Universe Today

December 1, 2004March 24, 2012 by Fraser Cain

Supernova in a Distant Galaxy NGC 6118

Images of beautiful galaxies, and in particular of spiral brethren of our own Milky Way, leaves no-one unmoved. It is difficult indeed to resist the charm of these impressive grand structures. Astronomers at Paranal Observatory used the versatile VIMOS instrument on the Very Large Telescope to photograph two magnificent examples of such “island universes”, both of which are seen in a southern constellation with an animal name. But more significantly, both galaxies harboured a particular type of supernova, the explosion of a massive star during a late and fatal evolutionary stage.

This image is of the impressive spiral galaxy NGC 6118 [1], located near the celestial equator, in the constellation Serpens (The Snake). It is a comparatively faint object of 13th magnitude with a rather low surface brightness, making it pretty hard to see in small telescopes. This shyness has prompted amateur astronomers to nickname NGC 6118 the “Blinking Galaxy” as it would appear to flick into existence when viewed through their telescopes in a certain orientation, and then suddenly disappear again as the eye position shifted.

There is of course no such problem for the VLT’s enormous light-collecting power and ability to produce sharp images, and this magnificent galaxy is here seen in unequalled detail. The colour photo is based on a series of exposures behind different optical filters, obtained with the VIMOS multi-mode instrument on the 8.2-m VLT Melipal telescope during several nights around August 21, 2004.

About 80 million light-years away, NGC 6118 is a grand-design spiral seen at an angle, with a very small central bar and several rather tightly wound spiral arms (it is classified as of type “SA(s)cd” [2]) in which large numbers of bright bluish knots are visible. Most of them are active star-forming regions and in some, very luminous and young stars can be perceived.

Of particular interest is the comparatively bright stellar-like object situated directly North of the galaxy’s centre, near the periphery (see PR Photo 33b/04): it is Supernova 2004dk that was first reported on August 1, 2004. Observations a few days later showed this to be a supernova of Type Ib or Ic [3], caught a few days before maximum light. This particular kind of supernova is believed to result from the demise of a massive star that has somehow lost its entire hydrogen envelope, probably as a result of mass transfer in a binary system, before exploding.

Also visible on the image is the trail left by a satellite, which passed by during one of the exposures taken in the B filter, hence its blue colour. This is an illustration that even in such a remote place as the Paranal Observatory in the Atacama desert, astronomers are not completely sheltered from light pollution.

The second galaxy imaged by the VLT is another spiral, the beautiful multi-armed NGC 7424 that is seen almost directly face-on. Located at a distance of roughly 40 million light-years in the constellation Grus (the Crane), this galaxy was discovered by Sir John Herschel while observing at the Cape of Good Hope.

This other example of a “grand design” galaxy is classified as “SAB(rs)cd” [2], meaning that it is intermediate between normal spirals (SA) and strongly barred galaxies (SB) and that it has rather open arms with a small central region. It also shows many ionised regions as well as clusters of young and massive stars. Ten young massive star clusters can be identified whose size span the range from 1 to 200 light-years. The galaxy itself is roughly 100,000 light-years across, that is, quite similar in size to our own Milky Way galaxy.

Because of its low surface brightness, this galaxy also demands dark skies and a clear night to be observed in this impressive detail. When viewed in a small telescope, it appears as a large elliptical haze with no trace of the many beautiful filamentary arms with a multitude of branches revealed in this striking VLT image. Note also the very bright and prominent bar in the middle.

On the evening of 10 December 2001, Australian amateur astronomer Reverend Robert Evans, observing from his backyard in the Blue Mountains west of Sydney, discovered with his 30cm telescope his 39th supernova, Supernova 2001ig in the outskirts of NGC 7424. Of magnitude 14.5 (that is, 3000 times fainter than the faintest star that can be seen with the unaided eye), this supernova brightened quickly by a factor 8 to magnitude 12.3. A few months later, it had faded to an insignificant object below 17th magnitude. By comparison, the entire galaxy is of magnitude 11: at the time of its maximum, the supernova was thus only three times fainter than the whole galaxy. It must have been a splendid firework indeed!

By digging into the vast Science Archive of the ESO Very Large Telescope, it was possible to find an image of NGC 7424 taken on June 16, 2002 by Massimo Turatto (Observatorio di Padova-INAF, Italy) with the FORS 2 instrument on Yepun (UT4). Although, the supernova was already much fainter than at its maximum 6 months earlier, it is still very well visible on this image (see PR Photo 33d/04).

