Posted on by Fraser Cain

Strange Hyperion Looks Like a Sponge

Saturn’s unusual moon, Hyperion. Image credit: NASA/JPL/SSI. Click to enlarge.
Two new Cassini views of Saturn’s tumbling moon Hyperion offer the best looks yet at one of the icy, irregularly-shaped moons that orbit the giant, ringed planet.

The image products released today include a movie sequence and a 3D view, and are available at , and .

The views were acquired between June 9 and June 11, 2005, during Cassini’s first brush with Hyperion.

Hyperion is decidedly non-spherical and its unusual shape is easy to see in the movie, which was acquired over the course of two and a half days. Jagged outlines visible on the moon’s surface are indicators of large impacts that have chipped away at its shape like a sculptor.

Preliminary estimates of its density show that Hyperion is only about 60 percent as dense as solid water ice, indicating that much of its interior (40 percent or more) must be empty space. This makes the moon more like an icy rubble pile than a solid body.

In both the movie and the 3D image, craters are visible on the moon?s surface down to the limit of resolution, about 1 kilometer (0.6 mile) per pixel. The fresh appearance of most of these craters, combined with their high spatial density, makes Hyperion look something like a sponge.

The moon’s spongy-looking exterior is an interesting coincidence, as much of Hyperion?s interior appears to consist of voids. Hyperion is close to the size limit where, like a child compacting a snowball, internal pressure due to the moon?s own gravity will begin to crush weak materials like ice, closing pore spaces and eventually creating a more nearly spherical shape.

The images used to create these views were obtained with Cassini’s narrow-angle camera at distances ranging from approximately 815,000 to 168,000 kilometers (506,000 to 104,000 miles) from Hyperion. Cassini will fly within 510 kilometers (317 miles) of Hyperion on Sept. 26, 2005.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

Original Source: NASA News Release

Posted on by Fraser Cain

Astronomy Hacks Giveaway

The fine folks at O’Reilly Media have agreed to give away a free copy of their book, Astronomy Hacks, to one lucky Universe Today reader – click here to read our review. Just send me an email at [email protected] with the subject line Astronomy Hacks Giveaway by Friday, July 15 at 12:00 pm Pacific Daylight Time. I’ll choose one email from the list at random, and we’ll send you a copy of the book. (Don’t worry, I won’t save the addresses, I’ll delete all your emails right after I do the drawing.)

Good luck!

Fraser Cain
Publisher, Universe Today

Posted on by Fraser Cain

Old NASA Equipment Will Be Visible on the Moon

Apollo 17 rover on the Moon. Image credit: NASA. Click to enlarge.
Inside the lunar lander Challenger, a radio loudspeaker crackled.

Houston: “We’ve got you on television now. We have a good picture.”

Gene Cernan, Apollo 17 commander: “Glad to see old Rover’s still working.”

“Rover,” the moon buggy, sat outside with no one in the driver’s seat, its side-mounted TV camera fixed on Challenger. Back in Houston and around the world, millions watched. The date was Dec. 19, 1972, and history was about to be made.

Suddenly, soundlessly, Challenger split in two (movie). The base of the ship, the part with the landing pads, stayed put. The top, the lunar module with Cernan and Jack Schmitt inside, blasted off in a spray of gold foil. It rose, turned, and headed off to rendezvous with the orbiter America, the craft that would take them home again.

Those were the last men on the Moon. After they were gone, the camera panned back and forth. There was no one there, nothing, only the rover, the lander and some equipment scattered around the dusty floor of the Taurus-Littrow valley. Eventually, Rover’s battery died and the TV transmissions stopped.

That was our last good look at an Apollo landing site.

Many people find this surprising, even disconcerting. Conspiracy theorists have long insisted that NASA never went to the Moon. It was all a hoax, they say, a way to win the Space Race by trickery. The fact that Apollo landing sites have not been photographed in detail since the early 1970s encourages their claims.

And why haven’t we photographed them? There are six landing sites scattered across the Moon. They always face Earth, always in plain view. Surely the Hubble Space Telescope could photograph the rovers and other things astronauts left behind. Right?

Wrong. Not even Hubble can do it. The Moon is 384,400 km away. At that distance, the smallest things Hubble can distinguish are about 60 meters wide. The biggest piece of left-behind Apollo equipment is only 9 meters across and thus smaller than a single pixel in a Hubble image.

