On November 4, NASA’s mission EPOXI will make a flyby less than 450 miles from the comet Hartley 2. Here’s what to know about this dirty snowball.
1. It’s a frequent visitor.
Malcolm Hartley discovered this namesake comet 24 years ago, and it’s returned to swing around the sun a few times since.
Like the famous Halley’s Comet, Comet Hartley 2 is a periodic comet that follows a years-long loop around the sun. It takes 6.46 years to complete one circuit, compared with Halley’s 75.3 years. [Christian Science Monitor]
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The edge of the solar system is not some static line on a map. The boundary between the heliosphere in which we live and the vastness of interstellar space beyond is in flux, stretching and shifting more rapidly than astronomers ever knew, according to David McComas.
McComas and colleagues work with NASA’s Interstellar Boundary Explorer (IBEX), a satellite orbiting the Earth with its eye turned to the edge of the heliosphere—the bubble inflated by the solar wind that encapsulates the solar system and protects us from many of the high-energy cosmic rays zinging across interstellar space. This week in the Journal of Geophysical Research, the team published the results of IBEX’s second map of the region, and found that its makeup has changed markedly over the span of just six months. Says McComas:
“If we’ve learned anything from IBEX so far, it is that the models that we’re using for interaction of the solar wind with the galaxy were just dead wrong.” [National Geographic]
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In August 2006, Pluto received its official demotion to dwarf planet status, taking our solar system down to eight planets. In August 2010, exoplanet hunters say they’ve found a haul of new worlds around a single star; that alien solar system may have seven known planets, meaning the system could be more like our home system than any ever discovered. And one of those worlds could be the smallest exoplanet ever found, too.
The star these planets orbit is called HD 10180, and it lies 127 light years from here. Astronomers at the European Southern Observatory in Chile used a spectrograph called HARPS to track tiny variations in the starlight caused by the pull of the planets.
It found clear evidence for five giant planets similar in size to Uranus or Neptune in our own solar system. But there were also tantalising signs that two other planets are also present, one of which would be the smallest, or least-massive, yet found orbiting another star [Christian Science Monitor].
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Astronomers have confirmed it: Neptune has a stalker. They have spotted, for the first time, an asteroid follower that keeps a fairly constant distance behind the planet in its orbit around the sun. And there may be many more.
Asteroid 2008 LC18 can’t help itself. It’s caught in a balancing game between the gravitational tug of the sun and Neptune, and effects from its whirling course. The conflicting tugs cause the asteroid not to orbit Neptune or crash into it, but instead to follow the planet from a little distance behind (about 60 degrees on its path).
Neptune has five of the these pits–called Lagrangian points (see diagram below the fold)–but the spots ahead and behind the planet, researchers say, are best for asteroid-trapping, since the hold is particularly stable in these places. Researchers have previously spotted several asteroids in front of the planet (again by about 60 degrees), but this is the first time they’ve found one following it. The findings appeared online yesterday in Science.
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They went to investigate solar wind-stirred storms in our planet’s magnetic field, but, after working for three years, two NASA solar-powered probes faced a dark demise, trapped in the Earth’s shadow. NASA researchers now think they can give the twin satellites another shot by altering their courses and sending them instead to study the moon.
NASA launched the probes in 2007 as a set of five identical satellites in the THEMIS Mission (Time History of Events and Macroscale Interactions during Substorms), meant to orbit Earth and send information during brief (2-3 hour) “substorms” when the magnetic field surrounding the Earth releases stored energy from solar winds. To understand the start of these “space tornadoes” responsible for the northern and southern lights, NASA placed the probes in very precise orbits, but for two craft that meant, one day, they would face prolonged battery-draining time in the Earth’s shadow.
“When we realized that the satellites would be going into very deep shadows, we started thinking of different methods for saving them–even before they were launched,” lead scientist Vassilis Angelopoulos, at the University of California, Berkeley, told Discovery News. “We realized that if we had enough fuel to change their orbits, the moon’s gravity would start pulling them up.”[Discovery News]
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Lake Ontario has some key differences compared to her equally-sized sister lake, Ontario Lacus: The Great Lake has water; Ontario Lacus has methane, ethane, and propane. The Great Lake invites sunbathers; Lacus’ beaches, almost ten times further from the sun, are icy cold. The Great Lake is located on Earth; Lacus on Saturn’s largest moon, Titan. Despite all these distinctions, new research points to an important similarity: liquid levels in both lakes change with the seasons.
From June 2005 to July 2009, the Ontario Lacus shoreline has receded by about 6 miles, Alexander G. Hayes and his coauthors report in two papers submitted to Icarus and the Journal of Geophysical Research. Looking at other lakes in Titan’s southern hemisphere, it seems they are dropping in depth by about three feet per year.