Spectra taken with ESO’s 3.6-m telescope at La Silla over the months following the explosion showed the object to evolve to a Type Ib/c supernova. By October 2002, the transition to a Type Ib/c supernova was complete. It is now believed that this supernova arose from the explosion of a very massive star, a so-called Wolf-Rayet star, which together with a massive hot companion belonged to a very close binary system in which the two stars orbited each other once every 100 days or so. Future detailed observations may reveal the presence of the companion star that survived this explosion but which is now doomed to explode as another supernova in due time.

[1] NGC stands for “New General Catalogue”. Published in 1888 by J.L.E. Dreyer, this New General Catalogue of Nebulae and Clusters of Stars, being the Catalogue of the late Sir John F.W. Herschel contains 7840 objects of which 3200 are galaxies.

[2] Spiral galaxies take their name from the spectacular spiral arms that wind around in a very thin disc. Following the celebrated classification by American astronomer Edwin Hubble, spiral galaxies are classified into two families, so-called normal spirals (SA) and barred spirals (SB), and are further divided into types Sa, Sb and Sc depending on the opening of the spiral arms and the relative brightness of the central area. In barred spiral galaxies, the nucleus is crossed by a bar of stars at the ends of which the spiral arms begin. The (rs) in the classification testifies to the presence of an internal ring (r) surrounding the nucleus of the galaxy as well as to the fact that the spiral arms begin directly at the nucleus (s).

[3] Supernovae are classified into different types, depending on the appearance of their spectrum. Type II supernovae show the presence of hydrogen lines in their spectra while Type I lack this signature. Type I have been subdivided into Type Ia, Ib and Ic. Type I supernovae are all believed to arise in binary stellar systems.

Original Source: ESO News Release

November 30, 2004June 3, 2013 by Fraser Cain

Reminder: Year in Space 2005 Desk Calendar

With the holidays rapidly approaching, I just wanted to give you another reminder about the 2005 “Year in Space” desk calendar as a potential gift for all the space enthusiasts in your life. This 144-page calendar has a weekly space image, daily Moon phases, space trivia, and sky events. It only costs $10.95 (discounted from $14.95), and includes free shipping in the US. Just mention Universe Today on the order form.

Click here to learn more about the calendar.

Happy holiday shopping.

Fraser Cain
Publisher
Universe Today

November 30, 2004 by Fraser Cain

What’s Up This Week – Nov 29 – Dec 5, 2004

Image credit: NOAO/AURA/NSF
Monday, November 29 – With a short time until the Moon rises tonight, why not journey with me once again to Cassiopeia? We will start our studies with the western-most of the bright stars – Beta. Also known as “Caph”, Beta Cassiopeiae is approximately 45 light years away and known to be a rapid variable. Viewers with larger telescopes are challenged to find the 14th magnitude optical companion to Caph at about 23″ in separation. Tonight, using our previous study star Alpha and Beta, we are going to learn to locate a Messier object with ease!

By drawing an imaginary line between Alpha and Beta, we extend that line the same distance and angle beyond Beta and find the M52. Found on September 7, 1774 by Charles Messier, this magnitude 7 galactic cluster is easily seen in both binoculars and small telescopes. Comprised of roughly 200 members, this open cluster is roughly about 3,000 light years in distance and spans approximately 10-15 light years. Containing several different magnitudes, larger telescopes will easily perceive blue components as well as orange and yellow. The M52 (NGC7654) is a young, very compressed cluster whose approximate age is about the same as the Plieades. For those with large telescopes wanting a challenge? Try spotting a faint patch of nebulosity just 36′ to the southwest. This is the NGC7635, more commonly known as the “Bubble Nebula”. Best of luck!

Tuesday, November 30 – Tonight the Moon will be at apogee, or its greatest greatest distance from Earth. For those of you staying up late it will form a nearly straight line with Castor and Pollux with Saturn below and to the right. For those preferring to take your astronomy at an earlier hour? We’ll be delighted that the Moon will be out of the way for several hours as we adventure further into Cassiopeia! Returning the Cassiopeia’s central-most star – Gamma, tonight we will move towards the southeast and identify Delta. Also known as Ruchbah, this long-term and very slight variable star is about 45 light years away, but we are going to use it as our marker as we head just one degree northeast and discover the M103. As the last object in the original Messier catalog, the M103 (NGC581) was actually credited to Mechain in 1781. Easily spotted in binoculars and small scopes this rich open cluster is around magnitude 7, making it a prime study object. At about 8000 light years away and spanning approximately 15 light years, the M103 offers up superb views in a variety of magnitudes and colors, with a notable red in the south and a pleasing yellow and blue double to the northwest.

