November 4, 2013
Over the past 18 years, astronomers have discovered 1038 planets orbiting distant stars. Disappointingly, though, the vast majority don’t seem like candidates to support life as we know it—they’re either so close to their home star that all water would likely evaporate, or so far away that all of it would freeze, or they’re made up of gas instead of rock and more closely resemble our solar system’s gas giants than Earth.
Or so we thought. Today, a group of scientists from UC Berkeley and the University of Hawaii published a calculation suggesting that we’ve overlooked evidence of a vast number of Earth-sized exoplanets in the habitable zone of their stars, simply because these planets are harder to detect with current methods. They believe that, on average, 22% of Sun-like stars (that is, stars with a size and temperature similar to the Sun) harbor a planet that’s roughly Earth-sized in their habitable zones.
“With about 100 billion stars in our Milky Way galaxy, that’s about 20 billion such planets,” said Andrew Howard, one of the study’s co-authors, in a press conference on the findings. “That’s a few Earth-sized planets for every human being on the planet Earth.”
The team, led by Erik Petigura, came to these conclusions by taking an unconventional approach to planet-finding. Instead of counting how many exoplanets we’ve found, they sought to determine how many planets we’re unable to see.
Exoplanets are detected as a result of rhythmic dimming in a star’s brightness, which indicates that there’s a planet orbiting it and passing between the star and our vantage point. Because of this method, large planets that orbit closely to their stars have been the easiest to find—they block more light, more often—and thus disproportionately dominate the list of known exoplanets.
To estimate the number of exoplanets this technique misses, the Berkeley team wrote a software program that analyzed data from the Kepler mission, an exoplanet-hunting NASA telescope launched into orbit in 2009. Initially, to confirm the program’s accuracy, they fed it the same data from 42,557 Sun-like stars that had already been scrutinized by other astronomers, and it indeed detected 603 candidate planets, all of which had already been found.
When it parsed the data further to find Earth-like planets—using the length of time between dimmings to indicate how far out the planet orbits the star, and the degree of dimming to indicate us how much of the star is blocked by the planet, and thus the exoplanet’s size—it found 10 potential exoplanets that are between one and two times the size of Earth and orbit in what is likely the star’s habitable zone. This, too, aligned with previous findings, showing the program could accurately detect planets.
But what the researchers really wanted to do was determine the overall prevalence of Earth-like exoplanets. To calculate this number, they first had to determine just how many weren’t detected in the survey. “One way of thinking of it is that we’re doing a census of habitable exoplanets, but not everyone’s answering the door,” Petigura explained.
There are a few reasons that a planet might not be detected. If its orbit doesn’t take it into a location that would block the path of light between its star and our telescopes, we’d have no way of seeing it. Alternately, it could successfully block starlight, but the event could be lost amid natural variation in the brightness of the star as we perceive it on Earth.
Both of these possibilities, it turns out, make it disproportionately hard to find Earth-like exoplanets. “Planets are easier to detect if they’re bigger, and closer to their host stars,” Howard said. “Thus it’s no accident that hot Jupiters were the first planets to be discovered.” Simply by virtue of physics, smaller, Earth-sized planets that may orbit a bit farther out are less likely to pass directly in front of their stars, from our perspective.
To finding out how many Earth-like planets we likely miss as a result, the scientists altered the Kepler data by artificially introducing 40,000 more exoplanets similar to Earth—roughly one per star—then feeding the resulting data back into the planet detection software. This time, it only found about one percent of the Earth-like planets introduced, because the vast majority didn’t cause a detectable dimming of their star.
This means that, with current detection methods, 99 out of 100 Earth-like aren’t coming to the door when to answer our interstellar census. Accounting for this level of imperfection, the researchers calculated that far more Sun-like stars are home to a potentially habitable, Earth-sized exoplanet than we previously thought.
It’s important to note that this is a theoretical calculation: The scientists didn’t actually discover these sorts of planets orbiting 22% of the stars. But if the underlying assumptions are accurate, it does give hope to the possibility that we’ll find more potentially habitable planets in the future. In fact, the researchers calculated that if the prevalence of these sorts of planets is uniform across the galaxy, odds are that one can be found tantalizingly nearby—about 12 light years away from Earth.
