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.
The Earth’s moon may be a present from Venus, which once had a moon and then lost it, a new theory suggests. Under the theory, Earth’s gravity captured Venus’ old moon, giving our planet its big natural satellite.
This idea contrasts to the thinking of the vast majority of moon researchers, who believe that the Earth’s moon formed some 4.5 billion years ago when a planet-size body slammed into nascent Earth at high speed.
This giant impact hypothesis, however, has its own issues, as did all the alternative moon formation theories discussed this week at the Origin of the Moon conference at the Royal Society here. [The Moon: 10 Surprising Lunar Facts]
“I think part of the key to [understanding] the moon may be that Venus has no moon, and we certainly have to study it (Venus) more,” said Dave Stevenson, professor of planetary science at the California Institute of Technology, who proposed the Venus idea at the conference. In an interview with SPACE.com after his presentation, Stevenson said that he himself favored the impact theory on moon formation, but unfortunately this theory did not yet answer all the questions.
How did Earth get its moon?
The “moon capture” theory assumes that Earth used its gravitational pull to attract a pre-formed space body into its orbit, thus making a satellite of this object. [How the Moon Formed: A Lunar Tour (Video)]
However, the geochemical composition of the moon and Earth likely trips up this theory. Analyses of the lunar rocks brought back by NASA’s Apollo moon landing missions have shown that the satellite has an isotopic composition very similar to that of Earth.
Isotopes refer to varieties of chemical elements that have the same number of protons, but different numbers of neutrons. Two isotopes behave the same chemically.
And if both moon and Earth have very similar isotopes, it makes the capture theory difficult to maintain, said Alex Halliday, head of science at Oxford University. Such isotopic similarities suggest that “the material that makes up the moon did actually either come out of the Earth, or that the stuff that was in the disk that formed the moon got completely mixed up with the stuff in the Earth.”
Nonetheless, some aspects of the idea that the moon may have come from Venus are intriguing, he said.
“The reason why it’s interesting is that Earth and Venus are close to each other. They have similar mass, and people think they have probably formed in a similar way,” he said. “So the question is, if Earth and Venus formed in similar ways, how come the Earth has a moon and Venus doesn’t?”
Stevenson’s idea would answer that question, Halliday said, “throwing a new twist into the whole capture theory.”
There are many theories for what might have caused such a large moon for a planet as small as Earth. The most popular theory assumes an impact, where the debris of the collision — a mix of the material from Earth and the other body — gave birth to the moon. This body then stayed in orbit about the Earth, forever bound to its new home.
Another posits that the moon “fissioned” from the Earth’s crust and mantle due to the centrifugal force of a rapidly spinning early Earth.
Another theory, called binary accretion, assumes that the moon was born at the same time and place as Earth.
The biggest flaw of the fission, capture and binary accretion theories is that they cannot account for the high angular momentum of the Earth-moon system.
Scientists believe that initially the Earth was spinning so rapidly that a day lasted only five or six hours, and the moon was in a very low-altitude orbit. But gradually, tidal drag slowed the Earth’s spin and pushed the moon’s orbit up to its present level.
The capture theory will always face a challenge explaining the similar composition of the moon and Earth, Stevenson said. But if scientists analyze rocks from Venus and they turn out to be very similar to those on Earth, that would argue in favor of the capture theory. The giant impact idea also has trouble explaining why the Earth and the moon are so peculiarly similar.
Even though he himself favors the impact theory, Stevenson said he picked Venus for a larger purpose.
“We cannot understand the terrestrial planets unless we understand Venus, and at the moment, we don’t know anything about Venus in terms of the isotopes” it has, he says. “And I also think that as a test of our understanding of the origin of the moon, we need to understand whether Venus ever had a moon.”
If Venus indeed once had a moon and lost it, how might the planet have acquired a satellite in the first place?
Unlike what would have happened with Earth, the formation of any moon of Venus may have occurred much earlier, shortly after the formation of the solar system, Stevenson said.
Back then, there were still a lot of things whizzing around,” he said.
So Venus possibly would have gotten its moon after an even earlier giant impact of some sort, and the planet may have lost its moon either by collision or by escape. This would mean an object passed close by the Venus system and caused the moon to depart from its orbit, says Stevenson.
