Stunning close-ups of a comet's core were released Tuesday by NASA scientists who, along with other experts, called the images the best ever taken of a comet.

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In one of the closest photographs, the comet Borrelly appears like an eerie cosmic potato. In others, mysterious jets of gas and dust are seen shooting out from the comet in an unexpected direction.

All over, the surface of the oblong object, roughly the size of Mt. Everest, is revealed as rolling, pitted terrain marked by grand mesas. No one involved in comet science or the mission that yielded the images expected such variety on the surface of a frozen hunk of ice.

The observations, along with other measurements of Borrelly made by other telescopes in recent days, are expected to paint an entirely new picture of the frozen wanderers of the solar system, several comet experts said.

"These are the most detailed images of a comet ever obtained," said Humberto Campins, a University of Arizona astronomer. "They are likely to yield exciting new results as various research teams study the data in coming months."

Campins was not involved in the work but observed Borrelly before, during and after the Deep Space 1 encounter from a telescope atop Kitt Peak in Arizona. He also was involved in the 1986 observations of comet Halley by the Giotto spacecraft, which until now were the best views scientists had of a comet.

Don Yeomans, a Jet Propulsion Laboratory scientist who studies asteroids and comets, said the new images were better than those taken of Halley.

Yeomans described comet Borrelly as an icy dirtball. The new observations support other recent studies indicating that comets may not contain as much water as was once thought -- an assumption that had earned them the name "dirty snowballs."

The Deep Space 1 images push scientists a "giant step" forward in their understanding of comets, Yeomans said, and they provide the first view ever of variations on the surface of a comet.

One image (at right) was taken about three minutes before Deep Space 1's closest approach to Borrelly. The image shows the 5-mile-long (8-kilometer-long) nucleus about 2,000 miles (3417 kilometers) away.

Smooth, rolling plains containing brighter regions are present in the middle of the nucleus and seem to be the source of dust jets seen in the coma.

The rugged land found at both ends of the nucleus has many high ridges along the jagged line between day and night on the comet. Sunlight is coming from the bottom of the frame.

Close-up images also show bright and dark patches that likely represent areas of different chemical composition and physical properties, Yeomans and his colleagues said. The surface of the comet, made of a dark charcoal-like substance, reflects about 4 percent of the sunlight that hits it -- in line with expectations.

"It's kinda like that stuff you see inside the chimney in your fireplace," said Larry Soderblom, a U.S. Geological Survey scientist who led the Deep Space 1 imaging team. "These pictures have told us that comet nuclei are far more complex than we ever imagined."

From some regions, which appear like smooth plateaus and are lighter, jets of gas and dust can be seen shooting out. Three small jets combine to form what is seen in a more distant image as one large jet shooting outward about 37 miles (60 kilometers).

The jets are not the same as the tails that make comets famous. Tails point away from the Sun, driven outward by the solar wind. The newly spotted jets, however, point nearly toward the Sun and are thought to be created when sunlight burns water and other chemicals from the comet's surface.

The jets are the result of ice sublimating, or turning directly to a gas and evaporating off the comet. The gas carries dust with it, and the dust reflects sunlight and makes the jets visible, the researchers explained.

The jets may be important for future comet missions. Based on observations of comet Halley, researchers have long thought that comets were surrounded by a cloud of dust that might damage a spacecraft. But it's possible, the new observations suggest, that the jets carry some portion of this dust away in a certain direction, leaving much of the environment around some comets relatively dust free.

Comets are frozen chunks of rock and ice thought to have been around, relatively unblemished, since the early days of the solar system's formation more than 4 billion years ago. That makes them frozen treasure chests of valuable information for scientists. Comets are also thought to have provided much of the water that covered a dry early Earth with oceans, making life possible.

But very little is known about comets. The bulk of all assumptions about them come from the study of just one comet: Halley.

"That situation has now changed," said Robert Nelson, Deep Space 1's project scientist. Nelson called comets a gateway to the formation of the solar system, hence our best ultimate view of human origins.

Other researchers also hailed the new data.

"We're finally reaching the stage where the veil is being lifted from these mysterious interplanetary objects," said Harold Weaver, a Johns Hopkins University researcher who was not involved in the Borrelly flyby.

Weaver told SPACE.com that the lack of comet data until now has made it difficult to draw any broad conclusions about the few comets that have been studied.

"Having another in the bag will help us understand the similarities and differences among cometary nuclei," he said. Weaver and colleagues used the Hubble Space Telescope over the weekend to observe comet Borrelly, providing additional data on what is now one of the most closely scrutinized balls of ice in the cosmos.

Researchers said additional data collected by Deep Space 1 will be released in coming weeks, including data of the magnetic field surrounding the nucleus and infrared images that will provide a better view of the comet's composition.

The most highly anticipated release may be some 3-D views that the spacecraft generated as it imaged the comet from different angles on the way by.

"I guarantee you they will blow your mind," Soderblom said.

The close-up photo session was planned to occur when the comet was at its closest to the Sun during its 6.9-year orbit that carries it out beyond Jupiter. Near the Sun, a comet is most active as a wind of charged particles streaming out from the Sun burns ice and other material off the comet's nucleus.

During the close encounter, Borrelly was surrounded by a halo of gas and dust thought to be about the size of Earth.

The successful pass by comet Borrelly marked the final science task for Deep Space 1, which was intended primarily as a mission to test futuristic technologies.