Discoveries
Artist's impression of what the rocky "super Earth" CoRoT-7b might look like -- very hot and bothered. (ESO/L. Calcada)
Astronomers find 'super Earth' around another star; call it Rocky
Quick! Before you begin reading, drop down to the bottom of the post, activate the YouTube link, then quickly scroll back up here (all you really need is the sound).
Laydeeezzz and gentlemun, boyzzz and girlzzz, an international team of astronomers on the Third Rock from the sun gives you the best evidence yet for a rocky planet -- not too much bigger than Earth -- orbiting another star.
The planet is called CoRoT-7b. And it appears to have a sibling super-Earth, CoRoT-7c, though much less is known about it. This makes the system the first dual super-Earth system astronomers have found. The team summarized its findings today at the European Planetary Science Congress, meeting this week in Postdam, Germany.
You can find a lay-language summary here. You can find a PDF of the formal results, accepted for publication in the journal Astronomy and Astrophysics, here.
CoRoT-7b is the smallest exoplanet found so far. It's slightly more than 1.5 times as large as Earth. But any vague resemblance stops there.
The parent star -- 500 light-years away in the constellation Monoceros -- is some 1.5 billion years old. The planet orbits its star at a distance of less then 2 million miles, giving it a "year" that lasts about 20 hours.
With an orbit that close, the team estimates that the temperatures on the planet's surface range somewhere between 1,527 to 2,327 degrees Celsius on the sunlit portion (think molten on the surface) and a frosty -200 degrees C on the night portion.
The team first announced it had discovered the planet in February. But it took additional measurements from ground-based telescopes to provide enough data for astronomers to estimate the planet's mass and its radius. For now, the best the team can do is give a maximum estimate for the mass -- somewhere around 15 times Earth's mass. CoRoT-7b's radius is slightly more than 1.7 times Earth's radius.
Given those two clues, the team estimates that the planet's density is similar to Earth's. Ergo, it's a rocky planet.
A second team flipped on its computers and with some clever modeling came up with estimates of the planet's composition, as well as their own mass estimate. Based on their calculations, CoRoT-7b is likely to be made largely of iron and silicates, perhaps with a thin atmosphere of vaporized silicate. This team estimates that the planet's mass likely falls between 7 and 15 times Earth's mass. You can find the formal report of their results here. Their work, too, is slated to appear in Astronomy and Astrophysics.
Perhaps as intriguing are the range of possibilities for how the planet formed. It could have originated as a terrestrial-like planet, the team posits. Or it could be the remnant core of what once was a ice or gas giant that migrated too close to the star to retain its gases or ices.
For the record, CoRoT is the acronym for a French planet-hunting, star-studying satellite launched at the end of December 2006. The "7" refers to where this new solar system ranks on the list of systems CoRoT has found. And the "b" refers to the planet itself. Oh yes, there is no "a." If there was, it would be the star itself, but the star is known merely as CoRoT-7.
Jupiter bore the scar of an impact that caught astronomers by surprise in July. This image is from the Hubble Space Telescope. (NASA, ESA, and H. Hammel (Space Science Institute, Boulder, Colo.), and the Jupiter Impact Team)
Jupiter captures a comet, briefly
In July, when an object hurtled into Jupiter's clouds and scarred its cloud tops for all to see, humans had another chance to thank their lucky planet that Jupiter orbits where it does. It can act as a kind of one-planet offensive line, protecting the inner-planet backfield.
Now, a team of Japanese and British astronomers is reporting -- again* -- that Jupiter also can turn these objects into moons, at least or a few years.
The team found that from 1949 to 1961, Jupiter captured comet 147P/Kushisa-Muramatsu, which fell into an irregular orbit around the gas giant. It marked the fifth incident astronomers have uncovered so far where Jupiter has gained, then quickly lost, a potential moon.
The comet in question made two full trips around the planet before it beat cosmic feet and headed out again.