Better pictures are coming. In 2008 NASA’s Lunar Reconnaissance Orbiter will carry a powerful modern camera into low orbit over the Moon’s surface. Its primary mission is not to photograph old Apollo landing sites, but it will photograph them, many times, providing the first recognizable images of Apollo relics since 1972.

The spacecraft’s high-resolution camera, called “LROC,” short for Lunar Reconnaissance Orbiter Camera, has a resolution of about half a meter. That means that a half-meter square on the Moon’s surface would fill a single pixel in its digital images.

Apollo moon buggies are about 2 meters wide and 3 meters long. So in the LROC images, those abandoned vehicles will fill about 4 by 6 pixels.

What does a half-meter resolution picture look like? This image of an airport on Earth has the same resolution as an LROC image. Moon buggy-sized objects (automobiles and luggage carts) are clear:

“I would say the rovers will look angular and distinct,” says Mark Robinson, research associate professor at Northwestern University in Evanston, Illinois, and Principal Investigator for LROC. “We might see some shading differences on top from seats, depending on the sun angle. Even the rovers’ tracks might be detectable in some instances.”

Even more recognizable will be the discarded lander platforms. Their main bodies are 4 meters on a side, and so will fill an 8 by 8 pixel square in the LROC images. The four legs jutting out from the platforms’ four corners span a diameter of 9 meters. So, from landing pad to landing pad, the landers will occupy about 18 pixels in LROC images, more than enough to trace their distinctive shapes.

Shadows help, too. Long black shadows cast across gray lunar terrain will reveal the shape of what cast them: the rovers and landers. “During the course of its year-long mission, LROC will image each landing site several times with the sunlight at different angles each time,” says Robinson. Comparing the different shadows produced would allow for a more accurate analysis of the shape of the objects.

Enough nostalgia. LROC’s main mission is about the future. According to NASA’s Vision for Space Exploration, astronauts are returning to the Moon no later than 2020. Lunar Reconnaissance Orbiter is a scout. It will sample the Moon’s radiation environment, search for patches of frozen water, make laser maps of lunar terrain and, using LROC, photograph the Moon’s entire surface. By the time astronauts return, they’ll know the best places to land and much of what awaits them.

Two high-priority targets for LROC are the Moon’s poles.

“We’re particularly interested in the poles as a potential location for a moon base,” Robinson explains. “There are some cratered regions near the poles that are in shadow year-round. These places might be cold enough to harbor permanent deposits of water ice. And nearby are high regions that are sunlit all year. With constant sunlight for warmth and solar power, and a potential source of water nearby, these high regions would make an ideal location for a base.” Data from LROC will help pinpoint the best ridge or plateau for setting up a lunar home.

Once a moonbase is established, what’s the danger of it being hit by a big meteorite? LROC will help answer that question.

“We can compare LROC images of the Apollo landing sites with Apollo-era photos,” says Robinson. The presence or absence of fresh craters will tell researchers something about the frequency of meteor strikes.

LROC will also be hunting for ancient hardened lava tubes. These are cave-like places, hinted at in some Apollo images, where astronauts could take shelter in case of an unexpected solar storm. A global map of these natural storm shelters will help astronauts plan their explorations.

No one knows what else LROC might find. The Moon has never been surveyed in such detail before. Surely new things await; old abandoned spaceships are just the beginning.

Original Source: NASA News Release

Posted on by Fraser Cain

Deep Impact’s Plume Was Bigger Than Expected

The huge plume of material shooting out of Comet Tempel 1. Image credit: NASA/JPL. Click to enlarge.
Data from Deep Impact’s instruments indicate an immense cloud of fine powdery material was released when the probe slammed into the nucleus of comet Tempel 1 at about 10 kilometers per second (6.3 miles per second or 23,000 miles per hour). The cloud indicated the comet is covered in the powdery stuff. The Deep Impact science team continues to wade through gigabytes of data collected during the July 4 encounter with the comet measuring 5-kilometers-wide by 11-kilometers-long (about 3-miles-wide by 7-miles-long).

“The major surprise was the opacity of the plume the impactor created and the light it gave off,” said Deep Impact Principal Investigator Dr. Michael A’Hearn of the University of Maryland, College Park. “That suggests the dust excavated from the comet’s surface was extremely fine, more like talcum powder than beach sand. And the surface is definitely not what most people think of when they think of comets — an ice cube.”

How can a comet hurtling through our solar system be made of a substance with less strength than snow or even talcum powder?

