Diamond has been subjected to the wrath of the world’s largest laser, which compressed the stone to greater pressures than it has ever experienced on Earth. The results hint at the mysterious conditions deep inside giant planets.

The dense atmospheres of gas giants Jupiter and Saturn contain carbon. Chemical modelling suggests pressure deep inside the planets would crush it into a rain of diamond chips and perhaps create chunks of diamond large enough to impress even the Kardashians. But until now, no one had been able to replicate such pressures on Earth and test the notion.

“Our experiment provides the first actual data of diamonds under such high pressure,” says at the Lawrence Livermore National Laboratory in California.

Using the National Ignition Facility (NIF) at Livermore, Smith’s team bombarded tiny targets with 176 laser beams to put the squeeze on diamond. The trick was to compress the stone as slowly as possible, says Smith.

Slow pressure

“If you compress it too fast, it gets very hot and melts, and you’d just have liquid carbon,” he says. To avoid this, the team used a technique called ramp compression, which NIF engineers originally designed to implode fuel capsules for research into nuclear fusion power.

The team fixed a diamond inside a hole cut in a small gold cylinder, and then precisely timed laser pulses to strike the cylinder’s interior walls. This caused the gold to emit an avalanche of X-rays that bombarded the stone, triggering powerful compression waves inside it.

From start to finish, each run of the experiment lasted only about 20 nanoseconds – much faster than the blink of an eye, but slow enough not to melt the stone. During that short time, the team was able to squeeze diamond to pressures of up to 5 terapascals – about 50 million times the atmospheric pressure on Earth’s surface. The team’s data can now be used to improve models of gas giants and the suspected diamond in their depths.

Diamond planets

at the California Institute of Technology in Pasadena called the experiment an impressive achievement. “These findings contribute to an ongoing effort to put together an understanding of the cores of giant planets,” says Stevenson.

Nikku Madhusudhan at the University of Cambridge says the results can also aid our understanding of the insides of “diamond planets”. These exoplanets are rocky like Earth but are rich in carbon rather than silica, and may contain large layers of diamond. His team reported on models of such a world, dubbed 55 Cancri e, in October 2012.

“The present result is extremely valuable, because we can now use direct experimental data to model the deep interiors of carbon-rich planets,” says Madhusudhan.

Journal reference: Nature, DOI: 10.1038/nature13526

It’s a cool planet in a tight spot. A frigid world about 3000 light years away offers the first evidence that rocky planets can form in Earth-like orbits, even when they are jammed into close double-star systems. Although this planet probably cannot support life as we know it, the discovery greatly expands the places we can look for potentially habitable worlds outside our solar system.

In a binary star system the two partners are locked in an orbital embrace. Astronomers have found a handful of planets that orbit both partners in close binary pairs. But no one was convinced that a planet could orbit just one star at a sufficient distance to host life.

“Most stars are part of binary systems, and a significant fraction of these are close binary systems, so if you want to maximise the places you can look for habitable planets, you’re going to want to look at these close binaries as well,” says at Ohio State University (OSU) in Columbus.

Gaudi and his team used a technique called gravitational microlensing to study a binary system with two red dwarfs, small stars that are dimmer than the sun. The distance between the stars is about 10 to 15 times that of Earth and the sun. The team found a planet about twice the mass of Earth orbiting just one of the two stars, at about the same distance as we are to our home star.

Solar system snub

Some scientists argue that the planet formation process would get too disrupted if a star has a tight stellar companion, and the further it is from the star, the more difficult it would be for planets to form. “But this discovery argues that yes, indeed, at least in this system of two red dwarfs, you can form planets at these sorts of longer distances,” says Gaudi.

at the Paris Institute of Astrophysics in France called the newfound planet an important discovery. “This shows more than ever that our solar system is not the paradigm in our galaxy,” says Beaulieu.

While the planet is most likely rocky based on its mass, its surface is a frigid -213°C. That’s because, at its orbital distance, it does not get enough heat from its dim host star. But the same planet orbiting a sun-like star in a binary system would be in the habitable zone, where conditions could support liquid water and perhaps life as we know it.

