The double strikes occurred relatively recently — 1 to 2 billion years ago — and came to light only after researchers pored over high-resolution images snapped by the NASA Dawn spacecraft, which slipped into orbit around Vesta last year. The finding is reported in Friday’s issue of Science, which published a series of papers on the $466 million mission.

Vesta’s surface is pockmarked with pits caused by crashes. Scientists zeroed in on the southern hemisphere, which is dominated by a 310-mile-wide crater. Soon after arriving at Vesta, Dawn spotted a nearby feature that looked like a rim.

“It looked kind of weird. We thought, ‘What the heck is that?’” recalled Paul Schenk of the Lunar and Planetary Institute in Houston who is part of the mission.

Scientists determined the rim belonged to a smaller, older crater gouged by an impact 2 billion years ago. It had been obscured by the larger crater, created by an impact a billion years later.

The back-to-back pounding likely would have shattered any other asteroid, but Vesta somehow survived. Even so, the blows scooped out loads of material from Vesta’s surface — enough to fill 400 Grand Canyons, estimated team member David O’Brien of the Planetary Science Institute in Tucson, Ariz.

Some of the debris was hurled into space and fell to Earth as meteorites. About 1 out of every 20 meteorites found on our planet came from Vesta.

Located in the asteroid belt between Mars and Jupiter, Vesta is not your garden-variety asteroid. Many of the space rocks in the zone resemble potatoes, but Vesta is shaped more like an avocado with its iron core and differentiated layers. Measuring 330 miles across, it’s the second largest object in the asteroid belt.

Scientists are intrigued by asteroids because they’re leftovers from the solar system’s birth some 4.5 billion years ago and studying them can offer clues about how Earth and rocky planets emerged.

Dawn will depart Vesta in late August, firing its ion propulsion engines to cruise on to a bigger target — an asteroid named Ceres where it will arrive in 2015.

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Online:

Science journal: http://www.sciencemag.org

Dawn mission: http://dawn.jpl.nasa.gov

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Follow Alicia Chang at http://twitter.com/SciWriAlicia

The federally funded study is the largest look yet at how to treat diabetes in teens. Earlier studies mostly have been in adults, and most diabetes drugs aren’t even approved for youths. The message is clear: Prevention is everything.

“Don’t get diabetes in the first place,” said Dr. Phil Zeitler of the University of Colorado Denver, one of the study leaders.

A third of American children and teens are overweight or obese. They are at higher risk of developing Type 2 diabetes, in which the body can’t make enough insulin or use what it does make to process sugar from food. Until the obesity epidemic, doctors rarely saw children with Type 2 diabetes. The more common kind of diabetes in children is Type 1, which used to be called juvenile diabetes.

Doctors usually start Type 2 treatment with metformin, a pill to lower blood sugar. If it still can’t be controlled, other drugs and daily insulin shots may be needed. The longer blood sugar runs rampant, the greater the risk of suffering vision loss, nerve damage, kidney failure, limb amputation — even heart attacks and strokes.

The goal of the study was simple: What’s the best way for teens to keep diabetes in check?

The study involved 699 overweight and obese teens recently diagnosed with diabetes. All had their blood sugar normalized with metformin, then were given one of three treatments to try to maintain that control: metformin alone, metformin plus diet and exercise counseling, or metformin plus a second drug, Avandia.

After nearly four years, half in the metformin group failed to maintain blood sugar control. The odds were a little better for the group that took two drugs but not much different for those in the lifestyle group.

Even so, Zeitler said doctors would not recommend this combination drug therapy because Avandia has been linked to higher risk of heart attacks in adults. Those risks became known after this study had started.

Another study leader from Children’s Hospital Los Angeles, Dr. Mitchell Geffner, agreed that Avandia can’t be recommended for teens, but said the study makes clear they will need more than metformin to control their disease.

“A single pill or single approach is not going to get the job done,” he said.

Among all the teens in the study, 1 in 5 had a serious complication such as very high blood sugar, usually landing them in the hospital.

The results were published online Sunday by the New England Journal of Medicine and presented at a pediatric meeting in Boston. The National Institutes of Health funded the study and drug companies donated the medications.

The “discouraging” results point to the need to create “a healthier ‘eat less, move more’” culture to help avoid obesity that contributes to diabetes, Dr. David Allen of the University of Wisconsin School of Medicine and Public Health wrote in an accompanying editorial.

Judith Garcia still struggles to manage her diabetes with metformin and insulin years after taking part in the study at Children’s Hospital Los Angeles. She has to remember to watch her diet and set aside time to exercise.

“Trust me, I’m working on it,” said the 19-year-old who lives in Commerce, Calif.

Kelsi Amer, a 14-year-old high school freshman from Patriot, Ind., knows how tough it is to keep her blood sugar from skyrocketing. Diagnosed at age 12, she takes metformin and gives herself insulin shots before school and at bedtime.

There are times when she has to miss class because she has to prick her finger to check her blood sugar or go with her mother to Cincinnati Children’s Hospital Medical Center for check-ups.

“I try real hard and all of a sudden, I’m back to high blood sugar” levels, said Kelsi, who was not part of the research.

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Online:

New England Journal of Medicine: http://www.nejm.org

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Follow Alicia Chang’s coverage at http://www.twitter.com/SciWriAlicia

The biggest surprise? The largest Martian lava spiral measured 100 feet across — bigger than any on Earth. It is further evidence that Mars was volcanically active recently — geologically speaking within the past 20 million years.

For more than a decade, scientists debated whether this maze of valleys near the Martian equator was sculpted by ice or volcanic processes.

As part of a class project last year, Ryan analyzed about 100 high-resolution photos of the region snapped by the Mars Reconnaissance Orbiter, which has been photographing the Martian surface since 2006. One evening, while taking a second look at the images, Ryan zoomed in and noticed the lava coils. He counted 269 spirals ranging from 16 feet to 100 feet across.