“You have to think of it in the context of its environment,” said Dr. Pete Schultz, Deep Impact scientist from Brown University, Providence, R.I. “This city-sized object is floating around in a vacuum. The only time it gets bothered is when the Sun cooks it a little or someone slams an 820-pound wakeup call at it at 23,000 miles per hour.”

The data review process is not overlooking a single frame of approximately 4,500 images from the spacecraft’s three imaging cameras taken during the encounter.

“We are looking at everything from the last moments of the impactor to the final look-back images taken hours later, and everything in between,” added A’Hearn. “Watching the last moments of the impactor’s life is remarkable. We can pick up such fine surface detail that objects that are only four meters in diameter can be made out. That is nearly a factor of 10 better than any previous comet mission.”

The final moments of the impactor’s life were important, because they set the stage for all subsequent scientific findings. Knowing the location and angle the impactor slammed into the comet’s surface is the best place to start. Engineers have established the impactor took two not unexpected coma particle hits prior to impact. The impacts slewed the spacecraft’s camera for a few moments before the attitude control system could get it back on track. The penetrator hit at an approximately 25 degree oblique angle relative to the comet’s surface. That’s when the fireworks began.

The fireball of vaporized impactor and comet material shot skyward. It expanded rapidly above the impact site at approximately 5 kilometers per second (3.1 miles per second). The crater was just beginning to form. Scientists are still analyzing the data to determine the exact size of the crater. Scientists say the crater was at the large end of original expectations, which was from 50 to 250 meters (165 to 820 feet) wide.

Expectations for Deep Impact’s flyby spacecraft were exceeded during its close brush with the comet. The craft is more than 3.5 million kilometers (2.2 million miles) from Tempel 1 and opening the distance at approximately 37,000 kilometers per hour (23,000 miles per hour). The flyby spacecraft is undergoing a thorough checkout, and all systems appear to be in excellent operating condition.

The Deep Impact mission was implemented to provide a glimpse beneath the surface of a comet, where material from the solar system’s formation remains relatively unchanged. Mission scientists hoped the project would answer basic questions about the formation of the solar system by providing an in-depth picture of the nature and composition of comets.

The University of Maryland is responsible for overall Deep Impact mission science, and project management is handled by JPL. The spacecraft was built for NASA by Ball Aerospace & Technologies Corporation, Boulder, Colo. JPL is a division of the California Institute of Technology, Pasadena, Calif.

Original Source: NASA News Release

Posted on by Fraser Cain

What’s Up This Week – July 11 – July 17, 2005

Star cluster Epsilon Scorpii (M6). Image credit: N.A. Sharp and Mark Hanna, REU Program/NOAO/AURA/NSF. Click to enlarge.
Monday, July 11 – For viewers in west Europe and northwest Africa, you will have the opportunity to watch the Moon occult 4th magnitude Sigma Leonis on this universal date. Please check the IOTA webpage for precise times in your location.

Tonight on the lunar surface, aim your binoculars or telescope towards the south shore of Mare Nectaris where we will examine ruined crater Fracastorius. To lower power, this will be a delicate, almost bay-like feature softly outlined in white. This is all that remains of a once-great crater as the lava flow from the mare filled it in. To its southern edge, the old walls still rise, but much of the north border is completely obliterated. If you examine it telescopically, you will see that the north has been reduced to a low series of ridges and craterlets, yet in binoculars it still gives the illusion of a complete ring.

As the Moon sets and the constellation of Scorpius rises higher, tonight would be an ideal time to look at a brilliant open cluster about a fist width east of Epsilon Scorpii – M6. On a moonless night, the 50 or so members of this 2000 light year distant, 100 million year old cluster can usually be seen unaided as a small fuzzy patch just above the Scorpion’s tail. Tonight we visit because the brighter skies will aid you in seeing the primary stars distinctive asterism. Using binoculars or telescope at lowest power, the outline of stars does truly resemble its namesake – the “Butterfly Cluster”. The M6 is much more than “just a pretty face” and we’ll be back to study under darker skies.

Tuesday, July 12 – Watch the quick progress of Mercury as it cruises beneath Venus over the next two nights starting about 45 minutes after sunset. Venus will be quite low at about half a fist width above the west/northwest horizon, and you will probably need binoculars to spot Mercury another 3 degrees lower. Be sure to note the position of Regulus, a little more than a fist width above and to the left of Venus.

