Starshade” technology that could help astronomers find and characterize rocky, Earthlike alien worlds was put to the test earlier this year in the Nevada desert.
A starshade, also dubbed an external occulter, is a precisely shaped screen that flies in far-away formation with a space telescope. The device blocks a star’s light to create a high-contrast shadow, so that only light from an orbiting exoplanet enters the telescope for detailed study.
While a starshade to hunt alien planets has not been flown before, researchers studying the technique are drawing upon a track record of success in fielding large, deployable antennas in space. Some designs foresee a fully deployed starshade measuring some 110 feet (34 meters) in diameter, with a 65-foot (20 m) inner disk and 28 outstretched flowerlike petals, each over 22 feet (7 m) in length.
The starshade idea has moved beyond the drawing board.
Subscale versions of starshades have undergone nighttime desert testing, most recently at central Nevada’s Smith Creek dry lake bed over five nights in late May and early June of this year. Previously, a California test locale was used. [How the Planet-Hunting Starshade Unfolds in Space (Video)]
Desert appraisals of hardware have focused on how computational optical predictions stack up against in-the-field performance of two different starshade shapes, said Steve Warwick, program manager for starshade field testing at Northrop Grumman Aerospace Systems.
The recent Nevada test took advantage of the thin air and very dark skies at high-altitude Smith Creek, Warwick said. A six-person team made use of a modified Celestron telescope and ultrabright, light-emitting diodes (LEDs) placed about 1 mile (1.6 kilometers) away. The LEDs were all finely aligned with an automated stand topped by a starshade model sitting in the middle of the test range.
Data and images were gathered at the telescope stand.
“As you can imagine, we take a lot of data while we’re sitting out there in tents at night,” Warwick told Space.com. “There is a lot of post-processing that we have to do … and that’s underway at the moment.”
A lot will be asked of a starshade on a planet-hunting space mission.
“What we’re trying to do here is look at a lighthouse from a mile away and spot a firefly that’s just a half inch away from that lighthouse,” he said. “We’re trying to block the light from the lighthouse.”
In the simplest terms, a starshade is a specially shaped finger placed in front of a bright source to dim the light, said Ron Polidan, manager of science systems at Northrop Grumman Aerospace Systems.
“So in essence you can consider it a traveling dark spot,” Polidan said.
Deployment in space
Polidan said that company technologists are looking at several options on how best to unfold a large starshade in space. For example, there’s heritage to be found in Northrop’s lead work on NASA’s Tracking and Data Relay Satellite System, he said, as well as in building the space agency’s $8.8 billion James Webb Space Telescope (JWST).
“So part of the assessment going on with the desert tests is to understand simple and reliable deployment systems,” Polidan told Space.com.
Northrop Grumman’s starshade is “telescope agnostic,” said Warwick. That is, it could be used with JWST, which is scheduled to blast off in 2018, or with other space scopes being considered. In the end, it’s up to NASA, he said.
Starshades aid in direct imaging, helping telescopes gather photons arriving from a target planet. They can help deliver spectroscopic looks of the atmosphere of an exoplanet, “and that’s where it feeds into the search for life,” Warwick said.
Additional starshade testing in the desert is in the offing for next year, Warwick said. All the ground work, he said, is confidence-building in order to move forward on a future space-size starshade mission.
“We can never do an ‘end-to-end test’ of the starshade concept. So instead, we break the testing into two parts,” said Sara Seager, professor of planetary science and physics at the Massachusetts Institute of Technology in Cambridge, Massachusetts.
Seager is chair of a current 18-month NASA-sponsored Starshade Probe-Class mission Science and Technology Definition Team.
Seager told Space.com via email that one test phase involves fabrication and deployment to show that the required tolerances and construction of the starshade petals can be met. The other is subscale environmental testing in a lab or outdoors to demonstrate that starshade experts “understand the math and that diffraction behaves as we expect,” she said.
“This two-step process is our best option,” Seager said.
Seeing is believing
There’s one simple bottom line for Seager: Seeing is believing. The desert testing offers one way to make that happen.
“What we would absolutely love to see is an actual astronomical discovery using the starshade,” Seager said. “People have conceived putting the starshade on one mountain top and a telescope on a lower mountain peak.”
When an object of interest passes over the starshade — say a star with a debris disk — perhaps an interesting observation can be made, she said.
“We have to show the world that the starshade is a part of the astronomer’s tool kit,” Seager said.
A European spacecraft that launched late last year could eventually discover 70,000 exoplanets, helping researchers better understand the number and characteristics of alien worlds throughout the galaxy, a new study reports.
The European Space Agency’s star-monitoring Gaia mission, which launched in December 2013, should find about 21,000 alien planets over the course of its five-year mission and perhaps 70,000 distant worlds if it keeps operating for 10 years, the study found.
“It’s not just about the numbers. Each of these planets will be conveying some very specific details, and many will be highly interesting in their own way,” lead author Michael Perryman of Princeton University said in a statement. “If you look at the planets that have been discovered until now, they occupy very specific regions of discovery space. Gaia will not only discover a whole list of planets, but in an area that has not been thoroughly explored so far.”
The first alien world around a sunlike star was spotted in 1995. Since then, astronomers have found nearly 2,000 exoplanets, with more than half of the discoveries made by NASA’s Kepler space telescope.
But there are many more out there, waiting to be discovered. Astronomers think that, on average, every star in the Milky Way hosts at least one planet, meaning the galaxy probably teems with more than 100 billion alien worlds.
