# Life’s Precursors: The Interstellar Connection

by on March 27, 2008

Was the early Earth seeded with amino acids from deep space? The variety of molecules found between the stars makes the supposition provocative, but finding interstellar amino acids has been a challenge. Various amino acids have indeed been found in meteorites, but it has been argued that these could have been produced right here in the Solar System within asteroids. Yet laboratory experiments have shown that amino acids can form among the molecules found in interstellar clouds, including such important ones as glycine, alanine and serine.

What’s next is to identify amino acids in the interstellar medium, and we’re coming close. Ponder this: Since 1965, more than 140 molecules have been identified in space, both in interstellar clouds and circumstellar disks, many of them organic or carbon-based. Now researchers from the Max Planck Institute for Radio Astronomy in Bonn have detected amino acetonitrile (NH2CH2CN), a potential precursor of the simplest amino acid, glycine. The odds are rising that the processes that spread life are commonplace: Stars and planets forming within interstellar clouds where amino acids can be found would be subject to infalls of these materials, perhaps enhancing the chances of life elsewhere in the universe. (Addendum: I’ve added the ‘perhaps’ in that sentence as a result of the interesting comment thread that has developed on this topic; see below).

The focus of the Bonn team’s investigations has been Sagittarius B2. Located about 100 parsecs (326 light years) from galactic center, and some 8000 parsecs from Earth, this is a highly active region of star formation — massive, complex, and packed with interesting chemistry. Sagittarius B2 is composed of two dense cores of star formation separated by two parsecs, one of which is possessed of a chemistry so rich that it has been christened the Large Molecule Heimat (LMH) because of the numerous detections of complex molecules made there.

The Bonn team analyzed 3700 spectral lines from complex molecules using the IRAM 30-metre telescope in Spain, with results confirmed by instruments in France and Australia. The Institute’s Karl Menten sees the discovery as a sign of progress in our understanding of the regions where stars are born:

“Finding amino acetonitrile has greatly extended our insight into the chemistry of dense, hot star-forming regions. I am sure we will be able to identify in the future many new, even more complex organic molecules in the interstellar gas. We already have several candidates!”

Such molecules emit hundreds of weak spectral lines, producing spectra so crowded that untangling the components is an extraordinary challenge. And while the hunt for glycine has had a long and inconclusive history, the identification of amino acetonitrile gives us a molecule chemically related to glycine, one whose status as an amino acid precursor is argued in the paper on this work. Conclusive proof of amino acids in interstellar clouds seems closer than ever, an indication that life’s building blocks may predate the formation of the systems they seed.

The paper is Belloche et al., “Detection of amino acetonitrile in Sgr B2(N),” accepted by Astronomy & Astrophysics and available online.

Ron S March 27, 2008 at 9:56

“Stars and planets forming within interstellar clouds where amino acids can be found would be subject to infalls of these materials, enhancing the chances of life elsewhere in the universe.”

I’m not convinced of this. While it’s good to know that these basic compounds can be formed and survive in what could be seen as a hostile environment, this does not necessarily, or even probably lead to life on planets they may rain down upon. After all, amino acids can also form on the planet’s surface itself and so any infalling material can be redundant, and even a small contribution to the total amount of available organics on the surface.

Administrator March 27, 2008 at 13:35

I take your point, Ron, but surely the chances for life go up with more organics than fewer? It would indeed be interesting, though, to know the proportion of incoming organics vs. what forms on a planetary surface.

James M. Essig March 27, 2008 at 13:38

My brother John has told me, I think but I am no way certain, that it was Frank Zubrin of the Mars Society that worked on the Transpermia Theory that holds that if primitive DNA based life started at just one location within the Milky Way, over the course of billions of years of galactic evolution including that of the mass transport dynamics of the interstellar medium, such organisms and/or complex organic chemicals could have spread throughout the entire galaxy and deposited themselves on almost all, if not all, planets and moons capable of supporting DNA based lifeforms.

Since the diameter of the Milky Way Galaxy is about 100,000 LYs, a life forms propagation wavefront spreading thoughout the Galaxy at 3 Km/sec would permit the wavefront to have spread thoughout the entire Galaxy in 100,000 years. Obviously, any such life forms and/or complex organic compounds could travel within asteriodal debris and the like wherein the life containing rocks might have beem blasted out of a life bearing planetary body by a asteriodal or cometary impact. For small planetary bodies that evolved living organisms, the escape velocity is considerably less than that of Earth thus reducing the thermal intensity and pressure load limits required of rocks blasted into space. I believe that the Volcano Krakatoa (or however its spelled) in theory shot large boulders as high as 60 to 90 kilometers in hieght which is a velocity commensurate with the escape velocity of some small moons and planets perhaps capable of supporting life.