With the anniversary of the Apollo 11 moon landing only eight days away, tonight will be our opportunity to look at the landing site on the lunar surface. To the unaided eye, look almost central on the lunar disc for the grey oval of Mare Tranquillitatus. Near the terminator you will note a brightness where the shore curves around the south edge to join Mare Nectaris. By aiming binoculars at this area, you can distinguish the bright peninsula just north of the three rings of Theophilus, Cyrillus and Catherina. To the telescope at mid-to-high power, note shallow rings of craters Sabine and Ritter to the northwest of this bright area. If you have a steady night on your hands – step up the power to maximum. East of Sabine and Ritter are three tiny craters in the otherwise smooth surface. From west to east they are Aldrin, Collins and Armstrong – the only craters on the Moon named for the living. Just south of Collins is the actual landing site and we salute the crew of Apollo 11 by viewing tonight just shy of 36 years since their adventure.

Wednesday, July 13 – Tonight lucky viewers for almost all of South America will have the chance to witness a spectacular occultation of Jupiter by the Moon. You can find precise times for your location on this IOTA webpage. Even if you do not use a telescope, I strongly urge you to at least watch this event! For viewers in New Zealand, you will have the opportunity to watch the Moon occult Eta Virginis. The precise times for a city near you are listed on this IOTA webpage.

For most of us, Jupiter and the Moon will make a very pleasing pair tonight. but let’s venture to a deep impact crater on the Moon. You will find Manilius telescopically just north of center along the terminator on the eastern shore Mare Vaporum. While it doesn’t appear to be much more than a singular “hole” on the lunar surface, Manilius is incredibly deep. Spanning around 39 km (25 miles), this crater drops down 3010 meters (9500 feet) below the Moon’s topography. That’s about 2/3 the distance that Titanic lay beneath the ocean!

Thursday, July 14 – Forty years ago today, Mariner 4 performed the first flyby of Mars. If you’re up before dawn this morning, be sure to look for the “Red Planet” as it cruises through Pices and heads toward the Sun.

Tonight the star accompanying the Moon on the right is Spica, but let’s explore the lunar surface in hopes of catching an unusual event. On the southern edge of the Mare Nubium is the old walled plain Pitatus. Power up. On the western edge you will see smaller and equally old Hesiodus, sharing a common wall. Almost central along this wall there is a break to watch when the terminator is close. For a brief moment, sunrise on the Moon will pass through this break creating a beam of light across the crater floor known as the Hesiodus Sunrise Ray. If the terminator has moved beyond it at your observing time, look to the south for small Hesiodus A. This is an example of an extremely rare double concentric crater. This formation is caused by an impact being followed by another, slightly smaller impact on exactly the same location.

Friday, July 15 – For our friends in Australia comes one incredible event… Tonight the Moon will occult Comet 9/P Tempel 1. For more information on this event, please visit the IOTA webpages for times and locations. We wish you the very best of skies!

For the rest of us, we’re stuck with the Moon, but this is a great chance to explore under-rated crater Bullialdus. Once again, we’re in the southern quadrant of the Moon near the terminator. Even binoculars can make out this crater with ease near the center of Mare Nubium. If you’re scoping – power up – this one is fun! Very similar to Copernicus, note Bullialdus’ thick, terraced walls and central peak. If you examine the area around it carefully, you can note it is a much newer crater than shallow Lubiniezsky to its north and almost non-existant Kies to the south. On Bullialdus southern flank, it’s easy to make out both its A and B craters, as well as the interesting little Koenig to the southwest.

Saturday, July 16 – Today in 1850 at Harvard University, the first photograph of a star was made (other than the Sun). The honors went to Vega! In 1994, an impact event was about to happen as nearly two dozen fragments of Comet Shoemaker-Levy 9 were speeding their way to the surface of Jupiter. The result was spectacular and the visible features left behind on the planet’s atmosphere were the finest ever recorded. Why not take the time to look a Jupiter again tonight while it still holds good sky position? No matter where you observe from, this constantly changing planet offers a wealth of things to look at – be it the appearance of the “Great Red Spot”, or just the ever changing waltz of the galiean moons.

Tonight no feature on the Moon will be more prominent that the Sinus Iridium, but if you have steady skies, why not power up to look a some of the finer features such as Bianchinni and Sharp on its borders? It the night is exceptionally steady, you may see up to a half dozen very small craters within the “bay” itself. Just outside in Mare Ibrium, even modest power can make out Helicon and Le Verrier. If the Dorsum Heim captures your imagination, look for tiny C. Herschel in its center.

