m-telescope are shown, along with projections for the SO results (blue dots).  SO will have better angular resolution than Planck, and hence can make measurements to smaller angular scales.  Note also the clear improvement in measurements of polarized fluctuations, both the divergence-like E modes and the much fainter curl-like B modes.  The B mode polarization at large angular scales is a potential “smoking gun” for primordial gravitational waves. Other key SO statistics, not shown in the figure, are the TE primary spectrum, the CMB lensing power spectrum, the bispectrum, the kinematic Sunyaev-Zeldovich (kSZ) signal and the number of galaxy clusters detected via the thermal Sunyaev-Zeldovich (tSZ) effect. Additional details on SO’s science objectives can be found on the arXiv