Looking Up: Searching for other worlds

Peter Becker

So are we alone in this big universe? While probably not on most people’s minds, given the more urgent matters of daily life on planet Earth, a sector of humanity has been on a quest to know if other worlds out there may be inhabited. This is by far not a new idea. At least some astronomers in the 19th century were convinced that there are, or should be, other inhabited planets.

Reading or listening to reports dealing with America’s space program, it appears finding inhabited worlds is an important motivation for all the funding and effort to reach out to the cosmos, and no less so than in the late 19th century when the theory that Martians were building planet-wide irrigation canals was taken seriously.

Indeed, the ancient Greeks discussed the possibility of other inhabited worlds. The notion gained in acceptance in the 16th century once scientists determined that Earth was not the center of the universe but went around the sun with the other planets.

NASA’s Jet Propulsion Laboratory has a Web site ( detailing the expanding hunt for planets beyond our solar system. Abodes of life or lifeless, it is fascinating to find that the Milky Way Galaxy, and surely every galaxy, is teeming with planets orbiting their stars. This can be fascinating enough, but the added interest of seeking another Earth-like world is right up front. The homepage states boldly, “Searching for Earthlike Worlds” followed by a question, “Are we alone?”

Until 1995, we only assumed there were other solar systems. Since the first discovery of an extrasolar planet orbiting the star 51 Pegasi 12 years ago, astronomers have identified more than 300 far-off planets. Current technology does not allow us to take direct photographs of them, let alone peer through a telescope eyepiece and see them. Planets are simply too small and these so far away to send back enough reflected starlight; more importantly, at their vast distance, the planets are lost in the glare of their parent star.

Astronomers are using three indirect techniques to uncover signs of these worlds.

- Doppler shift: Planets orbiting a star produce a gravitational tug that causes the star to slightly wobble. This can be detected in examination of the star’s spectrum, or rainbow colors. A star’s spectrum is marked by numerous thin, black lines. Stars are hot balls of gas, and the elements making up that gas, such as hydrogen or oxygen, absorb a specific frequency of the starlight and it shows up as a black line in a specific part of the colorful spectrum. This way we can tell what the stars are made of. These lines also reveal that the star is being tugged. As the star pulls away from us, the black lines are shifted towards the red; as the planets orbit around and the star comes back our way, the lines shift to the blue. In the same way, the frequency of sound shifts -- changes in pitch -- as a car zooms by, hopefully followed by a noisy police siren.

- Transits: On rare occasions, we may find a solar system angled so that the planets cross the face of the star from our line of sight. The dark planet transiting the star causes measurable dips in the brightness of the star.

- Micro-lensing: Einstein’s theory of relativity predicted that light would be affected by gravity. Astronomers have been able to see far-off galaxies they would not have been able to detect otherwise because of this. By chance, a closer galaxy is positioned right in front of one much farther away. The distant galaxy’s light is bent around the closer one and amplified, showing up as ghostly arcs around the closer galaxy. Similarly, a planet in front of its star adds to the effect, and allows more distant starlight to come into view.

Most of the planets that have been found to date are very large, in the order of Jupiter or bigger. This is not unexpected, since the larger ones would be the easier to detect. Astronomers are hopeful of detecting smaller, Earth-size worlds with the proposed “Terrestrial Planet Finder,” an array of five spacecraft telescopes. These will be put far apart and aimed at the same star at a time; working together, they will act like one mammoth telescope.

You can see other worlds tonight. Full moon is Oct. 14, and last-quarter moon is on the 21st. Enjoy the sky the next clear night. Be sure to see Venus low in the west after sunset, and the bright Jupiter low in the south-southwest. Early risers may see bright Saturn in the east before sunrise (don’t confuse it with the bright star Regulus, which is higher).

Keep looking up!

Peter W. Becker is managing editor at The Wayne Independent in Honesdale, Pa. He has been an amateur astronomer since the age of 12, in 1969. He may be reached at