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Organics, Water in Protoplanetary Disk

We have interesting news coming up this week with regard to the first detection of methane in the atmosphere of an exoplanet, of significance because it demonstrates that we can detect organic molecules using spectroscopy in ways that will one day help us study the atmospheres of terrestrial worlds around other stars. More on this later in the week, after a NASA teleconference scheduled for the 19th. Today, though, let’s talk about another kind of detection in the circumstellar disk of a young star.

At work in the latter is the Spitzer Space Telescope‘s infrared spectrograph, which is being put to use to look at the composition of protoplanetary disks. Specifically, John Carr (Naval Research Laboratory) and Joan Najita (National Optical Astronomy Observatory, Tucson) have been examining gases in the planet forming region around the star AA Tauri, using refined methods that have allowed them to find the spectral signatures of three organic molecules: Hydrogen cyanide, acetylene and carbon dioxide, along with water vapor. Of some significance is the fact that these organics are more plentiful in the disk than in the cloud of interstellar gas from which the disk itself was formed. Says Carr:

“Molecular clouds provide the raw material from which the protoplanetary disks are created. So this is evidence for an active organic chemistry going on within the disk, forming and enhancing these molecules…Now that we can identify these molecules and inventory them, we will have a better understanding of the origins and evolution of the basic building blocks of life — where they come from and how they evolve.”

Data from AA Tauri disk

Image: This plot of infrared data shows the signatures of water vapor and simple organic molecules in the disk of gas and dust surrounding a young star. The data on the top line were captured by NASA’s Spitzer Space Telescope’s spectrograph, which collects light and sorts it according to color, or wavelength. In this case, infrared light from gases around the star AA Tauri was broken up into the wavelengths listed on the horizontal axis of the plot. The sharp spikes are called spectral lines, and each molecule has its own unique pattern, much like a fingerprint. The pattern of spikes reveals the signature of water vapor along with carbon dioxide, hydrogen cyanide, and acetylene–some of the basic building blocks of life. Credit: NASA/JPL-Caltech/Naval Research Laboratory.

450 light years from Earth, AA Tauri is thought to be less than a million years old. Carr and Najita are studying the region within three AU of the star, with results suggesting that water vapor is abundant in the inner part of the protoplanetary disk, which is where terrestrial planets may one day form. Meanwhile, a team at the California Institute of Technology has used Spitzer to examine two young stars, following up their observations with data from the Keck II telescope in Hawaii. Of that recently published work, Geoffrey Blake (Caltech) has this to say:

“While we don’t detect nearly as much water as exists in the oceans on Earth, we see essentially only the disk’s surface, so the implication is that the water is quite abundant. This is a much larger story than just one or two disks. Spitzer can efficiently measure these water signatures in many objects, so this is just the beginning of what we will learn.”

Thus the composition of planet-forming disks comes into greater focus in ways that may help us understand life’s potential for development. The AA Tauri paper is Carr and Najita, “Organic Molecules and Water in the Planet Formation Region of Young Circumstellar Disks,” Science Vol. 319. no. 5869 (14 March 2008), pp. 1504-1506 (abstract). The Caltech work, which has focused on the T Tauri stars AS 205A and DR Tau, is Salyk et al., “H2O and OH gas in the terrestrial planet-forming zones of protoplanetary disks,” slated to appear in the March 20 Astrophysical Journal (abstract).

Comments on this entry are closed.

  • dad2059 March 17, 2008, 12:40

    My question is with the star being so young, has it condensed down to it’s final spectral type yet? Probably not given it still has a dust disk, but wouldn’t that determine how the final product turned out, organic molecules not withstanding? Or is that what the ‘AA’ designation is for?

  • Administrator March 17, 2008, 13:04

    T Tauri stars, if I understand this correctly, are still in their contraction phase and have not yet reached hydrogen burning and the main sequence (and interestingly enough, many of them seem to be in binary systems). The spectral classes involved are F,G,K,M (more massive stars of A and B class that are pre-main sequence are known as Herbig Ae/Be stars rather than T Tauri). I’m not sure how early in the process we can tell what spectral class a T Tauri is evolving into; maybe some of the readers more knowledgable about these stars can chip in.

  • Adam March 18, 2008, 8:39

    Hi Paul

    Have to profess ignorance on this one, though I do know the ‘AA’ is part of the star’s name. As for spectral class it could be estimated from the mass of the star, which can be measured if it’s in a binary. Everything under ~0.5 solar masses is an M star, then 0.5-0.9 is K, 0.9-1.1 is G, and 1.1-1.5 is F… roughly. A disk is usually no more than 0.1 the star’s mass, I think. Heavier disks end up making brown dwarfs or falling into the star – angular momentum issues. Need to brush up on my star-making knowledge!