Telescopes and larger binoculars viewers are encouraged to move about a degree and half east of M103 to view a small and challenging chain of open clusters, the NGC654, NGC663 and NGC659! Surprisingly larger than the M103, NGC663 is a lovely fan-shaped concentration of stars with about 15 or so members that resolve easily to smaller aperture. For the telescope, head north for NGC654, (difficult, but not impossible to a 114mm scope) who has a bright star on its’ southern border. South of NGC663 is the NGC659 which is definitely a challenge for small scopes, but its presence will be revealed just northeast of two conspicuous stars in the field of view.

Wednesday, December 1 – What better way to start a new month than to get up early to see four planets and the Moon?! Just before dawn, the waning gibbous Moon will appear in the sky just above Saturn with the Gemini “Twins”, Castor and Pollux, to the west. Below and to the east of bright Luna is the mighty Jupiter, and you will find Venus and Mars slow dancing together near the horizon. What a fine show!

While Cassiopeia is still fresh in our minds, let’s return again tonight for some additional studies. Starting with Delta, let’s hop to the northeast corner of our “flattened W” and identify 520 light year distant Epsilon. For larger telescopes only, it will be a challenge to find 12″ diameter, magnitude 13.5 planetary nebula I.1747 in the same field with magnitude 3.3 Epsilon!

Using both Delta and Epsilon as our “guide stars” let’s draw an imaginary line between the pair extending from southwest to northeast and continue the same distance until you stop at visible Iota. Now go to the eyepiece! As a quadruple system, Iota will require a telescope and a night of steady seeing to split its three visible components. Approximately 160 light years away, this challenging system will show little or no color to smaller telescopes other than white, but to large aperture, the primary may appear slightly yellow and the companion stars a faint blue. At high magnification, the 8.2 magnitude “C” star will easily break away from the 4.5 primary 7.2″ to the east/southeast, but look closely at that primary.. hugging in very close (2.3″) to the west/southwest and looking like a “bump” on its side is the B star!

Dropping back to the lowest of powers, place Iota to the southwest edge of the eyepiece, it’s time to study two incredibly interesting stars that should appear in the same field of view to northeast. When both of these stars are at their maximum, they are easily the brightest of stars in the field. Their names are SU (southernmost) and RZ (northernmost) Cassiopeiae and both are unique! SU is a pulsing Cepheid variable located about 1000 light years away and will show a distinctive red coloration. RZ is a rapidly eclipsing binary that can change from magnitude 6.4 to magnitude 7.8 in less than two hours. Wow!

Thursday, December 2 – Once again utilizing early darkness, let’s go back to Cassiopeia. Remembering Alpha’s position as the westernmost star, go there with your finder scope or binoculars and locate bright Sigma and Rho (who both have a dimmer companion) and will appear to the southwest. It is between these two stars that you will find the NGC7789.

Absolutely one of the finest of rich galactic opens bordering on a loose globular, the NGC7789 has a population of about 1000 stars and spans a mind-boggling 40 light years. At well over a billion years old, the stars in this 5000 light year distant galactic cluster have already evolved into red-giants or super-giants. Discovered by Caroline Herschel in the 18th century, this huge cloud of stars has an average magnitude of 10, making it a great large binocular object, superb small telescope target, and a total fantasy of resolution for larger instruments.

Friday, December 3 – Tonight we will haunt Cassiopeia one last time – for the seasoned observer. Our first challenge of the evening will be to return to Gamma where we will locate two patches of nebulosity in the same field of view. The IC59 and IC63 are challenging because of the bright influence of the star, but by moving the star to the edge of the field of view you may be able to locate these two splendid small nebulae. If you do not have success with this pair, why not move on to Alpha? About one and a half degrees due east you will find a small collection of finder scope stars that mark the area of NGC281. This distinctive cloud of stars and ghostly nebula make this NGC object a fine challenge!

The last we will study will be two small elliptical galaxies that are achievable in mid-sized scopes. Locate Omicron Cassiopeiae about 7 degrees north of the M31 and discover a same field of view galactic pair that is associated with the Andromeda group, NGC185 and NGC147.

The constellation of Cassiopeia contains many, many more fine star clusters, nebulae and even more galaxies. For the casual observer, simply tracing over the rich star fields with binoculars is a true pleasure, for there are many bright asterisms best enjoyed at low power. Scopists will return to “rock with the Queen” year after year for its many challenging treasures. Enjoy it tonight!

Saturday, December 4 – It’s a comet hunter’s night… Are you ready? Then let’s be glad we have several hours until the Moon rises tonight so we have an opportunity to locate and view these fine comets!

If you were able to spot NGC654 and NGC659, earlier in the week, then you’ve got what it takes to find C/2004 Q1 (Tucker)! Holding an estimated magnitude 10.5, it is possible to see this comet with large binoculars and small telescopes. You will find Comet Tucker cruising through Andromeda just a bit southwest of M31.

