This graph of data from NASA's Spitzer Space Telescope demonstrates that the dust around a nearby star called HD 69830 (upper line) has a very similar composition to that of Comet Hale-Bopp. Spitzer spotted large amounts of this dust in the inner portion of the HD 69830 system. The bumps and dips seen in these data, or spectra, represent the "fingerprints" of various minerals. Spectra are created when an instrument called a spectrograph spreads light out into its basic parts, like a prism turning sunlight into a rainbow. These particular spectra reveal the presence of the silicate mineral called olivine, and more specifically, a type of olivine called forsterite, which is pictured in the inset box. Forsterite is a bright-green gem found on Earth, on the "Green Sand Beach" of Hawaii among other places; and in space, in comets and asteroids. Because the dust around HD 69830 has a very similar make-up to that of Comet Hale-Bopp, astronomers speculate that it might be coming from a giant comet nearly the size of Pluto. Such a comet may have been knocked into the inner solar system of HD 69830, where it is now leaving in its wake a trail of evaporated dust. Nonetheless, astronomers say the odds that Spitzer has caught a "super-comet" spiraling in toward its star -- an unusual and relatively short-lived event -- are slim. Instead, they favor the theory that the observed dust is actually the result of asteroids banging together in a massive asteroid belt. The data of HD 69830's dust were taken by Spitzer's infrared spectrograph. The data of Comet Hale-Bopp were taken by the European Space Agency's Infrared Observatory Satellite. The picture of forsterite comes courtesy of Dr. George Rossman, California Institute of Technology, Pasadena.

This artist's conception shows the relative size of a hypothetical brown dwarf-planetary system (below) compared to our own solar system. A brown dwarf is a cool or "failed" star, which lacks the mass to ignite and shine like our Sun. NASA's Spitzer Space Telescope set its infrared eyes on an extraordinarily low-mass brown dwarf called OTS 44 and found a swirling disk of planet-building dust. At only 15 times the mass of Jupiter, OTS 44 is the smallest known brown dwarf to host a planet-forming, or protoplanetary, disk. Astronomers believe that this unusual system will eventually spawn planets. If so, they speculate that OTS 44's disk has enough mass to make one small gas giant and a few Earth-sized rocky planets. Examples of these possible planets are depicted at the bottom of this picture, circling a low-mass brown dwarf. Above, the bodies of our own solar system have been drawn to the same scale. In each system, the terrestrial planets have been enlarged and the distances between the planets and their parent bodies have been scaled down for easier viewing.

This artist's concept shows a brown dwarf surrounded by a swirling disk of planet-building dust. NASA's Spitzer Space Telescope spotted such a disk around a surprisingly low-mass brown dwarf, or "failed star." The brown dwarf, called OTS 44, is only 15 times the size of Jupiter, making it the smallest brown dwarf known to host a planet-forming, or protoplanetary disk. Astronomers believe that this unusual system will eventually spawn planets. If so, they speculate that OTS 44's disk has enough mass to make one small gas giant and a few Earth-sized rocky planets. OTS 44 is about 2 million years old. At this relatively young age, brown dwarfs are warm and appear reddish in color. With age, they grow cooler and darker.

This image shows a close-up infrared view from NASA's Spitzer Space Telescope of the glowing Trifid Nebula, a giant star-forming cloud of gas and dust located 5,400 light-years away in the constellation Sagittarius.Data of this same region from the Institute for Radioastronomy millimeter telescope in Spain revealed four dense knots, or cores, of dust, which are "incubators" for embryonic stars. Astronomers thought these cores were not yet ripe for stars, until Spitzer spotted the warmth of rapidly growing massive embryos tucked inside.These embryos are revealed in the false-color Spitzer picture, taken by the telescope's infrared array camera (IRAC). Spitzer found clusters of embryos in two of the cores and only single embryos in the other two. This is one of the first times that multiple embryos have been observed in individual cores at this early stage of stellar development. In this false-color image, light from 3.6 microns is red, 4.5 microns is green, 5.8 microns is orange and 8 microns is red.

The glowing Trifid Nebula is revealed in an infrared view from NASA's Spitzer Space Telescope. The Trifid Nebula is a giant star-forming cloud of gas and dust located 5,400 light-years away in the constellation Sagittarius.The false-color Spitzer image reveals a different side of the Trifid Nebula. Where dark lanes of dust are visible trisecting the nebula in a visible-light picture, bright regions of star-forming activity are seen in the Spitzer picture. All together, Spitzer uncovered 30 massive embryonic stars and 120 smaller newborn stars throughout the Trifid Nebula, in both its dark lanes and luminous clouds. These stars are visible in the Spitzer image, mainly as yellow or red spots. Embryonic stars are developing stars about to burst into existence. Ten of the 30 massive embryos discovered by Spitzer were found in four dark cores, or stellar "incubators," where stars are born. Astronomers using data from the Institute of Radioastronomy millimeter telescope in Spain had previously identified these cores but thought they were not quite ripe for stars. Spitzer's highly sensitive infrared eyes were able to penetrate all four cores to reveal rapidly growing embryos.Astronomers can actually count the individual embryos tucked inside the cores by looking closely at this Spitzer image taken by its infrared array camera (IRAC). This instrument has the highest spatial resolution of Spitzer's imaging cameras. The embryos are thought to have been triggered by a massive "type O" star, which can be seen as a white spot at the center of the nebula. Type O stars are the most massive stars, ending their brief lives in explosive supernovas. The small newborn stars probably arose at the same time as the O star, and from the same original cloud of gas and dust.This Spitzer mosaic image uses data from IRAC showing light of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8.0 microns (red).