Based on the other four instances where Jupiter has briefly captured an object that completes at least one full Jovian orbit, such events occur on average about once every 10 years, the astronomers calculate.
The results imply that "impacts on Jupiter and temporary satellite-capture events may happen more frequently than we previously expected," according to David Asher, a scientist with the Armagh Observatory in Britain.
What sort of objects be these? A likely source is a group of comets known as quasi-Hilda comets.
Who's Hilda? Actually, an asteroid (yep, not a comet) in the belt of asteroids that orbit the sun between Mars and Jupiter. Discovered in 1875, the object had an unusual orbit for a main-belt asteroid. Similar discoveries followed, leading astronomers to group them into a family known as the Hilda family.
They are main-belt objects that are the closest to Jupiter. They orbit the sun at a pace that carries a unique mathematical relationship to Jupiter's orbital period. (They show a 3:2 orbital resonance with Jupiter, for the astronomically picky.)
The quasi-Hilda comets are a subgroup of comets that never travel farther from the sun than Jupiter. And they have orbital traits relative to Jupiter's that are similar to the Hilda asteroids' traits.
*The results were first reported formally last year in the journal Astronomy and Astrophysics Review. You can find a PDF "preprint" of the article here. The team reprised the results at this week's meeting of the European Planetary Science Congress in Potsdam, Germany.
Artist's rendering of planet WASP-18b, which is orbiting a sun-like star some 326 light-years from Earth. (European Space Agency)
Kiss this planet goodbye! (No, not Earth)
Bon Voyage, WASP 18b!
Astronomers say they have detected a planet orbiting another star that appears to be on the verge of plunging into its sun (within the next million years).
The amount of time it has left in the land of the orbiting is far shorter than for any known planet, according to University of Maryland astronomer Douglas Hamilton. If the team reporting the discovery is correct about the planet's future, astronomers should begin to see evidence of a long, very lazy plunge into the star within the next decade, he estimates.
The planet -- WASP-18b -- has 10 times Jupiter's mass, squeezed into an orb about Jupiter's size. The planet is orbiting its star at a distance of just under 2 million miles (Earth is 93 million miles from the sun). That means it's orbiting at an enormous pace: It makes one swing around the star, WASP-18, every 22.6 hours. Surface temperature? Don't even ask! But if you did anyway, the team would tell you it's about 3,800 degrees Fahrenheit. Steel melts at around 2,500 degrees F.
As for the star, WASP-18, it is 326 light years away. It has roughly the same mass and diameter as the sun. But at 630 million years old, it's a young turk. The sun is 4.6 billion years old.
The planet was discovered by an international team of scientists led by Coel Hellier, an astrophysicist at Keele University in Britain. The members are part of the Wide Angle Survey for Planets, an effort that is hunting for planets orbiting other stars using the transit approach. Their network of telescopes looks for the changes in a star's light as a planet passes in front of it, as viewed from Earth. A formal report of their discovery appears in the current issue of the journal Nature.
Finding a planet like this, apparently on the verge of bidding the cosmos adieu, is rare, according to Dr. Hamilton. Given what scientists have learned so far about how the gravity between two closely orbiting objects interacts, and the million-year life expectancy of WASP-18b, the odds, of finding a planet at this stage of its evolution are about 1 in 1,000, he explains.
So either the team was really lucky, or something more scientific (in some cases scientifically unsettling) is going on.
Among the possibilities Hamilton identifies:
1. Perhaps the star is particularly poor at dissipating the tidal energy that builds as the planet orbits the star. In an email exchange, Dr. Hellier explains that as the planet swings around, it triggers tidal bulges on the star. The moon sets up similar bulges in Earth's oceans, giving us tides at the beach. In a star, those bulges set up sound waves that move through the star until they dissipate. If the star turns out to be very inefficient at dissipating that energy, the planet's lifetime would be prolonged.
