Author: John Timmer

The history of humanity, as we've read it through DNA, has been written largely by females. Mitochondrial DNA, which is inherited only from our mothers, is short and easy to sequence, so researchers have frequently relied on it to study human DNA, both in present populations and in old bones.

But as DNA sequencing technology has improved, it has become progressively easier to sequence all the DNA that an individual carries. If said individual is a male, the resulting sequence will include the Y chromosome, which is inherited only from fathers. With more data in hand, researchers have been able to perform an analysis of the Y chromosome's history, and they've found that its sequence retains the imprint of both the migrations and technological innovations that have featured in humanity's past.

How to read a Y

Most chromosomes in the cell are present as two copies, which allows them to swap genetic material. Over time, this swapping will mix up the mutations that occur on the chromosome, making their history difficult to untangle.

Video edited by Jenifer Hahn. (video link)

OCOTILLO WELLS, Calif.—The area of the Southern California desert we were standing in made for a decent visual fill-in for the Red Planet—simply change the tint of the landscape and get rid of the sparse scrub on the nearby hillsides. At this site in a large, open-air mine near the Salton Sea, a few people in hard hats were gathered around a tall stand with a tether in the middle that dropped into a small hole in the ground.

The area was silent except for a hum of a large compressor. "That's for cooling," explained Kris Zacny, an engineer for Honeybee Robotics. "We won't need cooling on Mars."

Last night, after over 60 hours in the air and months of work on the ground, Solar Impulse completed its crossing of the Pacific. The landing at Moffett Field completed the most challenging part of its round-the-world journey, one interrupted by a long layover in Hawaii that allowed the team to sort out issues with the craft's batteries.

Solar Impulse is attempting to complete the first fuel-free circumnavigation of the Earth. It started the journey last year, with pilots Bertrand Piccard and André Borschberg completing legs that took the craft to Japan and then across the Pacific to Hawaii. Progress was slow, however, as the delicate aircraft has some very specific requirements in terms of wind and weather in order to take off and land safely. It also needs to complete the journey within the Northern Hemisphere's summer, or the on-board battery capacity would be insufficient to power it through the longer winter night.

Once in Hawaii, however, the team identified problems with overheating batteries that required a major overhaul. This put the completion of its journey on hold for the year. With the work completed and the longest day of the year about two months away, the team was ready to resume its journey.

Over the last few years, we've witnessed the start of two radically new ways of doing astronomy. For all of human history, everything we've learned about the cosmos has come from observing photons, from high-energy gamma rays down to the cosmic microwave background. But since the opening of the IceCube observatory at the South Pole, we've been able to track ultra-high-energy cosmic neutrinos. And earlier this year, the updated LIGO detector spotted gravitational waves, ushering in the ability to observe ripples in space itself.

While neutrinos and gravitational waves are a very different means of looking at the cosmos, the data that they generate has to be integrated with everything we've already learned about the Universe. In other words, when we spot the neutrinos or gravitational waves, it would be helpful to observe photons associated with whatever event is producing them. That will help us integrate the new information with things we already know about and come to grips with anything we don't know about.

This week, possible successes were announced, as people identified a likely source of cosmic neutrinos, as well as a possible detection of a gravitational-wave-generating event using more traditional astronomy.

Magnetic media, in the form of tapes and disks, have had a long run as the primary means of digital storage. In this hardware, clusters of magnetic atoms are set in a single magnetic orientation, which can be read back to determine whether a bit has a value of one or zero. Advances in capacity mostly come from figuring out how to make those clusters smaller. The ultimate limit, of course, would be a single atom, but here, quantum fluctuations will keep the bit from being stored stably. Single atom magnets have been created, but they have ended up holding a random value within a fraction of a second.

Now, a team of Swiss researchers has identified the two quantum effects that cause most of the problems for these single atom magnets and figured out how to limit them. The result is a device where individual atoms can hold onto their orientation for dozens of minutes. The big downside? It needs to be kept near absolute zero to work.

Magnetism in a bulk material, like a bar magnet, arises from the behavior of individual atoms within the material—more specifically, the behavior of some of the electrons orbiting those atoms. Although it would be possible for individual atoms to flip their orientation, the magnetic field created by all the neighboring atoms makes doing so very improbable. As a result, groups of atoms tend to maintain their orientation indefinitely, allowing us to stably write bits to them.

