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Does The Asteroid Belt Hold Key To The Building Blocks Of Planets

September 27, 2017 by  
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The asteroid belt may have started out empty, later becoming a “cosmic refugee camp” taking on leftovers of planetary formation from across the solar system, a new study finds.

The main asteroid belt, located between the orbits of Mars and Jupiter, makes up 0.05 percent the mass of Earth. The asteroids there can range greatly in mass, with the four largest ones — Ceres, Vesta, Pallas and Hygiea — holding more than half the belt’s mass.

To explain the dramatic range of sizes in the asteroid belt, previous models suggested that the primordial asteroid belt originally possessed a mass equal to at least that of Earth, and that its members had less disparity in mass. The gravitational pulls of the planets later helped whittle down this primordial belt, depleting asteroids of certain sizes more than others.  

However, these prior models of asteroid formation raised a question: how the belt could have lost more than 99.9 percent of its mass without losing all of it, said study lead author Sean Raymond, an astronomer at the University of Bordeaux in France.

“Our approach is the opposite. We asked the question, ‘Could the asteroid belt have been born empty?’,” Raymond told Space.com. “The answer is yes, effortlessly.”

The scientists developed computer models of an empty primordial asteroid belt to see whether leftovers from planetary formation could explain the belt’s current composition. The inner belt is dominated by dry S-type, or silicaceous, asteroids, which appear to be made of silicate materials and nickel iron and account for about 17 percent of known asteroids. The outer belt is dominated by water-rich C-type, or carbonaceous, asteroids, which consist of clay and stony silicate rocks and make up more than 75 percent of known asteroids.

The researchers found that an empty primordial asteroid belt could explain the mass and compositions of the current members of the asteroid belt. This model suggests that this zone between Mars and Jupiter is a repository of planetary leftovers, “a refugee camp housing objects that were kicked out of their homes and left to brave interplanetary space, finally settling onto stable orbits in the asteroid belt,” Raymond told Space.com. 

In this new model, the inner belt consists largely of rocky leftovers from the formation of the terrestrial planets — Earth, Mars, Venus and Mercury. In contrast, the outer belt is made up of remnants of the formation of the gas giant planets, such as Jupiter and Saturn.

“In terms of composition, Jupiter and Saturn grew in a region that was much colder than where the rocky planets grew,” Raymond said. “Being colder, their cores could incorporate ice and other volatiles. The C-types are about 10 percent water, whereas the S-types are much drier, having started off in the much hotter terrestrial planet zone.”

These findings suggest that the asteroid belt “is a treasure trove — it must contain relics of the building blocks of all the planets,” Raymond said. “There must be pieces of terrestrial building blocks out in the asteroid belt, as well as leftovers from building the giant planets’ cores.”

Future research can further test how well the various models of asteroid-belt formation match reality. Raymond hopes the team’s new concept “will help keep people’s minds open to potentially drastically different origins stories for the solar system, and for extra-solar planets, too.”

Raymond and his colleague Andre Izidoro at the University of Bordeaux detailed their findings online Sept. 13 in the journal Science Advances.

Courtesy-Space

After 40 Years Voyager Still Moving Through The Galaxy

September 14, 2017 by  
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NASA’s Voyager 1 probe lifted off on Sept. 5, 1977, a few weeks after its twin, Voyager 2. Together, the two Voyager spacecraft performed an epic “Grand Tour” of the solar system’s giant planets, flying by Jupiter, Saturn, Uranus and Neptune.

But their work didn’t stop there. Both spacecraft kept flying, pushing farther and farther into the dark, cold and little-known realms far from the sun. [Voyager: 40 Epic Photos from NASA’s Grand Tour]

Then, on Aug. 25, 2012, Voyager 1 popped free into interstellar space, becoming the first human-made object ever to do so. Voyager 2, which took a different route through the solar system, will likely exit the sun’s sphere of influence in the next few years as well, mission team members have said.

And both spacecraft still have their eyes and ears open, all these decades later.

