Phase III – Stealth Is.

But if NASA and DARPA – the agency responsible for some of the early innovations that led to the Internet – have their way, in the next 100 years, a spaceship would stand ready to visit another star.

The two agencies have teamed up on a 1 million-dollar project called the 100-Year Starship Study to begin contemplating technologies and organizational strategies to make the mission happen.

For three days, scientists from universities, NASA centers and private institutions will discuss the merits of fusion versus nuclear thermal propulsion, as well as the social and psychological implications of sending humans on a one-way mission to the stars.

Religious and philosophical aspects of interstellar travel will also be discussed.

“The 100-Year Starship is about more than building a spacecraft or any one specific technology,” Fox News quoted DARPA officials as writing in a statement.

“Through this effort, DARPA seeks to inspire several generations to commit to the research and development of breakthrough technologies and cross-cutting innovations across myriad disciplines,” they added.

But a note to would-be space travellers: It’s too soon to sign up for the trip.

“Neither DARPA nor NASA are actually building a 100-Year Starship,” DARPA officials wrote.

As children, we overproduce the connections – synapses – between brain cells. During puberty the body carries out a kind of topiary, snipping away some synapses while allowing others to strengthen. Over a few years, the number of synapses roughly halves, and the adult brain emerges.

Or so we thought. Pasko Rakic at Yale University and colleagues at the University of Zagreb, Croatia, and the VU University Medical Center in Amsterdam, the Netherlands, have now found that the brains of adults in their 20s are still subject to synaptic pruning.

Rakic’s team analysed post-mortem tissue from a brain region called the prefrontal cortex (PFC) in 32 people aged between 1 week old and 91 years. Specifically, they calculated the density of dendritic spines – the tiny projections that protrude from the neuron’s long dendrites, each of which facilitates communication with other neurons through a synapse.

As expected, Rakic’s team found that spine density increased rapidly during infancy, reaching a peak before the 9th birthday. It then began to fall away as pruning began. Intriguingly, though, spine density did not plateau after adolescence, as might have been expected, but continued to fall gradually until the late 20s.

Rakic says the result could be good news for those hoping to gain new skills in their third decade. The period of pruning is associated with a heightened ability to learn – whether that is in picking up language skills or understanding new concepts, he says. “You should not give up learning just because you’re in your 20s – it isn’t too late,” he says.

The current best theory for the origin of the Moon is the “giant impact” model. This holds that a Mars-sized object, sometimes called Theia, once shared Earth’s orbit and collided with it over four billion years ago, and the remains of this cataclysm ultimately formed into the Moon. Now it appears that that cosmic drama repeated itself in miniature with the Moon itself. Scientists are rather awesomely calling this “The Big Splat.”

It’s not just that the far side of the Moon is mountainous whereas the near side is flat – it actually has a substantially thicker crust than its lowland counterpart. That’s hard to explain if the Moon formed all at once, as the formation processes tend to even out such substantial irregularities. But planetary scientists at UC Santa Cruz propose a novel solution: what if the giant impact between Earth and Theia created not one, but two moons?

This second satellite would have been considerably smaller than the Moon we know today. It probably would have only been about 1/30 the mass of the Moon, which is still decently sized by the satellite standards (that’s a lot bigger than Mars’s moons, for instance). Both satellites would likely have shared the same orbit around Earth, with the second moon situated at one of the two Trojan points of stability relative to our Moon.

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So how did the two collide? The second moon was able to remain stable in the early days of the Earth-Moon system, because the still forming larger Moon was initially much closer to Earth. As the initial chaos passed, the primary Moon moved out further into its current orbit. The second moon was no longer able to remain in a stable orbit, and it began a slow, gentle (collision?) with its larger companion – well, slow and gentle by the standards of two moons smashing into each other, that is.

Because the colliding object was moving at a relatively low velocity, crater formation and melting of the lunar surface was minimal. Instead, the entire second moon simple flattened and accumulated on one side of its former orbital partner, piling on tens of kilometers worth of new crust. This piling would not have been totally even, however, and that’s where you get the lunar highlands.

And it’s not just the elevation differences that this hypothesis accounts for. It also explains why the two sides of the Moon have such radically different compositions. The near side is rich in potassium, phosphorus, thorium, uranium, and various rare-earth elements, all of which were deposited on that side by the Moon’s primordial magma ocean. Now we know why they all ended up on side – the collision flattened the far side and pushed the resource-rich magma around to the other side of the satellite.

The genes date from an event 1.5 billion years ago, when two kinds of simple cells, neither having a nucleus or cellular membrane, shacked up and created an entirely new form of life: eukaryotes.

While the two distinct communities of genes work together to keep cell machinery ticking, they otherwise stay out of each other’s hair, report biologists from the National University of Ireland.