The human brain can still outperform our best algorithms for a variety of tasks. Some tasks, like object identification, aren't really surprising—our brain itself has been optimized through evolution to be pretty good at this. But there are other classes of problems that are a bit of a surprise, like some forms of optimization.

You might expect a computer to be pretty good at finding optimal solutions. But when it came to figuring out the optimal structure of a protein, people playing the game FoldIt managed to beat some of our best software. Now you can add a second task where our brains come out ahead: figuring out the best way to perform some quantum manipulations. All it took was turning quantum mechanics into a game.

Algorithms often come up short in optimization problems because of how they're structured. It's easiest to think of this idea as a landscape with peaks and valleys. The algorithm simply starts off by picking a large number of random locations within this landscape and then tries to move uphill from each of these locations. Once it finds a collection of peaks, it can compare them to find the highest peak that it has located, which can represent the optimal solution.

NEW YORK CITY—The top of the new World Trade Center building was buried inside the clouds, but everyone's focus was on the stars. Yuri Milner, the man whose investments have helped fund the Breakthrough Prizes and Breakthrough Initiatives, was here to announce his newest venture: Breakthrough Starshot, an effort to send hardware to the nearest stars quickly enough for many of us to live to see their arrival.

Present to back the project was physicist Stephen Hawking. "I believe what makes us unique is transcending our limits," Hawking told the audience. "Gravity pins us to the ground, but I just flew to America."

He went on to ask, "How do we transcend these limits? With our minds and our machines. The limit that confronts us now is the great void between us and the stars. But now we can transcend it."

Late last week, NASA's Kepler planet-hunting spacecraft experienced some sort of problem that caused it to enter what's called emergency mode. This should only occur when the spacecraft experiences a serious problem, as it limits its activity and burns through the probe's limited fuel supply at an accelerated pace. This incident marked the first time since Kepler was launched in 2009 that it entered emergency mode.

Today, NASA announced that it had re-established normal communication with Kepler, allowing the spacecraft to exit emergency mode. The telescope's communication hardware is once again pointed directly at Earth. This has allowed controllers to put Kepler in an operational mode where it consumes far less fuel, which will extend its usable life.

But first, the controllers must figure out why Kepler entered emergency mode in the first place. Full communications will allow them to download telemetry and operational data, which will hopefully allow them to identify the underlying problem. Until they do, however, planned observations of the Milky Way's galactic core have been put on hold. The window for observing the core from Kepler's current location closes on July first. Its previous observation work ended in late March, and all data from that work has already been transferred to Earth.

The chemical that powers most of our cellular processes is produced through something called the electron transport chain. As its name suggests, this system shuffles electrons through a series of chemicals that leaves them at a lower energy, all while harvesting some of the energy difference to produce ATP.

But the ultimate destination of this electron transport chain doesn't have to be a chemical. There are a variety of bacteria that ultimately send the electrons off into the environment instead. And researchers have figured out how to turn these into a fuel cell, harvesting the electrons to do something useful. While some of these designs were closer to a battery than others, all of them consumed some sort of material in harvesting the electrons.

A team of researchers in the Netherlands figured out how to close the loop and create an actual bacterial battery. One half of the battery behaves like a bacterial fuel cell. But the second half takes the electrons and uses them to synthesize a small organic molecule that the first can eat. Its charging cycle is painfully slow and its energy density is atrocious, but the fact that it works at all seems rather noteworthy.

Today, the SLAC National Accelerator Laboratory is starting construction on a second X-ray laser that will be even brighter and more intense than its first. The new hardware, based on a superconducting linear accelerator (or linac), will replace about a third of the length of the original accelerator and leave the facility's existing X-ray laser intact.

The SLAC facility is a linear electron accelerator that was originally built to characterize the W and Z bosons. After the frontier of high-energy physics shifted to CERN, the hardware was repurposed to create an extremely powerful X-ray laser.

When charged particles are forced to move along a curved path, they lose energy in the form of radiation. If they're moving at sufficiently high energies, that radiation takes the form of X-rays. At SLAC, an X-ray laser is generated by accelerating electrons and then forcing them through a series of carefully space magnets (called undulators or wigglers) that cause the particles to curve back and forth. The end result of all the radiation they emit is an intense beam of X-rays that can be used for a variety of imaging applications.