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ScienceWeek
SCIENCE-WEEK
SCIENCE-WEEK - Part 1/3
A Free Weekly Digest of the News of Science
June 5, 1998
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Why does this magnificent applied science which saves work and
makes life easier bring us so little happiness? The simple answer
runs: Because we have not yet learned to make sensible use of it.
-- Albert Einstein
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Contents of This Issue:
Part 1:
1. A Commercial Venture to Sequence the Human Genome
2. On Science and the Craft Industries
3. Science News, Stock Prices, and Book Deals
Part 2:
4. Abderhalden's Fraud Revisited
5. On Quasars
Part 3:
6. Astrometric Signatures of Giant Planet Formation
---------------------------------------------
1. A COMMERCIAL VENTURE TO SEQUENCE THE HUMAN GENOME
This much seems clear: the next century will see the
Genomics Revolution, and major players in that era will be
international corporate entities focused on the making of profit
from detailed knowledge of the human genome, the various aspects
of the genetic basis of human diversity, the genetic basis of
human health risk, and of course from the entire array of non-
human genomics applications to microbial biotechnology,
pharmaceuticals, animal husbandry, agriculture, and so on.
All of these are essentially trivial predictions that follow
immediately from the central idea that we will soon know enough
of the human genome and the genomes of other life forms to
completely understand and control genetic programming. This will
be a serious watershed, but it is part of the intellectual
evolution of the human species, there is no way to avoid it, and
by itself it will certainly not provoke the end of civilization.
One hundred and fifty years ago, there were analysts who declared
the Industrial Revolution would make a great deal of money for a
few people, make many more people miserable, but better the life
of the multitude in incalculable ways. And so it was; and so,
hopefully, it will be for the Genomics Revolution.
But it will not be easy. Watersheds in the application of
science and technology to human existence cannot be expected to
be easy to negotiate. There will be problems, many problems, and
the legislative and managerial people will need to solve these
problems as best they can to minimize the harm to the multitude.
It took a century to achieve in the West a modicum of social
control of the Industrial Revolution. It may take as long as that
to achieve similar control of the Genomics Revolution.
Recently, the scientific community learned that molecular
biologist J. Craig Venter (The Institute for Genomic Research,
US) and the Perkin-Elmer Corporation (US) (the world's largest
manufacturer of automated sequencing machines) will form a new
company to complete the sequence of the entire human genome in 3
years. If successful, this for-profit venture could preempt the
work of the US$3 billion Human Genome Project, a government-
financed coalition of nearly a dozen academic and contract
centers, and apparently do it for a fraction of the cost, as
little as US$300 million. This commercial plan has evidently
split the genome community, and many researchers are concerned
that the new company will not release sequence data as quickly as
the Human Genome Project. In fact, Venter and Perkin-Elmer have
announced that partly to safeguard its proprietary claims, the
new company plans to release raw DNA data quarterly, rather than
on a daily basis as is done now by many federally-funded genome
centers. Delays in releasing genome data are apparently a
sensitive issue in the genome community, and heated debates on
the issue are expected in the near future. Venter and Perkin-
Elmer have also announced they expect to put together from the
work a proprietary set of approximately 100,000 single nucleotide
polymorphisms, and a whole-genome database that will be marketed
to academic researchers and companies on a subscription basis. [A
genetic polymorphism is a naturally occurring variation in the
normal nucleotide sequence of the genome within individuals in a
population.]
(Science 15 May 98 280:994) (Science-Week 5 Jun 98)
2. ON SCIENCE AND THE CRAFT INDUSTRIES
Freeman J. Dyson (Institute for Advanced Study Princeton,
US) reviews the relationship between science and entrepreneurial
craft industries. Dyson proposes that during the past 50 years,
science has given birth to a new golden age of craft industry, a
revival of the application of tool-making hands and inquisitive
brains. The writing of software, for example, remains in large
part a craft industry. The author makes the following points:
1) Science is constantly changing, and the craft industries
that it engenders must change too.
2) Today the most successful craft industries are concerned
with software and biotechnology. The craft industries of the
future might be concerned with neurophysiology or ecology, with
technologies not yet invented or with sciences not yet named.