The organisms in these rocks upon reentry could have been shielded from the heat of reentery and may impact the ground, due to atmospheric friction based decelleration, with a velocity on the order of a couple hundred meters/sec or less provided that the originating meteor was small enough to be slowed down within the planetary atmosphere but not too small so as to be vaporized in the upper atmosphere of the planet it impacted. Various meteoric minenal compostions would be less thermally conducting then others as well as have a higher heat capacity, a situation that would also effect the survivability of organisms deep within small meteorites.

Thanks;

Jim

phil.gs March 27, 2008 at 13:46

I really love the notion of panspermia and that we’re all made of stars. I get excited every time I hear about organic molecules found elsewhere. I had never thought about amino acids being formed in interstellar space. That’s pretty cool.

dad2059 March 27, 2008 at 16:18

Ahh, but could these molecules necessarily condense into biologicals we are familiar with, i.e., water solvent and carbon based? Or could they possibly start using other compounds like ammonia or silicon?

I agree with Paul’s reasoning of the more organics in an area, the better. But are we also implying a water and carbon bias?

Athena March 27, 2008 at 16:22

As I’m fond (perhaps overfond) of saying, the devil’s in the details. All biomolecules on earth, including amino acids, are chiral. That is, asymmetric and non-superimposable on their mirror images, aka isomers. Amino acids in space are invariably racemic (equal or almost equal mixtures of isomers). So if something was seeded from a molecular cloud out there, it was either something simpler than an amino acid or it passed through some type of filter that totally destroyed one set of isomers for every class of future biocompounds.

We are still made of star stuff, in terms of elements… that is exciting enough!

dad2059 March 27, 2008 at 16:28

Speaking of organics, remember the Cassini Probe flying through the geyser plume of Enceladus?

http://www.planetark.com/dailynewsstory.cfm/newsid/47670/story.htm

Ron S March 27, 2008 at 16:29

Paul, it does very much depends on the quantity of infalling vs. locally-produced organics, and the timing. For example (sorry, don’t recall the reference), amino acids were shown in an experiment 1/2 century ago to be formed naturally in conditions that may have existed early in Earth’s history. How does this compare with the quantity vs infalling, and which might occur first? We have no way of knowing, so assigning probabilities is speculative at best.

I’m not trying to exclude the utility of infalling organics. I am simply arguing against the perception of some that because organics exist in many nebulae that this *must* be the source of organic precursors on life-bearing planets. We know no such thing. This is one form of panspermia that, while it is certainly possible, I suspect is unnecessary, and possibly misleading, in understand how life arises.

Administrator March 27, 2008 at 19:05

Re Ron’s comment “I am simply arguing against the perception of some that because organics exist in many nebulae that this *must* be the source of organic precursors on life-bearing planets.”

I have no problem at all with that line of thinking. We simply don’t have the evidence, as far as I can see, to argue for a confirmed causal relationship here. The evidence is provocative and interesting, but I wouldn’t push it further either. I’ve included a slight addendum in the original post to reflect this.

djlactin March 28, 2008 at 1:38

Mr Essig. I catch a calculation error. Moving at 3km/sec a wave front would travel 1 light year in 100000 years, not 100000 light years. To travel the (50000 Ly) radius of the milky way, this wave front would require 5 e9 years

The consequences of this error on the transpermia idea are important.

Adam March 28, 2008 at 3:56

Hi Ron & Paul

Organics can be made in a huge variety of conditions – in molecular clouds, in comet ices, in high atmospheres of gas giants and ice moons, under the deep sea, in the sea’s crust, in the troposphere via lightning, and so on. What’s interesting about meteoritic organics is that they provide a supply to worlds that might not otherwise form organics (say under the ice of Ceres, or in liquid water pools under ice in craters.) For Earth they might be an irrelevance, but perhaps they’ve been kindled to Life elsewhere?

Stanley Miller did the original organic synthesis experiment in c.1953, making amino acids in a reducing atmosphere mix (CH4, NH3, etc.) Since then a variety of gas mixes, including plain old CO, N2, H2O, have been induced to make organics, but with very low efficiencies for some mixes – in which case infall would be the dominant source. The efficiency of making complex organics might actually be higher in interstellar clouds or pre-planetary disks, so the infall might prove vital in the final analysis.