Sunday, July 17 – Today in 1963, the Nuclear Test Ban Treaty is signed. This treaty prohibits the detonation of nuclear devices in our atmosphere. To be sure all countries were in compliance, the United States afterward launched the first gamma ray detectors into orbit. In 1967 these detectors picked up a new discovery – the first of many cosmic gamma ray sources.

Observers located along a path that includes Mexico, Central America, northern South America, and the extreme southern and western U.S. have the opportunity to witness the occultation of Antares tonight, while most of the U.S. will see the Moon graze just south. For times of the event at selected cities, see this page or Dr. David Dunham’s personal webpages which includes graze information. For central South America viewers and lower California, you will also be treated to the occulation of Sigma Scorpii on the universal date. Check IOTA wepages for more details. Clear skies!

If you chose to view the lunar surface, be sure to look for crater Schiller near the terminator on the southern cusp. Its long oval form is a real treat.

Yes, the Moon is back, but I’ll do my best to find more great events to enjoy! May all your journeys be at Light Speed… ~Tammy Plotner

Posted on by Fraser Cain

Japanese Astro-E2 Satellite Launched

Artist illuatration of Astro-E2. Image credit: JAXA. Click to enlarge.
The M-V Launch Vehicle No. 6 (M-V-6) with the 23rd scientific satellite (ASTRO-EII) onboard was launched at 12:30 p.m. on July 10, 2005 (Japan Standard Time, JST) from the Uchinoura Space Center (USC). The launcher was set to a vertical angle of 80.2 degrees, and the flight azimuth was 87.6 degrees.

The launch vehicle flew smoothly, and the third stage motor was ignited at 205 seconds after liftoff. The third stage flight was also smooth, and after its motor burnout, it was confirmed to be safely injected into its scheduled orbit of an apogee altitude of approximately 247 km and a perigee altitude of approximately 560 km with an inclination of approximately 31.4 degrees.

JAXA received signals from the ASTRO-EII at the Santiago tracking station and the USC, and from those signals we verified that the ASTRO-EII had successfully separated.

The in-orbit ASTRO-EII was given the International Designator of 2005-025A and a nickname of “Suzaku.”

The weather at the time of the launch was slightly cloudy with a wind speed of 7m/s from the west-south-west, and the temperature was 31.7 degrees Celsius.

Original Source: JAXA News Release

Posted on by Fraser Cain

How Much Material Was Blasted Off By Deep Impact?

X-ray detections from Tempel 1 after Deep Impact collision. Image credit: Swift. Click to enlarge.
Here come the X-rays, on cue. Scientists studying the Deep Impact collision using NASA’s Swift satellite report that comet Tempel 1 is getting brighter and brighter in X-ray light with each passing day.

The X-rays provide a direct measurement of how much material was kicked up in the impact. This is because the X-rays are created by the newly liberated material lifted into the comet’s thin atmosphere and illuminated by the high-energy solar wind from the Sun. The more material liberated, the more X-rays are produced.

Swift data of the water evaporation on comet Tempel 1 also may provide new insights into how solar wind can strip water from planets such as Mars.

“Prior to its rendezvous with the Deep Impact probe, the comet was a rather dim X-ray source,” said Dr. Paul O’Brien of the Swift team at the University of Leicester. “How things change when you ram a comet with a copper probe traveling over 20,000 miles per hour. Most of the X-ray light we detect now is generated by debris created by the collision. We can get a solid measurement of the amount of material released.”

“It takes several days after an impact for surface and sub-surface material to reach the comet’s upper atmosphere, or coma,” said Dr. Dick Willingale, also of the University of Leicester. “We expect the X-ray production to peak this weekend. Then we will be able to assess how much comet material was released from the impact.”

Based on preliminary X-ray analysis, O’Brien estimates that several tens of thousands of tons of material were released, enough to bury Penn State’s football field under 30 feet of comet dust. Observations and analysis are ongoing at the Swift Mission Operations Center at Penn State University as well as in Italy and the United Kingdom.

Swift is providing the only simultaneous multi-wavelength observation of this rare event, with a suite of instruments capable of detecting visible light, ultraviolet light, X-rays, and gamma rays. Different wavelengths reveal different secrets about the comet.