But even aside from the Venus idea, the widely preferred giant impact theory still “is not satisfactory in all respects,” Stevenson said.
Sean Solomon, the director of the Lamont-Doherty Earth Observatory of Columbia University, agrees. “We are still on the trail of the detailed scenario that would seem both likely and complete in its ability to account for all the geochemical and geophysical observations,” he said.
Until scientists have figured out that scenario, even the escaped moon of Venus is a plausible theory, he said.
“Even with the giant impact idea, we don’t know the origin of the impacting object. It could’ve been an early protoplanet. It could’ve been a moon of another object that was removed from the gravitational field of its original [planet]. It could’ve been a very large asteroid. All of those scenarios are still open.”
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.”
If a dangerous asteroid appears to be on a collision course for Earth, one option is to send a spacecraft to destroy it with a nuclear warhead. Such a mission, which would cost about $1 billion, could be developed from work NASA is already funding, a prominent asteroid defense expert says.
Bong Wie, director of the Asteroid Deflection Research Center at Iowa State University, described the system his team is developing to attendees at the International Space Development Conference in La Jolla, Calif., on May 23. The annual National Space Society gathering attracted hundreds from the space industry around the world.
An anti-asteroid spacecraft would deliver a nuclear warhead to destroy an incoming threat before it could reach Earth, Wie said. The two-section spacecraft would consist of a kinetic energy impactor that would separate before arrival and blast a crater in the asteroid. The other half of the spacecraft would carry the nuclear weapon, which would then explode inside the crater after the vehicle impacted. [Gallery: Potentially Dangerous Asteroids]
The goal would be to fragment the asteroid into many pieces, which would then disperse along separate trajectories. Wie believes that up to 99 percent or more of the asteroid pieces could end up missing the Earth, greatly limiting the impact on the planet. Of those that do reach our world, many would burn up in the atmosphere and pose no threat.
Wie’s study has focused on providing the capability to respond to a threatening asteroid on short notices of a year or so. The plan would be to have two spacecraft on standby — one primary, the other backup — that could be launched on Delta 4 rockets. If the first spacecraft failed on launch or didn’t fragment the asteroid, the second would be sent aloft to finish the job.
Wie admitted that sending nuclear weapons into space would be politically controversial. However, he said there are a number of safety features that could be built into the spacecraft to prevent the nuclear warhead from detonating in the event of a launch failure.
A nuclear weapon is the only thing that would work against an asteroid on short notice, Wie added. Other systems designed to divert an asteroid such as tugboats, gravity tractors, solar sails and mass drivers would require 10 or 20 years of advance notice.
Much of the technology for the mission has already been successfully demonstrated in flight, Wie said. NASA’s Deep Impact spacecraft sent a kinetic impactor to collide with Comet Tempel 1 on July 4, 2005. Four years later, the space agency sent a Centaur upper stage crashing into the moon during the LCROSS mission (Lunar Crater Observation and Sensing Satellite), followed by a sub-satellite that photographed the impact before crashing into the surface itself.
Funding the mission
Wie’s work has been funded under the NASA Innovative Advanced Concepts (NIAC) program. He received a $100,000 Phase I grant for 2011-2012 and then a Phase II grant worth $500,000 for 2012-2014.
NIAC doesn’t provide any additional funding after Phase II, so Wie will have to convince some agency — whether it be NASA or the Department of Defense — to fund the program through completion. This could be a difficult issue because there is no one agency in charge of planetary defense, he said.
The first step would be a $500 million flight validation mission that would target an asteroid approximately 50 meters in size. A nuclear weapon probably would not be required to destroy a body of that size, Wie said.
The point would be to demonstrate the capability to accurately target an asteroid that small, something that neither Deep Impact nor LCROSS accomplished. Accurately hitting a larger, more threatening asteroid would be easier.
The meteorite crashed on March 17, slamming into the lunar surface at a mind-boggling 56,000 mph (90,000 kph) and creating a new crater 65 feet wide (20 meters). The crash sparked a bright flash of light that would have been visible to anyone looking at the moon at the time with the naked eye, NASA scientists say.
