A section of Vesta’s southern hemisphere imaged by NASA’s Dawn spacecraft from low orbit in 2011-12. Click for large version with a resolution of 75 feet per pixel. All photos credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Before voice navigation and cellphones we all kept our car glovebox stuffed with maps of favorite states traveled. Some of us still do. When you needed directions to a city, you unfolded the map or atlas on your lap and followed the vein-like red and blue lines to the your destination.
Vesta’s equatorial regions are scarred by a series of deep, parallel grooves or geologic faults, likely created when a smaller asteroid blasted out the huge Rheasilvia basin at the asteroid’s south pole. One of the bigger ones is named Divalia Fossa. Click to enlarge.
Now there’s an out-of-this-world virtual atlas that let’s you do the same. If you’re ever in a mood to drive around the asteroid Vesta, you can have at it. NASA has released 29 maps created from 10,000 images shot by Dawn spacecraft’s framing camera from 130 miles (210 kilometers) high. The maps are at a level similar to the state maps you’d pick up at a roadside rest; one inch covers a little more than 3 miles of asteroid (1cm = 2km).
Antonia Crater in Vesta’s southern hemisphere is about 9 miles (15 km) across and appears partly filled with debris possibly deposited by another impact. This picture is a tight crop from one of the 29 maps. Click to enlarge.
The level of detail is astonishing. Just click on one of the photos, allow a couple minutes to download and then go for a ride with your mouse. Each of the maps was pieced together as a mosaic using 400 images. Three different projections were applied depending on latitude: Mercator for equatorial regions, Lambert conical projections for mid-latitudes and a stereographic projection for the Rheasilvia Basin at Vesta’s south pole.
Vesta was the fourth asteroid discovered. It’s 326 miles (525 km) across, large and bright enough to occasionally be visible with the naked eye. Credit: NASA
Because Vesta’s north pole was still in mid-winter darkness during part of the mapping, a small patch there escaped coverage. Otherwise the map is complete.
Vesta, first seen by German astronomer Heinrich Olbers in 1807, was only the 4th object to be discovered in the asteroid belt between Mars and Jupiter, hence its formal designation of 4 Vesta. It was named after the goddess of the hearth, home and family in ancient Rome. All the names of geological features on Vesta relate to Roman Vestals (priestesses of Vesta), famous Roman women and cities in which the cult of Vesta is known or festivals in which the Vestals participated.
Vast aprons of rock and soil fallen from the walls of Matronalia Cliff on Vesta are highlighted in this image. Click for large version.
To see all the maps as well as a helpful series of pdf files identifying features and locations, click HERE. I’ve been enjoying my ramble across Vesta and hope you’ll do the same. The only thing missing are the roads.
Comet C/2012K5 passes near the bright star cluster M36 in the constellation Auriga the Charioteer last night. The comet is fading now but still visible in binoculars from a dark sky. Details: 200mm lens at f/2.8, ISO 800 and 2-minute exp. Photo: Bob King
Last night I attached my camera to a battery-operated mount designed to track the stars. What a comedy. Polar alignment kept slipping, the camera-lens weight was too much for the mount and focusing the telephoto lens proved tedious. All I wanted was a single picture of comet C/2012 K5. In the end, I got a lot of exercise hopping back and forth making adjustments … and a somewhat serviceable image.
Up around 6 a.m. this weekend? Look south and you’ll see the last quarter moon pass the bright star Spica in Virgo Saturday and then Saturn on Sunday. Created with Stellarium
The comet had faded a bit but was still a fuzzy blotch in binoculars and showed an obvious northeastward-pointing tail at low magnification through the telescope. Although the tail color was too subtle to be seen with the eye, a time exposure reveals the yellow tint caused by sunlight reflecting off dust particles. Heat from the sun vaporizes comet ice, releasing embedded rocks and dust into the tail behind the comet’s head.
Scene from Yellowknife Bay on Mars photographed today Jan. 4, 2013. Credit: NASA/JPL-Caltech with color added by Bob King
Not much news has been reported from the Curiosity rover of late. NASA mission specialists are probably happy they can work in peace out of the media spotlight. Pictures keep pouring in just the same. You can view the most recent set of raw images HERE.
The rover’s been exploring a shallow basin called Yellowknife Bay. It’s one bleak-looking landscape that begs for the introduction of a few saguaro cacti. After finishing up exploration of the bay, scientist plans to spend most of 2013 piloting the rover toward the mission’s primary science destination – the 3-mile-high layered mound at center of Gale Crater center named Mt. Sharp. There the robot will study and sample water-rich clays deposited long ago when Mars was a wetter world.
