dust Archives

May 4, 2014December 23, 2015 by Bob King

Revisit Halley’s Comet – Stay Up Late for This Week’s Eta Aquarid Meteor Shower

The Eta Aquarid meteor shower is active in early May and peaks before dawn on Tuesday and Wednesday May 6-7 this year. Watch for it before the start of morning twilight in the eastern sky. Created with Stellarium

UPDATE: Watch a live webcast of the meteor shower, below, from NASA’s Marshall Space Flight Center during the night of Monday, May 5 to the early morning of May 6.

Halley’s Comet won’t be back in Earth’s vicinity until the summer of 2061, but that doesn’t mean you have to wait 47 years to see it. The comet’s offspring return this week as the annual Eta Aquarid meteor shower. Most meteor showers trace their parentage to a particular comet. The Perseids of August originate from dust strewn along the orbit of comet 109P/Swift-Tuttle, which drops by the inner solar system every 133 years after “wintering” for decades just beyond the orbit of Pluto, but the Eta Aquarids (AY-tuh ah-QWAR-ids) have the best known and arguably most famous parent of all – Halley’s Comet. Twice each year, Earth’s orbital path intersects dust and rock particles strewn by Halley during its cyclic 76-year journey from just beyond Uranus to within the orbit of Venus. When we do, the grit meets its demise in spectacular fashion as wow-inducing meteors.

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Composite of Aquarid meteors from the 2012 shower. Credit: John Chumack

Meteoroids enter the atmosphere and begin to glow some 70 miles high. The majority of them range from sand to pebble sized but most no more than a gram or two. Speeds range from 25,000-160,000 mph (11-72 km/sec) with the Eta Aquarids right down the middle at 42 miles per second (68 km/sec). Most burn white though ‘burn’ doesn’t quite hit the nail on the head. While friction with the air heats the entering meteoroid, the actual meteor or bright streak is created by the speedy rock exciting atoms along its path. As the atoms return to their neutral state, they emit light. That’s what we see as meteors. Picture them as tubes of glowing gas.

The farther south you live, the higher the shower radiant will appear in the sky and the more meteors you’ll see. For southern hemisphere observers this is one of the better showers of the year with rates around 30-40 meteors per hour. With no moon to brighten the sky, viewing conditions are ideal. Except for maybe the early hour. The shower is best seen in the hour or two before the start of dawn.

The Eta Aquarid shower originates with material left behind by Halley's Comet when the sun boils dust and ice from its nucleus around the time of perihelion. This photo from May 1986 during its last pass by Earth. Credit: Bob King — The Eta Aquarid shower originates with material left behind by Halley’s Comet when the sun boils dust and ice off its nucleus around the time of perihelion. This photo from May 1986 during Halley’s last visit. Credit: Bob King

From mid-northern latitudes the radiant or point in the sky from which the meteors will appear to originate is low in the southeast before dawn. At latitude 50 degrees north the viewing window lasts about 1 1/2 hours; at 40 degrees north, it’s a little more than 2 hours. If you live in the southern U.S. you’ll have nearly 3 hours of viewing time with the radiant 35 degrees high.

A bright, earthgrazer Eta Aquarids streaks across Perseus May 6, 2013. Because the radiant is low for northern hemisphere observers, earthgrazers - long, bright meteors that come up from near the horizon and have long-lasting trails. Credit: Bob King — A bright, earthgrazing Eta Aquarid meteor streaks across Perseus May 6, 2013. Because the radiant is low for northern hemisphere observers, watch for earthgrazers – long, bright meteors that come up from near the horizon and have long-lasting trails. Credit: Bob King

Northerners might spy 5-10 meteors per hour over the next few mornings. Face east for the best view and relax in a reclining chair. One good thing about this event – it won’t be anywhere near as cold as watching the December Geminids or January’s Quadrantids. We must be grateful whenever we can.

Meteor shower members can appear in any part of the sky, but if you trace their paths in reverse, they’ll all point back to the radiant. Other random meteors you might see are called sporadics and not related to the Eta Aquarids. Because Aquarius is home to at least two radiants, we distinguish the Etas, which radiate from near Eta Aquarii, from the Delta Aquarids, an unrelated shower active in July and August.

Wishing you clear skies and plenty of hot coffee at the ready.

April 24, 2014December 23, 2015 by Bob King

LADEE Sees Zodiacal Light before Crashing into Moon, but Apollo Mystery Remains

The zodiacal light (left) reaches up from the eastern horizon to "touch" the Milky Way at right on Sept. 23, 2012. Credit: Bob King

Sunrise over the surface of the moon: a series of star tracker images taken by LADEE Saturday, April 12. The lunar horizon is ahead, a few minutes before orbital sunrise. Image Credit: NASA Ames.

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NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) literally ‘saw the light’ just days before crashing into the lunar farside last Thursday April 17. Skimming just a few kilometers above the moon’s surface, mission controllers took advantage of this unique low angle to gaze out over the moon’s horizon in complete darkness much like the Apollo astronauts did from lunar orbit more than 40 years ago.

