Posted on by Fraser Cain

SMART-1 Goes Into Lunar Orbit

Image credit: ESA
ESA?s SMART-1 is successfully making its first orbit of the Moon, a significant milestone for the first of Europe’s Small Missions for Advanced Research in Technology (SMART) spacecraft.

A complex package of tests on new technologies was successfully performed during the cruise to the Moon, while the spacecraft was getting ready for the scientific investigations which will come next. These technologies pave the way for future planetary missions.

SMART-1 reached its closest point to the lunar surface so far – its first ?perilune? ? at an altitude of about 5000 kilometres at 18:48 Central European Time (CET) on 15 November.

Just hours before that, at 06:24 CET, SMART-1?s solar-electric propulsion system (or ?ion engine?) was started up and is now being fired for the delicate manoeuvre that will stabilise the spacecraft in lunar orbit.

During this crucial phase, the engine will run almost continuously for the next four days, and then for a series of shorter burns, allowing SMART-1 to reach its final operational orbit by making ever-decreasing loops around the Moon. By about mid-January, SMART-1 will be orbiting the Moon at altitudes between 300 kilometres (over the lunar south pole) and 3000 kilometres (over the lunar north pole), beginning its scientific observations.

The main purpose of the first part of the SMART-1 mission, concluding with the arrival at the Moon, was to demonstrate new spacecraft technologies. In particular, the solar-electric propulsion system was tested over a long spiralling trip to the Moon of more than 84 million kilometres. This is a distance comparable to an interplanetary cruise.

For the first time ever, gravity-assist manoeuvres, which use the gravitational pull of the approaching Moon, were performed by an electrically propelled spacecraft. The success of this test is important to the prospects for future interplanetary missions using ion engines.

SMART-1 has demonstrated new techniques for eventually achieving autonomous spacecraft navigation. The OBAN experiment tested navigation software on ground computers to determine the exact position and velocity of the spacecraft using images of celestial objects taken by the AMIE camera on SMART-1 as references. Once used on board future spacecraft, the technique demonstrated by OBAN will allow spacecraft to know where they are in space and how fast they are moving, limiting the need for intervention by ground control teams.

SMART-1 also carried out deep-space communication tests, with the KaTE and RSIS experiments, consisting of testing radio transmissions at very high frequencies compared to traditional radio frequencies. Such transmissions will allow the transfer of ever-increasing volumes of scientific data from future spacecraft. With the Laser Link experiment, SMART-1 tested the feasibility of pointing a laser beam from Earth at a spacecraft moving at deep-space distances for future communication purposes.

During the cruise, to prepare for the lunar science phase, SMART-1 made preliminary tests on four miniaturised instruments, which are being used for the first time in space: the AMIE camera, which has already imaged Earth, the Moon and two total lunar eclipses from space, the D-CIXS and XSM X-ray instruments, and the SIR infrared spectrometer.

In all, SMART-1 clocked up 332 orbits around Earth. It fired its engine 289 times during the cruise phase, operating for a total of about 3700 hours. Only 59 kilograms of xenon propellant were used (out of 82 kilograms). Overall, the engine performed extremely well, enabling the spacecraft to reach the Moon two months earlier than expected.

The extra fuel available also allowed the mission designers to significantly reduce the altitude of the final orbit around the Moon. This closer approach to the surface will be even more favourable for the science observations that start in January. The extra fuel will also be used to boost the spacecraft back into a stable orbit, after six months of operations around the Moon, in June, if the scientific mission is extended.

Original Source: ESA News Release

Posted on by Fraser Cain

A Brief Interview With Sir Patrick Moore

Richard Pearson: How are you doing? Have you made a full recovery?

Sir Patrick: I am still here! Yes that was a nasty business and people had written me off at the time, however, I have made a good recovery. It was all caused by a duck egg, fortunately on this occasion I won, so yes I have. Very sadly, I have a crack in my spine, which over the last five years has prevented me from doing any kind of astronomical observations through my collection of telescopes, and during the war I had a knee injury which also causes problems now.

Have you been surprised by any changes in space exploration since you started presenting the Sky at Night almost 47 years ago?

I had expected manned exploration to continue after the Apollo program, and sadly the space shuttle has caused some problems leading to the loss of life, and the manned exploration of space seems to have stalled.

I was most surprised that the robotic exploration of our solar system has sprinted a head, and today space probes have visited all of the planets, except Pluto. I did not think that such interplanetary probes would be able to travel as far as the planets Uranus or Neptune in the early Sky at Night days.

David A. Hardy once painted two space suited humans on the surface of Titan, looking up through a sky tinged green with methane at the parent planet Saturn. By 1978, he had painted a dirigible cruising through red smog, Saturn barely visible. Both represent the best available science of the time. Today the Cassini Huygens space probe has sent back a series of remarkable images of the Moon, and we now believe there are strange Cryogenic (Cold) volcanoes on its surface.

In your new book, Futures: 50 Years in Space, you state that Europa could contain life if the sub-ice seas do exist there. Do you believe that this may be our best chance to find extra-terrestrial life? Or do you believe that we may find life “out there” first through the work of organizations such as SETI?

