$4-billion telescope that could rewrite gravity launches on Sunday — An illustration shows Nasa’s Nancy Grace Roman Space Telescope in orbit. Image: Nasa

Nasa, the US space agency, is preparing to launch its next flagship space observatory, one that scientists plan to use to investigate some of the universe’s biggest mysteries including dark energy and dark matter, while also testing gravity at vast scales and hunting for planets beyond our solar system.

The launch of the Nancy Grace Roman Space Telescope, a roughly US$4-billion (R64-billion) project, is planned for Sunday at Nasa’s Kennedy Space Centre in Florida, with the observatory to be lofted into orbit aboard a SpaceX Falcon Heavy rocket. The launch comes nine months ahead of schedule, according to US space agency officials.

Roman is a follow-on to the Hubble Space Telescope, launched in 1990, and the James Webb Space Telescope, launched in 2021, and has capabilities that can expand on the knowledge gained by those pioneering observatories, both of which continue to operate.

The new telescope’s panoramic view of space and its rapid survey speeds offer the opportunity for scientists to study the cosmos as never before, with wide-field surveys examining its structure, composition and evolution.

“Roman’s vast reach will allow us to find the weird, the rare and the unusual,” Julie McEnery, Roman’s senior project scientist at Nasa’s Goddard Space Flight Centre in Maryland, told reporters. “Roman’s primary instrument combines exquisite performance and sensitivity with the ability to quickly and efficiently survey the large regions of the sky.”

The telescope’s main survey will take more than a year, McEnery said.

Fabric of the universe

“The survey will contain over two billion galaxies and enable us to study how the structures in our universe — the stars, the galaxies, the clusters of galaxies — grew and evolved. We’ll also measure how our universe has expanded over time. And these are the keys that will allow us to unlock the fundamental nature of dark matter and dark energy and the fabric of the universe itself,” McEnery said.

The Big Bang event roughly 13.8 billion years ago initiated the universe, and it has been expanding ever since. Scientists in 1998 disclosed that this expansion was actually accelerating, with an invisible force called dark energy as the hypothesised reason.

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The universe’s contents include ordinary matter — stars, planets, gas, dust and all the familiar stuff on Earth — as well as dark matter and dark energy, whose physical nature remains unknown. Ordinary matter represents perhaps 5% of the contents. Dark matter, known through its gravitational influences on galaxies and stars, may represent about 27%. Dark energy may represent about 68%.

“The key questions are: is dark energy simply a property of empty space that remains constant over time, or does it evolve in time?” said cosmologist Mustapha Ishak of the University of Texas at Dallas, a member of Roman’s scientific collaboration.

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Nasa's Nancy Grace Roman Space Telescope stands after engineers and technicians working inside the Payload Hazardous Servicing Facility mated the observatory to its payload adapter and a strut payload attach fitting, a specialised piece of hardware designed for large, heavy loads. Jolearra Tshiteya/Nasa — Nasa’s Nancy Grace Roman Space Telescope stands after engineers and technicians working inside the Payload Hazardous Servicing Facility mated the observatory to its payload adapter and a strut payload attach fitting, a specialised piece of hardware designed for large, heavy loads. Jolearra Tshiteya/Nasa

“The recent results from the DESI — Dark Energy Spectroscopic Instrument — collaboration indicate tantalising hints of a time evolution of dark energy. Could the observed acceleration instead indicate that our theory of gravity needs modification on the largest scales? Answering these questions is one of the most important goals of modern cosmology,” Ishak said.

Physicist Albert Einstein in 1915 presented his theory of general relativity explaining gravity, and it remains foundational. Roman will map how galaxies cluster and how matter bends light through a phenomenon called gravitational lensing.

“These measurements allow us to test whether Einstein’s theory remains valid across billions of light years or whether modifications to gravity theory are required,” said Ishak. “This is important because it addresses one of the most fundamental questions in physics: what law governs the universe on its largest scales?”

To date, more than 6 350 exoplanets — planets outside our solar system — have been discovered, as scientists search for evidence of potential life beyond Earth.

Roman will conduct one of the most comprehensive searches ever for exoplanets. It is expected to discover thousands of new ones and provide the first statistical census of planetary systems similar to our own. It also will demonstrate new technology to directly image some relatively nearby exoplanets.

After launch and separation from the rocket, the telescope will travel towards a location called Lagrange Point 2, situated about 1.6 million kilometres from Earth, about four times the distance to the moon. Webb also resides at this orbital location. Hubble is in low-Earth orbit.

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Roman’s mission is planned for five years, though Nasa said the telescope may have enough fuel for five additional years. US President Donald Trump’s administration tried during both his first and second terms to reduce or eliminate funding for Roman, but the US congress preserved it.