Based on what scientists have learned about tidal interactions by looking at planets and moons in our solar system, as well as at binary-star systems (where two stars orbit each other), this option "would be a spectacular find," Hamilton writes in a commentary that accompanies the formal report of the discovery in the current issue of the journal Nature.
2. Maybe the star hasn't been slowly winding its way inward from a more distant birthplace, where enough raw material for planets would be available to build an orb as massive as WASP-18b. Maybe it was nudged out of a more distant orbit by a close encounter with another, as-yet undetected planet.
3. Something is keeping the planet in one piece -- some unknown bit of physics related to tidal interaction or to aspects of the star's behavior perhaps. Or it could be a kind of counter-tug from that pesky, undiscovered planet.
Whatever the explanation, this is one system astronomers will want to monitor over the next few decades for evidence of the planet's impending demise.
East Coast to get ringside seat for shuttle Discovery's launch, V 2.0
It's a bad-hair day for meteorologists when they predict an 80 percent chance that weather will favor a space-shuttle launch. Then, shortly before lift-off, unexpected storms roll in and the launch gets scrubbed at the last possible moment.
That's what happened to the space shuttle Discovery and its seven-member crew in the wee hours of Aug. 25. The crew was strapped in and ready to go. And they quickly went nowhere. So, NASA will try for another launch at 1:10 a.m. Aug. 26.
That means you have another chance to watch the launch -- assuming clear skies and a willingness to set the alarm. Weather willing (from the launch pad to your pad), some portion of Discovery's ascent should be visible from as far west as eastern Mississippi to as far north as Halifax, Nova Scotia (for all of about 25 seconds there).
For a list of major East Coast cities where the shuttle can be viewed, appearance times, and length of viewing time visit CelesTrak, a website run by T.S. Kelso, a researcher at Analytical Graphics, Inc.'s Center for Space Standards and Innovation (CSSI) in Colorado Springs, Colo. The list appears toward the bottom of the web page.
Oh, and the forecast for the wee hours of Aug. 26? A 70 percent chance of decent launch weather.
You can read more about the mission's objectives here.
Farmers plough a rice field with a water buffalo, locally called "carabao", and a hand tractor in a village in Dinalupihan town, northwest Philippines (REUTERS/Erik de Castro)
Scientists find key ingredients in genetic recipe for hardier rice
As rice genes go, SNORKEL1 and 2, and SUBMERGENCE1a, b, and c have more evocative names than most. Not so much with pi21.
Taken together, however, some of these genes hold the promise of helping rice farmers in developing countries -- who feed more than 2 billion people -- keep the harvests coming under increasing pressure from rising populations and extreme climate events expected from global warming.
This week, two groups of Japanese scientists are reporting progress on two important fronts: boosting disease resistance in rice; and giving rice the ability to withstand prolonged, deep-water flooding. In the case of flooding, they do this not by temporarily shutting down rice growth, as other researchers have, but by triggering a growth spurt when the rice finds itself in over its head.
The good news is that these look like they can be bred into current strains without resorting to the kind of high-tech genetic engineering that sets so many people's teeth on edge, explains Susan McCouch, a Cornell University plant geneticist who specializes in rice research.
"There's been a lot of hype around moving genes around from once species to another with genetic engineering" to develop more stress-resistant crops, Dr. McCouch said during a phone chat. "But both of these studies are based on the utilization of natural variations" enhanced through traditional crossing-breeding.
This sidesteps the need for regulations imposed on growers who want to use crops that get their hardiness from genes introduced from other plant species, she adds.
Who cares? More than 2 billion people, who rely on rice as a staple. And the developing-country farmers that have to grow the grain under increasingly marginal conditions.
One team of Japanese scientists report in tomorrow's issue of the journal Science that they've isolated a naturally occurring, but odd form of a rice gene dubbed pi21. Pi21 is present in all rice varieties. But this version -- which, ironically, is missing some pieces compared with the "normal" gene -- increases the plant's ability to win out over rice-blast infections. Rice blast is one of the most prevalent diseases rice faces worldwide.