The $1 billion Gaia mission operates from a gravitationally stable spot 930,000 miles (1.5 million kilometers) from Earth called the Earth-Sun Lagrange Point 2. The spacecraft’s main goal is to catalog and closely monitor 1 billion Milky Way stars, helping researchers create a detailed 3D map that should shed light on the galaxy’s structure and evolution.
But Gaia’s precise tracking work should also reveal the presence of many alien planets by noting how their gravity tugs the stars slightly this way and that, researchers say.
Perryman and his colleagues wanted to get a better idea of just how many alien worlds Gaia could be expected to find. They arrived at their estimates after integrating a number of sources of information, including a comprehensive model of Milky Way star and planet positions, the latest exoplanet-distribution data (much of it from Kepler) and details of Gaia’s measurement capabilities, researchers said.
“Our assessment will help prepare exoplanet researchers for what to expect from Gaia,” Perryman said. “We’re going to be adding potentially 20,000 new planets in a completely new area of discovery space. It’s anyone’s guess how the field will develop as a result.”
The new study has been accepted for publication in The Astrophysical Journal and is available now on the preprint site arXiv.
The spectacular view of planet birth, taken by the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile, shows numerous concentric rings in the disk of dust and gas surrounding HL Tau, a sunlike star found about 450 light-years away from Earth.
“These features are almost certainly the result of young planetlike bodies that are being formed in the disk,” ALMA deputy director Stuartt Corder said in a statement. “This is surprising, since HL Tau is no more than a million years old and such young stars are not expected to have large planetary bodies capable of producing the structures we see in this image.
The stunning detail and clarity of the new ALMA radio telescope image surprised scientists.
“The first time I saw this image, I thought it was actually probably a simulation. It was just way too good,” Tony Beasley, director of the National Radio Astronomy Observatory (NRAO) in Charlottesville, Virginia, said in a new video about the planet-formation image. (The NRAO manages ALMA operations on behalf of North American astronomers.)
The new image is the sharpest ever captured by ALMA, researchers said. In fact, it’s sharper than most photos taken in visible light by NASA’s famous Hubble Space Telescope, they added.
HL Tau is veiled by dust and gas, making the star tough to observe in visible light. But ALMA was able to pierce this veil, because the telescope is optimized to view the universe in much longer wavelengths, which fall between the radio and infrared portions of the electromagnetic spectrum.
“This is truly one of the most remarkable images ever seen at these wavelengths,” said NRAO astronomer Crystal Brogan. “The level of detail is so exquisite that it’s even more impressive than many optical images. The fact that we can see planets being born will help us understand not only how planets form around other stars, but also the origin of our own solar system.”
ALMA’s design calls for 66 individual radio telescopes to work together as a single instrument. These dishes can be moved around the site using giant, 28-wheeled transporters.
ALMA obtained the new planet-formation picture with its antennas spaced up to 9 miles (15 kilometers) apart, researchers said. This “baseline” enables a resolution of 35 milliarcseconds — the equivalent of being able to spot a penny from 68 miles (110 km) away, they added.
“Such a resolution can only be achieved with the long baseline capabilities of ALMA, and provides astronomers with new information that is impossible to collect with any other facility, including the best optical observatories,” said ALMA Director Pierre Cox.
Frigid lakes bombarded by UV radiation and boiling, acidic springs are some of the otherworldly Earth environments where scientists plan to hunt for clues to life on Mars.
Funded by a new, five-year NASA grant, the researchers will tour the three ages of Mars on Earth — when Mars was cold, wet and habitable; the transition period when water disappeared; and the modern, dry period. The Mars-like environments include hot springs in California and Yellowstone National Park, permafrost on cold Arctic islands, some of Earth’s oldest rocks in Australia, and volcanic lakes and soils in Chile. [Out-of-this-World Photos: Finding Mars on Earth]
“We chose these environments because we want to understand the signature of life on Mars at different times,” said Nathalie Cabrol, the project leader and a senior research scientist at the SETI Institute in Mountain View, California.
The SETI-led team will scope out “biosignatures,” or evidence of life, with instruments similar to those NASA plans to install on the next Mars rover, expected to launch in 2020. The car-size robot is designed to seek out ancient life.
On Mars, the clues could be concealed in rocks more than 3.5 billion years old. If the planet’s ancient environment was akin to that of early Earth, then the rover might discover fossils of microbial mats similar to stromatolites, which are some of Earth’s oldest fossils. Or primitive microbes could have left behind chemical calling cards, such as the altered minerals created by rock-eating bacteria known as chemolithotrophs. The rover may also find subtle shifts in carbon, hydrogen and nitrogen isotopes, trapped and preserved in rock layers, which can signal the presence of life. (An isotope is an atom of an element with a different number of neutrons.)
Cabrol and her team will practice searching for promising rocks from the air, by scanning sites with a quadcopter or octocopter, she said. They’ll also analyze samples in the field with portable instruments, and in a laboratory for more-precise measurements.
“Our goal is not to prove more efficient at finding biosignatures,” Cabrol told Live Science. “We want to get metrics and data that will lead us to detection.”
By honing their skilles in Earth’s extreme environments, the scientists will learn where and how to look for life for when the rover arrives at Mars. The research may also help narrow down the list of best landing sites for the rover.
“We’re not saying we’re going to detect life, but we’re increasing the chances we’re going to the right outcrop,” Cabrol told Live Science.
The $8 million grant is one of five awarded to seven research groups across the United States to study the origin of life. The teams will be affiliated with NASA’s Astrobiology Institute at Ames Research Center in Moffett Field, California.
The close-orbiting alien planet, known as WASP-18b, is apparently disrupting the magnetic field of its host star so much that the object is behaving like a much older star, researchers said.
