Ancient Earth hammered by double space impact

We've all seen the films where an asteroid hurtles towards our planet, threatening civilisation.

What's less well known is that menacing space rocks sometimes come in twos.

Researchers have outlined some of the best evidence yet for a double space impact, where an asteroid and its moon apparently struck Earth in tandem.

Using tiny, plankton-like fossils, they established that neighbouring craters in Sweden are the same age - 458 million years old.

Details of the work were presented at the 45th Lunar and Planetary Science Conference in The Woodlands, Texas, and the findings are to be published in the Meteoritics and Planetary Science journal.

However, other scientists cautioned that seemingly contemporary craters could have landed weeks, months or even years apart.

A handful of possible double impacts (or doublets) are already known on Earth, but Dr Jens Ormo says there are disputes over the precision of dates assigned to these craters.

"Double impact craters must be of the same age, otherwise they could just be two craters right next to each other," the researcher from the Centre for Astrobiology in Madrid, Spain, told BBC News.

Dr Ormo and his colleagues studied two craters called Lockne and Malingen, which lie about 16km apart in northern Sweden. Measuring about 7.5km wide, Lockne is the bigger of the two structures; Malingen, which lies to the south-west, is about 10 times smaller.

Binary asteroids are thought to form when a so-called "rubble pile" asteroid begins to spin so fast under the influence of sunlight that loose rock is thrown out from the object's equator to form a small moon.

Telescope observations suggest that about 15% of near-Earth asteroids are binaries, but the percentage of impact craters on Earth is likely to be smaller.

Only a fraction of the binaries that strike the Earth will have the necessary separation between the asteroid and its moon to produce separate craters (those that are very close together will carve out overlapping structures).

Calculations suggest around 3% of impact craters on Earth should be doublets - a figure that agrees with the number of candidates already identified by researchers.

The unusual geological characteristics of both Lockne and Malingen have been recognised since the first half of the 20th Century. But it took until the mid-1990s for Lockne to be formalised as a terrestrial impact crater.

In the last few years, Dr Ormo has drilled about 145m down into the Malingen structure, through the sediment that fills it, down to crushed rocks known as breccias and deeper, reaching the intact basement rock.

Lab analysis of the breccias revealed the presence of shocked quartz, a form of the quartz mineral that is created under intense pressures and is associated with asteroid strikes.

This area was covered by a shallow sea at the time of the Lockne impact, so marine sediments would have begun to fill in any impact craters immediately after they were created.

One-two punch

Dr Ormo's team set out to date the Malingen structure using tiny fossilised sea creatures called chitinozoans, which are found in sedimentary rocks at the site.

Their method, known as biostratigraphy, allows geologists to assign relative ages to rocks based on the types of fossil creatures found within them.

The results revealed the Malingen structure to be the same age as Lockne - about 458 million years old. This seems to confirm that the area was rocked by a double asteroid strike during the Ordovician Period.

Dr Gareth Collins, who studies impact cratering at Imperial College London, and was not involved with the research, told BBC News: "Short of witnessing the impacts, it is impossible to prove that two closely separated craters were formed simultaneously.

"But the evidence in this case is very compelling. Their proximity in space and consistent age estimates makes a binary-impact cause likely."

Simulations suggest the asteroid that created Lockne was some 600m in diameter, while the one that carved out Malingen was about 250m. These measurements are somewhat larger than might be suggested by their craters because of the mechanics of impacts into marine environments.

Dr Ormo added that Malingen and Lockne were just the right distance apart to have been created by a binary. As mentioned, if two space rocks are too close, their craters will overlap. But to qualify as a doublet, the craters can't be too far apart, because they will exceed the maximum distance at which an asteroid and its moon can stay bound by gravitational forces.

"The Lockne impactor was big enough to generate what's known as an atmospheric blow-out, where you blow away the atmosphere above the impact site," said Dr Ormo.

This can cause material from the asteroid strike to spread around the globe, as happened during the huge Chicxulub impact thought to have killed off the dinosaurs 66 million years ago.

The Ordovician event wasn't powerful enough for that material to be traced, as it would have been very dilute in the atmosphere. But the impact would have had regional effects; for example, any sea creatures unlucky enough to be swimming nearby would have been instantly vaporised.

Other candidate double impact craters include Clearwater East and West in Quebec, Canada; Kamensk and Gusev in southern Russia; and Ries and Stenheim in southern Germany.

Source: BBC News

Saturn’s Largest Moon Would Host Really, Really Weird Life

Ah, Titan. Saturn’s largest, haziest moon had a brief starring role in last night’s Cosmos: A Spacetime Odyssey. Toward the end of the episode, Neil DeGrasse Tyson eases his spaceship into one of the moon’s dark, oily seas. He wanted to see what was down there—more specifically, what kind of life might be down there.