It’s still unknown whether these planets might have the other ingredients that we believe are likely necessary for life: a protective atmosphere, the presence of water and a rocky surface. But the researchers say another recent finding makes them hopeful that some of them have potential. Earlier this week, scientists found a rocky, Earth-sized exoplanet roughly 700 light-years away. Although that planet is certainly too hot to harbor life, it has density similar to that of Earth—suggesting that at least some of the Earth-sized planets we’ve failed to detect so far have a geologic composition similar to our own planet’s.
October 10, 2013
The star GD61 is a white dwarf. As such, it’s insanely dense—similar in diameter to Earth, but with a mass roughly that of the Sun, so that a teaspoon of it is estimated to weigh about 5.5 tons. All things considered, it’s not a particularly promising stellar locale to find evidence of life.
But a new analysis of the debris surrounding the star suggests that, long ago, GD61 may have provided a much more hospitable environment. As part of a study published today in Science, scientists found that the crushed rock and dust near the star were once part of a small planet or asteroid made up of 26 precent water by volume. The discovery is the first time we’ve found water in a rocky, Earth-like planetary body (as opposed to a gas giant) in another star system.
“Those two ingredients—a rocky surface and water—are key in the hunt for habitable planets,” Boris Gänsicke of the University of Warwick in the UK, one of the study’s authors, said in a press statement. “So it’s very exciting to find them together for the first time outside our solar system.”
Why was water found in such a seemingly unhospitable place? Because once upon a time, GD61 wasn’t so different from our Sun, scientists speculate. But roughly 200 million years ago, when it exhausted its supply of fuel and could no longer sustain fusion reactions, its outer layers were blown out as part of a nebula, and its inner core collapsed inward, forming a white dwarf. (Incidentally, this fate will befall an estimated 97 percent of the stars in the Milky Way, including the Sun.)
When that happened, the tiny planet or asteroid in question—along with all the other bodies orbiting GD61—were violently knocked out of orbit, sucked inward, and ripped apart by the force of the star’s gravity. The clouds of dust, broken rock and water that the scientists recently discovered near the star are the remnants of these planets.
Even in its heyday, the watery body was probably still very small—perhaps comparable in size to our solar system’s dwarf planet Ceres, which orbits in the asteroid belt and is about .015 percent the mass of Earth. Additionally, like Ceres, the ancient planet or asteroid was extremely water-rich (26 percent water, far more than Earth’s .023 percent), and this water was similarly constituted as ice locked within a rocky crust.
To find all this out, the group of scientists (which also includes Jay Farihi of the University of Cambridge and Detlev Koester of the University of Kiel) used observations from two sources: a spectrograph on board the Hubble Space Telescope, through which they obtained data on ultraviolet light emitted by GD61, and a telescope at the W.M. Keck Observatory on Mauna Kea on Hawaii.
By looking at the light emitted from the star, which glows in certain patterns depending on the chemical signatures of gases present, they were able to determine the proportions of a number of elements (including oxygen, magnesium, aluminum, silicon, calcium and iron) contained within the cloud of dust that surrounds it. Using computer simulations of this stellar atmosphere, they were able to rule out a number of alternate possibilities that could have accounted for the abundance of oxygen, leaving only the explanation that it was brought there in water form.
Based on the amount of water and rocky minerals detected in the star’s atmosphere—and assuming it all came from one body—scientists speculate that the small planet or asteroid ripped up by the white dwarf was at least 56 miles in diameter, but perhaps much larger.
Although the star certainly isn’t home to any life at the moment due to its relatively cold temperature, the finding makes it seem more likely that other exoplanets contain water, which is necessary for life as we know it. Many scientists have speculated that small planets and asteroids like Ceres delivered water to Earth in the first place, so finding evidence of a watery body like this in another star system raises the possibility that the same process may have brought water to an Earth-sized planet elsewhere too.