“WASP-18b is an extreme exoplanet,” study lead author Ignazio Pillitteri, of the Instituto Nazionale di Astrofisica (INAF)-Osservatorio Astronomico di Palermo in Italy, said in a statement. “It is one of the most massive hot Jupiters known and one of the closest to its host star, and these characteristics lead to unexpected behavior. The planet is causing its host star to act old before its time.”
The star WASP-18, which lies about 330 light-years away, is about as massive as our own sun. The gas giant WASP-18b weighs in at more than 10 times the mass of Jupiter and completes one orbit around the star in less than 23 hours, leading scientists to classify it as a “hot Jupiter.”
WASP-18b’s tight orbit has led scientists to estimate that it may have only one million years of life or so remaining before it’s destroyed by the parent star.
Pillitteri’s team targeted WASP-18 with NASA’s Chandra X-ray Observatory and found it to be relatively quiet — a characteristic of older stars. Young stars tend to be more active, with stronger magnetic fields, larger flares and more intense X-ray emission. Stellar activity is connected to rotation, a process that slows with age.
Observations of WASP-18 using Chandra revealed no X-ray emission. This by itself would suggest that the star has an age similar to the sun’s 5 billion years, researchers said. However, Pillitteri and his team used other data as well as theoretical models to calculate that WASP-18 is actually just 500 million to 2 billion years old, and thus approximately 100 times less active than a star its age should be.
We think the planet is aging the star by wreaking havoc on its innards,” said co-author Scott Wolk, of the Harvard-Smithsonian Center for Astrophysics in Massachusetts.
WASP-18b’s strong gravitational pull may be disrupting the star’s magnetic field, researchers said. The planet’s tug exerts forces similar to those imposed on Earth’s tides by the moon, but on a much larger scale.
The strength of a star’s magnetic field depends on how much the hot gases within the star stir up its interior, a process known as convection. WASP-18 has a convection zone narrower than most stars, making it more vulnerable to the massive tidal forces exerted by WASP-18b, researchers said.
“The planet’s gravity may cause motions of gas in the interior of the star that weaken the convection,” said co-author Salvatore Sciortino, also of INAF-Osservatorio Astronomico di Palermo. “This has a domino effect that results in the magnetic field becoming weaker and the star to age prematurely.”
The results were published in the July issue of the journal Astronomy and Astrophysics.
The first spacecraft dedicated to exploring Mars’ upper atmosphere, scientists hope Maven (Mars Atmosphere and Volatile Evolution) will give them clues as to why Mars didn’t hold onto its water and become a lush planet like Earth.
If all goes as planned, Maven won’t be the only spacecraft to enter into Mars’ orbit this week.
Another orbiter, this one launched by the Indian Space Research Organization, is expected to reach Mars and enter its orbit on Wednesday.
As engineers and scientists at NASA’s mission control center waited anxiously for news to come back from its newest Mars-bound spacecraft, Maven took itself out of its traveling trajectory and began a planned burn that lasted a little more than 30 minutes to insert itself into orbit around Mars. It officially entered the Mars orbit at 10:24 p.m. ET on Sunday.
“Here’s a spacecraft hurtling toward Mars and we had no control over it,” said John Grunsfeld, an astronaut and associate administrator of NASA’s Science Mission Directorate. “It’s amazing we have the opportunity to build a spacecraft like Maven to learn about Mars. And it worked like clockwork.”
Grunsfeld took questions about the Maven mission in an interview on NASA TV just minutes after it was announced that the spacecraft had successfully entered the Martian orbit.
A NASA spokeswoman, giving commentary during the orbit integration, said the spacecraft, which launched on Nov. 18, 2013, had worked well throughout its long journey.
“Everything looks fantastic,” she said. “Maven has functioned perfectly since launch and we expect her to continue doing so today.”
Moments later, engineers received data from the spacecraft, confirming that it had entered orbit around Mars and had turned off its engines. Cheers and applause erupted in mission control.
Scientists used radio telescopes like the Atacama Large Millimeter/submillimeter Array — a vast array of receivers in Chile — used to probe galaxies within 40 million to 600 million light-years from Earth. After observing dozens of merging galaxies, astrophysics found that many galactic collisions will create disc galaxies similar to the Milky Way, a surprising finding.
Their observations of carbon monoxide in 37 colliding galaxies showed pancake-shaped zones of molecular gas, similar to the shape that disc galaxies — which include spiral galaxies and lenticular galaxies — would assume.
“This is a large and unexpected step towards understanding the mystery of the birth of disc galaxies,” lead researcher on the study Junko Ueda, a postdoctoral fellow at the Japan Society for the Promotion of Science, said in a European Southern Observatory statement.
Before, astronomers thought that only elliptical galaxies could arise from mergers. Simulations from the 1970s, however, concluded that elliptical galaxies should be the most popular type of galaxy in the universe. Yet these odd-shaped entities comprise less than 30 percent of galaxies. The new study could help explain why scientists see so many spiral galaxies like the Milky Way in the universe, according to ESO.
The astronomers’ work is the biggest molecular gas study so far, but they said they plan more work to follow up on their research. Astronomers emphasized more observations of older galaxies are required to see if mergers behaved similarly in the young universe.
“We have to start focusing on the formation of stars in these gas discs. Furthermore, we need to look farther out in the more distant universe,” Ueda said. “We know that the majority of galaxies in the more distant universe also have discs. We, however do not yet know whether galaxy mergers are also responsible for these, or whether they are formed by cold gas gradually falling into the galaxy. Maybe we have found a general mechanism that applies throughout the history of the universe.”
The research was published in the Astrophysical Journal Supplement.