3) Two facts of life will not change. Science will continue
to generate unpredictable new ideas and opportunities. And human
beings will continue to respond to new ideas and opportunities
with new skills and inventions. We remain tool-making animals,
and science will continue to exercise the creativity programmed
into our genes.
QY: Freeman J. Dyson (dyson@sns.ias.edu)
EMAIL
(Science 15 May 98 280:1014) (Science-Week 5 Jun 98)
3. SCIENCE NEWS, STOCK PRICES, AND BOOK DEALS
A cogent example of the interaction of science, medicine,
the media, the stock market, and personal riches came into public
view recently. The sequence of events in this episode was
apparently as follows:
1) On Sunday, May 3, 1998, *The New York Times* ran a front
page story by Gina Kolata, one of the chief science writers of
*The New York Times*, and a reporter who has been writing about
science for at least 30 years. The story concerned the two
chemicals angiostatin and endostatin that have been known for
some time to block angiogenesis in tumors in mice (see background
material following this report). The chemicals have never been
tested in humans, they are not the only chemicals that achieve
this effect, and they are not available as "drugs" that can be
administered by a physician. But the thrust of the story was that
this was new information, the headline, "A Cautious Awe Greets
Drugs That Eradicate Tumors in Mice." The story quoted Nobel
Laureate James Watson as telling Kolata that Judah Folkman, one
of the primary researchers in the field of anti-angiogenesis
chemicals, "will cure cancer within 2 years" and "will be
remembered along with scientists like Darwin as someone who
permanently altered civilization. Kolata also reported that
Richard Klausner, director of the US National Cancer Institute
said the two chemicals were "the single most exciting thing on
the horizon" for the treatment of cancer, and that they were the
top priority of the National Cancer Institute.
2) On the afternoon of the same day the story was published
in *The New York Times*, a New York book agent named John
Brockman telephoned reporter Gina Kolata about the story and
apparently told her he could get her a US$2 million advance for a
book on the subject. Kolata immediately began writing a book
proposal, and sent the proposal via Email to Brockman within
hours.
3) That evening, all major television networks highlighted
the story that had appeared in *The New York Times*. Brockman
sent the proposal to New York publishers at midnight of that
first day, following the network news reports.
4) At 9:30 the next morning (Monday), Brockman informed
Kolata that he already had the first offer from a major New York
publishing house.
5) Also on Monday morning, the stock of EntreMed Inc. (US),
the company that holds the rights to turn the two chemicals
angiostatin and endostatin into drugs, rose immediately from a
previous Friday closing of US$12 a share to a Monday morning
opening at US$83 a share.
6) Also beginning Monday morning, oncologists and other
physicians around the country found themselves deluged with
inquiries from cancer patients, many of whom were saying they
would be putting off chemotherapy to wait for the new drugs.
7) By the end of the week, the bubble had completely burst:
Other reporters published stories revealing the chemicals named
in the May 3rd *New York Times* story were already well-known,
tested only on mice, and not available at all as drugs. Both
Watson and Klausner backed off from their reported comments,
saying they had been misinterpreted. The price of EntreMed shares
fell back to $30. Kolata withdrew her revealed book proposal
after a discussion with her editors, and the agent Brockman
already had a substitute deal in the works for a book on the
subject by a reporter at another newspaper. Finally, around the
country, physicians had the task of explaining to their patients
that no, a miracle cancer cure was not yet available.
As expected, much is being written about this episode, with
one question in the minds of many people: Why does this happen?
Well, one reason why it happens is that these days news editors
are prone to present features to their readers as "news". This
was a feature article, and it should have appeared as an article
in a magazine, and not on the front news page of *The New York
Times*.
Secondly, the habit that reporters have of using direct
sound-bite quotes from scientists to bolster the apparent
importance of their stories too often produces misinformation,
inappropriate emphasis, and whatnot, and certainly there is a
tendency to avoid quotes that reduce the significance of the
"news". Science-news reporting propped and hyped to be "exciting"
does a disservice to the public and can be dangerous as well. The
James Watson comment, apparently, actually occurred during a
conversation Kolata had with Watson *two months before* at a
dinner table.