  • ljk March 19, 2008, 11:16


    Water is an essential ingredient for forming planets, yet has
    remained hidden from scientists searching for it in protoplanetary
    systems, the spinning disks of particles surrounding newly formed
    stars where planets are born. Now the detection of water vapor in
    the inner part of two extrasolar protoplanetary disks brings
    scientists one step closer to understanding water’s role during
    terrestrial planet formation.

    “This is a much larger story than just one or two disks,” says Geoffrey
    Blake, professor of cosmochemistry and planetary sciences and
    professor of chemistry at Caltech. “With upcoming observations of
    tens of young stars and disks, we can construct a story for how
    water concentrations evolve in disks, and hopefully answer questions
    like how Earth acquired its oceans.”

    Details: http://mr.caltech.edu/media/Press_Releases/PR13121.html

  • ljk March 19, 2008, 13:39

    Hubble finds first organic molecule on extrasolar planet

    The NASA/ESA Hubble Space Telescope has made the first
    detection ever of an organic molecule in the atmosphere of a
    planet orbiting another star. This breakthrough is an important
    step in eventually identifying signs of life on a planet outside
    our Solar System.

    More at:


  • James M. Essig March 21, 2008, 22:39

    Hi Folks;

    For those of you who read Carl Sagan’s popular book “Cosmos” and/or saw the amazing several part made for TV series “Cosmos”, you probably remember the concepts and artists’depictions of organisms drifting in the atmospheres of Jupiter and Saturn refered to as floaters and sinkers which would float in the upper atmospheres of these planets and feed off of the atmospheric elemental and molecular species. When I first saw the artists’ renditions, my emotional reaction was something like, Holy “****”!!.

    Given the large number of extrasolar gas giant planets found so far, they are obviously ubiquitous in our universe. Therefor, obviously, there are many more thermodynamic degrees of freedom wherein such creatures could evolve in the universe than in just our solar system alone.

    I just began to wonder for the first time tonight, if such creatures could somehow develop crude tools, than machines, computers, and ultimately star ships. I am not sure how such soft bodied membranous creatures could develop such, however, it is good to realize that we went from crude wooden and relatively weak stone implements to super strong material like Titanium Aluminide, Cobalt Steel, Tungstun Carbide, Tantulum Carbide, and carbon nitride which in some forms might have a bulk modulus greater than pure diamond in certain crystaliine directions, carbon nanotubes although on a small scale as yet. We have developed extraordinarilly high strength flexible plyable materials such as Kevlar, and recently Zylon which has a tensile strength 2 1/2 times greater than Kevlar. We even talk about the possible distant future production of spatially macroscopicly sized samples of solid neutronium especially in science fiction circles.

    Given billions of years of evolution, I think that perhaps even floaters and sinkers might develope durable interstellar space craft.

    Just a thought.



  • george scaglione March 22, 2008, 12:38

    jim,it would really really streeeeetch my imagination to be able to see floaters and sinkers piloting spacecraft! and yes i have read cosmos and i have it on dvd as well.i can vividly see in front of me the very hypotetical creaures you mention.heck buddy when we do get out there we might find some suprises that would make star trek pale by comparrison! no doubt. just wish,lol,that we could hurry up and get out there! thank you very much, george

  • ljk March 28, 2008, 13:35

    Planet Formation Revealed?

    Written by Nancy Atkinson

    One of the biggest unresolved questions of planet formation is how a thick disc of debris and gas surrounding young stars eventually evolves into a thin, dusty region with planets. This entire process, of course, has never actually been observed. But recently, and for the first time, a group of astrophysicists produced an image of material surrounding a star which seems to be coalescing into a planet.

    The image was produced from a coronagraph attached to a telescope in Hawaii. It shows a horseshoe-shaped void in the disc of materials surrounding the star AB Aurigae, with a bright point appearing as a dot in the void.

    “The deficit of material could be due to a planet forming and sucking material onto it, coalescing into a small point in the image and clearing material in the immediate surroundings,” said researcher Ben Oppenheimer, an astrophysicist at the American Museum of Natural History in New York.

    “It seems to be indicative of the formation of a small body, either a planet or a brown dwarf.”