With the glow of Earth well-hidden, any dust in the moon’s scant atmosphere around the time of orbital sunrise should become visible. Scientists also expected to see the softly luminous glow of the zodiacal light, an extensive cloud of comet and asteroid dust concentrated in the flat plane of the solar system. The zodiacal light gets its name from the zodiac, that familiar band of constellations the planets pass through as they orbit the sun. Back on Earth, the zodiacal light looks like a big thumb of light standing up from the western horizon a couple hours after sunset in spring and before sunrise in fall.

Frame from LADEE's star tracker camera showing the zodiacal light rising on the moon's horizon from its extremely low orbit on April 12, 2014. Credit: NASA — Frame from LADEE’s star tracker camera showing the zodiacal light rising on the moon’s horizon from its extremely low orbit on April 12, 2014. Credit: NASA

So what did LADEE see? As you watch the animation above, comprised of images taken from darkness until sunrise, you’ll see a yellow haze on the horizon that expands into large diffuse glow tilted slightly to the right. This is the zodiacal light along with a smaller measure of light coming from sun’s outer atmosphere or corona. Together they’re referred to as CZL or ‘coronal and zodiacal light’. At the very end, the sun peaks over the lunar horizon.

This is a sketch of the lunar sunrise seen from orbit by Apollo 17 astronaut Eugene Cernan. On the right, the sketch is highlighted to show the sources of the scattered light: red indicates Coronal and Zodiacal Glow, blue is the Lunar Horizon Glow, perhaps caused by exospheric dust, and green indicates possible "streamers" of light (crepuscular rays) formed by shadowing and scattered light. Credit: NASA — This is a sketch of the lunar sunrise seen from orbit by Apollo 17 astronaut Eugene Cernan. On the right, the sketches are highlighted in color to show the sources of the scattered light: red indicates coronal and zodiacal light (CZL), blue is a glow along the lunar horizon possibly caused by dust suspended in the moon’s exosphere, and green may be crepuscular rays formed by shadowing and scattered light. Credit: NASA/phys.org

What appears to be missing from the pictures are the mysterious rays seen by some of the Apollo astronauts. The rays, neatly sketched by astronaut Eugene Cernan of Apollo 17, look a lot like those beams of light and shadow streaming though holes in clouds called crepuscular rays.

Crepuscular rays form a crown of rays made of alternating shadows and light scattered by dust in the atmosphere. Credit: Bob King — Crepuscular rays form a crown of rays made of alternating shadows and light scattered by dust and moisture in the atmosphere. Credit: Bob King

Only thing is, Earth’s atmosphere is thick enough for cloud beams. The dust in the moon’s atmosphere appears much too thin to cause the same phenomenon. And yet the astronauts saw rays as if sunlight streamed between mountain peaks and scattered off the dust just like home.

Low level horizon glow photos on the moon captured by the Surveyor 7 unmanned lander in 1968. It's possible this low altitude glow is caused by larger dust particles that don't travel as high as the smaller motes. Credit: NASA — Low level horizon glow photos on the moon captured by the Surveyor 7 unmanned lander in 1968. It’s possible this low altitude glow is caused by larger dust particles that don’t travel as high as the smaller motes. Credit: NASA

It’s believed that dust gets lofted into the spare lunar atmosphere via electricity. Ultraviolet light from the sun knocks electrons from atoms in moon dust, giving them a positive charge. Since like charges repel, bits of dust push away from one another and move in the direction of least resistance: up. The smaller the dust particle, the higher it rises until dropping back down to the surface. Perhaps these “fountains” of lunar dust illuminated by the sun are what the astronauts recorded.

Unlike Cernan, LADEE saw only the expected coronal and zodiacal light but no rays. Scientists plan to look more closely at several sequences of images made of lunar sunrise in hopes of finding them.

March 20, 2014December 23, 2015 by Bob King

Happy Equinox! – A Perfect Time to See the Zodiacal Light

Zodiacal light tilts upward from the western horizon and points at the Pleiades star cluster in this photo taken March 19, 2009. Clouds at bottom reflect light pollution from nearby Duluth, Minn. U.S. Credit: Bob King

Welcome to the first day of spring! If you have a clear night between now and April 1, celebrate the new season with a pilgrimage to the countryside to ponder the eerie glow of the zodiacal light. Look for a large, diffuse, tapering cone of light poking up from the western horizon between 90 minutes and two hours after sunset. While the zodiacal light appears only as bright as the Milky Way, you’re actually looking at the second brightest object in the night sky. No kidding. If you could crunch it all into a little ball, it would shine at magnitude -8.5, far brighter than Venus and bested only by the full moon.

The zodiacal (Zo-DIE-uh-cull) light is centered on the plane of the solar system called the ecliptic. On late March nights, you can trace it from near the western horizon more than 45 degrees (halfway up the sky). Stellarium — The zodiacal (Zo-DIE-uh-cull) light is centered on the plane of the solar system called the ecliptic. This is the same band of sky where you’ll find the planets and zodiac constellations, hence the name. On late March nights, you can trace it from near the western horizon more than 45 degrees (halfway up the sky). Created with Stellarium

Sunlight reflecting off countless dust particles shed by comets and spawned by asteroid collisions creates the luminous cone of light. First time observers might think they’re looking at skyglow from light pollution but the tapering shape and distinctive tilt mark this glow as interplanetary dust.

