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.
A new test could determine once and for all whether NASA’s Voyager 1 probe has indeed entered interstellar space, some researchers say.
While mission team members declared last year that Voyager 1 reached interstellar space in August 2012, not all scientists are sold. Two researchers working with Voyager 1 have drawn up a test to show whether the spacecraft is inside or outside of the heliosphere — the bubble of solar particles and magnetic fields that the sun puffs around itself.
The scientists who came up with the test predict that Voyager 1 will cross the current sheet — a huge surface within the heliosphere — at some point within the next one to two years. When that happens, Voyager team members should see a reversal in the magnetic field surrounding the probe, proving that it is still within the heliosphere. If this change doesn’t occur in the next two years or so, then Voyager is almost certainly already in interstellar space, researchers said.
“The proof is in the pudding,” George Gloeckler of the University of Michigan, lead author of the new study detailing the test, said in a statement. “This controversy will continue until it is resolved by measurements.”
Scientists have recently made measurements that seem to bolster the belief that Voyager is in interstellar space. Researchers measuring data from a solar eruption that shook the particles around Voyager 1 found that the density of the probe’s surroundings was much higher than earlier measurements, when it was thought to be inside the heliosphere.
Because of this difference, some team members have come to the conclusion that Voyager 1 is, in fact, outside of the heliosphere. (While particle densities are higher in the inner solar system than they are in interstellar space, this is not the case at the extreme outer reaches of the heliosphere, scientists said.)
Voyager 1 has measured cosmic rays and other signs indicating that it may have passed into interstellar space, it still hasn’t detected the predicted magnetic field change, Gloeckler pointed out. He expects that the polarity reversal may happen in 2015.
“If that happens, I think if anyone still believes Voyager 1 is in the interstellar medium, they will really have something to explain,” Gloeckler said in the statement. “It is a signature that can’t be missed.”
The developers of the new test think Voyager 1 is moving faster than the solar wind, meaning that it will cross over parts of the current sheet where the magnetic field reversal will happen. This data could prove that the probe is inside the heliosphere, according to a statement from the University of Michigan and the American Geophysical Union.
Other scientists working with Voyager also welcome the test.
“It is the nature of the scientific process that alternative theories are developed in order to account for new observations,” Ed Stone, NASA’s Voyager project scientist, said in a statement. “This paper differs from other models of the solar wind and the heliosphere and is among the new models that the Voyager team will be studying as more data are acquired by Voyager.”
Voyager 1 and its twin Voyager 2 launched to space in 1977 to study the planets of the solar system. Voyager 2 is still in communication with Earth and is expected to continue on, potentially entering into interstellar space a few years from now.
The new test, detailed in a study by Gloeckler and his co-author Len Fisk of the University of Michigan, has been accepted for publication in the journal Geophysical Research Letters.
New data collected by NASA’s Voyager 1 spacecraft have helped scientists confirm that the far-flung probe is indeed cruising through interstellar space, the researchers say.
Voyager 1 made headlines around the world last year when mission scientists announced that the probe had apparently left the heliosphere — the huge bubble of charged particles and magnetic fields surrounding the sun — in August 2012.
They came to this conclusion after analyzing measurements Voyager 1 made in the wake of a powerful solar eruption known as a coronal mass ejection, or CME. The shock wave from this CME caused the particles around Voyager 1 to vibrate substantially, allowing mission scientists to calculate the density of the probe’s surroundings (because denser plasma oscillates faster.) [Photo Timeline: Voyager 1's Trek to Interstellar Space]
This density was much higher than that observed in the outer layers of the heliosphere, allowing team members to conclude that Voyager 1 had entered a new cosmic realm. (Interstellar space is emptier than areas near Earth, but the solar system thins out dramatically near the heliosphere’s edge.)
The CME in question erupted in March 2012, and its shock wave reached Voyager 1 in April 2013. After these data came in, the team dug up another, much smaller CME-shock event from late 2012 that had initially gone unnoticed. By combining these separate measurements with knowledge of Voyager 1′s cruising speed, the researchers were able to trace the probe’s entry into interstellar space to August 2012.
And now mission scientists have confirmation, in the form of data from a third CME shock, which Voyager 1 observed in March of this year, NASA officials announced Monday (July 7).
“We’re excited to analyze these new data,” Don Gurnett of the University of Iowa, the principal investigator of Voyager 1′s plasma wave instrument, said in a statement. “So far, we can say that it confirms we are in interstellar space.”
Interstellar space begins where the heliosphere ends. But by some measures, Voyager 1 remains inside the solar system, which is surrounded by a shell of comets known as the Oort Cloud.
While it’s unclear exactly how far away from Earth the Oort Cloud lies, Voyager 1 won’t get there for quite a while. NASA scientists have estimated that Voyager 1 will emerge from the Oort Cloud in 14,000 to 28,000 years.
The craft launched in September 1977, about two weeks after its twin, Voyager 2. The probes embarked upon a “grand tour” of the outer solar system, giving the world some its first good looks at Jupiter, Saturn, Uranus, Neptune and the moons of these planets.
Like Voyager 1, Voyager 2 is still active and operational. It took a different route through the solar system and is expected to follow its twin into interstellar space a few years from now.
NASA’s Voyager 1 and Voyager 2 spacecraft are still going strong after nearly 37 years in space.
“Both spacecraft are still operating, still very healthy. I guess as healthy as we are at the table right now,” Suzanne Dodd, the Voyager project manager at NASA’s Jet Propulsion Laboratory (JPL) said, drawing a big laugh from the audience at the SpaceFest VI conference in Pasadena, California, on May 11.
Dodd was fresh out of college in 1985 when JPL recruited her as it geared up for Voyager 2′s upcoming encounter with Uranus. Nearly 30 years later, she is project manager of the Voyager Interstellar Mission under which the two spacecraft continue to explore the vast expanse of space beyond the planets.