And the team identified the gene's location on the rice plant's chromosome. This solves a decades-old puzzle that allows the mutant gene to be bred into many rice varieties without sacrificing flavor -- a goal that has been elusive in the past.
Rice defense strategies
Most approaches to conferring disease resistance in rice involve coaxing an existing gene into overdrive to generate the compounds that will knock the fungus flat as soon as it tries to infect the plant, say the researchers, led by Shuichi Fukuoka, with the QTL Genomics Research Center in Japan's Tsukuba City.
Two problems make this a less-than-ideal approach, they argue. The rice blast fungus evolves resistance to the plant's intense burst of fungus-fighting agents. And each variety of rice has its own unique variation on the genetic blueprint for the agents, making it difficult to come up with a more-universal weapon.
Breeders had noticed that some varieties of rice have defense mechanisms that allow the fungus to gain a foothold. But then the rice plant builds its counterattack over time. The Japanese team identified the oddities in the mutant pi21 gene that made this possible.
Breeders had noticed this slo-mo defense. So they tried to breed the trait in different rice varieties. But the rice ended up with other traits that breeders -- and customers -- didn't like, such as bad-tasting rice.
By identifying a gene near Pi21 associated with the yuck factor, the team has made it easier to use precision breeding techniques to get disease-resistance without triggering upturned noses.
We like water, but not that much water
A second group has tackled another problem -- ensuring rice can survive prolonged flooding. Rice germinates in flooded fields. But not all rice can endure prolonged flooding.
Three years ago, scientists reported that by throwing a naturally occurring rice gene into overdrive, they could induce a rice plant to in effect suspend its growth for far longer than usual. The gene in question was one of three variations of the plant' native "submergence" gene. The variety in question typically could endure up to a couple of weeks under water, but not much longer.
Once the new rice variety resumed its normal growth, the rice yields and quality matched those of rice unaffected by excessive flooding.
This time around, a team of Japanese scientists identified genes from so-called deep-water varieties that allow them to survive prolonged inundation. Then they bred these with non-deep-water varieties in ways that passed along the water wings. Their results appear in this week's issue of the journal Nature.
The genes involved in this work (cleverly named SNORKEL1 and SNORKEL2) in effect accelerate growth when the rice plant becomes inundated, allowing it to rise above the surface of the water. Plants could survive this way in up to 4 meters (a shade more than 13 feet) of water.
The yin and yang of rice survival
These discoveries represent a kind of yin and yang for conferring greater stress tolerance to rice as climate changes, McCouch suggests.
With global warming come projections of increases in severe weather, including an increased frequency of drought, and more frequent flooding -- either in brief, flash-flood form, or as larger floods, depending on location ans season.
The ability to ward off rice blast is important when rice is stressed by drought and high temperatures. And you've gotta love SUBMERGENCE and SNORKEL when the water runs high for a long period of time.
NASA's Aqua satellite captured this image of Hurricane Bill on Aug. 18, as it was gathering strength in the Atlantic Ocean. Emergency managers from the Windward Islands to the Northeastern US through the Canadian Maritimes are keeping an eye on this powerful storm. (NASA MODIS Rapid Response Team)
Hurricane Bill keeping you up? Take time for personal preparedness
With Hurricane Bill churning northwestward in the Atlantic, storm-track charts are in hot demand, ones that take advantage of the power and reach of the worldwide web.
But what do you do with that information, other than become mesmerized by it? Use it as a prod to be sure you and your family are ready for a storm if and when it comes. That means having a family emergency plan, which will stand you in good stead for other natural hazards, including wildfires, earthquakes, or floods.
Several sources can walk you through the steps to being prepared, not the least of which is the American Red Cross's Hurricane Preparedness Guide, which downloads as a PDF file.
High on the list of items: Gather important papers -- wills, house deeds or rental agreements, birth certificates and passports, financial documents, pack them in a waterproof bag, and have them ready to grab on the way out the door in case you're ordered to evacuate. Essentially, you'll still need to pay bills and prove that you are who you say you are and own what you claim you own.