This image of coronal and zodiacal light (CZL) was taken by the Clementine spacecraft, when the sun was behind the moon. The white area on the edge of the moon is the CZL, and the bright is Venus. (Credit: NASA) — Photo of coronal and zodiacal light taken by the Clementine spacecraft when the sun was hidden by the moon. At right is Venus. Clementine measured the brightness of the light to arrive at an integrated magnitude of -8.5. It also estimated dust particle sizes and origin. Credit: NASA

Like the planets, the dust resides in the plane of the solar system. In spring, that plane (called the ecliptic) tilts steeply up from the western horizon after sunset, “lifting” the chubby thumb of light high enough to clear the horizon haze and stand out against a dark sky for northern hemisphere observers. In October and November the ecliptic is once again tilted upright, but this time before dawn. While the zodiacal light is present year-round, it’s usually tipped at a shallow angle and camouflaged by horizon haze. No so for skywatchers in tropical and equatorial latitudes. There the ecliptic is tilted steeply all year long, and the light can be seen anytime there’s no moon in the sky.

The combined glow of dust particles in the plane of the solar system reaching from the sun's vicinity to beyond Mars is responsible for creating the zodiacal light. Planets are shown as colored disks. Illustration: Bob King — The combined glow of dust particles in the plane of the solar system reaching from the sun’s vicinity out to at least Jupiter is responsible for creating the zodiacal light. Dust closest to the sun glow more brightly, the reason the bottom of the zodiacal light cone is brighter than the tip. Planets are shown as colored disks. Illustration: Bob King

Now through April 1 and again from April 17-30 are the best nights for viewing because the moon will be absent from the sky. The cone is widest near the western horizon and narrows as you direct your gaze upward and to the left. At its apex, where it touches the V-shape Hyades star cluster, it continues into the even fainter zodiacal band and gegenschein, but more about that in a moment. Sweep your gaze in broad strokes back and forth across the western sky to help you discern the Z-light’s distinctive conical shape. And be sure to look for something HUGE. This thing is a monster – indeed, one of the largest entities in the solar system.

Scanning electron microscope photo of an interplanetary dust particle collected by a high-altitude plane. It measures about 8 microns across or a little less than twice the size of a human red blood cell. Scientists recently discovered that dust particles can act as tiny factories to built water molecules. Credit: Donald Brownlee and Elmar Jessberger

Observers fortunate enough to live under or with access truly dark skies can trace the zodiacal light all the way across the sky as the zodiacal band.

Midway along its length, 180 degrees opposite the sun, a slightly brighter circular patch called the gegenschein (German for ‘counter glow’) embedded in the band.

Dust particles there get an extra brightness boost because they face the sun square on, much like the moon does when full. While I usually see only a section of the zodiacal band from my dark observing site, the gegenschein is often visible as a diffuse, hazy patch of light about 6 degree across a little brighter than the sky background.

Incredible 360-degree-wide view of morning and evening zodiacal light cones (far left and right), the fainter zodiacal band and the brighter spot of gegenschein. Click to enlarge. Credit: Miloslav Druckmuller and Shadia Habbal — Incredible 360-degree-wide view of morning and evening zodiacal light cones (far left and right), the fainter zodiacal band and the brighter spot of gegenschein (center) and the Milky Way photographed from Mauna Kea. Click to enlarge. Credit: Miloslav Druckmuller and Shadia Habbal

Dutch astronomer H. C. van de Hulst determined that the dust particles responsible for the zodiacal light and its cousins the zodiacal band and gegenschein are about 0.04 inch (1 mm) in diameter and separated, on average, by about 5 miles (8 km).

The gegenschein, an oval shaped brighter spot within the faint zodiacal band, is easiest to when due south and highest in the sky at local midnight (1 a.m. Daylight Saving Time). Currently it's in northern Virgo. Since the 'counter glow' will always be opposite the sun, it will slide down closer to Spica in April. Created with Stellarium — The gegenschein, an oval shaped brighter spot within the faint zodiacal band, is easiest to when due south and highest in the sky at local midnight (1 a.m. Daylight Saving Time). Currently it’s in northern Virgo. Since the ‘counter glow’ will always be opposite the sun, it will slide down closer to Spica in April. Created with Stellarium

The particles form a low density, lens-shaped cloud of dust that’s thickest within the plane of the solar system but in reality covers the entire sky but ever so thinly. Sunlight absorbed by the particles is re-emitted as invisible infrared (heat) radiation. This re-radiation robs the dust of energy, causing the particles to spiral slowly into the sun. Fresh dust from the vaporization of cometary ices as well as collisions of asteroids replenishes the cloud.

Zodiacal light cones in the fall morning sky (left) and in late March. Both times of year, we see the plane of the solar system tipped at high angle in the sky. Credit: Bob King — Zodiacal light cones in the fall morning sky (left) and in late March. Both times of year we see the plane of the solar system tipped at a high angle in the sky. Credit: Bob King

According to a study by Joseph Hahn and colleagues of the Clementine Mission data, comet dust accounts for the majority of the zodiacal dust within 1 a.u. (93 million miles) of the sun; a mix of asteroidal and comet dust makes up the remainder.