Before Southern Hemisphere viewers begin to feel left out, why don’t we try chasing a comet tonight viewable to both of us? Comet 78P/Gehrels has an estimated magnitude of 10.7, putting it within range of most large binoculars and small telescopes. You will find it at the corner southern corner of the Aries/Taurus border, but it will be moving through Aries on this date and nearer to the border of Cetus and not too far from Lambda.

Next up is a comet suitable for mid-size to large aperture telescopes. Comet 29P/Schwassmann-Wachman will be at an estimated magnitude 12 but is beginning to fade. At this time you may be able to see about 55″ of coma! The hunting directions for 29/P show that it’s located on the Pegasus/Pices border and roughly halfway between 80 Pegasus and 26 Pices.

Northern viewers? Break out the big muscle for C/2001 Q4 (NEAT). At an estimated magnitude 12, it can be found in Draco buzzing along just south of Psi and a bit north of Omega. While you’re there, head on south to Iota and see if you can locate C/2003 T4 (LINEAR). At a rough magnitude of 12.5, T4 will sport a slight coma of 1.7″ and is moving west just slightly south of Iota.

How about one more? Then let’s go for 32P/Comas Sola. With an estimated magnitude of 12 with a slight coma of 1.1′, 39P has now moved into Aries and can be found just slightly northwest of Mu Cetii. Talk about some great challenges… I’ll race you there!

Sunday, December 5 – Although no one likes to get up early in the morning, you might find the trip quite worth it to see Mars and Venus together in the pre-dawn skies. The fat and gibbous Venus will make a splendid contrast with tiny, dusty red Mars as they stand together in the skies at just slightly more than one degree apart.

(We’re a little “uncertain”, but we do believe Werner Heisenberg was born on this day in 1901.)

Until next week? Keep looking up and enjoying the wonders of the Cosmos! Wishing you clear skies and light speed… ~Tammy Plotner

November 30, 2004March 24, 2012 by Fraser Cain

Why Eros Has So Few Craters

Image credit: NASA/JPL
University of Arizona scientists have discovered why Eros, the largest near-Earth asteroid, has so few small craters.

When the Near Earth Asteroid Rendezvous (NEAR) mission orbited Eros from February 2000 to February 2001, it revealed an asteroid covered with regolith — a loose layer of rocks, gravel and dust — and embedded with numerous large boulders. The spacecraft also found places where the regolith apparently had slumped, or flowed downhill, exposing fresh surface underneath.

But what NEAR didn’t find were the many small craters that scientists expected would pock Eros’ landscape.

“Either the craters were being erased by something or there are fewer small asteroids than we thought,” James E. Richardson Jr. of UA’s planetary sciences department said.

Richardson concludes from modeling studies that seismic shaking has obliterated about 90 percent of the asteroid’s small impact craters, those less than 100 meters in diameter, or roughly the length of a football field. The seismic vibrations result when Eros collides with space debris.

Richardson, Regents’ Professor H. Jay Melosh and Professor Richard Greenberg, all with UA’s Lunar and Planetary Laboratory, report the analysis in the Nov. 26 issue of Science.

“Eros is only about the size of Lake Tahoe — 20 miles (33 kilometers) long by 8 miles (13 kilometers) wide,” Richardson said. “So it has a very small volume and a very low gravity. When a one-to-two-meter or larger object hits Eros, the impact will set off global seismic vibrations. Our analysis shows how these vibrations easily destabilize regolith overlaying the surface.”

A rock-and-dust layer creeps, rather than crashes, down shaking slopes because of Eros’ weak gravity. The regolith not only slides down horizontally, but also is launched ballistically from the surface and ‘hops’ downslope. Very slowly, over time, impact craters fill up and disappear, Richardson said.

If Eros were still in the main asteroid belt between Mars and Jupiter, a 200-meter crater would fill in about 30 million years. Because Eros is now outside the asteroid belt, that process takes a thousand times longer, he added.

Richardson’s research results match the NEAR spacecraft evidence. Instead of the expected 400 craters as small as 20 meters (about 70 feet) per square kilometer (three-fifths mile) on Eros’ surface, there are on average only about 40 such craters.

The modeling analysis also validates what scientists suspect of Eros’ internal structure.

“The NEAR mission showed Eros to most likely be a fractured monolith, a body that used to be one competent piece of material,” Richardson said. “But Eros has been fractured throughout by large impacts and is held together primarily by gravity. The evidence is seen in a series of grooves and ridges that run across the asteroid’s surface both globally and regionally.”

