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.
Explosive volcanic eruptions apparently shaped Mercury’s surface for billions of years — a surprising finding, given that until recently scientists had thought the phenomenon was impossible on the sun-scorched planet.
This discovery could shed new light on the origins of Mercury, investigators added.
On Earth, explosive volcanic eruptions can lead to catastrophic damage, such as when Mount St. Helens detonated in 1980 in the deadliest and most economically destructive volcanic event in U.S. history.
Explosive volcanism happens because Earth’s interior is rich in volatiles — water, carbon dioxide and other compounds that vaporize at relatively low temperatures. As molten rock rises from the depths toward Earth’s surface, volatiles dissolved within it vaporize and expand, increasing pressure so much that the crust above can burst like an overinflated balloon.
Mercury was long thought to be bone-dry when it came to volatiles. As such, researchers thought explosive volcanism could not happen there.
However, in 2008, after the initial flyby of Mercury by NASA’s MESSENGER spacecraft (short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging), researchers found unusually bright reflective material dotting the planet’s surface.
This stuff appears to be pyroclastic ash, which is a sign of volcanic explosions. The large number of these deposits suggested that Mercury’s interior was not always devoid of volatiles, as scientists had long assumed.
It was unclear from MESSENGER’s first flybys over what time periods those explosions had occurred. Now scientists find Mercury’s volatiles did not escape in a rash of explosions early in the planet’s history. Instead, explosive volcanism apparently lasted for billions of years on Mercury.
Investigators analyzed 51 pyroclastic sites across Mercury’s surface using data from MESSENGER collected after the spacecraft began orbiting around the innermost planet in the solar system in 2011. These orbital readings provided a far more detailed view of the deposits and the vents that spewed them out compared with data from the initial flybys.
The orbital data revealed that some of the vents were much more eroded than others. This revealed the explosions did not all happen at the same time.
If the explosions did happen over a brief period and then stopped, “you’d expect all the vents to be degraded by approximately the same amount,” study lead author Timothy Goudge, a planetary scientist at Brown University, said in a statement. “We don’t see that; we see different degradation states. So the eruptions appear to have been taking place over an appreciable period of Mercury’s history.”
The researchers noted that about 90 percent of these ash deposits are located within craters formed by meteorite impacts. These deposits must have accumulated after each crater formed; if a deposit were laid down before a crater formed, it would have been destroyed by the impact that formed the crater.
Scientists can estimate the age of an impact crater by looking at how eroded its rims and walls are. Using that method, Goudge and his colleagues found that some pyroclastic deposits were found in craters ranging in age between 1 billion years to more than 4 billion years old. Explosive volcanic activity was thus not confined to a brief time after Mercury’s formation about 4.5 billion years ago, researchers said.
“The most surprising discovery was the range of ages over which these deposits appear to have formed, as this really has implications for how long Mercury retained volatiles in its interior,” Goudge told Space.com.
Earlier models of how Mercury formed suggested most of its volatiles would not have survived the planet-formation process. For instance, since Mercury has an unusually large iron core, past models posited that the planet might have once been much larger, but had its outer layers and its volatiles removed by a huge impact early in the planet’s history.
This scenario now seems unlikely given these new findings, in combination with other data collected by MESSENGER showing traces of the volatiles sulfur, potassium, and sodium on Mercury’s surface.
Future research will aim to identify more of these pyroclastic deposits and their source vents.
“More detailed observations and studies of single vents and associated deposits will elucidate some of the detailed aspects of what pyroclastic activity might have been like on Mercury,” Goudge said.
The scientists detailed their findings online March 28 in the Journal of Geophysical Research: Planets.
This new discovery about the origin of the moon may help solve a mystery about why the moon and the Earth appear virtually identical in makeup, investigators added.
Scientists have suggested the moon was formed 4.5 billion years ago by a gigantic collision between a Mars-size object named Theia and Earth, a crash that would have largely melted the Earth. This model suggested that more than 40 percent of the moon was made up of debris from this impacting body. (Current theory suggests that Earth experienced several giant impacts during its formation, with the moon-forming impact being the last.)
However, researchers suspected Theia was chemically different from Earth. In contrast, recent studies revealed that the moon and Earth appear very similar when it comes to versions of elements called isotopes — more so than might be suggested by the current impact model. (Isotopes of an element have differing numbers of neutrons from one another.)
“This means that at the atomic level, the Earth and the moon are identical,”study lead author Seth Jacobson, a planetary scientist at the Côte d’Azur Observatory in Nice, France, told Space.com. “This new information challenged the giant impact theory for lunar formation.”
How the moon evolved
No one seriously disputed an impact as the most likely scenario for the formation of the moon, Jacobson said. However, a virtually atomically identical moon and Earth threw the exact circumstances of the collision into question, he said.
Now, by pinpointing when the moon formed, Jacobson and his colleagues could help explain why the moon and Earth are mysteriously similar. The scientists detailed their findings in the April 3 issue of the journal Nature. [How the Moon Formed: 5 Wild Lunar Theories]
Efforts to date the moon-forming impact have proposed a range of ages. Some have argued for an early event, about 30 million years after the birth of the solar system, whereas others suggested that it occurred more than 50 million years and possibly as much as 100 million years after the solar system formed.
To help solve this mystery, Jacobson and his colleagues simulated the growth of the solar system’s rocky planets — Mercury, Venus, Earth and Mars — from a protoplanetary disk of thousands of planetary building blocks orbiting the sun.
By analyzing how these planets formed and grew from more than 250 computer simulations, the researchers discovered that if the moon-forming impact was early, the amount of material accreted onto Earth afterward was large. If the impact was late, the amount would then be small.
Past research had calculated the amount of material accreted onto Earth after the moon-forming impact. These estimates are based on how on how so-called highly siderophile or “iron-loving” elements such as iridium and platinum show a strong tendency to move into Earth’s core. After each giant impact the nascent Earth sustained, these elements would have leached from Earth’s mantle and bonded with heavy, iron-rich material destined to sink to Earth’s heart.
Moon birth mystery
After the last giant impact that formed the moon, the mantle should have been almost completely stripped of iridium, platinum and their cousins. These elements are still present in the mantle, but only in small amounts, which suggests only a small amount of material accreted onto Earth after the moon-forming impact.
The researchers calculated the moon-forming impact must have occurred about 95 million years after the formation of the solar system, give or take 32 million years.
“A late moon-forming event, as suggested by our work, is very consistent with an identical Earth and moon,” Jacobson said.
In addition, recent analyses propose that the impact that created the moon required a faster, more energetic collision than previously suggested. This makes sense if the impact took place relatively late with an older protoplanetary disk, as the new findings suggest.
“Older disks tend to be dynamically more active, since there are fewer bodies left in the disk to distribute energy amongst,” Jacobson said.
These new findings raise an interesting new puzzle. While they suggest the moon and the Earth formed together nearly 100 million years after the solar system arose, evidence from meteorites from Mars suggests that the Red Planet formed as little as a few million years after the solar system was born.
“This means that Earth and Mars formed over dramatically different timescales, with Mars forming much faster than the Earth,” Jacobson said. “How can this be? Is it just a matter of size? Location? What about Mercury and Venus? Did they grow on similar timescales to the Earth or on timescales more similar to Mars? I think these are some of the really important questions that we, as a community of planetary scientists, will be addressing in the future.”
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.