Hidden rocks from infant Earth hint at planet's origin
A reservoir of rock that remained intact for nearly the entire history of Earth could tell us about how our planet was built. Its chemistry hints that Earth's building blocks may have had a rough time of it, losing their skins before they could unite.
The rocks were thrown up by volcanoes in the Arctic wastes of Baffin Island and Greenland only 62 million years ago, but it seems they came from a store of rock in the mantle that formed 4.5 billion years ago – just after Earth formed.
Because the mantle slowly churns and chemically alters, this comes as a surprise. "We had almost given up hope of finding anything that had survived so long," says Matt Jackson of Boston University. But Jackson and colleagues found that their samples carry isotopes of helium, hafnium and lead in ratios that would only be found in such ancient rocks.
Rasmus Andreasen of Imperial College London is cautious about the claimed age, because radioactive decay deep in the Earth can throw results off. "The isotope evidence is intriguing, but not conclusive," he says.
If the dates are right, however, these rocks were undisturbed for almost all of Earth's history, and so hold chemical clues to our planet's origin. It is widely thought that Earth was assembled from material similar to that found in meteorites called chondrites. But Baffin's ancient rocks are different: they contain less of certain heavy elements than chondrites do.
The rocks were thrown up by volcanoes in the Arctic wastes of Baffin Island and Greenland only 62 million years ago, but it seems they came from a store of rock in the mantle that formed 4.5 billion years ago – just after Earth formed.
Because the mantle slowly churns and chemically alters, this comes as a surprise. "We had almost given up hope of finding anything that had survived so long," says Matt Jackson of Boston University. But Jackson and colleagues found that their samples carry isotopes of helium, hafnium and lead in ratios that would only be found in such ancient rocks.
Rasmus Andreasen of Imperial College London is cautious about the claimed age, because radioactive decay deep in the Earth can throw results off. "The isotope evidence is intriguing, but not conclusive," he says.
If the dates are right, however, these rocks were undisturbed for almost all of Earth's history, and so hold chemical clues to our planet's origin. It is widely thought that Earth was assembled from material similar to that found in meteorites called chondrites. But Baffin's ancient rocks are different: they contain less of certain heavy elements than chondrites do.
Jupiter swallowed a super-Earth
JUPITER might have secured its position as the solar system's mightiest planet by killing an up-and-coming rival, new simulations suggest. The work could explain why the planet has a relatively small heart, and paints a grisly picture of the early solar system, where massive, rocky "super-Earths" were snuffed out before they could grow into gas giants.
Jupiter and Saturn are thought to have begun life as rocky worlds with the mass of at least a few Earths. Their gravity then pulled in gas from their birth nebula, giving them dense atmospheres.
In this picture, all gas giants should have cores of roughly the same size. Yet spacecraft-based gravity measurements suggest Jupiter's core weighs just two to 10 Earth masses, while Saturn's comes in at 15 to 30.
New simulations by Shu Lin Li of Peking University in China, and colleagues, may explain why. They calculated what would happen when a super-Earth of 10 times the mass of our planet slammed into a gas giant. The rocky body flattened like a pancake when it hit the gas giant's atmosphere, then barrelled into the giant's core about half an hour later. The energy of the collision could have vaporised much of the core.
Jupiter and Saturn are thought to have begun life as rocky worlds with the mass of at least a few Earths. Their gravity then pulled in gas from their birth nebula, giving them dense atmospheres.
In this picture, all gas giants should have cores of roughly the same size. Yet spacecraft-based gravity measurements suggest Jupiter's core weighs just two to 10 Earth masses, while Saturn's comes in at 15 to 30.
New simulations by Shu Lin Li of Peking University in China, and colleagues, may explain why. They calculated what would happen when a super-Earth of 10 times the mass of our planet slammed into a gas giant. The rocky body flattened like a pancake when it hit the gas giant's atmosphere, then barrelled into the giant's core about half an hour later. The energy of the collision could have vaporised much of the core.