Voyagers of the solar system
Dodd was actually the youngster on the Voyager reunion panel. She was joined by Voyager Project Scientist Ed Stone and retired Voyager Mission Design Manager Charley Kohlhase, who were both on the project when it was in the planning stages in the early 1970s.
When the Voyagers were launched in 1977, NASA expected them to last four or five years, long enough to get them through close encounters with Jupiter and Saturn. But, they just kept going and going.
Voyager 2 went on to flybys of Uranus in 1986 and Neptune in 1989. It is now about 105 astronomical units from Earth. (One AU is the average distance between the Earth and sun, about 92 million miles.) Voyager 1, which flew out of the plane of the solar system after its 1980 flyby of Saturn, is in interstellar space at 127 AUs.
Stone and Kohlhase recalled their astonishment when an image showing two exploding volcanoes on Jupiter’s moon Io came into JPL late on a Friday afternoon in March 1979. The plumes went hundreds of miles above the surface, and the fallout covered an area the size of France.
“We had what I call a terracentric view, which was based on understanding Earth,” Stone said. “Before Voyager, the only known active volcanoes in the solar system were on Earth. Then we flew by Io, a little moon about the size of our moon, with 10 times the volcanic activity of Earth. And suddenly our terracentric extrapolation just was falling way short, and that was happening time after time after time.
“It was an incredible time where every day there were so many things we were discovering that we just moved on to the next one,” Stone added. “If we didn’t understand what we were seeing right away, we said, all right, let’s wait ’til tomorrow to see what else we get.”
A groundbreaking mission
The Voyager missions also forever changed the way spacecraft were built and operated.
“The key thing about Voyager that was a revolution was it was a totally computer-controlled spacecraft that flies itself and has fault protection on board so that if something goes wrong, it takes action,” he said. “Because now it takes us 17 and a half hours to get a command up there, and it’s 17 and a half hours before we know if anything has happened.” Before the spacecraft were launched, Kohlhase had the job of sorting through some 10,000 trajectories for projected launch windows in 1976 through 1978. He used computers to determine which ones would allow the spacecraft to make the best approaches to Jupiter, Saturn and their moons. Kohlhase and the scientists settled on 110 trajectories and ultimately used two of them.
Dodd says the Voyager mission continues to throw up challenges today. The spacecraft have 20-watt transmitters – the equivalent of a refrigerator light bulb – and signals are only 1 billionth of a billionth of a watt in strength by the time they reach Earth. JPL uses the powerful antennas of the Deep Space Network to communicate with the distant spacecraft.
“The engineering challenges are extremely unique to Voyager,” Dodd said. “You’re operating instruments below temperatures that we can’t even measure. Challenges of finding out if we turn on a component that’s next to a hydrazine line, would that hydrazine line freeze or not. We don’t know.
“Another unique challenge to it is that the engineers who built this are retired, some have passed away, you need to get people like Charley out of retirement to come and talk to us,” Dodd added. “It’s a challenge engineering-wise, it’s a challenge from a knowledge standpoint of what people know. And that’s what makes this project fun.”
The Voyagers still have a lot of life left in them even after nearly four decades on space.
“Looking forward, we expect to get 10 more years of scientific data out of the Voyager spacecraft,” Dodd said. “We basically turned off everything we can turn off to save power. Backup heaters are off, backup systems are off. We’re having some serious discussions about how to move forward, because we’re almost down to the scientific instruments now.”
After that, the spacecraft could continue on for another five to seven years sending engineering signals to Earth. Engineers are already in discussions with the Deep Space Network about what experiments could be conducted with those signals before the spacecraft fall silent.
By analyzing photos taken by the Hubble Space Telescope, scientists at the SETI Institute in Mountain View, Calif., have caught sight of Naiad, the innermost of Neptune’s moons. The 62-mile-wide (100 kilometers) moon has remained unseen since the cameras on NASA’s Voyager 2 spacecraft discovered it in 1989.
Scientists recently tracked Naiad across a series of eight archival images taken by Hubble in December 2004 after using a different technique to help cancel out Neptune’s glare. Neptune is 2 million times brighter than Naiad, so Naiad is difficult to see from Earth, SETI officials said. [See photos of Neptune, the mysterious blue planet]
“Naiad has been an elusive target ever since Voyager left the Neptune system,” SETI scientist Mark Showalter said in a statement. Showalter announced the new findings today (Oct. during a session at the annual meeting of the American Astronomical Society’s Division for Planetary Sciences, held in Denver.
Now that scientists have spotted the small moon again, there are other mysteries to be solved. Naiad seems to have drifted off course: The new observations show that the moon is now ahead of its predicted path in orbit around Neptune, SETI officials said.
Scientists expect that the new trajectory could have something to do with Naiad’s interaction with one of Neptune’s other moons that caused the innermost moon to speed up in its orbit. The exact cause of the moon’s new orbit won’t be known until researchers collect more data.
The images taken in 2004 also reveal something about the ring arcs surrounding Neptune. Voyager observed four arcs during its flyby of the system, but the newly processed images show that the two leading arcs are absent, while the two trailing arcs haven’t changed, SETI officials said. Scientists aren’t sure what is causing this change, but the arcs have been shifting since their discovery.
“It is always exciting to find new results in old data,” Showalter said. “We keep discovering new ways to push the limit of what information can be gleaned from Hubble’s vast collection of planetary images.”
The same images taken by Hubble also helped Showalter and his colleagues find another small moon orbiting Neptune — a discovery they announced in July. The newfound moon, called S/2004 N 1, is much smaller than Naiad, at 12 miles (20 km) across, but it was easier to spot in the images because its orbit takes it farther from Neptune than Naiad’s orbit takes it from the planet, SETI officials said.
