Much of science is about incremental findings, where knowledge builds on what's already known. But as discoveries go, it's the ones you don't expect that are the most fun.

New objects, new phenomena, new puzzles.

With the blistering pace of significant findings in 1999, one can be led to feel that it's all been discovered. But if you've ever felt even a twinge of that sentiment, hold onto your star charts and get ready for the year 2000.

Historians may one day call it the space renaissance that developed at the turn of the millennium.

Space.com has learned that several important discoveries -- of the variety that weren't entirely expected when the observations were made -- will be presented in January at the annual meeting of the American Astronomical Society in Atlanta.

Curious about what seems like an increasing pace of discovery, we asked an international mix of leading space scientists, many of whom were involved in important discoveries during 1999, what they think are the most significant questions that might be answered in the next year or the next decade.

"In the next year, there may be many new systems discovered."

Among the recurring responses are questions that humans have been pondering nearly as long as science has been around:

Are there other Earth-like planets out there?

What is the fate of the Universe?

Is there life elsewhere?

It was therefore remarkable to hear that the answers to these questions may well be within humanity's grasp during the first decade of the new millennium.

And despite focusing on their various fields, the researchers we questioned share a common vision: The year 2000 should be an extremely satisfying one for scientists and space enthusiasts alike.

During 1999, researchers confirmed that planets exist around other stars. After some 30 planets had been found over four years using an indirect method of observations (looking for wobbles in stars produced by the gravitational effect of supposed planets) two separate groups watched a planet transit in front of a distant star.

The planet was detected by measuring a slight drop -- roughly 1.5 percent -- in starlight.

The distant worlds found so far have mostly been very large planets, bigger than Jupiter, orbiting inexplicably close to their host stars. While this needs to be explained, a bigger question looms:

"The next big step is to find systems with 'Jupiters' that are at our own Jupiter's distance from their stars, thereby leaving room for terrestrial-size planets closer to the star," said Tobias Owen of the University of Hawaii's Institute for Astronomy.

"This might happen next year. After that, we need to find those Earth-like planets. This will be technologically feasible within the next 3 to 5 years."

Such a search would need to be conducted from space, said David Charbonneau of the Harvard-Smithsonian Center for Astrophysics, who led one of the groups that confirmed the existence of extrasolar planets.

"But the concept is exactly the same," he said. "Because the planet is smaller and farther out, the signal is fainter and rarer in occurrence."

Charbonneau said a number of large surveys on some of the world's largest telescopes have only just begun to return evidence of more extrasolar planets.

"In the next year, there may be many new systems discovered," he said.

Imagine how disconcerting it would feel if you did not understand the house you live in. You don't know when or how your house was built, how long it will last, and you can't even find 90 percent of the stuff that's mysteriously hidden away in the corners.

Such is the problem cosmologists face when contemplating the origin, structure and fate of the ultimate house we all live in.

Cosmologists aren't yet sure when the Universe began.

Most estimates of the Big Bang vary from 12 to 15 billion years ago, and some are outside that range. Supposedly firm numbers offered up during 1999 were not widely agreed upon.

Another tough one is whether the Universe will expand forever or slow down, reverse course and fall back on itself in a Big Crunch. And then there's that troubling problem of dark matter.

"The problem here is that astronomers seem to find that we live in a Universe in which most of the mass is invisible!" said Amina Helmi of the Leiden Observatory in The Netherlands.

"We simply know it is there because of its gravitational effects in galaxies and galaxy clusters, but we can't see it directly, because it emits no light. This is why we call it 'dark-matter,'" she said.

Helmi and other experts expect the year 2000 and the entire first decade of the new millennium to be a watershed period for our understanding of these and other major questions about the cosmos.

"In the coming 5 to 10 years, we will probably know how much mass there is in the Universe," said Helmi, who during 1999 lead a team that discovered streams of stars in the Milky Way Galaxy, helping prove that a lot of the stars in our galaxy were absorbed during collisions with other, probably smaller, galaxies.

"There are various fronts where significant progress will be made in the next couple of years," Helmi added, including an understanding of how fast the Universe is expanding and whether or not it will expand forever.

Much of our understanding of these concepts relies on grasping how the pieces and parts all work.

And one of the most elusive pieces is the black hole. While widely accepted as being a real phenomenon, possibly existing at the center of many or maybe even all galaxies, black holes are still no more than theory.

But knowledge of black holes is growing. In August, researchers at NASA's Goddard Space Flight Center said for the first time they had detected matter swirling into a black hole.

While the objects may not be seen anytime soon -- they are so dense that they suck matter and even light into their small spheres -- there is hope that scientists may soon spot the shadow of a black hole. An international group of researchers announced this month a computer model showing what the shadow would look like, then challenged scientists to go and find it.

The technique would use advance short-wave radio observation techniques to measure radiation from the mysterious fringes of the black hole -- an area known as the event horizon -- believed to be at the center of our galaxy.