Most of the dark, carbonaceous material on Vesta can be found on the rims of smaller craters (left) or scattered in their surroundings (right). Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
A recent paper published in the November-December issue of the journal Icarus describes the dark splotches of carbon-containing materials exposed along the rims of small craters as well as along the edges of the huge impact craters Rheasilvia and Venenaeia on the asteroid Vesta.
NASA’s Dawn mission to Vesta last year took thousands of photos, some of which show dark patches of carbonaceous (car-bon-NAY-shuss) material that matches the dark, carbon-rich mineral fragments found in Vesta meteorites here on Earth.
Dark materials streak Vesta’s Cornelia crater in this three-dimensional image from Dawn. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
“The dark material was most probably delivered during the formation of the older Veneneia basin (large impact crater in Vesta’s southern hemisphere) when a slow impacting asteroid collided with Vesta. Dark material from this two to three billion year old basin was covered up by the impact that Dark material from this two to three billion year old basin was covered up by the impact that subsequently created the Rheasilvia basin,” according to Lucille Le Corre and Vishnu Reddy, lead authors of the study.
In this slice of a Howardite meteorite found in the Sahara Desert, some of the small, dark chips are carbon-rich rocks from an asteroid that collided with Vesta long ago. Howardites and eucrites were blasted from the crust of Vesta by later impacts and arrived on Earth as meteorites. Photo: Bob King
The scientists measured the light from the dark patches on Vesta and discovered they were made of the same material as the dark carbon-rich fragments inside a group of fallen space rocks called eucrites and Howardites.
Asteroids, many of which orbit in the main belt between Mars and Jupiter, come in all flavors. Some are made of bone-dry, rocky materials, others contain clays and water and still others are nearly pure metal. Bashing and smashing into one another they left their marks not only on each other but in the pieces that came (and still come) to Earth.
Circumscribed halo around last night’s half moon. Photo: Bob King
Today the Mayan calendar rolls over to a new Baktun or 144,000 day cycle as it has for centuries. Coincidentally, it’s also the first day of winter in the northern hemisphere and summer for folks down under. Winter tiptoed in at 5:12 a.m. (CST) this morning while many of us were snug in our beds. Looking out my window, the world looks much the same as it did yesterday – with a difference. It’s sunny!
Come join Duluth’s celebration of the solstice at the University of Minnesota-Duluth’s planetarium.
That means a clear sky tonight and a chance to celebrate the new season. If you live in the Duluth, Minn. region, the Marshall Alworth Planetarium will feature a special “End of the World – Winter Solstice” party with shows on the half-hour in the dome, telescope viewing, pizza, cider, a raffle and a free 2013 calendar. Cost is $8 per person or $15 per family. The event starts at 6 p.m. and runs until 9. More information HERE.
Only 8 hours and 32 minutes separate sunrise and sunset in Duluth, Minn. today. The rest belongs to the night. Solstice is combination of two Latin words – sol for sun and sistere to stand still. That’s what it feels like for a week or two at the time of the summer and winter solstices, when the sun reaches its highest and lowest points in the sky.
The seasons are caused by the 23.5 degree tilt of our axis. In summer, Earth’s north polar axis is tipped toward the sun, causing it to appear higher in the sky and making for longer days. Half an orbit later in winter, the north polar axis is tilted away from the sun, making for a low sun and short days. In spring and fall, the axis is tilted neither toward nor away and day and night are equal. Credit: Tau’olunga with additions by Bob King
On Dec. 21 the sun reaches its lowest altitude above the southern horizon at noon for the year. Here in Duluth, that’s about 20 degrees or two fists held at arm’s length. For Chicagoans, it’s 25 degrees, a bit higher. But if you live in Anchorage, the yellow orb of day climbs to just under 6 degrees before slinking back toward the west. My dear brother Mike who lives there must wait until 10:14 a.m. for the sun to rise today. With sunset at 3:42 p.m., he’ll need to be vigilant to catch sight of it. Buildings and trees could easily block the sun from view. .
Excellent, short video on how the seasons happen
These extremes of daylight and night are brought on by Earth’s tipped axis. If it ran straight up and down, much as Jupiter’s axis does, sunrise and sunset times would barely vary for your location. The sun would rise in the east and set in the west 12 hours later every day of the year. No variation and no seasons. Who wants that?
Thanks to the Earth’s tipped axis we experience the joys winter and the ice it brings. These are air bubbles trapped in pond ice near my home yesterday. Photo: Bob King
The tip ensures that the northern hemisphere of the planet tilts toward the sun in the summer and away in the winter. As a consequence, the sun appears very high in the sky in summer. Its longer, steeper path naturally means longer days and more intense heat. In the winter, we’re tipped away from the sun. Slanted, less intense solar rays and short days follow.