S/2004 N 1 evaded Voyager 2′s cameras in 1989 because of its tiny size. During its flyby, Voyager revealed six previously unknown moons circling Neptune. Scientists have now discovered 14 moons in orbit around the blue planet.
NASA’s Voyager 1 probe won’t rest on its laurels after becoming the first manmade object ever to reach interstellar space.
Voyager 1 arrived in interstellar space in August 2012 after 35 years of spaceflight, researchers announced Thursday (Sept. 12). While this milestone is momentous enough in its own right, it also opens up a new science campaign whose potential already has scientists salivating.
“For the first time, we’re actually going to be able to put our hands in the interstellar medium and ask what it does and what characteristics it possesses,” Gary Zank, director of the Center for Space Plasma and Aeronomic Research at the University of Alabama in Huntsville, told reporters Thursday. “It’s a tremendous opportunity.”
Into the unknown
Voyager 1 and its twin, Voyager 2, launched a few weeks apart in 1977 to study Jupiter, Saturn, Uranus and Neptune, as well as the moons of these outer planets.
The probes completed this historic “grand tour” in 1989, then embarked on a quest to study the outer reaches of the solar system and beyond.
Voyager 1 finally popped free of the heliosphere — the huge bubble of charged particles and magnetic fields that the sun puffs out around itself — on or around Aug. 25, 2012, becoming humanity’s first envoy to the vast realms between the stars.
“This is truly a remarkable achievement,” Zank said. “We’ve exited the material that’s created by the sun, and we’re in a truly alien environment. The material in which Voyager finds itself is not created by the sun; it’s created, in fact, by our neighboring stars, supernova remnants and so forth.”
Many discoveries to come
This new vantage point should yield big scientific dividends, Zank added. For example, Voyager 1 should now help researchers get a much better look at galactic cosmic rays, charged particles accelerated to incredible speeds by far-off supernova explosions.
Observations of galactic cosmic rays made from within the heliosphere are not ideal, since the solar wind tends to affect these high-energy particles substantially.
“Being outside the heliosphere allows us an opportunity to, in a sense, look at the undiluted galactic cosmic ray spectrum,” Zank said. “That will tell us a great deal more about the interstellar medium at very distant locations. It’ll tell us about how the galactic cosmic rays propagate through this very complicated interstellar medium.”
Voyager 1 should also be able to shed light on the nature of the instellar medium, and how material from other stars flows around the heliosphere, researchers said.
“Now we will be able to understand and measure and observe that interaction, which is a very important part of how the sun interacts with what’s around it,” Voyager chief scientist Ed Stone, a physicist at the California Institute of Technology in Pasadena, told SPACE.com.
In short, reaching interstellar space does not mark the end of the road for Voyager 1, which should be able to continue gathering data for a dozen more years as long as nothing too important breaks down. (The probe’s dwindling power supply will force the mission team to turn off the first instrument in 2020, and all of Voyager 1′s science gear will be shut down by 2025.)
“This mission is not over,” said Voyager project manager Suzanne Dodd, of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Many, many more discoveries are out there, yet to come.”
Astronomers using the planet-hunting Kepler spacecraft have found two planets circling different stars in the violent environment of an ancient open star cluster called NGC 6811 located about 3,300 light-years from Earth. Until now, four of the more than 850 planets known outside the solar system were spotted in clusters.
The planets — Kepler-66b and Kepler-67b — are both smaller than the planets previously found in clusters. They are slightly smaller than Neptune, but larger than the Earth and circle sunlike stars. [The Strangest Alien Planets (Gallery)]
“We don’t have any planet that falls in that size bin or that mass bin between the Earth and Neptune, so we have to try to speculate about how they might be, structurally speaking,” lead study author Soren Meibom, of the Harvard-Smithsonian Center for Astrophysics, said. “It’s unlikely that they’re completely solid like the Earth because there is no precedence for that. If you have a planet this size, three-quarters the size of Neptune, about three Earth radii, it’s very likely to have a gaseous envelope, so it’s kind of in between a rocky planet like a Neptune … but we don’t have any analogue in the solar system, so we’re left guessing a little bit.”
The new research is detailed in the June 27 issue of the journal Nature.
Forming in a cluster
Some scientists thought that it would be more difficult for exoplanets to survive in star clusters because of the turbulent environment that surrounds them. Supernova explosions and the movements of other stars in the cluster can change the orbits of planets that formed around relatively stable stars. [How Alien Planet Sizes Stack Up (Infographic)]
The orbits of Kepler-66b and Kepler-67b, however, do not seem to have been disturbed since their formation one billion years ago, Meibom said.
These planets are also unique because they are the first cluster-based planets to be discovered by transiting — passing between their star and the Earth. This allowed Meibom to measure their relatively small size.
“Big planets are easier to find, but if they are less common than small ones, we may not find them,” William Welsh, an astronomer at San Diego State University who is unaffiliated with the research, said. “Previous searches for transiting planets in clusters didn’t find any planets, but it’s not because planets are rare. It’s because 1) planets as small as the ones in this paper are extremely hard, if not impossible, to detect using a ground-based telescope; and (2) the large Jupiter-size planets that could have been found are less common than the harder-to-see and more common small planets.”
Just as common
Meibom and his team used data they collected from 377 stars in the cluster to understand the frequency of finding cluster-based planets versus planets circling stars in the open field. They found that astronomers can expect to detect a similar number of mini-Neptunes in both the field and in clusters.
These types of planets could be just as commonly found orbiting stars in clusters as they are around other kinds of stars.
“The two planets we found are going around their stars over a time of 15 and 17 days respectively and that is also a very typical orbital period for planets found outside of clusters,” Meibom said. “Both the frequency and the properties in terms of size and orbital period are consistent with what we see outside of clusters.”
This finding might also help scientists understand whether habitable alien planets could form in clusters, however, it is still unclear whether life could exist while a young star remains within a cluster.