Stepping out on a spring evening to look at the zodiacal light, we can appreciate how small things can come together to create something grand.

March 18, 2014December 23, 2015 by Elizabeth Howell

Dusty Galaxies Shine Across The Universe In New Herschel Survey

A portion of a collage of galaxies included in the Herschel Reference Survey, in false color to show different dust temperatures. (Blue is colder, and red is warmer). Credit: ESA/Herschel/HRS-SAG2 and HeViCS Key Programmes/L. Cortese (Swinburne University)

While dust is easy to ignore in small quantities (says the writer looking at her desk), across vast reaches of space this substance plays an important role. Stick enough grains together, the theory goes, and you’ll start to form rocks and eventually planets. On a galaxy-size scale, dust may even effect how the galaxy evolves.

A new survey of 323 galaxies reveals that dust is not only affected by the kinds of stars in the vicinity, but also what the galaxy is made of.

“These dust grains are believed to be fundamental ingredients for the formation of stars and planets, but until now very little was known about their abundance and physical properties in galaxies other than our own Milky Way,” stated lead author Luca Cortese, who is from the Swinburne University of Technology in Melbourne, Australia.

“The properties of grains vary from one galaxy to another – more than we originally expected,” he added. “As dust is heated by starlight, we knew that the frequencies at which grains emit should be related to a galaxy’s star formation activity. However, our results show that galaxies’ chemical history plays an equally important role.”

Galaxies in the Herschel Reference Survey in infrared/submillimeter wavelengths (with the Herschel space telescope, at left) and the Sloan Digital Sky Survey (right). Herschel's false-color image shows galaxies with cold dust (blue) and warm dust (red). Sloan highlights young stars (blue) and old stars (red). "Together, the observations plot young, dust-rich spiral/irregular galaxies in the top left, with giant dust-poor elliptical galaxies in the bottom right," the European Space Agency stated. Credit: ESA/Herschel/HRS-SAG2 and HeViCS Key Programmes/Sloan Digital Sky Survey/ L. Cortese (Swinburne University) — Galaxies in the Herschel Reference Survey in infrared/submillimeter wavelengths (with the Herschel space telescope, at left) and the Sloan Digital Sky Survey (right). Herschel’s false-color image shows galaxies with cold dust (blue) and warm dust (red). Sloan highlights young stars (blue) and old stars (red). “Together, the observations plot young, dust-rich spiral/irregular galaxies in the top left, with giant dust-poor elliptical galaxies in the bottom right,” the European Space Agency stated. Credit: ESA/Herschel/HRS-SAG2 and HeViCS Key Programmes/Sloan Digital Sky Survey/ L. Cortese (Swinburne University)

Data was captured with two cameras on the just-retired Herschel space telescope: Spectral and Photometric Imaging Receiver (SPIRE) and Photodetecting Array Camera and Spectrometer (PACS). These instruments examined different frequencies of dust emission, which shows what the grains are made of. You can see a few of those galaxies in the image above.

“The dust-rich galaxies are typically spiral or irregular, whereas the dust-poor ones are usually elliptical,” the European Space Agency stated. “Dust is gently heated across a range of temperatures by the combined light of all of the stars in each galaxy, with the warmest dust being concentrated in regions where stars are being born.”

Astronomers initially expected that a galaxy with speedy star formation would display more massive and warmer stars in it, corresponding to warmer dust in the galaxy emitting light in short wavelengths.

“However, the data show greater variations than expected from one galaxy to another based on their star formation rates alone, implying that other properties, such as its chemical enrichment, also play an important role,” ESA said.

You can read more about the research in the Monthly Notices of the Royal Astronomical Society or in preprint version on Arxiv.

Sources: Royal Astronomical Society and European Space Agency

June 13, 2013December 23, 2015 by Elizabeth Howell

Should This Alien World Even Exist? This Young Disk Could Challenge Planet-Formation Theories

An image of TW Hydrae and the protoplanetary stuff surrounding the star. Astronomers believe a planet is forming within the gas and dust and sweeping up debris, as shown by the gap in this picture. Credit: NASA, ESA, J. Debes (STScI), H. Jang-Condell (University of Wyoming), A. Weinberger (Carnegie Institution of Washington), A. Roberge (Goddard Space Flight Center), and G. Schneider (University of Arizona/Steward Observatory)

Take a close look at the blurry image above. See that gap in the cloud? That could be a planet being born some 176 light-years away from Earth. It’s a small planet, only 6 to 28 times Earth’s mass.

That’s not even the best part.

This alien world, if we can confirm it, shouldn’t be there according to conventional planet-forming theory.

The gap in the image above — taken by the Hubble Space Telescope — probably arose when a planet under construction swept through the dust and debris in its orbit, astronomers said.

That’s not much of a surprise (at first blush) given what we think we know about planet formation. You start with a cloud of debris and gas swirling around a star, then gradually the bits and pieces start colliding, sticking together and growing bigger into small rocks, bigger ones and eventually, planets or gas giant planet cores.

But there’s something puzzling astronomers this time around: this planet is a heck of a long way from its star, TW Hydrae, about twice Pluto’s distance from the sun. Given that alien systems’ age, that world shouldn’t have formed so quickly.