Ron S March 28, 2008 at 15:47

Adam, I appreciate the point you’re making, however I remain doubtful of the value to life of organics raining down on a sterile planet. Unfortunately I can only argue qualitatively so the weight of my argument is limited. Let me try.

Life is at its earliest stages is, in part, one of assembling more complex organic molecules from simpler ones plus energy and non-organics. My thinking is that an environment that permits this process to occur is also able to assemble those simpler, precursor compounds from available raw materials. If I am wrong about this, the raining down of organics from space would be accomplishing one or more of the following:
– Provide the raw materials to enable the assembly processes, because those raw materials are not available on the planet’s surface.
– Prime the pump for more complex biochemistry, because simple organics cannot form on the planet’s surface.
– Feed biochemical reactions and/or metabolic processes (food), because there is insufficient local organic material without external replenishment. Sort of ‘manna from heaven’, if you will.

I believe these are all unlikely requirements to start and maintain biochemistry and life, therefore there is no need for organics from the space. Of course I can’t prove this so take it as you will.

ljk March 28, 2008 at 16:31

Low oxygen and molybdenum in ancient oceans delayed
evolution of life by 2 billion years

http://www.spaceref.com/news/viewpr.html?pid=25057

International team of scientists discover clue to delay of life on Earth

http://www.spaceref.com/news/viewpr.html?pid=25056

“Scientists from around the world have reconstructed changes in
Earth’s ancient ocean chemistry during a broad sweep of geological
time, from about 2.5 to 0.5 billion years ago. They have discovered
that a deficiency of oxygen and the heavy metal molybdenum in the
ancient deep ocean may have delayed the evolution of animal life
on Earth for nearly 2 billion years.”

NAS SSB Report: Assessment of the NASA Astrobiology Institute

http://www.spaceref.com/news/viewsr.html?pid=27495

“At the request of NASA’s Associate Administrator for the Science
Mission Directorate (SMD), the Committee on the Review of the
NASA Astrobiology Institute undertook the assignment to determine
the progress made by the NAI in developing the field of astrobiology
(Appendix A).

It must be emphasized that the purpose of this study was not to
undertake a review of the scientific accomplishments of NASA’s
Astrobiology program, in general, or of the NAI, in particular.”

ljk March 28, 2008 at 22:34

Survival of gas phase amino acids and nucleobases in space radiation conditions

Authors: S. Pilling (LNLS), D. P. P. Andrade (Chemistry Institute/UFRJ), R. B. de Castilho (Chemistry Institute/UFRJ), R. L. Cavasso-Filho (LNLS), A. F. Lago (LNLS), L. H. Coutinho (UEZO), G. G. B. de Souza (Chemistry Institute/UFRJ), H. M. Boechat-Roberty (Valongo Observatory/UFRJ), A. Naves de Brito (LNLS)

(Submitted on 26 Mar 2008)

Abstract: We present experimental studies on the photoionization and photodissociation processes (photodestruction) of gaseous amino acids and nucleobases in interstellar and interplanetary radiation conditions analogs. The measurements have been undertaken at the Brazilian Synchrotron Light Laboratory (LNLS), employing vacuum ultraviolet (VUV) and soft X-ray photons. The experimental set up basically consists of a time-of-flight mass spectrometer kept under high vacuum conditions. Mass spectra were obtained using photoelectron photoion coincidence technique.

We have shown that the amino acids are effectively more destroyed (up to 70-80%) by the stellar radiation than the nucleobases, mainly in the VUV. Since polycyclic aromatic hydrocarbons have the same survival capability and seem to be ubiquitous in the ISM, it is not unreasonable to predict that nucleobases could survive in the interstellar medium and/or in comets, even as a stable cation.

Comments: 4 pages, 2 figures. To be published in the Proceedings of the IAU-251 symposium – Organic Mater in Space, Hong Kong, China (2008)

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0803.3751v1 [astro-ph]

Submission history

From: Sergio Pilling [view email]

[v1] Wed, 26 Mar 2008 15:38:09 GMT (820kb)

http://arxiv.org/abs/0803.3751

James M. Essig March 29, 2008 at 1:00

Hi djlactin;

Oops!