NASA's Spitzer Space Telescope recently captured these images of the star Vega, located 25 light years away in the constellation Lyra. Spitzer was able to detect the heat radiation from the cloud of dust around the star and found that the debris disk is much larger than previously thought.This side-by-side comparison, taken by Spitzer's multiband imaging photometer, shows the warm infrared glows from dust particles orbiting the star at wavelengths of 24 microns (on the left in blue) and 70 microns (on the right in red).Both images show a very large, circular and smooth debris disk. The disk radius extends to at least 815 astronomical units. (One astronomical unit is the distance from Earth to the Sun, which is 150-million kilometers or 93-million miles).Scientists compared the surface brightness of the disk in the infrared wavelengths to determine the temperature distribution of the disk and then refer the corresponding particle size in the disk. Most of the particles in the disk are only a few microns in size, or 100 times smaller than a grain of Earth sand.These fine dust particles originate from collisions of embryonic planets near the star at a radius of approximately 90 astronomical units, and are then blown away by Vega's intense radiation. The mass and short lifetime of these small particles indicate that the disk detected by Spitzer is the aftermath of a large and relatively recent collision, involving bodies perhaps as big as the planet Pluto.The images are 3 arcminutes on each side. North is oriented upward and east is to the left.

This is an artist's impression of the view from the vicinity of a hypothetical terrestrial planet and moon orbiting the red dwarf star AU Microscopii. The relatively newborn 12 million year-old star is surrounded by a very dusty disk of debris from the collision of comets, asteroids, and planetissimals swirling around the young star. Though no planets have been discovered around the star, the disk is strong circumstantial evidence for planets. Not only is it dusty, but also it is warped, possibly by the pull of one or more planets. In this view the glow of starlight reflecting off the disk creates a broad lane across the sky because the planet is in the disk's plane. Similarly, from Earth we see light reflected from interplanetary dust as the zodiacal light (though it is 1/10,000th as dusty as the AU Microcsopii disk). The star AU Microscopiii is 32 light-years from Earth. From this distance, familiar constellations are still recognizable. In the background, the Beehive cluster in Cancer the Crab is seen. Our Sun appears as a bright star in Cancer.

This graph of data from NASA's Spitzer Space Telescope indicates that stars with known planets (blue) are more likely to have "debris disks" than stars without known planets (red).Debris disks are made up of dust and small rocky bodies, like comets. They are the leftover remnants of the planet-building process. Our solar system has a debris disk called the Kuiper Belt, which is filled primarily with comets. Until now, these disks had not been detected around any stars with known planets.Spitzer sampled 84 stars, 26 with and 58 without known planets. Of the 26 planet-bearing stars, six had disks; of the 58 stars without planets, six had disks. The presence of these debris disks was inferred from the amount of excess infrared light measured at a wavelength of 70 microns, relative to that emitted by the parent star. While most of the observed stars have a ratio near unity, indicating that the 70-micron light is coming from the star itself, several stars show a high degree of excess emission. It is these stars that are surrounded by Kuiper Belt-like debris disks.On the graph, stars with increasingly large disks are located farther to the right. The right side of the graph reveals that four out of the five stars with the highest 70-micron excess are known to have planets.

This is a false-color view of a planetary debris disk encircling the star HD 107146, a yellow dwarf star very similar to our Sun, though it is much younger (between 30 and 250 million years old, compared to the almost 5 billion years age of the Sun). The star is 88 light-years away from Earth. This is the only disk to have been imaged around a star so much like our own. The slight brightness on one side of the disk is due to the fact that small dust particles scatter more light when they are between Earth and the star, rather than behind the star. This suggests that the bright side is closer to us. The disk is redder than the star whose light it reflects, indicating that it contains grains one two-thousandth of a millimeter in size (about 100 times smaller than household dust). Our Sun is believed to have a ring of dust around it, lying just beyond the orbit of Neptune, although it is ten times narrower than the one around HD 107146. Our solar system also has between 1,000 and 10,000 times less dust. The size of the ring, its the thickness, and the amount of dust make it unlikely that HD 107146 will ever evolve into a system like our own. This is interesting, as it shows that the planetary systems around the same kind of stars may have very different evolutionary paths.