The Swift team hopes to compare the satellite’s ultraviolet data, collected hours after the collision, with the X-ray data. The ultraviolet light was created by material entering into the lower region of the comet’s atmosphere; the X-rays come from the upper regions. Swift is a nearly ideal observatory for making these comet studies, as it combines both a rapidly responsive scheduling system with both X-ray and optical/UV instruments in the same satellite.

“For the first time, we can see how material liberated from a comet’s surface migrates to the upper reaches of its atmosphere,” said Prof. John Nousek, Director of Mission Operations at Penn State. “This will provide fascinating information about a comet’s atmosphere and how it interacts with the solar wind. This is all virgin territory.”

Nousek said Deep Impact’s collision with comet Tempel 1 is like a controlled laboratory experiment of the type of slow evaporation process from solar wind that took place on Mars. The Earth has a magnetic field that shields us from solar wind, a particle wind composed mostly of protons and electrons moving at nearly light speed. Mars lost its magnetic field billions of years ago, and the solar wind stripped the planet of water.

Comets, like Mars and Venus, have no magnetic fields. Comets become visible largely because ice is evaporated from their surface with each close passage around the Sun. Water is dissociated into its component atoms by the bright sunlight and swept away by the fast-moving and energetic solar wind. Scientists hope to learn about this evaporation process on Tempel 1 now occurring quickly — over the course of a few weeks instead of a billion years — as the result of a planned, human intervention.

Swift’s “day job” is detecting distant, natural explosions called gamma-ray bursts and creating a map of X-ray sources in the universe. Swift’s extraordinary speed and agility enable scientists to follow Tempel 1 day by day to see the full effect from the Deep Impact collision.

The Deep Impact mission is managed by NASA’s Jet Propulsion Laboratory, Pasadena, California. Swift is a medium-class NASA explorer mission in partnership with the Italian Space Agency and the Particle Physics and Astronomy Research Council in the United Kingdom, and is managed by NASA Goddard. Penn State controls science and flight operations from the Mission Operations Center in University Park, Pennsylvania. The spacecraft was built in collaboration with national laboratories, universities and international partners, including Penn State University; Los Alamos National Laboratory, New Mexico; Sonoma State University, Rohnert Park, Calif.; Mullard Space Science Laboratory in Dorking, Surrey, England; the University of Leicester, England; Brera Observatory in Milan; and ASI Science Data Center in Frascati, Italy.

Original Source: PSU News Release

Posted on by Fraser Cain

Transit Method Turns Up Planets

Perhaps 1 in 4 stars have planets. Image credit: Hubble. Click to enlarge.
In the past decade, more than 130 extrasolar planets have been discovered to date. Most of these have been found using a technique that measures tiny changes in a star’s radial velocity, the speed of its motion relative to Earth. In a talk at a recent symposium on extrasolar planets, astronomer Alan Boss, of the Carnegie Institution of Washington, presented this overview of the difficult measurements – and the profound discoveries – made by planet-hunters using the radial-velocity technique.

In 1991, Michel Mayor and Antoine Duquennoy published a classic survey of binary stars in our solar neighborhood. They found all the binary companions that they could, but there were another 200 or so G-type stars that didn’t seem to have any binary companions. Subsequently, Michel Mayor, along with Didier Queloz, decided to look at these 200-odd stars, potential solar analogs, to see if they had planetary systems. The technique they used involved looking for stellar wobbles, cyclical changes in the stars’ radial velocity, induced by the gravitational tug of orbiting planets.

In the spring of 1994, they installed a new spectrometer on their telescope at the Haute Provence Observatory, ELODIE, which had a resolution of about 13 meters per second. This was just about the right level to be able to see the velocity wobble, the Doppler wobble, induced in the Sun by a Jupiter-like planet. By the end of 1994 they had noticed a very interesting wobble in a star called 51 Peg.

Unfortunately, 51 Peg at that point was getting closer and closer to the Sun and couldn’t be observed, so they had to take a 6-month sabbatical, and come back in the summer of 1995 and start looking at 51 Peg again. They had an 8-night observing run at the Haute Provence Observatory, and by the end of that observing run, they were ready to go to Nature and publish.

The curve they produced fit a model of 51 Peg, a solar-type star, being orbited by a planet with roughly a half of a Jupiter mass, on a nice, circular orbit. The only problem was that the object had an orbital period of 4.23 days. It was orbiting in at about 0.05 AU, nowhere near where people had been expecting to find Jupiter-mass planets. So it was a bit of a puzzle. But it was clear early on that this had to be a planet, which perhaps had formed farther out and migrated in. That was the only way to explain how it could exist at that location.