In summary, this so-called news story should never have
appeared in the first place as "news", should never have included
quotes from scientists with the quotes deliberately used to hype
the material beyond any significance attributed by specialists,
should never have been used as a prop for a quick lucrative book
deal, should never have been reported the way it was by
television broadcasters. The media, and in particular *The New
York Times*, have been deservedly embarrassed by this episode,
and the credibility of science-reporting by *The New York Times*
has been seriously and unfortunately compromised.
[Editor's note: concerning the science, we are appending
here several relevant reports from past issues of SCIENCE-WEEK.
The reader will observe that the anti-angiogenesis chemical
endostatin was already noted here in December 1997.]
(Science 15 May 98 280:996) (Science-Week 5 Jun 98)
-------------------
Related Background:
CANCER TREATMENT BY TARGETING TUMOR BLOOD VESSELS
Bacteriophage (phage) is a virus type that infects bacteria,
and it has been useful as a cloning vector in genetic
engineering. The phage injects its own DNA into the bacterium,
effectively assuming enough control of the bacterial genome to
replicate itself, with the ultimate disintegration of the
bacterium and liberation of the phage clones.
A "phage library" is a collection of genomic DNA fragments,
each contained in a bacteriophage cloning vector and propagated
by infection of a host bacterium (usually E. coli). The essential
idea, in the context of this report (and in many other research
efforts), is to use the genetic machinery of the phage to control
the metabolic machinery of the bacterium to produce (synthesize)
particular complex biomolecules (such as polypeptides) needed
for
testing.
"Nude mice" are a genetic variant of laboratory mice lacking
a thymus gland, which means they are unable to produce the
T-cells (Thymus-cells) necessary for various aspects of the
mammalian immune response.
The origin and development of tumor blood vessels
(angiogenesis), is an important consideration in the growth of
cancerous tumors, since the tumor provokes directed angiogenesis
into itself with the end result that the tumor is supplied with
oxygen and nutrients. Without angiogenesis, tumors can attain
only a small size before becoming self-inhibiting. A "xenograft"
is a graft of tissue from one species into the body of another
species.
... ... Arap et al (3 authors at Burnham Institute, US)
report the use of in vivo selection of phage libraries to isolate
peptides that home specifically to tumor blood vessels. When
coupled to the anticancer drug doxorubicin, two peptides were
found that enhance the efficacy of the drug against human breast
cancer xenografts in nude mice and also reduced the toxicity of
the drug. The authors suggest their results indicate it may be
possible to develop targeted chemotherapy strategies based on
selective expression of receptors in tumor blood vessels.
QY: Erkki Ruoslahti
(Science 16 Jan 98) (Science-Week 30 Jan 98)
-------------------
Related Background:
CANCER: NO ACQUIRED DRUG RESISTANCE TO ANTI-ANGIOGENIC AGENT
Angiogenesis is the generation of new blood vessels, a
controlled sequence of cell differentiation and tissue formation
programmed by the genome. It is of obvious importance during
embryological development, since new tissues need a blood supply
in order to continue macroscopic growth, and the angiogenesis
process is also of great importance during tissue trauma repair.
Like new embryological tissue, a neoplasm (a tumor) also
needs a blood supply, and one of the characteristics of tumor
growth is the provocation of angiogenesis by the cancer cells so
that the mass of such cells becomes supplied with adequate
vascularization. It is known, for example, that tumors will not
grow beyond a few millimeters in diameter in the absence of a
newly forming blood supply.
Cancer cells apparently provoke angiogenesis by secreting
growth factor substances, and if this is prevented, tumor growth
will be severely limited.
But attempts to chemically interfere with the secretion of
growth factors by cancer cells usually fail because the high
proliferation rate of cancer cells ultimately results in drug
resistance produced by a mutational selection process.
However, the normal epithelial tissue involved in
angiogenesis is not rapidly mutating. Recently, a substance named
endostatin, a 20,000 molecular weight fragment of a type of
collagen, has been found to be a specific inhibitor of
endothelial cell proliferation (which means also of new blood
vessel growth), and it was found that endostatin effects only
proliferating endothelial cells, not resting cells, and not
normal, transformed, or neoplastic cells. It has been shown that
systemic administration of endostatin to tumor bearing mice
results in the regression of tumors to a microscopic size, and
one important question has been whether drug resistance to
endostatin would develop.
