A close look at pebble-filled layers of rock has convinced scientists that NASA's Curiosity rover is driving through a dried-up stream bed on Mars where water flowed vigorously billions of years ago. They say it's the kind of place that just might have supported life when the planet was young.

"This is a rock that was formed in the presence of water," Caltech's John Grotzinger, project scientist for the $2.5 billion Mars Science Laboratory mission, said today during a televised news conference at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

The evidence is in the shape, size and composition of the rocks that Curiosity came across at multiple sites during its landing on Aug. 5. Conglomerate rocks, consisting of pebbles cemented together within layers of sediment, were seen at three sites:

• Goulburn, a bedrock formation that was exposed by the blast from Curiosity's descent.
• Link, a rock outcrop that was seen once Curiosity headed out from the landing site.
• Hottah, an uplifted slab of craggy rock that was given a visual inspection two weeks ago.

Hottah in particular showed clear evidence of rounded pebbles that were too big to be smoothed by the action of the wind. Some of the rocks are as big as golf balls. The best explanation for the gravelly pebbles was that they were eroded by the vigorous flow of water, said Curiosity science team member Rebecca Williams, a senior scientist at the Arizona-based Planetary Science Institute.

The Hottah slab, which measures 4 to 6 inches (10 to 15 centimeters) thick, looks as if "somebody came along the surface of Mars with a jackhammer and lifted up a sidewalk that you might see in downtown LA, sort of like in a construction site," Grotzinger said.

NASA / JPL-Caltech / MSSS

A closeup view of the "Hottah" rock outcrop shows the characteristic pebbly rock that is associated with the action of a flowing stream. Broken surfaces of the outcrop have rounded, gravel clasts, such as the one circled in white, which is about 1.2 inches (3 centimeters) across. The rock formation was named after Hottah Lake in Canada's Northwest Territories.

NASA / JPL-Caltech / MSSS / PSI

This set of images compares the Link outcrop of rocks on Mars (left) with similar rocks seen on Earth (right). The image of Link, obtained by NASA's Curiosity rover, shows rounded gravel fragments, or clasts, up to a couple of inches (few centimeters) wide, within the rock outcrop. In accordance with the Mars mission's tradition, Link takes its name from a rock formation in Canada's Northwest Territories.

The evidence from the ground meshes well with the evidence from orbit indicating that Curiosity is near an 11-mile-wide (18-kilometer-wide) fan of material that may have washed down a channel in ancient times, when Mars was warmer and wetter, according to William Dietrich, a planetary scientist at the University of California at Berkeley.

"These stones ... are very, very revealing to us about the process," Dietrich said. Some previous research has suggested that water flowed on Mars only for brief periods, separated by long, cold, dry spells. That scenario might not have provided enough time for life to get a foothold on the Red Planet in ancient times. But Dietrich said the patterning of the channels within the fan suggested that water streamed through the area for well beyond a thousand-year time scale.

"We can step away from the idea that there was a single burst of water ... that built it all in a day," he told reporters.

Based on the size of the gravel seen by Curiosity, Dietrich estimated that the water moved at a speed of about 3 feet (1 meter) per second, at a depth somewhere between ankle and hip deep.

"Plenty of papers have been written about channels on Mars with many different hypotheses about the flows in them," Dietrich said in a NASA news release. "This is the first time we're actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it."

NASA / JPL-Caltech / Univ. of Ariz.

This image shows the topography, with shading added, around the area where NASA's Curiosity rover landed. Higher elevations are colored in red, with cooler colors indicating transitions downslope to lower elevations. The map highlights an alluvial fan of material, apparently issuing from a channel named Peace Vallis. The black oval indicates the targeted landing area for the rover known as the "landing ellipse," and the cross shows where the rover actually landed.