These vaporised heavy elements would then have mixed with the hydrogen and helium of the gas giant's atmosphere, leaving only a fraction of the gas giant's former core behind. This could explain not only why Jupiter's core is so small, but also why its atmosphere is richer in heavy elements compared with the sun, whose composition is thought to mirror that of the nebula that gave birth to the solar system's planets .
The super-Earth might have grown into a gas giant itself one day if it had not collided with Jupiter, says study co-author Douglas Lin at the University of California, Santa Cruz. "It may very well have been on its way to becoming a gas giant, but lost the race and got gobbled up," he says.
Saturn has a similar overabundance of heavy elements in its atmosphere. The team argues that this could be due to impacts by rocky objects smaller than Earth that decelerated and broke up before they could reach Saturn's core. The team's simulations suggest that this would have left the core intact, or even added to its mass as fragments rained down onto it.
"It's an interesting explanation of why you might have a variety of core masses in giant planets," says William Hubbard of the University of Arizona in Tucson. "It's a very useful contribution."
David Stevenson of the California Institute of Technology in Pasadena says he is "favourably disposed" towards the idea to explain the core size difference. But he says it is not needed to explain Jupiter's heavy-element enrichment, which, like Saturn's, could be due to numerous impacts by much smaller rocky objects.
NASA mulls sending part of space station to an asteroid
The International Space Station, the $100 billion outpost that has steadfastly orbited the Earth for more than a decade, may get a chance to explore new horizons when it retires in 2020. NASA is considering using part of it to build a spaceship that would be sent to an asteroid, while also mulling more exotic artificial-gravity designs reminiscent of Arthur C Clarke.
President Barack Obama jettisoned his predecessor's plan to return astronauts to the moon by 2020 and in April proposed to send them to an asteroid by 2025 instead.
NASA is now trying to work out the details of how to carry out such a mission and is hosting a conference on the topic in Washington, DC, on Tuesday and Wednesday.
On Tuesday, Brian Wilcox of NASA's Jet Propulsion Laboratory in Pasadena, California, presented (pdf) some of the ideas generated by the agency's engineers during brainstorming sessions in January and June.
President Barack Obama jettisoned his predecessor's plan to return astronauts to the moon by 2020 and in April proposed to send them to an asteroid by 2025 instead.
NASA is now trying to work out the details of how to carry out such a mission and is hosting a conference on the topic in Washington, DC, on Tuesday and Wednesday.
On Tuesday, Brian Wilcox of NASA's Jet Propulsion Laboratory in Pasadena, California, presented (pdf) some of the ideas generated by the agency's engineers during brainstorming sessions in January and June.
Mother ship Tranquility
One idea is to take apart the International Space Station, which is currently set to be retired in 2020, and use one of its crew compartments to build an asteroid-bound spacecraft in orbit instead of launching a similar capsule from Earth.
"These [asteroid] missions are going to occur at about the time that the space station is near retirement, so one has to wonder, 'Is it possible to use assets from the station as part of your mission complement?'" he said.
A space station compartment called Node 3 or Tranquility, which launched to the station aboard a shuttle mission in February, is particularly attractive for recycling because it has docking ports that could be used to attach to a pair of smaller, more nimble spacecraft. After arriving at the asteroid, astronauts could enter the smaller spacecraft and detach from the main ship in order to inspect the asteroid up close (see an illustration of the docked craft).
"These [asteroid] missions are going to occur at about the time that the space station is near retirement, so one has to wonder, 'Is it possible to use assets from the station as part of your mission complement?'" he said.
A space station compartment called Node 3 or Tranquility, which launched to the station aboard a shuttle mission in February, is particularly attractive for recycling because it has docking ports that could be used to attach to a pair of smaller, more nimble spacecraft. After arriving at the asteroid, astronauts could enter the smaller spacecraft and detach from the main ship in order to inspect the asteroid up close (see an illustration of the docked craft).
