Two such observations, of the same planet, were made independently, one by David Charbonneau and Tim Brown and another by Greg Henry and colleagues.

The findings were complemented by the use of another method for viewing distant worlds: Earlier this month, British astronomer Andrew Collier Cameron led a team that used reflected starlight to make the first direct measurements of an extrasolar planet's size and mass, as well as a guess at the color (blue-green).

The method, still unconfirmed, would be a first step toward understanding the composition of exoplanets.

Owen thinks Jupiter probably formed earlier and more quickly than current models speculate. If true, the idea could explain why so many extrasolar planets have been found so close to their stars, he says.

Owen's colleagues suggested Jupiter might have wandered in from farther out in the solar system. And other researchers think there might be an unfound planet still lurking in the distant fringes of our solar system. Which brings up a story from 1999 which, while not yet a discovery, could easily be considered among the most intriguing:

In two separate studies that came to light in October, researchers provided more evidence suggesting there really might be a 10th planet, larger than Jupiter, circling our sun far beyond the orbit of Pluto. The possible object could also be a brown dwarf, or failed star, the researchers say, citing the gravitational effects on comets in their work.

"It is important because if it does exist, it's going to change radically our view of the solar system, in that it had previously been though highly unlikely that a large planet could exist at such a great distance beyond Pluto," says British scientist John Murray of the Open University.

"It might also tend to suggest that objects intermediate in size between large planets and small stars might be much more common than was previously thought," he said.

Murray, who led one of the studies, said he hoped the question would be resolved in the next two or three years.

Depending on a particular researcher's point of view, the most important stories of 1999 can vary. Brian Marsden, director of the International Astronomical Union's Minor Planet Center, pointed to a very visible event -- the Leonid meteor storm.

"The most significant solar-system finding in 1999 was the successful prediction, on genuine scientific principles, of a meteor storm," Marsden said.

The prediction was based on modeling of comet Tempel-Tuttle's previous passes through the inner solar system, and the meteor showers that were produced and, in some cases, not produced.

"David Asher and Rob McNaught predicted that an 1899 ejection of material (from the comet) would produce a modest storm three revolutions later," Marsden said. Those revolutions were forecast to produce a meteor storm on Nov. 18, 1999. "And they hit it right, within a matter of minutes."

A sampling of other significant stories in space science from 1999:

-- Evidence continued to build supporting a theory of a wet Mars in ancient times. The Mars Climate Orbiter produced the first global topographical map of the Red Planet earlier in the year, and researchers mining the data presented a study in December supporting the idea of a vast coastline that indicates the long-ago presence of an ocean.

-- Earth's only natural satellite still holds many secrets, one of which was unveiled in June. Researchers announced the Moon has a tail, an enormous cloud of sodium gas that trails the satellite and may help scientists understand the ephemeral lunar atmosphere.

-- In counting newly found moons that seem to have been trapped into orbit by Uranus, scientists reported that the seventh planet from the sun apparently took the lead in the number of known satellites for a planet, with 21.

-- Scientists and skygazers in many parts of the world watched (or unfortunately missed due to cloudy skies) the grand spectacle of a solar eclipse Aug. 11. Meanwhile, the SOHO spacecraft continued to provide insight into our favorite star, including new clues about where and how the solar wind leaks out from the fiery ball.

If you've been following space science all year, you might remember that 1999 began with a bang, when in January scientists imaged for the first time visible light emitted at the same time as a gamma-ray burst, a mysterious explosion in the far reaches of the universe that was said to have the power of nearly ten million billion suns.

Gamma-ray bursts are brief flashes of energy lasting from a few milliseconds to a few hundred seconds. They occur randomly, and their source is still being investigated.

Evidence published in the journal Science in October rekindled an old idea that the powerful bursts may sometimes be related to giant stellar explosions known as supernovae. Combined with other studies, a picture is emerging that links the colossal events to the creation of black holes.

Meanwhile, one of the most powerful tools ever created to study the heavens was launched in July. The Chandra X-ray Observatory began by snapping a stunning image of a supernova. The picture, released in August, marked the beginning of what many scientists expect will be a new era of exploration and discovery into the far corners of the Universe and the many mysterious objects that await explanation.

"Already Chandra is putting forth fabulous new results," said Martin Weisskopf, project scientist for NASA's Chandra X-ray Observatory. "Every time we look at something we see something we've never seen before."

Chandra, its European cousin -- the X-ray Multimirror Mission successfully launched this month, and other space telescopes schedule to go up in 2000, may soon pin down the curious relationship between gamma-ray bursts, supernovae and black holes, researchers say.

So while 1999 was a stellar year for space science, there is no reason to think 2000 will be any slouch. In a story next week, several space scientists themselves will tell about the sure bets for next year, as well as possible surprises.