... ... Now Boehm et al (4 authors at Harvard Univ., US)
report that endostatin causes three tumor types in mice to
regress without the production of drug resistance, and that
repeated cycles of anti-angiogenic therapy are followed by
prolonged tumor dormancy without further therapy. The authors
suggest that angiogenesis inhibitors that do not induce drug
resistance may be valuable for long-term maintenance therapy.
This is important work, and one expects much will be heard about
endostatin in the future.
QY: Thomas Boehm
(Nature 27 Nov 97) (Science-Week 19 Dec 97)
-------------------
Related Background:
MOLECULAR TARGET OF ANTI-ANGIOGENESIS COMPOUNDS DISCOVERED
... Any clinically useful anti-angiogenesis compound is of
great interest to cancer specialists (oncologists). There are 10
or so anti-angiogenesis agents presently undergoing clinical
trials. One of these (TNP-470) is a derivative of the natural
fungal product fumagillin, whose anti-angiogenesis activity was
first discovered in 1985. Now the cellular target of fumagillin
and TNP-470 has been discovered, a specific protein which appears
to play an important role in the proliferation of endothelial
cells, the cells that line blood vessels. The work was reported
by Craig M. Crews et al (Yale University, US), who suggests the
identification of this protein target will open new avenues of
research for the understanding of tumor-induced
neo-vascularization. The results have been independently
confirmed by Jun O. Liu et al (Massachusetts Institute of
Technology, US).
(Proc. U. S. National Academy of Sciences, 94:6099 1997)
(Chemistry & Biology June 1997) (Science-Week 26 Jun 97)
(continued in Part 2)
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SCIENCE-WEEK - Part 2/3
A Free Weekly Digest of the News of Science
June 5, 1998
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4. ABDERHALDEN'S FRAUD REVISITED
Last year was not a good year for German biological and
medical science, since 1997 was marked by a major fraud scandal
involving two full professors apparently involved in the
fabrication of data published in dozens of scientific papers
during a 9-year period. That story is not yet finished (see
background material below).
Now from Germany comes the publication of a "commentary" by
two scientists, U. Deichmann and B. Muller-Hill, the commentary
revisiting what has come to be considered the fraudulent career
of German scientist Emil Abderhalden (1877-1950). Abderhalden was
a biochemist involved in designing tests for various clinical
disease entities, the tests involving what he called "defense
enzymes" (Abwehrfermente), enzymes which he claimed to have
identified, and which according to his analyses were specific
proteases produced when humans were challenged by foreign
proteins.
During the years 1912 to 1950, Abderhalden enjoyed the
status of one of the most eminent scientists in Germany, was
professor of physiology and physiological chemistry at Halle
University, president of the oldest German academy of science
(the Leopoldina), editor of several journals, and author of
several books and more than 1000 research papers -- and all of
this notwithstanding, the consensus today is that nearly all of
his research on the so-called "defense enzymes" was completely
fraudulent, with scores of colleagues and underlings either
explicitly or implicitly colluding in the fraud over a period of
decades.
It is an ugly story with political tangents (e.g., Joseph
Mengele, the notorious Auschwitz doctor, was one of Abderhalden's
proteges).
In their commentary, Deichmann and Muller-Hill conclude:
"The elite of today [the biomedical elite in Germany] are loyal
students of the old elite, and they have learned and internalized
the old values. Has medical, clinical science in Germany today
really changed that much? We doubt it. The Brach-Herrmann-
Mertelsmann affair provides a brief glimpse into the abyss of
medical science in Germany. Will it be soon forgotten by the
German medical elite, or will there be real change in the spirit
of true science?" [Editor's note: Roland Mertelsmann, Professor
Herrmann's department head, was co-author of 25 suspected papers
produced by Herrmann, but has pleaded non-involvement in the
research.]
QY: Ute Deichmann, Institute of Genetics, Cologne University,
Weyertal 121, 50931, Koeln, DE.