“It’s amazing that the two spacecraft are still working after 40 years,” said Ed Stone, who has been a Voyager project scientist since the mission’s inception in 1972. [Voyager at 40: An Interview with Ed Stone]

“When we launched, the Space Age itself was only 20 years old, so this is an unparalleled journey, and we’re still in the process of seeing what’s out there,” Stone, who’s based at the California Institute of Technology in Pasadena, told Space.com.

As of Friday (Sept. 1), Voyager 1 was a whopping 12.97 billion miles (20.87 billion kilometers) from Earth — more than 139 times the distance from our planet to the sun. Voyager 2 was about 10.67 billion miles (17.17 billion km) from its home planet.

Voyager 1 cruised by Jupiter in March 1979 and Saturn in November 1980. This latter encounter also included a close flyby of Saturn’s huge moon Titan. [Voyager at 40: NASA Retrospective Videos Look Back]

Voyager 2 pulled off its own Jupiter-Saturn double, flying by those two planets in July 1979 and August 1981, respectively. Then, the spacecraft had encounters with Uranus, in January 1986, and Neptune, in August 1989.

During this Grand Tour, both spacecraft beamed home data that surprised and excited scientists.

For example, before the Voyagers launched, the only known active volcanoes were here on Earth. But Voyager 1 spotted eight erupting volcanoes on the Jupiter moon Io, showing that the little world is far more volcanically active than our own planet. [More Photos from the Voyager 1 and Voyager 2 Probes]

The mission also determined that Titan has a nitrogen-dominated atmosphere, just as Earth does.

“It may, in some important ways, resemble what the Earth’s atmosphere was like before life evolved and created the oxygen that we all breathe,” Stone said.

Furthermore, Voyager observations suggested that the Jupiter moon Europa may harbor an ocean of water beneath its icy crust — a notion that subsequent NASA missions have pretty much confirmed.

“I think what Voyager has done is reveal how diverse the planets and the moons and the rings, and the magnetic fields of the planets, are,” Stone said. “Our terracentric view was just much narrower than, in fact, reality.”

Interstellar ambassadors

Voyager 1 has found that cosmic radiation is incredibly intense beyond the sun’s protective bubble, Stone said. The probe is also revealing how the “wind” of charged particles from the sun interact with the winds of other stars. [5 Surprising Facts About NASA’s Voyager Probes]

Meanwhile, Voyager 2 is studying the environment near the solar system’s edge. After it enters interstellar space, Voyager 2 will make its own measurements, revealing more about this mysterious region.

But this work cannot go on forever.

The Voyagers are powered by radioisotope thermoelectric generators, which convert the heat produced by the radioactive decay of plutonium-238 into electricity. And that heat is waning.

“We have about 10 years or so of power remaining until we have only enough to power the spacecraft itself, without any of the instruments,” Stone said.

But even after the probes power down, they’ll continue speeding through the cosmos for eons, making one lap around the Milky Way every 225 million years.

What if intelligent aliens intercept the Voyagers during this journey? Well, the probes’ makers planned for this unlikely scenario: Both Voyagers carry a copy of the “Golden Record,” which is full of images and sounds of Earth, as well as directions to our planet.

In the far future, the Voyagers will “be our silent ambassadors, with messages about where the place was that sent them so many billions of years earlier,” Stone said.

Courtesy-Space

Astronomers Celebrate 40 Years Of Voyager

August 18, 2017 by  
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Nearly 40 years after lifting off, NASA’s historic Voyager mission is still exploring the cosmos.

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The twin spacecraft launched several weeks apart in 1977 — Voyager 2 on Aug. 20 and Voyager 1 on Sept. 5 — with an initial goal to explore the outer solar system. Voyager 1 flew by Jupiter and Saturn, while its twin took advantage of an unusual planetary alignment to visit Jupiter, Saturn, Uranus and Neptune.

And then the spacecraft kept on flying, for billions and billions of miles. Both remain active today, beaming data home from previously unexplored realms. Indeed, in August 2012, Voyager 1 became the first human-made object ever to reach interstellar space. [Photos from Voyager 1 and 2’s Grand Tour]

The mission’s legacy reached into film, art and music with the inclusion of a “Golden Record” of Earth messages, sounds and pictures designed to give any prospective alien who encountered it an idea of what humanity and our home planet are like. This time capsule is expected to last billions of years.

