Now that NASA’s Nancy Grace Roman Space Telescope is on its way toward its Lagrange Point 2 (L2) destination, more of its mission goals are coming into focus, including the possibility that it could detect an Earth-like planet orbiting a star like our own Sun using gravitational microlensing.
The Roman team said such a detection could identify targets for the proposed Habitable Worlds Observatory project, including scanning their atmospheres for signs of extraterrestrial life.
Searching for Another Earth with the Nancy Grace Roman Space Telescope
In NASA’s mission fact sheet, Roman’s planners pose several questions. These include:
- How common are solar systems like our own?
- What kinds of planets exist in the cold, outer regions of planetary systems?
- What determines the habitability of Earth-like worlds?
Although scientists have used several methods to detect exoplanets, including Earth-like planets, Roman will employ three. These include the transit method, microlensing, and direct imaging. NASA said the combination of approaches will allow mission scientists to conduct a “sweeping search expected to uncover around 100,000 new exoplanets — a staggering leap compared to the nearly 6,200 currently known.”
“It is hoped that Roman will discover thousands of new exoplanets and significantly expand our knowledge of the diversity of planetary systems in our Galaxy,” explained Associate Professor Edita Stonkutė, an astrophysicist at Vilnius University unconnected to the Roman team, in a statement emailed to The Debrief.
Microlensing Can Reveal Earthlike Planets Orbiting Sunlike Stars
Most exoplanets have been detected by the dimming of their host star when they transit between it and Earth, giving the transit method its name. Roman plans to use that same method for most of its larger planetary detections. However, among the expected tens of thousands of transit-method detections, mission planners expect a small but sizeable percentage to come from microlensing.
NASA said the “light-bending” microlensing phenomenon occurs when two distant stars “align closely from our vantage point.” Due to the strength of the nearer star’s gravity, the light from the more distant one is “warped” around the nearer one, essentially focusing it very briefly for a distant observer.
“If the alignment is especially close, the nearer star acts like a cosmic lens, focusing and magnifying light from the background star.” Professor Stonkutė explained. “By analysing these changes, astronomers can determine that the planet exists and estimate its mass and orbital characteristics.”
Critically, Professor Stonkutė also noted that microlensing can occur with objects other than stars, including exoplanets.
“This is Precisely Where Roman Has the Edge”
Using its Wide-Field Array, Roman will monitor hundreds of millions of stars. NASA said the observatory will monitor these target stars for “tiny surges in starlight” that typically signal a microlensing event.
Although the transit method is employed to detect larger exoplanets, NASA noted that microlensing “specializes in finding planets like those in our solar system.” The space agency added that this includes “worlds as lightweight as Mars in their star’s habitable zone or farther out.”
A star’s habitable zone is typically defined as the orbital plane where an exoplanet could sustain liquid water on its surface, a key ingredient for life as we know it.
Professor Stonkutė described microlensing as “particularly valuable” since it can detect planets that are difficult to spot with other planet-hunting methods. The professor said this includes “small Earth-like planets located far from their star.” The Roman team hopes to find “more than 1,000 microlensing planets.”
The professor warned that “most microlensing events cannot be predicted in advance.” As a result, telescopes need to actively scan large areas of the sky to increase the chances of a microlensing detection
“This is precisely where Roman has the edge over other telescopes that have searched for exoplanets using different methods,” the professor added.
A “Stepping Stone” Toward NASA’s Habitable Worlds Observatory Concept
While Roman is tasked with directly imaging exoplanets, finding another Earth around a Sun-like star will still require an indirect detection, most likely from a microlensing event. However, the Roman team notes that their observatory “will provide a crucial stepping stone for NASA’s Habitable Worlds Observatory concept.”
According to the space agency, that “flagship” telescope, still awaiting final approval, “would be designed to photograph Earth-like planets for the first time ever.”
Roman may also be able to scan the atmospheres of planets detected with the transit method. The space agency said Roman “would also look for signs of life called biosignatures by measuring atmospheric gases like oxygen and ozone that could signal the presence of living things.”
Christopher Plain is a Science Fiction and Fantasy novelist and has spent the last six years as Associate News Editor and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him at christopher@thedebrief.org.