[LEFT: AU Microscopii] - A visible-light image of a debris disk around the red dwarf star AU Microscopii. Planets may be forming, or might already exist, within it. The disk glows in starlight reflected by tiny grains of dust created by the collisions of asteroids and comets. Because it is composed of the pulverized remnants of these objects, it is called a "debris disk." More than 40 billion miles across, it appears like a spindle of light because we view it nearly edge on (like looking at a dinner plate along its side). The star is about 12 million years old and is only 32 light-years from Earth. This makes its disk the closest yet seen in reflected starlight. It is also the first disk imaged around an M-type red dwarf, the most common type of star in the stellar neighborhood around the Sun. The Hubble Space Telescope images, taken with the Advanced Camera for Surveys (ACS) reveal that the disk has been cleared of dust within about a billion miles of the star (first indicated from infrared-light measurements). The ACS images confirm that the disk is warped and has small variations in dust density that, along with the central clearing, may be caused by the tugging of an unseen companion, perhaps a large planet. ACS shows that this is the only debris disk known that appears bluer than the star it surrounds. This may indicate that there are more small grains of dust, compared to large ones, than has been seen before in other such disks. Smaller grains scatter blue light better than red. The surplus of small grains may be due to the fact that the star is not bright enough to blow away these tiny particles. In brighter, hotter stars, the pressure from radiation can actually push small dust grains out of the disk and far out into space. [RIGHT: HD 107146] - This is a false-color view of a planetary debris disk encircling the star HD 107146, a yellow dwarf star very similar to our Sun, though it is much younger (between 30 and 250 million years old, compared to the almost 5 billion years age of the Sun). The star is 88 light-years away from Earth. This is the only disk to have been imaged around a star so much like our own. The slight brightness on one side of the disk is due to the fact that small dust particles scatter more light when they are between Earth and the star, rather than behind the star. This suggests that the bright side is closer to us. The disk is redder than the star whose light it reflects, indicating that it contains grains one two-thousandth of a millimeter in size (about 100 times smaller than household dust). Our Sun is believed to have a ring of dust around it, lying just beyond the orbit of Neptune, although it is ten times narrower than the one around HD 107146. Our solar system also has between 1,000 and 10,000 times less dust. The size of the ring, its the thickness, and the amount of dust make it unlikely that HD 107146 will ever evolve into a system like our own. This is interesting, as it shows that the planetary systems around the same kind of stars may have very different evolutionary paths.

This is a so-called scatter model based on the Hubble Space Telescope image of the planetary debris encircling the star AU Microscopii. Though the real disk is tilted nearly edge-on to Earth, this oblique view is from 30 degrees above the disk plane. This model clearly shows a central hole that may have been swept out by an unseen planet. Holes in the centers of young dusty disks are common among stars and are compelling circumstantial evidence for planets.

A visible-light image of a debris disk around the red dwarf star AU Microscopii. Planets may be forming, or might already exist, within it. The disk glows in starlight reflected by tiny grains of dust created by the collisions of asteroids and comets. Because it is composed of the pulverized remnants of these objects, it is called a "debris disk." More than 40 billion miles across, it appears like a spindle of light because we view it nearly edge on (like looking at a dinner plate along its side). The star is about 12 million years old and is only 32 light-years from Earth. This makes its disk the closest yet seen in reflected starlight. It is also the first disk imaged around an M-type red dwarf, the most common type of star in the stellar neighborhood around the Sun. The Hubble Space Telescope images, taken with the Advanced Camera for Surveys (ACS) reveal that the disk has been cleared of dust within about a billion miles of the star (first indicated from infrared-light measurements). The ACS images confirm that the disk is warped and has small variations in dust density that, along with the central clearing, may be caused by the tugging of an unseen companion, perhaps a large planet. ACS shows that this is the only debris disk known that appears bluer than the star it surrounds. This may indicate that there are more small grains of dust, compared to large ones, than has been seen before in other such disks. Smaller grains scatter blue light better than red. The surplus of small grains may be due to the fact that the star is not bright enough to blow away these tiny particles. In brighter, hotter stars, the pressure from radiation can actually push small dust grains out of the disk and far out into space.