“On March 17, 2013, an object about the size of a small boulder hit the lunar surface in Mare Imbrium,” Bill Cooke of NASA’s Meteoroid Environment Office said in a statement. “It exploded in a flash nearly 10 times as bright as anything we’ve ever seen before.” [The Greatest Lunar Crashes Ever]
NASA astronomers have been monitoring the moon for lunar meteor impacts for the past eight years, and haven’t seen anything this powerful before.
Scientists didn’t see the impact occur in real time. It was only when Ron Suggs, an analyst at NASA’s Marshall Space Flight Center in Huntsville, Ala., reviewed a video of the bright moon crash recorded by one of the moon monitoring program’s 14-inch telescopes that the event was discovered.
“It jumped right out at me, it was so bright,” Suggs said.
Scientists deduced the rock had been roughly 1-foot-wide (between 0.3 to 0.4 meters) and weighted about 88 lbs (40 kg).The explosion it created was as powerful as 5 tons of TNT, NASA scientists said.
When researchers looked back at their records from March, they found that the moon meteor might not have been an isolated event.
“On the night of March 17, NASA and University of Western Ontario all-sky cameras picked up an unusual number of deep-penetrating meteors right here on Earth,” Cooke said. “These fireballs were traveling along nearly identical orbits between Earth and the asteroid belt.”
Though Earth’s atmosphere protected our planet’s surface from being hit by these meteors, the moon has no such luck. Its lack of an atmosphere exposes it to all incoming space rocks, and the NASA monitoring program has spotted more than 300 meteor strikes that reached its surface since 2005.
Part of the motivation for the program is NASA’s eventual intent to send astronauts back to the moon. When they arrive, they’ll need to know how often meteors impact the surface, and whether certain parts of the year, coinciding with the moon’s passage through crowded bits of the solar system, pose special dangers.
“We’ll be keeping an eye out for signs of a repeat performance next year when the Earth-Moon system passes through the same region of space,” Cooke said. “Meanwhile, our analysis of the March 17th event continues.”
The scientists also hope to use NASA’s Lunar Reconnaissance Orbiter to photograph the impact site to learn more about how the crash occurred.
Titan, an ocean-covered moon around Saturn that’s usually so cold methane falls as rain, actually warms up enough in the summertime for high-speed cyclones to whip across its seas, according to new research.
Sea evaporation could create enough energy to produce winds as high as 44 miles per hour (70 km/h) on Titan, which is the largest of Saturn’s dozens of moons.
But whether cyclones form at all depends very much on what Titan’s seas are made of. If more than half of an ocean is composed of methane, the chemical recipe would be perfect for a storm.
“In the next few years, we will approach summer in the [northern] polar region and we might have the chance to see a cyclone, if the condition is favorable,” said Tetsuya Tokano, a researcher with the Institute for Geophysics and Meteorology at the University of Cologne.
Tokano’s research is appearing in the April 2013 issue of the journal Icarus.
Cyclones on Earth happen principally in two ways. The first, which cannot happen on Titan because the temperature range is too small, occurs when cold fronts and warm fronts run into each other. Warm and cold air bend around each other and generate high-speed winds.
The second happens when heat from Earth’s water warms the air and makes it rise, creating an energy cycle that produces high-speed winds. As the cycle continues, it fuels a spinning storm. This is what could happen on Titan.
Such winds could occur on Titan only above its mid-latitude seas, where there is the right combination of moisture and temperature to create the rising air. Tokano said the difficulty is that we don’t yet know the exact chemical composition of Titan’s seas.
“There is big uncertainty, and many possible types of hydrocarbons,” he said. However, if the seas are mostly methane, they could transfer enough energy from the surface of the sea into the atmosphere to create cyclones. Methane is the only liquid on Titan that can condense like water vapor on Earth.
‘No problem to detect’
Cassini hasn’t spotted any cyclones on Titan yet because it’s been too cold in the north. (The average surface temperature on Titan is minus 289 degrees Fahrenheit, or minus 178 degrees Celsius).
Summer won’t arrive on the moon until 2015, but Cassini should have at least two years of observations after that before ceasing operations.
