Almost a decade ago, the European Space Agency launched the Planck satellite to study the first light in the universe, the cosmic microwave background (CMB). The first data release was in 2013 and now the Planck consortium has delivered the final set of data.

The findings have been improved upon but the message remains unchanged. The standard model of cosmology is still the best explanation for what we see in the universe. The standard model is based on the theory of general relativity with some special additions in terms of dark matter and dark energy. Even though we do not know what these components are, the observations match the theoretical models that use them.

“This is the most important legacy of Planck,” Jan Tauber, ESA’s Planck Project Scientist, said in a statement. “So far the standard model of cosmology has survived all the tests, and Planck has made the measurements that show it.”

The picture painted by Planck is one of both extreme simplicity and hidden complexity. The data shows that in the very beginning, the universe was the same everywhere and in every direction, but subtle differences were already paving the way for the variation in structures we see today, such as galaxy clusters and cosmic voids.

Planck measured this in two ways. The main goal was to establish the temperature of the universe in every direction. This is what the map of the CMB is. We can see temperature differences of the order of a ten-thousandth of a degree, caused by slight differences in the mass of regions imprinted in the photons that we detect.

The other approach is more complicated. Planck also measured the polarization of light in the CMB. Light can vibrate in a particular direction, and interactions between light and matter can influence this direction. So mapping this property can help researchers work out more about the early universe. The polarization data was part of Planck's second data release, published in 2015, although the consortium stated that some of the data was not high quality enough.

The team has spent the last few years re-analyzing the data and now they are confident in the results. The 2018 legacy data release has both temperature and polarization of the CMB accurately determined.

“Now we really are confident that we can retrieve a cosmological model based on solely on temperature, solely on polarisation, and based on both temperature and polarisation. And they all match,” said Reno Mandolesi, principal investigator of Planck's Low Frequency Instrument at the University of Ferrara, Italy.

There are still many questions surrounding the standard model but it seems to be our best bet, uncertainties and all.