Yes I did say that, however, I believe our best chance of finding life in our solar system is on the planet Mars. We now know that a lot of water once existed on this planet sometime in the past, and the latest surface rovers (Spirit and Opportunity), along side orbiting space probes like Mars Express, have shown that the Martian conditions are more favorable for life to evolve their today than at any time in the past. If the conditions are right, life will always find a way to exit. So right now, Mars is my number one choice.?

I am sure there are many people who are curious to know who you would pick to (eventually) replace you to become the future presenter of the BBC’s Sky At Night program … Could this be Chris Lintott?

I really do not know because it is not my decision. Chris Lintott is a very good speaker and comes across very well indeed. I had Chris on the program earlier this year, and he did very well, so I now have Chris Lintott on The Sky at Night more often.

If you’re interested in Futures: 50 Years in Space, please read Universe Today’s review. You can also visit Amazon.com to read more reviews, or purchase a copy online (or Amazon.co.uk). You can also BBC’s website for Sir Patrick Moore’s “The Sky at Night”.

Sir Patrick Moore was interviewed by Richard Pearson.

Posted on by Fraser Cain

What’s Up This Week – Nov 15 – 21, 2004

Image credit: NASA
Monday, November 15 – On this day in 1738, William Herschel is born in Hanover, Germany. He left for England at age 19 to work as a music teacher, but ended up devoting all his spare time to mathematics and astronomy. Building his own telescope, in 1774 he enlisted the aid of his sister Caroline (also an astronomer) and began exploring the cosmos. In 1781 he discovered a new planet which he named Georgium Sidus for the king, but we more commonly know it as Uranus. The king then appointed Herschel as his private astronomer allowing him to devote all of his time to study. He built a 48 inch (1.22 meter) aperture scope at Slough, which enabled his discovery of two moons belonging to Uranus and the sixth and seventh moons of Saturn. He also studied rotation of the planets – as well as the motion of double stars, cataloging more than 800 of them. Herschel’s studies of nebulae increased the numbers of the observed from 100 to 2500 and was the first to speculate they were comprised of stars. Knighted in 1816, Sir William Herschel is considered the founder of sidereal astronomy. Happy Birthday!

As darkness falls, the tender crescent Moon appears low in the southwest among the stars of teapot-shaped constellation, Sagittarius. Mercury may be visible to the west and much lower on the horizon.

Tonight this three-day old Moon will provide a splendid view of crater Cleomides. It’s a very old crater, and as a “Class Five” is thought to have experienced different degrees of lava flooding, or perhaps filled with ashes, during its formation causing it to be more shallow than its original depth. For those with stable skies and instruments capable of supporting high power, Cleomides also has a fine and beautiful rima that extends approximately 30 km across its northern floor.

Since the Moon will be well out of the way at an early hour, why not take the opportunity tonight to study a globular cluster? Located in the eastern part of the constellation of Capricornus, the M30 is about six degrees south of bright star Gamma and located in the field of view with 41 Capricorni. Found in August of 1764 by Charles Messier, most binoculars from a dark sky location will have little problem distinguishing this small globular cluster. Telescopes will enjoy the M30 for its bright beauty and fine resolving powers with larger instruments. At approximately 26,000 light years away, the core of M30 is extremely dense and believed to have suffered a core collapse, making its linear radius span approximately 139 light years. Any stars beyond that distance would escape the influence of the globular structure simply because of the Milky Way Galaxy’s tidal gravitational forces. As an added treat as you will discover 41 Capricorni (in the same field of view) is a double star!

Tuesday, November 16 – Venus will hold court 4 degrees north of the bright blue star, Spica, in the constellation of Virgo in the predawn eastern sky. Appearing with it will be Jupiter and faint red Mars forming nearly a straight line across the east-southeast. Spica will be above and to the right of Mars.

Tonight the four-day old Moon will provide the opportunity to note a very changeable and eventually bright feature on the lunar surface – Proclus. At around 28 km (18 miles) in diameter and 2400 meters (11,900 feet) deep, crater Proclus will appear on the terminator on the west mountainous border of Mare Crisium. Tonight Proclus will seem to be about 2/3 black, but 1/3 of the exposed crater will be exceptionally brilliant. The reason for this is that crater Proclus has an albedo, or surface reflectivity of about 16%, which is an unusually high value for a lunar feature. Watch this area over the next few nights as two rays from the crater will widen and lengthen, extending approximately 322 km (200 miles) to both the north and south.

Take the opportunity tonight to study an extremely fine, colorful star system that is wonderful in binoculars and outstanding in the telescope. Located northeast of previous study star Deneb, (and visible to the naked-eye) Omicron 1 Cygni (aka 31 Cygni) is a premier object. Its blue secondary stars contrast wonderfully with the brilliant gold of the primary. Omicron is a widely “spaced” system providing easy resolution with the most modest of optical aids. You’ll like this one!

November 17 – 19 – The annual Leonid meteor shower will be underway, but for those of you seeking a definitive date and time, it doesn’t always happen. The degree of the meteor shower itself belongs to the debris shed by comet 55/P Tempel-Tuttle as it passes our Sun in its 33.2 year orbital period. Although it was once assumed that we would merely add around 33 years to each observed “shower”, we later came to realize that the debris formed a cloud that lagged behind the comet and dispersed irregularly. With each successive pass of Tempel-Tuttle, new filaments of debris were left in space as well as the old ones, creating different “streams” that the orbiting Earth would cross through at varying times making blanket predictions unreliable at best.