The next step was to see if anyone else could reproduce the result. Because, of course, the critical problem with the planet around Barnard’s star was that no one could confirm it. There were several other planet-hunting efforts underway at the time in 1995, but the folks who got to the telescope first were Paul Butler and Geoff Marcy. They were able to confirm 51 Peg’s planet, with even smaller scatter than the original discovery measurements.

We realized at this point that the field of extrasolar planets had truly been born. In October 1995 a new era was entered, where we actually had convincing, solid proof of the existence of extrasolar planets around normal stars.

Now Geoff and Paul had been working in this field for many years. They had actually started seriously around 1987, and so they had a lot of data ready to analyze. They immediately began to reduce all of their data, looking for short period orbits, took some more measurements, and by January of 1996, they were able to announce a couple more planets. One of them, 47 UMa b, was considerably more reassuring a planet than the one discovered orbiting 51 Peg. It was roughly a 2 or 3 Jupiter-mass object orbiting at a distance of 2 or so AU, more like what we were expecting to find based on the planets in our own solar system. We now know that this is a multiple-planet system, but at the time they fit it with a single Keplerian orbit.

Almost all of the known extrasolar planets have been found using this radial-velocity technique; roughly 117 planets have been discovered that way. But there’s another way of finding planets, transit detection. The first transit detection was achieved by David Charboneau and colleagues and separately by Greg Henry and colleagues in 2000. This was a planet which had been found originally by radial velocity, but then these other researchers went on and did both ground-based and later Hubble photometry of the host star and found a really wonderful light curve, indicative of the planet passing in front of the star, dimming its light slightly. The initial detection by Charbonneau’s team was done, believe it or not, using a 4-inch telescope in a parking lot in Boulder, Colorado.

The dip in the star’s light amplitude is about 1.5 percent, so it’s truly amazing that this very first transit detection could have been made by a good amateur telescope. When HST went back and re-did the photometry with much higher precision, it produced an incredibly beautiful light curve, which is so precise you could use it to try to search for moons around the planet and place limits on how large they could be.

So transits are now coming into their own. I think they’re the second leading way of finding planets. Six planets have been discovered by transits now.

Original source: NASA Astrobiology

Posted on by Fraser Cain

No, Mars Won’t Look as Big as the Moon

Hubble Space Telescope view of Mars at its closest point 2 years ago. Image credit: Hubble. Click to enlarge.
There’s a rumor going around. You might have heard it at a 4th of July BBQ or family get-together. More likely you’ve read it on the Internet. It goes like this:

“The Red Planet is about to be spectacular.”

“Earth is catching up with Mars [for] the closest approach between the two planets in recorded history.”

“On August 27th ? Mars will look as large as the full moon.”

And finally, “NO ONE ALIVE TODAY WILL EVER SEE THIS AGAIN.”

Those are snippets from a widely-circulated email. Only the first sentence is true. The Red Planet is about to be spectacular. The rest is a hoax.

Here are the facts: Earth and Mars are converging for a close encounter this year on October 30th at 0319 Universal Time. Distance: 69 million kilometers. To the unaided eye, Mars will look like a bright red star, a pinprick of light, certainly not as wide as the full Moon.

Disappointed? Don’t be. If Mars did come close enough to rival the Moon, its gravity would alter Earth’s orbit and raise terrible tides.

Sixty-nine million km is good. At that distance, Mars shines brighter than anything else in the sky except the Sun, the Moon and Venus. The visual magnitude of Mars on Oct. 30, 2005, will be -2.3. Even inattentive sky watchers will notice it, rising at sundown and soaring overhead at midnight.

You might remember another encounter with Mars, about two years ago, on August 27, 2003. That was the closest in recorded history, by a whisker, and millions of people watched as the distance between Mars and Earth shrunk to 56 million km. This October’s encounter, at 69 million km, is similar. To casual observers, Mars will seem about as bright and beautiful in 2005 as it was in 2003.

Although closest approach is still months away, Mars is already conspicuous in the early morning. Before the sun comes up, it’s the brightest object in the eastern sky, really eye-catching. If you have a telescope, even a small one, point it at Mars. You can see the bright icy South Polar Cap and strange dark markings on the planet’s surface.