A new cosmic map is giving scientists an unprecedented look at the boundaries for the giant supercluster that is home to Earth’s own Milky Way galaxy and many others. Scientists even have a name for the colossal galactic group: Laniakea, Hawaiian for “immeasurable heaven.”
The scientists responsible for the new 3D map suggest that the newfound Laniakea supercluster of galaxies may even be part of a still-larger structure they have not fully defined yet.
“We live in something called ‘the cosmic web,’ where galaxies are connected in tendrils separated by giant voids,” said lead study author Brent Tully, an astronomer at the University of Hawaii at Honolulu.
Galactic structures in space
Galaxies are not spread randomly throughout the universe. Instead, they clump in groups, such as the one Earth is in, the Local Group, which contains dozens of galaxies. In turn, these groups are part of massive clusters made up of hundreds of galaxies, all interconnected in a web of filaments in which galaxies are strung like pearls. The colossalstructures known as superclusters form at the intersections of filaments.
The giant structures making up the universe often have unclear boundaries. To better define these structures, astronomers examined Cosmicflows-2, the largest-ever catalog of the motions of galaxies, reasoning that each galaxy belongs to the structure whose gravity is making it flow toward.
“We have a new way of defining large-scale structures from the velocities of galaxies rather than just looking at their distribution in the sky,” Tully said.
Laniakea, our home in the universe
The new 3D map developed by Tully and colleagues shows that the Milky Way galaxy resides in the outskirts of the Laniakea Supercluster, which is about 520 million light-years wide. The supercluster is made up of about 100,000 galaxies with a total mass about 100 million billion times that of the sun.
The name Laniakea was suggested by Nawa’a Napoleon, who teaches Hawaiian language at Kapiolani Community College in Hawaii. The name is meant to honor Polynesian navigators who used their knowledge of the heavens to make long voyages across the immensity of the Pacific Ocean.
“We live in the Local Group, which is part of the Local Sheet next to the Local Void — we wanted to come up with something a little more exciting than ‘Local,’” Tully told Space.com.
This supercluster also includes the Virgo cluster and Norma-Hydra-Centaurus, otherwise known as the Great Attractor. These new findings help clear up the role of the Great Attractor, which is a problem that has kept astronomers busy for 30 years. Within the Laniakea Supercluster, the motions of galaxies are directed inward, as water flows in descending paths down a valley, and the Great Attractor acts like a large flat-bottomed gravitational valley with a sphere of attraction that extends across the Laniakea Supercluster.
Tully noted Laniakea could be part of an even larger structure.
“We probably need to measure to another factor of three in distance to explain our local motion,” Tully said. “We might find that we have to come up with another name for something larger than we’re a part of — we’re entertaining that as a real possibility.”
If Professor Hubert Farnsworth’s “Smell-O-Scope” actually existed, astrobiologists would have pointed it at dozens of alien planets by now.
The Professor’s odor-detecting invention, which was featured in several episodes of the animated sci-fi series “Futurama,” would be a good life-hunting tool, researchers say, because alien organisms may betray their presence by pumping stinky chemicals into their home planets’ skies.
“I joke often that maybe you want to smell for life on other planets instead of look for it with a telescope,” Shawn Domagal-Goldman, a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said last month during a NASA panel discussion about ancient Earth and habitable exoplanets.
Hunting for biosignatures
Domagal-Goldman and other researchers spend a lot of time thinking about the best biosignatures, or signs of life, to look for in the atmospheres of faraway planets.
Two good candidates are oxygen and methane, both of which disappear from atmospheres without replenishment. While each substance can be created by geological as well as biological processes, detecting both oxygen and methane in an exoplanet’s skies simultaneously would be strongly suggestive of alien life, many scientists say.
“They destroy each other,” Domagal-Goldman said. “If they’re both there together, you know someone is bringing the methane in an atmosphere rich in oxygen, so that’s what you’re looking for. The most likely explanation is, it’s life that’s bringing the methane and oxygen to the party.”
The methane-oxygen strategy is informed by the biosignatures that currently swirl in Earth’s skies: Plants and cyanobacteria generate oxygen, while many other types of bacteria, as well as animals, pump out methane.
But a comprehensive hunt for alien biosignatures should also look deeper into Earth’s biological history, drawing further inspiration from the planet’s pioneering first organisms, Domagal-Goldman stressed.
Life first appeared on Earth perhaps 3.7 billion years ago and had become indisputably established by 3.5 billion years ago, scientists say. It took a long, long time, however, for the biosphere we’re familiar with today to take shape.
Simple microbial life dominated the planet for billions of years, with complex multicellular forms getting a firm foothold just 800 million years ago or so. And while oxygen-producing cyanobacteria may have evolved as early as 3 billion years ago, oxygen apparently didn’t start accumulating in the planet’s atmosphere until 2.3 billion years ago or so, said Tim Lyons of the University of California-Riverside, who also participated in the NASA panel discussion last month.
So the oxygen-methane strategy would not have picked up signs of life on the early (“Archaean”) Earth, even though the planet was teeming with organisms — just as it may result in false negatives when applied to exoplanets as well, researchers said.
But studying the microbes that thrive today in Earth’s oxygen-free environments suggests a way to broaden the search for alien life. For example, Archaean life probably released some pretty stinky stuff into the ancient planet’s air, such as sulfur-methyl gases, which Domagal-Goldman recalled smelling while walking past a colleague’s lab.
“They don’t last long in modern-day Earth’s environment because they get oxidized,” he said. “But if you went back to the Archaean, or any planet without oxygen, and you had life making these gases — which they clearly do; I detected them myself — then they might have built up enough for us to see with a telescope from far away.”
Scientists have proposed looking for other biosignatures as well, including industrial pollutants such as cholorfluorocarbons that could be indicators of advanced alien civilizations.