Each year during November, we pass through these filaments – both old and new – and the chances of impacting a particular “stream” from any one particular year of Tempel-Tuttle’s orbit becomes a matter of mathematical equations. We know when it passed… We know where it passed… But will we encounter it and to what degree? Traditional dates for the peak of the Leonid Meteor shower occur as early as the morning of November 17 and as late as November 19, but what about this year? On November 8, the Earth passed through an ancient stream shed in 1001. Predictions ran high for viewers in Asia, but the results turned out to be a dud. There is no doubt that we crossed through that stream, but its probability of dissipation is incalculable. Debris trails left by the comet in 1333 and 1733 look the most promising this year. For November 19, Jeremie Vaubaillon, Esko Lyytinen, Markku Nissinen, and David Asher predict that U.S. observers will be favoured as we cross the trail at around 06:42 UT. Fall rates are not incredible (about 10 per hour) but observers in Asia are far more favoured as we encounter the second stream left in 1733 at around 21:49 UT. The predicted fall rate for this one jumps to a respectable 65 per hour.

We may never know precisely where and when the Leonids might strike, but we do know that a good time to look for this activity is well before dawn on November 17, 18 and 19th. With the Moon out of the way long before the radiant constellation of Leo rises, the chances are good of spotting one of the offspring of periodic comet Tempel-Tuttle. Your chances increase significantly by traveling a dark sky location, but remember to dress warmly and provide for your viewing comfort. If it is cloudy? Remember to try the simple trick of tuning an FM radio receiver to the lowest frequency that does not receive a clear signal and “listen” for the blips, beeps and bongs that signify meteor scatter!

Wednesday, November 17 – According to tradition, the peak of the Leonid meteor shower will occur this morning in the predawn hours. Since you have read the above explanation, you realize that we may not pass through the “stream” at this time and we just might! All predictions indicate a low level of activity – around 15 to 35 per hour – but if skies are clear? I’ll see you out there!

On this day in 1970, long running Soviet mission Luna 17 successfully landed on the Moon. Its Lunokhod 1 rover became the first wheeled vehicle on the Moon. Lunokhod was designed to function three lunar days but actually operated for eleven. The machinations of Lunokhod officially stopped on October 4, 1971, the anniversary of Sputnik 1. Lunokhod had traversed 10,540 meters, transmitted more than 20,000 television pictures, over 200 television panoramas and performed more than 500 lunar soil tests. Spaseba!

Tonight will also be a perfect opportunity to study crater Theophilus in either binoculars or telescopes. Located on the terminator and bordered on the northern edge by Mare Nectaris and the south by Mare Tranquillitatus, Theophilus has an average diameter of 105 km (65 miles) and contains a wonderful multiple mountain peaked center. This particular crater is unusual in the sense that the floor is parabolic. The interior may be dark, but you will see a bright point of light that is the summit of its huge central peak.

Using the Moon as our guide tonight, why not try to find Neptune once again? At 21h Neptune will be located just 5 degrees north or the Moon!

Thursday, November 18 – Be sure to get up extra early today in hopes of catching the Leonid meteor shower! (see above for predictions.) In the darkness before dawn, blue Spica appars to the right of bright Venus. Mars is below and Jupiter above. Mars will occult TYC 5561-00614-1 (11.7 Magnitude Star) and Mercury will occult TYC 6815-04687-1 (9.1 Magnitude Star). See link for times and areas.

Tonight’s outstanding lunar feature will be a pair of craters that you cannot miss – Aristotle and Eudoxus. Located to the north, this pair of Class 1 craters will be highly prominent in both binoculars and telescopes. The northernmost, Aristotle was named for the great philosopher and has an expanse of approximately 87 km. Its deep and rugged walls show a wealth of detail for high power and two small interior peaks. Companion crater to the south, Eudoxus, spans 67 km and offers up equally rugged details.

Although skies will be bright, you can still do a little bit of binocular study on a very fine asterism known as the “Coathanger”. The proper name is Collider 399, but the pattern of stars wonderfully resembles a coat hanger. It is easy located in the constellation of Vulpecula. Find previous study star, Albireo once again and the relatively bright star south of that is Alpha Vulpeculae. Just aim your binoculars there and enjoy the smiles it brings!

Friday, November 19 – Are the predawn hours going to be the peak of the Leonid meteor shower for 2004? We just don’t know for certain, but if skies are clear, I plan on observing again this morning! (Let’s see just how accurate those predications are…)

The First Quarter Moon occurs at 12:50 UT and Algol will reach minima at 07:22 UT today. The Moon will reach its maximum libration tonight of 8.4 degrees, permitting those of you interested a view of Gauss and Hahn on the northeastern limb. On this day in 1969, Apollo 12, the second manned mission to the Moon, lands safely in the Oceanus Procellarum (Ocean of Storms). Why not celebrate by observing our nearest astronomical neighbor tonight?