The cyclone’s signature would be obvious and would be “no problem to detect,” Tokano said. If cyclones occur, there would be a huge energy transfer along with a storm size of at least 62 miles (100 kilometers), he predicted, making it easy to spot by the spacecraft. Cassini already has imaged cyclones on Saturn.
At Cassini’s resolution, the spacecraft wouldn’t necessarily need to be close by Titan to see a feature as large as a cyclone, he said. There are several close flybys of Titan scheduled between 2015 and 2017 as well.
While it’s difficult to predict what an observed cyclone would teach us, Tokano said it would fundamentally show changes in temperature in the northern hemisphere between winter and summer.
“This would indicate Titan’s weather has similarities with Earth,” Tokano added.
Chunks of hydrocarbon ice may float atop the lakes and seas of Saturn’s huge moon Titan, a new study reveals.
The presence of such ice floes in the ethane and methane seas on Titan would make the moon an even more exciting target for astrobiologists, researchers said.
“One of the most intriguing questions about these lakes and seas is whether they might host an exotic form of life,” study co-author Jonathan Lunine of Cornell University said in a statement. “And the formation of floating hydrocarbon ice will provide an opportunity for interesting chemistry along the boundary between liquid and solid, a boundary that may have been important in the origin of terrestrial life.”
Titan — Saturn’s largest moon, with a diameter of 3,200 miles (5,150 kilometers) — is the only body in our solar system apart from Earth known to host stable bodies of liquid on its surface. While Earth’s weather cycle is based on water, Titan’s involves hydrocarbons, with liquid ethane and methane falling as rain and pooling in large lakes and seas. [Amazing Photos of Titan]
NASA’s Cassini spacecraft has spotted a huge network of these seas in Titan’s northern hemisphere, along with a handful in the moon’s southern reaches.
Cassini scientists had previously assumed that these seas would not have floating ice, since solid methane is denser than its liquid counterpart and should thus sink. But the new study suggests that things are not so simple.
The researchers created a model investigating how Titan’s seas interact with the moon’s nitrogen-rich atmosphere, creating pockets of varying composition and temperature.
The team determined that hydrocarbon ice should indeed float in the moon’s seas, as long as the temperature is just below methane’s freezing point — minus 297 degrees Fahrenheit, or minus 183 degrees Celsius — and the ice is at least 5 percent “air,” which is the average composition for young sea ice here on Earth.
This ice may be colorless, perhaps with a reddish-brown tint provided by Titan’s atmosphere, researchers said.
“We now know it’s possible to get methane-and-ethane-rich ice freezing over on Titan in thin blocks that congeal together as it gets colder — similar to what we see with Arctic sea ice at the onset of winter,” lead author Jason Hofgartner, also of Cornell, said in a statement. “We’ll want to take these conditions into consideration if we ever decide to explore the Titan surface some day.”
Floating sea ice could be a fleeting phenomenon on Titan, if it exists at all. If the temperature drops a few degrees, the ice will begin to sink, researchers said.
Cassini should be able to test the new model out, and soon. Titan’s northern spring is underway, meaning lakes and seas in the moon’s northern reaches are warming up.
As this happens, ice may rise to the top, creating a surface that appears brighter and more reflective to Cassini’s radar instrument. As the area continues to warm, the ice should melt, producing an entirely liquid surface that will look darker to Cassini, researchers said.
“Cassini’s extended stay in the Saturn system gives us an unprecedented opportunity to watch the effects of seasonal change at Titan,” Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., said in a statement. “We’ll have an opportunity to see if the theories are right.”
The $3.2 billion Cassini mission, a joint effort of NASA, the European Space Agency and the Italian Space Agency, launched in 1997 and arrived at Saturn in 2004. It will continue to observe the ringed planet and its many moons through at least 2017.
The discovery of huge amounts of water ice and possible organic compounds on the heat-blasted planet Mercury suggests that the raw materials necessary for life as we know it may be common throughout the solar system, researchers say.
Mercury likely harbors between 100 billion and 1 trillion metric tons of water ice in permanently shadowed areas near its poles, scientists analyzing data from NASA’s Messenger spacecraft announced Thursday (Nov. 29).
Life on sun-scorched Mercury remains an extreme longshot, the researchers stressed, but the new results should still put a spring in the step of astrobiologists around the world.
