Where is spitzer

On Jan. It's science legacy lives on via the Spitzer Data Archive. Interactive 3D model of Spitzer. View the full interactive experience at Eyes on the Solar System.

What's Up - October What's Up - September Stars Are Exploding in Dusty Galaxies. What's Up - August Herschel Space Observatory. A cooled telescope reduces the background infrared brightness of the sky by about six orders of magnitude; this is about the factor by which the sky brightness at visible wavelengths drops from high noon on a sunny day to midnight on a moonless night.

The effects of the background reduction are so powerful that Spitzer, with its relatively small mirror, is more sensitive for many infrared observations than even the largest ground-based telescopes. Although infrared wavelengths are invisible to human eyes and instead we perceive them as heat, it is ironically the colder objects, too frigid and with too little energy to glow visibly, that emit primarily in the infrared.

And happily, infrared signals can be seen through much of the dust that enshrouds objects of interest, such as stellar nurseries and very energetic galactic nuclei. Spitzer has made remarkable progress in studying such objects, and also has been incredibly successful at directly measuring light from exoplanets planets orbiting other stars for the first time.

Within a few thousand light-years of the Sun, in our corner of the Milky Way galaxy, new stars and planetary systems are forming from the gravitational collapse of dense interstellar clouds. Much of the formation and early evolution of stars occurs at temperatures and densities that are particularly well suited to study in the infrared. Spitzer has proved to be a very powerful instrument both for studying large-scale patterns of star formation and for detailed studies of individual nascent stars.

Figure 4. Spitzer can detect a drop in intensity when an extrasolar planet transits, or travels in front of, its star. When the planet blue goes into a secondary eclipse behind the star, the intensity drops again, this time because of the loss of infrared emission from the planet. This technique allowed Spitzer to directly detect light from exoplanets for the first time. The gravitationtal tug from unseen planets green can alter transit times.

Illustration adapted from image courtesy of the author; graph adapted from H. Knutson et al, Nature — In addition, Spitzer has reinforced our previous understanding that the early star will be embedded in a circumstellar disk that develops as a result of the conservation of angular momentum in the collapsing cloud. The material in the disk can evolve into a planetary system, and the recent discovery of planets around literally hundreds of nearby, solar-type stars indicates that this occurs very frequently.

The dense, planet-forming or protoplanetary disk is an ideal target for infrared studies as it is heated by the star and reradiates in the infrared. The protoplanetary disk dissipates as planets form and the star evolves, leaving behind a tenuous, residual debris disk consisting of dust particles that are generated and regenerated by evaporation or by collisions of asteroidal or cometary objects within the planetary system.

Spitzer can easily study these debris disks—which are useful indicators of planetary-system evolution—around numerous solar-type stars because their large surface area makes the disks brighter in the infrared than are the stars themselves. At the other end of the process of planetary production, Spitzer has directly measured the light from fully formed planets circling other stars.

Most known exoplanets have been discovered by observing their effects on the star they orbit. With one or two startling exceptions, however, the light from an exoplanet cannot currently be spatially separated from that of its parent star; the star is too bright and the planet too close.

Figure 5. Computer-generated images based on Spitzer data chart severe weather patterns on HD b, an exoplanet in a highly eccentric orbit. Langton [UC Santa Cruz]. The exoplanets found by the radial-velocity technique tend to be large planets close to the stars, as these produce the largest signal.

Now we know of more than exoplanets orbiting more than stars near the Sun. Even as further discoveries pour in, it is important to start characterizing these exoplanets, to understand both the universal features of planetary systems and any idiosyncrasies that may have been at play in the formation of our own solar system.

The results continue to show that the formation and evolution of planetary systems is a much richer topic than we had thought. A large exoplanet close to its star—and therefore heated to, say, 1, kelvins or more—can be bright enough in the infrared for Spitzer to detect if it lies within about light-years of the Sun. Spitzer has detected these hot Jupiters in numerous cases by temporally, rather than spatially, separating the light of the star from that of the planet. This technique is applied most simply to exoplanets in an orbit that lies edge-on as seen from Earth.

When the planet passes in front of the star or transits , there is a drop in the infrared signal from the star-planet system due to the physical blockage of the stellar disk, and this phenomenon permits an estimate of the size of the planet. The size of this drop relative to the signal from the star measures the amount of infrared radiation from the planet.