You may not be ordered to evacuate. Many communities are beginning to realize that it may be better to have residents not threatened by hurricane storm surges or who live above flood zones to shelter in place. Or if they need to evacuate, they do so to shelters near by.
But shelter in place implies having plenty of food (of the right kind), water, and other supplies on hand.
Good eats!
Some useful food tips come from nutritionists at Florida International University in Miami. Five years ago, they developed the Healthy Hurricane Cook Book. It's loaded with tips on what to buy, as well as with recipes that ensure people eat well-balanced meals, even when the power is out.
The book grew out of FIU nutritionist Marcia Magnus's observations that people stocking up on groceries ahead of hurricanes that hit Florida in 2004 largely picked junk food or food high in salt and sugar. A lot of the most nutritious food remained on the store shelves.
As for shoring up a home, that generally means shuttering or boarding windows and reinforcing garage doors, which can be particularly vulnerable to high winds. For protecting windows, merely taping them won't cut it.
You can find some good tips on how to get your home ready from the Extension Disaster Education Network at Texas A&M University. The files download as PDFs, and may require that you enter a zip code before you download the file. It's their way of keeping track of the geographic reach of their information.
The instructions for boarding windows are very thorough. Don't overlook the four small holes drilled in each plywood window cover to equalize air pressure. They show up in the diagram only after you enlarge the page in your PDF reader to more than 100 percent of its original size.
Preparation timeline
If you were to think in terms of a time line, the first things to do, long before a storm is even a gleam in the National Hurricane Center's eye, is to develop the family plan and gather what you need for the grab-and-go bags that the Red Cross and other emergency management agencies recommend having at the ready.
This also is the time to custom cut that plywood, and carefully mark on it the window or door it pairs with. Then stash the plywood covers and their fasteners in one easy-to-reach location.
The National Hurricane Center cautions that physical preparations -- boarding windows, clearing yards of loose objects that can become projectiles, and other around-the-house actions should begin once the Center issues a hurricane watch. That's generally about 36 hours before a hurricane is expected to strike an area.
The time to cut and fit the window boards is long before a hurricane approaches. Otherwise, you may show up at Lowes or Home Depot only to find they've sold out of plywood!
And the window preps aren't just for those who live along the Southeast or Gulf Coasts.
At least one insurance company in New England recently increased its homeowners insurance rates. The reinsurance company that insured the insurance company had just boosted its rates over concerns that the region is overdue for a major hurricane.
And the homeowners-insurance provider was passing that increase along to ratepayers. The only way to shave some money off the increase was to prove that you had a new roof installed recently, or that you had FEMA-approved storm shutters for your windows. And that covers all policyholders, not just those right along the coast. Plywood certainly does not equal FEMA-approved, but clearly someone thinks shuttering isn't just for the Southeast or Gulf Coasts.
These are just a smattering of ideas and sources for emergency-preparedness information. As you visit some of these sites, they will give you additional ideas and in more detail.
Don't overlook your state emergency-management office web site. It will have more detailed tips specific to your area. FEMA has a list of the state and territorial agencies with links to their websites.
Scientists find a building block for life in a comet's halo
Life -- at least in simple forms -- may be quite common around the cosmos, if new results from NASA's Stardust mission are any indication.
Researchers have discovered glycine molecules in samples of cometary material the Stardust spacecraft returned to Earth after its encounter with comet 81P/Wild 2 in 2004.
Glycine is a simple amino acid. It provides the foundation around which other biologically important molecules are built -- including proteins and key components of DNA and RNA.
The discovery "supports the theory that some of life's ingredients formed in space and were delivered to Earth long ago by meteors and comets," notes Jamie Elsila, a researcher with NASA's Goddard Space Flight Institute in Greenbelt, Md.