NASA / JPL-Caltech / UC-Berkeley

This image shows a dry streambed on an alluvial fan in Chile's Atacama Desert, revealing the typical patchy, heterogeneous mixture of grain sizes deposited together. On Mars, Curiosity has seen two rock outcrops close to its Bradbury Landing site that also record a mixture of sand and pebbles transported by water. Scientists say the mixture was probably deposited along an ancient streambed.

So far, the scientists' conclusions are based exclusively on visual observations by Curiosity's high-resolution Mastcam imager. Further imagery, along with chemical readings from other instruments on the rover, will likely be used to fill out the story of the ancient stream bed, Grotzinger said.

The main goal of Curiosity's two-year primary mission is to assess how habitable Mars was in ancient times. That's why mission managers chose 96-mile-wide (154-kilometer-wide) Gale Crater as Curiosity's landing site. It has that alluvial fan, which appears to issue forth from a channel that has now officially been designated Peace Vallis. It also has a 3-mile-high (5-kilometer-high) mountain, known as Aeolis Mons or Mount Sharp, which could preserve billions of years' worth of Mars' geological record.

Grotzinger noted that the three requirements for habitability typically listed by astrobiologists are the presence of liquid water, the availability of an energy source (such as sunlight) and the presence of carbon-based compounds that can be used as the building blocks of life. 

"Now we've got a hall pass for the water examination," Grotzinger joked.

Theoretically, a long-flowing stream could be a habitable environment. "It is not our top choice as an environment for preservation of organics, though," Grotzinger said in NASA's news release. "We're still going to Mount Sharp, but this is insurance that we have already found our first potentially habitable environment."

Even if the rover's instruments detect the right kinds of carbon compounds, that would not serve as confirmation of ancient life on Mars. That would "have to wait for another mission," Grotzinger said.  

More from Mars Curiosity:

• See a crescent moon in Martian sky
• Curiosity touches first rock, then takes off
• Mars rover spots mini-moon's transit
• Cosmic Log archive on the Mars mission

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the dwarf planet and the search for new worlds.

The first rock that NASA's Curiosity rover will touch for science's sake on Mars is a pyramid-shaped chunk that's been named in honor of a top engineer who worked on every one of NASA's rover missions — but passed away just days after Curiosity's landing.

Curiosity's study of the rock, dubbed "Jake Matijevic," will dominate the next few days of the rover's operations on Mars, just as its observations of Martian mini-eclipses dominated the past few days.

Jake the rock, which measures about 10 inches (25 centimeters) tall and 16 inches (40 centimeters) wide, isn't all that exotic. It seems to consist of garden-variety basalt, similar to the first Martian rock that NASA's Spirit rover examined eight and a half years ago. And that's exactly the point, according to Caltech's John Grotzinger, project scientist for the Curiosity mission. Jake will provide a good yardstick for sophisticated instruments such as the Alpha Proton X-Ray Spectrometer, or APXS, and the laser-zapping ChemCam analyzer.

By matching up the chemical readings from the different instruments, Curiosity's science team will be able to confirm that the findings from the fancy-schmancy ChemCam are consistent with the readings from the APXS, an upgraded version of a device that was included on the Spirit and Opportunity rovers. Grotzinger told reporters today that it's an opportunity to compare "something which is tried and true with the latest and greatest new technology."

ChemCam can focus on areas that are less than a millimeter (0.04 inch) wide, while the APXS' best resolution ranges around 1.5 centimeters (0.6 inch).

Grotzinger estimated that the testing could begin on Friday — which is the Martian day, or sol, after tomorrow ("solorrow," he quipped). It could take a couple of sols for the rover to reach out its 7-foot-long (2.1-meter-long) robotic arm and use the APXS as well as the fine-resolution Mars Hand Lens Imager, or MAHLI. The rover might have to back up a bit to give the rock a proper zapping with ChemCam's laser. The flashes of light from the tiny laser blasts will be analyzed by an onboard spectrometer to determine the rock's elemental composition.