For binoculars and telescopes, the Moon will provide a piece of scenic history as we take an in-depth look at crater Albategnius. This huge, hexagonal mountain walled plain will appear near the terminator about one third the way north from the south limb. This 81 mile (136 km) wide crater is approximately 14,400 feet deep and the west wall will cast a black shadow on the dark floor. Albategnius is very ancient formation, filled partially with lava at one point in its development, and is home to several wall craters like Klein (which will appear telescopically on its southwest wall). Albategnius holds more than just the distinction of being a prominent crater tonight – it holds a place in history. On May 9, 1962 Louis Smullin and Giorgio Fiocco of the Massachusetts Institute of technology aimed a red laser beam toward the lunar surface and Albategnius became the first lunar object to be illuminated and detected by a laser from Earth!

On March 24, 1965 Ranger 9 took this “snapshot” of Albategnius (lower right) from an altitude of approximately 2500 km. Companion craters in the image are Pltomaeus and Alphonsus, which will be revealed tomorrow night. The Ranger 9 was designed by NASA for one purpose – to achieve a lunar impact trajectory and to send back high-resolution photographs and high-quality video images of the lunar surface. It carried no other scientific experiments, and its only destiny was to take pictures right up to the moment of final impact. It is interesting to note that Ranger 9 slammed into Alphonsus approximately 18.5 minutes after this photo was taken. They called that… A “hard landing.”

Tonight would also be a great time to re-locate Uranus. It’s only 4.1 degrees north of the Moon!

Saturday, November 20 – Today is Edwin Hubble’s 115th birthday! Born in 1889, U.S. astronomer Edwin Hubble, became the father of modern cosmology. His extensive list of accomplishments could fill pages, so please take the time to learn about one of the finest astronomers of our times.

Tonight’s featured lunar crater will be located on the south shore of Mare Ibrium right where the Apennine mountain range meets the terminator. Eratosthenes is a 37 mile (58 km) diameter and 12,300 foot deep unmistakable crater. Named after ancient mathematician, geographer and astronomer Eratosthenes, this splendid Class 1 crater will display a bright west wall and a black interior which hides its massive crater capped central mountain (3570 meters high!) tonight. Extending like a tail, a 50 mile long mountain ridge angles away to the southwest. As beautiful as Eratostenes appears tonight, it will fade away to total obscurity as the Moon becomes more full. See if you can spot it in five days!

After having looked at the Moon tonight, take the time out to view bright southern star – Formalhaut. Also known as “The Lonely One”, Alpha Pices Austrinis seems to sit in a rather empty area in the southern skies 23 light years away. At magnitude 1, this main sequence A3 giant is the southern-most visible star of its type to northern hemisphere viewers and it is the 18th brightest star in the sky. “The Lonely One” is about twice the diameter of our own Sun, but 14 times more luminous!

Sunday, November 21 – Mercury at greatest elongation east (22 degrees) of the Sun, appearing low in the southwestern sky after sunset, or try looking for it in the darkness just before dawn.

Tonight’s lunar feature can sometimes be spotted with only the naked eye. Located to the northern hemisphere of the Moon, the dark ellipse of crater Plato is unmistakable. Named after the famous philosopher, this Class 5 crater spans approximately 64 by 67 miles (101 km) but is a shallow 8000 feet deep. Plato’s floor is 2700 square miles of lava and has been studied for over 300 years. This crater has the distinction of being one of the only mountain-walled plains that doesn’t “disappear” as the Moon grows full! For those of you with very fine optics, or who wish a web cam challenge? Try finding Plato’s interior craterlets. Good luck!

For Southern Hemisphere viewers, tonight would be a wonderful opportunity to re-discover one of the finest double stars in the sky – Rigel Kentarus! Located low to the southwest, Alpha Centauri is the third brightest star in the sky, yet the most famous because it is the nearest star to our solar system at a distance of only 4.34 light years!

Until next week? Keep looking up! I wish you clear skies and light speed… ~Tammy Plotner

Posted on by Fraser Cain

Baby Planet Puzzles Astronomers

Image credit: NASA/JPL
In June, researchers from the University of Rochester announced they had located a potential planet around another star so young that it defied theorists’ explanations. Now a new team of Rochester planet-formation specialists are backing up the original conclusions, saying they’ve confirmed that the hole formed in the star’s dusty disk could very well have been formed by a new planet. The findings have implications for gaining insight into how our own solar system came to be, as well as finding other possibly habitable planetary systems throughout our galaxy.

“The data suggests there’s a young planet out there, but until now none of our theories made sense with the data for a planet so young,” says Adam Frank, professor of physics and astronomy at the University of Rochester. “On the one hand, it’s frustrating; but on the other, it’s very cool because Mother Nature has just handed us the planet and we’ve got to figure out how it must have been created.”

Intriguingly, working from the original team’s data, Frank, Alice Quillen, Eric Blackman, and Peggy Varniere revealed that the planet was likely smaller than most extra-solar planets discovered thus far – about the size of Neptune. The data also suggested that this planet is about the same distance from its parent star as our own Neptune is from the Sun. Most extra-solar planets discovered to date are much larger and orbit extremely close to their parent star.

The original Rochester team, led by Dan Watson, professor of physics and astronomy, used NASA’s new Spitzer Space Telescope to detect a gap in the dust surrounding a fledgling star. The critical infrared “eyes” of the infrared telescope were designed in part by physics and astronomy professors Judith Pipher, William Forrest, and Watson, a team that has been among the world leaders in opening the infrared window to the universe. It was Forrest and Pipher who were the first U.S. astronomers to turn an infrared array toward the skies: In 1983, they mounted a prototype infrared detector onto the University telescope in the small observatory on top of the Wilmot Building on campus, taking the first-ever telescopic pictures of the moon in the infrared, a wavelength range of light that is invisible to the naked eye as well as to most telescopes.