After spending most of an hour describing the evolution of life on Earth, it was time to turn toward alien terrains and chemistries—to a place that, while not so very far away, could host some very, very strange lifeforms.

“There’s a world I want to take you to, a world far different from our own, but one that may harbor life. If it does, it promises to be unlike anything we’ve ever seen before,” Tyson says, in the episode.

Titan is deceptively Earth-like. It has a thick, nitrogen atmosphere. Seasonal rainstorms produce wet patches that are visible from orbit. It has lakes. In fact, Titan is the only place in the solar system, besides Earth, with stable liquids on its surface. Those liquids flow through rivers and streams, pool into lakes and seas, sculpt shorelines and surround islands, just like on Earth.

But Titan’s puddles aren’t filled with water—the moon is soaked in hydrocarbons. Methane and ethane, compounds that are gassy on Earth, are liquid on Titan’s frigid surface. Here, temperatures hover around -179 Celsius (or -290 Fahrenheit). It’s so cold that water ice is rock-hard—in fact, the rocks littering the moon’s surface are made from water. Water is everywhere on Titan, but it’s locked in a state that’s inaccessible for life-sustaining chemistries.

Ask an astrobiologist about the prospect of finding life on Titan, and they’ll say the shrouded, orange moon is the place to go if you’re looking for bizarre life. Life that’s not at all like what we know on Earth. Life that, instead of being water-based, uses those slick, liquid hydrocarbons as a solvent. Life that, if we find it, would demonstrate a second genesis—a second origin—and be suggestive of the ease with which life can populate the cosmos.

Life that’s worth taking a chance to find?

“We will never know if liquid water is the only special solvent in which life can form and propagate unless we go and sample these damn lakes and seas,” planetary scientist Jonathan Lunine of Cornell University said during a recent astrobiology conference. Lunine has spent years studying Titan; at one point, he and his colleagues designed a spacecraft that could land on the moon and float in one of its hydrocarbon seas [pdf].

Thinking about life on Titan isn’t new. In the 1970s, Carl Sagan and chemist Bishun Khare, then at Cornell University, were already publishing papers describing the organic chemistry that might be taking place on the Saturnian moon. At that point, though, the large bodies of liquid on the moon’s surface hadn’t yet been spotted, so Sagan and Khare were thinking about the types of reactions that might be taking place in the moon’s atmosphere (in 1982, Sagan and Stanley Dermott proposed that such lakes might exist). Later, Sagan and Khare would show it was possible to make amino acids using the elements found in the moon’s haze.

In the 1990s, the Hubble space telescope offered hints of a wet world, but it wouldn’t be until NASA’s Cassini mission that scientists got a good look at the moon. In 2004, the spacecraft began peering beneath Titan’s cloudy shroud; in 2005, Cassini sent the Huygens probe parachuting through the haze to a spot on Titan’s equator. Data sent back to Earth revealed a world that looks very much like ours—just with a completely different chemistry.

What that different chemistry means for the possibility of life is still speculative.

“Think about life on Earth—we’re all either in water or we’re fancy bags of water,” says astrobiologist Kevin Hand of the Jet Propulsion Laboratory. “On Titan, life in the lakes would be ‘bags’ of liquid methane and/or ethane. That 90[Kelvin] liquid would be the solvent and then whatever is dissolved into the lakes would be the material that’s used to build the other components needed for life, and to power metabolism.”

Powering metabolism is tricky at those temperatures, though, which is one of the reasons why some scientists are hesitant to focus on sending a probe to Titan. Nonetheless, astrobiologists are studying the reactions and pathways that life might use to gain some traction on Titan—including things like breathing hydrogen and eating acetylene.

“Which elements are easy and which elements are hard to access if you’re a ‘weird’ microbe living in Titan’s lakes?” Hand says. “At this point we don’t really know—work is ongoing.”

I had a few questions after watching the Cosmos depiction of Titan’s alien seas. First, if I were a weird life form on Titan, would I be able to see Saturn through Titan’s hundreds of kilometers of haze? Or would the most spectacular planetscape in the solar system be hidden behind that smoggy curtain?

“Even with the human eye, Saturn would be visible as a faint, bright-ish blob in the nighttime haze,” Lunine says. “And if you have eyes that extend even a bit beyond human sight into the nearest part of the infrared, the ringed world would be clearly seen floating ethereally in the skies of Titan.”

Phew.

Second, the scene with Tyson in the spacecraft shows a craggy, chaotic seafloor, with things that look like hydrothermal vents. How much do we really know about Titan’s seafloors?