“The sun was once part of a cluster, and our solar system planets formed while part of the cluster,” Welsh wrote in an email to SPACE.com. “Life probably did not emerge while the sun was part of the cluster, though that depends on how long it took for the cluster to dissolve. But the reason for that may be more due to the bombardment of the very young Earth by proto-planetary debris than anything to do with the cluster environment … Life probably did not get a permanent foot-hold on Earth while we were part of a cluster, if the cluster dispersed in less than 700 million years.”
It could also be possible to search for planets in closer star clusters like the Pleiades or the Hyades, but it might not happen for a while, Meibom said. Kepler cannot hunt for planets in those closer clusters because it is focused on only one part of the distant sky, and ground-based methods have not been powerful enough to detect any small planets as of yet.
Future missions, however, could help scientists investigate these closer clusters, Meibom said. NASA’s planned Transiting Exoplanet Survey Satellite, launching in 2017, will search for planets transiting in front of smaller and cooler stars — the most common in the galaxy.
This is the second bit of surprising exoplanet news in as many days. Scientists recently found three planets within the habitable zone of a star 22 light-years from Earth.
The group, led by a postdoctoral researcher at MIT, proposes to use the venerable observatory to find small, rocky exoplanets around brown dwarfs, which are larger than planets but too small to ignite the nuclear fusion reactions that power stars.
Astronomers will seek planets crossing the face of these brown dwarfs, in the hopes that some of them will end up being capable of supporting life as we know it. [9 Exoplanets That Could Host Alien Life]
The planets sought would orbit more closely than Mercury does to the sun, but the faint warmth of brown dwarfs could still make such inner regions habitable, researchers said.
“Our program represents an essential step towards the atmospheric characterization of terrestrial planets and carries the compelling promise of studying the concept of habitability beyond Earth-like conditions,” the team’s paper stated.
Spotting small planets around brown dwarfs
The team is aiming for Mars-size planets because of their importance in planetary formation models, lead author Armaury Triaud told SPACE.com.
Models suggest our solar system emerged from a spinning disk of dust and gas, with planets slowly clumping together as particles collided, Triaud said, cautioning that we can’t be completely sure of what actually occurred.
Our nascent solar system crossed an important threshold when those protoplanets reached the size of Mars, he said.
“Eventually these planet embryos, the size of Mars, those would collide and form bigger rocky planets, or the core of [gas giant] planets such as Jupiter,” Triaud said.
It would be easier to spot such small, rocky worlds around a brown dwarf than a larger star, he added. Brown dwarfs are brighter in the infrared – the wavelength in which heat radiates – and those we can see are relatively close to Earth, making it easier to detect the effect of any planets on their motions.
Spitzer’s data on planets could then be used by the forthcoming James Webb Space Telescope. James Webb should be able to probe planetary atmospheres, possibly to search for “biomarker” molecules such as oxygen, Triaud noted, although the orbiting observatory would need to stare at the planet for a long time.
“Right now, there are no projects able to find an Earth-sized planet whose atmosphere can be studied with the James Webb,” he said. “Our project is the only path.”
Short orbits, lots of data
In a brown dwarf’s “habitable zone” — the range of distances in which liquid water could exist on a world’s surface — it’s possible that a planet could pass between the brown dwarf and Earth more than 50 times a year, providing ample opportunity for the science team to conduct observations.
“Our simulation shows that with only 50 occultations, you’ll be able to reliably detect the atmosphere of a planet. It’s 50 years, in a sense, of research.”
The same data, Triaud noted, would be useful for studying brown dwarfs themselves — specifically their rotations and what happens in their atmosphere.
The team’s paper, which is a portion of an observing proposal made for NASA, is available on the online preprint site Arxiv.org.
Triaud said the proposal is being considered, along with many others, as cases to further extend Spitzer’s mission. If the extension is accepted, his team’s proposal will compete against those of others for valuable telescope time.
Spitzer launched in August 2003. It ran out of coolant four years agobut is observing new targets (such as near-Earth objects) as part of an extended mission.
Numerous rocky, Earth-like worlds have been discovered by transit surveys such as NASA’s Kepler mission.
For those familiar with the transit of Venus last year, exoplanet transits are the same idea — an exoplanet crosses the face of its parent star as perceived by observers on or near Earth. By comparing the amount of starlight the transiting planet blocks and the total starlight emitted by the host star, astronomers can determine the radius of a transiting planet.
Recent surveys have hinted at the existence of exoplanets with rocky surfaces, making them similar to our own “terrestrial” planets Mercury, Venus, Earth and Mars. However, a number of the exoplanets thought to have rocky surfaces appear to not have any significant atmospheres. [The Strangest Alien Planets]
One such exoplanet is Corot-7b, which orbits very close to its parent star. Exoplanet 55 Cancri e, estimated to have roughly twice Earth’s radius and eight times Earth’s mass, also may be a rocky planet, and perhaps even made of diamond.
The first rocky exoplanet discovered by the Kepler mission was Kepler-10b, with roughly 4 1/2 times Earth’s mass. The Kepler mission has since discovered numerous “super-Earth” type exoplanets, which have masses greater than Earth but less than planets such as Neptune. Due in part to their high mass, super-Earths could be rocky or have very thick gaseous atmospheres like Neptune.
In order to better understand the composition of terrestrial exoplanets, researchers from MIT and Caltech have proposed a method to identify unique chemical signatures from various surface materials by studying exoplanets in the infrared portion of the electromagnetic spectrum. A better understanding of exoplanet surface compositions will help researchers determine how prevalent Earth-like planets are in our galaxy, they say.
“Looking for Earth-like planets is one of key endeavors shared by many astronomers and a broader scientific community,” says lead author Renyu Hu of MIT.