(Nature 14 May 98 393:109) (Science-Week 5 Jun 98)
-------------------
Related Background:
GERMAN RESEARCHER ADMITS FRAUD AND CHARGES ACADEMIC COVER-UP
Producing another chapter in the scientific fraud case that
has caused an apparent sensation in Germany, Marion A. Brach, one
of the accused scientists, has published a letter in the journal
Nature in which she points out the following:
1) She has confessed to falsifying scientific papers;
2) she has resigned her position as a full professor at the
University of Lubeck;
3) she does not believe further victimization is
appropriate;
4) she has concluded that the various German investigating
commissions met only with the intention of limiting damage to the
German academic community rather than with the intention of
discovering the full extent of culpability;
5) the German government has reneged on its legal agreement
to provide her with severance pay following her early confession
and resignation;
6) official bodies have found it expedient to imply that she
was the major or only culprit in the affair.
QY: Marion A. Brach, c/o Walter F. Kalthoff, Pacellistr. 14,
D-80333, Muenchen, DE.
(Nature 2 Apr 98) (Science-Week 17 Apr 98)
-------------------
Related Background:
MORE DEVELOPMENTS IN GERMAN SCIENTIFIC FRAUD CASE
The scientific fraud case that has been shocking the German
intellectual community these past months, and which is claimed to
be the worst case of scientific fraud in that country since
1945,
continues to be a public spectacle.
The scandal involves two German molecular biologists, Marion
Brach (who has resigned as a Professor at Lubeck University),
and
Friedhelm Herrmann (a suspended Professor at Ulm University).
Brach has admitted falsifying published data while she
worked under the supervision of Herrmann at the Max Delbruck
Center for Molecular Medicine a few years ago.
Herrmann claims he is only a clinician and had nothing to do
with the laboratory bench work. Herrmann is a prominent
hematologist and a leading genetic therapy researcher.
The two biologists had worked together for some time, and
each received professorships on the basis of that work.
(Herrmann's salary was apparently US$278,000 per year).
Now it has been announced that Herrmann is suing various
academic investigators in the case for DM10 million (US5.6
million) in compensation for damage to his career. In addition,
there is now a claim by a new investigation team that the two
accused researchers also published falsified data earlier in
their careers.
(Nature 11 Sep) (Science-Week 26 Sep 97)
-------------------
AN UPROAR OVER SCIENTIFIC FRAUD IN GERMANY
The German scientific community was rocked by scandal this
spring, and the resulting repercussions are apparently not yet
complete. The brouhaha involves two German molecular biologists,
Marion Brach (recently resigned as a Professor at Lubeck
University), and Friedhelm Herrmann (a suspended Professor at Ulm
University). Brach has admitted falsifying published data while
she worked under the supervision of Herrmann at the Max Delbruck
Center for Molecular Medicine a few years ago. Herrmann claims he
is only a clinician and had nothing to do with the laboratory
bench work. Herrmann is a prominent hematologist and a leading
genetic therapy researcher. The two biologists have worked
together for some time, and each received professorships on the
basis of that work. All of that work is now being investigated,
and the German government has established a commission of
international scientific experts to discuss research standards
and the procedures for scientific oversight in German and
internationally.
(Science 11 Jul 97) (Science-Week 18 Jul 97)
5. ON QUASARS
If the terminal stages of star death leave a remnant star
mass greater than 3 solar masses, the ultimate gravitational
collapse will produce a black hole, a relativistic singularity.
A black hole is a localized region of space from which
neither matter nor radiation can escape. The "trapping" occurs
because the requisite escape velocity, which can be calculated
from the relevant equations, exceeds the velocity of light and is
therefore unattainable.
Another view of a black hole is that it is a mass that has
collapsed to such a small volume that its gravity prevents the
escape of all radiation.
Space and time essentially have no meaning in a black hole.
The boundary of the black hole is called the "event horizon",
because any event within the boundary is invisible outside, the
invisibility resulting from the fact that no radiation can escape
to be detected.
The radius of the black hole depends upon how much matter
has fallen into the region; it is called the "Schwarzchild
radius", and it is usually a few kilometers. However, massive
black holes are possible and are thought to be the source of
quasars (quasi-stellar objects), which are extremely luminous
sources radiating energy over the entire spectrum from x-rays to
radio waves, and which are apparently the oldest and most distant
objects in the universe. If quasars indeed involve black holes,
the radiation is from material just outside the black hole, and
not from anything within it. Nothing inside a black hole can get
out of it.