Robust detection

The discovery was announced the same week that other scientists sounded a note of caution on exoplanet finds. An analysis led by astronomer Paul Robertson at Pennsylvania State University concluded that Gliese 581 d and g, two of the first potentially habitable worlds ever found, are actually illusions created by sunspots on the parent star.

Gaudi’s co-author Andrew Gould, also at OSU, says his team’s evidence for the existence of their frozen planet is airtight. Microlensing detects planets by watching how their gravity affects the light of a distant background star. As one star passes in front of another, as seen from Earth, light from the background star is gravitationally bent and magnified, projecting images next to the foreground star. But if the foreground star hosts a planet, the world’s gravity can sometimes eliminate one of these images. “The planet isn’t blocking the background star’s light. It’s just that the mathematics of focusing is disrupted by the planet’s gravity,” he says.

“There’s absolutely no doubt that what we’ve detected is a rocky planet in a binary star system,” adds Gould. “Ten thousand years from now, people will go visit this system and find out that it’s exactly what we say it is.”

Beaulieu also expressed confidence in the frozen exoplanet discovery: “In the case of the planet announced by Gould’s team, stellar variability could not mimic the observed signal. This is a very robust detection.”

Journal reference:

ASTEROIDS have a killer reputation, taking the blame for death and destruction on massive scales. But results fresh from a space experiment show ancient impacts may have been vital for cradling the first life on Earth.

Several hundred million years after Earth formed, when life was emerging, our young planet had an atmosphere, oceans and primordial continents. But it did not yet have an ozone layer to shield the surface from the sun’s harshest ultraviolet rays. Because UV radiation can damage DNA, that would have made it difficult for any but the most extreme forms of life to survive.

In 2002, a team led by astrobiologist at the University of Edinburgh, UK, discovered a unique group of cyanobacteria in Haughton crater in northern Canada. The bacteria live in tiny pores and cracks of near-translucent rock, formed during the intense heat and pressure of the asteroid or comet impact that made the crater, about 23 million years ago.

Cockell’s team found that the altered crystal structure of the rocks absorbed and reflected UV rays. This suggests the rock could shield the bacteria while letting enough sunlight through to allow them to photosynthesise.

Complex life evolved long before the crater formed, but there have been countless space rock strikes in Earth’s history. “That raised a whole bunch of questions about whether the unique geology of impact craters could have been a good UV shield on the early Earth,” says , a member of Cockell’s lab.

Bryce and her colleagues got an unusual chance to test the notion in 2008. As part of the European Space Agency’s EXPOSE mission, the team sent some of the crater rocks to the International Space Station (ISS). Before lift-off, they grew samples of the cyanobacteria either in plain glass discs or in discs of the impact-altered rock. Once in space, these discs were mounted on the outside of the ISS, where they were left exposed for nearly two years.

The bacteria received radiation doses far more intense than conditions on early Earth. When the samples were returned to the lab, the microbes in the glass discs were dead.

“However, when we cracked open the impact-shocked rocks we were able to detect chemical signals of life and rejuvenate the dormant cyanobacteria,” says Bryce. The team’s findings provide the first direct evidence that crystal cocoons formed by impacts might have been radiation-proof cradles for early life (International Journal of Astrobiology, ).

at the University of Western Ontario in Canada says the ISS experiment is a fantastic proof of concept. “Until now, we weren’t sure if any of these cells would remain viable in that type of environment.”

Asteroid and comet impacts are ubiquitous in the solar system, so Pontefract thinks impacts could have helped kick-start life on rocky planets and then shielded whatever emerged. Crater rocks could provide refuges even now for life on other planets, such as Mars, she says.

This article appeared in print under the headline “Space rock strikes protected early life”

Firing lasers at supercooled water has given us a first glimpse into a “no-go area” that has never been explored before.

Water is an unusual liquid with many strange properties. For one, below 4 °C it gets less dense as the temperature falls, which is why ice floats. Even weirder, many of water’s unique properties appear to become exaggerated the more it is cooled.

“People have wondered for a long time why water behaves this way, and what will happen if you supercool it down to really low temperatures,” says at Stanford University in California. One controversial idea is that water starts to transform at about -45 °C, entering a “bulk liquid” state in which two different densities of water can coexist.