“I believe that few missions can ever match the achievements of the Voyager spacecraft during their four decades of exploration,” Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA headquarters in Washington, D.C., said in a statement. “They have educated us to the unknown wonders of the universe and truly inspired humanity to continue to explore our solar system and beyond.”

Voyager 2 launched atop a Titan/Centaur rocket on Aug. 20, 1977, from NASA’s Kennedy Space Center in Florida.

The spacecraft are now flying through space far away from any planet or star; their next close encounter with a cosmic object isn’t expected to occur for 40,000 years. Their observations, however, are giving scientists more insight into where the sun’s influence diminishes in our solar system, and where interstellar space begins.

Voyager 1 is nearly 13 billion miles (21 billion kilometers) from Earth and has spent five years in interstellar space. This zone is not completely empty; it contains material left over from stars that exploded as supernovas millions of years ago. The “interstellar medium” (as the space in this region is called) is not a threat to Voyager 1. Rather, it’s an interesting environment that the spacecraft is studying.

Voyager 1’s observations show that the huge bubble of the sun’s magnetic influence, which is known as the heliosphere, protects Earth and other planets from cosmic radiation. Cosmic rays (atomic nuclei traveling almost at the speed of light) are four times less abundant near Earth than they are in interstellar space, Voyager 1 has found.

Voyager 2 is nearly 11 billion miles (18 billion km) from Earth and will likely enter interstellar space in a few years, NASA officials have said. Its observations from the edge of the solar system help scientists make comparisons between interstellar space and the heliosphere. When Voyager 2 crosses the boundary, the two spacecraft can sample the interstellar medium from two different locations at the same time.

“None of us knew, when we launched 40 years ago, that anything would still be working, and continuing on this pioneering journey,” Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena, said in the same statement. “The most exciting thing they find in the next five years is likely to be something that we didn’t know was out there to be discovered.”

Mission designers made the spacecraft robust to make sure they could survive the harsh radiation environment at Jupiter. This included so-called redundant systems — meaning the spacecraft can switch to backup systems if needed — and power supplies that have lasted well beyond the spacecraft’s primary mission.

Each of the spacecraft is powered by three radioisotope thermoelectric generators, which convert the heat produced by the radioactive decay of plutonium-238 into electricity. The power available to each Voyager, however, decreases by about 4 watts per year. This requires engineers to dig into 1970s documentation (or to speak with former Voyager personnel) to operate the spacecraft as its power diminishes.

Even with an eye to efficiency, the last science instrument will have to be shut off around 2030, mission team members have said. But even after that, the Voyagers will continue their journey (albeit without gathering data), flying at more than 30,000 mph (48,280 km/h) and orbiting the Milky Way every 225 million years.

In their four decades in space, the spacecraft have set many records and made key discoveries about the outer solar system and interstellar space. These include:

First and only spacecraft to enter interstellar space (Voyager 1).

First and only spacecraft to fly by all four outer planets (Voyager 2).

First active volcanoes seen beyond Earth, on Jupiter’s moon Io (both Voyagers).

Finding evidence of a subsurface ocean on Jupiter’s moon Europa (both Voyagers).

Discovering an early-Earth-like atmosphere on Saturn’s moon Titan (both Voyagers).

Imaging the chaotic terrain of Uranus’ moon Miranda (Voyager 2).

Imaging icy geysers on Neptune’s moon Triton (Voyager 2).

 

Courtesy-Space

Should The Moon Be Considered A Planet?

March 31, 2017 by  
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Every now and then a scientific paper makes a real splash. We had one recently, to judge from recent headlines. “Moon rises to claim its place as a planet” said The Sunday Times on February 19, while the Mail Online asked “Is this lunarcy?”. The articles were among many responding to the humble paper: “A Geophysical Planet Definition,” which suggested that the criteria for determining what constitutes a planet need an overhaul. It argued that the moon, Pluto and several other bodies in the solar system should be upgraded to planets.