An illustration of TW Hydrae's disk in comparison with that of Earth's solar system. Credit: NASA, ESA, and A. Feild (STScI) — An illustration of TW Hydrae’s disk in comparison with that of Earth’s solar system. Credit: NASA, ESA, and A. Feild (STScI)

Astronomers believe that Jupiter took about 10 million years to form at its distance away from the sun. This planet near TW Hydrae should take 200 times longer to form because the alien world is moving slower, and has less debris to pick up.

But something must be off, because TW Hydrae‘s system is believed to be only 8 million years old.

“There has not been enough time for a planet to grow through the slow accumulation of smaller debris. Complicating the story further is that TW Hydrae is only 55 percent as massive as our sun,” NASA stated, adding it’s the first time we’ve seen a gap so far away from a low-mass star.

The lead researcher put it even more bluntly: “Typically, you need pebbles before you can have a planet. So, if there is a planet and there is no dust larger than a grain of sand farther out, that would be a huge challenge to traditional planet formation models,” stated John Debes, an astronomer at the Space Telescope Science Institute in Baltimore.

Protoplanet Hypothesis — Like a raindrop forming in a cloud, a star forms in a diffuse gas cloud in deep space. As the star grows, its gravitational pull draws in dust and gas from the surrounding molecular cloud to form a swirling disk called a “protoplanetary disk.” This disk eventually further consolidates to form planets, moons, asteroids and comets. Credit: NASA/JPL-Caltech

At this point, you would suppose the astronomers are seriously investigating other theories. One alternative brought up in the press release: perhaps part of the disc collapsed due to gravitational instability. If that is the case, a planet could come to be in only a few thousand years, instead of several million.

“If we can actually confirm that there’s a planet there, we can connect its characteristics to measurements of the gap properties,” Debes stated. “That might add to planet formation theories as to how you can actually form a planet very far out.”

A rare double transit of Jupiter's moon Ganymede (top) and Io on Jan. 3, 2013. Here, the sun is shining from the left causing shadows cast by the moons to fall onto the planet's cloud tops. Credit: Damian Peach — A rare double transit of Jupiter’s moon Ganymede (top) and Io on Jan. 3, 2013. Here, the sun is shining from the left causing shadows cast by the moons to fall onto the planet’s cloud tops. Credit: Damian Peach

There’s a trick with the “direct collapse” theory, though: astronomers believe it takes a bunch of matter that is one to two times more massive than Jupiter before a collapse can occur to form a planet.

Recall that this world is no more than 28 times the mass of Earth, as best as we can figure. Well, Jupiter itself is 318 times more massive than Earth.

There are also intriguing results about the gap. Chile’s Atacama Large Millimeter/submillimeter Array (ALMA) — which is designed to look at dusty regions around young stars — found that the dust grains in this system, orbiting nearby the gap, are still smaller than the size of a grain of sand.

Astronomers plan to use ALMA and the James Webb Space Telescope, which should launch in 2018, to get a better look. In the meantime, the results will be published in the June 14 edition of the Astrophysical Journal.

Source: HubbleSite

May 22, 2013April 26, 2016 by Bob King

What Do Comet PANSTARRS And Pinocchio Have In Common?

Comet C/2011 L4 PANSTARRS on May 21, 2013, when its anti-tail had grown to more than 12 full moons in length. The original main tail of the comet - to the right of the head - has faded and shortened. Credit: Damian Peach

While comets can’t tell lies, they do sometimes grow long noses. As the weeks click by and our perspective on Comet L4 PANSTARRS changes, its original plume-like dust tail has shrunk and faded while a second tail just won’t stop growing.

Comet PANSTARRS' orbital plane slices (marked by gray lines) slices right through the plane of the planets. Earth crosses that orbital plane on May 27. As we look up into space at the comet (blue arrow), all the dust it shed along its path - including a fine sheet of particles - stacks up to create a narrow, streak-like tail pointing toward the sun. The shorter, active dust tail sticks up and away (top). Credit: NASA with my own additions — Comet PANSTARRS’ orbital plane slices (marked by gray lines) slices right through the plane of the planets. Earth crosses that orbital plane on May 27. As we look up into space at the comet (blue arrow), all the dust it shed along its path – including a fine sheet of particles – stacks up to create a narrow, streak-like tail pointing toward the sun. The shorter, active dust tail sticks up and away (top). Credit: NASA with my own additions

I’m talking about the anti-tail, so called because it points toward the sun instead of away. Like the normal dust tail, an anti-tail is formed from fresh dust blown back from the comet’s head by the pressure of sunlight. As the comet continues along its orbital path, last week’s dust lingers behind, forming a “trail of breadcrumbs” in its wake. Right now those breadcrumbs look like a light saber straight out of Star Wars. Time exposure photographs show a striking sunward-pointing appendage more than 6 degrees (12 full moons) long. I’ve been keeping an eye on Comet PANSTARRS here at home and can report that the anti-tail is plainly visible with a telescope under dark skies. Watching it grow from a short nub to the most dominant feature of this remarkable object has been the highlight of many a clear night.