The discovered gap strongly signaled the presence of a planet. The dust in the disk is hotter in the center near the star and so radiates most of its light at shorter wavelengths than the cooler outer reaches of the disk. The research team found that there was an abrupt dearth of light radiating at all short infrared wavelengths, strongly suggesting that the central part of the disk was absent. Scientists know of only one phenomenon that can tunnel such a distinct “hole” in the disk during the short lifetime of the star – a planet at least 100,000 years old.

This possibility of a planet on the order of only 100,000 to half a million years old was met with skepticism by many astronomers because neither of the leading planetary formation models seemed to allow for a planet of this age. Two models represent the leading theories of planetary formation: core accretion and gravitational instability. Core accretion suggests that the dust from which the star and system form begins to clump together into granules, and those granules clump into rocks, asteroids, and planetoids until whole planets are formed. But the theory says it should take about 10 million years for a planet to evolve this way – far too long to account for the half-million-year-old planet found by Watson.

Conversely, the other leading theory of planetary formation, gravitational instability, suggests that whole planets could form essentially in one swoop as the original cloud of gas is pulled together by its own gravity and becomes a planet. But while this model suggests that planetary formation could happen much faster – on the order of centuries – the density of the dust disk surrounding the star seems to be too sparse to support this model either.

“Even though it doesn’t fit either model, we’ve crunched the numbers and shown that yes, in fact, that hole in that dust disk could have been formed by a planet,” says Frank. “Now we have to look at our models and figure out how that planet got there. At the end of it all, we hope we have a new model, and a new understanding of how planets come to be.”

This research was funded by the National Science Foundation.

Original Source: University of Rochester News Release

Posted on by Fraser Cain

Getting Out of Endurance Might Not Be Easy

Operators of NASA’s Mars Exploration Rover Opportunity have determined that a proposed route eastward out of “Endurance Crater” is not passable, so the rover will backtrack to leave the crater by a southward route, perhaps by retracing its entry path.

“We’ve done a careful analysis of the ground in front of Opportunity and decided to turn around,” said Jim Erickson, rover project manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “To the right, the slope is too steep — more than 30 degrees. To the left, there are sandy areas we can’t be sure we could get across.”

Before turning around, Opportunity will spend a few days examining the rock layers in scarp about 10 meters (33 feet) high, dubbed “Burns Cliff.” From its location at the western foot of the cliff, the rover will use its panoramic camera and miniature thermal emission spectrometer to collect information from which scientists hope to determine whether some of the layers were deposited by wind, rather than by water. The rover will not reach an area about 15 meters (50 feet) farther east where two layers at different angles meet at the base of the cliff.

“We have pushed the vehicle right to the edge of its capabilities, and we’ve finally reached a spot where we may be able to answer questions we’ve been asking about this site for months,” said Dr. Steve Squyres, rover principal investigator at Cornell University, Ithaca, N.Y. “But after we’re done here, it’ll be time to turn around. Going any farther could cut off our line of retreat from the crater, and that’s not something anybody on the team wants to do.”

Opportunity entered the stadium-size crater on June 8 at a site called “Karatepe” along the crater’s southern rim. Inside the crater, it has found and examined multiple layers of rocks that show evidence of a wet environment in the area’s distant past.

Opportunity and its twin, Spirit, successfully completed their primary three-month missions on Mars in April. NASA has extended their missions twice, most recently on Oct. 1, because the rovers have remained in good condition to continue exploring Mars longer than anticipated.

Engineers have finished troubleshooting an indication of a problem with steering brakes on Spirit. The brakes are designed to keep the rover wheels from being bumped off course while driving. Spirit has intermittently sent information in recent weeks that the brakes on two wheels were not releasing properly when the rover received commands to set a new course. Testing and analysis indicate that the mechanism for detecting whether the brakes are released is probably sending a false indication. The rover team will disregard that signal and presume the brakes have actually released properly when commanded to do so. This anomaly has not been observed on the Opportunity rover.

“We’re going back to using the full steering capabilities of Spirit,” Erickson said.

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA’s Science Mission Directorate, Washington, D.C. Additional information about the project is available from JPL at http://marsrovers.jpl.nasa.gov/ and from Cornell University, Ithaca, N.Y., at http://athena.cornell.edu.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Hubble’s Accidental Asteroid Discovery

While analyzing NASA Hubble Space Telescope images of the Sagittarius dwarf irregular galaxy (SagDIG), an international team of astronomers led by Simone Marchi, Yazan Momany, and Luigi Bedin were surprised to see the trail of a faint asteroid that had drifted across the field of view during the exposures. The trail is seen as a series of 13 reddish arcs on the right in this August 2003 Advanced Camera for Surveys image.

As the Hubble telescope orbits around the Earth, and the Earth moves around the Sun, a nearby asteroid in our solar system will appear to move with respect to the vastly more distant background stars, due to an effect called parallax. It is somewhat similar to the effect you see from a moving car, in which trees by the side of the road appear to be moving much more rapidly than background objects at much larger distances. If the Hubble exposure were a continuous one, the asteroid trail would appear like a continuous wavy line. However, the exposure with Hubble’s camera was actually broken up into more than a dozen separate exposures. After each exposure, the camera’s shutter was closed while the image was transferred from the electronic detector into the camera’s computer memory; this accounts for the many interruptions in the asteroid’s trail.