“We humans, as part of the eukaryotes, we’re still a community of two prokaryotes,” said James McInerney, co-author of a study published in Genome Biology and Evolution, July 27.

While some scientists think prokaryotes evolved directly into eukaryotes, others think it required a merger, with two cells — one archaebacteria and one eubacteria — joining at some prehistoric point to make a cell capable of complex internal structures.

The merger led to an explosion of innovation. Suddenly cells could divide labor into ministructures, known as organelles, letting them specialize and grow larger. The extra biochemical whiz-bangery in eukaryotic cells makes lifeforms like orchids and dolphins possible.

“This idea is a hundred years old,” said McInerney. “But we wanted to ask, ‘If you have two types of organisms coming together to form a new kind of cell, do their metabolisms become completely blended together? What happens when genomes fuse?’”

To find out, McInerney and his colleague David Alvarez-Ponce surveyed the human genome and separated the genes into three groups based on taxonomic molecular signatures. One set contained genes inherited from our eubacterial ancestor, one from the archaebacterial ancestor and one held genes unique to eukaryotes. (Fingernail protein, for example, has no ancient doppelganger.)

Molecular tests showed that proteins coded by ancient parent cells still interact mostly with each other.

“They’ve found an imprint of this original symbiosis remaining after 1.5 billion years,” said Bill Martin, an endosymbiosis researcher at Heinrich-Heine-Universität Düsseldorf, in Germany and editor of the journal publishing the study. “This is a brilliant discovery. You would have thought someone would have noticed this, but nobody ever did.”

Beyond that, McInerney and Alvarez-Ponce found gene communities hold different functions. Archaebacterial genes are usually responsible for information processing, and appear to be especially important. They’ve accumulated fewer DNA mutations than eubacterial genes, suggesting that changes are more likely to have major consequences.

Eubacterial genes tended to be involved in biochemical processes. They were also more likely to be implicated in heritable human disease risk.

That more-important archaebacterial genes are found less frequently in disease might seem counterintuitive, but McInerney thinks the imbalance might exist because archaebacterial gene mutations often prevent organisms from developing at all.

Mutations to eubacterial biochemical process genes may cause problems, but organisms at least live long enough for disease to occur.

About 15 years ago, NASA’s Galileo mission revealed curious inconsistencies in the planet’s atmosphere. Models of the solar system suggest Jupiter formed near its current location, just outside the solar system’s “frost line”, a boundary beyond which water vapour condenses. Yet when Galileo launched a probe into the planet’s atmosphere in 1995, the probe found surprisingly little water.

Did the probe hit a rare dry spot on Jupiter? Or is all of Jupiter depleted in water? Juno will try to find out by searching the planet for water’s signature at six different microwave frequencies, which will reveal the molecule’s concentration from the top of the atmosphere to pressures of about 100 Earth-atmospheres. If the whole planet is dry, our very understanding of how and where objects came together in the solar system may need a rethink.

“Water is the key question that got this mission started,” says mission member Fran Bagenal of the University of Colorado, Boulder. “Not knowing where the water is in the solar system is a big deal. It puts a spanner in the works for solar system formation.”

The Juno spacecraft is a novel design. Three solar-panel wings, each about 9 metres long, will unfold after launch. The large panels are crucial because sunlight is only a few per cent as bright near Jupiter as it is on the Earth.

After its launch, Juno will travel for five years before slipping into an elongated, polar orbit around the planet that will dodge Jupiter’s deadly radiation belts. It will make 32 trips around Jupiter over a one-year period, skimming only 5000 kilometres above its cloud tops.

As it does so, it will glean data about the planet’s gravitational and magnetic fields, which could shed light on its internal structure, including whether it has a solid core. This is a mystery because no one knows what matter does at the extreme pressures inside such a massive body.

The revelation comes a day after a committee of scientists warned of a nightmare Planet of the Apes scenario in which work on human-animal creations goes too far.

Last night a campaigner against the excesses of medical research said he was disgusted that scientists were “dabbling in the grotesque”.

Figures seen by the Daily Mail show that 155 “admixed” embryos, containing both human and animal genetic material, have been created since the introduction of the 2008 Human Fertilisation Embryology Act.

This legalised the creation of a variety of hybrids, including an animal egg fertilised by a human sperm; “cybrids”, in which a human nucleus is implanted into an animal cell; and “chimeras”, in which human cells are mixed with animal embryos.

The new search, which began last week, is scanning 86 alien worlds for radio signals that could suggest the presence of an advanced civilization. The extrasolar planets are thought to be the most Earth-like of the 1,235 candidate planets discovered so far by NASA’s prolific Kepler space observatory.

“We’ve picked out the planets with nice temperatures — between zero and 100 degrees Celsius [32 and 212 degrees Fahrenheit] — because they are a lot more likely to harbor life,” said physicist Dan Werthimer of the University of California, Berkeley, in a statement.