Euclid is an infrared telescope like the Webb, but since it's smaller than Webb (and smaller than Hubble), it can't have the resolution (ability to optically separate sources that are close to each other) or the sensitivity that the "big brothers" provide. Still the telescope will observe billions of galaxies during its six-year survey of the sky, measuring their shapes and positions going back 10 billion years, more than 70 percent of cosmic history.
Led by the European Space Agency, the Euclid mission has the ambitious goal of helping astronomers and cosmologists learn about the properties and influence of dark matter and dark energy, which are thought to make up about 95 percent of the Universe. The rest of the cosmos is made of regular atoms and molecules that we can see and touch.
From Henk Hoekstra, a professor and cosmologist at Leiden Observatory in the Netherlands anxiously waiting for the data from Euclid to start pouring in, we get the quote of the day, “It’s very difficult to find a black cat in a dark room, especially if there’s no cat.”
The current "standard model" of cosmology postulates the existence of "dark matter" we can't see and an even more obscure "dark energy" that's filling space. The ideas for dark matter and energy came from observations of galaxies; how they rotate and how the stars are distributed. Astronomers eventually concluded that there had to be far more stars in galaxies than could be seen, to provide the gravitational attraction to hold everything together the way the stars are distributed.
All the atoms in the universe only make up about 5% of its total contents. The rest is dark matter and dark energy. Dark matter, which is about 27% of the contents of the universe, provides the gravitational foundation for building galaxies and galaxy clusters. The large-scale structure of the universe is produced by dark matter, but we still don’t know what it’s made of. Dark energy, making up the remaining 68% of the universe’s contents, causes the expansion of the universe to accelerate. The push-pull of dark matter and energy are what makes the universe look the way it does, so understanding exactly what these mysterious substances are and how they work is a major challenge of modern cosmology.
Together, dark matter and energy as currently envisioned say that 95% of our Universe is something that's totally invisible to us. The stars, planets, and everything else we can see are the other 5%. Together, dark matter and energy have been called, “[the] biggest embarrassment that we have currently in cosmology.”
Data pouring in?
Euclid is expected to downlink about 100 gigabytes of compressed data every day, and over the course of its mission, will produce more than 100 petabytes of information after automated processing at nine ground-based data centers, said Gaitee Hussain, head of the science division at the European Space Agency.
That's from a 600-megapixel visible light camera, a 64-megapixel near-infrared camera and a spectrometer.
Euclid will take about a month to reach its L2 orbit and another few months for equipment checkouts after that.
The regions Euclid will survey during its six-year mission, totaling about 36% of the sky. ESA Graphic
Scientists say it would take Hubble hundreds of years to complete the same extra-galactic survey as Euclid, which will cover in a week the same area of sky that Hubble has observed in its 33-year mission.
Think of Euclid versus Webb or Hubble as a wide angle lens versus a telephoto. As is often the case in photography, knowing which lens to grab for a picture makes all the difference.