“If you had a glass of bulk liquid water, it would separate into two liquids, one with a higher density that will sink to the bottom of the glass, and a lower density one that will float on top,” says Nilsson. But oddities of liquid water at very low temperatures have long been impossible to study, because below about -45 °C, ice crystals quickly develop in the drops, clouding the measurements.

Droplet explodes

Nilsson and his team found a way to take snapshots of liquid water cooled to -46 °C. They shot a jet of liquid through a vacuum, creating water drops that rapidly chilled due to evaporation. Some of the drops remained ice-free for about a millisecond – just long enough for the team to hit them with X-ray laser pulses.

“We are only shooting one laser pulse per droplet, and the X-ray is so intense that the droplet explodes,” says Nilsson. When the laser encounters a water drop, its light is scattered, creating patterns that reveal the drop’s structure and density. Early results show that water gradually evolves towards a low-density liquid as it cools, and that the change accelerates once it reaches the previously unexplored temperature range.

Pablo Debenedetti at Princeton University says the new technique is clever and elegant, adding that it will pave the way for further studies of supercooled water. In addition to uncovering new water physics, fresh insights could have key practical applications.

“Large inventories of supercooled water exist as tiny droplets in high-altitude clouds,” says Debenedetti. “The properties of supercooled water are therefore not only of inherent scientific interest, but are also very important in atmospheric science.”

Journal reference: Nature, DOI: 10.1038/nature13266

Clarification, 2 July 2014: When this article was first published, we did not make clear that water decreases in density only below 4 °C

Snuggle up, Pluto. The cold and distant dwarf planet may share a thin cloak with its largest moon.

Simulations show that nitrogen from Pluto’s atmosphere could be flowing over to its moon Charon. If this is confirmed, Pluto and Charon would be the first known example of a planet and its moon sharing an atmosphere.

Charon is almost half the size of Pluto and orbits much closer to the dwarf planet than our moon does to Earth. Studies in the 1980s suggested the two bodies might be able to exchange gases, but that work assumed Pluto’s atmosphere is made up primarily of methane, and that the gas was escaping at relatively high speeds.

Using telescopes on Earth, astronomers took a closer look at the light coming from Pluto and scanned it for clues about the planet’s composition. It turns out that Pluto’s atmosphere consists mainly of nitrogen, a heavier gas than methane, and that the escape rate is lower. “People thought that even if Charon did gain an atmosphere through this process, it was too thin to ever detect,” says at the University of Virginia in Charlottesville.

Puffy atmosphere

Now Johnson and his team have updated models of Pluto’s upper atmosphere, taking into account the way the nitrogen molecules would move and collide with each other. Their simulations show that the dwarf planet’s atmosphere could be warmer than thought, and so may be up to three times as thick as previously predicted.

That means it may extend far enough into space for some gas to be pulled across by Charon’s gravity, giving it a tenuous covering. NASA’s New Horizons spacecraft is set to fly through the Pluto system in July 2015. It is carrying instruments that could detect any atmosphere that exists around Charon and figure out what it is made of, says mission leader Alan Stern at the Southwest Research Institute in Boulder, Colorado.

Knowing the identities and concentrations of any gases around Charon will be essential for determining whether the moon’s atmosphere is borrowed from Pluto or created by some other means. It is also possible that gas from Charon’s interior is escaping through geysers or vents to create a thin atmosphere. And Stern’s latest study suggests that comet impacts on the moon’s surface could release clouds of gas to create a transient atmosphere.

But if Pluto and Charon do share a shroud, the system could provide a real example of gas transfer between two bodies, helping us refine models of the phenomenon elsewhere in the galaxy.

“It’s thought to happen all the time in astronomy, such as in the case of binary stars or exoplanets located close to their stars,” says Johnson. “Calculations and computer models are one thing. But here we have a spacecraft that’s going to fly by and directly test our simulations, which is quite exciting.”

Journal references: Icarus, and

KILLING Pluto was only the beginning. The dwarf planet Eris, named for the Greek goddess of strife, could also bring down the most popular explanations for dark matter and dark energy.

Many galaxies appear to have stronger gravity – and thus more mass – than can be explained by their visible matter alone. Overly massive galaxies are most often attributed to dark matter, an invisible substance that interacts with matter through gravity. To date, though, no one has directly detected dark matter particles.