Since the trajectory of the Hubble spacecraft around the Earth is known very accurately, it is possible to triangulate the distance to the asteroid in a manner similar to that used by terrestrial surveyors. It turns out to be a previously unknown asteroid, located 169 million miles from Earth at the time of observation. The distance places the new object, most likely, in the main asteroid belt, lying between the orbits of Mars and Jupiter. Based on the observed brightness of the asteroid, the astronomers estimate that it has a diameter of about 1.5 miles.

The brightest stars in the picture (easily distinguished by the spikes radiating from their images, produced by optical effects within the telescope), are foreground stars lying within our own Milky Way galaxy. Their distances from Earth are typically a few thousand light-years. The faint, bluish SagDIG stars lie at about 3.5 million light-years (1.1 Megaparsecs) from us. Lastly, background galaxies (reddish/brown extended objects with spiral arms and halos) are located even further beyond SagDIG at several tens of millions parsecs away. There is thus a vast range of distances among the objects visible in this photo, ranging from about 169 million miles for the asteroid, up to many quadrillions of miles for the faint, small galaxies.

The team reported their science findings about the asteroid in the October 2004 issue of New Astronomy.

Original Source: Hubble News Release

Posted on by Fraser Cain

Close View of Phobos

This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA?s Mars Express spacecraft, is Europe?s highest-resolution picture so far of the Martian moon Phobos.

This HRSC image shows new detail that will keep planetary scientists busy for years, working to unravel the mysteries of this moon. The image shows the Mars-facing side of the moon, taken from a distance of less than 200 kilometres with a resolution of about seven metres per pixel during orbit 756.

Images of Phobos as shown here had already been taken at lower resolution in previous orbits (413, 649, 682, 715 and 748). In the coming months, these first pictures will be followed by a series of images taken in subsequent fly-bys.

The Mars Express spacecraft periodically passes near Phobos about one hour before it flies at an altitude of only 270 kilometres above the Martian surface, just above the atmosphere. Within minutes, the orbiting spacecraft turns from its attitude where it points at Mars to train its camera on this little world.

The HRSC provided an unprecedented near-simultaneous group of 10 different images of the surface, enabling the moon’s shape, topography, colour, ?regolith? light-scattering properties, and rotational and orbital states to be determined. The regolith is the small-grained material covering most non-icy planetary bodies, resulting from multiple impacts on the body?s surface.

These images have surpassed all previous images from other missions in continuous coverage of the illuminated surface, not blurred and at the highest resolution. The US Viking Orbiter obtained a few small areas sampled at an even higher resolution of a few metres per pixel, but these were not so sharp due to the close and fast fly-by.

The global ?groove? network is seen in sufficient detail to cover the Mars-facing surface continuously from near the equator up to the north pole with regular spacing between the grooves. It now may be possible to determine whether the grooves existed before the large cratering events, and exist deep within Phobos, or came after the cratering events and were superimposed on them.

Much more detail is seen inside the various-sized craters, showing some with marked albedo variations. Some craters have dark materials near the crater floors, some have regolith that slid down the crater walls, and some have very dark ejecta, possibly some of the darkest material in our Solar System.

This tiny moon is thought to be in a ?death spiral?, slowly orbiting toward the surface of Mars. Here, Phobos was found to be about five kilometres ahead of its predicted orbital position. This could be an indication of an increased orbital speed associated with its secular acceleration, causing the moon to spiral in toward Mars.

Eventually Phobos could be torn apart by Martian gravity and become a short-lived ring around Mars, or even impact on the surface. This orbit will be studied in more detail over the lifetime of the Mars Express.

Original Source: European Space Agency

Posted on by Fraser Cain

Mapping the Early Universe in 3 Dimensions

The invention of the CAT scan led to a revolution in medical diagnosis. Where X-rays give only a flat two-dimensional view of the human body, a CAT scan provides a more revealing three-dimensional view. To do this, CAT scans take many virtual “slices” electronically and assemble them into a 3D picture.

Now a new technique that resembles CAT scans, known as tomography, is poised to revolutionize the study of the young universe and the end of the cosmic “dark ages.” Reporting in the Nov. 11, 2004, issue of Nature, astrophysicists J. Stuart B. Wyithe (University of Melbourne) and Abraham Loeb (Harvard-Smithsonian Center for Astrophysics) have calculated the size of cosmic structures that will be measured when astronomers effectively take CAT scan-like images of the early universe. Those measurements will show how the universe evolved over its first billion years of existence.

“Until now, we’ve been limited to a single snapshot of the universe’s childhood-the cosmic microwave background,” says Loeb. “This new technique will let us view an entire album full of the universe’s baby photos. We can watch the universe grow up and mature.”

Slicing Space
The heart of the tomography technique described by Wyithe and Loeb is the study of 21-centimeter-wavelength radiation from neutral hydrogen atoms. In our own galaxy, this radiation has helped astronomers to map the Milky Way’s spherical halo. To map the distant young universe, astronomers must detect 21-cm radiation that has been redshifted: stretched to longer wavelengths (and lower frequencies) by the expansion of space itself.

