In one of the most fascinating NASA projects for a long while, on August 30, 2026 the Nancy Grace Roman space telescope was launched from Cape Canaveral in Florida. The planned 5 year mission cost about $4 billion and has some very ambitious objectives. It is designed to investigate one of the greatest of cosmic enigmas – Dark Matter and Dark Energy. But it will also investigate gravity at vast scales and look for exoplanets (planets beyond our solar system). While its mission has been planned for 5 years, it is hoped that it will survive for up to 10 years.
This space telescope was named after Nancy Grace Roman (1925-2018), who was the first female executive at NASA. She is best remembered as being the “Mother of Hubble”. The Hubble Space Telescope was launched in 1990 and revolutionised modern astronomy by the clarity of the images it collected (and still collects). Hubble orbits the earth 15 times a day at a height of about 500km. Nancy Roman not only organised the astronomers, but she also convinced Congress to fund the Hubble project.
The Roman Space Telescope will be stationed about 1.6 million km from earth at an L2 Lagrange point. These points (there are 5 of them) are positions in space where the gravitational pull of two large masses (Earth and the Sun in this case) equals the centripetal force needed for small objects to move with them. In other words, at this point, that small object needs minimal fuel to keep moving. This point is behind Earth, relative to the Sun, so telescopes there have a view of the Universe without the Sun’s glare. The James Webb Space Telescope and the European space telescopes Gaia and Euclid already reside at this point.
What is the Universe made of?
For the universe to exist as it does, there must be far more matter than we can see. It is estimated that all ordinary matter (stars, planets, gas, dust and all the “stuff” on Earth) represents about 5% of the Universe’s contents. Dark Matter may represent 27% and Dark Energy may represent 68%. Since, together, these forms of matter constitute 95% of the Universe, we need to understand what they are.
What do we currently know about Dark Matter and Dark Energy? At this stage, both are hypothetical only. Their existence has been invoked to explain some of the great mysteries of the observed Universe. Fundamentally, Dark Matter is attractive and pulls structures together, while Dark Energy is repulsive and stretches space apart.
Dark Matter:
Currently envisaged as an invisible substance acting as “cosmic glue” – providing extra gravitational pull. Without it spinning galaxies would rotate too fast and fly apart. If it exists, it is invisible to light – it does not emit, absorb, or reflect light. Scientists measure it by observing how its gravity bends starlight or affects the movement of stars. One theory expects Dark Matter to be composed primarily of some type of not-yet-characterised subatomic particle – specifically, weakly interacting massive particles (WIMPs). Such particles would pass through normal matter (stars, bodies, etc) unnoticed.
Dark Energy:
The nature of Dark Energy is even more hypothetical than that of Dark Matter, and many things about it remain in the realm of speculation. It is thought to be very homogeneous but not dense and is not known to interact through any of the fundamental forces other than gravity. In other words, it is unlikely to be detectable in a laboratory.
Current theory says that the Big Bang occurred about 13.8 billion years ago, initiating the existing universe; it has apparently been expanding ever since. Not only that, but it appears that this expansion is accelerating. The theory states that Dark Energy is driving this accelerated expansion.
One of many possible explanations is a cosmological constant which remains constant across time and space. Such a constant was first proposed by Einstein as an addition to his field equations of general relativity. Part of this theory showed that gravity should cause the Universe to collapse inward. Since Einstein originally believed that the Universe was static, he introduced this constant to counter the collapsing effects of gravity. Once Edwin Hubble discovered, in 1929, that the Universe was not static, but actually expanding, this static-balancing term became unnecessary, so Einstein withdrew it and called it his biggest blunder. Now that we believe that the Universe’s expansion is accelerating, the concept of the cosmological constant is back in favour – this time as a repulsive force (Einstein’s biggest blunder may turn out to be another stroke of genius!).
The Roman Space Telescope is designed to gain further insight into these two very mysterious forms of matter.
Other earth-bound ways of detecting Dark Matter and Dark Energy have been underway for some time. Ironically, one of these experiments – the Lux-Zeplin (LZ) experiment – announced a possible detection of evidence for Dark Matter at about the same time as the launch of the Roman telescope. Full investigation is still underway. This experiment is based 1,500 metres underground in South Dakota and uses 7 tonnes of liquid Xenon to hunt for signals of WIMPs. The project is being run collaboratively by institutes in the US, Portugal, and South Korea.
Just for the record, like every meaningful scientific concept, there are a minority of astrophysicists who do not accept the need to invoke Dark Matter and Dark Energy to explain the Universe. Their alternative explanations, however, are yet to gain acceptance.
Perhaps the Roman Space Telescope will help arbitrate between these alternatives. Whatever happens, the data collected will greatly expand our understanding of the Universe. As somebody said of the launch – it represented an endpoint for the engineers, but a starting point for scientists.