Michael Garcia, of the Harvard/Smithsonian Center for Astrophysics, said the approach is "entirely plausible" and that the technology could be available within the decade.

"The picture itself would be great, and would likely become one of the most popular astronomy pictures around!" said Garcia, who was not involved in the research.

"Scientifically, it could give a direct and independent measure of the mass of the black hole, and provide some direct proof for the existence of the event horizon. This 'proof' is very had to come by, so this would be a very important measurement."

Before there is a black hole, there is thought to be a supernova -- an exploding star that momentarily shines as bright as the whole Universe before it's spent core collapses.

Research released in October suggested that these supernova might be linked to gamma-ray bursts, which can be thousands of times brighter.

When researchers gain a better grasp these phenomena and how they are related, we're likely to know a whole lot more about how the Universe formed, what went on in the earlier days of our own galaxy, and possibly even why the dust that long ago spun around the Sun decided to gather itself into planets.

The primary tool looking into all this is likely to be the Chandra X-ray Observatory, the much heralded new space telescope launched in July.

Martin Weisskopf, project scientist for Chandra, sees a renaissance in space science, both in terms of discovery and in renewed public interest.

The renaissance is fueled in part, he says, by imagery returned by Chandra and Hubble. Japan and the European Space Agency will each launch complimentary observatories during 2000.

Together, all these powerful new eyes in the sky will answer questions that Weisskopf says we haven't even asked yet.

Some of those answers -- observations that surprised the observers -- have already been provided by Chandra, but won't be made public until next year.

"The answers will be there in profusion in January," Weisskopf said in a telephone interview. "And they are either going to change people's view of phenomena that they haven't understood or they will introduce new thinking."

Weisskopf said that in the next year we can expect Chandra to improve understanding of how much mass there is in the Universe, how black holes release their energy, and where X-ray energy goes when galaxies cool.

We asked Weisskopf why it's important to understand all these distant, fuzzy topics. First, he said, is the obvious and straightforward desire to understand the physics of how things work.

Also, by improving our ability to observe distant phenomena, we inevitably create tools and techniques that have practical applications back here on Earth, he said. But his last answer is the most intriguing:

"All these questions bear on formation and evolution of the Universe," Weisskopf said. "This is interesting as a scientific pursuit, and it seems to touch something in our souls. We do have a fascination with our place in the Universe and the Universe itself. That's a good reason --- to satisfy that itch."

The search for life could be considered the ultimate goal for many other avenues of research. We explore the surfaces, interiors and atmospheres of other planets and moons to gain an understanding of the processes that created them and which continue to control their composition and evolution.

All of this bears on the ability to sustain life. We search for planets around other stars in large part because we hope (or fear) there may be life there.

But if the search for life outside our solar system ever comes up with anything, it may well not happen within the next decade, experts say.

Then again, the ongoing search for radio waves, conducted by millions of PC owners through the SETI project, is likely the great unknown in this equation. A signal from ET could pop up today, tomorrow, or never.

But SETI searches for intelligent life, and many scientists would be ecstatic to find life in any form. So closer to home, the race is on to find a microbial version of ET. Among the most likely candidates are Mars and two ice-covered moons of Jupiter -- Europa and Callisto.

Currently planned missions to Mars (NASA plans to launch a new mission roughly every two years) might answer the question within the decade. To explore the subsurface of Jupiter's moons, as-yet unfunded missions will have to move from the drawing boards to the launch pad.

But as life on Earth is found to live in more extreme places, many researchers say that if there's water, and any form of energy at all, there may be life.

The recent discovery of microbes living in the ice above a lake buried deep in the Antarctic further increases the chances that something could be swimming in the liquid oceans suspected to exist below the frozen crusts of Europa and Callisto.

"With each discovery of life in another extreme Earth environment we learn that much more about microbial adaptation, and survival and physiological strategies for life," said David Karl of the University of Hawaii.

"I was involved in the discovery and exploration of deep sea hydrothermal vents two decades ago and edited a book on microbial life in that extreme environment," he said.

"Now we find microbes buried deep beneath the most extensive ice cover, perhaps the opposite end of the spectrum. As we learn more about adaptation we will improve our predictability of life elsewhere."

Finding any form of life on Mars, Europa or Callisto would be stunning. It would mean that life has cropped up on two of only a few celestial bodies that we've been able to explore, raising the possibility that life throughout the Universe is a very common thing indeed.

Still, it's another habitable world, around another star, that fuels our grandest imaginations.

Charbonneau, the extrasolar planet hunter from the Harvard-Smithsonian Center for Astrophysics, says that during the next year scientists will begin to understand the atmospheres of extrasolar planets by analyzing how a star's light spectra changes as it passes through a distant planet's atmosphere.

This is the next important step, he says, toward figuring out if there might be habitable planets out there. Illustrating how much all space science research is tied together, Charbonneau said "the search for life involves the understanding of planets and the stars."