But a well-established notion in physics could hold another explanation for their size. This says that empty space is really a frothy, turbulent sea full of virtual particles – matter and antimatter that spring in and out of existence so fast that we can’t see them.

Though they are tiny, quantum objects, Dragan Hajdukovic, a physicist at CERN near Geneva, Switzerland, thinks these bubbling particles may have opposing gravitational charges, similar to electrical charges. In the presence of a gravitational field, the particles would generate a secondary field, which, in the case of galaxies, could explain the mass discrepancy.

Hajdukovic’s theory could also explain dark energy, the baffling force thought to be driving the universe apart at an accelerated pace. If virtual particles have gravitational charges, then space-time itself is imbued with a small charge that could be causing objects in the universe to speed away from each other.

To test whether quantum-scale gravity is at work, Hajdukovic plans to borrow a trick from Einstein (see diagram). Due to gravitational effects in the solar system, such as the tug of other planets, Mercury’s oval-shaped path around the sun slowly turns, or precesses. In the 1800s astronomers noticed that this happens at a different rate than predicted by Newtonian physics. Einstein showed that the sun’s mass creates a curvature in space-time that affects Mercury enough to explain the difference, lending credence to his theory of general relativity.

Hajdukovic’s quantum gravity might create a similar discrepancy with more distant orbiting bodies, he says – which is where Eris and its moon Dysnomia come in.

Best known for depriving Pluto of planethood by showing that there are many similar bodies in orbit beyond Neptune, Eris’s great distance from the sun means the effects of general relativity become negligible. Newtonian physics should dominate, putting Dysnomia’s precession rate around Eris at 13 arc seconds per century. But if quantum gravity exists, the rate should be -190 arc seconds per century, Hajdukovic calculates (Astrophysics and Space Science, ).

He thinks the required measurements could be made from Earth using existing observatories. “Einstein was lucky that there is a planet so close to the sun as Mercury,” he says. “My theory might be lucky that there are trans-Neptunian objects allowing astronomical tests.”

of Longwood University in Farmville, Virginia, is sceptical that Earth-based tests would be sensitive enough to pick up the effect. Still, he praises Hajdukovic for going beyond the party line. “It’s always good when people are willing to go a little bit out on a limb.”

Editorial: “When it comes to defence, our priorities are wrong“

A LACK of cash could end the only survey dedicated to searching the southern skies for Earth-grazing comets and asteroids. That would create a blind spot in our global view of objects that could cause significant devastation should they hit Earth.

The uses images from the Siding Spring observatory in Australia as part of the global , an effort to discover and track potentially dangerous near-Earth objects. Astronomers sift through virtually identical images of the sky, looking for moving objects.

Catalina uses a range of northern hemisphere telescopes – and the Sliding Spring Survey. But in October, Catalina cut off cash to the survey due to growing costs, caused partly by changes in the exchange rate between the Australian and US dollars. That decision was “very difficult”, says Steve Larson, who heads Catalina.

Since then, the southern survey has been limping along with temporary funding from the Australian National University in Canberra, but the extension is set to expire at the end of July, says survey operator Rob McNaught.

The leftover building blocks of planets, near-Earth objects orbit the sun in highly elliptical orbits, and sometimes graze or hit Earth. Seeing an asteroid before it hits could save lives by providing time to evacuate a region. “Given the very best circumstances, you can predict an impact to 1 second and 1 kilometre,” says McNaught. “There’s no other natural disaster that you can do that for.”

“Given the very best circumstances, you can predict an impact to 1 second and 1 kilometre”

But without a southern lookout, any object approaching Earth from below 30 degrees latitude would be invisible, says Tim Spahr of the International Astronomical Union’s in Cambridge, Massachusetts.

That won’t be much of a problem for massive objects like the asteroid that wiped out the dinosaurs. These are rare and astronomers estimate they have already found and are tracking 94 per cent of them via software models. The worry is asteroids about 30 metres wide, which could flatten a city. Such a hit is blamed for the Tunguska event in 1908, which levelled a 2000-square-kilometre swathe of forest in Siberia.