Large impacts fracture Eros to its core, but many smaller impacts fracture only the upper surface. This gradient of big fractures deep inside and numerous small fractures near the surface is analogous to fractures in the upper lunar crust, Richardson said. “And we understand the lunar crust — we’ve been there. We’ve put seismometers on the moon. We understand how seismic energy propagates through this kind of structure.”

The UA scientists’ analysis of how impact-induced seismic shaking has modified Eros’ surface has a couple of other important implications.

“If we eventually do send spacecraft to mine resources among the near-Earth asteroids or to deflect an asteroid from a potential collision with the Earth, knowing internal asteroid structure will help address some of the strategies we’ll need to use. In the nearer future, sample return missions will encounter successively less porous, more cohesive regolith as they dig farther down into asteroids like Eros, which has been compacted by seismic shaking,” Richardson noted.

“And it also tells us about the small asteroid environment that we’ll encounter when we do send a spacecraft out into the main asteroid belt, where Eros spent most of its lifetime. We know the small asteroids — those between the size of a beachball and a football stadium — are out there. It’s just that their ‘signature’ on asteroids such as Eros is being erased,” Richardson said.

This finding is important because the cratering record on large asteroids provides direct evidence for the size and population of small main-belt asteroids. Earth-based telescopic surveys have catalogued few main-belt asteroids that small. So scientists have to base population estimates for these objects primarily on visible cratering records and asteroid collisional history modeling, Richardson said.

Original Source: UA News Release

November 30, 2004June 3, 2013 by Fraser Cain

Astronauts Move Soyuz on Station

Image credit: NASA
The Expedition 10 crewmembers are back inside the International Space Station after taking a short ride this morning. They flew their Soyuz spacecraft from one docking port to another to clear the way for two spacewalks next year.

Having configured Station systems for autonomous operation, Expedition 10 Flight Engineer and Soyuz Commander Salizhan Sharipov and Expedition 10 Commander Leroy Chiao undocked the Soyuz from the Station’s Pirs Docking Compartment at 4:32 a.m. EST, as they flew 225 miles over the southern Atlantic Ocean.

Sharipov, seated in the center seat of the Soyuz descent module compartment, and Chiao seated to his left, backed the capsule away from the Station approximately 98 feet. They flew the Soyuz laterally along the Station approximately 45 feet before rotating the craft 135 degrees to align it with the Earth-facing docking port on the adjacent Zarya module. The vehicle was held in position for eight minutes of station-keeping, ensuring correct alignment of docking mechanisms, before the crew began the final approach toward the Station.

Docking was at 4:53 a.m. EST, as the Soyuz and the Station passed over western Asia. Within minutes, hooks and latches engaged between the Soyuz and Zarya firmly linking the return vehicle and the Station. After a series of leak checks, the crew reentered the Station at 6:54 a.m. EST, and they began reconfiguring Station systems for normal operations.

Repositioning of the Soyuz cleared Pirs, which also serves as an airlock, for a pair of spacewalks by Chiao and Sharipov planned for early next year.

Information about crew activities on the Space Station, future launch dates and Station sighting opportunities from Earth, is available on the Internet at: http://spaceflight.nasa.gov/

Details about Station science operations are available on the Internet from NASA’s Marshall Space Flight Center, Huntsville, Ala., Payload Operations Center at: http://scipoc.msfc.nasa.gov/

For information about NASA and other agency missions, visit: http://www.nasa.gov

Original Source: NASA News Release

November 30, 2004March 24, 2012 by Fraser Cain

Portrait of Mimas in Saturn’s Rings

In a splendid portrait created by light and gravity, Saturn’s lonely moon Mimas is seen against the cool, blue-streaked backdrop of Saturn’s northern hemisphere. Delicate shadows cast by the rings arc gracefully across the planet, fading into darkness on Saturn’s night side.

The part of the atmosphere seen here appears darker and more bluish than the warm brown and gold hues seen in Cassini images of the southern hemisphere, due to preferential scattering of blue wavelengths by the cloud-free upper atmosphere.

The bright blue swath near Mimas (398 kilometers, or 247 miles across) is created by sunlight passing through the Cassini division (4,800 kilometers, or 2,980 miles wide). The rightmost part of this distinctive feature is slightly overexposed and therefore bright white in this image. Shadows of several thin ringlets within the division can be seen here as well. The dark band that stretches across the center of the image is the shadow of Saturn’s B ring, the densest of the main rings. Part of the actual Cassini division appears at the bottom, along with the A ring and the narrow, outer F ring. The A ring is transparent enough that, from this viewing angle, the atmosphere and threadlike shadows cast by the inner C ring are visible through it.

Images taken with red, green and blue filters were combined to create this color view. The images were obtained with the Cassini spacecraft narrow angle camera on Nov. 7, 2004, at a distance of 3.7 million kilometers (2.3 million miles) from Saturn. The image scale is 22 kilometers (14 miles) per pixel.

