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A galaxy of new worlds: Dispatch from the American Astronomical Society meeting


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Exoplanet Corot-7-BWASHINGTON, D.C.—The American Astronomical Society meeting, held here this week, was officially the largest congregation of astronomers (3,400 of them) in history—the most extraordinary collection of cosmic knowledge that has ever gathered together with the possible exception of when Isaac Newton dined alone. The breadth of topics was astounding, but the one that stood out was the study of planets beyond our solar system. The Kepler space observatory‘s discoveries got the most attention, but I filled an entire notebook with other exoplanetary findings and theorizing.

What makes exoplanets so much fun is not only that they bring astronomers closer to their dream of finding another Earth out there, but that the planets never fail to surprise. Every new planet-finding technique brings new looks of astonishment. For the Doppler-shift technique that discovered the first exoplanet around a sunlike star, the surprise was that planets can orbit so close to their stars. For the transit technique now being employed by Kepler, it’s that the planets have unexpected densities.

Jupiter- and Saturn-mass planets in tight orbits are less dense than expected—as low as about 0.1 gram per cubic centimeter. Styrofoam was the metaphor of choice at the meeting, perhaps because sleep-deprived astronomers and journalists had coffee on their minds. One reason for such fluffy planets might be that stars heat them up and puff them out, but theorist Dimitar Sasselov of Harvard University says he’s doubtful. For one thing, stellar radiation warms the top of the atmosphere, whereas to puff up a planet you need to inject the energy deep inside. Tidal heating—whereby the star’s gravitational forces knead the planet and warm it up as surely as bending a paper clip back and forth makes it hot—could do the trick for planets that have noncircular orbits, but most don’t. Another idea is that the planet may retain more of the heat generated during its formation.

For more modest worlds like Uranus and Neptune, the problem is that the planet mass and size don’t form a continuum. There’s a distinct gap between these planets and the larger ones. One idea is that those smaller worlds used to be bigger and their outer layers of gas boiled off after billions of years of relentless stellar heating. Brian Jackson of NASA’s Goddard Space Flight Center calculates that a Saturn-like planet close to its star could shed 100 Earth-masses over a few billion years.

At the very lowest end of known planetary size, approaching Earth in size, the density mystery is the wide range of density values, which hints at a diversity of composition scarcely imagined a decade ago.

Properties such as density reflect how planets form and evolve, but reconstructing this history has been hindered by observational selection effects. In perhaps my favorite talk at the meeting, Scott Gaudi of Ohio State University described how neither the Doppler nor the transit technique so far has been able to take a representative sample of planets—partly because they are inherently sensitive to large, close-in planets, partly because astronomers have organized their observations to maximize their chances of discovering planets rather than getting good statistics. So astronomers don’t know whether they’re seeing the rule or the exceptions.

Gaudi’s own technique of gravitational microlensing—whereby a planet reveals itself by passing in front of a background star and temporarily magnifying the starlight—avoids the second problem (sample selection). It monitors millions of background stars and imposes no prejudice about what might pass in front of them. It doesn’t avoid the first problem (biased sensitivity), but complements other techniques by picking up planets on more distant orbits. That’s where giant planets, even those that are on tight orbits, are thought to originate.

Gaudi’s µFUN survey—a shoestring operation that combines the efforts of professional and amateur astronomers—has found five planetary systems so far, one with a pair of planets analogous to Jupiter and Saturn. If each of the 13 stars in the survey had planets, a total of 18 should have turned up, taking into account the biases of the technique.

Venturing to do statistics with this tiny sample, Gaudi and his colleagues conclude that one in three stars has a planet—whereas the Doppler technique implies only one in 20. If so, most planets stay in the distant orbits where they form rather than migrate inwards. Moreover, the occurrence of one planetary pair out of six cases hints that such pairs occur in one of six systems—which makes our solar system a minority, but not a complete outlier.