Vesta shown at 9:30 p.m. (CST) every 5 days now through Jan. 10, 2013 as it glides near the Hyades cluster. 97 Tauri is mag. 5. Stars shown to 7.5 magnitude. Created with Chris Marriott’s SkyMap software
If you’re looking for an interesting astronomical treat in the night sky this solstice, face east anytime during the evening hours and find the brightest “star” you can see. That’s the planet Jupiter. Just below Jupiter is the bright star Aldebaran and a V-shaped pattern of stars called the Hyades star cluster. Not far from the cluster is the famous asteroid Vesta. You’ll recall it was was orbited and studied by NASA’s Dawn spacecraft this past year.
Vesta shines at magnitude 6.5 (just under the naked eye limit), as bright as it gets this year. The star-like asteroid is super easy to see right now in binoculars, especially with Jupiter to help point you there. Take a look the next clear night.
Both the asteroid Vesta (left) and dwarf planet / asteroid Ceres are easily visible in binoculars this month and next as they travel through the early winter constellations Taurus and Gemini. Ceres is 590 miles in diameter; Vesta 326 miles. Credit: NASA, ESA
Would you like to pretend you’re riding piggyback on NASA’s Dawn mission hopping from the asteroid Vesta to its next target Ceres? All you need is a pair of 7×35 binoculars, a reasonably dark sky and a bit of imagination. November may not be the most pleasant month for skywatching in the northern hemisphere, but Ceres and Vesta, two of the brightest, biggest asteroids, are making their closest approach to the Earth in 2012 at nearly the same time. Surely this fortunate coincidence will inspire you to bundle up and brave the chill.
Vesta comes to opposition (closest to Earth) on December 9 when it will shine just below the naked eye limit at magnitude 6.4; Ceres reaches opposition only nine days later at magnitude 6.7. While the two almost-planets will be brightest then, they’re already nearly as bright and an easy catch now that the moon has retired from the evening sky.
Ceres is close to Eta Geminorum the next few nights. Later it passes under the open cluster M35. Positions are shown for 11 p.m. (CST) every five days. Stars are plotted to magnitude 9. North is up and west to the right. Maps created with Chris Marriott’s SkyMap software
Ceres is especially easy to spot over the next few nights since it keeps close company with the naked eye star Eta Geminorum in the toes of Gemini the Twins. Watch for it to buzz just south of M35 – one of the prettiest star clusters in the sky for both telescopes and binoculars – around Thanksgiving time. Consider their juxtaposition another reason to be thankful.
Ceres begins November at magnitude 8.0 but brightens to 7.3 by month’s end. Vesta meanwhile sidles up the south side of Taurus the Bull, home to the V-shaped Hyades star cluster and brilliant Jupiter. At magnitude 7.2 this week, you’ll find it a tad brighter and easier to see than Ceres. On the map, notice that Vesta glides through the northern edge of the bright, loose star cluster Collinder 65. Another bonus.
Vesta spends the next week crossing through the edge of the open cluster Collinder 65 as it works it way in Jupiter’s direction in the constellation Taurus. Stars plotted to magnitude 8. West is up and north to the left.
Both asteroids are presently traveling west – opposite their normal orbital motion – in what astronomers call a retrograde loop. The outer planets perform the same crazy backwards move around the time of their oppositions, too. Ceres and Vesta aren’t defying orbital mechanics. They only appear to move backwards because the faster Earth is passing them by, much like a car in the right lane appears to move backward as you pass it on the left. Soon enough, they’ll resume their routine eastern motion through the constellations as the viewing geometries of Earth and asteroids change.
A wide view of the sky facing east around 11 p.m. (CST) will help you get oriented when you look for the asteroids. The boxes show the general area covered in the more detailed charts above. Created with Stellarium
Dawn spent about a year in orbit around Vesta and finally departed late this summer with its sights set on a February 2015 encounter with Ceres. We learned lots at Vesta including that it differentiated into core and crust much like planets do. Rocks in its crust studied from orbit are a match for a suite of meteorites found on Earth called eucrites, diogenites and Howardites. No need for a sample return mission – pieces of Vesta have been falling from the sky for centuries.
Ceres is the largest asteroid – a dwarf planet actually – and another place altogether. By examining sunlight reflected from its surface, Ceres appears more carbon and water-rich than Vesta and a closer match to carbonaceous chondrite meteorites.
You can share in these discoveries and the road ahead by stepping outside the next clear night with binoculars and chart in hand. There’s nothing like seeing the real thing.
Let me know how you like the maps. I reversed the stars, going with black-on-white for greater clarity. Hopefully, they’re easier to read. To use a map, right-click and save to your desktop and then print out a copy. I’ll update them later this month, so you can continue to “mission along”.