Of course, even looking back to the biosignatures of ancient Earth still involves a very large assumption — that alien life will probably resemble Earth life in important ways.
That would seem to suggest that it will be tough to detect lifeforms vastly different from those of Earth — organisms with exotic and undreamed of metabolic pathways. But Lyons thinks astrobiologists shouldn’t view the challenge as insurmountable.
“We have chemical principles, and we hope that those are universal,” Lyons said. “Life today is about the flow of electrons amongst bacteria, simple, single-celled organisms. And so if you had a sense for the chemistry on that [alien] planet that you’re inferring from an atmosphere, you could start to envision reactions that could lead to that chemistry that could be a source of energy.”
Scientists have found a strange structure resembling a microbial cell inside a Martian meteorite, but they’re not claiming that it’s evidence of Red Planet life.
The researchers discovered the microscopic oval object within the Nakhla Mars meteorite, which fell to Earth in Egypt in 1911. While the structure’s appearance is intriguing, it most likely formed as a result of geological rather than biological processes, team members said.
“The consideration of possible biotic scenarios for the origin of the ovoid structure in Nakhla currently lacks any sort of compelling evidence,” the scientists write in a new study published this month in the journal Astrobiology. “Therefore, based on the available data that we have obtained on the nature of this conspicuous ovoid structure in Nakhla, we conclude that the most reasonable explanation for its origin is that it formed through abiotic processes.” [The Search for Life on Mars (A Photo Timeline)]
A cell-like structure
The hollow ovoid is about 80 microns long by 60 microns wide, researchers said — far larger than most terrestrial bacteria but in the normal size range for eukaryotic Earth microbes (single-celled organisms that possess nuclei and other membrane-bound interior “organelles”). The study team is confident that the object is native to the sample and not the result of terrestrial contamination.
The scientists studied the structure using a number of different techniques, including electron microscopy, X-ray analysis and mass spectrometry. This work revealed that the ovoid is composed of iron-rich clay and contains a number of other minerals.
The researchers run through a number of possible formation scenarios in the new study, eventually concluding that the ovoid most likely formed when materials partially filled in a pre-existing vesicle — a vapor bubble, for example — in the rock.
But this supposition doesn’t rule out the possibility that Martian lifeforms had something to do with the structure, team members said.
“Despite the extremely biomorphic overall shape of the ovoid, it is highly unlikely that it itself was an organism,” said lead author Elias Chatzitheodoridis, of the National Technical University of Athens in Greece.
“However, it could have been formed directly by micro-organisms, or it could trap organic material that came from elsewhere,” Chatzitheodoridis told Space.com via email. “That the ovoid is hollow means that there is enough space to accommodate colonies of microorganisms.”
Making a firm link to Mars life would require further study and further discoveries, he added.
“We would be happy if we could have found more than one ovoid, with exactly the same texture both in the micro and the nanoscale,” Chatzitheodoridis said. “However, we require to open up enough sample in a very careful way. Compelling evidence, though, would be if we could really find many of the same, clearly in a form of a colony, together with chemical and mineralogical biosignatures that are common for terrestrial microbes.”
Habitable Martian environments?
Nakhla is a well-studied meteorite — scientists have spotted possible signs of Mars life within it before —and previous research has mapped out its history in some detail. Nakhla’s parent rock apparently crystallized about 1.3 billion years ago, Chatzitheodoridis and his colleagues write in the new study, then experienced two shock events that heated it up considerably.
The first of these shocks likely occurred around 910 million years ago and the second 620 million years ago. This latter event, which was triggered by a nearby meteorite strike on Mars, apparently included the flow of hot water through Nakhla’s parent outcrop, the authors write. Finally, about 10 million years ago, another impact blasted Nakhla free of Mars, sending it on a looping trip through space that ended with its arrival at Earth in 1911.
Whether or not the Nakhla ovoid has some connection to Martian life, study of the meteorite can help researchers better understand the Red Planet’s past (and, perhaps, present) potential to support life, Chatzitheodoridis said.
Martian meteorites contain “important information, and latest work has shown that now one has to look more carefully at them and in finer detail,” he told Space.com.
“In our case, it is such work that allowed us to see from a small volume of sample a big story, i.e., that hydrothermal waters have actually acted also in the latest periods of Martian history, even if they were caused by a bolide impact, and that they were capable of initiating a number of complicated processes that resulted in the formation of niche environments which can sustain life, if life [ever] emerged on the planet,” Chatzitheodoridis added.
Such exoplanets could potentially be the longest-lived life-friendly areas in the universe, enduring for up to 10 trillion years, scientists added.
As planets age, they cool, with their hot molten cores solidifying over time. This probably makes them geologically active and therefore less habitable for life as we know it, scientists say. On Earth, life depends on the geological activity of plate tectonics to circulate rocks that can absorb or release carbon dioxide, a greenhouse gas that absorbs heat. Without plate tectonics, the planet might experience runaway heating or cooling, and thus potentially become uninhabitable.
In a new study, scientists have found that if a world has a companion planet that gravitationally tugs on it, this could prevent that world from cooling, and thus extend its chances of hosting life.
Strange twin worlds
The researchers analyzed red dwarfs stars, also known as M dwarf stars. These stars are up to 50 times dimmer than the sun and up to less than 10 percent as massive. Red dwarfs are the most common kind of star, making up to 70 percent of the stars in the universe, and this fact has made scientists wonder if these red dwarfs might be the best places to look for alien life.
