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At a glance

Why do we need the Roman Space Telescope?

Thirty years ago, we couldn't even say for certain that exoplanets—planets around other stars—existed. Now, we know of more than 4,000, thanks in large part to NASA’s Kepler Space Telescope, which taught us that most stars in our galaxy have their own solar systems. Kepler found mostly large planets around dim stars. TESS, NASA’s Transiting Exoplanet Survey Satellite, is building on Kepler's survey work by hunting for smaller planets around brighter stars.

Now it's time to complete the initial galactic exoplanet census by searching for even smaller, Earth-sized, rocky worlds. NASA's tool to accomplish that is the Roman Space Telescope, which will help us learn how unique our own solar system is, and bring us closer to finding an Earth-like planet that could support life as we know it.

What's in a name?

The Roman Space Telescope is named after Nancy Grace Roman, NASA's first chief astronomer. Roman, who died in 2018, set up a committee of astronomers and engineers in the 1960s to envision how in-space telescopes could revolutionize scientific research. Those efforts eventually led to the Hubble Space Telescope. 

The Roman Space Telescope will launch in the mid-2020s on a 5-year mission to survey 100 million stars and find 2,500 new exoplanets. Many will be rocky, Earth-size worlds. The Roman Space Telescope will also use a light-blocking disc called a coronagraph to directly image select planets, uncovering these worlds’ compositions for the very first time. Only a handful of exoplanets have been imaged to date.

More than just exoplanets

The Roman Space Telescope is also an astrophysics mission that will help scientists search for dark energy, a mysterious force that may be causing the universe to expand at an accelerating rate. The Roman Space Telescope will study dark energy by mapping the distribution of matter in the cosmos and measuring how the universe has expanded over time.

How the Roman Space Telescope will search for exoplanets

The Roman Space Telescope's camera is just as sensitive as the Hubble Space Telescope's, but with a field of view 100 times bigger. That means no matter what the Roman Space Telescope is looking at, it will be able to collect a lot more data at one time.

Roman Space Telescope field of view versus Hubble

NASA/Goddard

Roman Space Telescope field of view versus Hubble
The Roman Space Telescope's camera is just as sensitive as the Hubble Space Telescope's, but with a field of view 100 times bigger.

The Roman Space Telescope will search for exoplanets using an extraordinary technique called microlensing. You can think of microlensing as Einstein's magnifying glass: Planets, stars, and galaxies have such immense gravity fields, they can actually bend and magnify the light from other objects behind them, producing dramatic halos in space. 

When one star crosses in front of another as seen from Earth, the light from the background star is bent and magnified around the foreground star. If that foreground star has planets around it, they will bend and magnify the background starlight further, producing spikes in the amount of light we see from Earth. Scientists will examine survey images from the Roman Space Telescope to look for these microlensing events, allowing them to detect even small, rocky exoplanets.

How We Detect Exoplanets: The Microlensing Method

The Planetary Society

How We Detect Exoplanets: The Microlensing Method
Star gravity makes space bend near it. When a star passes in front of another star, it bends the distant starlight like a lens, making it brighter. If the lensing star has an exoplanet, it acts like another lens, making the star even brighter.
Microlensing Exoplanet Detection Illustration

ESO

Microlensing Exoplanet Detection Illustration
Star gravity makes space bend near it. When a star passes in front of another star, it bends the distant starlight like a lens, making it brighter. If the lensing star has an exoplanet, it acts like another lens, making the star even brighter.

The Roman Space Telescope will also examine certain individual stars using a light-blocking disc called a coronagraph. Because exoplanets are millions of times dimmer than their host stars, trying to image them directly is like taking a picture of a firefly next to a spotlight. A coronagraph blocks the host star's light, allowing us to see exoplanets directly. This seven-year timelapse of exoplanets orbiting a star called HR 8799 was made possible by a coronagraph:

The Roman Space Telescope will be able to detect some of the light wavelengths coming from the exoplanets it directly images. This will tell scientists more about the composition of the exoplanets' atmospheres. It will work best on Jupiter-size planets, meaning we probably won't be able to peer into the atmospheres of Earth-sized exoplanets. However, the Roman Space Telescope coronagraph is specifically meant to test coronagraph technology for future missions. Scientists have proposed using giant star shades to block the light from stars so perfectly that we can directly image Earth-size planets to look for signs of life.

What you can do to support the Roman Space Telescope

Despite being the astrophysics community's highest-priority mission this decade, the Trump administration has tried 3 times to cancel the mission, citing a lack of funding. Fortunately, Congress rejected those proposals the past 2 years, though it must do so again for 2021. The Planetary Society has submitted a statement urging Congress in January 2020 to continue funding the mission.

Three ways you can be a space advocate

You can also support The Planetary Society’s exoplanets research. To find more Earth-like exoplanets, we need new, revolutionary technologies. Since 2009, Planetary Society members have supported work by Debra Fischer, one of the world's top exoplanet researchers. These projects have greatly improved our ability to search for Earth-like exoplanets. Right now you can help Fischer search for 100 Earth-like exoplanets by funding equipment that sounds straight out of science fiction!

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