Since the discovery of the first exoplanet in 1992, astronomers have detected more than 5,000 planets orbiting other stars. But when astronomers detect a new exoplanet, we don’t learn much about it: we know it exists and some characteristics about it, but the rest is a mystery.
To circumvent the physical limitations of telescopes, astrophysicists at Stanford University have been working on a new conceptual imaging technique that would be 1,000 times more accurate than the most powerful imaging technology currently in use. By taking advantage of the warping effect of gravity on spacetime, called lensing, scientists could potentially manipulate this phenomenon to create imagery far more advanced than any present today.
In an article published on May 2 in The Astrophysical Journalresearchers describe a way to manipulate solar energy gravitational lens to see planets outside our solar system. By positioning a telescope, the sun and the exoplanet in a line with the sun in the middle, scientists could use the sun’s gravitational field to amplify the light from the exoplanet as it passes. As opposed to a magnifying glass who has a curved surface which bends the light, a gravitational lens has a curvature space-time which makes it possible to image distant objects.
“We want to take pictures of planets orbiting other stars that are as good as the pictures we can take of planets in our own solar system,” said Bruce Macintosh, professor of physics at the School of Humanities and Sciences. from Stanford and deputy director of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC). “With this technology, we hope to take a picture of a planet 100 light years away that has the same impact as the image of Earth from Apollo 8.”
The catch, at present, is that their proposed technique would require more advanced space travel than is currently available. Still, the promise of this concept and what it might reveal on other planets deserves continued examination and development, the researchers said.
The benefits of light bending
The gravitational lens was observed experimentally only in 1919 during a solar eclipse. With the moon obstructing sunlight, scientists were able to see stars near the sun shifted from their known positions. It was unequivocal proof that gravity could bend light and the first observational proof that Einstein’s theory of relativity was correct. Later, in 1979, Von Eshleman, a Stanford professor, published a detailed account of how astronomers and spacecraft could exploit the Sun’s gravitational lens. (Meanwhile, astronomers, many at Stanford’s KIPAC, now routinely use the powerful gravity of the most massive galaxies to study the early evolution of the universe.)
But it will be necessary to wait until 2020 for the imaging technique to be explored in detail in order to observe the planets. Slava Turyshev of the Jet Propulsion Laboratory at the California Institute of Technology described a technique in which a space telescope could use rockets to scan light rays from a planet to reconstruct a clear image, but the technique would require a lot of fuel and weather.
Building on Turyshev’s work, Alexander Madurowicz, a Ph.D. student at KIPAC, invented a new method that can reconstruct a planet’s surface from a single image taken by looking directly at the sun. By capturing the ring of light around the sun formed by the exoplanet, the algorithm designed by Madurowicz can distort the light from the ring by reversing the curvature of the gravitational lens, which turns the ring into a round planet.
Madurowicz demonstrated his work using images of the rotating Earth taken by the DSCOVR satellite which sits between the Earth and the sun. Then he used a computer model to see what Earth would look like when looking through the sun’s gravity warping effects. By applying his algorithm to the observations, Madurowicz was able to retrieve the images of Earth and prove that his calculations were correct.
In order to capture an image of an exoplanet through the solar gravitational lens, a telescope would need to be placed at least 14 times farther from the sun than Pluto, beyond the edge of our solar system, and further than humans have ever sent a spacecraft. But, the distance is a tiny fraction of light years between the sun and an exoplanet.
“By unfolding light bent by the sun, an image can be created far beyond that of an ordinary telescope,” Madurowicz said. “So the scientific potential is an untapped mystery because it opens up this new capacity for observation that doesn’t yet exist.”
Sites beyond the solar system
Currently, to image a exoplanet at the resolution described by scientists, we would need a telescope 20 times larger than Earth. By using the sun’s gravity as a telescope, scientists can harness it as a massive natural lens. A Hubble-sized telescope in combination with the solar gravitational lens would be enough to image exoplanets with enough power to capture fine surface detail.
“The solar gravitational lens opens up a whole new window of observation,” Madurowicz said. “This will allow studying the detailed dynamics of the planet’s atmospheres, as well as the distribution of clouds and surface features, which we have no means of studying now.”
Madurowicz and Macintosh both say it will be at least 50 years before this technology can be deployed, probably longer. For this to be adopted, we will need faster spacecraft because, with current technology, it could take 100 years to get to the goal. Using solar sails or the sun as a gravitational slingshot, time could be as short as 20 or 40 years. Despite the uncertainty of the timeline, the ability to see whether certain exoplanets have continents or oceans, Macintosh said, motivates them. The presence of either is a strong indicator that there may be life on a distant planet.
“This is one of the last steps in finding out if there is life on other planets,” Macintosh said. “Taking a photo of another planet, you might look at it and maybe see green swatches which are forests and blue specks which are oceans – with that it would be hard to say that it isn’t. has no life.”
Alexander Madurowicz et al, Integral field spectroscopy with the solar gravitational lens, The Astrophysical Journal (2022). DOI: 10.3847/1538-4357/ac5e9d
Quote: Scientists Describe Gravity Telescope That Could Image Exoplanets (2022, May 2) Retrieved May 3, 2022 from https://phys.org/news/2022-05-scientists-gravity-telescope-image-exoplanets.html
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