Airless rocky planets
While the end goal would help researchers with the search for Earth-like exoplanets, the researchers’ methods are currently aimed at “airless” rocky worlds. Because there are similar objects in our solar system — notably our moon, Mars and Mercury — the team may be able to compare detected minerals in the solar system against signatures from rocky exoplanets.
The team proposes to analyze exoplanets in the infrared portion of the electromagnetic spectrum in order to determine the surface composition of exoplanets. Ideal exoplanets to study using the team’s method are those that transit their host star. With current technology however, the team cautions that determining surface composition of exoplanets is a very different process than studying their solar system counterparts. Due to the limits of technology, the team proposes to concentrate on the most prominent mineral signatures detected from exoplanets.
Mark Swain of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., who is not on the research team, said, “We’re most likely to discover signs of life through atmospheric discoveries.”
By focusing their method on “airless” rocky exoplanets with surface temperatures under 3,140 degrees Fahrenheit (1,727 degrees Celsius), the team can analyze the unique chemical signatures of different materials.
Several exoplanets detected by the Kepler mission (Kepler-22b, Kepler-20f and Kepler-11b) may in fact have silicate (rocky) surfaces, making them ideal candidates for the team’s method. The team states that a large number of exoplanets detected by Kepler are the right distance from their host star to have rocky surfaces. [A World of Kepler Planets (Gallery)]
“We propose to determine whether an exoplanet has rocky surfaces by astronomical observations, via the unique thermal emission feature of silicate rocks,” Hu said. “By spectroscopy one may literally ‘see’ the rocks, or more precisely planetary regoliths.”
Different surface minerals provide unique signatures in different wavelengths. For example, in the visible and near-infrared, minerals such as pyroxene, olivine and hematite provide strong chemical signatures. Minerals such as hematite have prominent signals in the visible and ultraviolet wavelengths. Additionally, materials formed with water offer signals in the near-infrared.
“Several types of surfaces that can be distinguished by observing the reflection are ultramafic surfaces (indicating active volcanism on the planet), clay surfaces (indicating past or extant liquid water), and water ice,” Hu said. “Understanding the surface composition of a rocky exoplanet is one of the key steps to access the habitability and the availability of natural resources on the planet.”
Reading the rocks
Using infrared analysis techniques, the surface compositions of rocky objects in the solar system have been studied in detail.
On our moon, the basaltic nature of dark lunar regions, commonly referred to as “mare,” indicate they were formed by volcanic eruptions. Conversely, lunar highlands are bright, and their composition indicates the formation from a magma ocean.
Mars features strong iron signatures, which, combined with its red color, helped determine that a major component of the Martian surface is a mineral known as hematite. Additional surface signatures on Mars also indicate the presence of minerals such as pyroxene and olivine.
Observations of Mercury indicate similarities to the lunar highlands. However, recent observations by NASA’s Messenger spacecraft orbiting Mercury have challenged that view due to more precise surface composition readings.
The team asserts that rocky surfaces on exoplanets exhibit unique chemical signatures, along with volcanic surfaces, and surface water ice. If an exoplanet has a thin atmosphere, it may introduce additional signatures, especially if said atmosphere contains water vapor, carbon dioxide, methane, or ammonia. The team also stresses that without prior knowledge of a planet’s atmosphere, it can be difficult to determine exact surface compositions.
“Once you add an atmosphere, disentangling the signals becomes more work,” Swain said. “Sorting out what’s present is non-trivial, and detecting these mineralogy features in the presence of molecular features from the planet’s atmosphere will be a challenge. More papers in the future will most likely explore how to separate atmospheric and surface signals.”
“The key to resolve this is broad wavelength coverage and sensitive measurements,” he added. “The team really did a good job of focusing on this.”
In contrast to an atmosphere’s effect on determining surface composition, space weathering may alter the surface chemistry on an airless planet. Constant bombardment of a surface by cosmic rays, the solar wind, and micrometeorites can darken and redden the surface.
While current space-based observatories do not possess the necessary instruments to identify exoplanet surfaces, space telescopes such as the upcoming James Webb Space Telescope are thought to have the capability to detect rocky surfaces on planets orbiting sun-like stars.
Eventually, direct imaging of exoplanets may be necessary to determine the exact surface composition. Determining the surface composition of an exoplanet will provide a better understanding of its geological history and its odds for hosting life, scientists say.
“In the more distant future, the detailed composition of rocky surfaces on an exoplanet can be investigated by observing the stellar light reflected by the planetary surfaces,” Hu said. “To do this, the rocky exoplanet needs to be directly imaged, which requires space-based telescopes with great power.”
The newfound world — nicknamed “Einstein’s planet” by the astronomers who discovered it — is the latest of more than 800 planets known to exist beyond our solar system, and the first to be found through this method.
The planet, officially known as Kepler-76b, is 25 percent larger than Jupiter and weighs about twice as much, putting it in a class known as “hot Jupiters.” The world orbits a star located about 2,000 light-years from Earth in the constellation Cygnus. [7 Ways to Discover Alien Planets]
The researchers capitalized on subtle effects predicted by Albert Einstein’s special theory of relativity to find the planet. The first is called the “beaming” effect, and occurs when light from the parent star brightens as its planet tugs it a nudge closer to Earth, and dims as the planet pulls it away. Relativistic effects cause light particles, called photons, to pile up and become focused in the direction of the star’s motion.
“This is the first time that this aspect of Einstein’s theory of relativity has been used to discover a planet,” research team member Tsevi Mazeh of Tel Aviv University in Israel said in a statement.
Additionally, gravitational tides from the orbiting planet caused its star to stretch slightly into a football shape, causing it to appear brighter when its wider side faces us, revealing more surface area. Finally, the planet itself reflects a small amount of starlight, which also contributed to its discovery.
“We are looking for very subtle effects,” said team member David Latham of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. “We needed high quality measurements of stellar brightnesses, accurate to a few parts per million.”