A huge glacial erratic versus a small human on the Superior Hiking Trail this week. Photo: Bob King
Wait a minute. What is this thing? Asteroid, alien spacecraft, rock of doom? No, it’s only a 20-foot-high glacial erratic astride the Superior Hiking Trail 5 miles east of Finland, Minn. The guidebook indicated its location but I wasn’t prepared for the sight of this behemoth. Erratics are boulders plucked by glaciers and deposited miles from their source. This one , composed of the mineral anorthosite, appeared to have been dropped in the middle of nowhere, hence it’s otherworldly appearance.
A very tight closeup of lichens (center) and crystal structure (right) on a small patch of the erratic. Photo: Bob King
When seen up close up, the bland, gray exterior of the rock proved to be composed of coarse crystals. Tiny patches of tough lichens hid parts of the weathered surface.
The boulder probably parted company with the glacier 10,000 years ago. Anything around that long in one place becomes a time machine into the past. Through its dark crystal panes, we glimpse a long-gone world of mile-thick ice and numbing cold. Given enough time, life’s tiny fungal tentacles, working in tandem with nature’s freeze-thaw cycle, will reduce this titan to shards and finally soil.
The Dawn spacecraft used its gamma ray and neutron detectors to discover hydrogen hot spots on the asteroid Vesta this past year. Red indicates the greatest amount of hydrogen; gray the lowest. Credit: NASA/JPL-Caltech
Another big rock – this one in the asteroid belt – shares an even more ancient past than my erratic. Rather than rocks dropped by ice, Dawn was hit with hunks of water-rich asteroids from the asteroid belt called carbonaceous chondrites. The probe found Vesta’s equatorial zone laced with hydrogen from water chemically bound to the rocks as -OH, also called hydroxyl. Free water’s formula is OHH, described more simply as H2O.
“The source of the hydrogen within Vesta’s surface appears to be hydrated minerals delivered by carbon-rich space rocks that collided with Vesta at speeds slow enough to preserve their volatile content,” said Thomas Prettyman, the lead scientist for Dawn’s gamma ray and neutron detector (GRaND) at the Planetary Science Institute in Tucson, Ariz.
Hundreds of small pits inside Vesta’s crater Marcia may have formed when late bombardment heated earlier materials deposited by water-rich asteroids. Heated by impact, water bound in rocks escaped to create the pits. Credit: NASA/JPL-Caltech/University of Arizona/MPS/DLR/IDA/JHUAPL
If any ice itself were to survive, you’d think Vesta’s polar regions would be the best places for preservation just as on the moon. The moon’s rugged terrain and an axis tipped just 1.5 degrees to the plane of Earth’s orbit create permanently shadowed havens for ice in craters at its north and south poles. Unlike the moon, Vesta’s axis has a considerable 29-degree tilt. As it rotates and orbits the sun, both north and south polar regions are repeatedly exposed to sunlight just as they are on Earth. If ice once languished there, it’s long gone.
The Sutter’s Mill carbonaceous chondrite, which fell on April 22, 2012 in California, is dark colored like most of its class. Photo: Bob King
In fact, most of the hydrogen was found in darker-colored rocks encircling the equator. Since carbonaceous chondrites are themselves dark and water-rich compared to other meteorites, they’re a good match for what Dawn found on Vesta.
More evidence for ancient water comes from strange clusters of pits measuring about 100-800 feet across discovered in the 40-mile diameter crater Marcia. They resemble similar features on Mars that likely formed when water within the rocks vaporized explosively during an impact leaving behind pothole-shaped depressions.
Similar pits on Mars from water boiling from the surface by the heat of impact. Credit: NASA/JPL-Caltech
It’s thought that a second round of high-speed impacts accomplished the same on Vesta. Marcia’s center is pocked with pits and has very low levels of hydrogen, consistent with water boiling off into space when the crater was formed.
Water. It’s always at the center of the story when it comes to space exploration. Earth’s water is believed to have arrived the same way as Vesta’s through comet and “wet” asteroid bombardment. Much later, water would build the glacier that plucked the boulder that now reposes alongside a woodland trail. You never know what adventures may lie ahead when you go with the flow.
NASA’s Dawn spacecraft, which has been in orbit around the asteroid Vesta since mid-July 2011, left Vesta this week to fly to its next target, the dwarf planet Ceres. Photo: Bob King / Vesta image: NASA
NASA’s Dawn spacecraft departed the asteroid Vesta early yesterday morning en route to a rendezvous with the carbon-rich dwarf planet Ceres in early 2015. The probe quietly entered into orbit around Vesta last July and began mapping its surface in great detail. Before the mission, the best photos we had resolved only the largest feature on the little world, the 310-mile-wide impact crater named Rheasilvia Basin. Now we have 31,000 photos of cliffs, basins and the tiniest of craters just meters across. Other instruments measured the elements in the rocks below, the composition of minerals in the crust and looked for signs of water. Scientists used Dawn’s radio antenna in combination with antennas on Earth to probe the protoplanet’s interior.