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.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org .

Original Source: NASA/JPL News Release

November 25, 2004March 24, 2012 by Fraser Cain

Future Robots May “Hop” Across Mars

Image credit: Pioneer Astro
Part lander, part aircraft, the gashopper (no, not grasshopper) is a unique concept being considered by NASA for future robotic exploration of Mars. Unlike landers, such as the Viking spacecraft, Beagle 2, or the upcoming Phoenix lander which can only examine a few square metres of ground, the gashopper could land, perform scientific analysis and launch itself back into the air to fly hundreds of kilometres to a new location.

The gashopper would get its electricity from a large set of solar panels built on top of its wings. It would use this electricity to retrieve carbon dioxide from the Martian atmosphere, and then store it as a liquid inside the aircraft. When enough gas was stored up to make a flight, it would heat up a hot bed of pellets and then pass the CO2 through it. Now hot, the gas would act as a propellant, and allow the gashopper to lift off vertically from the surface of Mars. Once airborne, it could then fire more gas out a rear thruster and begin flying as an airplane, using its large wings for lift and maneuverability. When it was ready to land, the aircraft could slow its airspeed, and then touch down gently as a vertical lander.

The proposal comes from the mind of Robert Zubrin, author of The Case for Mars, President of the Mars Society, and the President of Pioneer Astronautics. It’s one of 219 research projects selected by NASA for Small Business Research and Development contract awards.

Zubrin sees the gashopper not only as a technology for exploring Mars, but as a proof of concept for many engineering challenges that NASA will have to overcome in future missions, both robotic and human. “If we’re going to do a sample return mission, we’ll want to know how to make propellant for the return journey,” explains Zubrin, “and the gashopper will also let us test many liftoffs and landings with hazard avoidance in all kinds of terrain.

“The gashopper will be using native carbon dioxide for fuel, so it won’t contaminate the soil with hydrocarbons,” continues Zubrin. This is important, because spacecraft from Earth using hydrocarbons for fuel could contaminate the landing site with chemicals that could confuse the search for life. “Once the gashopper gets moving, it’ll find a pristine Martian surface to explore.”

The simplest gashopper could actually be quite light, as little as 50 kg (110 pounds). Compare this to the current Mars Exploration Rovers, which both weigh in at 185 kg (380 pounds). Tack on some more weight, and the gashopper could carry a few mini-rovers, like the tiny Sojourner that visited Mars as part of the Pathfinder mission. These could be targeted at the most interesting features based on the gashopper’s aerial reconnaissance of the area.

Image credit: Pioneer Astro
Another advantage of the gashopper is that is could completely ignore terrain. When NASA selected the landing sites for its Mars landers, it purposefully chose locations that were relatively flat, so the rovers could drive at a useful speed. The gashopper could land at the edge of a deep chasm, examine the area, jump down to the bottom and get back out again. It would give scientists unprecedented range and flexibility when searching for evidence of past water or life on Mars.

Of course, there’s a catch. The limiting feature of the gashopper is the electricity required to pressurize and heat the carbon dioxide propellant. This process consumes a lot of power, and the gashopper would need more than a month using its solar cells to refuel and recharge its batteries before it could take off again.

To generate more electricity, NASA could consider using a Radioisotope Thermal Generator, similar to those carried by Cassini, the Viking landers, or the upcoming Mars Science Laboratory (due for launch in 2009). With a more powerful electrical system, the gashopper could lift off every few days, and essentially be able to roam the entire planet of Mars.

Zubrin’s company, Pioneer Astronautics, has already done a significant amount of testing and research for the concept, and they developed a prototype ballistic gashopper for NASA’s Jet Propulsion Lab in 2000. The engine worked well in the lab, and they were able to get a remote-controlled vehicle with a mass of 50 kg to fly in a simulated Martian gravity (using a helium balloon to provide stability).

Instead of sitting on one spot, or slowly crawling across the surface of Mars, future robotic explorers to visit the Red Planet may take to the skies and soar. Well… hop, anyway.

Written by Fraser Cain

November 25, 2004March 24, 2012 by Fraser Cain

Ingredients are There to Make Rocky Planets

One of the currently hottest astrophysical topics – the hunt for Earth-like planets around other stars – has just received an important impetus from new spectral observations with the MIDI instrument at the ESO VLT Interferometer (VLTI).

An international team of astronomers [2] has obtained unique infrared spectra of the dust in the innermost regions of the proto-planetary discs around three young stars – now in a state possibly very similar to that of our solar system in the making, some 4,500 million years ago.

