Europe's Euclid space telescope took off on Saturday on a mission to shine light on dark energy and dark matter in space.
It left Cape Canaveral in Florida, at 11.12 am local time (1512 GMT) aboard a Falcon 9 carrier rocket supplied by the US company SpaceX.
The European Space Agency turned to billionaire Elon Musk's company after Russia withdrew its Soyuz rockets in response to sanctions over the war in Ukraine.
After a month-long journey through space, Euclid will join the James Webb Space Telescope at a point about 1.5 million kilometres from Earth called the second Lagrange Point.
From there, Euclid will chart the largest map of the universe yet, encompassing up to two billion galaxies across more than a third of the sky.
By capturing light that has taken 10 billion years to reach Earth's vicinity, the map will also offer a new view of the 13.8-billion-year-old universe's history.
Scientists hope to use this information to address what the Euclid project manager Giuseppe Racca calls a “cosmic embarrassment” that 95 per cent of the universe remains unknown to humanity.
About 70 per cent is thought to be dark energy, the name given to the unknown force that is causing the universe to expand at an accelerated rate.
And 25 per cent is dark matter, thought to bind the universe together and make up about 80 per cent of its mass.
“Ever since we could see stars we've wondered, is the universe infinite? What is it made out of? How does it work?” Nasa Euclid project scientist Michael Seiffert told AFP.
“It's just absolutely amazing that we can take data and actually start to make even a little bit of progress on some of these questions.”
Euclid consortium member Guadalupe Canas said that the space telescope was a “dark detective” which can reveal more about both elements.
Euclid, which is 4.7 metres tall and 3.5 metres wide, will use two scientific instruments to map the sky.
Its visible light camera will let it measure the shape of galaxies, while its near-infrared spectrometer and photometer will allow it to measure how far away they are.
So how will Euclid try to spot things that cannot be seen? By searching for their absence.
The light coming from billions of light years away is slightly distorted by the mass of visible and dark matter along the way, a phenomenon known as weak gravitational lensing.
“By subtracting the visible matter, we can calculate the presence of the dark matter which is in between,” Mr Racca told AFP.
While this may not reveal the true nature of dark matter, scientists hope it will provide clues that will help to provide answers in the future.
For dark energy, French astrophysicist David Elbaz compared the expansion of the universe to blowing up a balloon with lines drawn on it.
By “seeing how fast it inflates,” scientists hope to measure the breath – or dark energy – making it expand.
A major difference between Euclid and other space telescopes is its wide field of view, which takes in an area equivalent to two full moons.
Project scientist Rene Laureijs said that this wider view means Euclid will be able to “surf the sky and find exotic objects” like black holes that the Webb telescope can then investigate in greater detail.
Beyond dark energy and matter, Euclid's map of the universe is expected to be a “gold mine for the whole field of astronomy,” said Yannick Mellier, head of the Euclid consortium.
Scientists hope that Euclid's data will help them learn more about the evolution of galaxies, black holes and more.
The first images are expected once scientific operations start in October, with major data releases planned for 2025, 2027 and 2030.
The €1.4 billion ($1.5 billion) mission is intended to run until 2029, but could last longer if all goes well.
