Tenth planet possible?

Press, 28 July 1987, Page 11

Tenth planet possible?

By

DEAN LOKKEN

NZPA-Reuter Mountain View, California Data from two United States Pioneer spacecraft pointed to the likelihood of an undiscovered tenth planet beyond the orbit of Jupiter, an American scientist said. A National Aeronautics and Space Administration scientist, John Anderson, told a news conference that data from Pioneer 10 and 11 have ruled out other possibilities for what caused irregularities in the orbits of Uranus and Neptune. He said the most likely theory is that a planet, with a mass about' five

times that of Earth, is orbiting the Sun at a right angle to the rest of the known planets. Mr Anderson had no other explanation for the data.

Scientific observations dating back to the 1830 s show Uranus and Neptune were pulled off their predicted courses, possibly as early as the 1700 s. Anderson said, as late as five years ago, that scientists speculated that the celestial tug on the two planets could have been caused by a number of phenomena, including a “brown dwarf” star, a dim companion to the Sun.

However, Mr Anderson said data from Pioneer 10 and 11, launched in 1973 and 1974 and now nearing the outer reaches of the solar system, ruled out the star theory. He said the spacecraft have detected no gravitational force that could have changed the predicted courses of Neptune and Uranus.

The absence of a force supports the belief a planet on a huge, elongated and irregular orbit, probably circling the Sun every 700 to 1000 years, pulled the two planets off course on its last approach, he said.