Because there is life nearly wherever there is water on Earth, scientists typically define planets as potentially habitable if their surfaces are warm enough to sustain water on their surfaces. Red dwarfs are cold stars, which means their habitable zones are closer than Mercury is to the sun — sometimes less than 0.1 astronomical units (AU), or one-tenth the average distance from Earth to the sun. The average distance between Earth and the sun is about 93 million miles (150 million kilometers).
Red dwarfs are colder than the sun, which means they burn fuel more slowly and live far longer. Prior research has suggested that the most readily discoverable Earth-size habitable-zone planets are likely to be about 10 billion years old — more than twice the age of 4.6-billion-year-old Earth.
Ordinarily, plate tectonics ends due to cooling long before a planet reaches 10 billion years in age. However, the researchers found that if this old world has a companion planet orbiting a bit farther away from the star, this outer planet can pull the old world into an orbit that will keep it warm enough for plate tectonics.
Rocky companion planet pals
The scientists modeled a rocky planet with the same mass and diameter as Earth’s in the habitable zone of a red dwarf just 10 percent of the sun’s mass. This red dwarf is about 1,000 times less luminous than the sun, meaning its habitable zone is only about 3 percent of an AU.
The researchers modeled outer planets with masses equal to those of Earth, Neptune, Saturn, Jupiter and larger. They found that the gravitational pulls of outer planets with a variety of masses and orbits can drag an inner rocky planet into an eccentric oval-shaped orbit. This means that the distance of the inner planet from its star changes over time.
“When the planet is closer to the star, the gravitational field is stronger, and the planet is deformed into an American football shape,” study co-author Rory Barnes, an astrobiologist and planetary scientist at the University of Washington in Seattle,said in a statement. “When farther from the star, the field is weaker, and the planet relaxes into a more spherical shape.”
This constant tidal flexing causes layers inside the planet to rub against each other, producing warmth. This effect, known as tidal heating, is what drives volcanism on Jupiter’s moon Io.
“For planets in the habitable zone around low-mass stars, tides raised on the planet by the star can be very important,” lead study author Christa Van Laerhoven, a planetary scientist who will soon be a postdoctoral researcher at the Canadian Institute for Theoretical Astrophysics in Toronto, told Space.com. “Tides raised on the habitable zone planet by its star can provide a long-term internal heat source if there is another well-placed planet in the system.”
Tidal heating could help keep a rocky planet internally warm and tectonically active in the habitable zone of a red dwarf for the star’s lifetime of up to 10 trillion years, or more than 700 times the 13.7-billion-year history of the universe, Barnes said.
“Perhaps in the distant future, after our sun has died out, our descendants will live on worlds like these,”Barnes said in a statement.
The researchers suggested that if astronomers were to find any Earth-size planetsin the habitable zones of red dwarfs, they should follow up with searchers for outer companion planets that might improve the inner world’s chance at hosting life. In the future, they also hope to model systems with three or more planets.
Van Laerhoven, Barnes and their colleague Richard Greenberg detailed their findings in the July issue of the journal Monthly Notices of the Royal Astronomical Society.
The solar system coalesced from a huge cloud of dust and gas that was isolated from the rest of the Milky Way galaxy for up to 30 million years before the sun’s birth nearly 4.6 billion years ago, a new study published online today (Aug. 7) in the journal Science suggests. This cloud spawned perhaps tens of thousands of other stars as well, researchers said.
If further work confirms these findings, “we will have the proof that planetary systems can survive very well early interactions with many stellar siblings,” said lead author Maria Lugaro, of Monash University in Australia.
“In general, becoming more intimate with the stellar nursery where the sun was born can help us [set] the sun within the context of the other billions of stars that are born in our galaxy, and the solar system within the context of the large family of extrasolar planetary systems that are currently being discovered,” Lugaro told Space.com via email.
A star is born
Radiometric dating of meteorites has given scientists a precise age for the solar system — 4.57 billion years, give or take a few hundred thousand years. (The sun formed first, and the planets then coalesced from the disk of leftover material orbiting our star.)
But Lugaro and her colleagues wanted to go back even further in time, to better understand how and when the solar system started taking shape.
This can be done by estimating the isotope abundances of certain radioactive elements known to be present throughout the Milky Way when the solar system was forming, and then comparing those abundances to the ones seen in ancient meteorites. (Isotopes are versions of an element that have different numbers of neutrons in their atomic nuclei.)
Because radioactive materials decay from one isotope to another at precise rates, this information allows researchers to determine when the cloud that formed the solar system segregated out from the greater galaxy — that is, when it ceased absorbing newly produced material from the interstellar medium.
Estimating radioisotope abudances throughout the Milky Way long ago is a tall order and involves complex computer modeling of how stars evolve, generate heavy elements in their interiors and eventually eject these materials into space, Lugaro said.
But she and her team made a key breakthrough, coming up with a better understanding of the nuclear structure of one radioisotope known as hafnium-181. This advance led the researchers to a much improved picture of how hafnium-182 — a different isotope whose abundances in the early solar system are well known — is created inside stars.
“I think our main advantage has been to be a team of experts in different fields: stellar astrophysics, nuclear physics, and meteoritic and planetary science so we have managed to exchange information effectively,” Lugaro said.
A long-lasting stellar nursery
The team’s calculations suggest that the solar system’s raw materials were isolated for a long time before the sun formed — perhaps as long as 30 million years.
“Considering that it took less than 100 million years for the terrestrial planets to form, this incubation time seems astonishingly long,” Martin Bizzarro, of the University of Copenhagen in Denmark, wrote in an accompanying “Perspectives” piece in the same issue of Science.
Bizzarro, like Lugaro, thinks the new results could have application far beyond our neck of the cosmic woods.