Thanks very much for pointing out my error. At 3 km/sec, it would take 10 billion years for a wavefront to travel across the entire diameter of the Galaxy if it started at the very outer edge of the galaxy. My math should have been something like (100,000 years)(100,000) or 10 EXP 10 years to travel 100,000 lightyears at (10 EXP – 5)C which is about 3 km/sec. Your math of 5 x 10 EXP 9 years to travel 50,000 LY at 3 km/sec is more realistic than my math since it is likely that the first organisms would develope further in from the galactic edge based on statistical probabilities based on the distribution of stars within the galaxy since the bulk of the stars are not located at the very outer edge of the galaxy and since a good portion of the stars are located within the core or central bulge near the center of the Galaxy.

Thanks again for pointing out my error and making this important correction. As a space head who sometimes gets over excited about the content on Tau Zero, I can and sometimes make some really dumb calculational mistakes.

Regards;

Jim

ljk April 2, 2008 at 6:31

A Search for Interstellar CH$_2$D$^+$

Authors: Alwyn Wootten, Barry E. Turner

(Submitted on 31 Mar 2008)

Abstract: We report on a search for Interstellar CH2D+. Four transitions occur in easily accessible portions of the spectrum; we report on emission at the frequencies of these transitions toward high column density star-forming regions. While the observations can be interpreted as being consistent with a detection of the molecule, further observations will be needed to secure that identification. The CH2D+ rotational spectrum has not been measured to high accuracy. Lines are weak, as the dipole moment induced by the inclusion of deuterium in the molecule is small.

Astronomical detection is favored by observations toward strongly deuterium-fractionated sources. However, enhanced deuteration is expected to be most significant at low temperatures. The sparseness of the available spectrum and the low excitation in regions of high fractionation make secure identification of CH2D+ difficult. Nonetheless, owing to the importance of CH3+ to interstellar chemistry, and the lack of rotational transitions of that molecule owing to its planar symmetric structure, a measure of its abundance would provide key data to astrochemical models.

Comments: 2 pages, 1 figure, submitted to IAU Symposium 251, Organic Matter

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0804.0021v1 [astro-ph]

Submission history

From: H. Alwyn Wootten [view email]

[v1] Mon, 31 Mar 2008 20:40:50 GMT (37kb)

http://arxiv.org/abs/0804.0021

ljk April 7, 2008 at 9:12

Meteorites delivered the ‘seeds’ of Earth’s left-hand life

PhysOrg.com April 6, 2008

*************************

Columbia University scientists
presented evidence today that desert
heat, a little water, and meteorite
impacts may have been enough to cook
up one of the first prerequisites
for life: The dominance of
left-handed amino acids, the
building blocks of life on this
planet. The finding suggests a
higher probability that there is
life somewhere…

http://www.kurzweilai.net/email/newsRedirect.html?newsID=8355&m=25748

ljk May 2, 2008 at 14:47

Formation of hydrogen peroxide and water from the reaction of cold hydrogen atoms with solid oxygen at 10K

Authors: N.Miyauchi, H.Hidaka, T.Chigai, A.Nagaoka, N.Watanabe, A.Kouchi

(Submitted on 1 May 2008)

Abstract: The reactions of cold H atoms with solid O2 molecules were investigated at 10 K. The formation of H2O2 and H2O has been confirmed by in-situ infrared spectroscopy. We found that the reaction proceeds very efficiently and obtained the effective reaction rates.

This is the first clear experimental evidence of the formation of water molecules under conditions mimicking those found in cold interstellar molecular clouds. Based on the experimental results, we discuss the reaction mechanism and astrophysical implications.

Comments: 12 pages, 3 Postscript figures, use package amsmath, amssymb, graphics

Subjects: Astrophysics (astro-ph)

Journal reference: Chem. Phys. Lett. Vol.456, p27-30 (2008)

Cite as: arXiv:0805.0055v1 [astro-ph]

Submission history

From: Naoki Watanabe [view email]

[v1] Thu, 1 May 2008 05:22:22 GMT (465kb)

http://arxiv.org/abs/0805.0055

ljk May 29, 2008 at 14:28

Tentative detection of phosphine in IRC+10216

Authors: M. Agúndez, J. Cernicharo, J. R. Pardo, M. Guélin, T. G. Phillips

(Submitted on 28 May 2008)

Abstract: The J,K = 1,0-0,0 rotational transition of phosphine (PH3) at 267 GHz has been tentatively identified with a T_MB = 40 mK spectral line observed with the IRAM 30-m telescope in the C-star envelope IRC+10216. A radiative transfer model has been used to fit the observed line profile. The derived PH3 abundance relative to H2 is 6 x 10^(-9), although it may have a large uncertainty due to the lack of knowledge about the spatial distribution of this species.