Despite its shoreline’s rapid retreat, there is little worry that Ontario Lacus and other Titan lakes will disappear forever. Scientists expect that the evaporation is just part of a cycle of evaporation and condensation, that changes with the seasons. The four years of observation, carried out by NASA’s Cassini spacecraft, represents only the period from about mid-summer to fall, since a Titan year lasts 29.5 Earth years.
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Kamil crater, at only about 150 feet wide and 50 feet deep, may not break any size records–but what the Egyptian crater lacks in range it makes up for with cleanliness. In an paper published yesterday in Science, researchers say that its “pristine” impact, spotted in 2009 during a Google Earth survey, makes the crater an ideal model to understand similar impacts.
The best place to see a clean crater? Rocky or icy planets without an atmosphere. Earth’s weather quickly erodes a crater’s structures, making it difficult to determine how exactly a meteorite struck. The Kamil crater, study leader Luigi Folco says, has avoided this fate:
“This crater is really a kind of beauty because it’s so well-preserved that it will tell us a lot about small-scale meteorite impacts on the Earth’s crust…. It’s so nice. It’s so neat. There is something extraordinary about it.” [Space.com]
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Our sun and a much bigger star that resides 10,000 light years away have something in common: the way they were born. Though scientists had previously wondered if stars 10 to 20 times the sun’s size required a different setup to grow, new observations show that both our sun and plus-sized stars can form from large hoops of dust called accretion disks.
Astronomers arrived at the findings, published online today in Nature, by weaving together observations from two observatories–the Very Large Telescope Interferometer of the European Southern Observatory in Chile and NASA’s orbital Spitzer Space Telescope. Researchers combined the observatories’ power to get a “virtual” telescope of much better resolution, the equivalent of one with a 280-foot mirror.
Lead researcher Stefan Kraus and his colleagues took a close peek at a 60,000-year-old stellar infant about 20 times our sun’s mass, called IRAS 13481-6124. The researchers were able to piece together temperature data to make a model of stellar birth that might resemble something from our 4.6 billion-year-old sun’s baby-book.
The team’s observations yielded a jackpot result: the discovery of a massive disk of dust and gas encircling the giant young star. “It’s the first time something like this has been observed,” Kraus said. “The disk very much resembles what we see around young stars that are much smaller, except everything is scaled up and more massive.” [Jet Propulsion Laboratory]
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In the 1980s, fossil record research showed a curious cycle: Every 27 million years, Earth hosted a mass extinction. Some scientists suggested that a dim star dubbed Nemesis was in a deadly dance with our sun, periodically kicking comets out of the distant Oort Cloud to shower our planet with destruction. Morbidly fascinating as it may be, the authors of a new study argue that this “death star” theory doesn’t hold up.
The cyclical extinctions do make a solid pattern, say Adrian Melott of the University of Kansas and Richard Bambach of Smithsonian Institution Museum of Natural History, whose paper is available through arXiv.org. The two have gone back in the record to 500 million years ago, further than any other researchers, and have confirmed the 27 million year cycle at a 99 percent confidence.
According to Bambach, there’s no doubt at all that every 27 million years-odd, huge numbers of species suddenly become extinct. He says this is confirmed by “two modern, greatly improved paleontological datasets of fossil biodiversity” and that “an excess of extinction events are associated with this periodicity at 99% confidence”. This regular mass slaughter has apparently taken place around 18 times, back into the remote past of half a billion years ago. [The Register]
The problem, Nemesis fans, is that the cycle is too precise, the researchers say. If these extinctions result from a dance between our sun and Nemesis, the researchers note, the period of these mass extinctions would change as other stars buffeted the pair and changed the courses of Nemesis’s orbit around the sun.
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The bits that make up Earth apparently took their time pulling themselves together. New research hints that our home didn’t form as a fully-fledged planet until 70 million years after its currently accepted birth date, making the planet younger than scientists believed.
The evidence appears in Nature and looks at the Earth’s “accretion”–the swirling together of gas and dust that formed our planet. Researchers previously believed that the Earth’s accretion was a fairly steady process, happening in about 30 million years, but this study suggests that Earth took a lot longer to form.
“The whole issue hinges on working out how long it took for the core of the Earth to form, which is one of the big unknowns in this area of science,” said Dr. John Rudge, one of the authors at the University of Cambridge. “One of the problems has been that scientists usually presume Earth’s accretion happened at an exponentially decreasing rate. We believe that the process may not have been that simple and that it could well have been a much more staggered, stop-start affair.” [The Telegraph]
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On Saturday, the European Space Agency’s Rosetta probe took the world’s closest pictures of the 80- by 50-mile-wide asteroid known as 21 Lutetia. Though the Lutetia visit is just a stop on the way to Rosetta’s real destination–a 2014 visit to the comet 67P/Churyumov-Gerasimenko–Saturday’s pictures document the closest visit to this big asteroid, the largest we’ve ever visited with a spacecraft.
