On the road to discover alien life
“We estimate that there are up to several billion Earth-size planets in the habitable zone of our galaxy alone,” says Nick Siegler, chief technologist for NASA’s Exoplanet Exploration Program at JPL. The habitable zone is the area around a star where temperatures are suitable for liquid water. “We want to probe the atmospheres of these exoplanets to look for oxygen, methane, water vapor and other chemicals that could indicate the presence of life. We won’t see little green men, but rather spectral signatures of these key chemicals. Or what we call biosignatures.”
According to Siegler, NASA decided to focus on the coronagraph trajectory of the HWO concept, building on recent investments in NASA’s Nancy Grace Roman Space Telescope, which will use the advanced coronagraph to image gas giant exoplanets. (Caltech’s IPAC is home to the Romanian Science Support Center.) Today, coronagraphs are used in many other telescopes, including the orbiting James Webb Space Telescope, Hubble, and ground-based observatories.
Mawet developed the corona maps for use with instruments at the W.M. Keck Observatory atop Mount Mauna Kea, a mountain on the Big Island of Hawaii. The most recent version, known as the Vortex Coronagraph, was invented by Mauette and is housed within the Keck Planet Imager and Characterizer (KPIC), an instrument that allows researchers to directly image and study the thermal emissions of young, warm gas giant exoplanets. The coronagraph cancels starlight to the point where the instrument can take pictures of planets about a million times dimmer than their stars. This allows researchers to characterize in detail the atmospheres, orbits and cycles of young gas giant exoplanets, helping answer questions about the formation and evolution of other solar systems.
But direct imaging of Earth’s twin planet – where life as we know it is most likely to thrive – will require a massive improvement of existing technologies. Planets like Earth that orbit Sun-like stars in the habitable zone easily get lost in the glow of their own stars. Our Sun, for example, outshines Earth by 10 billion times. For a coronagraph to be able to achieve this level of starlight suppression, researchers will have to push their techniques to the limits. “As we get closer and closer to this required level of starlight suppression, the challenges become exponentially more difficult,” Mawet says.
Participants at the Caltech workshop discussed coronagraph technology, which involves controlling light waves using an ultra-fine deformable mirror inside the device. While the corona can block much of the star’s light, stray light can still make its way into the final image, appearing as spots. By using thousands of motors that push and pull on the reflective surface of the deformable mirror, researchers can cancel out the remaining blobs of starlight.
The upcoming Nancy Grace Romanian Space Telescope will be the first to use this type of coronagraph, which is referred to as an “active” coronagraph because its mirror will actively distort. After further testing at JPL, the Roman coronagraph will eventually be integrated into the final telescope at NASA’s Goddard Space Flight Center and launched into space no later than 2027. The Roman coronagraph instrument will enable astronomers to image exoplanets possibly up to to a billion times dimmer than the outer planets. their stars. This includes both mature and young gas giants, as well as disks of debris left over from the planet formation process.
Focal plane mask of the Coronagraph instrument on NASA’s Nancy Grace Roman Space Telescope. Each circular section contains multiple “masks” – opaque obstacles carefully designed to block starlight.
Image credit: NASA/JPL-Caltech
“The Romanian Coronagraph is the next step for NASA along the path to finding life beyond our solar system,” said Vanessa Bailey, a Romanian coronagraph instrument technology expert at JPL. “The performance gap between current telescopes and the Observatory of Habitable Worlds is too great to bridge at once. The Romanian Coronagraph is intended as an intermediate stepping stone. Many of the necessary technologies, including coronagraph masks and deformable mirrors, will emerge at levels of performance not yet seen.” It is achieved by outside the laboratory.”
Seeking to directly image Earth’s twin around a sun-like star would mean pushing the technology behind the Roman corona even further. “We need to be able to distort the mirrors to a picometric level of accuracy,” Mawet explains. “We would need to suppress starlight by another factor of about 100 compared to Roman’s chronograph. The workshop helped guide us in knowing where the gaps are in our technology, and where we need to develop further in the next decade.”
Other topics of conversation at the workshop included the best type of primary mirror for use with a coronagraph, mirror coatings, dealing with micrometeor damage to mirrors, deformable mirror techniques, as well as detectors and advanced tools for modeling and integrated design. Engineers also provided an update on the status of the star canopy and its technology readiness.
Meanwhile, as technology advances, other scientists are setting their eyes to the stars in search of Earth-like planets that HWO could image. More than 5,500 exoplanets have been discovered so far, but none of them are truly Earth-like. Planet-hunting instruments, such as the new Keck Planet Finder (KPF) led by the Caltech at Keck Observatory, are becoming better equipped to find planets by looking for the tugs they exert on their stars as they orbit them. Heavier planets exert more gravitational pull, as do planets orbiting closer to their stars. KPF is designed to find Earth-sized planets in the habitable zones of small red stars (the habitable zones for red stars are closer). With further improvements over the next few years, KPF may be able to detect terrestrial twins.
By the time HWO launches in the late 2030s or early 2040s, scientists hope to have a catalog of at least 25 Earth-like planets to explore.
Despite the long road ahead, the scientists at the workshop eagerly discussed these challenges with colleagues who traveled to Pasadena from all over the country. JPL Director Lori Lesin (MS’89, PhD’95) gave an impassioned speech at the start of the meeting. “It’s an exciting and worrying challenge,” she said. “But this is what we all live for. We don’t do it alone. We do it together.”
