MYSTERIOUS
PLANET X
I heard that a tenth planet or a star may exist in our outer solar system. Why do astronomers think this and how will they confirm it? Jorge Esparza, Santa Ana, California

Something must be out there, astronomers believe, because the orbits of Neptune and Uranus deviate slightly from what they should be, according to the laws of physics. A mysterious object-aplanet or perhaps a "brown dwarf"-seems to be tugging them off course. Pioneers 10 and 11, American space probes headed beyond the planets, may serve as supersleuths that help identify and locate the source of these gravitational disturbances.
.... The deviation in the orbits of the two gaseous planets is tiny, only a matter of a few seconds of arc (one second of arc is the width of a penny as it would appear to the naked eye from 2.5 miles). But to astronomers this is a significant amount that needs to be explained. Neptune was discovered in 1846 because of it's telltale gravitational pull on Uranus. Now, however, the unexplained deviations of Neptune and Uranus are much smaller than those that tipped off scientists more than a century ago. The new search hasn't been as easy.
.... For a while, Pluto was blamed for the effect. But-with the 1978 discovery of the planet's small moon, Charon, Pluto's mass was found to be far too small for it to be the culprit. (Scientists have no direct way to figure out the mass of a planet that has no moon; the calculation is easy if a moon exists.) Pluto's mass is over 100 times less than was estimated; it's only 0.2 percent that of the Earth. Consequently, astronomers have cast their sights farther out.

Caption: As pioneers 10 and 11 zip out of the solar system, tiny changes in their speeds may reveal just what type of object is now altering the orbits of Neptune and Uranus.

Is it possible to see stars during the day from the bottom of a deep well? To test this bit of folk wisdom, I once tried it with a number of students from Ohio, State University, substituting a tall smokestack (an idle one!) for a deep well. Our cosmic target was the very bright star Vega in the constellation Lyra. This star passes directly overhead at the latitude of Columbus, Ohio, on autumn afternoons.
.... One clear day, we stationed ourselves at the bottom of the smokestack. The sky looked just as blue and bright from within our "well" as it had from the outside. At the precise moment Vega passed through our field of view, we saw nothing.

.... Can the object be a planet? Or is it a brown dwarf-a star that didn't quite make it, a body not massive enough to produce the high internal temperatures necessary to ignite it's nuclear furnace and thus shine like the sun? Or could it be a neutron star-a star that has gravitationally collapsed into a densely packed, dark remnant of it's former luminous self?
.... The two Pioneers, which are leaving the solar system in opposite directions, still transmit radio signals earthward. If they continue to do so for the next several years, astronomer John Anderson of the Jet Propulsion Laboratory will be able to calculate minute changes in their speeds, down to a fraction of an inch per second. Planet X, which would have to be relatively close by-between 4 and 7 billion miles away-would tug evenly on both Pioneers. If the results point to a brown dwarf, it will be the first of these theoretical objects to be identified.
.... A nearby brown dwarf may be located by another means. Although not hot enough to shine, such a dark star radiates in the infrared region of the electromagnetic spectrum. Planetary scientist Ray Reynolds and his colleagues at NASA Ames research Center plan to use the Infrared Astronomy Satellite, scheduled for launch next month, to try to find a brown dwarf in our solar system or even farther out in space.
.... These theories have their critics. Planet X, skeptics say, would have to be as massive as Uranus to alter the paths of it and Neptune. Were that the case, it should long since have been discovered by conventional observations. As for it's being a more distant, more massive body, Thomas Van Flandern of the U.S. Naval Observatory argues that the influence of such an object should have produced disturbances in the orbits of other planets-including the Earth.

Caption: (I'd like to thank Brenda Alexander of Kansas City, Missouri, and Steve MacDougall of Oakville, Ontario, for their questions on this same topic.)

Small binoculars didn't help; even blindfolding students beforehand to increase light sensitivity proved fruitless.
.... Perhaps the myth that stars can be seen from the bottom of wells, which has indeed appeared from time to time in literature, started with the Greek philosopher Thales (c. 636-c. 546 B.C.), who is said to have absentmindedly fallen into a deep well. He probably saw stars of a different order of magnitude.

Caption: J. Allen Hynek, Ph.D., professor emeritus of astronomy at Northwestern University, asks you to address your cosmic queries to the Astronomy Column, Science Digest, 888 Seventh Avenue, New York, New York 10106.

Credit: Diagram by April Leigh Pahl, based on information in Mercury News, San Jose, CA