He and his colleagues reported the results at this week's meeting of the American Chemical Society and a formal report on the work has been accepted for publication in the journal Meteoritics and Planetary Science. You can also find a plain-English version here.
Comets are lumps of ice, rock, and dust several kilometers across that are thought to represent some of the most primitive building blocks for what would become planets and moons. They grow out of the same large cloud of interstellar dust, ice, and gas that spawned the stars they orbit.
Comet Wild 2 was discovered in 1978 after a close encounter with Jupiter in 1974 shifted its orbit. Before the comet felt Jupiter's tug, it spent more than 4 billion years orbiting the sun once every 43 years. Now it swings around the sun in a much more elliptical orbit once ever six years.
Grabbing the samples
The glycine molecules that Stardust found came from gas the comet released as the sun warmed it. It was captured in the spacecraft's sampling gear -- akin to an oversized circular ice-cube tray filled with aerogel, a remarkably spongy material that can withstand high heat while at the same time slowing, then cradling, comet material that zips into it at faster-than-bullet speeds.
Stardust passed through the comet's coma -- a halo of dust and gas that surrounds the comet's core. The team found glycine in the aerogel as well as on some of the foil that lines the aerogel-filled collection chambers.
But the researchers still had to rule out possible contamination from Earth. Glycine consists of carbon, hydrogen, nitrogen, and oxygen. By analyzing the forms of carbon in the glycine molecules, they found that the samples had much higher proportions of a heavy isotope of carbon than does glycine on Earth. The verdict: It's extraterrestrial, born and bred on the comet itself.
Interstellar recipe for glycine
How might glycine form on a comet? Researchers in South Korea showed how it might happen, via lab experiments. Take some water ice. Add carbon dioxide. Throw in a dash of methylamine, an ammonia-like compound found as grains in the dust and gas between stars. Then subject the mixture to ultraviolet radiation at about the intensity you'd expect to see in interstellar space. Violà! Glycine.
The Korean team also found that while glycine can be destroyed by the same process that formed it, the cycle can reach a balance that allows glycine to be carried along through interstellar space. One could imagine that same process taking place on a comet hurtling around a star.
The team published its results in May in the Astrophysical Journal.
This image shows the spiral galaxy NGC 2770 taken Jan. 18, 2008, by the Swift satellite. Two bright supernovae, SN2007uy and the more recent SN2008D first detected through X-ray observations (labeled as XRF080109) plus the location of a third, originally spotted in 1999 but now faded from view, are indicated in this image of the edge-on spiral. For a look at a new Galaxy Zoo supernova, move to the next image. (AP/NASA)
Galaxy Zoo wants YOU for its supernova hunt!
The good folks over at Galaxy Zoo are looking for volunteers. But maybe they need to give their new project its own name: Supernova Zoo.
In any case, astronomers are looking for volunteers to pore over images that might contain supernovae. These are stars that end their lives in violent explosions. All that's left is either a neutron star or a black hole.
Either way, the result is exotic.
A neutron star has about the sun's mass. But it's squeezed into an object only about 12 kilometers (nearly 7.5 miles) across. And a black hole, well, you know that one already -- an object whose gravity is so powerful that not even light, traveling at 186,000 miles a second, can escape. At least on a neutron star, the escape velocity is marginally more reasonable: roughly a third of the speed of light.
And the need for help is immense.
The GZ team has two telescopes at work. One to hunt for candidates, the other to conduct follow-up studies once supernovae are identified.
Step 1: Have the Palomar Transient Factory on California's Mt. Palomar supply images that they are taking for supernova-hunting purposes, as well as to spot other cosmic events that happen in a flash. The factory picks the best supernovae candidates for posting on the GZ's website.
Step 2: Get volunteers to sign up and hunt through the images on the website for evidence of the stellar explosions.
Step 3: The GZ astronomers then tap the 4-meter William Herschel Telescope in Chile to conduct follow-up studies, according to project director Chris Lintott, an Oxford University astrophysicist.