    Full article here:


  • ljk March 28, 2008, 22:20

    The Solar-System-Scale Disk Around AB Aurigae

    Authors: Ben R. Oppenheimer (1), Douglas Brenner (1), Sasha Hinkley (2), Neil Zimmerman (2), Anand Sivaramakrishnan (1), Remi Soummer (1), Jeffrey Kuhn (3), James R. Graham (4), Marshall Perrin (4), James P. Lloyd (5), Lewis C. Roberts, Jr. (6), David M. Harrington (3) ((1)AMNH, (2) Columbia, (3) IfA Hawaii, (4) UC Berkeley, (5) Cornell, (6) Boeing)

    (Submitted on 25 Mar 2008)

    Abstract: The young star AB Aurigae is surrounded by a complex combination of gas-rich and dust dominated structures. The inner disk which has not been studied previously at sufficient resolution and imaging dynamic range seems to contain very little gas inside a radius of least 130 astronomical units (AU) from the star. Using adaptive-optics coronagraphy and polarimetry we have imaged the dust in an annulus between 43 and 302 AU from the star, a region never seen before. An azimuthal gap in an annulus of dust at a radius of 102 AU, along with a clearing at closer radii inside this annulus, suggests the formation of at least one small body at an orbital distance of about 100 AU.

    This structure seems consistent with crude models of mean motion resonances, or accumulation of material at two of the Lagrange points relative to the putative object and the star. We also report a low significance detection of a point source in this outer annulus of dust. This source may be an overdensity in the disk due to dust accreting onto an unseen companion. An alternate interpretation suggests that the object’s mass is between 5 and 37 times the mass of Jupiter. The results have implications for circumstellar disk dynamics and planet formation.

    Comments: 11 pages, 5 figures, accepted for publication in Astrophysical Journal, V. 680, June 10, 2008

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0803.3629v1 [astro-ph]

    Submission history

    From: Sasha Hinkley [view email]

    [v1] Tue, 25 Mar 2008 20:17:45 GMT (818kb)


  • ljk April 2, 2008, 7:11

    Hydro-Gravitational-Dynamics Interpretation of the Tadpole VV29 Merging Galaxy System: Dark-Matter-Halo-Planet Star-Cluster Wakes

    Authors: Carl H. Gibson (Univ. Cal. San Diego)

    (Submitted on 29 Mar 2008)

    Abstract: Hubble Space telescope (HST) images of merging galaxy system VV29 reveal the 0.3 Mpc baryonic-dark-matter (BDM) halo composed of primordial protoglobularstarcluster (PGC) clumps of planets. Star-cluster-wakes trace the merger by formation of stars from the planets. Aligned young globular star clusters (YGCs), star-wakes and dust-trails show the frictional, spiral passage of galaxy fragments VV29cdef in a long tail-like galaxy (VV29b) as the fragments merge on the accretion disk plane of the central spiral galaxy VV29a. The observations confirm the hydro-gravitational-dynamics (HGD) prediction of Gibson 1996 and quasar microlensing inference of Schild 1996 that the dark matter of galaxies is dominated by planets (PFPs) in million-solar-mass clumps. Globular star clusters (YGCs, OGCs, PGCs) preserve the density of the plasma epoch 30,000 years after the big bang when viscous supercluster-fragmentation began. Tadpole images show linear galaxy clusters reflecting turbulent vortex lines of protogalaxy fragmentation at the 0.003 Mpc Kolmogorov-Nomura scale of the plasma before transition to gas. The halo size indicates strong diffusion of PGC primordial-planet-clumps from a cooling protogalaxy as its planets freeze.

    Comments: 8 pages, 7 figures, Practical Problems in Cosmology 2008, St. Petersburg RU, June 23-27

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0803.4288v1 [astro-ph]

    Submission history

    From: Carl H. Gibson [view email]

    [v1] Sat, 29 Mar 2008 21:07:40 GMT (859kb)


  • ljk April 3, 2008, 13:50

    Composition of Ices in Low-Mass Extrasolar Planets

    Authors: Ulysse Marboeuf, Olivier Mousis, David Ehrenreich, Yann Alibert, Arnaud Cassan, Valentine Wakelam, Jean-Philippe Beaulieu

    (Submitted on 2 Apr 2008)

    Abstract: We study the formation conditions of icy planetesimals in protoplanetary disks in order to determine the composition of ices in small and cold extrasolar planets. Assuming that ices are formed from hydrates, clathrates, and pure condensates, we calculate their mass fractions with respect to the total quantity of ices included in planetesimals, for a grid of disk models.