As theorists struggle to interpret the data, observers continue to improve their instrumentation. Ron Walsworth of the Harvard-Smithsonian Center for Astrophysics described a new technology that could allow the Doppler technique, still the gold standard, to detect Earths. The technique looks for a planet’s slight tug on its host star; Earth causes the sun to move about 10 centimeters per second. Today’s state of the art can detect a velocity of perhaps 1 meter per second. One problem is the lack of a sufficiently stable and precise yardstick for measuring spectral lines and their minute Doppler shifts. Walsworth argued that the answer may be laser frequency combs, which sounds like a scary cousin of laser hair removal, but is in fact an ultraprecise frequency standard created by rapidly pulsing lasers.

Despite these advances, Kepler is still the best hope for finding the first true Earth analogue. A planet in an Earth-like orbit only goes in front of its star once a year, by definition, so it will take Kepler a few more years to spot one. In the meantime, it will generate plenty of excitement—and not just about planets. By monitoring millions of stars for planets, the observatory can’t help but glean information about those stars. Natalie Batalha of San Jose State University used Kepler to tackle an old question: how typical is the sun? The sun’s brightness oscillates by a fraction of a percent. Are other stars of its spectral type similarly serene?

The answer appears to be yes. The 20 brightest G-type stars are just as stable. Indeed, of 43,000 G-type stars that Batalha examined, two-thirds are, if anything, less prone to activity such as solar flares. Their relative tranquility, as much as the discovery of planets, improves the prospects for life elsewhere in the Milky Way.

Artist’s impression of CoRoT-7b, the smallest-known exoplanet around a sunlike star: ESO/L. Calçada





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  1. 1. fyngyrz 5:55 pm 01/8/2010

    "of 43,000 G-type stars that Batalha examined, two-thirds are, if anything, less prone to activity such as solar flares."

    This relative tranquility also means that for intelligent life there, radio will have different characteristics, and those frequencies that we used to such good effect, the shortwave bands, will be nearly useless for long distances much of the time.

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  2. 2. jtdwyer 7:10 am 01/9/2010

    Even if a right sized planet at the right distance from a right sized star were found, there now appears to be many other factors critical to the development of complex life, including post-accretion deposition of sufficient water. These conditions may only be detectable through spectroscopy of directly observed reflected light from the subject planet. Other necessary conditions may be practically undetectable, including the presence of a persistent sufficiently protective magnetic field and a stable climate, which may require a lucky collision with a smaller planet to create a singular relatively massive moon.

    It took billions of years of photosynthesis for pervasive simpler life forms to produce the oxygen required by the prevailing complex life forms on Earth. Observations of the Earth made during much if not most of its existence may have not clearly indicated conditions favorable to the development of complex life.

    The search for intelligent life based on EM transmissions seems even less promising. Out of the 4.5B year history of our planet, radio transmissions have been detectable for perhaps 150 years, and may be discontinued at any time. Detection of transmissions from a simultaneously developing Earth duplicate could not be made for a period of time nearly equal to its transmission distance from Earth. Detection of transmissions from distant planets may require anomalous, so far undemonstrated, persistence of transmitting technological societies.

    The search for complex life may be likened to a search for a needle of specific sharpness in a stack of needles. Such a huge investment of precious astronomical resources for so little benefit! The present efforts cannot even claim to be collecting useful inventory data. Endeavors such as these may disqualify humanity as intelligent life on Earth but, as long as we’re having fun…

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  3. 3. wolfkiss 1:57 pm 01/9/2010

    "Huge investment"; not really.

    http://www.thespacereview.com/article/898/1

    Not only is understanding our place in the Universe fun, it has more benefit than our bloated military and social systems, which we pay fantastically more for.

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  4. 4. jtdwyer 2:52 pm 01/9/2010

    Point taken – good luck on politicians solving world problems.
    I do believe there are some scarce resources committed to this effort, including telescope and astronomer time, that could better be used for other scientific purposes.

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  5. 5. tylatkin 12:05 am 01/11/2010

    I like the reference to the JFK quote regarding a gathering of Nobel laureates at the white house "I think this is the most extraordinary collection of talent, of human knowledge, that has ever been gathered at the White House – with the possible exception of when Thomas Jefferson dined alone."

    I wonder, is the author purposefully trying to suggest the superiority of Newton over Jefferson? He does specify the congregation as a "collection of cosmic knowledge" which may be distinct from the respect given to Jefferson.