These observations, which require measurements with a precision of better than 0. Because hot Jupiters are rich in gas, different wavelengths arise from different levels in the atmosphere or different chemical constituents. Spitzer data have allowed the determination of planetary temperatures and of constraints on chemical composition including the identification of water vapor , atmospheric structure and atmospheric dynamics. Spitzer has already characterized more planets at least 19 in total orbiting other stars than exist in our solar system; the planets characterized lie between about 50 and light-years from Earth.

One study compared Spitzer measurements at five wavelengths of the exoplanet HD b with predictions for radiation from a gaseous planet of solar composition at the observed temperature of the planet.

The results indicate that HD b does not have a high-altitude temperature inversion as has been inferred for other hot Jupiters, so there must be at least two different classes of atmospheres for this group of exoplanets.

The key measurement of temperature inversion will be carried out for numerous other exoplanets during the upcoming Warm Spitzer mission, so we are likely in for more surprises. Because the exoplanet is tidally locked to its star, the same hemisphere faces the star continually, just as tidal locking keeps one hemisphere of the Moon perpetually facing the Earth.

In its edge-on orbit, the illuminated hemisphere comes gradually into view as the planet moves from transit to eclipse. This led to the first mapping of the day-to-night temperature variation in an extrasolar planet, where days reached around 1, kelvins and night dipped to around kelvins.

It is estimated that winds in excess of 5, kilometers per hour are required in the upper atmosphere of the planet to account for the observed redistribution of the stellar heat.

Fortuitously, the geometry was just right for the observations to include a secondary eclipse as well. In these early days of exoplanet characterization, one can but marvel at the variety of behaviors exhibited by the planets that have been studied to date. Recall that the results were all obtained without spatially isolating or imaging the exoplanet.

Looking ahead, we can anticipate that newly launched and planned instruments will greatly extend these results, leading up to our first direct images of Earth-like exoplanets sometime in the next to years. The formation of rocky planets such as Mars and Earth is thought to proceed over a few tens of millions of years by further coalescence and coagulation of the dust particles.

Figure 6. Generations of stars are seen in this one region, located about 6, light-years away in the constellation Cassiopeia. The oldest stars are blue dots in the centers of the cavities that they excavated in the interstellar medium, whereas younger stars line the rims of the cavities. The white knots are stellar nurseries, where young stars are forming.

The red color shows heated dust, and green depicts dense clouds of dust and gas. Allen and X. Koenig [Harvard-Smithsonian CfA]. More recently, research emphasis has shifted towards spectroscopic studies of both the dust and the gaseous component of the disks, as a means of assaying the composition and physical condition of material in exoplanetary systems. Observations of disks in the active planet-forming stages have revealed a rich complex of gas-phase organic molecules, including water, carbon dioxide and carbon monoxide—precursors of the complex organic chemistry that took place on Earth, which eventually led to the formation of life.

These observations are unique to the infrared because the principal bands in which such molecules vibrate and produce their spectra fall in this region, and they all are easily excited to do so at the temperature of the protoplanetary material.

Now that spectra of this type are available for literally dozens of disks, it is possible to look for significant variations of the abundance pattern and compare it with other properties of the disk and the central star. One such trend with interesting implications has been the demonstration that the nitrogen-bearing compound hydrogen cyanide HCN is less abundant than expected in the gaseous material around forming stars of low mass having less than half the mass of the Sun than in more massive solar-type stars.

It is thought that the absence of HCN reflects the photochemistry in the planet-forming disk rather than an anomaly in the material from which the star is forming.

A possible implication of this measurement is that planetary systems forming around stars in this mass range might be relatively nitrogen-poor.

As nitrogen is a major player in biological molecules on Earth, this could suggest that a different set of processes would govern development of life on planets orbiting lower-mass stars than were in play in the terrestrial environment.

Figure 7. Sharp peaks, or spectral lines, correspond to specific molecules. The overall pattern of spectral lines is a signature for water vapor; peaks for several other simple organic molecules are also present.

Comparing the observated data with a model, in the lower half of the figure, reveals the amount, distribution and temperature of each material. This spectrum shows that organic materials abound in protoplanetary disks, within which planets may be forming. Carr [Naval Research Laboratory]. Spectroscopy of the dust, in addition to the gas, associated with protoplanetary disks and exoplanetary systems also has been productive.

In general these spectra show smooth, continuous emission, punctuated by broad emission and absorption features due to ices or silicate minerals. The implied composition of the dust particles agrees with that of dust spread diffusely through the interstellar medium, but the physical state of the material can vary dramatically.

In particular, the silicate material in the interstellar medium appears, based on its spectral characteristics, to be amorphous in form, whereas that associated with planet-forming and debris disks often shows the sharper emission features of crystalline silicates.

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