    We find that the composition of ices weakly depends on the adopted disk thermodynamic conditions, and is rather influenced by the initial composition of the gas phase. The use of a plausible range of molecular abundance ratios and the variation of the relative elemental carbon over oxygen ratio in the gas phase of protoplanetary disks, allow us to apply our model to a wide range of planetary systems.

    Our results can thus be used to constrain the icy/volatile phase composition of cold planets evidenced by microlensing surveys, hypothetical ocean-planets and carbon planets, which could be detected by Corot or Kepler.

    Comments: Accepted for publication in The Astrophysical Journal

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0804.0406v1 [astro-ph]

    Submission history

    From: Olivier Mousis [view email]

    [v1] Wed, 2 Apr 2008 18:09:48 GMT (643kb)


  • ljk May 7, 2008, 6:54

    The origin of short-lived radionuclides and the astrophysical environment of solar system formation

    Authors: Gounelle Meibom

    (Submitted on 5 May 2008)

    Abstract: Based on early solar system abundances of short-lived radionuclides (SRs), such as $^{26}$Al (T$_{1/2} = 0.74$ Myr) and $^{60}$Fe (T$_{1/2} = 1.5$ Myr), it is often asserted that the Sun was born in a large stellar cluster, where a massive star contaminated the protoplanetary disk with freshly nucleosynthesized isotopes from its supernova (SN) explosion. To account for the inferred initial solar system abundances of short-lived radionuclides, this supernova had to be close ($\sim$ 0.3 pc) to the young ($\leqslant$ 1 Myr) protoplanetary disk.

    Here we show that massive star evolution timescales are too long, compared to typical timescales of star formation in embedded clusters, for them to explode as supernovae within the lifetimes of nearby disks. This is especially true in an Orion Nebular Cluster (ONC)-type of setting, where the most massive star will explode as a supernova $\sim$ 5 Myr after the onset of star formation, when nearby disks will have already suffered substantial photoevaporation and/or formed large planetesimals.

    We quantify the probability for {\it any} protoplanetary disk to receive SRs from a nearby supernova at the level observed in the early solar system. Key constraints on our estimate are: (1) SRs have to be injected into a newly formed ($\leqslant$ 1 Myr) disk, (2) the disk has to survive UV photoevaporation, and (3) the protoplanetary disk must be situated in an enrichment zone permitting SR injection at the solar system level without disk disruption. The probability of protoplanetary disk contamination by a supernova ejecta is, in the most favorable case, 3 $\times$ 10$^{-3}$.

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0805.0569v1 [astro-ph]

    Submission history

    From: Matthieu Gounelle [view email]

    [v1] Mon, 5 May 2008 16:29:42 GMT (1139kb)


  • ljk May 17, 2008, 0:07

    The birth and death of organic molecules in protoplanetary disks

    Authors: Thomas Henning (1), Dmitry Semenov (1) ((1) Max Planck Institute for Astronomy, Heidelberg, Germany)

    (Submitted on 15 May 2008)

    Abstract: The most intriguing question related to the chemical evolution of protoplanetary disks is the genesis of pre-biotic organic molecules in the planet-forming zone. In this contribution we briefly review current observational knowledge of physical structure and chemical composition of disks and discuss whether organic molecules can be present in large amounts at the verge of planet formation.

    We predict that some molecules, including CO-bearing species such as H$_2$CO, can be underabundant in inner regions of accreting protoplanetary disks around low-mass stars due to the high-energy stellar radiation and chemical processing on dust grain surfaces. These theoretical predictions are further compared with high-resolution observational data and the limitations of current models are discussed.

    Comments: 8 pages, 3 figures, to be published in the IAU 251 proceedings book

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0805.2341v1 [astro-ph]

    Submission history

    From: Dmitry Semenov [view email]

    [v1] Thu, 15 May 2008 15:50:26 GMT (164kb)


  • ljk May 21, 2008, 11:45

    Baroclinic Generation of Potential Vorticity in an Embedded Planet-Disk System

    Authors: Ji Jianghui (1), Ou Shangli (2), Liu Lin (3) ((1)Purple Mountain Observatory, CAS, (2)Louisiana State Univ., (3)Nanjing Univ.)

    (Submitted on 20 May 2008)

    Abstract: We use a multi-dimensional hydrodynamics code to study the gravitational interaction between an embedded planet and a protoplanetary disk with emphasis on the generation of vortensity (Potential Vorticity or PV) through a Baroclinic Instability.

