Top 10 Roman Space Telescope science breakthroughs
Scientific American · LC · trust 35/100
NASA’s Roman Space Telescope will open a whole new window on the cosmos. Here are 10 things it’s likely to show us
A payload fairing containing NASA’s Nancy Grace Roman Space Telescope is towed to a hangar at NASA’s Kennedy Space Center, ahead of its mating to a SpaceX Falcon Heavy rocket, on August 25, 2026.
After more than a decade of development, NASA’s Nancy Grace Roman Space Telescope is at last set to launch this weekend. With its unprecedented field of view—100 times that of the Hubble Space Telescope—Roman is guaranteed to tell astronomers all sorts of new things about our universe, both near and far from home. What will they learn? Here are 10 of the most exciting cosmic lessons we can expect.
Every moment since the big bang, the universe has been getting bigger—something first hinted when astronomer Edwin Hubble found that surrounding galaxies are speeding away from our own. As the space between them stretches, the galaxies grow farther apart, like raisins in a rising loaf of bread. Astronomers can measure the rate of this expansion—which they call the Hubble constant—by looking out at myriad other galaxies and seeing how fast they’re moving away from us. Researchers can also measure the Hubble constant through its subtle imprints on the earliest light in the universe.
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But for decades now, these two measurements have yielded diverging values that have so far proved impossible to reconcile. Assuming it’s not simple mismeasurement, this so-called Hubble tension challenges our basic picture of the universe’s history. Roman will greatly increase the number of galaxies with precisely clocked speeds—which may not break the tension but may at least help clarify its still-murky origins.
In the late 1990s astronomers realized that the universe’s expansion is actually getting faster as time goes on, almost as if each successive stretching of space between galaxies also summons extra energy that makes it stretch further still. Physicists call this unexplained, self-perpetuating cosmic fuel “dark energy,” and it’s quickly taking over the universe: dark energy already outweighs the gravitational influence of all the matter in the cosmos some three times over.
But recent data from projects such as the Dark Energy Survey (DES) and the Dark Energy Spectroscopic Instrument (DESI) suggest that this mysterious energy source is fading away ever so slowly. The revelation of a constant and unchanging dark energy has already shaken the foundations of our cosmic understanding; an even more unexpected discovery that dark energy is evolving over time could shatter them entirely . Roman’s expansive catalog will help confirm—or refute—these tentative results from other surveys.
If you’re a true space nerd, you’ve heard of the Hubble tension. If you’re a nerd who keeps up with the news, you may even know that dark energy might be changing. But unless you’re a card-carrying cosmologist, you probably don’t know about “sigma-eight.”
Never mind the jargon—what “sigma-eight” should mean to you is that cosmic structures don’t seem as “clumpy” as they should be . We have a good sense of how these structures (not just galaxies but clusters of galaxies) formed in the early universe—and how they evolved as the cosmos continued to grow and cool. This is based not just on dark energy but on dark matter, the inferred 85 percent of the universe’s mass that seems to be the invisible glue holding galaxies and galaxy clusters together. But dark matter’s influence, to the best of our understanding, should yield structures that are slightly more diffuse than what we observe. Astronomers hope Roman’s galaxy-rich panoramic view will help resolve this underappreciated cosmological mystery , too.
The advent of exoplanet research has reshaped astronomy, revealing that planets around stars are the norm rather than exceptions. The most successful way that scientists have found and studied these faraway worlds has been to watch a star’s light very closely, looking for periodic dips in its shine caused by a planet passing in front of it and partially obscuring our view.
These “transiting” exoplanets make up the majority in our catalogs, which now include more than 6,300 worlds in total. Astronomers expect to find as many as 100,000 additional transiting exoplanets with Roman when the telescope surveys the Milky Way’s star-packed galactic bulge. That massive boost will allow a deeper statistical understanding of how planetary systems form and evolve—and whether our own is common or rare.
The transit technique mainly reveals large planets that are close enough to their star to block a lot of its light from our view—but these are only a small fraction of what’s probably out there .
Roman’s most impactful exoplanet science may come from an entirely different detection technique called microlensing, which can probe for small planets at wider separations from their stars. This involves looking not for shadowy transits but for transient blips of stellar brightening. When a star drifting through space by chance passes across a much more distant background star, as seen from our solar system, the “foreground” star’s gravity bends and distorts the more distant star’s light. And if the foreground star has planets, they can add their own distortion to the mix. Roman’s sight is so keen that it can discern these tiny signals; its microlensing survey should unveil 1,000 or so exoplanets we never…
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