If our identification is correct, it implies that PH3 has a similar abundance to that reported for HCP in this source, and that these two molecules (HCP and PH3) together take up about 5 % of phosphorus in IRC+10216. The abundance of PH3, as that of other hydrides in this source, is not well explained by conventional gas phase LTE and non-LTE chemical models, and may imply formation on grain surfaces.

Comments: 4 pages, 2 figures; accepted for publication in A&A Letters

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0805.4297v1 [astro-ph]

Submission history

From: Marcelino Agundez [view email]

[v1] Wed, 28 May 2008 09:50:24 GMT (139kb)

http://arxiv.org/abs/0805.4297

ljk July 1, 2008 at 11:51

Formation of water and methanol in star forming molecular clouds

Authors: Ankan Das (1), Kinsuk Acharyya (2), Sonali Chakrabarti (1 and 3), Sandip Kumar Chakrabarti (1 and 2) ((1) Indian Centre For Space Physics, Kolkata, India. (2) S.N. Bose National Center For Basic Sciences, Kolkata, India. (3) Maharaja Manindra Chandra College, Kolkata, India.)

(Submitted on 29 Jun 2008)

Abstract: We study the formation of water and methanol in the dense cloud conditions to find the dependence of its production rate on the binding energies, reaction mechanisms, temperatures, and grain site number. We wish to find the effective grain surface area available for chemical reaction and the effective recombination timescales as functions of grain and gas parameters.

We used a Monte Carlo simulation to follow the chemical processes occurring on the grain surface. We find that the formation rate of various molecules is strongly dependent on the binding energies. When the binding energies are high, it is very difficult to produce significant amounts of the molecular species. Instead, the grain is found to be full of atomic species. The production rates are found to depend on the number density in the gas phase.

We show that the concept of the effective grain surface area, which we introduced in our earlier work, plays a significant role in grain chemistry. We compute the abundance of water and methanol and show that the results strongly depend on the density and composition in the gas phase, as well as various grain parameters. In the rate equation, it is generally assumed that the recombination efficiencies are independent of the grain parameters, and the surface coverage.

Presently, our computed parameter $\alpha$ for each product is found to depend on the accretion rate, the grain parameters and the surface coverage of the grain. We compare our results obtained from the rate equation and the one from the effective rate equation, which includes $\alpha$. At the end we compare our results with the observed abundances.

Comments: 12 pages, 16 figures in eps format

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0806.4740v1 [astro-ph]

Submission history

From: Ankan Das [view email]

[v1] Sun, 29 Jun 2008 08:44:40 GMT (937kb)

http://arxiv.org/abs/0806.4740

ljk November 25, 2008 at 14:00

First detection of glycolaldehyde outside the Galactic Center

Authors: M.T. Beltran (1), C. Codella (2), S. Viti (3), R. Neri (4), R. Cesaroni (5) ((1) Universitat de Barcelona-CSIC (2) INAF-Istituto di Radioastronomia (3) University College London (4) IRAM (5) INAF-Osservatorio Astrofisico di Arcetri))

(Submitted on 24 Nov 2008)

Abstract: Glycolaldehyde is the simplest of the monosaccharide sugars and is directly linked to the origin of life. We report on the detection of glycolaldehyde (CH2OHCHO) towards the hot molecular core G31.41+0.31 through IRAM PdBI observations at 1.4, 2.1, and 2.9 mm. The CH2OHCHO emission comes from the hottest (> 300 K) and densest (>2E8 cm^-3) region closest (< 10^4 AU) to the (proto)stars.

The comparison of data with gas-grain chemical models of hot cores suggests for G31.41+0.31 an age of a few 10^5 yr. We also show that only small amounts of CO need to be processed on grains in order for existing hot core gas-grain chemical models to reproduce the observed column densities of glycolaldehyde, making surface reactions the most feasible route to its formation.

Comments: Comments: 8 pages, 2 tables, 2 figures. Accepted for publication in ApJ Letter. This is an author-created, un-copyedited version of an article accepted for publication in The Astrophysical Journal Letters. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0811.3821v1 [astro-ph]

Submission history

From: Maria T. Beltran [view email]

[v1] Mon, 24 Nov 2008 08:58:14 GMT (144kb)

http://arxiv.org/abs/0811.3821

ljk November 26, 2008 at 8:49

November 25, 2008

Sweet molecule could lead us to alien life

Scientists have detected an organic sugar molecule that is directly linked to the origin of life, in a region of our galaxy where habitable planets could exist.