Ryan said he was not surprised the features were overlooked in the past since they blended in with the terrain. The coils looked strikingly similar to Hawaiian lava flows, leading Ryan to conclude that lava — not ice — was the driving force.

Planetary scientist David Paige of the University of California, Los Angeles, said the new work provides convincing evidence that the curious patterns were forged from volcanic activity.

This “illustrates just how complicated Mars’ geologic history appears to really be,” Paige wrote in an email. He was not part of the research team.

It’s believed that rivers of molten lava flowed through the Martian valleys into a broad basin where they settled and formed the coil shapes. The spiral shapes were preserved as the lava cooled.

There are no clear signs that the region today is volcanically active. With more observations, Ryan said it is possible lava coils may exist elsewhere on the red planet.

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Online:

Science journal: http://www.sciencemag.org

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Follow Alicia Chang’s coverage at http://www.twitter.com/SciWriAlicia

Using high-tech sonar, an expedition spearheaded by Bezos has discovered what he claimed were discarded engines from the mission lurking 14,000 feet deep.

In an online announcement Wednesday, Bezos said he is drawing up plans to recover the sunken engines, part of the mighty Saturn V rocket that launched Armstrong, Buzz Aldrin and Michael Collins on their moon mission.

It was not immediately clear when Bezos’ team spotted the Apollo engines. Bezos offered few details about the discovery and did not say how he knew the engines were from Apollo 11. The cost of the recovery was not disclosed, but Bezos said it will be done with private funds.

Amazon spokesman Drew Herdener said Bezos was not available for comment.

The five engines, which produced nearly 7.7 million pounds of thrust, dropped into the sea as planned minutes after liftoff in 1969. Four days later, Armstrong and Aldrin walked on the moon.

“We don’t know yet what condition these engines might be in,” he wrote. “They hit the ocean at high velocity and have been in salt water for more than 40 years. On the other hand, they’re made of tough stuff, so we’ll see.”

Bezos acknowledged the engines were the property of NASA, but said he hoped they will be displayed in museums.

NASA expressed excitement about the find. The space agency said it has not been formally contacted by Bezos and waited for more information.

“There has always been great interest in artifacts from the early days of space exploration and his announcement only adds to the enthusiasm of those interested in NASA’s history,” NASA spokesman Bob Jacobs said in a statement.

No timetable has been set for the recovery. When it happens, it’ll undoubtedly take longer to hoist the 19-foot engines off the sea floor than the 2 1/2 minutes it took for them to power off the launch pad.

The sea floor is littered with spent rockets and flight parts from missions dating back to the dawn of the Space Age and it’s unknown what survived decades later after crashing into the ocean.

In 2009, a private company salvaged Gus Grissom’s Mercury capsule that accidentally sank in the Atlantic after splashdown in 1961. It was restored and displayed at the Kansas Cosmosphere and Space Center.

Bezos’ planned Apollo recovery is the latest deep-sea adventure by the wealthy. “Avatar” director James Cameron over the weekend rode a mini-sub to Earth’s deepest spot in the western Pacific Ocean, seven miles below the surface, which he described as an alien world. Sir Richard Branson plans a similar dive to the deepest part of the Atlantic, the Puerto Rican trench, later this year.

The five engines, which produced nearly 7.7 million pounds of thrust, dropped into the sea as planned minutes after liftoff in 1969. Four days later, Armstrong and Aldrin walked on the moon.

“We don’t know yet what condition these engines might be in,” he wrote. “They hit the ocean at high velocity and have been in salt water for more than 40 years. On the other hand, they’re made of tough stuff, so we’ll see.”

Bezos acknowledged the engines were the property of NASA, but said he hoped they will be displayed in museums.

NASA expressed excitement about the find. The space agency said it has not been formally contacted by Bezos and waited for more information.

“There has always been great interest in artifacts from the early days of space exploration and his announcement only adds to the enthusiasm of those interested in NASA’s history,” NASA spokesman Bob Jacobs said in a statement.

No timetable has been set for the recovery. When it happens, it’ll undoubtedly take longer to hoist the 19-foot engines off the sea floor than the 2 1/2 minutes it took for them to power off the launch pad.

The sea floor is littered with spent rockets and flight parts from missions dating back to the dawn of the Space Age and it’s unknown what survived decades later after crashing into the ocean.

In 2009, a private company salvaged Gus Grissom’s Mercury capsule that accidentally sank in the Atlantic after splashdown in 1961. It was restored and displayed at the Kansas Cosmosphere and Space Center.

Bezos’ planned Apollo recovery is the latest deep-sea adventure by the wealthy. “Avatar” director James Cameron over the weekend rode a mini-sub to Earth’s deepest spot in the western Pacific Ocean, seven miles below the surface, which he described as an alien world. Sir Richard Branson plans a similar dive to the deepest part of the Atlantic, the Puerto Rican trench, later this year.

Bezos was 5 years old when he watched the moon landing on television and became hooked on getting to space. NASA “sure inspired me, and with this endeavor, maybe we can inspire a few more youth to invent and explore,” he wrote.

It was not immediately clear when Bezos’ team spotted the Apollo engines. Bezos offered few details about the discovery and did not say how he knew the engines were from Apollo 11. The cost of the recovery was not disclosed, but Bezos said it will be done with private funds.

Amazon spokesman Drew Herdener said Bezos was not available for comment.

Bezos’ Blue Origin has been developing a vertical takeoff and landing rocketship that would fly passengers to suborbital space. It has NASA funding to compete to go into orbit as a space taxi now that the space shuttle fleet is retired.

Last year, a test flight went awry when the vehicle became unstable at 45,000 feet and crashed.