NASA's Spitzer Space Telescope recently captured these infrared images of six older stars with known planets. The yellow, fuzzy blobs are stars circled by disks of dust, or "debris disks," like the one that surrounds our own Sun. Though astronomers had predicted that stars with planets would harbor debris disks, they could not detect such disks until now. Spitzer was able to sense these dusty disks via their warm infrared glows. Specifically, the presence of the disks was inferred from an excess amount of infrared emission relative to what is emitted from the parent star alone. The stars themselves are similar in age and temperature to our Sun. In astronomical terms, they are stellar main sequence stars, with spectral types of F, G, or K. These planet-bearing stars have a median age of four billion years. For reference, our Sun is classified as a G star, with an age of approximately five billion years. The disks surrounding these planetary systems are comprised of cool material, with temperatures less than 100 Kelvin (-173 degrees Celsius). They are10 times farther away from their parent stars than Earth is from the Sun, and are thought to be analogues of the comet-filled Kuiper Belt in our solar system. The contrast scale is the same for each image. The images are approximately 2 arcminutes on each side. North is oriented upward and east is to the left. The pictures were taken with the 70-micron filter of Spitzer's multiband imaging photometer. The telescope resolution at 70 microns is 17 arcseconds and there is no evidence for any emission extended beyond the telescope resolution.

The "Cores to Disks" Spitzer Legacy team is using the two infrared cameras on NASA's Spitzer Space Telescope to search dense regions of interstellar molecular clouds (known as "cores") for evidence of star formation. Part of the study targeted a group of objects with no known stars to study the properties of such regions before any stars have formed. The first of these "starless cores" to be examined held a surprise: a source of infrared light appeared where none was expected. The core is known as L1014, the 1,014th object in a list of dark, dusty "clouds" compiled by astronomer Beverly Lynds over 40 years ago. These have proved to be homes to a rich variety of molecules and are the birthplaces of stars and planets. The Spitzer image is a 3.6 micron (blue), 8.0 micron (green) and 24.0 micron (red) composite image. The light seen in the infrared image originates from very different sources. The bright yellow object at the center of the image is the object detected in the "starless core". The red ring surrounding the object is an artifact of the reduced spatial resolution of the telescope at 24 microns. At 3.6 microns the light comes mainly from the object at the heart of the core. At longer wavelengths, the light from the object becomes stronger, a signature that it is not a background star. Also in the longer wavelengths (8.0 to 24.0 microns), astronomers saw the glow from interstellar dust, glowing green to red in the Spitzer composite image. This dust consists mainly of a variety of carbon-based organic molecules known collectively as polycyclic aromatic hydrocarbons. The red color traces a cooler dust component. No previous observations showed any hint of a source in L1014. For example, the visible light image is from the Digital Sky Survey and is a B-, R-, and I-band composite image (wavelengths ranging from 0.4 to 0.7 microns). The dark cloud in the center of the image is the core, completely opaque in the visible due to obscuration by dust. The L1014 core lies in the direction of Cygnus. It is thought to be about 600 light years away, but the distance is somewhat uncertain. The results from this study are published by C. Young and the "Cores to Disks" team in the Astrophysical Journal.

Astronomers have made the first clear detection of a variety of ices -- water, ammonium, and carbon dioxide -- in the inner planet-forming region near a young star about 120 light years away. Such an observation is only possible by combining the unique sensitivity of NASA's Spitzer Space Telescope with the fortunate alignment of this particular system. Planet-forming discs are seen in a variety of orientations, ranging from edge-on (where the discs block the light of the star entirely) to face-on (where the disc is lost in the glare of the star). In this system, known to astronomers as CRBR 2422.8-3423, the disc lies at a unique angle. The light from the star just peeks out over the disc, like a distant sunrise, and contains clues about the disc material through which it has passed. These observations use Spitzer's infrared spectrograph which acts much like a prism, spreading light out into its component parts, or spectrum. Astronomers study this infrared rainbow, measuring how much light from the star reaches us at different wavelengths. From this they can determine the composition of the disc. Different ices in the disc each have their own unique infrared "colors" and will block the light in different parts of the star's spectrum. For example, the dip in the spectrum around 6 microns indicates the presence of water ice. The feature at 7 microns is caused by warmed ammonium ions and therefore must be close to the star, within the inner planet-forming region of the disc. This result has given astronomers a new tool in probing the inner workings of planet-forming discs. By looking for other young stars with discs lined up at just the right angle, they can learn more about the stuff that formed our own solar system almost 5 billion years ago.

In this artist's conception, we peer through the dark dust of L1014 to witness the birth of a star. NASA's Spitzer Space Telescope has detected a faint, warm object inside the apparently starless core of a small, dense molecular cloud. If, as astronomers suspect, there is a young star deep inside the dusty core, it would have a structure similar to this illustration.Dark dust from the cloud, attracted by the gravity of the newborn star, forms a disc as it spirals inward. Often, the hidden birth of a star is heralded by bipolar outflows, jets of material moving outward from the star's poles. Although astronomers do see a faint "fan-shaped nebulosity" where they might expect the jet to be, the existence of the jet has yet to be confirmed.