Remembering Jake
Richard Cook, project manager for the $2.5 billion Mars Science Laboratory mission, said the rock's name pays tribute to Jacob Matijevic, a leading engineer at NASA's Jet Propulsion Laboratory who was involved in NASA's rover missions since Mars Pathfinder and the Sojourner rover in 1997. Matijevic was a Chicago native who earned his Ph.D. in mathematics and came up with the Matijevic Theorem, which was once described as "one of the most beautiful results of recent years in commutative algebra."

Matijevic's obituary in the Chicago Tribune notes that he came to JPL in 1981 and took on a variety of assignments. Eventually, he came to specialize in systems engineering for the Mars rover designs as well as rover surface operations. "He was probably one of the top one or two experts on surface operations here at JPL," Cook said.

Matijevic played a key role in the Spirit and Opportunity rover missions, which were originally planned to last just 90 days on Mars. Grotzinger recalled that Matijevic once said "if this rover lasts six months, it'll probably last six years."

"He seems to have come pretty close," Grotzinger observed.

The engineer switched over from Opportunity to the Mars Science Laboratory mission, but passed away at the age of 64 on Aug. 20, after battling respiratory problems, the Tribune reported.

Grotzinger said Matijevic would have loved dealing with the complexities involved in studying the rock that's named after him. "All that activity and all those considerations are what honor Jake Matijevic so well," he said.

The chief aim of Curiosity's two-year primary mission is to analyze Mars' geology and surface chemistry and determine whether the planet could have been potentially habitable in ancient times. After studying Jake's memorial rock, Curiosity is due to move on to an area known as Glenelg, where three types of geological formations come together.

Since its landing on Mars on Aug. 5, the six-wheeled rover has covered more than half of the quarter-mile (400-meter) distance to Glenelg, and its cameras are getting a better view of the place. Grotzinger said the pictures show thin bands of dark rock that appear to alternate with lighter-toned rock. "As we get closer in to the Glenelg area, we'll understand better and better what these areas are," Grotzinger said. Curiosity is expected to get to the area in a couple of weeks, he said.

NASA / JPL-Caltech / Univ. of Ariz.

This map shows the route driven by the Curiosity rover through the mission's 43rd Martian day, or sol (Sept. 19). By Sol 43, Curiosity had driven about 950 feet (290 meters). The area known as Glenelg is indicated by a red dot and label.

NASA / JPL-Caltech / MSSS

A scan of the Martian terrain looking toward Glenelg reveals areas of light and dark rock.

NASA / JPL-Caltech / MSSS An animated GIF image shows Phobos crossing over the sun, as seen by NASA's Curiosity rover.

Messages from mini-eclipses
The Curiosity team is also planning to receive more pictures of the partial solar eclipses that the rover's high-resolution Mastcam system has observed over the past week. Mark Lemmon, a science team co-investigator from Texas A&M University, said close analysis of the imagery could provide insights into the interior structure of Mars and its two moons, Phobos and Deimos.

Mastcam took hundreds of pictures when Phobos made two passes over the sun's disk, and again when Deimos made one pass. Such transits occur multiple times during a short season, and then they don't occur again for nearly one Earth year. Lemmon explained that the timing of the eclipses could be compared with past sightings to produce precise measurements of how the moons' orbits have changed due to Mars' gravitational tides.

"We can't go inside Mars, but we can use these to tell how much Mars is deformed when the moons go by," Lemmon said. "So we measure the transits very precisely [and] we get information on Mars' interior structure."

Some high-resolution images from Phobos' first transit were sent down to Earth over the weekend, but most of the imagery is still saved in the rover's computer memory on Mars, awaiting the right opportunity for transmission, Lemmon said.

Phobos and Deimos have irregular shapes, and the prevailing wisdom is that they're both asteroids that were pulled into orbit by Mars' gravitational pull. Phobos averages 14 miles (22.2 kilometers) in width, and Deimos is roughly 8 miles (12.6 kilometers) wide. Deimos circles Mars at a distance of 14,580 miles (23,460 kilometers), while Phobos is much closer (5,800 miles, or 9,400 kilometers). Phobos is gradually coming even closer to Mars, which makes the moon's orbit unstable over the long term: One of these days, it will break up into pieces and perhaps produce a ring of debris around the Red Planet.