Reporting in this week’s issue of the science journal Nature, and thanks to the unequalled, sharp and penetrating view of interferometry, they show that in all three, the right ingredients are present in the right place to start formation of rocky planets at these stars.

“Sand” in the inner regions of stellar discs
The Sun was born about 4,500 million years ago from a cold and massive cloud of interstellar gas and dust that collapsed under its own gravitational pull. A dusty disc was present around the young star, in which the Earth and other planets, as well as comets and asteroids were later formed.

This epoch is long gone, but we may still witness that same process by observing the infrared emission from very young stars and the dusty protoplanetary discs around them. So far, however, the available instrumentation did not allow a study of the distribution of the different components of the dust in such discs; even the closest known are too far away for the best single telescopes to resolve them. But now, as Francesco Paresce, Project Scientist for the VLT Interferometer and a member of the team from ESO explains, “With the VLTI we can combine the light from two well-separated large telescopes to obtain unprecedented angular resolution. This has allowed us, for the first time, to peer directly into the innermost region of the discs around some nearby young stars, right in the place where we expect planets like our Earth are forming or will soon form”.

Specifically, new interferometric observations of three young stars by an international team [2], using the combined power of two 8.2-m VLT telescopes a hundred metres apart, has achieved sufficient image sharpness (about 0.02 arcsec) to measure the infrared emission from the inner region of the discs around three stars (corresponding approximately to the size of the Earth’s orbit around the Sun) and the emission from the outer part of those discs. The corresponding infrared spectra have provided crucial information about the chemical composition of the dust in the discs and also about the average grain size.

These trailblazing observations show that the inner part of the discs is very rich in crystalline silicate grains (“sand”) with an average diameter of about 0.001 mm. They are formed by coagulation of much smaller, amorphous dust grains that were omnipresent in the interstellar cloud that gave birth to the stars and their discs.

Model calculations show that crystalline grains should be abundantly present in the inner part of the disc at the time of formation of the Earth. In fact, the meteorites in our own solar system are mainly composed of this kind of silicate.

Dutch astronomer Rens Waters, a member of the team from the Astronomical Institute of University of Amsterdam, is enthusiastic: “With all the ingredients in place and the formation of larger grains from dust already started, the formation of bigger and bigger chunks of stone and, finally, Earth-like planets from these discs is almost unavoidable!”

Transforming the grains
It has been known for some time that most of the dust in discs around newborn stars is made up of silicates. In the natal cloud this dust is amorphous, i.e. the atoms and molecules that make up a dust grain are put together in a chaotic way, and the grains are fluffy and very small, typically about 0.0001 mm in size. However, near the young star where the temperature and density are highest, the dust particles in the circumstellar disc tend to stick together so that the grains become larger. Moreover, the dust is heated by stellar radiation and this causes the molecules in the grains to re-arrange themselves in geometric (crystalline) patterns.

Accordingly, the dust in the disc regions that are closest to the star is soon transformed from “pristine” (small and amorphous) to “processed” (larger and crystalline) grains.

Spectral observations of silicate grains in the mid-infrared wavelength region (around 10 ?m) will tell whether they are “pristine” or “processed”. Earlier observations of discs around young stars have shown a mixture of pristine and processed material to be present, but it was so far impossible to tell where the different grains resided in the disc.

Thanks to a hundred-fold increase in angular resolution with the VLTI and the highly sensitive MIDI instrument, detailed infrared spectra of the various regions of the protoplanetary discs around three newborn stars, only a few million years old, now show that the dust close to the star is much more processed than the dust in the outer disc regions. In two stars (HD 144432 and HD 163296) the dust in the inner disc is fairly processed whereas the dust in the outer disc is nearly pristine. In the third star (HD 142527) the dust is processed in the entire disc. In the central region of this disc, it is extremely processed, consistent with completely crystalline dust.

An important conclusion from the VLTI observations is therefore that the building blocks for Earth-like planets are present in circumstellar discs from the very start. This is of great importance as it indicates that planets of the terrestrial (rocky) type like the Earth are most probably quite common in planetary systems, also outside the solar system.

The pristine comets
The present observations also have implications for the study of comets. Some – perhaps all – comets in the solar system do contain both pristine (amorphous) and processed (crystalline) dust. Comets were definitely formed at large distances from the Sun, in the outer regions of the solar system where it has always been very cold. It is therefore not clear how processed dust grains may end up in comets.

In one theory, processed dust is transported outwards from the young Sun by turbulence in the rather dense circumsolar disc. Other theories claim that the processed dust in comets was produced locally in the cold regions over a much longer time, perhaps by shock waves or lightning bolts in the disc, or by frequent collisions between bigger fragments.