Redshift is directly correlated to distance. The farther a cloud of hydrogen is from the Earth, the more its radiation is redshifted. Therefore, by looking at a specific frequency, astronomers can photograph a “slice” of the universe at a specific distance. By stepping through many frequencies, they can photograph many slices and build up a three-dimensional picture of the universe.

“Tomography is a complicated process, which is one reason why it hasn’t been done before at very high redshifts,” says Wyithe. “But it’s also very promising because it’s one of the few techniques that will let us study the first billion years of the universe’s history.”

A Soap Bubble Universe
The first billion years are critical because that is when the first stars began to shine and the first galaxies began to form in compact clusters. Those stars burned hotly, emitting huge amounts of ultraviolet light that ionized nearby hydrogen atoms, splitting electrons from protons and clearing away the fog of neutral gas that filled the early universe.

Young galaxy clusters soon were surrounded by bubbles of ionized gas much like soap bubbles floating in a tub of water. As more ultraviolet light flooded space, the bubbles grew larger and gradually merged together. Eventually, about a billion years after the Big Bang, the entire visible universe was ionized.

To study the early universe when the bubbles were small and the gas mostly neutral, astronomers must take slices through space as if slicing a block of swiss cheese. Loeb says that just as with cheese, “if our slices of the universe are too narrow, we’ll keep hitting the same bubbles. The view will never change.”

To get truly useful measurements, astronomers must take larger slices that hit different bubbles. Each slice must be wider than the width of a typical bubble. Wyithe and Loeb calculate that the largest individual bubbles reached sizes of about 30 million light-years across in the early universe (equivalent to more than 200 million light-years in the expanded universe of today). Those crucial predictions will guide the design of radio instruments to conduct tomographical studies.

Astronomers soon will test Wyithe and Loeb’s predictions using an array of antennas tuned to operate at the 100-200 megahertz frequencies of redshifted 21-cm hydrogen. Mapping the sky at these frequencies is extremely difficult because of manmade interference (TV and FM radio) and the effects of the earth’s ionosphere on low-frequency radio waves. However, new low-cost electronics and computer technologies will make extensive mapping possible before the end of the decade.

“Stuart and Avi’s calculations are beautiful because once we have built our arrays, the predictions will be straightforward to test as we take our first glimpses of the early universe,” says Smithsonian radio astronomer Lincoln Greenhill (CfA).

Greenhill is working to create those first glimpses through a proposal to equip the National Science Foundation’s Very Large Array with the necessary receivers and electronics, funded by the Smithsonian. “With luck, we will create the first images of the shells of hot material around several of the youngest quasars in the universe,” says Greenhill.

Wyithe and Loeb’s results also will help guide the design and development of next-generation radio observatories being built from the ground up, such as the European LOFAR project and an array proposed by a US-Australian collaboration for construction in the radio-quiet outback of Western Australia.

Original Source: Harvard CfA News Release

Posted on by Fraser Cain

Density Waves in Saturn’s Rings

A University of Colorado at Boulder-built instrument riding on the Cassini-Huygens spacecraft is being used to distinguish objects in Saturn’s rings smaller than a football field, making them twice as sharp as any previous ring observations.

Joshua Colwell of CU-Boulder’s Laboratory for Atmospheric and Space Physics said the observations were made with the Ultraviolet Imaging Spectrograph, or UVIS, when Cassini was about 4.2 million miles, or 6.75 million kilometers, from Saturn in July. Saturn orbits the Sun roughly 1 billion miles from Earth.

Colwell and his colleagues used a technique known as stellar occultation to image the ring particles, pointing the instrument through the rings toward a star, Xi Ceti. The fluctuations of starlight passing through the rings provide information on the structure and dynamics of the particles within them, said Colwell, a UVIS science team member.

He likened the Saturn system to a mammoth phonograph record, with the planet in the middle and the rings stretching outward more than 40,000 miles, or 64,000 kilometers. The size of the ring particles varies from dust specks to mountains, with most ranging between marbles and boulders, he said.

The Cassini observations show dramatic variations in the number of ring particles over very short distances, Colwell said. The particles in individual ringlets are bunched closely together, with the amount of material dropping abruptly at the ringlet edge.

“What we see with the new observations is that some of the ring edges are very sharp,” said Colwell. The sharp edges of small ringlets are especially evident in the C ring and in the so-called Cassini Division on either side of the bright B ring, Saturn’s largest ring.

The Cassini observations with UVIS show that the distance between the presence and absence of orbiting material at some ring edges can be as little as 160 feet, or 50 meters, about the length of a typical commercial jetliner, he said.

The sharp edges illustrate the dynamics that constrain the ring processes against their natural tendency to spread into nearby, empty space, said Colwell. “Nature abhors a vacuum, so it is likely gravity from a nearby small moon and ongoing meteoroid collisions confine the particles in the ring.”

Colwell presented his findings at the 36th annual Division of Planetary Sciences Meeting held in Louisville, Ky., Nov. 8 to Nov 12.

The stellar occultation process using UVIS also shows very high-resolution views of several density waves visible in the rings, including a previously unstudied one, he said. Density waves are ripple-like features in the rings caused by the influence of Saturn’s moons — in this case, the small moon, Janus.