Unlike the original Galaxy Zoo project, here speed is of the essence. Astronomers can extract the most information about the supernova when they can track the evolution of its so-called light curve -- which rises, peaks, then tails off with time.
Ideally, astronomers would like to train Herschel on a supernova before it reaches peak brightness so they can follow the evolution of the light curve, which identifies the type of supernova it is (yes, there's more than one form of supernova).
By taking spectra of the light, easiest when it's at its brightest, they can identify the chemical elements the supernova has generated. These events seed interplanetary space with essentially all the elements heavier than hydrogen and helium.
And for a class of supernovae called Type 1A, they can also measure how significantly the light's spectra is shifted up or down the wavelength scale by the universe's expansion.
One 1A supernova is just as inherently bright as any other, making them valuable "standard candles" for calculating cosmic distances. Among their other accolades, they were the events that allows astrophysicists to discover "dark energy," a mysterious force that is increasing the pace at which the universe is expanding, when by all rights that pace should be slowing.
The Galaxy Zoo team is shooting for no more than a 24-hour turn-around between the time the Transient Factory uploads images to the time confirmed supernovae are sent to Herschel, Dr. Lintott explains in an email. In many cases, the time will be much less.
"This is the first time we've attempted this, and we expect to learn enough to make this a regular feature" of the Transient Factory's observing runs, he writes.
Planets too close for comfort? This artist's rendering shows two planets around the star WASP-17 that astronomers say nearly smacked into each other about 1 billion years ago. The close encounter sent one planet into a backwards orbit. The other? Hurtling somewhere through deep space, for all we know. (KASI/CBNU/ARCSEC)
Oops! This planet is orbiting in the wrong direction
If astronomers have any notion of giving their newly discovered planet, WASP-17b, a more decent-sounding name, they should consider naming it after Wrong Way Corrigan.
The crafty Mr. Corrigan was a pilot from California who took off from an airport in Brooklyn, N.Y., on a foggy July evening in 1938. He claimed he was heading back to California. He wound up in Dublin, Ireland, 28 hours and 13 minutes later. (He told grumpy federal officials that he misread his compass in the fog; he actually headed east on purpose. But that's another story.)
Anyway, the new planet in question – about 1,000 light-years away – appears to be orbiting its parent star in the wrong direction. This is the first navigationally challenged planet anyone has seen. You can download a PDF of the formal report of the discovery here. A plain-English version appears here.
So, how can there be a "wrong" direction? This is outer space, after all. Oh, it's way wrong!
Researchers explain that when a star and its solar system form, they do so from the same rotating cloud of dust and gas. Everything that forms – from the star itself to the objects that orbit it – initially spins in the direction in which the cloud was rotating. The objects orbiting that star also orbit in the direction of the cloud's original rotation.
But the star WASP-17 is spinning in one direction. WASP-17b is orbiting in the opposite direction. That means that somewhere along the way, the latter was yanked in the opposite direction, either by a close encounter with another planet or perhaps a passing star.
Astronomers have found no evidence yet for a second planet, says Coel Hellier, an astronomer at Keele University in Britain and a leading member of the team reporting the discovery.
In an e-mail he explains that a second planet could still be orbiting the star, but at a much greater distance, making it harder to detect. Or the encounter could have sent the second planet packing – ejecting it from the system.
Based on models of the evolution of orbits, he estimates that the orbit-reversing event took place about 1 billion years ago. Based on the studies of the system's star, the researchers estimate that the system is about 3 billion years old.
WASP-17b is intriguing for other reasons. It has half Jupiter's mass, but is twice Jupiter's size. It orbits WASP-17 once every 3.7 Earth days.
The planet's backwards orbit could help explain its girth, the research team says. After the encounter, it would have been knocked into a highly elliptical orbit. The constant squeezing and stretching of WASP-17b by the star's gravity as the planet approached and left the star's immediate vicinity probably heated the planet. Over time, the orbit would have grown increasingly circular, leading to the orbit that astronomers see today.