Turns out, we know quite a lot about Titan’s seashores, and slightly less about its seafloors. Until now, scientists had mostly used seashore shapes and surrounding topography to infer what the seafloors might be like. But in May 2013, Lunine and his colleagues aimed the Cassini spacecraft’s radar at the depths of Ligeia Mare, the second largest sea on Titan (Kraken Mare, which Tyson took a swim in, is the largest). Using the radar data, the team created a map of the sea’s floor—its bathymetry—and saw that Ligeia Mare plunges to a depth of 160 meters (524 feet). The northern seabed is gentler and smoother than the southern, which is riven with flooded valleys and punctuated by steep peaks.

Getting the depth profile meant that scientists could estimate how much liquid hydrocarbon rests in Ligeia Mare: As much as 100 times more than the oil and gas reserves on Earth combined.

Next up? Peering into the depth of Kraken Mare, which covers an area of at least 400,000 square kilometers, or approximately equal to the size of Germany. “Kraken appears to consist of no fewer than three distinct basins, each about the size of Ligeia Mare,” Lunine says. “So there’s a lot of sea to see on Titan.”

Source: NATIONAL GEOGRAPHIC

Cosmic inflation: 'Spectacular' discovery hailed

Scientists say they have extraordinary new evidence to support a Big Bang Theory for the origin of the Universe.

Researchers believe they have found the signal left in the sky by the super-rapid expansion of space that must have occurred just fractions of a second after everything came into being.

It takes the form of a distinctive twist in the oldest light detectable with telescopes.

The work will be scrutinised carefully, but already there is talk of a Nobel.

"This is spectacular," commented Prof Marc Kamionkowski, from Johns Hopkins University.

"I've seen the research; the arguments are persuasive, and the scientists involved are among the most careful and conservative people I know," he told BBC News.

The breakthrough was announced by an American team working on a project known as BICEP2.

This has been using a telescope at the South Pole to make detailed observations of a small patch of sky.

The aim has been to try to find a residual marker for "inflation" - the idea that the cosmos experienced an exponential growth spurt in its first trillionth, of a trillionth of a trillionth of a second.

Theory holds that this would have taken the infant Universe from something unimaginably small to something about the size of a marble. Space has continued to expand for the nearly 14 billion years since.

Inflation was first proposed in the early 1980s to explain some aspects of Big Bang Theory that appeared to not quite add up, such as why deep space looks broadly the same on all sides of the sky. The contention was that a very rapid expansion early on could have smoothed out any unevenness.

But inflation came with a very specific prediction - that it would be associated with waves of gravitational energy, and that these ripples in the fabric of space would leave an indelible mark on the oldest light in the sky - the famous Cosmic Microwave Background.

The BICEP2 team says it has now identified that signal. Scientists call it B-mode polarisation. It is a characteristic twist in the directional properties of the CMB. Only the gravitational waves moving through the Universe in its inflationary phase could have produced such a marker. It is a true "smoking gun".

Speaking at the press conference to announce the results, Prof John Kovac of the Harvard-Smithsonian Center for Astrophysics, and a leader of the BICEP2 collaboration, said: "This is opening a window on what we believe to be a new regime of physics - the physics of what happened in the first unbelievably tiny fraction of a second in the Universe."

The signal is reported to be quite a bit stronger than many scientists had dared hope. This simplifies matters, say experts. It means the more exotic models for how inflation worked are no longer tenable.

The results also constrain the energies involved - at 10,000 trillion gigaelectronvolts. This is consistent with ideas for what is termed Grand Unified Theory, the realm where particle physicists believe three of the four fundamental forces in nature can be tied together.

But by associating gravitational waves with an epoch when quantum effects were so dominant, scientists are improving their prospects of one day pulling the fourth force - gravity itself - into a Theory of Everything.

The sensational nature of the discovery means the BICEP2 data will be subjected to intense peer review.

It is possible for the interaction of CMB light with dust in our galaxy to produce a similar effect, but the BICEP2 group says it has carefully checked its data over the past three years to rule out such a possibility.

Other experiments will now race to try to replicate the findings. If they can, a Nobel Prize seems assured for this field of research.

Who this would go to is difficult to say, but leading figures on the BICEP2 project and the people who first formulated inflationary theory would be in the running.

One of those pioneers, Prof Alan Guth from the Massachusetts Institute of Technology, told the BBC: "I have been completely astounded. I never believed when we started that anybody would ever measure the non-uniformities of the CMB, let alone the polarisation, which is now what we are seeing.

"I think it is absolutely amazing that it can be measured and also absolutely amazing that it can agree so well with inflation and also the simplest models of inflation - nature did not have to be so kind and the theory didn't have to be right."

British scientist Dr Jo Dunkley, who has been searching through data from the European Planck space telescope for a B-mode signal, commented: "I can't tell you how exciting this is. Inflation sounds like a crazy idea, but everything that is important, everything we see today - the galaxies, the stars, the planets - was imprinted at that moment, in less than a trillionth of a second. If this is confirmed, it's huge."

Source: BBC News