The paper, published in Planetary and Lunar Science, was written by a team including Alan Stern. Stern is famous for NASA’s New Horizons mission, which made its spectacular flyby of Pluto in July 2015. The paper is a bit technical, but it basically argues that the geophysics of a body should determine whether it is a planet – not just whether it orbits the sun.

Of course, Stern has an axe to grind. He remains furious that, in 2006, the International Astronomical Union [IAU] deemed that Pluto was not a planet. By the time his probe reached its destination, Pluto was a mere “plutoid,” a “trans-Uranian dwarf planet”. In the article he strikes back. He is fed up with people asking “why did you send New Horizons to Pluto if it’s not a planet anymore?”

Lessons from the past

We are so used to thinking of the Earth’s satellite as a moon that the idea that it could be a planet is truly shocking. But ancient Greek and medieval astronomers all assumed that the moon was indeed a planet.

Ancient observers knew that the stars maintain their relative positions night after night: they saw constellations such as Leo or Gemini just as we do. But they also saw seven heavenly bodies slowly change their positions, wandering from west to east through the sky. The most important was the sun. The 12 signs of the Zodiac it passed through marked out the circle astronomers call the ecliptic (see figure below). The sun (we would say the Earth, of course) orbited in one year, while Saturn wandered through this plane every 30 years, Jupiter every 12 years and Mars every two years. Planet Moon did so in 1/12 year – one month. In fact, the word for planet comes from the Greek πλανήτης (Latin planeta) meaning “wanderer.”

The moon was of special interest. Its proximity made it the only “planet” with visible features – “the man in the moon”. Aristotle (384-322 BCE) asked several questions about the physics of the moon – including why we always see the same face, and never the far side? It’s a good question, and astronomers now explain it as the result of gravitational forces between planets and large moons, and they call it “tidal locking”.

Aristotle drew a different conclusion. He thought it proved that the moon had no innate ability to rotate or move. He assumed the same was true of all planets. They only move, he said, because they are carried in a circle. This was the origin of elaborate Medieval cosmology in which the planets and stars are rotated by a nest of celestial spheres. Had our moon not been tidally locked, astronomy might have taken a different path.

Did our predecessors have good reason to include the moon with the other planets? I think so, but mainly because of a strange astronomical coincidence. Almost all large moons orbit in, or very close to, the equatorial plane of their parent planet, but our moon does not – it inclines by as much as 28 degrees. However, Earth’s equatorial plane is tilted with respect to the ecliptic by angle of 23.5. The combination of these two unusual circumstances means that the moon does appear to move in the plane of the ecliptic – and never more than 5 degrees above or below it. Without it, ancient astronomers might not have treated the moon as a typical planet.

Lingering ambivalence?

With Copernicus’s heliocentric astronomy, published in 1543, the moon ceased to be a typical planet. Uniquely, as Copernicus’s critics pointed out, its orbit was centred on the Earth, not the sun. It was now

Earth’s “satelles”, meaning servant, from which our word satellite derives. And there was more loss of status in store. When Galileo trained his telescope on Jupiter in 1610, he discovered four satellites. Lovely news for Copernicans, but not for Luna. It was no longer THE moon, but one of five, a number which rose rapidly towards the 182 moons we know today.

Seemingly, there is nothing new under the sun. In Galileo’s time the moon was the subject of an argument between the new cosmologists, who saw it as Earth-like with seas and lands, and the old astronomers who insisted that it was a proper, perfect heavenly body.

With his new definition of a planet, Alan Stern has renewed that battle. According to his paper, astronomers “may find the IAU definition perfectly useful” but “our geophysical definition is more useful for planetary geoscience practitioners, educators and students.” Or, as Stern put it bluntly in 2015: “Why would you listen to astronomers about a planet [instead of] planetary scientists that know something about this subject”. And they know, or think they know, that the moon should become a planet again. Whether that will actually happen is completely down to the International Astronomical Union, which would have to make the decision.

Stephen Pumfrey, Senior Lecturer, Lancaster University

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Voyager 1 Gets Hit By Cosmic Tsunami Wave

December 19, 2014 by  
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It turns out that sailing through interstellar space isn’t so peaceful.