What does an extremely young planetary system look like? The answer depends on your point of view -- literally! Astronomers are very interested in the chemical composition of the inner regions of discs around young stars; after all, our own solar system formed from similar material. To probe the chemistry of different regions in the disc, you have to view the system at just the right angle.In nature, stars are randomly oriented on the sky, so even though astronomers may be looking at similar objects, the stars' angle of inclination makes them appear different. When looking at a young star system, if your line of sight looks directly down on the star, then the starlight swamps the fainter disc. If you look at the disc edge-on, thick dust in the outer disk blocks all the starlight, and again, you can't get any information about the chemistry of the disc close to the star.If, however, you hit the "sweet spot," as astronomers are calling it, light from the star just grazes the edge of the disc. In this case, the light passes through material in the disc, but is not completely absorbed by the thick dust. This allows astronomers to peer into the inner region of the disc, and sample its chemistry for the building blocks of planets and life.

RCW 108 is a region where stars are actively forming within the Milky Way galaxy about 4,000 light years from Earth. This is a complicated region that contains young star clusters, including one that is deeply embedded in a cloud of molecular hydrogen. By using data from different telescopes, astronomers determined that star birth in this region is being triggered by the effect of nearby, massive young stars. This image is a composite of X-ray data from NASA's Chandra X-ray Observatory (blue) and infrared emission detected by NASA's Spitzer Space Telescope (red and orange). More than 400 X-ray sources were identified in Chandra's observations of RCW 108. About 90 percent of these X-ray sources are thought to be part of the cluster and not stars that lie in the field-of-view either behind or in front of it. Many of the stars in RCW 108 are experiencing the violent flaring seen in other young star-forming regions such as the Orion nebula. Gas and dust blocks much of the X-rays from the juvenile stars located in the center of the image, explaining the relative dearth of Chandra sources in this part of the image. The Spitzer data show the location of the embedded star cluster, which appears as the bright knot of red and orange just to the left of the center of the image. Some stars from a larger cluster, known as NGC 6193, are also visible on the left side of the image. Astronomers think that the dense clouds within RCW 108 are in the process of being destroyed by intense radiation emanating from hot and massive stars in NGC 6193. Taken together, the Chandra and Spitzer data indicate that there are more massive star candidates than expected in several areas of this image. This suggests that pockets within RCW 108 underwent localized episodes of star formation. Scientists predict that this type of star formation is triggered by the effects of radiation from bright, massive stars such as those in NGC 6193. This radiation may cause the interior of gas clouds in RCW 108 to be compressed, leading to gravitational collapse and the formation of new stars.

This graph shows the extent of planetary debris discs around nearby stars of various ages, as measured by NASA's Spitzer Space Telescope. Disc brightness or size (vertical axis) is plotted against the age of the stars observed by Spitzer (horizontal axis). The data show that there can be huge amounts of debris from collisions between large asteroid-like bodies around young stars, up to ages of 100 to 200 million years. However, even around some of the youngest stars, there is no detectable debris, indicating that the collision rate shows a large range of properties from star to star. Planets are built up as a result of rocky objects smashing into each other and merging to make larger bodies. The violence of these collisions causes immense clouds of dust to escape and spread out into rings, or "debris discs." These discs are warmed by the star, which allows Spitzer to detect them with its infrared vision. As the graph shows, Spitzer has found that violent collisions persist for much longer than the 10 million years predicted by some theories. Properties of late phase debris discs (those around stars 100 to 200 million years old) suggests that single, catastrophic collisions may have produced nearly all the debris we see in them. Such events may be analogous to the creation of our Moon, which arose out of a huge collision between Earth and a smaller planet-like body.

This graph of data from NASA's Spitzer Space Telescope shows that an extraordinarily low-mass brown dwarf, or "failed star," is circled by a disk of planet-building dust. The brown dwarf, called OTS 44, is only 15 times the mass of Jupiter, making it the smallest known brown dwarf to host a planet-forming disk. Spitzer was able to see this unusual disk by measuring its infrared brightness. Whereas a brown dwarf without a disk (red dashed line) radiates infrared light at shorter wavelengths, a brown dwarf with a disk (orange line) gives off excess infrared light at longer wavelengths. This surplus light comes from the disk itself and is represented here as a yellow dotted line. Actual data points from observations of OTS 44 are indicated with orange dots. These data were acquired using Spitzer's infrared array camera.

In this artist's conception, a possible newfound planet spins through a clearing in a nearby star's dusty, planet-forming disc. This clearing was detected around the star CoKu Tau 4 by NASA's Spitzer Space Telescope. Astronomers believe that an orbiting massive body, like a planet, may have swept away the star's disc material, leaving a central hole.The possible planet is theorized to be at least as massive as Jupiter, and may have a similar appearance to what the giant planets in our own solar system looked like billions of years ago. A graceful ring, much like Saturn's, spins high above the planet's cloudy atmosphere. The ring is formed from countless small orbiting particles of dust and ice, leftovers from the initial gravitational collapse that formed the possible giant planet.If we were to visit a planet like this, we would have a very different view of the universe. The sky, instead of being the familiar dark expanse lit by distant stars, would be dominated by the thick disc of dust that fills this young planetary system. The view looking toward CoKu Tau 4 would be relatively clear, as the dust in the interior of the disc has fallen into the accreting star. A bright band would seem to surround the central star, caused by light scattered back by the dust in the disc. Looking away from CoKu Tau 4, the dusty disc would appear dark, blotting out light from all the stars in the sky except those which lie well above the plane of the disc.