One day people will walk among those dark markings, exploring and prospecting, possibly mining ice from the polar caps to supply their settlements. It’s a key goal of NASA’s Vision for Space Exploration: to return to the Moon, to visit Mars and to go beyond.

Every day the view improves. Mars is coming–and that’s no hoax.

Original Source: NASA News Release

Posted on by Fraser Cain

Shuttle Exhaust Can Make Clouds in Antarctica

Space shuttle Discovery on the launch pad. Image credit: NASA. Click to enlarge.
A new study, funded in part by the Naval Research Laboratory and the National Aeronautics and Space Administration (NASA) reports that exhaust from the space shuttle can create high-altitude clouds over Antarctica mere days following launch, providing valuable insight to global transport processes in the lower thermosphere[mhs1]. The same study also finds that the shuttle’s main engine exhaust plume carries small quantities of iron that can be observed from the ground, half a world away.

The international team of authors of the study, to appear in the July 6 issue of Geophysical Research Letters, used the STS-107 Shuttle mission as a case study to show that exhaust released in the lower thermosphere, near 110 kilometers altitude, can form Antarctic polar mesospheric clouds (PMCs). The thermosphere is the highest layer in our atmosphere, with the mesosphere (between 50-90 kilometers above the Earth), stratosphere, and troposphere below.

New observations presented by the research team from the Global Ultraviolet Imager (GUVI) on NASA’s Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite reveal transport of the STS-107 exhaust into the southern hemisphere just two days after the January 2003 launch. Water from the exhaust ultimately led to a significant burst of PMCs during the 2002-2003 southern polar summer, observed by the Solar Backscatter Ultraviolet (SBUV) satellite experiment. The inter-hemispheric transport followed by Antarctic PMC formation were unexpected.

PMCs, also known as noctilucent clouds, appear near 83 kilometers altitude and are made up of water ice particles created through microphysical processes of nucleation, condensation, and sedimentation. They typically appear in the frigid polar summer mesosphere where temperatures plummet below 130? Kelvin (-220? F). Little is known about the specific processes that lead to PMC formation.

According to the study’s lead author, Dr. Michael Stevens, a research physicist at the E.O. Hulburt Center for Space Research at the Naval Research Laboratory, the research produced multiple groundbreaking science results.

“This research is exciting in that it extends a new explanation for the formation of these clouds by demonstrating the global effect of a Shuttle exhaust plume in a region of the atmosphere that has traditionally not been well understood,” said Stevens.

Some believe that the impact of anthropogenic change in the lower atmosphere is reflected in these upper atmospheric clouds. Although historically PMCs have only been seen in the polar region, in recent years PMCs have been spotted at lower latitudes as far south as [mhs2]Colorado and Utah, renewing interest and sparking debate on the implications. However, the findings of this work, “call into question the interpretation of the impact of late 20th century PMC trends solely in terms of global climate change,” Stevens said. The team concludes that the water from a space shuttle’s exhaust plume can contribute a remarkable 10-20 percent to PMCs observed during one summer season in Antarctica.

A key piece of data that confirmed the plume’s arrival in Antarctica was the ground-based observation of iron atoms near 110 km. The presence of iron at this altitude originally perplexed scientists because there is no known natural source there. The data imply that iron ablated, or vaporized, by the main engines of the Shuttle was transported along with the water plume, arriving in Antarctica three to four days after the January 2003 launch. Both the water plume and the presence of iron demonstrate that the mean southward wind inferred from the team’s data is much faster than gleaned from global circulation models or wind climatologies.

“This tells us something new and exciting about transport in this region of the atmosphere,” said Stevens. “It can be so fast that a shuttle plume can form ice over Antarctica before other loss processes can really take effect. We must take great care in interpreting the long-term implications to observations and features of these clouds because of this contribution from the shuttle and the potential contribution from many other smaller launch vehicles.”

NRL and NASA funded the study, with contributions from the National Science Foundation, the British Antarctic Survey in Cambridge, United Kingdom, and the University of Illinois, Urbana-Champaign. Other researchers on the study include Robert Meier of George Mason University, Fairfax, Va.; Xinzhao Chu of the University of Illinois, Urbana-Champaign; Matthew DeLand of Science Systems & Applications, Inc., Lanham, Md.; and John Plane of the University of East Anglia, Norwich, United Kingdom.

Original Source: NRL News Release