We’ve known about Lutetia for quite a while: since 1852, according to Sky and Telescope. In November of that year, Hermann Goldschmidt spotted the space rock from his Paris balcony. The asteroid is now around 280 million miles from the Sun. From only 2,000 miles away, Rosetta got a much closer look at Lutetia, whipping around it at about 10 miles per second (30,000 miles per hour) as its OSIRIS camera snapped pictures recording details down to a few dozen meters.
“The fly-by has been a spectacular success with Rosetta performing fautlessly,” ESA said in a statement. “Just 24 hours ago, Lutetia was a distant stranger. Now, thanks to Rosetta, it has become a close friend.” [AFP]
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Water, water (or ice) everywhere—that’s the refrain this year. This week we covered the study declaring that the moon was home to perhaps 100 times more water than previously thought, and it was just two months ago that sky-watchers spotted the first frosty asteroid out in the Asteroid Belt. Now, in a study in Nature, a team of astronomers says they’ve found another icy surprise in our solar system: a bright shiny object way out in the Kuiper Belt.
The Kuiper Belt is that mess of objects orbiting the sun out beyond Neptune, but not as far as the Oort Cloud (once-proud Pluto is a Kuiper Belt object). There are plenty of icy bodies out there, including Pluto. But what doesn’t make sense about this one, KBO 55636, is how it stayed so pristine after a billion years of floating alone. MIT’s James Elliot, who led the study, says the object’s albedo, or reflectivity, is striking:
“That turned out to be very high, almost 90 percent… That’s consistent with it having a very highly reflective surface like water ice.” The finding was surprising because such old, distant bodies tend to have weathered, dull surfaces. “Objects orbiting that far out in space get generally darkened by accumulating dust… We don’t have an explanation for how it could stay so pristine” [Space.com].
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When you saw the Hale-Bopp comet, you may have seen material from a distant star passing by. In a new study, a team of astronomers argues that most of the comets that streak through our solar system were actually born in other solar systems.
Given their eccentric orbits and infrequent visits, comets seem like worthy candidates for an exotic origin. But the prevailing thinking said no, they are rather ordinary. Researchers thought most of the comets that pay us a visit initially formed from the sun’s protoplanetary disk—the same swirling mass that formed our own planet—and came to reside in the weird Oort cloud region at the periphery of our solar system. From there, the gravitational bullying of larger bodies can dislodge a few like Halley’s Comet or Hale-Bopp, which swerve into an orbit that sees them visit the inner solar system now and then.
In a study in Science this week, researchers led by Harold Levison posit a different idea: Many of the comets hanging around our solar system are stolen. It goes like this:
Like most stars, the sun may very well have been created in a tightly nestled birth cluster, a stellar nursery with tens, hundreds or possibly even thousands of stars. During millions of years of intimate infancy, the newborn stars could have exchanged vast numbers of comets from the fringes of their disks, each of them winding up with an ensemble of hand-me-downs from their stellar siblings [Scientific American].
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They’re new, they’re small, and they didn’t make sense.
That’s what could be said for five of the littlest members of Saturn’s expansive satellite family. The largest of this group, Janus, measures barely more than 100 miles in diameter, but it’s the age of these little moons that’s the odd bit. Their clean, crater-free surfaces help reveal that they’re only 10 million years old, meaning they didn’t form the way the planet’s other moons did—from the accretion disk that formed mighty Saturn itself billions of years ago. This week in Nature, astronomers published evidence to support an explanation for that oddity: Those moons formed from Saturn’s rings.
Like so much new knowledge about the sixth planet and its moons, including Titan and Enceladus, the research team’s findings come from the Cassini mission:
Sailing past Saturn’s outer rings, it found lumps of ice up to 100 metres across, ten times bigger than the rings’ other icy particles. For some researchers, the discovery called to mind another intriguing fact: that the moons and the rings share a composition of the purest ice in the Solar System. “When you put all this together, you had the strange feeling that something is going on in the rings’ outer edge,” says Sébastien Charnoz at Paris Diderot University, who was involved in the latest research [Nature].
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That’s not cloud cover. It’s polar ice on Mars, about 600 miles across and covered with deep etchings. The dark valley on the right, named Chasma Boreale, is about the size of the Grand Canyon.
This riven Martian arctic was a mystery to scientists for over forty years. But data from NASA’s Mars Reconnaissance Orbiter has given researchers some important clues to how the ice spirals formed. Their findings appear in two papers published in the journal Nature.
Data from Mars now points to both the canyon and spiral troughs being created and shaped primarily by wind. Rather than being cut into existing ice very recently, the features formed over millions of years as the ice sheet grew. By influencing wind patterns, the shape of underlying, older ice controlled where and how the features grew. [NASA] (more…)