“The finding of water in a large asteroid means the building blocks of habitable planets existed—and maybe still exist—in the GD 61 system, and likely also around a substantial number of similar parent stars,” Farihi said. “These water-rich building blocks, and the terrestrial planets they build, may in fact be common.”
September 4, 2013
Sometime in the next two or three months, something special will happen: the magnetic field that emanates from the Sun and extends throughout the entire solar system will reverse in polarity.
“It’s really hard to say exactly when it’s going to happen, but we know it’ll be in the next few months, for sure,” says Andrés Muñoz-Jaramillo, a researcher at the Harvard-Smithsonian Center for Astrophysics who studies the Sun’s magnetic cycle. “This happens every solar cycle, and it’s a very special day when it does.”
First, the basics: the Sun, like Earth, naturally generates a magnetic field. The massive solar magnetic field is a result of the flow of plasma currents within the Sun, which drive charged particles to move from one of the Sun’s poles to another.
Every 11 years, the strength of this magnetic field gradually decreases to zero, then emerges in the opposite direction, as part of the solar cycle. It’s as if, here on Earth, compasses pointed towards the Arctic as “North” for 11 years, then briefly wavered, then pointed towards Antarctica as “North” for the next 11 years (in fact, the Earth’s magnetic field does reverse as well, but it occurs with much less regularity, and takes a few hundred thousand years to do so).
Recent observations indicate that the next solar magnetic reversal is imminent—in August, NASA announced that it was three or four months away. The reversal, explains Muñoz-Jaramillo, won’t be a sudden, jarring event but a gradual, incremental one. “The strength of the polar field gradually gets very close to zero,” he says. “Some days, it’s slightly positive, and other days, it’s slightly negative. Then, eventually, you see that it’s consistently in one direction day after day, and you know the reversal has occurred.” His research group’s measurements of the magnetic field suggest this reversal is a few months away, but it’s impossible to say for sure which day it’ll occur.
Because the region that the solar magnetic field influences includes the entire solar system, the effects of the reversal will be felt widely. “The magnetic field flows out into interplanetary space, and it forms a bubble that encloses the solar system as it travels through the galaxy,” Muñoz-Jaramillo says.
One aspect of this bubble—formally known as the heliosphere—is an invisible electrically-charged surface called the current sheet pervades the solar system and resembles a twisted ballerina’s skirt, because the rotation of the Sun twists its far-flung magnetic field into a spiral. The reversal of the field will cause the sheet to become more rippled, which in turn will lead the Earth to pass through the sheet more frequently as it orbits the Sun.
Passing through more often could cause more turbulent space weather, potentially leading to disruptions in satellite transmissions and telecommunications equipment. On the other hand, the current sheet also blocks high-energy cosmic rays that arrive from other areas of the galaxy, so a more wavy sheet could provide satellites and astronauts in space more robust protection from harmful radiation.
Additionally, the magnetic field reversal coincides with the maximum of other solar activity, which means a greater number of sunspots, more powerful solar flares, brighter aurorae and more frequent coronal mass ejections. Most of these events have little or no effect on Earth, but an especially powerful flare or plasma ejection aimed in the right direction could knock out Earth-based telecommunications systems. At the same time, this solar cycle has been especially weak—NASA solar physicist David Hathaway called it “wimpy” in an interview with Scientific American—so there’s not a ton to worry about with this particular reversal.
For Muñoz-Jaramillo, who spends his days monitoring and analyzing the Sun’s magnetic activity, the reversal will also have personal significance. “Because the cycle is such a long process, in terms of a human’s lifetime, a solar scientist is going to see maybe four reversals in a career,” he says. “That makes every turning point special—and this is the first time I’m seeing one of these since I started studying solar physics.”
For more on the solar reversal, take a look at NASA’s video:
June 28, 2013
Every day, it seems, a new exoplanet is found (or, in the case of Tuesday, scientists discovered three potentially habitable exoplanets orbiting one star). But there are loads of hurdles that we’ll have to clear before we ever have the chance to visit them: the massive doses of radiation that would be absorbed by would-be astronauts, the potential damage caused by interstellar dust and gas to a craft moving at extremely high speeds, and the fact that traveling to even the nearest habitable exoplanet would take almost 12 years in a spacecraft traveling at the speed of light.