The researchers used data from NASA’s Kepler spacecraft, which provided the extremely detailed observations necessary. While Kepler was designed to hunt for alien planets, it normally does so using the transit method, which looks for stars that dim periodically as planets pass in front of them.
“This was only possible because of the exquisite data NASA is collecting with the Kepler spacecraft,” said study leader Simchon Faigler of Tel Aviv University.
The other most popular planet-hunting tactic is called the wobble method, and searches for slight signs of movement in stars’ radial velocities caused by tugging planets.
The new Einstein-based method is best for larger worlds, and is currently incapable of finding Earth-sized planets, the scientists said. Still, it offers some benefits, as it does not require high-precision measurements of a star’s velocity, or for a star and its planet to align perfectly as viewed from Earth — the two main drawbacks of the most common methods.
“Each planet-hunting technique has its strengths and weaknesses. And each novel technique we add to the arsenal allows us to probe planets in new regimes,” said Avi Loeb, also from the Center for Astrophysics.
A paper detailing the planet discovery will be published in an upcoming issue of The Astrophysical Journal.
A new simulation of Pluto’s upper atmosphere shows that it extends so far from the planet that stray molecules may be deposited on its largest moon, Charon.
“That is amazing, from my perspective,” said Justin Erwin, the lead author of the paper and a Ph.D. student at the University of Virginia.
Researchers combined two previously known models of Pluto‘s atmosphere to better estimate the escape rate of molecules into space. Their refinement made a big difference.
“Our [calculated escape rate] is a little bit smaller, but the small change in the escape rate causes a large change in the structure of the atmosphere,” Erwin added.
Erwin’s supervisor at the University of Virginia, Robert Johnson, was a co-author of the paper reporting the findings, which was published on the preprint site Arxiv and has been submitted to the journal Icarus for publication.
Fire and ice
Pluto’s tenuous atmosphere is mainly composed of methane, nitrogen and poisonous carbon monoxide that likely comes from ice on the dwarf planet’s surface. The size of the atmosphere changes as Pluto moves closer and farther from the sun in its elliptical orbit.
When Pluto swings near the sun, the sun’s heat evaporates the ice and gases slowly escape into space. This process continues until Pluto moves away and the sun’s heat fades. Then, the ice builds up until Pluto approaches the sun again.
Pluto’s last close approach to the sun was in 1989. That is considered a fairly recent event, because it takes 248 years for the dwarf planet to orbit the sun once.
Researchers are trying to refine the escape rate of the gases ahead of the arrival of NASA’s New Horizons probe at Pluto in 2015, so that the spacecraft knows what to look for. For the new calculations, Erwin’s team used previously published research from themselves and other scientists. [Destination Pluto: NASA's New Horizons Mission in Pictures]
Uncertain atmospheric model
It’s difficult to figure out the size of Pluto’s atmosphere because of a debate over how best to measure it.
Pluto’s atmosphere is heated by infrared and ultraviolet light from the sun. Closer to the planet, ultraviolet light is absorbed in the atmosphere and only infrared heating takes place.
But farther away from the planet, the atmosphere is thin enough that the ultraviolet light affects the molecules. This is why researchers use ultraviolet heating models for the upper reaches of the atmosphere.
Molecules that are escaping from Pluto’s atmosphere move through a region called the thermosphere. The thermosphere is where much of the ultraviolet light is absorbed in the atmosphere; this heating drives the escape process.
In the exosphere, at the top of Pluto’s atmosphere, the atmosphere is so tenuous that collisions between particles do not happen as frequently.
The boundary between the thermosphere and the exosphere is called the exobase. Researchers aren’t sure where the “boundary” is. Because the mathematical model for each section of the atmosphere is different, this leads to vast uncertainties in calculating the size of Pluto’s atmosphere.
Last year, Erwin participated in an Icarus paper that demonstrated a new model to estimate the upper atmosphere’s extent during the solar minimum (when Pluto receives the least heat from the sun).
This time around, Erwin and his co-authors extended that model to include solar maximum — when Pluto is warmest — and solar medium, or average heating.
Pluto is so far from Earth, and so small, that its size isn’t precisely known. When forming their model, the researchers assumed that the diameter of Pluto is roughly 1,429 miles (2,300 kilometers). However, the accepted range for the diameter differs by as much as 62 miles (100 km).
The New Horizons team plans to better measure the size of Pluto and its atmosphere when the spacecraft swings by Pluto in 2015.
The photo, taken by a telescope at the European Southern Observatory’s La Silla Observatory, shows the head portion of the Seagull Nebula. The cloud of gas spotlighted in the image glows intensely due to radiation blasted out by a hot young star at its heart, scientists said.
Like other nebulas, the Seagull is a stellar nursery — an enormous cloud of dust, hydrogen, helium and other ionized gases where stars are being born. Nebulas come in a variety of sizes and shapes, some of which spur astronomers’ imaginations and evoke comparisons to animals or familiar objects.
The Seagull Nebula is so named because it resembles a gull in flight. The nebula, which is formally known as IC 2177, spans about 100 light-years from wingtip to wingtip. It’s found about 3,700 light-years from Earth, on the border between the constellations Monoceros (The Unicorn) and Canis Major (The Great Dog).
The nebula appears to be close to Sirius, the brightest star in the sky. But IC 2177 actually lies more than 400 times farther away from us than Sirius, researchers said.
The bright star lighting up the Seagull’s head is known as HD 53367. This star, which is visible in the center of the image and could be taken to be the bird’s eye, is about 20 times more massive than our own sun, researchers said.
Radiation streaming from the nebula’s young stars causes surrounding hydrogen gas to glow a rich red color. Light from these hot bluish-white stars also scatters off tiny dust particles, creating the blue haze seen in parts of the picture.