NASA’s Voyager 1 spacecraft — the only object made by humans to reach interstellar space — might still be caught what scientists have described as a cosmic “tsunami wave,” a shock wave that first hit the probe in February, according to new research. You can hear the eerie interstellar vibrations in a video, courtesy of NASA.

“Most people would have thought the interstellar medium would have been smooth and quiet,” study researcher Don Gurnett, professor of physics at the University of Iowa, and the principal investigator of Voyager 1’s plasma wave instrument, said in a statement from NASA. “But these shock waves seem to be more common than we thought.” [Photo Timeline: Voyager 1 in Interstellar Space]

Such a shock wave was what helped scientists determine that Voyager 1, which launched in 1977 on a “grand tour” of the outer planets, had officially left the solar system.

Last year, researchers keeping tabs on the car-sized spacecraft (12 billion miles away) analyzed measurements the Voyager 1 made in the aftermath of a powerful eruption from the sun known as a coronal mass ejection, or CME. This solar blast occurred in March 2012 and hit Voyager 1 from April to May 2013. The shock wave caused the particles around the spacecraft to vibrate substantially. Based on the frequency of these vibrations, scientists could measure the density of the probe’s surroundings.

The density of the particles around Voyager 1 was 40 times higher than scientists had previously observed when the space probe was still in the outer layers of the heliosphere, the giant bubble of charged particles and magnetic fields that surrounds the sun and the planets in our solar system. Voyager 1 team members concluded that the spacecraft had exited the heliosphere and entered a new cosmic realm. After researchers went back and looked at old data, they concluded that Voyager 1 crossed into interstellar space on August 25, 2012.

Voyager 1 detected its third and most recent interstellar shock wave in February. The vibrations were still going on as of November data, according to NASA. That’s remarkable considering that over the course of this event, the spacecraft has traveled 250 million miles (400 million kilometers).

The researchers say they are not sure how fast the wave is moving or how big a region it covers. And they’re still trying to understand what they can learn from these waves.

“The density of the plasma is higher the farther Voyager goes,” Ed Stone, project scientist for the Voyager mission from the California Institute of Technology, said in a statement from NASA. “Is that because the interstellar medium is denser as Voyager moves away from the heliosphere, or is it from the shock wave itself? We don’t know yet.”

Courtesy-Space

 

Did The Milky Way Galaxy Form From Colossal Crashes?

September 19, 2014 by  
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The history of the Milky Way has a new wrinkle.

Scientists used radio telescopes like the Atacama Large Millimeter/submillimeter Array — a vast array of receivers in Chile — used to probe galaxies within 40 million to 600 million light-years from Earth. After observing dozens of merging galaxies, astrophysics found that many galactic collisions will create disc galaxies similar to the Milky Way, a surprising finding.

Their observations of carbon monoxide in 37 colliding galaxies showed pancake-shaped zones of molecular gas, similar to the shape that disc galaxies — which include spiral galaxies and lenticular galaxies — would assume.

“This is a large and unexpected step towards understanding the mystery of the birth of disc galaxies,” lead researcher on the study Junko Ueda, a postdoctoral fellow at the Japan Society for the Promotion of Science, said in a European Southern Observatory statement.

Before, astronomers thought that only elliptical galaxies could arise from mergers. Simulations from the 1970s, however, concluded that elliptical galaxies should be the most popular type of galaxy in the universe. Yet these odd-shaped entities comprise less than 30 percent of galaxies. The new study could help explain why scientists see so many spiral galaxies like the Milky Way in the universe, according to ESO.

The astronomers’ work is the biggest molecular gas study so far, but they said they plan more work to follow up on their research. Astronomers emphasized more observations of older galaxies are required to see if mergers behaved similarly in the young universe.

“We have to start focusing on the formation of stars in these gas discs. Furthermore, we need to look farther out in the more distant universe,” Ueda said. “We know that the majority of galaxies in the more distant universe also have discs. We, however do not yet know whether galaxy mergers are also responsible for these, or whether they are formed by cold gas gradually falling into the galaxy. Maybe we have found a general mechanism that applies throughout the history of the universe.”