The biggest problem, though, might be the enormous amount of energy such a craft would require. How do you fuel a spacecraft for a journey more than 750,000 times farther than the distance between the Earth and the Sun?
Based on our current technology for exploring space and potential future approaches, here’s a rundown of the possible ways of propelling spacecraft.
Conventional Rockets: These create thrust by burning a chemical propellant stored inside, either a solid or liquid fuel. The energy released as a result of this combustion lifts a craft out of Earth’s gravitational field and into space.
Pros: Rocket technology is well-established and well-understood, as it dates to ancient China and has been used since the very beginning of the space age. In terms of distance, its greatest achievement thus far is carrying the Voyager 1 space probe to the outer edge of the solar system, roughly 18.5 billion miles away from Earth.
Cons: The Voyager 1 is projected to run out of fuel around the year 2040, an indication of how limited in range conventional rockets and thrusters can carry a spacecraft. Moreover, even if we could fit a sufficient amount of rocket fuel onto a spacecraft to carry it all the way to another star, the staggering fact is that we likely don’t even have enough fuel on our entire planet to do so. Brice Cassenti, a professor at Rensselaer Polytechnic Institute, told Wired that it would take an amount of energy that surpasses the current output of the entire world to send a craft to the nearest star using a conventional rocket.
Ion engines: These work somewhat like conventional rockets, except instead of expelling the products of chemical combustion to generate thrust, they shoot out streams of electrically-charged atoms (ions). The technology was first successfully demonstrated on NASA’s 1998 Deep Space 1 mission, in which a rocket closely flew past both an asteroid and a comet to collect data, and has since been used to propel several other spacecraft, including an ongoing mission to visit the dwarf planet Ceres.
Pros: These engines produces much less thrust and initial speed than a conventional rocket—so they can’t be used to escape the Earth’s atmosphere—but once carried into space by conventional rockets, they can run continuously for much longer periods (because they use a denser fuel more efficiently), allowing a craft to gradually build up speed and surpass the velocity of one propelled by a conventional rocket.
Cons: Though faster and more efficient than conventional rockets, using an ion drive to travel to even the nearest star would still take an overwhelmingly long time—at least 19,000 years, by some estimates, which means that somewhere on the order of 600 to 2700 generations of humans would be needed to see it through. Some have suggested that ion engines could fuel a trip to Mars, but interstellar space is probably outside the realm of possibility.
Nuclear Rockets: Many space exploration enthusiasts have advocated for the use of nuclear reaction-powered rockets to cover vast distances of interstellar space, dating to Project Daedalus, a theoretical British project that sought to design an unmanned probe to reach Barnard’s Star, 5.9 light-years away. Nuclear rockets would theoretically be powered by a series of controlled nuclear explosions, perhaps using pure deuterium or tritium as fuel.
Pros: Calculations have shown that a craft propelled in this way could reach speeds faster than 9000 miles per second, translating to a travel time of roughly 130 years to Alpha Centurai, the star nearest the Sun—longer than a human lifetime, but perhaps within the realm of a multi-generational mission. It’s not the Millenium Falcon making the Kessel Run in less than 12 parsecs, but it’s something.
Cons: For one, nuclear-powered rockets are, at present, entirely hypothetical. In the short-term, they’ll probably stay that way, because the detonation of any nuclear device (whether intended as a weapon or not) in outer space would violate the Partial Nuclear Test Ban Treaty, which permits such explosions in exactly one location: underground. Even if legally permitted, there are enormous safety concerns regarding the launch of a nuclear device into space atop a conventional rocket: An unexpected error could cause radioactive material to rain across the planet.