Fortunately, that day isn't expected to come for 10 million to 15 million years. "Curiosity will be safe for a little while," Lemmon said.

More about Mars:

• How a rover on Mars is blazing a trail on Earth
• Martian moon bites into the sun
• Spheres spark new Martian mystery
• Cosmic Log archive on the Curiosity mission

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the dwarf planet and the search for new worlds.

NASA's Curiosity rover made its first drive on Mars today, more than two weeks after its high-stakes landing on the Red Planet. To celebrate the day, as well as what would have been the late science-fiction writer Ray Bradbury's 92nd birthday, NASA said the rover's landing site would be forever known as Bradbury Landing.

The raw images, displayed on the Mars Science Laboratory mission's Web portal, showed the tracks of the rover's wheels curling around and backing up, in accordance with the driving plan that was sent up overnight.

Today's drive amounted to only about 23 feet (7 meters) of maneuvers, but it represented the first step in a $2.5 billion, two-year trek that's expected to go at least 12 miles (20 kilometers) and take in a commanding view from the flanks of a 3-mile-high (5-kilometer-high) mountain within 96-mile-wide (154-kilometer-wide) Gale Crater.

The mission's project manager, Peter Theisinger, said the drive "couldn't be more important."

"We built a rover," he told reporters during today's briefing at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "So unless the rover roves, we couldn't really accomplish anything. It's a big moment."

The drive also marked a transition for the Curiosity team — from the entry, descent and landing phase of the mission, known as EDL, to surface operations and rover mobility. "Wheel tracks on Mars. The EDL team is finally done. :) Congrats to the mobility and surface teams!" Allen Chen, the mission's EDL operations and flight dynamics lead, declared in a Twitter update.

Lead rover driver Matt Heverly said that today's drive started at 7:17 a.m. PT (10:17 a.m. ET) and lasted roughly 16 minutes. "The majority of that time was spent taking images," he said. The rover rolled out 15 feet (4.5 meters), made a 120-degree turn in place, and then backed up 8 feet (2.5 meters) to a new spot for scientific observations.

NASA / JPL-Caltech

A polar projection image, assembled from pictures taken by the Curiosity rover's navigation cameras, shows the tracks of the rover at Bradbury Landing on Mars as seen from above.

NASA / JPL-Caltech

An image from the navigation-camera system on NASA's Curiosity rover shows the six-wheeled craft's hardware in the foreground, and wheel tracks going around a rock just a few yards (meters) away.

NASA / JPL-Caltech

A mosaic of black-and-white images shows a panoramic view of the Curiosity rover's trail, including wheel tracks leading to an area where the rover turned in a circle, and then backed up to its current position. Four blast marks, or "scours," can be made out near where the rover landed. The flanks of Mount Sharp can be seen in the far background, toward the upper left corner of the frame.

First trek will follow checkouts
Since the rover's landing on the night of Aug. 5, Curiosity has been going through a series of checkouts and taking pictures of its immediate surroundings. Nearly all of the systems are working as planned — with the sole exception of wind sensors on one of the booms connected to the rover's weather station. Scientists speculate that the circuit boards for those sensors were probably damaged by small rocks that were thrown up onto the rover during landing. Despite the damage, the weather station will be able to gather wind speed data using other sensors.

Curiosity's first destination will be a spot known as Glenelg, about a quarter-mile (400 meters) from the landing site, where three types of geological formations come together. That months-long trek could begin in about a week, deputy project scientist Joy Crisp said today. The rover's first scoop sample could be taken on the route between Bradbury Landing and Glenelg, she said, but the first drilling sample would probably be extracted at Glenelg.

