This futuristic telescope would use Einsteinian physics to find Earth 2.0
A future telescope design could one day allow scientists to see fine details of the atmospheres of Earth-sized exoplanets, establishing whether or not they are potentially livable worlds. It would accomplish it by utilizing the Sun’s gravity and an Einsteinian physics quirk.
According to new study, the so-called “gravity telescope” would use the Sun to examine very distant worlds, possibly as soon as a few decades from now if funding, technology, and will come together in the correct way.
Co-author and Stanford University exoplanet researcher Bruce Macintosh tells Inverse that his team’s article, published May 2 in The Astrophysical Journal, draws on decades of research by engineers and scientists looking to learn more about the 5,000 known planets outside our solar system.
HOW DOES IT WORK?
The idea of using the Sun as a telescope is also decades old, but publications like this just released one can provide further information on the project, he says.
The gravity telescope uses a well-known astronomy technique known as gravitational lensing. When a big object in the foreground of view (such as a galaxy) bends the light of a distant object in the background, the effect occurs (like a planet). At the very least, Einstein correctly predicted this effect at least as far back as 1936
The study imagines a Hubble-class telescope being used at a long distance (550 astronomical units, or Sun-Earth distances). In astronomical standards, that is relatively close yet still daunting. “It’s about two times further away than Pluto, or about seven or eight times further away than the Voyager spacecraft,” Macintosh says.
The focal zone of the Sun’s gravitational lens is 550 AU, allowing the source requiring magnification (the exoplanet) and the Sun’s lens to align, allowing the telescope to observe distant objects behind, refracted by the Sun’s gravity.
DIGGING INTO THE DETAILS
Macintosh emphasized that his team is not engineers, but the telescope would almost certainly need a sunshield (a coronagraph) to protect it from stray light and to block out the Sun’s light. Coronagraphs have been thoroughly tested in space, and various instruments aboard the James Webb Space Telescope use them.
Individual star or planet gravitational lensing events are frequently unintentional. Typically, astronomers are unaware that the background objects exist until they appear in an archival photograph from a telescope that happened to be looking in that part of the sky. However, NASA’s James Webb Space Telescope intends to use the approach on a recently discovered old star that will be traveling behind foreground members of a star cluster.
In theory, utilizing the Sun as a gravitational lens would be considerably simpler. After all, it is closer to us, and the gravitational lensing effect would be much stronger as a result. In addition, the Sun would be utilized to study previously identified planets, making the investigation process more efficient. However, there are significant technological problems that astronomers and engineers must address before this vision can become a reality, according to Macintosh.
“Part of the point of this paper was to look really carefully at the math and physics, and try to understand how well it would work to have a picture you could make [of a planet], and how you would go about making that picture,” Macintosh, who is also deputy director of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), says.
In principle, the futuristic telescope might examine the spectrum of a distant rocky planet’s atmosphere to look at chlorophyll signals, the “shiny and reflective” signal of water, or the chemical compositions of clouds, he noted.
In comparison, the freshly launched NASA James Webb Space Telescope will examine at gas giant atmospheres in less detail. According to Macintosh, astronomers will task observatories to seek for the signal of oxygen in rocky world atmospheres in 20 years.
According to him, the gravity telescope would be the next natural step and a significant milestone. “I think there’s also something just compelling about making that first picture of a life-bearing world,” he said.
He said, “It’s like Galileo looking through the telescope for the first time.” referring to his pioneering 1600s telescopic investigations of the moon, Saturn’s rings, and Jupiter with one of the first telescopes.
“One of the things about the Sun, as a lens, is that it’s actually not a very good lens,” Macintosh joked. “If somebody tried to sell you that lens, we would send it back to the shop.”
One major impediment is the Sun’s sheer brightness, which, if not regulated properly, might quickly wash out the subtle light of an exoplanet. As noted in a 2021 study in Physical Review D, the lensing may also be prone to spherical aberrations and astigmatism.
However, solar lensing feasibility studies have been continuing for decades, including a key 1979 effort by Stanford professor Von Russel Eshleman, now a professor emeritus of electrical engineering. Eshelman pondered how astronomers and spacecraft could use the lens, and his publication aided in the direction of the most recent investigation.
The successful Voyager spacecraft give an interesting case study for how technology could need to adapt to make this prospective telescope more efficient. Their radio signals take nearly a day to reach Earth, about 21.5 hours for Voyager 1 and about 18 hours for Voyager 2. It also takes that long for a NASA transmission to reach the distant spacecraft via Earth’s Deep Space Network of radio dishes.
It was the best we could do with 1970s technology, but Macintosh said the new telescope would ideally leverage artificial intelligence and advances in data compression technology to speed communications back and forth, possibly using lasers, based on numerous recent NASA feasibility studies with spacecraft. (While lasers, like radio waves, are limited by the speed of light, this would increase the data transfer rate.)
“The telescope would have to be pretty autonomous, both to plan the observations and track the planet,” he said. “It would also have to make intelligent decisions about what data to send back, and how to compress it.”
Of course, all of this assumes that the telescope can reach this region in the first place. Given that the Voyagers were launched 45 years ago and only recently entered interstellar space, the new study advocates for additional advancement in rocket technology to get the Hubble-sized exoplanet lensing telescope out there sooner.
However, once in place, the telescope, according to lead author Alexander Madurowicz, a Ph.D. student at KIPAC, will represent a “remarkable” milestone in astronomical imaging.
“Recently, the Event Horizon Telescope (EHT) collaboration released their famous image of the supermassive black hole at the center of the galaxy M87,” he said in a blog post. “Using a vast interferometric array of radio dishes spread over the surface of Earth and combining all of the measurements to act like a single Earth-sized telescope, they were able to produce the highest angular resolution image of all time.”
He claims that the solar gravitational lens will provide images with an angular resolution of 25 nanoarcseconds, which is far finer than the EHT’s resolution of 25 microarcseconds. In other words, the solar lens would be a significant step forward in imaging detail.
Madurowicz also paved the way for future engineers to face some of the world’s most difficult tasks. “First, a target planet must be recognized and precisely located in the sky,” he says. “First, a target planet must be identified and located in the sky with sufficient precision,” he says. “Then, the telescope must navigate to align the orbits of the craft, Sun, and target planet.”
“Lastly, optical instrumentation strategies which can remove contaminating light from the Sun, corona, host star, and background objects must be deployed to improve the signal to noise ratio,” he adds.