NASA seeks secrets of commercial moon landers
Swallowing its pride, NASA says it wants to learn from future commercial missions to the moon – and it is willing to pay up to $30 million for the privilege.
The space agency wants to take advantage of the flurry of activity sparked by the Google-funded Lunar X PrizeMovie Camera, says Michael Braukus, a spokesperson at NASA Headquarters in Washington, DC.
That competition, announced in 2007, offers $20 million for the first non-government entity to land a robotic rover on the moon, provided it occurs before the end of 2012. Twenty-one teams are vying for the prize (see a gallery showing some of the rover prototypes).
NASA believes it can learn from these missions, Braukus says. The agency is prepared to spend a total of $30 million – up to $10 million per mission – for data returned to Earth that would be useful for future human or robotic missions of its own, it has announced.
The space agency wants to take advantage of the flurry of activity sparked by the Google-funded Lunar X PrizeMovie Camera, says Michael Braukus, a spokesperson at NASA Headquarters in Washington, DC.
That competition, announced in 2007, offers $20 million for the first non-government entity to land a robotic rover on the moon, provided it occurs before the end of 2012. Twenty-one teams are vying for the prize (see a gallery showing some of the rover prototypes).
NASA believes it can learn from these missions, Braukus says. The agency is prepared to spend a total of $30 million – up to $10 million per mission – for data returned to Earth that would be useful for future human or robotic missions of its own, it has announced.
NASA is interested in technology that would allow spacecraft coming in for a landing to recognise hazards like boulders and automatically avoid them. If any of the Google Lunar X Prize vehicles incorporates this technology, NASA will pay for information about how it works and how well it performs.
Although NASA landed both robots and humans on the moon decades ago, it could benefit from designs that incorporate modern computers and other state-of-the-art technologies, says David Gump, president of Astrobotic Technology, a team based in Pittsburgh, Pennsylvania, that is competing for the prize.
"We went to the moon when TVs had vacuum tubes, cars had fins, and computers had punch cards," he says. "You have more computing power in your MP3 player than Apollo astronauts did going to the moon."
Although NASA landed both robots and humans on the moon decades ago, it could benefit from designs that incorporate modern computers and other state-of-the-art technologies, says David Gump, president of Astrobotic Technology, a team based in Pittsburgh, Pennsylvania, that is competing for the prize.
"We went to the moon when TVs had vacuum tubes, cars had fins, and computers had punch cards," he says. "You have more computing power in your MP3 player than Apollo astronauts did going to the moon."
Rethinking Einstein: The end of space-time
IT WAS a speech that changed the way we think of space and time. The year was 1908, and the German mathematician Hermann Minkowski had been trying to make sense of Albert Einstein's hot new idea - what we now know as special relativity - describing how things shrink as they move faster and time becomes distorted. "Henceforth space by itself and time by itself are doomed to fade into the mere shadows," Minkowski proclaimed, "and only a union of the two will preserve an independent reality."
And so space-time - the malleable fabric whose geometry can be changed by the gravity of stars, planets and matter - was born. It is a concept that has served us well, but if physicist Petr Horava is right, it may be no more than a mirage. Horava, who is at the University of California, Berkeley, wants to rip this fabric apart and set time and space free from one another in order to come up with a unified theory that reconciles the disparate worlds of quantum mechanics and gravity - one the most pressing challenges to modern physics.
Since Horava published his work in January 2009, it has received an astonishing amount of attention. Already, more than 250 papers have been written about it. Some researchers have started using it to explain away the twin cosmological mysteries of dark matter and dark energy. Others are finding that black holes might not behave as we thought. If Horava's idea is right, it could forever change our conception of space and time and lead us to a "theory of everything", applicable to all matter and the forces that act on it.