“The more we examine the solar system, the more we realize it’s a soggy place,” Jim Green, the director of NASA’s Planetary Science Division, said during a press conference today.
“And that’s really quite exciting, because that means the amount of water that we have here on Earth — that was not only inherent when it was originally formed but probably brought here — that water and other volatiles were brought to many other places in the solar system,” Green added. “So it really bodes well for us to continue on the exploration, following the water and its signs throughout the solar system.” [Latest Mercury Photos from Messenger]
The observations by Messenger, which has been orbiting Mercury since March 2011, provide compelling evidence that reflective patches first spotted near the planet’s poles by the Arecibo radio telescope in Puerto Rico two decades ago are indeed water ice, researchers said.
In the coldest parts of Mercury — permanently shadowed regions where temperatures drop to perhaps minus 370 degrees Fahrenheit (minus 223 degress Celsius) — this ice can lie bare and exposed. But Messenger’s data also show that much more frozen water is found in slightly warmer areas, buried beneath a strange dark material that acts as an insulator.
This dark stuff is likely a mixture of complex organic compounds, the carbon-containing building blocks of life as we know it, researchers said during Thursday’s news conference.
“This organic material may be the same type of organic material that ultimately gave rise to life on Earth,” said Messenger participating scientist David Paige of UCLA.
Planet Mercury: Simple Facts, Tough Quiz
The closest planet to the sun is also an elusive world, revealing itself in our night sky only fleetingly. But that doesn’t excuse you from knowing some basic facts. Don’t think this’ll be easy, though.
Helping scientists read the book of life
Mercury probably acquired much of its water and organic material the same way Earth did, researchers said — via comet impacts and asteroid strikes. Ice and organics are common on the frigid bodies in the solar system’s outer reaches.
“There’s a lot of water out there, as there is a lot of water around other stars, but at substantial distance,” said Messenger principal investigator Sean Solomon, of Columbia University’s Lamont-Doherty Earth Observatory.
With its ultra-thin atmosphere and proximity to the sun, Mercury is probably not a good bet to host life as we know it. But finding ice and organics there should still inform the hunt for organisms beyond Earth and aid scientists’ quest to learn more about how life took root on our planet.
“The history of life begins with the delivery to some home object of water and of the building blocks, the organic building blocks, that must undergo some kind of chemistry, which we still don’t understand on our own planet,” Solomon said.
“And so Mercury is becoming an object of astrobiological interest, where it wasn’t much of one before,” Solomon added. “That’s not say to say that we expect to find any lifeforms — I don’t think anybody on this table does — but in terms of the book of life, there are some early chapters, and Mercury may indeed inform us about what’s in those chapters.”
Cassini took the spectacular Saturn storm photos yesterday (Nov. 27) and relayed it back to Earth the same day, mission scientists said in a statement. The pictures reveal a swirling storm reminiscent of the recent Hurricane Sandy that recently plagued our own planet.
The tempest is located in a strange hexagonal cloud vortex at Saturn’s north pole that was first discovered by the Voyager spacecraft in the early 1980s, and sighted more closely by Cassini since then. The strange six-sided feature, which is nearly 15,000 miles (25,000 kilometers) across, is thought to be formed by the path of a jet stream flowing through the planet’s atmosphere.
“Cassini’s recent excursion into inclined orbits has given mission scientists a vertigo-inducing view of Saturn‘s polar regions, and what to our wondering eyes has just appeared: roiling storm clouds and a swirling vortex at the center of Saturn’s famed northern polar hexagon,” Cassini scientists wrote in an online update.
Storms like this are common on many of the solar system’s planets, including Saturn.
“These phenomena mimic what Cassini found at Saturn’s south pole a number of years ago,” the scientists wrote.
Cassini, the first spacecraft to orbit Saturn, was launched in 1997 and arrived at the gas giant in July 2004. The probe has logged more than 3.8 billion miles (6.1 billion kilometers), and made some major discoveries about the Saturn system, including revealing the presence of hydrocarbon lakes on the moon Titan and spewing water geysers on the moon Enceladus.
“Eight and a half years into our history-making expedition around the ringed planet and we are still astounded by the seemingly endless parade of new planetary phenomena,” the mission scientists wrote.