By the end of the year, the nuclear-powered rover is expected to retrace its route and head toward the mountain, known as Aeolis Mons or Mount Sharp. The layers of rock along the mountainside are thought to preserve a geological record going back billions of years.

The primary goal of Curiosity's mission is to look for geological and chemical evidence that could reveal how habitable Mars might have been over eons of geological time. To take on that challenge, the 1-ton, car-sized rover has been equipped with a bevy of scientific instruments — including high-resolution color cameras, two onboard chemical labs, an X-ray spectrometer and a rock-zapping laser.

Theisinger said Curiosity was making "excellent progress" at Bradbury Landing, 16 days into a mission that could last far longer than its scheduled duration of nearly two Earth years. "We've got a long way to go before this mission reaches its full potential," he said. "But the fact that we haven't had any early problems is fantastic."

In memoriam
Michael Meyer, the lead scientist for the Mars Exploration Program at NASA Headquarters, announced the naming of the landing site at the start of today's news briefing. He began by airing a clip of Bradbury discussing Mars with Arthur C. Clarke, Carl Sagan and other luminaries, just before NASA's Mariner 9 probe entered the Red Planet's orbit in 1971. During that session, Bradbury read a short poem titled "If Only We Had Taller Been."

Bradbury, best known for science-fiction tales such as "The Martian Chronicles" and "Fahrenheit 451," passed away in June at the age of 91. "Today would have been Ray Bradbury's 92nd birthday, but he's already reached immortality in his short stories and books," Meyer observed. In his honor, Meyer said the landing site would "forever be known as Bradbury Landing."

In a statement issued by NASA, Meyer said deciding on the name "was not a difficult choice for the science team."

"Many of us, and millions of other readers were inspired in our lives by stories Ray Bradbury wrote to dream of the possibility of life on Mars," he said.

Today's christening adds to NASA's list of Martian landing sites named after VIPs, including:

• Mutch Memorial Station, the Viking 1 lander site, named after Thomas Mutch, former NASA associate administrator and Viking team member.
• Soffen Memorial Station, the Viking 2 lander site, named after Gerald Soffen, NASA scientist and leader of the Viking mission.
• Sagan Memorial Station, the Mars Pathfinder landing site, named after astrophysicist Carl Sagan.
• Challenger Memorial Station, the Opportunity rover landing site, named in honor of the shuttle Challenger's fallen crew.
• Columbia Memorial Station, the Spirit rover landing site, named in honor of the shuttle Columbia's fallen crew.

More about Mars:

• 3-D adds depth to tracks on Mars
• Watch the rover fall to Mars ... in HD!
• Where's Curiosity going? Arm points the way
• Mars mega-rover wiggles its wheels
• Mars Curiosity rover flexes arm for first time
• Curiosity shoots at rock with its laser
• Britney Spears to Mars rover: What's new?
• Rover reveals more of Martian peak
• Mars rover team faces the masses
• Mars fans make viral video
• Panoramas add spin to Mars
• Mars rover survives its 'brain transplant'
• Mars orbiter gets a long look at Curiosity rover
• Reprogrammed rover getting ready to roll
• Obama tells rover team: Watch out for Martians
• Search for life to shape future Mars missions
• Why the rover has such a dinky camera and computer
• How to build your own Mars rover with Lego blocks
• The Puff on Mars: Photo mystery solved!
• Panorama reveals a colorful Mars
• NBC video: Panorama featured on 'Nightly News'
• Curiosity reveals a Martian Mojave
• Tour the Martian Mojave in 3-D
• Flying saucer spotted over Mars
• First 3-D pictures sent by Curiosity
• Orbital photo spots rover and its trash
• Curiosity sends color snapshot from Mars
• Rover video looks down on Mars during landing
• Mars orbiter spots rover in midair
• NASA's Mohawk Guy marvels at his fame
• Curiosity rover scores touchdown on Mars

This report was last updated at 5 p.m. ET.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the dwarf planet and the search for new worlds.

