WMAP is an observatory positioned 1.5 x 10⁶ km from earth at Lagrange point L2. This is a stable environment where the detectors can always point away from the sun, moon, and earth, and thus work non-stop on mapping. It covers nearly one-third of the sky each day, completing a full sky survey every six months, the time required for earth’s orbital motion to rotate the point of view through 180 °.

In #4, Charles L. Bennett (NASA Goddard Spaceflight Center) and the science team present detailed microwave maps in five wavebands (23 to 94 GHz), results from the first year of operation. As you would expect, these are of unprecedented precision, resolution, and sensitivity. A further plus is the inclusion of valuable new results on polarization in the CMB. A power-spectrum comparison of temperature and polarization maps provides a fix on the epoch of recombination in the hot expanding universe: at a redshift ~ z= 20, and a time 180 Myr after the Big Bang. This is the moment at which the universe ends its dark ages, as the first stars emit light. This early age is incompatible with the presence of significant warm dark matter. The data also give a new determination for the direction of motion of the Galaxy.

Naturally we turn to the values of the cosmological parameters as the most interesting application for the new data, and the values of these are in the paper at #1, by David Spergel (Princeton University) and the science team. The WMAP data are powerful for observational cosmology because the mission designers placed high priority on limiting systematic error. The best fit of WMAP data to the Standard Model yields the following composition: ordinary matter 4%, cold dark matter 23%, and dark energy 73%. Combining WMAP results with other astronomical data sets a limit of < 0.23 eV on the mass of the neutrino species.

While cosmologists will be glad to have a standard model (at last), there are still profound open questions: What is the dark matter? What is the dark energy? How does inflation work? Continuing improvements in technique should push beyond testing the Standard Model (WMAP’s role) to a quest for new physics. All very familiar to particle physicists, but novel for cosmologists!

This session, two further new papers, #5 and #7, continue a theme of space-led observations. Both describe instrumental aspects of the European Space Agency’s INTEGRAL mission—the International Gamma-Ray Astrophysics Laboratory—which launched on October 17, 2002. INTEGRAL is designed for high-resolution spectroscopy and imaging of gamma ray sources, in the energy range 15 keV to 10 MeV.

Gamma-ray bursts provided the first big surprise from INTEGRAL, which detects on average one burst a day. These occur without warning and fade in seconds. By networking with data from other gamma-ray observatories, INTEGRAL contributes to the important process of position finding, so that the optical afterglow of a burst can be studied. The surprising—or lucky—aspect is that about once a month a burst goes off in INTEGRAL’s field of view. This provides an immediate position, triggering very many follow-up observations, some of them by INTEGRAL’s four instruments.

Scientists with the mission have an exotic list of objectives. Once a week the galactic plane is scanned to check on the behavior of known gamma-ray sources in the Milky Way. The spectroscopy of extragalactic supernovas will contribute to stellar nucleosynthesis. Also under scrutiny: the black hole at the heart of the Milky Way. The pickings are so rich that researchers are calling for ESA to extend the mission beyond December 2004.