The present team of astronomers now conclude that the first theory is the most likely explanation for the presence of processed dust in comets. This also implies that the long-period comets that sometimes visit us from the outer reaches of our solar system are truly pristine bodies, dating back to an era when the Earth and the other planets had not yet been formed.

Studies of such comets, especially when performed in-situ, will therefore provide direct access to the original material from which the solar system was formed.

More information
The results reported in this ESO PR are presented in more detail in a research paper “The building blocks of planets within the “terrestrial” region of protoplanetary disks”, by Roy van Boekel and co-authors (Nature, November 25, 2004). The observations were made in the course of ESO’s early science demonstration programme.

Notes

[1]: This ESO press release is issued in collaboration with the Astronomical Institute of the University of Amsterdam, The Netherlands (NOVA PR) and the Max-Planck-Institut f?r Astronomie (Heidelberg, Germany (MPG PR).

[2]: The team consists of Roy van Boekel, Michiel Min, Rens Waters, Carsten Dominik and Alex de Koter (Astronomical Institute, University of Amsterdam, The Netherlands), Christoph Leinert, Olivier Chesneau, Uwe Graser, Thomas Henning, Rainer K?hler and Frank Przygodda (Max-Planck-Institut f?r Astronomie, Heidelberg, Germany), Andrea Richichi, Sebastien Morel, Francesco Paresce, Markus Sch?ller and Markus Wittkowski (ESO), Walter Jaffe and Jeroen de Jong (Leiden Observatory, The Netherlands), Anne Dutrey and Fabien Malbet (Observatoire de Bordeaux, France), Bruno Lopez (Observatoire de la Cote d’Azur, Nice, France), Guy Perrin (LESIA, Observatoire de Paris, France) and Thomas Preibisch (Max-Planck-Institut f?r Radioastronomie, Bonn, Germany).

[3]: The MIDI instrument is the result of a collaboration between German, Dutch and French institutes. See ESO PR 17/03 and ESO PR 25/02 for more information.

Original Source: ESO News Release

November 25, 2004March 24, 2012 by Fraser Cain

Detailed View of Dione

A gorgeous Dione poses for Cassini, with shadowed craters and bright, wispy streaks first observed by the Voyager spacecraft 24 years ago. The wispy areas will be imaged at higher resolution in mid-December 2004. Subtle variations in brightness across the surface of this moon are visible here as well. Dione’s diameter is 1,118 kilometers, (695 miles).

The image shows primarily the trailing hemisphere of Dione, which is the side opposite the moon’s direction of motion in its orbit. The image has been rotated so that north is up.

The image was taken in visible light with the Cassini spacecraft narrow angle camera on Oct. 27, 2004, at a distance of about 1.2 million kilometers (746,000 miles) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 28 degrees. The image scale is 3.5 kilometers (2.2 miles) per pixel.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org .

Original Source: NASA/JPL News Release

November 24, 2004June 3, 2013 by Fraser Cain

Next Station Crew Named

Image credit: NASA
Veteran NASA astronaut John Phillips and seasoned Russian Cosmonaut Sergei Krikalev are the next crew of the International Space Station. Their six-month mission is set for launch in April 2005.

Phillips and Krikalev are the eleventh crew for the orbiting research complex. Krikalev will serve as Station Commander, and Phillips is Flight Engineer and NASA International Space Station Science Officer. Designated Expedition 11, they will be on board the Station when the Space Shuttle makes its first Return to Flight mission. The Shuttle is scheduled to dock with the Space Station in May 2005.

Both crewmembers have previously been to the International Space Station. Phillips flew to the Station aboard the Shuttle on the STS-100 mission in 2001. During that 12-day mission, the crew installed the Canadarm2 Station robotic arm.

In 2000, Krikalev was a member of Expedition 1, the first International Space Station crew. Expedition 11 will be his sixth space flight and fourth long-duration mission. He has the most flights for any Russian cosmonaut.

Selected in 1985, Krikalev flew aboard the Mir Space Station in 1988-89, 1991-92 and the International Space Station in 2000-01. He flew aboard the Shuttle on the first joint U.S.-Russian mission, STS-60 in 1994, and on the first International Space Station assembly mission, STS-88 in 1998. Krikalev has accumulated 625 days in space. At the completion of a six-month stay aboard the Station on Expedition 11, Krikalev will have spent more time in space than any other person.

The Expedition 11 backup crewmembers are astronaut Daniel Tani and cosmonaut Mikhail Tyurin.

For more information about NASA astronauts, Russian cosmonauts, and the Space Station, on the Web, visit:

http://spaceflight.nasa.gov

For information about NASA missions and projects, visit: http://www.nasa.gov

Original Source: NASA News Release