“With the anticipated discovery of Earthlike planets in habitable zones, the development of a unified model for the formation and evolution of our solar system is timely,” Bizarro wrote. “The study of Lugaro et al. nicely illustrates that the integration of astrophysics, astronomy and cosmochemistry is the quickest route toward this challenging goal.”
The researchers plan to investigate other heavy radioactive elements to confirm and refine their timing estimates, Lugaro said.
The abstract of the new study can be found here, while this link leads to the abstract of Bizzarro’s companion piece.
Only a handful of these rapid, millisecond-duration events, known as “fast radio bursts” (FRBs), had been detected previously, all of them by a single instrument — the Parkes Observatory in Australia. As a result, some astronomers have speculated that FRBs have local origins.
But the latest burst, which was observed on Nov. 2, 2012 by the Arecibo radio telescope in Puerto Rico, puts the lie to that notion, researchers said.
“Our result is important because it eliminates any doubt that these radio bursts are truly of cosmic origin,” study co-author Victoria Kaspi, of McGill University in Montreal, Canada, said in a statement. “The radio waves show every sign of having come from far outside our galaxy — a really exciting prospect.”
Kaspi is principal investigator of the Pulsar ALFA (PALFA) survey, a search for pulsars — fast-spinning, super-dense objects that emit beams of light (which appear to pulse at a regular interval, because they can be observed only when the pulsar is pointed at Earth). The research team, led by Laura Spitler of the Max Planck Institue in Germany, discovered the new FRB in the PALFA data.
The newly observed burst is the first of its kind discovered by a telescope other than Parkes, researchers said.
“The brightness and duration of this event, and the inferred rate at which these bursts occur, are all consistent with the properties of the bursts previously detected by the Parkes telescope in Australia,” said Spitler, who was completing her PhD at Cornell University when the research began.
The short lifetime of FRBs makes it tough to study them; only seven events, including the newest burst, have been recorded since their 2007 discovery. But the new study should help researchers get a better grip on FRBs.
Their presumed extragalactic origins mean that fast radio bursts could provide unprecedented opportunities to study the intergalactic medium — the dust and gas between galaxies — according to the research paper, which was published in the Astrophysical Journal.
By extrapolating how much of the sky was studied and for how long, scientists have calculated that FRBs probably occur roughly 10,000 times a day. Based on this occurrence rate, PALFA is expected to find two to three more FRBs in the coming years.
The source of fast radio bursts remains a mystery that astrophysicists are eager to solve. A number of exotic possibilities include evaporating primordial black holes, merging or collapsing neutron stars and superconducting cosmic strings. Flares from magnetically active neutron stars, known as magnetars, could also be responsible for the events, researchers said.
Extremely bright flashes from pulsars outside the galaxy are another possibility. The research team suggested that FRBs could be pulses that repeat over even longer timescales than anticipated. If this is the case, longer observation times would be required to spot them.
“We cannot be certain that the bursts are non-repeating,” the team wrote in the paper. “Detecting an astrophysical counterpart will be an important step in determining whether we expect repeated events.”
In our solar system, the orbits of most planets are nearly circular, orbiting the sun’s equator. However, many of the exoplanets astronomers have discovered in the past two decades or so have mysteriously skewed orbits. They may be eccentric — that is, oval-shaped. They could also be inclined — tilted at an angle from the equators of their stars.
One potential explanation for these skewed orbits might be the gravitational influence of a companion star near the host stars of those exoplanets. Although the sun is a solitary star, most stars form in binary pairs, with both stars orbiting each other. In fact, there are many three-star systems as well, and even some that harbor up to seven stars.
Now, astronomers have captured the clearest picture yet of planet-forming disks around binary stars. They found these disks may be wildly misaligned around their stars, hinting that exoplanets may often be found in eccentric or inclined orbits from the moment they are born.
The researchers made this discovery while surveying a series of binary stars using the Atacama Large Millimeter/submillimeter Array (ALMA) of radio telescopes in Chile. ALMA is the largest and most expensive ground-based astronomical project to date.
The scientists focused on the two stars in the young HK Tauri system, which is about 450 light-years from Earth in the constellation of Taurus. These stars are less than 5 million years old and are separated by about 36 billion miles (58 billion kilometers), or 13 times the distance of Neptune from the sun.
Stars and planets form out of vast clouds of dust and gas. As the material in these clouds contracts under gravity, it begins to rotate until most of the dust and gas falls into flattened disks swirling around stars. Eventually worlds are born from these protoplanetary disks.
The star in the pair that looks dimmer, HK Tauri B, appears that way because the protoplanetary disk around it blocks out much of its light. The disk itself, however, can be easily observed by the visible and near-infrared starlight it scatters.
The star that appears brighter, HK Tauri A, also has a protoplanetary disk, but it is tilted in a way that does not block out its star’s light. Therefore, the disk cannot be seen in visible light because its faint glow is swamped by the dazzling brightness of its star. This disk does shine brightly in millimeter-wavelength light, however, which ALMA can readily detect. [7 Ways to Discover Alien Planets]
Using ALMA’s unprecedented resolution and sensitivity, the researchers successfully measured the rotation of HK Tauri A’s disk. This revealed the two disks are tilted with each other by at least 60 degrees. This means that instead of being in the same plane as the orbits of the two stars, at least one of the disks must be significantly misaligned.
“What was surprising to me was how clearly the result — misalignment of the disks — popped out of the data when we were first looking at it,” said study author Eric Jensen, an astronomer at Swarthmore College in Pennsylvania. “That’s partly a testament to the high quality of the data from ALMA, but partly a result of just how misaligned the two disks are with each other.”