Solar Sails: In comparison to all the other technologies on this list, these operate on a rather different principle: Instead of propelling a craft by burning fuel or creating other sorts of combustion, solar sails pull a vehicle by harnessing the energy of the charged particles ejected from the Sun as part of the solar wind. The first successful demonstration of such a technology was Japan’s IKAROS spacecraft, launched in 2010, which traveled towards Venus and is now journeying towards the Sun, and NASA’s Sunjammer, seven times larger, is going to launch in 2014.
Pros: Because they don’t have to carry a set amount of fuel—instead using the power of the Sun, much like a sailboat harnesses the energy of the wind—a solar sail-aided spacecraft can cruise more-or-less indefinitely.
Cons: These travel much slower than rocket-powered crafts. But more important for interstellar missions—they require the energy ejected from the Sun or another star to travel at all, making it impossible for them to traverse the vast spaces between the reach of our Sun’s solar wind and that of another star system’s. Solar sails could potentially be incorporated into a craft with other means of propelling itself, but can’t be relied upon alone for an interstellar journey.
Antimatter Rockets: This proposed technology would use the products of a matter-antimatter annihilation reaction (either gamma rays or highly-charged subatomic particles called pions) to propel a craft through space.
Pros: Using antimatter to power a rocket would theoretically be the most efficient fuel possible, as nearly all of the mass of the matter and antimatter are converted to energy when they annihilate each other. In theory, if we were able to work out the details and produce enough antimatter, we could build a spacecraft that travels at speeds nearly as fast as that of light—the highest velocity possible for any object.
Cons: We don’t yet have a way to generate enough antimatter for a space journey—estimates are that a month-long trip to Mars would require about 10 grams of antimatter. To date, we’ve only been able to create small numbers of atoms of antimatter, and doing so has consumed a large amount of fuel, making the idea of an antimatter rocket prohibitively expensive as well. Storing this antimatter is another issue: Proposed schemes involve the use of frozen pellets of antihydrogen, but these too are a far way off.
More speculative technologies: Scientists have proposed all sorts of radical, non-rocket-based technologies for interstellar travel. These include a craft that would harvest hydrogen from space as it travels to use in a nuclear fusion reaction, beams of light or magnetic fields shot from our own Solar System at a distant spacecraft that would be harnessed by a sail, and the use of black holes or theoretical wormholes to travel faster than the speed of light and make an interstellar journey possible in a single human’s lifetime.
All of these are extremely far away from implementation. But, if we do ever make it to another star system at all (a big if, to be sure), given the problems with most existing and near-future technologies, it might indeed be one of these pie-in-the-sky ideas that carry us there—and perhaps allow us to visit a habitable exoplanet.
April 19, 2013
Last year, to celebrate the 42nd Earth Day, we took a look at 10 of the most surprising, disheartening, and exciting things we’d learned about our home planet in the previous year—a list that included discoveries about the role pesticides play in bee colony collapses, the various environmental stresses faced by the world’s oceans and the millions of unknown species are still out in the environment, waiting to be found.
This year, in time for Earth Day on Monday, we’ve done it again, putting together another list of 10 notable discoveries made by scientists since Earth Day 2012—a list that ranges from specific topics (a species of plant, a group of catfish) to broad (the core of planet Earth), and from the alarming (the consequences of climate change) to the awe-inspiring (Earth’s place in the universe).
1. Trash is accumulating everywhere, even in Antarctica. As we’ve explored the most remote stretches of the planet, we’ve consistently left behind a trail of one supply in particular: garbage. Even in Antarctica, a February study found (PDF), abandoned field huts and piles of trash are mounting. Meanwhile, in the fall, a new research expedition went to study the Great Pacific Garbage Patch, counting nearly 70,000 pieces of garbage over the course of a month at sea.
2. Climate change could erode the ozone layer. Until recently, atmospheric scientists viewed climate change and the disintegration of the ozone layer as entirely distinct problems. Then, in July, Harvard researcher Jim Anderson (who won a Smithsonian Ingenuity Award for his work) led a team that published the troubling finding that the two might be linked. Some warm summer storms, they discovered, can pull moisture up into the stratosphere, an atmospheric layer 6 miles up. Through a chain of chemical reactions, this moisture can lead to the disintegration of ozone, which is crucial for protecting us from ultraviolet (UV) radiation. Climate change, unfortunately, is projected to cause more of these sorts of storms.