Artist’s view of Vesta showing its 136-mile-wide iron core in brown, the mantle in green and crust in gray. Vesta is “differentiated” or layered in composition just like the inner planets. Credit: NASA/JPL-Caltech
As the craft slowly spiraled away from Vesta, it took a final set of pictures showing its north polar region, which has been in shadow until recently. So what did we learn during our sojourn around this distant world?
* That Vesta is very much like a planet with a crust, mantle and iron core. Scientists estimate Vesta’s core at 136 miles in diameter. Vesta melted billions of years ago just like the Earth, Mars and other rocky planets. Iron trickled down to make the core while the lighter elements floated to the top to form a crust.
Vesta’s two biggest hits – the Rheasilvia and Veneneia impact basins. The map is color-coded by elevation with red highest and blue lowest. Rheasilvia is about a billion years old; Veneneia happened 2 billion years ago. Credit: NASA
* Dawn revealed Vesta’s giant Rheasilvia impact basin at its south pole in detail, showing that the asteroid impact that created it was powerful enough to launch chunks of Vesta’s crust into space. Scientists called the debris “vestoids”.
Some of the material was nudged by Jupiter’s powerful gravity into orbits that eventually sent pieces to Earth as meteorites millions of years later.
* The clan of meteorites from Vesta are called HED (Howardite-eucrite-diogenite) meteorites and have the same composition as the asteroid’s surface, confirming that they originated there. Vesta joins Mars and the moon as the only other solar system body we know we have samples or right here on Earth. (Bits of Vesta are available through a variety of meteorite dealers’ websites. E-mail me for recommendations if interested.)
Three slices of meteorites that fell to Earth that Dawn has confirmed as originating from the giant asteroid Vesta. The meteorites, known as howardite, eucrite and diogenite meteorites, are seen through a polarizing microscope, where different minerals appear in different colors. Credit: University of Tennessee
* Devoid of smooth plains and lava flows, Vesta shows no signs of the volcanic activity that must have been present in its early history when the asteroid was still molten. Scientists suspect activity must have shut down early in its history – perhaps within the first 100 million years. Since then, meteorites have pulverized the surface and obliterated any evidence. Craters pock the crust everywhere you look.
* The blows that created the two largest impact scars, Rheasilvia and the newly discovered Veneneia Basin (250 miles across), reverberated through the asteroid to create a sprawling network of nearly parallel troughs hundreds of miles long stripping Vesta’s equator. Any more force and the asteroid would have been blown apart.
* Vesta has the tallest mountain discovered to date in the solar system – a 14-mile-high peak formed by rebound after the impact that blasted out the giant Rheasilvia basin. That’s more than twice the height of Mt. Everest.
Craters, craters, everywhere, including a dark splat that may have been from a carbon-rich meteorite strike. Either that or the impact excavated darker material from beneath the surface. Credit: NASA/ JPL-Caltech
Both Vesta and Ceres are currently visible in the constellation Taurus in the pre-dawn sky. Later this fall, when they’ll both be bright enough to be easily viewable in binoculars at a more convenient hour, I’ll prepare maps for you to find them. In the meantime, you can browse a gallery of Vesta photos and learn a lot about this almost-planet by reading the accompanying captions.
Huge parallel troughs, probably related to the stress of the huge impact that created the south polar crater Rheasilvia, stripe the 326-mile-diameter asteroid’s equator. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
On July 25 at 11:45 a.m. (CDT) the Dawn spacecraft, which has been orbiting the asteroid Vesta since July 16, 2011, powered up its xenon ion engine and began raising its altitude in preparation for departure. Dawn’s exit is a drawn-out affair – not until August 26 will the probe slip free of Vesta’s gravity and once again orbit the sun. Its next and final target is the asteroid Ceres, which along with Pluto and a couple other asteroids, is now classified as a dwarf planet.
Artist’s view of Dawn in orbit around Vesta. Credit: NASA/JPL-CalTech
The mission’s not over yet. Thrusting will be stopped four times during the month-long ascent to allow Dawn to photograph regions of the asteroid’s northern hemisphere that have been in seasonal shadow for most of the mission.
I can’t wait for Wednesday August 22. On that day mission controllers will halt the craft to look back and photograph Vesta as a thin crescent “moon”, a perspective never before seen. The purpose of the photos will be to measure the reflective properties of Vestan dust, but we’ll all appreciate the aesthetic bonus.