Since material that will eventually form planets is in skewed orbits around these stars, the worlds that emerge from these disks may also end up in eccentric or inclined orbits. “Binary star companions may influence the orbits of planets, possibly explaining some, though not all, of the weird orbits we see among extrasolar planets,” Jensen told Space.com.
However, most exoplanets with skewed orbits are not in known binary systems.
“There are almost certainly some of these systems that have low-mass binary companions that haven’t been discovered yet, but that won’t be the case for all systems,” Jensen said. “So while this binary-star-driven mechanism can explain some of the misaligned systems, it can’t explain everything. That’s an interesting puzzle that people are still working on.”
One probable mechanism for what causes exoplanets to have skewed orbits around solitary singleton stars is interactions among the planets in those systems.
“If you form a lot of planets around a given star, especially if their orbits are pretty closely packed together, you are going to have interactions between planets, which can change their orbits,” Jensen said. “In fact, even in our own solar system, people think that Uranus and Neptune have been pushed into wider orbits than those in which they originally formed, due to interactions with Jupiter and Saturn.”
In the future, the researchers want to look at more binary systems with protoplanetary disks to see how typical or atypical skewed disks are. Jensen and his colleague Rachel Akeson detailed their findings in the July 31 issue of the journal Nature.
In fact, clouds might help Earth-like planets remain hospitable to life even when orbiting a sun-like star as closely as the hellish Venus circles the sun in our solar system, the scientists added.
This finding suggests that many alien worlds previously thought to be too hot for life as we know it may actually be habitable, investigators said.
Astronomers have confirmed the existence of more than 1,700 worlds beyond the solar system in the past 20 years, and may soon prove the existence of thousands more such exoplanets. Of key interest are exoplanets in habitable, or Goldilocks, zones, the regions around stars just warm enough to possess liquid water on their surfaces, as there is life virtually wherever liquid water is found on Earth.
Habitable alien planets
The distance at which a planet orbits its star is one factor behind how much light from the star heats up that world’s surface. Another factor controlling how much energy a planet gets from its star are clouds in that world’s atmosphere, which can reflect light away from a world and cool it down — for instance, clouds account for most of the sunlight reflected away from Earth. [Habitable Zones for Alien Planets Explained (Infographic)]
Now scientists find that on planets that rotate much slower than Earth, clouds form that can help those worlds maintain Earth-like climates, even when they receive levels of light from their stars that would make Earth uninhabitable for life as we know it.
The amount of clouds a planet has and where these clouds are located on that world are primarily controlled by how its atmosphere circulates. This in turn is determined in part by how slowly that planet spins. For instance, the more slowly a planet rotates, the longer both its days and nights are — this increases the difference in temperature between the day and night sides, and to even out this imbalance, the atmosphere will circulate more.
In addition, when a planet spins, masses of air on its surface will rotate as well, a phenomenon known as the Coriolis effect that influences how powerfully major wind patterns such as hurricanes whirl. The faster a world spins, the stronger the Coriolis effect, and the more the atmosphere will separate into multiple bands running parallel to the equator in which the winds circulate in distinct patterns. The slower a planet whirls, the weaker the Coriolis effect, and the less divided the atmosphere will be into distinct regions.
Cloudy with a chance of life?
To investigate the effects of a planet’s rotation on its habitability, scientists investigated how three-dimensional models of atmospheric circulation behaved on computer-simulated planets with the same mass and diameter as the Earth. These virtual worlds had rotation speeds ranging from twice as fast as Earth’s to 365 times slower than Earth’s, and received from about 0.25 to 2.5 times as much light from their stars as Earth does.
On Earth, cloud formation begins when heat from the sun causes water to evaporate. As this invisible water vapor rises, it cools and condenses into clouds of visible water droplets or ice crystals.
The scientists found that on what they considered rapidly rotating planets — ones that rotated about as fast as Earth — the atmosphere broke up into distinct bands, and clouds behaved much like they do on Earth. The habitable zones of these rapidly rotating worlds matched previous calculations for planets in general.
However, slowly rotating planets — ones that spin 100 times slower than Earth or more — had significantly wider habitable zones. They could maintain Earth-like climates even when receiving nearly twice as much light as rapidly rotating planets.
The scientists explained that on slowly rotating planets, the area on the planet that faces its star — the “substellar point” — gets heated for a long time. This causes air to rise from the substellar point.
“Clouds tend to form where air rises because moist warm air is cooled, leading to condensation,” said study co-author Dorian Abbot, a geophysicist at the University of Chicago.
Without a strong Coriolis effect to break up atmospheric circulation into distinct bands, more clouds form. At the substellar point, the researchers found cloud cover would be present 90 percent or more of the time, reflecting a significant amount of light away from the planet, Abbot said.
Venus-like planets and life
Intriguingly, “the model finds a habitable climate for a planet with Earth’s atmosphere in Venus’ orbit with Venus’ rotation rate because of increased cloud cover,” Abbot told Space.com. In comparison, Venus rotates more than 240 times slower than Earth, and orbits the sun at a distance of less than three-quarters of an astronomical unit (AU), the average distance from Earth to the sun, where it receives nearly twice as much light from the sun as Earth.
However, Venus is a hellish planet that is definitely not habitable. Temperatures on Venus reach 870 degrees F (465 degrees C), more than hot enough to melt lead. This makes the surface of Venus extremely dry — there is no liquid water on its surface because the scorching heat would cause any to boil away. The researchers suggest that Venus once rotated more rapidly, at a rate only about 10 to 100 times slower than Earth’s, which helped make it uninhabitable.
The researchers suggest their findings should be checked with other climate models and with more sophisticated cloud models. They detailed their findings in the April 25 edition of the Astrophysical Journal Letters.