It might seem as if astronomers and astrophysicists have had enormous success at unlocking the mysteries of space.
Impressive evidence has been gathered to support the theory that our universe was created about 13.7 billion years ago with an explosion of energy that eventually formed the innumerable galaxies still spinning away from one another to uncharted expanses of space.
We've discovered distant planets that might be friendly to life as we know it and have estimated distances to remote pulsing stars to help map the universe. We've assessed the power of black holes and remain awestruck by the extraordinary beauty of images of distant galaxies, young and old, captured by the Hubble Space Telescope.
But central mysteries of the universe remain unsolved, and from a scientific viewpoint, there are still more questions than answers. Most scientists would agree that we know very little about what really makes up our universe - and little about its origin and possible fate.
Once we thought the universe was filled with shining stars, dust, planets and galaxies. We now know that about 20 percent to 25 percent of the universe is made up of dark matter, a force that keeps stars speeding around galaxies, emits no light and bends space and time.
And dark matter is only part of the story. Scientists have recently discovered a more abundant and mysterious substance called dark energy that makes up 70 percent to 75 percent of the universe.
Dark energy's existence and the mysteries that surround it have prompted astronomers and physicists to fundamentally re-examine their theories.
Scientists generally agree that dark energy is accelerating the expansion of the universe but are sharply divided over other implications.
Some theorize that it signals the existence of parallel universes that may someday collide. Others say that, depending on what dark energy turns out to be, our visible universe might gradually disappear, or tear itself apart in a Big Rip, or collapse in a Big Crunch down to a universe the size of nothing, ready to be reincarnated in another Big Bang.
Now, researchers in Maryland and elsewhere are preparing proposals for a new space telescope aimed at exploring dark energy's secrets.
"It addresses arguably the biggest problem physics is facing right now," said Mario Livio, a senior astrophysicist at the Space Telescope Science Institute in Baltimore. "Dark energy makes up 74 percent of the universe, it's the dominant type of energy in the universe, and we haven't a clue of what it is."
Plans for a dark energy space telescope won major support this fall when a National Research Council panel recommended that NASA and the Department of Energy make it a top priority. Government scientists plan to formally call for proposals next year to build and operate a $600 million to $700 million dark energy telescope.
The Maryland team of astrophysicists that hopes to capture a NASA dark telescope contract includes astrophysicists from the Johns Hopkins University, Baltimore's Space Telescope Science Institute, the Goddard Space Flight Center and other institutions. The group is led by Charles Bennett, a professor of astrophysics at Hopkins.
For Maryland, winning the contract would mean added prestige for a scientific community that already employs hundreds of people who help operate the Hubble Space Telescope and are planning for launch of the James Webb Space Telescope.
Bennett is unsure how many scientists and researchers would be hired if they secure the contract. But it would guarantee some work not only leading up to the launch, tentatively slated for sometime around 2015, but for years of operations.
The Maryland group has avid competitors.
"It's always frustrating if you're the scientist planning these projects because we're always raring to go," said Saul Perlmutter, a researcher at the Lawrence Berkeley National Lab in California who is credited with co-discovering dark energy and is heading a team competing with Bennett's group.
NASA awarded the teams headed by Bennett and Perlmutter, along with a group from the National Optical Astronomy Observatory in Arizona, between $1.5 million and $2 million each last year to develop preliminary mission designs.
Six teams competed for the awards, but any number could submit proposals when a mission design contract is formally announced by NASA and the Department of Energy, said Jon Morse, NASA's director of astrophysics. NASA is expected to solicit design contract proposals by September 2008, he said.
Bennett and the dozen scientists on his team have spent much of the past two years drawing up preliminary plans. Being beaten by a competitor would be a blow.
"I don't know about devastating, but it would definitely be more fun to win than to lose," Bennett said.
Bennett feels he might have an edge. His group includes several members from a team he formed to design the $150 million Wilkinson Microwave Anisotropy Probe, launched in 2001, that used sound waves to confirm the existence of dark energy and nailed down the age of the universe at 13.7 billion years. That experience should help, he said.
"I held the cost, and I held the schedule, and at NASA, that means something," he said.
He knows his team faces talented competitors but says its design will use state-of-the-art science. Plans call for an infrared telescope that would identify the position of 100 million galaxies, in part by reading sound waves that played a major role in determining where they formed.
"This stuff is all pretty new, by science standards," he said.
Dark energy itself was only discovered in 1998, and scientists have been wanting to explore it ever since - in no small part because it has turned astrophysics on its head.
"It's like rebuilding your car with pieces and after you think you think you've put it together, there's a giant piece still sitting on the curb, and is about the size of the car itself," said Adam Riess, an astronomer at the space telescope institute who is on Bennett's team and is also credited with co-discovering dark energy.
Albert Einstein theorized that some type of "cosmological constant" was keeping the universe in a steady state - neither expanding out of control nor collapsing in on itself.
Edwin P. Hubble clarified some of the mystery in 1929 when he peered at distant galaxies from California's Mount Wilson Observatory and saw that they were moving away from us, a discovery that meant that the universe was expanding.
But in 1998, Riess and Perlmutter's teams, looking separately at a specific class of exploding stars, published evidence showing that an unknown something they called dark energy was exerting an anti-gravitational effect on galaxies, not only driving them apart, but doing it at an accelerated rate. The universe isn't just expanding, but expanding faster.
"It was thought before that, that gravity should be slowing down the rate of universe's expansion, but it wasn't," said Livio, the space telescope astronomer.
Observers don't see evidence of dark energy on Earth because its effect is so weak, experts say, and it takes the vast reaches of space to exert its influence.
"You have to have huge amounts of it before you see any effects of it," Perlmutter said.
The mission is intended to fill in at least some of the knowledge gaps, including whether dark energy will continue to accelerate the universe's expansion, slow it down or cause it to collapse on itself, experts say.
"In terms of questions, the 800-pound gorilla is, 'What is the origin of the universe, and what is its fate going to be?' " said Riess.
The NRC report estimated a $1 billion price tag on the dark energy mission - much higher than the $600 million to $700 million NASA plans to spend, Morse said.
Bennett says that the NRC estimates were too high and that he can complete the project within NASA's fiscal limits. His proposal includes using engineers from General Dynamics to build the spacecraft and from ITT Corp. to build the infrared telescope for collecting distant starlight.
Bennett becomes philosophical when asked about the work's potential benefits.
"It's the same thing as asking what good is it to know there's poetry around, or plays, or that there's certain kinds of music. After all, we don't need it," he said. "But one of the things that makes us human is that we care about the bigger questions."
Key Cosmological Concepts
Dark energy: In the late 1990s astronomers discovered an effect causing the expansion of the universe to accelerate. Lacking any deep understanding of this effect, and unable to probe it directly with existing technology, physicists coined the generic term "dark energy" to describe it. One of today's greatest scientific challenges is understanding what is causing the acceleration, and that's what the dark energy mission is about.
Dark matter: We also know very little about dark matter other than how much there is - about 25 percent of the universe's mass. Dark matter can be measured indirectly, by calculating the mass required to create enough gravity to make galaxies behave the way they do.
Cosmological constant: When Einstein formulated his General Theory of Relativity in 1915, he assumed the universe was neither expanding nor contracting. But he knew that gravity would tend to make the universe contract, so he postulated that even empty space would still contain an energy-a "cosmological constant"-that counters gravity to maintain the balance. When Edwin Hubble discovered the expansion of our universe in 1929, Einstein rejected his own idea and called it his greatest scientific blunder. In fact, his constant reflected the apparent existence of dark energy