Our current "edge on" view of Comet PANSTARRS is similar to seeing from high above the Earth's north pole, where the dust stacks up to create a bright, streak-like tail. Credit: NASA/JPL/my own additions — Our current “edge on” view of Comet PANSTARRS is similar to looking down on it from high above the Earth’s north pole, where the dust stacks up to create a bright, streak-like tail. Credit: NASA/JPL/my own additions

Nothing stands still in our solar system. Earth’s moving, the comet’s moving. Later this week on May 26-27, Earth will pass directly through the comet’s orbital plane, which slices through the plane of the planets at a very steep angle. As the Earth approaches this intersection, we look up (from the northern hemisphere) and stare squarely into the long trail of dusty debris deposited by PANSTARRS during its recent swing around the sun in March. It gets better.

If we step back in time to May 9, we see that the anti-tail was neither as long or as pronounced because the Earth was further from the comet's orbital plane. Credit: Michael Jaeger — If we step back in time to May 9, we see that the anti-tail was neither as long nor as pronounced because the Earth was further from the comet’s orbital plane. Because we were more broadside to the comet then, the dust sheet is much more obvious. It extends millions of miles into space but is only 5,000-10,000 miles thick. Credit: Michael Jaeger

Sunlight pushes the smaller particles into a vast, thin sheet or fan extending millions of miles into space well beyond the path traveled by the comet’s nucleus. Since we now see PANSTARRS almost “edge-on”, all that dust overlaps from our perspective to form a thick, bright line sticking out of the comet’s head. It’s as if we’re seeing the ghost of PANSTARRS from the recent past still lingering in space. If we could somehow see the whole works broadside, the comet would appear fainter, spread out and much more diffuse.

Simulated view of looking at the dust shed in PANSTARRS' tail edge-on vs. broadside. Dust piles up in the edge-on view to create a skinny, saber-like tail. Illustration: Bob King — Simulated views of dust shed by PANSTARRS’ in its orbit around the sun. Dust piles up in the edge-on view to create a skinny, saber-like tail vs. a faint, broad tail (right). Illustration: Bob King

The Milky Way stands out as a band of light distinct from the thin scree of stars for the very same reason; our gaze cuts edge-on through our galaxy’s flattened disk where stars are most concentrated. Like comet dust, they pile atop one other to create a distinct ribbon of fuzzy light slicing across the night sky.

Back on April 10 the anti-tail (short stub to left) was just getting its start. It's completely dwarfed by the comet's main dust tail and fan of tinier dust particles. Credit: Michael Jaeger — Going back even further to April 10, the anti-tail (short stub to left of bright head) was just getting started. It’s completely dwarfed by the comet’s main dust tail and fan of tinier dust particles. Compare this photo to the current view. Click to enlarge. Credit: Michael Jaeger

In the next few days the tail could grow considerably longer and intensify in brightness as we move closer to the comet’s orbital plane. Unfortunately the moon will be at or near full at the same time, making it tougher to fully appreciate this amazing apparition at least with binoculars and telescopes. Cameras will have better luck. Will that stop you from looking? I hope not. Either way, you can use this map to help you find Comet PANSTARRS and check it out yourself.

Map showing Comet C/2011 L4 PANSTARRS' location tonight through June 21. Positions are marked off every three nights. Stars are shown to about magnitude 8. Credit: created with Chris Marriott's SkyMap software — Map showing Comet C/2011 L4 PANSTARRS’ location tonight through June 21. Positions are marked off every three nights with stars are shown to about 8th magnitude. Credit: created with Chris Marriott’s SkyMap software

When you do spot the anti-tail, don’t be fooled. It may appear to be pointing at the sun, but it’s only dust spread along a path once tread.

A magnificent view of the very thin anti tail of Comet PANSTARRS, as seen on May 22, 2013 from near Payson, Arizona. Credit and copyright: Chris Schur.

A negative image showing Comet PANSTARRS and its very thin anti tail, as seen on May 22, 2013 from near Payson, Arizona. Credit and copyright: Chris Schur.

November 14, 2012December 23, 2015 by Jason Major

Closely-Orbiting Stellar Companions Surrounded by “Mystery Dust”

Artist’s concept showing a dust disk around a binary system containing a white dwarf and a less-massive M (red) dwarf companion. (P. Marenfeld and NOAO/AURA/NSF)

Even though NASA’s Wide-field Infrared Survey Explorer spacecraft — aka WISE — ran out of coolant in October 2010, bringing its infrared survey mission to an end, the data that it gathered will be used by astronomers for decades to come as it holds clues to some of the most intriguing and hard-to-find objects in the Universe.

Recently astronomers using WISE data have found evidence of a particularly curious disk of dust and gas surrounding a pair of stars — one a dim red dwarf and the other the remains of a dead Sun-sized star — a white dwarf. The origin of the gas is a mystery, since based on standard models of stellar evolution it shouldn’t be there… yet there it is.

The binary system (which has the easy-to-remember name SDSS J0303+0054) consists of a white dwarf and a red dwarf separated by a distance only slightly larger than the radius of the Sun — about 700,000 km — which is incredibly close for two whole stars. The stars orbit each other quickly too: once every 3 hours.