It's been a crazy 24 hours for flight director Bobak Ferdowsi, and not just because he and the rest of his team at NASA's Jet Propulsion Laboratory landed an SUV on Mars. Ferdowsi has catapulted to Internet fame — thanks to his star-spangled Mohawk hairdo and the warm-hearted hotness he exuded during TV coverage of the Curiosity rover's landing.

He's picked up 20,000-plus Twitter followers, with most of those added just since last night. He's getting come-ons from fans of both sexes ("I'd let that be-mohawked NASA dude land his rover on my red planet any time," one admirer wrote). A Tumblr tribute site has been created in his honor. And there's a widely distributed LOL picture with the caption, "Becomes an Internet sensation ... Too busy landing a robot on Mars to notice."

Well, Ferdowsi has noticed.

"It's a little surreal," he told me this morning. "I'm still just getting over the 'We're on Mars' thing. That's the thing I can't believe."

As Ferdowsi strolls through JPL's campus in Pasadena, Calif., he can't resist going over to teammates for hugs. He's been working at the lab for nine years. For most of that time he's been preparing for the $2.5 billion Mars Science Laboratory mission, and particularly for Sunday night's successful landing. These people are not only his co-workers. They're his friends.

"What a wonderful moment to share together," he said.

Ferdowsi has a habit of adopting a fresh hairdo for each of the space missions for which he's at the controls, based on a vote by his teammates. For the Mars mission, they came up with a variety of fashion choices.

"We had a Martian red," he said. "One vote to shave my head. Natural black. Then we had the Captain America look."

He went with the Captain America Mohawk: black hair flecked with blue and red highlights, plus some bleached white stars on the side. He didn't ponder the effect of having his edgy 'do broadcast on NASA TV, and he was so wrapped up in Curiosity's entry, descent and landing that it took him a while to notice he was becoming a star himself. But then the messages and tweets started popping up on his phone.

"I'm looking down, and thinking, 'This is crazy,'" he recalled.

He was back at work today, trying to do his job while coping with media requests and watching the evolution of a meme.

"I am laughing pretty hard at some of the captions," he said. "I think it's hilarious."

I didn't have the nerve to ask him about his, um, personal relationships — but for all his admirers, here are a couple of factoids: He's 32 years old. He's originally from the Bay Area and still has family there. He earned his bachelor's degree in aeronautical and astronautical engineering from the University of Washington, and he went to MIT to get a master's degree in the same subject.

You can join the Bobak fan club by following @tweetsoutloud. But if his fans really want to get Ferdowsi's attention, they probably shouldn't tweet him a marriage proposal. Instead, they should talk about Mars.

"I hope that they are as excited about Curiosity as I am," the Mohawk Guy said.

Update for 7:35 p.m. ET Aug. 7: Is Mohawk Guy taken? In a follow-up chat with BuzzFeed's Chris Geidner, Ferdowsi reports that he's "dating somebody," and "she's awesome."

"She's put up with me working a lot of long hours on this project, and I am definitely looking forward to things being calmed down a little bit so I can actually hang out with her," Ferdowsi says. A photo on the MemeGenerator website shows Ferdowsi with his arm around a lady friend. The caption reads, "Behind every great Mohawk is a great woman."

Meanwhile, other Internet celebrities are welcoming Mohawk Guy to the fold. Felicia Day told Ferdowsi in a tweet that "your mohawk made my night" — to which Ferdowsi replied, "Your tweet made me blush." Wil Wheaton registered his yen for a NASA Mohawk Guy Fan Club T-shirt — and reportedly put in an order with CafePress. 

More about Mars:

• Mars orbiter spots rover in midair
• Curiosity rover scores touchdown on Mars
• Scientists want to look for Martian life
• Last-minute guide to the Mars landing
• What will we see from Mars, and when will we see it?
•  Why we're obsessed with Mars
• Mars probe provides radiation revelations

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the dwarf planet and the search for new worlds.