Under such gravitational tugging and hauling, WASP-17b expanded to the point where its density is now about the same as Styrofoam peanuts used for boxing up breakables.
Artist's impression of a collision between two planet wannabes forming around a star 100 light-years away. Scientists who spotted evidence of the collision's aftermath say it's similar to the collision Earth is held to have had with a Mars-sized object 30 million to 50 million years after the solar system formed. The result? The moon. (NASA/JPL-Caltech)
Astronomers spot planetary wreckage around distant star
It must have been one bodacious crunch -- akin to the moon and Mercury racing to occupy the same spot at more than 22,300 miles an hour.
The story of a collision between nascent planets is written in a disk of dust around a star 100 light-years away, according to an international team of astronomers formally reporting the results in an upcoming issue of the Astrophysical Journal. A plain-English version appears here.
The dust surrounds a 12-million-year-old star labeled HD172555. The dust disk shouldn't be there. It should long since have clumped into larger objects that form the building blocks of planets.
But the dust is there. Its make-up, revealed via NASA's Spitzer Space Telescope, suggests that it formed in a collision between two so-called planetesimals. The smash-up took place within the last 100,000 years, and perhaps as recently as 1,000 years ago.Among the minerals the team identified in the disk's spectra: obsidian and tektites, glassy rocks that forms at very high temperatures. Tektites in particular form during a collision. Rock melted by the heat of impact hurtles from the impact site, cooling as it travels.
The observations recorded vast amounts of silicon-oxide gas, which forms when silicate-bearing rocks vaporize. The scientists also detected large amounts of cold, sizable dust. But the smoking gun was the presence of unusually large amounts of warm, fine dust, opening a unique window on the dust's chemical make-up.
The relative abundance of each led them to conclude that an object at least as large as the moon was the loser plano-a-plano with an object at least as large as Mercury.
"In any system that's older than 10 million years, when we see warm dust" returning remarkably detailed information about its chemical composition, "it tells us that something extraordinary has happened," says Carey Lisse, a senior research scientist at the Johns Hopkins University's Applied Physics Laboratory in Laurel, Md.
Why? He explained during a phone chat that above a certain size, say, 100 microns (100 millionths of an inch), dust grains are essentially opaque. They may re-radiate light they receive from a star they orbit. But they do it equally well across all wavelengths. So astronomers have a hard time picking up changes in the spectra they look for that uniquely signal each chemical compound in the dust.
But if the grains are thin enough, say around 1 micron, they in effect become transparent. Light can interact with the mineral crystals in the grains, revealing their chemical composition.
In essence, Lisse concludes, something remarkable must have happened to pulverize material to the point where it would reveal its chemical fingerprints in a solar system where dust that small, in amounts large enough for Spitzer to detect, should have disappeared a long time ago.
The ability to glean this information traces its roots at least in part to NASA's Deep Impact mission to study comet Tempel 1, another project Lisse took part in.
The highlight of the mission came when the spacecraft release an impactor to collide with the comet. The Spitzer Space Telescope was one of the tools scientists used to track the material the impact kicked up. And it showed researchers what the spectra from warm dust from a collision would look like, Lisse says. The spectra went from fairly boring to stunningly detailed in an instant.
To be sure, you don't have to look beyond our solar system to find plenty of evidence that planets absorb mighty whacks as they evolve. Mercury's current surface is thought to represent lower layers of what originally was a heftier planet. Venus spins backward compared with other planets. Mars is more heavily cratered in its southern hemisphere than in its northern hemisphere. Uranus got knocked on its side -- spinning almost as if it had an east pole and west pole, rather than a north pole and south pole.
The detritus from HD172555's blast from the not-so-distant-past, however, is giving astronomers a unique opportunity to monitor such collisions at a far earlier stage of the clean-up process.
And it's giving scientists the "look" they can hunt for around other young stars as they try to gather data from different periods along a time line from "ooof" to "ahhhh."
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