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.
Long landslides spotted on Saturn’s moon, Iapetus, could help provide clues to similar movements of material on Earth. Scientists studying the icy satellite have determined that flash heating could cause falling ice to travel 10 to 15 times farther than previously expected on Iapetus.
Extended landslides can be found on Mars and Earth, but are more likely to be composed of rock than ice. Despite the differences in materials, scientists believe there could be a link between the long-tumbling debris on all three bodies.
“We think there’s more likely a common mechanism for all of this, and we want to be able to explain all of the observations,” lead scientist Kelsi Singer of Washington University told SPACE.com.
Giant landslides stretching as far as 50 miles (80 kilometers) litter the surface of Iapetus. Singer and her team identified 30 such displacements by studying images taken by NASA’s Cassini spacecraft. [Photos: Latest Saturn Photos from NASA's Cassini Orbiter]
Composed almost completely of ice, Iapetus already stands out from other moons. While most bodies in the solar system have rocky mantles and metallic cores, with an icy layer on top, scientists think Iapetus is composed almost completely of frozen water. There are bits of rock and carbonaceous material that make half the moon appear darker than the other, but this seems to be only a surface feature.
“It’s more like what we experience on Earth as rock, just because it’s so cold,” Singer said.
Slow-moving ice creates a lot of friction, so when the ice falls from high places, scientists expected that it would behave much like rock on Earth does. Instead, they found that it traveled significantly farther than predicted.
How far a landslide runs is usually related to how far it falls, Singer explained. Most of the time, debris of any type loses energy before traveling twice the distance it fell from. But on Iapetus, the pieces of ice move 20 to 30 times as far as their falling height.
Flash heating could be providing that extra push.
Faster and farther
Flash heating occurs when material falls so fast that the heat doesn’t have time to dissipate. Instead, it stays concentrated in small areas, reducing the friction between the sliding objects and allowing them to travel faster and farther than they would under normal conditions.
“They’re almost acting more like a fluid,” Singer said.
On Iapetus, falling material has a good chance of reaching great speeds because there are a number of great heights to fall from. The moon hosts a ring of mountains around its bulging equator that can tower as high as 12 miles (20 km), and the longest run-outs discovered are associated with the ridge and with impact-basin walls.
Scientists think that the landslides are relatively recent, and could have been triggered by impacts in the last billion years or so.
“You don’t see a lot of small craters on the landslide material itself,” Singer said, although the surrounding terrain boasts evidence of bombardment. Over time, landscapes tend to be dotted by falling rocks, so the less cratered a surface is, the younger it is thought to be. [Photos of Saturn's Moons]
Resting on the ridges and walls, the material gradually becomes more unstable. Close impacts could set them off, but powerful, distant impacts reverberating through the ice could also send them tumbling.
The research was published in the July 29 issue of the journal Nature Geoscience.
Connecting ice and rock
Differences in gravity, atmosphere and water content make landslides seen on Iapetus difficult to duplicate in the laboratory. But the fact that they happen on different types of worlds makes it more likely that the mechanism triggering the extended slide is dependent on things unique to either environment.
“We have them on Iapetus, Earth and Mars,” Singer said. “Theoretically, they should be very similar.”
Singer pointed out the implications for friction within fault lines, which produces earthquakes. As plates on Earth move, the rocks within a fault snag on each other, until forces drag them apart. But sometimes, the faults slip farther than scientists can explain based on their understanding of friction. If flash heating occurs within the faults, it could explain why the two opposing faces slide the way they do, and provoke a better understanding of earthquakes.
In such cases, flash heating would cause minerals to melt and reform, producing an unexpected material around the faults. Some such materials have been identified at the base of long landslides on Earth.
“If something else is going on, like flash heating, or something making [the material] have a lower coefficient of friction, this would affect any models that use the coefficient of friction,” Singer said.
The thick, hazy atmosphere of Titan, Saturn’s largest natural satellite, hides a complex moon with a perplexing geological past, a new study finds.
Researchers from the Massachusetts Institute of Technology (MIT) in Cambridge and the University of Tennessee at Knoxville studied images of Titan to investigate the erosion of its terrain, over millions of years, by rivers of liquid methane.