There are around a million of these smaller objects, making them the most likely to hit Earth, yet locations for less than 1 per cent of them are known. Without a southern telescope, “you could easily get blindsided by one of these”, says , of NASA’s Near-Earth Object Program at the Jet Propulsion Laboratory in Pasadena, California. “Whether that’s a 1 per cent, 10 per cent or 20 per cent increased risk, I don’t know. But it is an increased risk.”

What’s more, as most asteroids and comets are tracked across both hemispheres, those discovered in the north could get lost without follow-up from the south. There will also be objects seen in the north that could have been spotted sooner in the south, giving more time to prepare.

McNaught estimates that the survey needs about US$180,000 per year, plus a one-off $30,000 to fix the observatory dome. “I really wish I could tell you that the chances are very good that we’ll be able to find some money, but I can’t,” says , who heads the team at Australian National University that is providing temporary funding.

If the survey shuts down, there won’t be another ground telescope capable of fulfilling its duties until the 2020s, when the Large Synoptic Survey Telescope is due to go online in Chile.

The non-profit B612 Foundation plans to build a space telescope to scan for small asteroids but it won’t launch until at least 2017 (see “The people’s asteroid defence“). “In the interim, having one eye closed when the cost of having it open is so little seems to be penny wise and pound foolish,” says B612 co-founder Russell Schweickart, a former NASA astronaut.

Please try to resist the childish jokes, but the fact is that the odd tilt of Uranus may be the result of a particularly large moon.

Uranus spins on an axis almost parallel with the plane of the solar system, rather than perpendicular to it – though why it does this nobody knows. One theory is that the tilt is the result of a collision with an Earth-sized object, but this “hasn’t succeeded in explaining much of anything”, says Ignacio Mosqueira of the SETI Institute in Mountain View, California. Why, for example, are the orbits of Uranus’s 27 known moons not also tilted?

Now and at the Paris Observatory in France have come up with another explanation: Uranus may once have had an unusually massive extra moon. If the moon had 1 per cent of the mass of Uranus – and orbited at a certain distance – it would slightly unbalance the planet and increase its wobble about its axis. After about 2 million years, the wobbling could have become exaggerated enough to tip the planet on its side, their model has shown ().

The moon may since have been ejected by the tug of another planet passing nearby. Its fate is unclear, but it may have crashed into another gas giant if it is not still roaming the solar system.

at the Southwest Research Institute in Colorado finds the theory plausible but points out there is no evidence for the extra moon other than the effect Boué and Laskar suggest it has had on Uranus’s orientation.

Mars’s distinctive red hue may be the result of thousands of years of wind-borne sand particles colliding with one another – and not rust, a new study argues.

żěè¶ĚĘÓƵs generally agree that Mars’s red colour is caused when a dark form of iron called magnetite oxidises into a reddish-orange form called haematite.

Just how the transformation came about is a matter of debate. Many researchers say water caused the oxidation. But some argue that hydrogen peroxide and ozone, which might be created when ultraviolet light breaks down carbon dioxide and oxygen in the Martian atmosphere, could be to blame.

Now, planetary scientist Jonathan Merrison of Aarhus University in Denmark and colleagues say the trigger may be wind.

Clothes dryer

To simulate the wind transport of sand in the laboratory, they sealed tiny particles of magnetite and quartz – a mineral present on both Earth and Mars – in a glass flask filled with carbon dioxide. For several months, they mechanically tumbled it like clothes in a dryer, noticing that the flask got redder over time as more of the magnetite changed into haematite.

The team suspects that the constant collisions split the quartz grains apart, exposing chemically reactive surfaces that oxidise the particles of magnetite.

On Mars, this tumbling could be caused by winds in dust devils and global dust storms, Merrison told żěè¶ĚĘÓƵ.

No quartz dust?

Assuming there was not enough water on early Mars to rust the planet, the wind might have taken just a few hundred thousand years to transform it from a charcoal colour to red, the team says.

Joel Hurowitz of NASA’s Jet Propulsion Laboratory in California, who was not involved in the study, called the work “interesting” but said more research is necessary to test its conclusions.

Quartz has been detected in the bedrock in some regions of Mars. But it is a relatively hard mineral that may not be easily broken down into sand by the wind on Mars, he says, adding that NASA’s twin Mars rovers have not found much of it in the sand and dust during their travels.

Journal reference: (doi:10.1016/j.icarus.2009.09.004)