This idea would turn the Earth into a giant space telescope | Science News for Students

This idea would turn the Earth into a giant space telescope

The ‘terrascope’ would use a detector on a satellite to collect light bent by Earth’s atmosphere
Aug 27, 2019 — 6:45 am EST
an illustration of how a terrascope would be created

The bending of starlight caused by Earth’s atmosphere could be used to create a giant telescope, one scientist suggests. It would require placing a detector out in space (illustrated).

James Tuttle Keane

Telescopes keep getting bigger — and more expensive. Researchers with the European Southern Observatory are building one telescope in Chile, for instance, called the Extremely Large Telescope. It will cost more than $1 billion. But one astronomer thinks there might be a better way. He suggests turning our entire planet into a telescope lens. It would rely on Earth’s atmosphere to bend and focus light.

When it hits Earth’s atmosphere, starlight will bend, or refract. That bending concentrates the rays. It focuses them in a region of space on the opposite side of the planet. Put a spacecraft in the right place and it could catch the focused rays, says David Kipping. He’s an astronomer at Columbia University in New York City. A good place to put the spacecraft is about 1.5 million kilometers (900,000 miles) from Earth, he estimates. He describes such a system as a “terrascope.”

Instruments aboard the spacecraft might be able to collect more light from dim objects than is possible with current telescopes on Earth. That means the terrascope might be able to make ultrasensitive measurements. Such measurements might reveal, for instance, new features of exoplanets, he says. These features might be something like mountain ranges or clouds.

Kipping has outlined the idea in a paper accepted in Publications of the Astronomical Society of the Pacific. But some scientists question the idea's merits.

Slava Turyshev is an astrophysicist. He works at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. The new concept is not feasible for a variety of reasons, he suspects. For instance, it would be difficult to block out unwanted light from Earth. That light would make it hard to see the stars. Another problem: The images could be blurry. That’s because light would be bent by a different amount depending on how high in the atmosphere it travels.

Other researchers are a bit more optimistic. “There’s clearly a lot of work to do before we’ll know if it will work,” says Martin Elvis. He’s an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. “Even if this neat idea doesn’t pan out, this is the kind of creative thinking that will get astronomy out of the linear thinking trap of wanting a bigger version of what we already have.”

Power Words

(more about Power Words)

astronomy     The area of science that deals with celestial objects, space and the physical universe. People who work in this field are called astronomers.

astrophysics     An area of astronomy that deals with understanding the physical nature of stars and other objects in space. People who work in this field are known as astrophysicists.

atmosphere     The envelope of gases surrounding Earth or another planet.

exoplanet     Short for extrasolar planet, it’s a planet that orbits a star outside our solar system.

focus     The point at which rays (of light or heat for example) converge sometimes with the aid of a lens. (In vision, verb, "to focus") The action a person's eyes take to adapt to light and distance, enabling them to see objects clearly.

lens     (in optics) A curved piece of transparent material (such as glass) that bends incoming light in such a way as to focus it at a particular point in space. Or something, such as gravity, that can mimic some of the light bending attributes of a physical lens. 

NASA     Short for the National Aeronautics and Space Administration. Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It also has sent research craft to study planets and other celestial objects in our solar system.

observatory     (in astronomy) The building or structure (such as a satellite) that houses one or more telescopes.

planet     A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood. 

propulsion     The act or process of driving something forward, using a force. For instance, jet engines are one source of propulsion used for keeping airplanes aloft.

range     The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists. (in math or for measurements) The extent to which variation in values is possible. Also, the distance within which something can be reached or perceived.

refract     (n. refraction) To change the direction of light (or any other wave) as it passes through some material. For example, the path of light leaving water and entering air will bend, making partially submerged objects to appear to bend at the water’s surface.

star     The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.

telescope     Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.


Journal:​ ​​ D. Kipping. The ‘terrascope’: On the possibility of using the Earth as an atmospheric lens. Publications of the Astronomical Society of the Pacific, in press, 2019.