The scientists found that in some regions, Titan’s network of rivers caused surprisingly little erosion, which could indicate that erosion processes on Titan occur extremely slowly, or that a different, more recent phenomena is to blame for altering or eliminating ancient riverbeds and landforms, the researchers said.
“It’s a surface that should have eroded much more than what we’re seeing, if the river networks have been active for a long time,” study co-author Taylor Perron, an assistant professor at MIT, said in a statement. “It raises some very interesting questions about what has been happening on Titan in the last billion years.”
Peering into Titan’s past
Titan is estimated to be approximately four billion years old, roughly the same age as the rest of the solar system, the researchers explained. The moon’s dense atmosphere, largely made up of methane and nitrogen, created a thick orange haze that prevented astronomers from being able to see through to the surface.
In 2004, however, NASA’s Cassini spacecraft pierced through Titan’s cloudy cloak and snapped the first set of detailed radar images of the moon’s surface. Cassini occasionally flies past Titan as it orbits Saturn.
The images showed that Titan’s icy terrain was carved out over millions of years by rivers of liquid methane, similar to how rivers on Earth leave their mark on the planet’s rocky continents, the researchers said. But, while Titan’s current landscape is now well documented, its geologic past remains a mystery. [Amazing Photos: Titan, Saturn's Largest Moon]
Most moons in the solar system are heavily pockmarked, with impact craters dotting their surfaces. Titan, on the other hand, is relatively smooth, despite the moon being roughly the same age as the rest of the solar system. Simply judging by its surface features, Titan would appear to be much younger, between 100 million and 1 billion years old, the researchers said.
To explain Titan’s lack of craters, the researchers pointed to our own planet.
“We don’t have many impact craters on Earth,” Perron said. “People flock to them because they’re so few, and one explanation is that Earth’s continents are always eroding or being covered with sediment. That may be the case on Titan, too.”
Finding clues on Earth
Geological processes, such as plate tectonics, erupting volcanoes, advancing glaciers and river networks, have altered Earth’s surface over billions of years. According to the results of the new study, similar processes, including tectonic upheaval, icy lava eruptions, erosion and sedimentation by rivers, may also be factors on Saturn’s largest moon.
Still, pinpointing which specific phenomena may have reshaped Titan’s surface is a tricky task. Images taken by the Cassini spacecraft provide bird’s-eye views of the terrain, with no details about a landform’s elevation or depth.
“It’s an interesting challenge,” Perron said. “It’s almost like we were thrown back a few centuries, before there were many topographic maps, and we only had maps showing where the rivers are.”
To study how Titan’s methane rivers eroded the moon’s surface, the researchers mapped 52 prominent river networks from four regions. Images of these rivers were compared with a model developed by Perron of how a river network evolves over time.
Images of Titan were also compared with regions on Earth, including volcanic terrain on the island of Kauai and recently glaciated landscapes in North America. The researchers were able to draw parallels between our planet and Saturn’s hazy moon, suggesting that similar geological processes may have altered Titan’s icy surface in the recent past.
“It’s a weirdly Earth-like place, even with this exotic combination of materials and temperatures,” Perron said. “And so you can still say something definitive about the erosion. It’s the same physics.”
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.
NASA’s Voyager 1 spacecraft has encountered a new environment more than 11 billion miles from Earth, suggesting that the venerable probe is on the cusp of leaving the solar system.
The Voyager 1 probe has entered a region of space with a markedly higher flow of charged particles from beyond our solar system, researchers said. Mission scientists suspect this increased flow indicates that the spacecraft — currently 11.1 billion miles (17.8 billion kilometers) from its home planet — may be poised to cross the boundary into interstellar space.
“The laws of physics say that someday Voyager will become the first human-made object to enter interstellar space, but we still do not know exactly when that someday will be,” said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena, in a statement.
“The latest data indicate that we are clearly in a new region where things are changing more quickly,” Stone added. “It is very exciting. We are approaching the solar system’s frontier.” [Photos From NASA's Voyager 1 and 2 Probes]
Voyager 1 and its twin, Voyager 2, launched in 1977, tasked chiefly with studying Saturn, Jupiter and the gas giants’ moons. The two spacecraft made many interesting discoveries about these far-flung bodies, and then they just kept going, checking out Uranus and Neptune on their way toward interstellar space.