... ... Michael Disney (University of Wales, UK) provides an
excellent review of the history and current status of quasar
research. Recent observations have led astronomers to the idea
that quasars are associated with massive galactic-center black
holes generating huge amounts of energy under special
circumstances. The author suggests that in terms of theory, we
need to understand how and when massive black holes form in the
first place. Did they precede or follow the formation of their
host galaxies? Secondly, we need a convincing physical model to
explain exactly how such black holes convert in-falling matter
into all the varieties of quasar radiation, from gamma rays to
superluminal radio jets, and the formulation of such a model may
not be easy.
The author concludes with a quote by Carole Mundell of the
Jodrell Bank Observatory (UK): "Observing quasars is like
observing the exhaust fumes of a car from a great distance and
then trying to figure out what is going on under the hood."
QY: Michael Disney, University of Wales, Cardiff, UK.
(Scientific American June 1998) (Science-Week 5 Jun 98)
-------------------
Related Background:
... In contrast to quasar black holes, there have been
identified black holes of mere stellar mass associated with
"microquasars".
... ... Mirabel and Rodriguez (2 installations, FR MX)
review the accumulated evidence concerning microquasars in our
Galaxy. Microquasars mimic on a smaller scale many of the
phenomena seen in quasars, and their discovery opens the way for
a new understanding of the connection between the accretion of
matter onto black holes and the origin of the relativistic jets
observed in remote quasars. The repeated observation of two-sided
moving jets in microquasars has led to a much greater acceptance
of the idea that the emission from quasar jets is associated with
material moving at speeds close to that light.
QY: I.F. Mirabel (mirabel@discovery.saclay.cea.fr)
EMAIL
(Nature 16 Apr 98 392:673) (Science-Week 8 May 98)
-------------------
Related Background:
ON THE USE OF QUASAR SPECTRA TO STUDY GALAXY HALOS
Quasars (a contraction of quasi-stellar objects) were
discovered in the early 1960s. They are superluminous, evidently
compact, and they radiate over a wide range from x-rays through
the optical to radio wavelengths.
Every quasar shows an extremely large redshift, which means
they are at great distances, the greatest distances, in fact, of
any known astronomical objects. Assuming the redshifts result
from expansion of the universe, the quasars are thus also the
oldest astronomical objects known.
At the present time, quasars are considered to be the active
cores of extremely distant galaxies, black hole cores that
produce superluminosities external to the core as the black holes
slowly devour the stars that surround them.
Since they are so distant, and therefore so old, the spectra
of the quasars are of interest in themselves. But there is
another angle to spectroscopic investigations of the quasars: by
analyzing redshifts of certain absorption lines in quasar
spectra, one can learn a great deal about any interstellar
gaseous material that intervenes between a particular quasar and
Earth. The essential idea is that as the light from any
particular quasar passes through a gas cloud on its way to Earth,
the chemical constituents of the gas cloud absorb parts of the
quasar spectrum, leaving dark lines in the spectrum, the dark
lines associated with particular elements. By analyzing both the
wavelengths and redshifts of these lines, one can learn a great
deal about these interstellar gas clouds, particularly the
interesting gas clouds that apparently surround many galaxies.
... ... In a recent review of gas cloud absorption effects
in quasar spectra, Jill Bechtold (University of Arizona, US), a
specialist in quasar absorption line systems, summarizes the
evidence that suggests that galaxies are indeed surrounded by
huge halos of gas several hundred thousand light years in
diameter. There are many questions about these galactic halos
that need to be answered, and the hope is the Hubble Space
Telescope, which can be used to examine redshifts in the ultra-
violet, will provide important new information.