Using sensitive instruments onboard NASA's Spitzer Space Telescope, scientists have seen the first building blocks of planets, and possibly future life, deep within dusty discs around young stars. The image shows spectra, obtained by Spitzer's infrared spectrograph, of two stars that are so young they are still embedded in protoplanetary discs. These thick discs of gas and dust are the leftover material from the formation of the stars themselves. The spectra are graphical representations of a celestial object's unique blend of light. Characteristic patterns, or fingerprints, within the spectra allow astronomers to identify the object's chemical composition. In both infrared spectra, the presence of important chemicals for the formation of new worlds can be seen clearly. The broad depression in the center of each spectrum signifies the presence of silicates, which are chemically similar to beach sand. In fact, a good match for the chemistry of these crystalline silicates may be the famous green beaches of Hawaii, which get their color from olivine crystals in the sand. The depth of the silicate absorption feature indicates that the dusty cocoon surrounding the embedded protostar is extremely thick. Other absorption dips are produced by water ice (blue), methanol ice (red), and carbon dioxide ice (green). The fact that water, methanol and carbon dioxide appear in solid form suggests that the material immediately surrounding the protostar is cold.

How can you tell if a star has a protoplanetary disk around it, when the disk is too small to image directly? Using the technique of spectroscopy, scientists can deduce the temperature and chemical composition of material around a star, even if they cannot see the disk itself. Spectroscopy involves spreading the light from a star into a spectrum (in visible light, we are familiar with white light being spread out into a rainbow when it passes through a prism), and then measuring exactly how much light is present in each wavelength. The top illustration represents the spectrum of a star with no circumstellar disk or other surrounding material. The distribution of light at any given wavelength follows a specific and well-known line, determined by the laws of physics and the temperature of the star. In the case of a star, most of the light is produced at shorter wavelengths (the left side of the diagram), due to the high temperature of the star's surface. Moving to the right-hand side of the diagram, the wavelengths increase to lower energies (indicating lower temperatures) and, the starlight drops off. In the second diagram, we see the spectrum of a star with a disk of dust and gas around it. The warm dust and gas disk around the star produces its own infrared light, which changes the shape of the spectrum. The circumstellar material is cooler than the surface of the star, so it emits most of its light at longer infrared wavelengths, closer to the right-hand side of the diagram. Now, there is an excess of infrared emission, which can not be coming from the star itself. The disk is revealed. Going a step further, in the third diagram we see the spectrum of a star with a circumstellar disk around it, but in this case, the inner part of the disk has been swept away, perhaps by the formation of a planet. The dust closest to the star was also the hottest, so its absence means that there is less emission from the disk at higher temperatures. The only dust producing infrared light is much cooler than the star, and radiates only at long wavelengths. This low temperature "bump" on the spectrum indicates a disk with a missing center, and may be the first clue that planets have formed inside the disk.

Using sensitive instruments onboard NASA's Spitzer Space Telescope, scientists have seen the first building blocks of planets, and possibly future life, deep within dusty discs around young stars. The image shows spectra, obtained by Spitzer's infrared spectrograph, of two stars that are so young they are still embedded in protoplanetary discs. These thick discs of gas and dust are the leftover material from the formation of the stars themselves. The spectra are graphical representations of a celestial object's unique blend of light. Characteristic patterns, or fingerprints, within the spectra allow astronomers to identify the object's chemical composition. In both infrared spectra, the presence of important chemicals for the formation of new worlds can be seen clearly. The broad depression in the center of each spectrum signifies the presence of silicates, which are chemically similar to beach sand. In fact, a good match for the chemistry of these crystalline silicates may be the famous green beaches of Hawaii, which get their color from olivine crystals in the sand. The artist's conception in the background depicts a close-up view of tiny olivine crystals, which scientists believe make up at least some of the dust grains, becoming coated with ice deep within the disc. The depth of the silicate absorption feature indicates that the dusty cocoon surrounding the embedded protostar is extremely thick. Other absorption dips are produced by water ice (blue), methanol ice (red), and carbon dioxide ice (green). The fact that water, methanol and carbon dioxide appear in solid form suggests that the material immediately surrounding the protostar is cold.