“Small moons near Saturn’s rings stir the ring particles with their gravitational pull,” Colwell said. At certain locations in the rings, known as resonances, the orbit of a particular moon matches up with the orbit of certain ring particles in a way that enhances the stirring process, he said.

The density waves, which resemble a tightly wound spiral much like the groove in a phonograph record, slowly propagate away from the resonance toward the perturbing moon, he said. “This can create a wave in the ring that looks like a ripple in a pond,” said Colwell.

“The shapes of these wave peaks and troughs help scientists understand whether the ring particles are hard and bouncy, like a golf ball, or soft and less bouncy, like a snowball,” Colwell said. He noted that a density wave analysis by scientists involved in NASA’s Voyager 2 mission that visited Saturn in 1981 were used to determine the mass and thickness of the planet’s rings.

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 in Washington, D.C.

CU-Boulder Professor Larry Esposito of LASP is the principal investigator for the $12.5 million UVIS instrument, designed and built for JPL at CU-Boulder.

Original Source: CU Boulder News Release

Posted on by Fraser Cain

Icy Objects Could Be Smaller Than Previously Thought

Image credit: NASA/JPL
Pluto’s status as our solar system’s ninth planet may be safe if a recently discovered Kuiper Belt Object is a typical “KBO” and not just an oddball.

Astronomers have new evidence that KBOs (Kuiper Belt Objects) are smaller than previously thought.

KBOs – icy cousins to asteroids and the source of some comets – are the leftover building blocks of the outer planets. Astronomers using the world’s most powerful telescopes have discovered about 1,000 of these objects orbiting beyond Neptune since discovering the first one in 1992. These discoveries fueled debate on whether Pluto is a planet or a large (1,400-mile diameter) closer-in KBO.

Researchers estimate that the total mass of the Kuiper Belt is about a tenth of Earth’s mass. Most theorize that there are more than 10,000 KBOs with diameters greater than 100 kilometers (62 miles), compared to 200 asteroids known to be that large in the main asteroid belt between Mars and Jupiter.

“People were finding all these KBOs that were huge – literally half the size of Pluto or larger,” University of Arizona astronomer John Stansberry said. “But those supposed sizes were based on assumptions that KBOs have very low albedos, similar to comets.”

Albedo is a measure of how much light an object reflects. The more light an object reflects, the higher its albedo. Actual data on Kuiper Belt Object albedos have been hard to come by because the objects are so distant, dim and cold. Many astronomers have assumed that KBO albedos – like comet albedos – are around four percent and have used that number to calculate KBO diameters.

However, in early results from their Spitzer Space Telescope survey of 30 Kuiper Belt Objects, Stansberry and colleagues found that a distant KBO designated 2002 AW197 reflects 18 percent of its incident light and is about 700 kilometers (435 miles) in diameter. That’s considerably smaller and more reflective than expected, Stansberry said.

“2002 AW197 is believed to be one of the largest KBOs thus far discovered,” he said. “These results indicate that this object is larger than all but one main-belt asteroid (Ceres), about half the size of Pluto’s moon, Charon, and about 30 percent as large and a tenth as massive as Pluto.”

Stansberry and his colleagues took the data with Spitzer’s Multiband Imaging Photometer (MIPS) on April 13, 2004. George Rieke’s team at the University of Arizona developed and built the extremely heat-sensitive MIPS. It detects heat from very cold objects by taking images at far-infrared wavelengths.

In this case, MIPS detected heat from a Kuiper Belt Object with a surface temperature of around minus 370 degrees Fahrenheit at an astonishing distance of 4.4 billion miles (7 billion kilometers), or one-and-a-half times farther away frm the sun than Pluto.

Without MIPS, astronomers operating under the assumption that 2002 AW197 reflects four percent of its incident light would calculate that it is 1500 kilometers (932 miles) in diameter, or two-thirds as large as Pluto, Stansberry said.

“We’re finally starting to get data on the basic physical parameters of KBOs,” Stansberry said. “That will help us determine what their compositions are, how they evolve, how massive they are, what their real size distributions and dynamics are and how Pluto fits into the whole picture,” he said.

Such data will also offer insight on how comets are processed on their successive journeys around the sun, he added.

“It’s not surprising that comets are darker than KBOs,” Stansberry said.”When something in the Kuiper Belt chips off a piece of a Kuiper Belt Object, presumably that piece would have a higher albedo on its first swing through the inner solar system. But it doesn’t take long before it loses its high albedo surface and builds up a lot of very dark materials, at least in its outermost surface.”

Others with Stansberry in this Spitzer study are Dale Cruikshank and Josh Emery of NASA Ames Research Center, Yan Fernandez of the University of Hawaii, George Rieke of the University of Arizona and Michael Werner of NASA’s Jet Propulsion Laboratory.

Stansberry said the team will finish collecting their KBO data with Spitzer soon.

“We’ll know a lot more about how big and bright these things are by this time next year,” he said.

Stansberry is presenting the research today at the 86th annual meeting of the American Astronomical Society Division of Planetary Science in Louisville, Ky.

More information about this and other new results from the Spitzer Space Telescope is on the Web at http://www.spitzer.caltech.edu/Media/index.shtml The Spitzer Space Telescope is managed for NASA by the Jet Propulsion Laboratory in Pasadena, Calif.

Original Source: University of Arizona News Release