QY: J. Bechtold, Dept. of Astronomy, U. Arizona (602) 621-3237
(Sky and Telescope September 1997) (Science-Week 22 Aug 97)
(continued in Part 3)
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SCIENCE-WEEK - Part 3/3
A Free Weekly Digest of the News of Science
June 5, 1998
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6. ASTROMETRIC SIGNATURES OF GIANT PLANET FORMATION
The discoveries during the past two years of giant planets
orbiting nearby solar-type stars has raised again the question of
how these planets are formed. Two different models have been
proposed. The gravitational instability model involves formation
of planets directly from the gas in the accretion disk around the
young star. The alternative model is the core-accretion model, in
which rocky cores of about 10 Earth masses form first, with that
followed by hydrodynamical accretion of gas to form the massive
envelopes of the giant planets.
... ... Alan P. Boss (Carnegie Institution of Washington,
US) now proposes, on the basis of calculations, that these two
processes have very different astrometric signatures, and that it
should be observationally possible to distinguish between them.
Planets that form through gravitational instabilities do so
rapidly, so that within just a few hundred years of the onset of
the instability the nascent planet is making the young stellar
object wobble in its orbit. This can be seen in the youngest
stellar objects, with ages as little as 0.1 million years. If
planets form by core accretion, an observable wobble will not be
visible for 10-20 million years.
The author suggests that observations of a suitable ensemble
of optically visible young stellar objects (such as those in the
Taurus molecular cloud) over a period of several decades should
be able to determine which of the two processes is responsible
for the formation of giant planets.
QY: Alan P. Boss (boss@dtm.ciw.edu)
EMAIL
(Nature 14 May 98 393:141) (Science-Week 5 Jun 98)
-------------------
Related Background:
FURTHER EVIDENCE FOR A PLANET ORBITING STAR 51 PEGASI
Doppler-shift is an observed change in spectrum frequencies
when the source of the spectrum or the observer move either
toward or away from each other.
In astronomy, radial velocity is the velocity of a star
along the line of sight of an observer, determined by measuring
the Doppler-shift in the star's spectrum, and periodic
perturbations of an observed stellar Doppler-shift have in some
cases been interpreted as evidence for the existence of a massive
object orbiting the star. A massive planet around the star 51
Pegasi was reported last year by Meyor and Queloz, but a
subsequent paper by D. Gray challenged their interpretation of
the data on the basis of spectral line-shape oscillations that
would indicate the Doppler-shift perturbations originated in the
stellar surface.
... ... D. Gray (Univ. of Western Ontario, CA) now reports
that recent new monitoring of 51 Pegasi showed an absence of his
previously published spectral line-shape oscillations that
previously called into question the Doppler-shift data as
indicating an orbiting planet. The author suggests his previous
results were noise, and that these new results, together with
other high-precision measurements by other researchers, indicate
the planet hypothesis as the best explanation for the
radial-velocity perturbations. (cf. contiguous paper by Hatzes et
al).
QY: David F. Gray
(Nature 8 Jan 98) (Science-Week 23 Jan 98)
-------------------
Related Background:
A MODEL FOR THE MIGRATION OF MASSIVE PLANETS
Planetesimals are bodies with dimensions of 10^(-3) to
10^(3) meters that are believed to form planets by a process of
accretion.
The term "accretion" refers to an aggregation, an increase
in the mass of a body by the addition of smaller bodies that
collide and adhere to it, provided the relative velocities are
low enough for coalescence. As the mass of the agglomerate
increases, so does the rate of accretion, and this accretion
process is believed to generally occur in the form of a disk.
A stellar accretion disk is a swarm of dust grains that
evolve into planetesimals and then planets.
There is now evidence of apparent massive planets in close
orbits around stars, but the formation of such massive planets in
close orbits is unexplained. One possibility is that these
massive planets were formed in a more distant orbit and then
migrated inward.
... ... Murray et al (4 authors at 2 installations, CA) now
report a theoretical analysis of the behavior of planets and
planetesimals in a stellar disk. The calculations predict that
gravitational interactions and collisions between planet and
planetesimals, if total planetesimal surface density exceeds a
certain value, may drive the planet inward a great distance. The
authors suggest this mechanism may explain the presence of
Jupiter-mass objects in small orbits around nearby stars.
QY: N. Murray, Univ. of Toronto, Dept. of Theoretical Astro-
physics, Toronto, ON M5S 3H8 CA.