The discovery, part funded by the UK’s Science and Technology Facilities Council (STFC), is published today (25th November) on the Astro-ph website.

The international team of researchers, including a researcher at University College London (UCL), used the IRAM radio telescope in France to detect the molecule in a massive star forming region of space, some 26,000 light years from Earth.

Dr Serena Viti, one of the paper’s authors from University College London, said, “This is an important discovery as it is the first time glycolaldehyde, a basic sugar, has been detected towards a star-forming region where planets that could potentially harbour life may exist.”

The molecule – glycolaldehyde – has previously only been detected towards the centre of our galaxy where conditions are extreme compared to the rest of the galaxy. This new discovery, in an area far from the galactic centre, also suggests that the production of this key ingredient for life could be common throughout the galaxy.

This is good news in our search for alien life, as a wide spread of the molecule improves the chances of it existing along side other molecules vital to life and in regions where Earth-like planets may exist. The team were able to detect glycolaldehyde by using the telescope to observe the region with high-angular resolution and at different wavelengths. The observations confirmed the presence of three lines of glycolaldegyde towards the most central part of the core of the region.

Glycolaldehyde, the simplest of the monosaccharide sugars, can react with the substance propenal to form ribose, a central constituent of Ribonucleic acid (RNA), thought to be the central molecule in the origin of life.

Professor Keith Mason, Chief Executive of the Science and Technology Facilities Council (STFC), said, “The discovery of an organic sugar molecule in a star forming region of space is very exciting and will provide incredibly useful information in our search for alien life. Research like this, combined with the vast array of other astronomical projects involving UK researchers, is continually expanding our knowledge of the Universe and keeping the UK at the forefront of astronomy.”

Notes for editors

Contacts Julia ShortSTFC Press OfficeTel: + 44 (0)1793 442 012Mob: + 44 (0)777 027 6721 Email: julia.short@stfc.ac.uk

Dr Serena VitiReader and AFDept of Physics and AstronomyUniversity College LondonTel: +44 (0)20 7679 3435 Email: sv@star.ucl.ac.uk

The paper will also be published in the Astrophysical Journal Letters publication.

The international team of scientists are from:• The Universitat de Barcelona-CSIC, Barcelona• INAF-Istituto di Radioastronomia and INAF-OsservatorioAstrofisico di Arcetri in Florence• University College London• Institute de Radiastronomie Millimetrique, Grenoble

The massive star forming region where the sugar molecules were detected is known as G31.41+0.31

Online version of the Astrophysical Journal paper:

http://babbage.sissa.it/abs/0811.3821

ljk March 13, 2009 at 8:08

Galactic Dust Bunnies Found to Contain Carbon After All

Written by Raphael Rosen

March 12, 2009

Using NASA’s Spitzer Space Telescope, researchers have found evidence suggesting that stars rich in carbon complex molecules may form at the center of our Milky Way galaxy.

This discovery is significant because it adds to our knowledge of how stars form heavy elements — like oxygen, carbon, and iron — and then blow them out across the universe, making it possible for life to develop.

Astronomers have long been baffled by a strange phenomenon: Why have their telescopes never detected carbon-rich stars at the center of our galaxy even though they have found these stars in other places? Now, by using Spitzer’s powerful infrared detectors, a research team has found the elusive carbon stars in the galactic center.

“The dust surrounding the stars emits very strongly at infrared wavelengths,” says Pedro García-Lario, a research team member who is on the faculty of the European Space Astronomy Center, the European Space Agency’s center for space science. He co-authored a paper on this subject in the February 2009 issue of the journal Astronomy & Astrophysics.

“With the help of Spitzer spectra, we can easily determine whether the material returned by the stars to the interstellar medium is oxygen-rich or carbon-rich.”

The team of scientists analyzed the light emitted from 40 planetary nebulae — blobs of dust and gas surrounding stars — using Spitzer’s infrared spectrograph. They analyzed 26 nebulae toward the center of the Milky Way — a region called the “Galactic Bulge” — and 14 nebulae in other parts of the galaxy. The scientists found a large amount of crystalline silicates and polycyclic aromatic hydrocarbons, two substances that indicate the presence of oxygen and carbon.

This combination is unusual. In the Milky Way, dust that combines both oxygen and carbon is rare and is usually only found surrounding a binary system of stars. The research team, however, found that the presence of the carbon-oxygen dust in the Galactic Bulge seems to be suggestive of a recent change of chemistry experienced by the star.