Hidden behind a shroud of dust in the constellation Cygnus is a stellar nursery called DR21, which is giving birth to some of the most massive stars in our galaxy. Visible light images reveal no trace of this interstellar cauldron because of heavy dust obscuration. In fact, visible light is attenuated in DR21 by a factor of more than 10,000,000,000, 000,000,000,000,000,000,000,000,000,000 (ten thousand trillion heptillion). NASA's Spitzer Space Telescope allows us to peek behind the cosmic veil and pinpoint one of the most massive natal stars yet seen in our Milky Way galaxy. The never-before-seen star is 100,000 times as bright as the Sun. Also revealed for the first time is a powerful outflow of hot gas emanating from this star and bursting through a giant molecular cloud. This colorful image is a large-scale composite mosaic assembled from data collected at a variety of different wavelengths. Views at visible wavelengths appear blue, near-infrared light is depicted as green, and mid-infrared data from the InfraRed Array Camera (IRAC) aboard NASA's Spitzer Space Telescope is portrayed as red. The result is a contrast between structures seen in visible light (blue) and those observed in the infrared (yellow and red). A quick glance shows that most of the action in this image is revealed to the unique eyes of Spitzer. The image covers an area about two times that of a full moon.

Hidden behind a shroud of dust in the constellation Cygnus is a stellar nursery called DR21, which is giving birth to some of the most massive stars in our galaxy. Visible light images reveal no trace of this interstellar cauldron because of heavy dust obscuration. In fact, visible light is attenuated in DR21 by a factor of more than 10,000,000,000, 000,000,000,000,000,000,000,000,000,000 (ten thousand trillion heptillion). New images from NASA's Spitzer Space Telescope allow us to peek behind the cosmic veil and pinpoint one of the most massive natal stars yet seen in our Milky Way galaxy. The never-before-seen star is 100,000 times as bright as the Sun. Also revealed for the first time is a powerful outflow of hot gas emanating from this star and bursting through a giant molecular cloud. The colorful image (top panel) is a large-scale composite mosaic assembled from data collected at a variety of different wavelengths. Views at visible wavelengths appear blue, near-infrared light is depicted as green, and mid-infrared data from the InfraRed Array Camera (IRAC) aboard NASA's Spitzer Space Telescope is portrayed as red. The result is a contrast between structures seen in visible light (blue) and those observed in the infrared (yellow and red). A quick glance shows that most of the action in this image is revealed to the unique eyes of Spitzer. The image covers an area about two times that of a full moon. Each of the constituent images is shown below the large mosaic. The Digital Sky Survey (DSS) image (lower left) provides a familiar view of deep space, with stars scattered around a dark field. The reddish hue is from gas heated by foreground stars in this region. This fluorescence fades away in the near-infrared Two-Micron All-Sky Survey (2MASS) image (lower center), but other features start to appear through the obscuring clouds of dust, now increasingly transparent. Many more stars are discerned in this image because near-infrared light pierces through some of the obscuration of the interstellar dust. Note that some stars seen as very bright in the visible image are muted in the near-infrared image, whereas other stars become more prominent. Embedded nebulae revealed in the Spitzer image are only hinted at in this picture. The Spitzer image (lower right) provides a vivid contrast to the other component images, revealing star-forming complexes and large-scale structures otherwise hidden from view. The Spitzer image is composed of photographs obtained at four wavelengths: 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8 microns (red). The brightest infrared cloud near the top center corresponds to DR21, which presumably contains a cluster of newly forming stars at a distance of nearly 10,000 light-years. The red filaments stretching across the Spitzer image denote the presence of polycyclic aromatic hydrocarbons. These organic molecules, comprised of carbon and hydrogen, are excited by surrounding interstellar radiation and become luminescent at wavelengths near 8 microns. The complex pattern of filaments is caused by an intricate combination of radiation pressure, gravity, and magnetic fields. The result is a tapestry in which winds, outflows, and turbulence move and shape the interstellar medium.

Visible-light images of the Trifid taken with NASA's Hubble Space Telescope, Baltimore, Md. (inset) and the National Optical Astronomy Observatory, Tucson, Ariz., (background image) show a murky cloud lined with dark trails of dust. Data of this same region from the Institute for Radioastronomy millimeter telescope in Spain revealed four dense knots, or cores, of dust, which are "incubators" for embryonic stars. Astronomers thought these cores were not yet ripe for stars, until Spitzer spotted the warmth of rapidly growing massive embryos tucked inside.

This image composite compares visible-light views with an infrared view from NASA's Spitzer Space Telescope of the glowing Trifid Nebula, a giant star-forming cloud of gas and dust located 5,400 light-years away in the constellation Sagittarius. Visible-light images of the Trifid taken with NASA's Hubble Space Telescope, Baltimore, Md. (inside left) and the National Optical Astronomy Observatory, Tucson, Ariz., (outside left) show a murky cloud lined with dark trails of dust. Data of this same region from the Institute for Radioastronomy millimeter telescope in Spain revealed four dense knots, or cores, of dust (outlined by yellow circles), which are "incubators" for embryonic stars. Astronomers thought these cores were not yet ripe for stars, until Spitzer spotted the warmth of rapidly growing massive embryos tucked inside. These embryos are indicated with arrows in the false-color Spitzer picture (right), taken by the telescope's infrared array camera. The same embryos cannot be seen in the visible-light pictures (left). Spitzer found clusters of embryos in two of the cores and only single embryos in the other two. This is one of the first times that multiple embryos have been observed in individual cores at this early stage of stellar development.