    We show that the generation of PV is very common and effective in non-barotropic disks through the Baroclinic Instability, especially within the coorbital region. Our results also complement previous work that non-axisymmetric Rossby-Wave Instabilities (RWIs) are likely to develop at local minima of PV distribution that are generated by the interaction between a planet and an inviscid barotropic disk. The development of RWIs results in non-axisymmetric density blobs, which exert stronger torques onto the planet when they move to the vicinity of the planet. Hence, large amplitude oscillations are introduced to the time behavior of the total torque acted on the planet by the disk.

    In current simulations, RWIs do not change the overall picture of inward orbital migration but cause a non-monotonic behavior to the migration speed. As a side effect, RWIs also introduce interesting structures into the disk.

    These structures may help the formation of Earth-like planets in the Habitable Zone or Hot Earths interior to a close-in giant planet.

    Comments: 6 pages, 2 figures, accepted to IAU 249. Proceeding of IAU S249: Exoplanets: Detection, Formation and Dynamics, in press

    Subjects: Astrophysics (astro-ph)

    Journal reference: IAU Symposium 249. Cambridge: Cambridge University Press, 2008, pp.407-412

    DOI: 10.1017/S1743921308016918

    Cite as: arXiv:0805.3009v1 [astro-ph]

    Submission history

    From: Jianghui Ji [view email]

    [v1] Tue, 20 May 2008 06:45:30 GMT (252kb)


  • ljk May 22, 2008, 8:00

    Spectro-astrometric imaging of molecular gas within protoplanetary disk gaps

    Authors: Klaus M. Pontoppidan, Geoffrey A. Blake, Ewine F. van Dishoeck, Alain Smette, Michael J. Ireland, Joanna Brown

    (Submitted on 21 May 2008)

    Abstract: We present velocity-resolved spectro-astrometric imaging of the 4.7 $\mu$m rovibrational lines of CO gas in protoplanetary disks using the CRIRES high resolution infrared spectrometer on the Very Large Telescope (VLT). The method as applied to three disks with known dust gaps or inner holes out to 4-45 AU (SR 21, HD 135344B and TW Hya) achieves an unprecedented spatial resolution of $0.1-0.5$ AU.

    While one possible gap formation mechanism is dynamical clearing by giant planets, other equally good explanations (stellar companions, grain growth, photo-evaporation) exist.

    One way of distinguishing between different scenarios is the presence and distribution of gas inside the dust gaps. Keplerian disk models are fit to the spectro-astrometric position-velocity curves to derive geometrical parameters of the molecular gas. We determine the position angles and inclinations of the inner disks with accuracies as good as 1-2\degr, as well as the radial extent of the gas emission. Molecular gas is detected well inside the dust gaps in all three disks. The gas emission extends to within a radius of 0.5 AU for HD 135344B and to 0.1 AU for TW Hya, supporting partial clearing by a $< 1-10 M_{\rm Jup}$ planetary body as the cause of the observed dust gaps, or removal of the dust by extensive grain coagulation and planetesimal formation.

    The molecular gas emission in SR 21 appears to be truncated within $\sim 7 $AU, which may be caused by complete dynamical clearing by a more massive companion. We find a smaller inclination angle of the inner disk of TW Hya than that determined for the outer disk, suggestive of a disk warp. We also detect significant azimuthal asymmetries in the SR 21 and HD 135344B inner disks.

    Comments: 7 pages, accepted for publication in ApJ

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0805.3314v1 [astro-ph]

    Submission history

    From: Klaus Martin Pontoppidan [view email]

    [v1] Wed, 21 May 2008 17:18:36 GMT (2001kb)


  • Tory May 17, 2009, 17:46

    Hi everyone,
    I have been looking everywhere for how a protoplanetary disk is actually formed around the protostar, and I have found nothing that actually helps me to understand. I am an 8th grader, and can read some college level, but some of the definitions can be way too confusing. It would be great if someone could help me.


  • Administrator May 18, 2009, 9:14

    Tory, this stuff can indeed be confusing! One thing you might want to do is check your library for David Grinspoon’s book Lonely Planets. David is an astrobiologist who really knows his stuff, but he also writes clear prose aimed for people who aren’t necessarily scientists. I found his explanation of planet formation to be quite good. The book was published in 2004 and should be in many libraries. If not, it’s on Amazon. Because I’m re-reading it right now, there’s a link to it (and a picture of its cover) on the main Centauri Dreams page, about a third of the way down.