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  6. 6. grapedog 3:28 pm 01/11/2010

    I imagine that he specifically singled out cosmic knowledge to go with his usage of Issac Newton.

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  7. 7. debu 11:45 pm 01/11/2010

    Astronomical conferences are not benefitting much unless an agenda based discussion with concerned people are taken up. I expected my balloon inside balloon theory and theory of gravitoethertons will be taken up but there is no mention. First we have to discuss where Einstein has gone wrong and I have discussed in gravitoethertons theory precisely that to understand its application locally and not in vast cosmos. I have told ether is gravitoethertons and not dragable due to few times light speed and perpendicular to Michelsons table. But no confirmation and I think it is another copenhagen show and unless we want to acknowledge others and want to live in fools paradise of relativity, we may not understand the cosmos and cosmology.

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  8. 8. debu 10:18 am 01/13/2010

    Dr.Roger Penrose declared physics wrong and we are asking him why he is not mentioning Einstein was not very correct though partly locally correct and as such we must not apply his theory beyond locally and understand where he has gone wrong. So physics is maturing to a level more understandable if we understand and accept where Einstein gone wrong. All mathematical models may not describe reality and even reality may not be explained by mathematical model. We have to change our outlook of time, space and we must not combine space-time and time can never be a dimension. I have invented a coordinates theory of forward-backward,top-bottom and left right where string theory can be projected rejecting time as dimension but always positive . Then if you re strucure the theory converting into spherical coordinates then considering gravitoethertons as vibrating spots of planck length then you may be surprised of its many variations in a spectrum of frequency. Does that mean that our six quarks are nothing but symphony of the strings as in violin. Six dimension is more correct than three cartesian coordinates and time is entropical phenomena not dimension but always positive. This six dimensional string theory can be applied on avogadros law to see what happens in the solar like orbits of atoms and again miracle of mendeleefs periodic table . Very promising if we can go little further but our tends to type calculus is not powerful enough as it is good for engineers but not so accurate for scientists and we have think about it.

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  9. 9. Quinn the Eskimo 2:34 am 01/15/2010

    Thank god for Exo-planet research!

    Think about it. If it weren’t for these guys / gals having Star Trek to do, the havoc, mischief, mayhem they could cause.

    Better keep these "boy scouts" busy–or else they might actually do something with all that talent.

    Link to this
  10. 10. Weir 9:55 pm 01/16/2010

    There are curious resonances in the dynamics of the terrestrial planets that indicate deficiencies in current theories of celestial dynamics. Gravitational torque was believed to hold Mercury in autorotation about the sun in the same way as the Moon around the Earth. Then it was discovered that its rotation period is 58.65 days which is 2/3 (0.6667) of its revolution period of 87.97 days. A year is precisely half a day on Mercury since it exposes opposite faces to the sun on each revolution. It has no tilt to its axis and no seasons. One Venus day (117 Earth days) is 2/3 (0.665) of a Mercury day (175.94 Earth days). The rotation period of Venus is (243.17 Earth days) which is 2/3 (0.666) of an Earth Year (365.24 days). Moreover Venus is in retrograde rotation and every time it comes directly between the Earth and the sun it exposes the same face toward the Earth, even though exactly five Venus days have elapsed between such conjunctions. Mars is outside of Earth without direct resonances with other planets, however there are 666.8 Mars solar days of 24.6587 hours in a Mars year. It is an extraordinary coincidence that resonances such as these should arise with the terrestrial planets. There is no explanation for them in classical dynamical theory or in current theories of planetary formation.

    Current theories are based on the assumption of a continuous universe and there is a variety of evidence that space and time are discontinuous. Zeno’s arrow would never reach the target if space and time could be infinitely divisible. In 1888 the mathematician Richard Dedekind showed that continuous space is not consistent with irrational numbers. Bell’s Inequalities and quantum correlation indicate universal influences. In a discontinuous universe atoms are synchronously projected as a succession of independent space frames linked by light that together define space and time a posteriori to creation. Universals interact with particulars is such a way that the ratio of 2/3 tends to crop up, as it does in quark theory. As more evidence accumulates from more powerful detection techniques, a re-examination of celestial dynamics from a discontinuous perspective might help in the search for planets where organic life can evolve.

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