This image from NASA's Spitzer Space Telescope transforms a dark cloud into a silky translucent veil, revealing the molecular outflow from an otherwise hidden newborn star. Using near-infrared light, Spitzer pierces through the dark cloud to detect the embedded outflow in an object called HH 46/47. Herbig-Haro (HH) objects are bright, nebulous regions of gas and dust that are usually buried within dark clouds. They are formed when supersonic gas ejected from a forming protostar, or embryonic star, interacts with the surrounding interstellar medium. These young stars are often detected only in the infrared. The Spitzer image was obtained with the infrared array camera. Emission at 3.6 microns is shown as blue, emission from 4.5 and 5.8 microns has been combined as green, and 8.0 micron emission is depicted as red. HH 46/47 is a striking example of a low mass protostar ejecting a jet and creating a bipolar, or two-sided, outflow. Located at a distance of 1140 light-years and found in the constellation Vela, the protostar is hidden from view in visible-light because it lies inside a dark cloud (known as a 'Bok globule'). With Spitzer, the star and its dazzling jets of molecular gas appear with clarity. The 8-micron channel of the infrared array camera is sensitive to emission from polycyclic aromatic hydrocarbons. These organic molecules, comprised of carbon and hydrogen, are excited by the surrounding radiation field and become luminescent, accounting for the reddish cloud. Note that the boundary layer of the 8-micron emission corresponds to the lower right edge of the dark cloud in the visible-light picture. Outflows are fascinating objects, since they characterize one of the most energetic phases of the formation of low-mass stars (like our Sun). The jets arising from these protostars can reach sizes of trillions of miles and velocities of hundreds of thousands miles per hour. Outflows are clear evidence of the presence of a process that creates supersonic beams of gas. This mechanism is tightly bound to the presence of circumstellar discs which surround the young stars. Such discs are likely to contain the materials from which planetary systems form. Our Sun probably underwent a similar process some 4.5 billion years ago. Hence the interest in understanding how quickly and efficiently this mass accretion and loss process takes place in protostars.

NASA's Spitzer Space Telescope has lifted the cosmic veil to see an otherwise hidden newborn star, while detecting the presence of water and carbon dioxide ices, as well as organic molecules. Using near-infrared light, Spitzer pierces through an optically dark cloud to detect the embedded outflow in an object called HH 46/47. Herbig-Haro (HH) objects are bright, nebulous regions of gas and dust that are usually buried within dark dust clouds. They are formed when supersonic gas ejected from a forming protostar, or embryonic star, interacts with the surrounding interstellar medium. These young stars are often detected only in the infrared. HH 46/47 is a striking example of a low mass protostar ejecting a jet and creating a bipolar, or two-sided, outflow. The central protostar lies inside a dark cloud (known as a 'Bok globule') which is illuminated by the nearby Gum Nebula. Located at a distance of 1140 light-years and found in the constellation Vela, the protostar is hidden from view in the visible-light image (inset). With Spitzer, the star and its dazzling jets of molecular gas appear with clarity. The Spitzer image (inset) was obtained with the infrared array camera. Emission at 3.6 microns is shown as blue, emission from 4.5 and 5.8 microns has been combined as green, and 8.0 micron emission is depicted as red. The 8-micron channel of the camera is sensitive to emission from polycyclic aromatic hydrocarbons. These organic molecules, comprised of carbon and hydrogen, are excited by the surrounding radiation field and become luminescent, accounting for the reddish cloud. Note that the boundary layer of the 8-micron mission corresponds to the lower right edge of the dark cloud in the visible-light picture. The primary image shows a spectrum obtained with Spitzer's infrared spectrograph instrument, stretching from wavelengths of 5.5 microns to 20 microns. Spectra are graphical representations of a celestial object's unique blend of light. Characteristic patterns, or fingerprints, within the spectra allow astronomers to identify the object's chemical composition. The broad depression in the center of the spectrum signifies the presence of silicates, which are chemically similar to beach sand. The depth of the silicate absorption feature indicates that the dusty cocoon surrounding the embedded protostar star is extremely thick. Other absorption dips are produced by water ice (blue) and carbon dioxide ice (green). The fact that water and carbon dioxide appear in solid form suggests that the material immediately surrounding the protostar is cold. In addition, the Spitzer spectrum includes the chemical signatures of methane (red) and methyl alcohol (orange).