The south polar mountain inside the gigantic impact crater Rheasilvia rises 13 miles above the surrounding terrain. That’s almost three times higher than Mt. Everest. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
The scientific bonus from the mission has been immense – over 4,700 photos, 9 million spectra of the surface to help scientists unravel the composition of the asteroid’s minerals, measurements of Vesta’s gravity field to determine how matter is distributed in the planetoid’s interior and identifying many individual atomic elements in the uppermost yard of soil with a gamma ray and neutron detector.
Circling the asteroid at an altitude of only 420 miles (about twice the height the space station flies over Earth) every 4 hours, 21 minutes, Dawn snapped photos of Vesta’s sunlight hemisphere and then beamed the images back to Earth during its night side flight. Over a year’s time, the probe completely mapped the surface six times. Four of the maps were made with the camera pointed at an angle instead of straight down; scientists combined the two views to create a boatload of 3-D images.
The crust of Vesta is pocked with all variety of craters that have excavated both light and dark materials from beneath the surface. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
The biggest thrill has been seeing what was a pinpoint of light in most telescopes evolve into a misshapen sphere with craters, tall mountains, and a strange series of parallel troughs ringing the equator. Scientists believe the grooves were created by an impact that left a 314-mile diameter crater in the asteroid’s southern hemisphere called Rheasilvia.
This Howardite meteorite called NWA 3149 was found in the Sahara Desert. It almost certainly came from Vesta. Notice all the fragments. These were broken during earlier impacts on the asteroid and welded together under heat and pressure. Photo: Bob King
Material blown into space from the blast has even managed to make its way to Earth as HED meteorites. Known as Howardites, eucrites and diogenites, they’re made of the same materials Dawn found on the surface and within the crust of Vesta.
On September 1 Dawn will cast one last glance at Vesta from a vantage point 24,000 miles away before setting its sights on Ceres. We learned patience on the journey to Vesta, and we’ll need it again as we wait for the hardy craft to arrive at Ceres in February 2015.
The title of this blog refers not only to Dawn’s departure from Vesta but also to a live Twitter and Facebook event on September 8 to celebrate the mission. Click HERE for more information on how you can participate.
We first meet young Luke Skywalker, hero of the Star Wars movies, on the desert planet Tatooine on the fringe of the Galactic Republic. Luke worked on his Uncle Owen’s “moisture farm” but like any future Jedi knight, he knew he was destined for greater things. At the end of the first scene, Skywalker gazes skyward toward that planet’s two suns, pulled toward a fate he could only guess.
The fictional world Tatooine, Luke Skywalker’s home world in the Star Wars movie series. Credit: Star Wars/George Lucas
As far as planets go, Tatooine will always be one of my favorites. The exotic dual sunsets, wild expanses of desert and cool architecture of the future left a wonderful impression when I first saw Star Wars back in 1977.
American film producer George Lucas filmed scenes for his fictional planet at various locations across the real deserts of Tunisia. As for the name Tatooine, it was adapted from the Tunisian city Tatahouine, an oasis town in southern part of that country.
Roadside sign in the town of Tatahouine. There are several spellings for the name in common use. Credit: Alain Bachellier
In the film, it’s pronounced “tatoo-een” but the locals call it “tat-ween”. Although Lucas didn’t film any scenes in the city, the landscape there and across the deserts of Tunisia were the inspiration for Luke’s homeland.
A typical fragment of the Tatahouine meteorite – this one weighs 1.2 grams. Notice the green color and black shock veins. Penny shown for scale. Photo: Bob King
Tatooine/Tatahouine boasts yet another outer space connection. 81 years ago to the day on June 27, 1931 at 1:30 a.m. local time, a fireball exploded above the Tunisian desert 2.5 miles northeast of Tatahouine. Soon after the fall, local Bedouins collected hundreds of small meteorite fragments that peppered a hillside.
Vesta’s south pole is face on in this picture taken by Dawn. The dark area at center is a tall mountain peak. Scientists suspect the weird appearance of the polar region is due to an impact with another asteroid. Credit: NASA/JPL-Caltech
What they plucked from the dust was a rare, green-colored meteorite found deep within an asteroid’s crust called a diogenite. Many years later, scientists identified the Tatahouine meteorite’s true home – the asteroid Vesta – by analyzing light reflected from the meteorite and the asteroid. They were a close match.
More recently, the Dawn space probe, which has been keeping an orbital eye on Vesta for months, confirmed that Tatahouine and other diogenite meteorites originated on this little world. A likely scenario for Tatahouine’s delivery to Earth involved a massive impact on the asteroid. Chunks of crustal material were sent flying into space where they drifted for some 38 million years before finding their way to our planet on a tepid June morning in 1931.