(Science 2 Jan 98) (Science-Week 16 Jan 98)
-------------------
Related Background:
GIANT PLANET EVIDENCE CONFOUNDS SOLAR SYSTEM THEORISTS
Until recently, speculations and theories about planets
orbiting other stars than our sun have depended on our own solar
system as the guiding model. But during the past two years,
astronomers have been able to gather information about nine such
planets, and the evidence is apparently not in harmony with
expectations.
The three variables that are evidently making trouble for
theorists are planet size, proximity to the parent star, and
orbital eccentricity. For example, the planet orbiting the star
51 Pegasi is large enough to have about half the mass of Jupiter,
but seems to be orbiting the star at a radius of one-sixth the
radius of Mercury's to our sun. This is a puzzle, although there
appears to be still controversy about whether this planet is
actually a planet. Others of the discovered planets are
apparently in highly eccentric and unexplained orbits.
So the theorists are busy revising models for planet
formation, establishment of orbits, planetary orbital drift, and
so on. The major difficulty is that there are no direct
observations of these discovered planets -- their existence is
proposed to explain perturbations in the behavior of their parent
stars. Stephen Lubow of the Space Telescope Science Institute
(Baltimore MD US) says of the recent observations: "It's been a
revolution."
(Science 30 May 97) (Science-Week 5 Jun 97)
-------------------
Related Background:
A GRAVITATIONAL INSTABILITY MODEL FOR GIANT PLANET FORMATION
Until recently, the consensus theory for the formation of
large planets such as Jupiter was the core accretion model
involving the formation of cores of approximately 10 times Earth
mass, followed by rapid accretion of gas from the primitive solar
nebula. The problem with this model is that the time needed for
accretion (about 1 million years) is of the order of magnitude of
the time during which a young solar-type star's gas dissipates.
The other possible model is one involving a gravitational
instability mechanism in which the solar nebula breaks up into
giant gaseous protoplanets which then contract and collapse to
form giant planets. This model was in the past abandoned because
the extant data concerning the masses of Jupiter and the outer
planets seemed incompatible with the model. But there is now new
data concerning the masses of Jupiter and the outer planets, and
this week Alan P. Boss (Carnegie Institution of Washington, DC
US) reported a revisit to the gravitational instability model,
with computer solutions of the relevant equations of
hydrodynamics coupled with the Poisson equation in a spherical
coordinate system, such solutions providing evidence that the
formation of giant protoplanets in a gaseous nebula disk can
indeed occur. The old gravitational instability model has
therefore apparently been revived.
(Science 20 Jun 97) (Science-Week 26 Jun 97)
-------------------
Related Background:
EVIDENCE OF A PROTOPLANETARY DISK AROUND A YOUNG STAR
The current nebula theory of planet formation proposes that
star-planet systems begin as a contracting cloud of gas and dust
that flattens into a rotating disk. The center of this cloud
becomes the star, and the planets eventually form in the disk of
the nebula. In the inner part of the nebula, the hottest part,
only high density minerals can form solid grains. The outer
regions are cooler, and in those regions icy materials of lower
density are formed.
Planets grow from these solid materials, beginning as dust
grains, which grow by condensation and accretion into
planetesimals that range from a few centimeters to a few
kilometers in diameter. These planetesimals settle into a thin
plane around the star and accumulate into larger bodies, the
largest of which grow the fastest and eventually become
protoplanets.
Once the star becomes a luminous object, the remaining
nebula is cleared as the star's radiation and the stellar-wind
(powerful streams of charged particles from the star's surface)
push the remnants out of the system. Thus ends the phase of
planet-building.
As might be expected, the above theory is also the current
view of the history of our own solar system. Since the details of
disk formation, and the physical properties of protoplanetary
disks, can be modelled by quantitative theory, the general idea
is to investigate such disks that are apparent around stars to
test the theoretical models. There is no way to do that with our
own solar system, because the protoplanetary disk is long gone.
One needs young stars. ... ... This week Vincent Mannings et al
(California Institute of Technology, CA US) report observations
and analysis of the apparent protoplanetary disk of a star only 6
million years old, with a mass of 2.3 solar masses. The mass of
the disk is evidently greater than the minimum required to form a
planetary system like our own.
QY: V. Mannings
(Nature 7 Aug 97) (Science-Week 15 Aug 97)
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