These are the top 10 cosmic discoveries we expect from NASA’s Roman Space Telescope

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.

1. Cutting the cosmic tension

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.

2. Is dark energy changing?

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.

3. How clumpy is the universe?

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.

4. Exploding the exoplanet catalog

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.

5. Strange new worlds

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 would have otherwise seen—and, separately, the telescope will take snapshots of some exoplanets, too.

6. What wanders the Milky Way?

Roman microlensing surveys will find more than exoplanets, too. If a small black hole, a neutron star or even a rogue planet cruising through the void passes in front of a background star, the result will be another diagnostic blip of light. These microlensing events are exceedingly rare—but because Roman will be monitoring such giant swaths of sky, some are bound to trickle into its detectors. Finding just how many do so will help theorists estimate the total number of wandering nomads in our galaxy.

7. Astronomy in harmony

One of the most exciting astrophysical moments in scientific history happened on August 17, 2017. First, gravitational-wave detectors captured a faint wobbling of spacetime emanating from the general direction of the constellation of Hydra, indicating that a cataclysmic merger involving black holes or neutron stars was underway. Seconds later, two space telescopes picked up a burst of gamma rays from the same region of the sky, pinpointing the source to a galaxy some 140 million light-years from Earth. Additional ground- and space-based observatories rapidly piled on and spent the following days charting the afterglow of this cataclysm, which proved to be a “kilonova” produced by two colliding neutron stars.

Even today, nearly a decade later, this remains the pinnacle event for “multimessenger astronomy,” a powerful interdisciplinary approach in which traditional telescopes join forces with gravitational-wave and neutrino detectors to study cosmic happenings from every angle. But Roman’s expansive eye offers one of the best chances astronomers have for finding more, pinpointing afterglows to rapidly guide follow-up observations from other facilities.

8. Does dark matter come in clumps?

The stars in the Milky Way are moving too fast, sped up by the extra gravity of invisible dark matter suffusing the galaxy. But when it comes to the question of whether that cloud of dark matter has significant clumps, we’re not sure. Finding out would tell us a lot about how this mysterious substance works. Roman will make the best-yet dark matter map of our own galactic backyard, tracking streams of stars at the Milky Way’s periphery to check if any unseen clumps nudge them slightly off course.

9. Scanning for starquakes

Like the Earth, the sun sometimes rumbles and quakes, revealing hidden internal features. But scientists don’t have any seismic sensors beneath our star’s boiling plasma surface, so they know little about how those oscillations arise. Plus, the sun is the only star we can watch so closely and seems to be relatively quiet compared with ones we more crudely monitor from afar. Roman will be a boon to “asteroseismology”—by collecting sharper images of so many stars, it will give scientists a much better broader view of how “starquakes” happen throughout the Milky Way.

10. We’ll find out!

According to Julie McEnery, Roman’s senior project scientist, the most exciting science to come out of the telescope will probably be something no one’s even thought of. “History tells us that within any new telescope, the most exciting things are the surprises—the things that you didn’t know to look for,” she says. “And that will be true with Roman.”

The telescope’s data deluge, she says, guarantees that the coming years will be packed with discoveries of which we now can scarcely dream. “We don’t know all the things we’re going to find,” McEnery says.