3. This flower lives on exactly two cliffs in Spain. In September, Spanish scientists told us about one of the most astounding survival stories in the plant kingdom: Borderea chouardii, an extremely rare flowering plant that is found on only two adjacent cliffs in the Pyrenees. The species is believed to be a relic of the Tertiary Period, which ended more than 2 million years ago, and relies on several different local ant species to spread pollen between its two local populations.
4. Some catfish have learned to kill pigeons. In December, a group of French scientists revealed a phenomenon they’d carefully been observing over the previous year: a group of catfish in Southwestern France had learned how to leap onto shore, briefly strand themselves, and swim back into the water to consume their prey. With more than 2,000,000 Youtube views so far, this is clearly one of the year’s most widely enjoyed scientific discoveries.
5. Fracking for natural gas can trigger moderate earthquakes. Scientists have known for a while that whenever oil and gas are extracted from the ground at a large scale, seismic activity can be induced. Over the past few years, evidence has mounted that injecting water, sand and chemicals into bedrock to cause gas and oil to flow upward—a practice commonly known as fracking—can cause earthquakes by lubricating pre-existing faults in the ground. Initially, scientists found correlations between fracking sites and the number of small earthquakes in particular areas. Then, in March, other researchers found evidence that a medium-sized 2011 earthquake in Oklahoma(which registered a 5.7 on the moment magnitude scale) was likely caused by injecting wastewater into wells to extract oil.
6. Our planet’s inner core is more complicated than we thought. Despite decades of research, new data on the iron and nickel ball 3,100 miles beneath our feet continue to upset our assumptions about just how the earth’s core operates. A paper published last May showed that iron in the outer parts of the inner core is losing heat much more quickly than previously estimated
, suggesting that it might hold more radioactive energy than we’d assumed, or that novel and unknown chemical interactions are occurring. Ideas for directly probing the core are widely regarded as pipe dreams, so our only options remains studying it from afar, largely by monitoring seismic waves.
7. The world’s most intense natural color comes from an African fruit. When a team of researchers looked closely at the blue berries of Pollia condensata, a wild plant that grows in East Africa, they found something unexpected: it uses an uncommon structural coloration method to produce the most intense natural color ever measured. Instead of pigments, the fruit’s brilliant blue results from nanoscale-size cellulose strands layered in twisting shapes, which which interact with each other to scatter light in all directions.
8. Climate change will let ships cruise across the North Pole. Climate change is sure to create countless problems for many people around the world, but one specific group is likely to see a significant benefit from it: international shipping companies. A study published last month found that rising temperatures make it probable that during summertime, reinforced ice-breaking ships will be able to sail directly across the North Pole—an area currently covered by up to 65 feet of ice—by the year 2040. This dramatic shift will shorten shipping routes from North America and Europe to Asia.
9. One bacteria species conducts electricity. In October, a group of Danish researchers revealed that the seafloor mud of Aarhus’ harbor was coursing with electricity due to an unlikely source: mutlicellular bacteria that behave like tiny electrical cables. The organisms, the team found, built structures that traveled several centimeters down into the sediment and conduct measurable levels of electricity. The researchers speculate that this seemingly strange behavior is a byproduct of the way of the bacteria harvests energy from the nutrients buried in the soil.
10. Our Earth isn’t alone. Okay, this one might not technically be a discovery about Earth, but over the past year we have learned a tremendous amount about what our Earth isn’t: the only habitable planet in the visible universe. The pace of exoplanet detection has accelerated rapidly, with a total of 866 planets in other solar systems discovered so far. As our methods have become more refined, we’ve been able to detect smaller and smaller planets, and just yesterday, scientists finally discovered a pair of distant planets in the habitable zone of their stars that are relatively close in size to Earth, making it more likely than ever that we might have spied an alien planet that actually supports life.