Parts of the Seagull Nebula complex were first observed in 1785 by the famed German-British astronomer Sir William Herschel, but the region imaged in the new picture weren’t photographed until a century later, researchers said.
A new method used to scan the atmosphere of a distant “hot Jupiter” world could eventually reveal insights about many distant alien planets — including, perhaps, whether or not they support life, the researchers added.
“If we could detect gases like oxygen, these could point to biological activity,” study co-author Ignas Snellen, an astronomer at Leiden University in the Netherlands, told SPACE.com.
A new look at exoplanet atmospheres
Scientists have analyzed the atmospheres of exoplanets before, but only when those worlds passed in front of their parent stars, much like Venus did during its recent transit of the sun.
The change in the light of a star as it streams through an exoplanet’s atmosphere can reveal details about the air’s composition. Different molecules absorb light in distinct ways, resulting in patterns known as spectra that allow scientists to identify what they are. [Gallery: The Strangest Alien Planets]
Now scientists have for the first time analyzed the atmosphere of an exoplanet that, like most such alien worlds, does not pass between its star and Earth.
The planet in question is Tau Boötis b, one of the first exoplanets to be discovered back in 1996 and one of the nearest exoplanets to Earth known, at about 51 light-years away. The world is a “hot Jupiter” — a gas giant orbiting very close to its parent star.
The exoplanet’s parent star, Tau Boötis, is easily visible with the naked eye, but the planet is not. Up to now, Tau Boötis b was only detectable through its gravitational pull on the star.
An international team caught the faint infrared glow from Tau Boötis b using the European Southern Observatory‘s Very Large Telescope (VLT).
“We were able to study the spectrum of the system in much more detail than has been possible before,” study lead author Matteo Brogi, of Leiden Observatory in the Netherlands, said in a statement. “Only about 0.01 percent of the light we see comes from the planet, and the rest from the star, so this was not easy.”
A wealth of information
Seeing the planet’s light directly also enabled the astronomers to measure the angle of the planet’s orbit, helping them deduce its mass — six times that of Jupiter’s — accurately for the first time.
“The new VLT observations solve the 15-year-old problem of the mass of Tau Boötis b. And the new technique also means that we can now study the atmospheres of exoplanets that don’t transit their stars, as well as measuring their masses accurately, which was impossible before,” Snellen said. “This is a big step forward.”
The spectra also yielded details about the temperature of the exoplanet’s atmosphere at different altitudes. Surprisingly, they found the planet’s atmosphere seems to be cooler higher up, the opposite of what is seen with other hot Jupiters.
Earth’s atmosphere is cooler at higher altitudes, the closer air gets to the frigid depths of space. Hot Jupiters, on the other hand, typically have atmospheres that are warmer farther up, perhaps due to gases present in their higher layers, such as titanium oxide.
Tau Boötis is a star very high in ultraviolet activity, radiation that may destroy these heat-absorbing gases and give Tau Boötis b an atmosphere with temperature features more like Earth’s, researchers said.
The researchers focused on the spectrum of carbon monoxide, which is expected to be the second-most common gas in the atmospheres of hot Jupiters, after hydrogen. Unlike hydrogen, carbon monoxide has very strong and observable infrared spectral features. Future research can concentrate on other common gases in hot Jupiter atmospheres, such as water vapor and methane.
“Our method shows that exoplanet atmospheres can be very well studied using ground-based telescopes,” Snellen said. Although Tau Boötis b is much too hot for any life, “possibly in the future we can extend this method to study much cooler planets like the Earth.”
The scientists detailed their findings in the June 28 issue of the journal Nature.
It is science fiction made fact: Astronomers have discovered two alien planets around the same star whose orbits come so close together that each rises in the night sky of its sister world like an exotic full moon.
The newfound planets are 1,200 light-years from Earth and an unprecedented find, researchers said. They differ greatly in size and composition but come within just 1.2 million miles (1.9 million kilometers) of each other, closer than any other pair of planets known, according to a new study.
One of the newly discovered alien planets, called Kepler-36b, appears to be a rocky “super-Earth” 4.5 times as massive as our planet. The other, Kepler-36c, is a gaseous, Neptune-size world about eight times as massive as Earth. The two planets meet up every 97 days in a conjunction that would make each dramatically visible in the other’s sky.
“These two worlds are having close encounters,” said co-lead author Josh Carter, of the Harvard-Smithsonian Center for Astrophysics, in a statement.
At their closest approach, the two planets are separated by five times the distance between the Earth and the moon. How such different bodies ended up in such similar orbits may be tough for current theories of planet formation and migration to explain, researchers said.
“This is unprecedented,” co-lead author Eric Agol, of the University of Washington, told SPACE.com via email. “They are as different in density as Earth and Saturn (the highest and lowest density planets in our solar system), yet they are 30 times closer than any pair of planets in our solar system.” (Agol later clarified to SPACE.com that Kepler-36b and c are actually more like 20 times closer together than any two planets in our neck of the woods.) [Gallery: The Strangest Alien Planets]
The two known planets in the Kepler-36 system — which is located in the constellation Cygnus (The Swan) — were detected by NASA’s Kepler Space Telescope.
Kepler is staring continuously at more than 150,000 stars, watching for telltale brightness dips caused when planets cross in front of the stars from the telescope’s perspective. Since its March 2009 launch, Kepler has flagged more than 2,300 potential alien planets; while only a small fraction have been confirmed to date, mission scientists think more than 80 percent of them will end up being the real deal.
Kepler-36c, which is about 3.7 times wider than Earth, likely has a rocky core surrounded by a substantial atmosphere filled with lots of hydrogen and helium, researchers said.
Kepler-36b, on the other hand, is a super-Earth just 1.5 times wider than our planet. Iron likely constitutes about 30 percent of its mass, water around 15 percent and atmospheric hydrogen and helium less than 1 percent, researchers said.