And so space-time - the malleable fabric whose geometry can be changed by the gravity of stars, planets and matter - was born. It is a concept that has served us well, but if physicist Petr Horava is right, it may be no more than a mirage. Horava, who is at the University of California, Berkeley, wants to rip this fabric apart and set time and space free from one another in order to come up with a unified theory that reconciles the disparate worlds of quantum mechanics and gravity - one the most pressing challenges to modern physics.
Since Horava published his work in January 2009, it has received an astonishing amount of attention. Already, more than 250 papers have been written about it. Some researchers have started using it to explain away the twin cosmological mysteries of dark matter and dark energy. Others are finding that black holes might not behave as we thought. If Horava's idea is right, it could forever change our conception of space and time and lead us to a "theory of everything", applicable to all matter and the forces that act on it.
Chlorine study suggests moon is dry after all
The moon's interior may not be that wet after all, despite some recent studies that have suggested otherwise. A new analysis of Apollo rocks backs the old idea of a waterless world.
For decades after the Apollo astronauts touched down on the desolate lunar surface, the moon was considered to be parched. But that view began to change in 2008, when researchers found water inside tiny spheres of lunar volcanic glass at concentrations calculated to be similar to those found in some terrestrial volcanic rocks.
Now, researchers led by Zachary Sharp at the University of New Mexico in Albuquerque say measurements of chlorine in a dozen Apollo samples suggest that the moon's interior has always been extremely dry, containing 10,000 to 100,000 times less water than Earth's.
For decades after the Apollo astronauts touched down on the desolate lunar surface, the moon was considered to be parched. But that view began to change in 2008, when researchers found water inside tiny spheres of lunar volcanic glass at concentrations calculated to be similar to those found in some terrestrial volcanic rocks.
Now, researchers led by Zachary Sharp at the University of New Mexico in Albuquerque say measurements of chlorine in a dozen Apollo samples suggest that the moon's interior has always been extremely dry, containing 10,000 to 100,000 times less water than Earth's.
Water-loving element
Sharp's team found the heavier version is relatively more abundant in the moon samples than on Earth, suggesting the moon rocks formed in a very dry environment.
That is because hydrogen atoms contained in water readily bond with the heavy chlorine isotope to form hydrochloric acid gas, which then leaks away into space – leaving more of the lighter isotope behind.
The moon sample measurements suggest that water was present at concentrations of 180 parts per billion in the lunar mantle. That's in line with water concentrations recently measured in a lunar mineral called apatite by Francis McCubbin of the Carnegie Institution of Washington in Washington DC. "These water contents [are] very dry in comparison to Earth and Mars," he says, suggesting that previous studies that argued for Earth-like water concentrations "are likely extrapolating their data a bit too far".
That is because hydrogen atoms contained in water readily bond with the heavy chlorine isotope to form hydrochloric acid gas, which then leaks away into space – leaving more of the lighter isotope behind.
The moon sample measurements suggest that water was present at concentrations of 180 parts per billion in the lunar mantle. That's in line with water concentrations recently measured in a lunar mineral called apatite by Francis McCubbin of the Carnegie Institution of Washington in Washington DC. "These water contents [are] very dry in comparison to Earth and Mars," he says, suggesting that previous studies that argued for Earth-like water concentrations "are likely extrapolating their data a bit too far".
Giant balloons could clear out space junk
Dead satellites pose a hazard to other orbiting spacecraft. In 2009, one of them wandered into the path of a still-functioning satellite, destroying both craft and spawning thousands of pieces of new space junk.
One way to prevent such collisions is to have satellites fire their own engines at the end of their useful lives in order to push themselves into Earth's atmosphere, where they would be incinerated. But this requires launching them with extra fuel, adding mass that drives up the cost of launch.
Balloons would be a cheaper way to solve the problem, says a team of engineers. Kristin Gates of the Global Aerospace Corporation in Altadena, California, presented the idea on Tuesday at the Astrodynamics Specialist conference in Toronto, Canada.