The research was published in the Astrophysical Journal Supplement.

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Astronomers Get A Picture of The Milky Way’s Galactic Neighborhood

September 8, 2014 by  
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A new cosmic map is giving scientists an unprecedented look at the boundaries for the giant supercluster that is home to Earth’s own Milky Way galaxy and many others. Scientists even have a name for the colossal galactic group: Laniakea, Hawaiian for “immeasurable heaven.”

The scientists responsible for the new 3D map suggest that the newfound Laniakea supercluster of galaxies may even be part of a still-larger structure they have not fully defined yet.

“We live in something called ‘the cosmic web,’ where galaxies are connected in tendrils separated by giant voids,” said lead study author Brent Tully, an astronomer at the University of Hawaii at Honolulu.

Galactic structures in space

Galaxies are not spread randomly throughout the universe. Instead, they clump in groups, such as the one Earth is in, the Local Group, which contains dozens of galaxies. In turn, these groups are part of massive clusters made up of hundreds of galaxies, all interconnected in a web of filaments in which galaxies are strung like pearls. The colossalstructures known as superclusters form at the intersections of filaments.

The giant structures making up the universe often have unclear boundaries. To better define these structures, astronomers examined Cosmicflows-2, the largest-ever catalog of the motions of galaxies, reasoning that each galaxy belongs to the structure whose gravity is making it flow toward.

“We have a new way of defining large-scale structures from the velocities of galaxies rather than just  looking at their distribution in the sky,” Tully said.

Laniakea, our home in the universe

The new 3D map developed by Tully and colleagues shows that the Milky Way galaxy resides in the outskirts of the Laniakea Supercluster, which is about 520 million light-years wide. The supercluster is made up of about 100,000 galaxies with a total mass about 100 million billion times that of the sun.

The name Laniakea was suggested by Nawa’a Napoleon, who teaches Hawaiian language at Kapiolani Community College in Hawaii. The name is meant to honor Polynesian navigators who used their knowledge of the heavens to make long voyages across the immensity of the Pacific Ocean.

“We live in the Local Group, which is part of the Local Sheet next to the Local Void — we wanted to come up with something a little more exciting than ‘Local,'” Tully told Space.com.

This supercluster also includes the Virgo cluster and Norma-Hydra-Centaurus, otherwise known as the Great Attractor. These new findings help clear up the role of the Great Attractor, which is a problem that has kept astronomers busy for 30 years. Within the Laniakea Supercluster, the motions of galaxies are directed inward, as water flows in descending paths down a valley, and the Great Attractor acts like a large flat-bottomed gravitational valley with a sphere of attraction that extends across the Laniakea Supercluster.

Tully noted Laniakea could be part of an even larger structure.

“We probably need to measure to another factor of three in distance to explain our local motion,” Tully said. “We might find that we have to come up with another name for something larger than we’re a part of — we’re entertaining that as a real possibility.”

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Astronomers Develop New Theories On The Evolution Of Our Solar System

August 12, 2014 by  
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Astronomers have traced the growth of Earth’s solar system back to its cosmic womb, before the sun and planets were born.

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.

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Can A New Test Prove If Voyager Is In Interstellar Space?

July 29, 2014 by  
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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.

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Voyager 1 Goes Intersellar

July 11, 2014 by  
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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.

Courtesy-Space

NASA’s Voyager Probes Still Ticking Away

June 3, 2014 by  
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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.

 

 

Did Mercury Experience Volcanism?

April 18, 2014 by  
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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.

Courtesy-Space

 

Did Scientist Figure Out The Age Of The Moon?

April 7, 2014 by  
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Scientists have pinned down the birth date of the moon to within 100 million years of the birth of the solar system — the best timeline yet for the evolution of our planet’s natural satellite.

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.”

Courtesy-Space

 

Astronomers Find Neptune’s Lost Moon

October 11, 2013 by  
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A tiny, mysterious moon orbiting Neptune has been spotted for the first time in more than 20 years.

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. 8) 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.

Courtesy-Space

Did The Moon Come From Venus?

October 3, 2013 by  
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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.

Wandering moons

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.”

Courtesy-Space

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