Though they’re very different in size and makeup, the two planets travel on surprisingly similar paths around their host star. Kepler-36c orbits once every 16 days, at an average distance of 12 million miles (19 million km). Kepler-36b orbits each 14 days and sits about 11 million miles (18 million km) from the star.
Kepler-36b probably formed relatively close to the star, while Kepler-36c likely took shape farther out. Astronomers model large-scale migrations that can bring initially far-flung planets much closer together, but the peculiar Kepler-36 system may force some refinements, researchers said.
“These models rely on assumptions that will likely have to be ‘tweaked’ or refined to account for both b and c’s proximity and compositional differences,” Carter told SPACE.com via email. “The existence of Kepler-36 may help clarify or invalidate these assumptions.”
Both planets are likely too hot to support life as we know it, with Kepler-36b probably sporting lava flows on its surface. They orbit roughly three times closer to their host star, known as Kepler-36a, than the hellishly hot planet Mercury does to our sun. And Kepler-36a is likely a bit hotter than our star, researchers said.
The researchers publish their results Thursday (June 21) in the journal Science.
An impressive sky scene
Every 97 days, Kepler-36b and c experience a conjunction that brings them within just 1.2 million miles (1.9 million km) of each other — roughly five times the Earth-moon distance. This would be quite a sight for an observer on the surface of either planet.
“Planet c would appear roughly 2.5 times the size of the full moon when viewed from the surface of planet b. Conversely, planet b would appear about the size of the full moon on planet c,” Carter said.
“We can speculate on the appearance of planet c: It may appear slightly more purple that Neptune,” he added. “The purple hue owes to absorption of red and yellow by sodium and potassium. There could also be a slight brown tint owing to hazes of photo-disassociated methane.”
Such dramatic vistas could well be around for many years to come, researchers said, for the orbits of Kepler-36b and c appear unlikely to change anytime soon.
“We are addressing this in a follow-up paper, but the short answer is that yes, these do appear to be stable on a long timescale,” Agol said.
Think of it as a win for the little guys. Astronomers using a small ground-based telescope have discovered two unusual alien planets around extremely bright, distant stars.
The two extrasolar planets are gas giant worlds detected using the Kilodegree Extremely Little Telescope (KELT) in southern Arizona, which has a lens that is roughly as powerful as a high-end digital camera, the researchers said.
“KELT is slightly more diminutive than Kepler, but we like to think it’s small but fierce,” said Thomas Beatty, a doctoral student at Ohio State University in Columbus. NASA’s Kepler space telescope is an orbiting observatory specially built to seek out distant planets.
Beatty presented the findings on June 13 at the 220th meeting of the American Astronomical Society in Anchorage, Alaska.
Hot Jupiters revealed
One of the newly found planets, called KELT-1b, is a massive world that is both incredibly hot and dense. The alien planet, which is mostly metallic hydrogen, is slightly larger than Jupiter, but contains a whopping 27 times the mass. [Gallery: The Strangest Alien Planets]
These types of alien worlds are known as “hot Jupiters” because they are gas giant planets that orbit extremely close to their parent stars.
KELT-1b is so close to its host star that it completes one orbit in a mere 29 hours. Being this close to its star, the planet’s surface temperature is likely above 4,000 degrees Fahrenheit (roughly 2,200 degrees Celsius), in the process receiving 6,000 times the amount of radiation that Earth receives from the sun, Beatty explained.
“[It] resets the bar for weird,” he said. “It’s the sort of object that we would not have expected to find this close to its parent star.”
KELT-1b is located approximately 825 light-years away in the constellation of Andromeda. The massive planet stood out to astronomers not only because of its close proximity to its parent star, but because of its unusual orbital dynamics.
“It’s massive enough that KELT-1 has raised tides on its parent star and actually spun it up,” Beatty said. “KELT-1 grabbed the star it’s around, pulled it so it’s spinning at the same rate, so now both KELT-1 and its parent star are locked in each other’s gaze as they go around.”
Auriga’s alien world
The other newly identified planet is called KELT-2Ab, and is located about 360 light-years away in the constellation of Auriga. The alien world is 30 percent larger than Jupiter with 50 percent more mass.
This discovery more closely resembles other exoplanets found to date, except KELT-2Ab’s parent star is so bright it can be seen from Earth through binoculars. In fact, the star is so luminous that researchers will be able to make direct observations of the planet’s atmosphere by examining light that shines through it when the star passes within KELT North’s field of view again in November.
Follow-up observations are also being planned using other ground-based instruments, as well as several space observatories, including the Hubble Space Telescope and the infrared Spitzer Space Telescope.
“We want to look at what’s going on in its atmosphere and its interior,” Beatty said. “The reason why individual hot Jupiters like these are still interesting is because we still fundamentally do not understand what goes on inside them.”
KELT-2Ab orbits a star that is slightly bigger than the sun, within a binary system called HD 42176.
It resides in a binary system called HD 42176, with one star that is slightly bigger than our sun, and another star that is slightly smaller. KELT-2Ab orbits the bigger star, which is bright enough to be seen from Earth with binoculars.
How they were found
Astronomers use KELT to find large planets orbiting very bright stars using the so-called transit method, which involves watching for tiny dips in the star’s light that could indicate a planet is crossing, or transiting, in front.
Rather than staring at a small group of stars at high resolution, the twin KELT North and KELT South telescopes observe millions of very bright stars at low resolution, the researchers said. KELT North scans the northern sky from Arizona, while KELT South covers the southern sky from Cape Town, South Africa.
While NASA’s prolific Kepler Space Telescope has identified roughly 2,300 alien planet candidates, the small ground-based KELT telescopes provide a low-cost alternative for exoplanet hunters by primarily using off-the-shelf technology. The hardware for a KELT telescope costs less than $75,000, the researchers said.