They’re not quite out of the solar system yet, however. Both are still within a huge bubble called the heliosphere, which is made of solar plasma and solar magnetic fields. This gigantic structure is about three times wider than the orbit of Pluto, researchers have said.
Specifically, the Voyagers are plying the heliosphere’s outer shell, a turbulent region called the heliosheath. But Voyager 1′s new measurements — of fast-moving galactic cosmic rays hurled our way by star explosions — suggest the probe may be nearing the heliosphere’s edge.
“From January 2009 to January 2012, there had been a gradual increase of about 25 percent in the amount of galactic cosmic rays Voyager was encountering,” Stone said. “More recently, we have seen very rapid escalation in that part of the energy spectrum. Beginning on May 7, the cosmic ray hits have increased five percent in a week and nine percent in a month.”
More measurements needed
While it may be tough to identify the moment when Voyager 1 finally pops free into interstellar space, scientists are keeping an eye on the cosmic ray measurements and a few other possible indicators.
One is the intensity of energetic particles generated inside the heliosphere. Voyager 1 has recorded a gradual decline in these particles as it flies farther and farther away from Earth, but it hasn’t seen the dramatic dropoff that scientists expect would accompany an exit from the solar system.
The Voyager team also thinks the magnetic fields surrounding the spacecraft should change when it crosses the solar boundary. Those field lines run roughly east-west within the heliosphere, and researchers predict they’ll shift to a more north-south orientation in interstellar space. They’re currently looking at Voyager 1 data for any signs of such a transition.
In the meantime, both Voyagers just keep on flying and exploring. Voyager 2 trails its twin a little bit; it’s currently 9.1 billion miles (14.7 billion km) from home.
“When the Voyagers launched in 1977, the space age was all of 20 years old,” Stone said. “Many of us on the team dreamed of reaching interstellar space, but we really had no way of knowing how long a journey it would be — or if these two vehicles that we invested so much time and energy in would operate long enough to reach it.”
Big, bad Jupiter likely squashed any chance the giant asteroid Vesta may have had of growing into a full-fledged planet long ago, researchers say.
Scientists analyzing observations from NASA’s Dawn spacecraft announced on (May 10) that the enormous asteroid Vesta is actually an ancient protoplanet, a planetary building block left over from the solar system’s earliest days.
Many other Vesta-like objects were incorporated into rocky worlds such as Earth, but Vesta’s development along this path was halted.
Vesta’s stunted growth is chiefly a product of its location, researchers said. The protoplanets that glommed together to form Mercury, Earth, Mars and Venus did so in the inner solar system, relatively far from the disruptive gravitational influence of a giant planet.
The 330-mile-wide (530-kilometer) Vesta, on the other hand, grew up in the main asteroid belt between Mars and Jupiter. And the solar system’s largest planet made it tough for Vesta to hook up with others of its kind.
“In the asteroid belt, Jupiter basically stirred things up so much that they weren’t able to easily accrete with one another,” Dawn scientist David O’Brien, of the Planetary Science Institute in Tucson, Ariz., told reporters today.
“The velocities in the asteroid belt were really high, and the higher the velocity is, the harder it is for things to merge together under their own gravity,” O’Brien added.
Those high velocities also set the stage for some incredibly violent collisions, which probably destroyed a fair number of Vesta-like bodies. Vesta itself was battered and bloodied by some huge impacts; one crater near its south pole is 314 miles (505 km) wide, and another underneath that one measures 250 miles (400 km) across.
So while Vesta — the second-largest denizen of the asteroid belt — was doomed to a life of solitude, it has had the toughness and luck to stick around for the last 4.5 billion years. And scientists are thankful that it did.
“Vesta is special, because it survived the intense collisional environment of the main asteroid belt for billions of years, allowing us to interrogate a key witness to the events at the very beginning of the solar system,” said Dawn deputy principal investigator Carol Raymond, of NASA’s Jet Propulsion Laboratory in Pasadena, Calif.
“We believe Vesta is the only intact member of a family of similar bodies that have since perished,” she added.