The stars are so close that the system is referred to as a “post-common envelope” binary, because at one point the outer material of one star expanded out far enough to briefly engulf the other completely in what’s called a “common envelope.” This envelope of material brought the stars even closer together, transferring stellar material between them and ultimately speeding up the death of the white dwarf.

The system was first spotted during the Sloan Digital Sky Survey (hence the SDSS prefix) and was observed with WISE’s infrared abilities during a search for dust disks or brown dwarfs orbiting white dwarf stars. To find both a red (M) dwarf star 40-50 times the mass of Jupiter and a disk of dust orbiting the white dwarf in this system was unexpected — in fact, it’s the only known example of a system like it.

The entire mass of the dust (termed an infrared excess) is estimated to be “equivalent to the mass of an asteroid a few tens of kilometers in radius” and extends out to about the same distance as Venus’ orbit — just over 108 million kilometers, or 0.8 AU.

Why is the dust so unusual? Because, basically, it shouldn’t even be there. At that distance from the white dwarf, positioned just out of reach (but not terribly far away at all) anything that was within that zone when the original Sun-sized star swelled into its red giant phase should have spiraled inwards, getting swallowed up by the expanding stellar atmosphere.

Such is the fate that likely awaits the inner planets of our own Solar System — including Earth — when the Sun reaches the final phases of its stellar life.

So this requires that there are other sources of the dust. According to the WISE science update, “One possibility is that it is caused by multiple asteroids that orbit further away and somehow are perturbed close to the binary and collide with each other. [Another] is that the red dwarf companion releases a large amount of gas in a stellar wind that is trapped by the gravitational pull of its more massive white dwarf companion. The gas then condenses and forms the dust disk that is observed.

“Either way, this new discovery provides an interesting laboratory for the study of binary star evolution.”

See the team’s paper here, and read more on Berkeley’s WISE mission site here.

WISE launched into space on Dec. 14, 2009 on a mission to map the entire sky in infrared light with greatly improved sensitivity and resolution over its predecessors. From its polar orbit 525 kilometers (326 miles) in altitude it scanned the skies, collecting images taken at four infrared wavelengths of light. WISE took more than 2.7 million images over the course of its mission, capturing objects ranging from faraway galaxies to asteroids relatively close to Earth before exhausting the supply of coolant necessary to mask its own heat from its ultra-sensitive sensors.

Inset: Infrared images of SDSS J0303+0054. (NASA/JPL and John H. Debes et. al.)

July 5, 2012December 23, 2015 by Jason Major

The Case of the Disappearing Dust

Astronomy has always taught us that planets form from vast clouds of dust and gas orbiting young stars. It’s a gradual process of accretion that takes hundreds of thousands, perhaps even millions, of years… or does it?

During a 1983 sky survey with the Infrared Astronomical Satellite (IRAS) astronomers identified a young Sun-like star with a large cloud of dust surrounding it. The star, named TYC 8241 2652 1, is 450 light years away and what they had found around it was thought to be the beginnings of a solar system – the protoplanetary disc from which planets form.

Fast forward to 2008. Astronomers observed at the same star with a different infrared telescope, the Gemini South Observatory in Chile. What was observed looked a lot like what was previously seen in ’83.

Then, in 2009, they looked again. Curiously, the brightness of the dust cloud was only a third of what it was the year before. And in WISE observations made the very next year, it had disappeared entirely.

“It’s like the classic magician’s trick: now you see it, now you don’t. Only in this case we’re talking about enough dust to fill an inner solar system, and it really is gone.”

– Carl Melis, lead author and postdoctoral fellow at UC San Diego

Abracadabra?

“It’s as if you took a conventional picture of the planet Saturn today and then came back two years later and found that its rings had disappeared,” said study co-author and circumstellar disk expert Ben Zuckerman of UCLA.

It’s always been thought that planets take some time to form, in the order of hundreds of thousands of years. Although that may seem like forever to humans, it’s quick in cosmic time scales. But if what they’ve seen here with TYC 8241 is in fact planetary formation, well… it may happen a lot faster than anyone thought.

On the other hand, the star could have somehow blown all the dust out of the system. More research will be needed to see if that was the case.

The really interesting thing here is that astronomers have traditionally looked for these kinds of dust clouds around stars to spot planetary formation in action. But if planets form quicker than we thought, and the dust clouds are only fleeting features, then there may be a lot more solar systems out there that we can’t directly observe.

“People often calculate the percentage of stars that have a large amount of dust to get a reasonable estimate of the percentage of stars with planetary systems, but if the dust avalanche model is correct, we cannot do that anymore,” said study co-author Inseok Song, assistant professor of physics and astronomy at the University of Georgia. “Many stars without any detectable dust may have mature planetary systems that are simply undetectable.”

Top image: Gemini Observatory/AURA artwork by Lynette Cook.

December 18, 2010December 24, 2015 by Jon Voisey

M33’s “Object-X”

Often times, objects that are unremarkable in one portion of the spectra, can often be vivid in others. In M33, the Triangulum Galaxy, a star that’s barely visible in the optical, stands out as the second brightest source (and single brightest single star) in the mid-infrared. This unusual star has been the target of a recent study, led by Rubab Khan at the Ohio State University and may help astronomers to understand an unusual supernova from 2008.