Known informally as Tatooine, Kepler 16b orbits a pair of stars in the Milky Way. Credit: NASA
Evidence for the power of the impact can be seen in the web of black shock veins of melted rock created instantaneously upon impact. The large orthopyroxene crystals give Tatahouine a unique green color found in few meteorites.
Since the meteorite shattered into thousands of small pieces, tourists to the area can still find fragments to this day. Tatahouine fragments look “naked” or without the typical black fusion crust coating many other meteorites. It blew to bits at a very low altitude, too late and moving too slowly for air friction to melt the exterior of each small piece.
In 2011 NASA announced it had found the first planet in orbit about a double sun like the fictional Tatooine. Named Kepler 16b, the Saturn-mass planet orbits orange and red stars with a period 229 days. With temperatures ranging from 100 to 150 below F, this gas giant Tatooine sadly couldn’t host Jabba the Hut and the delightful cantina pictured in Star Wars.
Watch the local planets tonight in the southwestern sky at nightfall. Mars and Beta Virginis, also known as Zavijava, will be a tight pair. Created with Stellarium
Before we depart planets alien and otherwise, take a look tonight in the moon’s direction. To its left you’ll see the ever-present pair of Saturn and Spica. Right of the moon is Mars, which will be very close to the 3rd magnitude star Zavijava in the constellation Virgo tonight. Can you split the two apart with you eye? If not, enjoy this temporary “double star” in binoculars.
Jupiter approaches conjunction with the sun in this photo taken by the SOHO's C2 coronagraph this morning. A coronagraph uses a disk to block direct sunlight. Credit: NASA/ESA
Back in the day before orbiting telescopes and 24/7 sky surveillance, when a planet got too near the sun, it was invisible in the solar glare. Not anymore. Thanks to the two coronagraphs aboard the Solar and Heliospheric Observatory (SOHO), we can follow planets right through conjunction with the sun.
SOHO is located at a stable point some 930,000 miles sunward of Earth. With no atmosphere to contend with, SOHO studies the sun from the spotless window of outer space.
Jupiter reaches solar conjunction tomorrow when it will be closest to the sun. You can see from the photo that today it’s already very close – less than one degree away or one “pinkie” finger held at arm’s length against the sky. Notice that Jupiter is a little below or south of the sun. Tomorrow it will be even closer but still travel south and miss the solar disk. Rarely do planets line up exactly with the sun during conjunction. That’s why next month’s transit of Venus is so special.
Keep in mind as you look at the picture that Jupiter lies in the distant background on the opposite side of the sun from Earth. It’s currently 558 million miles away or six times the Earth-sun distance. As you might guess, if Jupiter precisely lined up, it would be hidden behind the sun. As for that big sunspot group, it’s still lively but no X-class flares yet.
Virtual flyover of the asteroid Vesta based on hundreds of actual photographs. Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
After almost a year’s study by the orbiting Dawn space probe, NASA shared new insights about the asteroid Vesta this week. We now know that the 326-mile-diameter orb was on its way to becoming a planet 4.6 billion years ago. It developed an iron core measuring 136 miles across, a dense, rocky mantle and crust made of lava flows that were soon battered by meteorite impacts.
Bright and dark craters on Vesta. Like everything else in the solar system, the asteroid was bombarded heavily by meteorites at the dawn of the solar system. Credit: NASA/JPL-Caltech
Terrestrial planets also possess these three basic layers. With Vesta, the decay of a radioactive form of aluminum around in the early solar system generated the heat that melted the asteroid. As it cooled, heavier elements like iron and nickel sunk to form a core, while lighter elements floated to the top and solidified into the mantle and crust.
The layering, known as differentiation, make Vesta more like a small planet or Earth’s moon than most asteroids. Smaller bodies never had enough radioactive material to melt and layer-cake.
The Rheasilvia Basin dominates Vesta's southern hemisphere. The crater is 90 percent as wide as the entire asteroid. Fragments from the collision have reached Earth over the ages as HED meteorites. Credit: NASA/JPL-Caltech
By counting craters, scientists determined the age of Vesta’s biggest crater, the 314-mile-wide Rheasilvia Basin in the southern hemisphere. The impact, which removed a sizable portion of the asteroid’s southern polar region, happened only about a billion years ago, long after Vesta formed and when most meteorite bombardment had ceased
Scientists were also able to determine what minerals are in Vesta’s crust by examining how they reflect sunlight. Here’s where things really get exciting. They discovered that the meteorites in the HED clan – howardites, eucrites and diogenties – are the same materials seen in Vesta’s crust. We’ve suspected this for years because the two reflect light in almost the same way, but this is the first time we’ve visited a source of meteorites found on Earth.
A slice of Vesta! This eucrite meteorite named NWA 2724 was found in the Sahara Desert . It represents a small cross section of an ancient lava flow on the asteroid. Photo: Bob King
Eucrites are similar to lava flows on Earth; diogenites are coarse-grained crystalline rocks from the mantle and howardites are a mix of the two, created when meteorites bash, mix and cement together fragments of both crust and mantle.
It sends a chill up my spine to touch the meteorite in the photo above and know that it came directly from Vesta, launched by an impact perhaps a billion years ago. Too bad Vesta never grew larger than it is today. You can blame Jupiter. Its dominating gravitational influence stirred up material in the asteroid belt, where Vesta resides, and prevented any large body from forming.
Illustration of an asteroid and its tiny moon making a close pass by Earth. Credit: ESA
Here we go again. Heard of the latest asteroid to strike terror across the Web? It’s 2012 DA14, a flying rock almost 150 feet across discovered on February 23 by astronomers at Observatorio Astronomico de La Sagra in Spain. The observatory uses robotic telescopes to find and track near-Earth asteroids. At the time of discovery, DA14 was passing Earth at a fairly typical distance of 1.5 million miles.
After calculating a preliminary orbit for 2012 DA14, astronomers learned that on February 15, 2013, it will zoom by only 17,000 miles from the surface of our planet. While this is very close by solar system standards, it’s a long ways for you and I. If you consider that the diameter of Earth is about 8,000 miles, this small object will miss us by more than twice that. While it will very briefly pass through the geosynchronous satellite belt, the odds of it hitting one are extremely small. The average separation between satellites there is59 miles. A geosynchronous satellite orbits 22, 236 miles above Earth, an altitude where the satellite’s orbital period matches Earth’s rotation. That means they’re essentially stationary in the sky, making them ideal for relaying communications around the globe. But I digress.
Most asteroids reside in the main belt beyond Mars, but there are additional asteroid families - the Apollos and Atens - whose orbits cross that of Earth's and have the potential to impact in the future. Mars orbit crossers are called Amors. Credit: ESA / Medialab
Some websites are saying a strike is imminent or at the very least possible. The fact is, it won’t happen in the foreseeable future. Yes, it’s possible that sometime in the distant future, there might be a closer pass or even a dead-on hit, but that’s not in the cards for now. On the Torino Impact Hazard Scale DA14 rates a “0″, defined as:
The likelihood of a collision is zero, or is so low as to be effectively zero. Also applies to small objects such as meteors and bodies that burn up in the atmosphere as well as infrequent meteorite falls that rarely cause damage.
And on the related Palermo Impact Scale, it comes in at a -4 , meaning there will be no consequences during this flyby. You might recall the hype surrounding the even closer flyby of asteroid 2011 MD last June. That asteroid, which measured between 3o and 150 feet across, came even closer than DA14 will at a distance of only 7,500 miles. We all survived.
2011 MD passed so near Earth last June our planet's gravity significantly changed the tip or inclination of its orbit. We're the gravity hog compared to these small objects. Credit: NASA
Ongoing surveys like the one at La Sagra are underway to find every possible rock big enough to put the hurt on Earth. Most of the asteroids measuring one kilometer or more have been seen and their orbits determined, but there are still plenty of extremely faint and small rocks out there like DA14. Expect many more to be found in the coming years.
Since we’re talking asteroids, let’s head out to the main belt to Vestaand see what the Dawn space probe’s been up to lately.
This 3-D photo shows the central complex in Vesta’s Rheasilvia impact basin. The central complex is approximately 120 miles in diameter and has about 12 miles of relief from its base, making it about two and a half times taller than Mt. Everest. Click to enlarge. Credit: all photos NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA
NASA’s Jet Propulsion Lab has released several excellent 3D images recently that give you that “being there” feeling. To see depth in the photos, you’ll need a pair of those red-blue specs called 3-D anaglyph glasses. Click HERE to order a free pair.
Caparronia crater is the large, roughly 18 mile diameter crater in the top part of the image. The 3D effect highlights the large ridge running across the base of the crater. Also visible is the large, degraded crater offset from the center of the image. Click to enlarge.
In addition to creating detailed photographic maps from its 130-mile-high orbit, Dawn’s been looking for water ice in the asteroid’s polar regions. While none has been discovered yet, the temperature there is colder than -200 F, the cutoff for water to exist in the top 10 feet of Vesta’s rocky soil. The “warmer” equatorial regions hovers around -190 F.
Vesta's equatorial troughs are visible around Vesta’s equator. These troughs encircle most of the asteroid and are up to 12 miles wide. To the north of these troughs are a number of old, highly eroded, large craters.