The supernova 2008S occurred February first in NGC 6946, the Fireworks Galaxy. Since it happened in a galaxy that is relatively nearby, astronomers seized the opportunity to explore the progenitor star in archival images. Yet images from the Large Binocular Telescope and other optical observatories could not find a star that could be identified as a parent. Instead, the detection of the star responsible came from Spitzer, an infrared observatory. Observations from this instrument indicated that the star responsible may have been unexpectedly low mass for such a powerful explosion leading other astronomers to question whether or not SN 2008S was a true supernova, or merely an impostor in the form of an eruption of a Luminous Blue Variable (LBV), which tend to be more massive stars and would be in stark contradiction to the Spitzer findings.

Yet, regardless of the nature of the nature of SN 2008S, teams all seemed to agree that the progenitor had only been detected in the infrared because it was veiled by a thick curtain of dust. So to help better understand this class of dusty stars, astronomers have been working to uncover more of them, against which they can test their hypotheses.

To find these objects, astronomers have been searching the infrared portion of the spectrum for objects that are exceptionally bright yet lack optical counterparts. The brightest of the stellar sources in M33 features faint star in the red portion of the optical spectrum from the Local Group Galaxies Survey published in 2007, but no star at all in archival records with similar limiting magnitudes from 1949 and 1991. The authors of the new study have dubbed this odd source, Object-X.

The team rules out the possibility that the object could be a young stellar object (YSO), blocked by a thick dust disc along the line of sight, noting that models of even the thickest dust discs still predict more light to be scattered back along the line of sight. Instead, the team concludes that Object-X must be a self-obscured star that has undergone relatively recent mass loss which has cooled to form either graphite or silicate dust. Depending on which type of dust is predominant, the team was able to fit the data to two wildly different temperatures for the star: either 5000 K for graphite, or 20,000 K for the silicate. In all cases, the predicted mass for the central star was always greater than 30 solar masses.

In general, there are two mechanisms by which a star can eject material to form such a curtain. The first is through stellar winds, which increase as the star enters the red giant phase, swelling up and lowering the force of gravity near the surface. The second is “impulsive mass ejections” in which stars shudder and throw mass off that way. A classical example of this is Eta Carinae. The team predicts from the features they found, that Object-X is most likely a cool hypergiant. The fact that the star was completely obscured until very recently hints that the mass loss is not constant (as stellar wind), but patchy, coming from frequent eruptions. As the shell of dust expands, the star should reemerge in the optical, becoming visible again in the next few decades.

January 26, 2010December 24, 2015 by Nancy Atkinson

Could Mars Dust Be “Levitated” Away?

The Spirit rover's solar panels were covered with dust until a gust of wind blew it off in 2006. Credit: NASA.

What could potentially be the biggest problem during a human mission to Mars? One NASA study says, surprisingly, that dust could be the number one risk for both humans and equipment. Human explorers could inhale the extremely fine but rough dust particles causing severe respiratory problems, and high winds on Mars could disperse the dust to coat solar panels, penetrate through seals and interfere with machinery. But scientists at the University of Vermont may have come up with a new way to combat dust: acoustic levitation. But will it work on Mars?

The researchers conducted a feasibility study to develop an acoustic dust removing system for use in space stations or habitations on the Moon or Mars. They found a high-pitched (13.8 kHz, 128 dB) standing wave of sound emitted from a 3 cm aperture tweeter and focused on a reflector 9 cm away was strong enough to dislodge and move extremely fine (<2 µm diameter) dust particles on the reflector surface. The sound waves overcome the van der Waals adhesive force that binds dust particles to the surface, and creates enough pressure to levitate the dust, which is then blown away. The team tested the system on a solar panel coated with mock lunar and Martian dust. The output of the clean panel was 4 volts, but when coated with dust it produced only 0.4 volts. After four minutes of acoustic levitation treatment the output returned to 98.4% of the maximum. Mars dust, although fine, is rougher that Earth dust, and likely is more similar to the dust that covers the Moon. The thin atmosphere on Mars means dust particles are not as rounded as they would be on Earth and can remain quite sharp and abrasive. [/caption] Mars dust, as we have found with the Mars rovers, has a high electrostatic charge, which means the fine dust clings to everything. The dust has severely decreased the efficiency of solar panels on the rovers, and over time has likely caused other problems with the mechanical operation on the rovers as well. We've had several articles here on Universe Today discussing the problems of dust on the solar panels of the Mars Exploration Rovers, and inevitably we get comments from readers suggesting "wiper blades" or other types of cleaning solutions for the solar panels. Amazingly, Mars itself has cleaned the rovers' solar panels several times with gusts of wind from the almost ubiquitous Martian dust devils. Acoustic levitation could be a solution, as it would be cheap and easily built. But there is a problem, and it is a big one: it will only work when it is sealed inside a space station or other habitation. It will not work where there is no atmosphere (such as the moon) or where the atmosphere is low pressure and thin (such as Mars) because sound is a pressure wave that travels through the air. So, we might be stuck with having to resort to wiper blades, or devising a way to mimic the dust devils and gusts of wind that have repeatedly benefited the Mars rovers. Unless we can figure out a way to get dust to levitate without sound. Nirvana anyone? Source: PhysOrg