by Paul Gilster | Jan 12, 2005 | Exoplanetary Science
The American Astronomical Society’s 205th national meeting, in San Diego, California, ends tomorrow. And this meeting is special: the last attendance projection Centauri Dreams saw was 2500, with 1640 papers submitted, 180 scientific sessions, and 70 new Ph.D dissertations presented. All in all, we’ll have material for months ahead coming out of AAS, and as always, we’ll pay special attention to extrasolar planetary studies, with the occasional foray into the mind-boggling world of cosmology.
Let’s start with Hubble data that support the idea there is a planet orbiting a brown dwarf 225 light years away in the constellation Hydra. Last spring, the European Southern Observatory’s Very Large Telescope reported on a possible planetary companion to the star, which has the mind-boggling designation 2MASSWJ 1207334-393254 (we prefer its nickname: 2M1207). The object in question is one-hundredth the brightness of the parent star, burning (according to this news release at the European homepage for Hubble) “…at barely 1000 degrees Celsius, which is cooler than a light bulb filament.”
The University of Arizona’s Glenn Schneider presented this work at AAS. From the news release:
“The NICMOS [Hubble’s Near Infrared Camera and Multi-Object Spectrometer] photometry supports the conjecture that the planet candidate is about five times the mass of Jupiter if it indeed orbits the brown dwarf,” says Glenn Schneider of the University of Arizona, USA. “The NICMOS position measurements, relative to VLT’s, indicate the object is a true (and thus orbiting) companion at a 99 percent level of confidence – but further planned Hubble observations are required to eliminate the 1 percent chance that it is a coincidental background object which is not orbiting the dwarf.”
Probable age of the object: approximately 8 million years, based on its position within the TW Hydrae stars, all of which are estimated to be about this old. Distance from the primary: 8 billion kilometers (4.97 million miles), 30 percent farther than Pluto from the Sun. It would take 2500 years for this planet to circle its star.
by Paul Gilster | Jan 11, 2005 | Astrobiology and SETI, Culture and Society
Centauri Dreams‘ hunch about extraterrestrial life is that it’s ubiquitous. The guess is that we’ll eventually find off-Earth biospheres right here in the Solar System, probably on Mars, perhaps on one or more of the Jovian moons, possibly in the atmospheres of one or more of the gas giants (and the Venusian atmosphere is now drawing serious interest). We’re likely to find simple life around extrasolar stars in equal profusion.
This is a heartening thought, but the key word is ‘simple.’ For the other half of the Centauri Dreams hunch is that extraterrestrial intelligence is rare. At one point, Carl Sagan was estimating there might be one million civilizations existing at any given time in our galaxy. The betting here is that the number is between 1 and 10, with the likelihood being 1. See Ward, Peter and Donald Brownlee, Rare Earth: Why Complex Life is Uncommon in the Universe (New York: Copernicus Books, 2000) for the background to this argument.
But we needn’t be troubled if we find no other civilizations, a point Martin Rees makes in Our Cosmic Self-Esteem, the third part of a three-part interview with Astrobiology Magazine. Rees is Britain’s Royal Astronomer, a professor of cosmology and astrophysics and Director of the Institute of Astronomy at Cambridge. His contributions range from the origins of the cosmological background radiation to the black holes that apparently reside at the heart of quasars. As always, Rees is worth quoting at length:
I think another perspective astronomy brings to bear on these issues is that astronomers are aware of the tremendous time span lying ahead of us. Most educated people are aware that we are the outcome of nearly four billion years of Darwinian selection, and I think many tend to think humans are the culmination of all that. But astronomers know that our sun is less than halfway through its life span. Our sun will flare up and die six billion years from now, a period of time longer than the sun’s history so far. Some people imagine that there will be humans watching the sun’s demise six billion years from now, but any creatures that exist then will be as different from us now as we are from bacteria or amoebae.
We should think of ourselves as still in the early stage of the emergence of complexity and intelligence. It’s hard to conceive what forms that might take on Earth or far beyond Earth. But I think we should see ourselves as nowhere near the culmination of evolution.
Even if life is now very rare in the galaxy or unique to Earth, that doesn’t mean life is forever going to be a trivial afterthought in the cosmos. In the time lying ahead, life from Earth could spread all through the galaxy. The Earth could be cosmically important as the seed from which life spreads more widely.
You can read the rest of the Rees interview here. And don’t miss Rees’ own take on long-term thinking, spurred by the fact that his new book The Final Century was published in America as The Final Hour. Seeing this as another example of our need for instant gratification, the bane of measured thought, Rees says “I was really annoyed about that.” Amen.
by Paul Gilster | Jan 10, 2005 | Exoplanetary Science, Missions
In Finding Other Worlds, Edna DeVore of the SETI Institute zeroes in on the importance of the Kepler Mission. Scheduled for an October 2007 launch, Kepler is likely to discover hundreds of extrasolar planets. And as DeVore writes, “Kepler is the first observatory capable of finding Earth-size worlds in the habitable zone of distant Suns. In other words, Kepler may find ‘good places to live.'”
Some key points about Kepler:
To find planets, the mission will use the transit method, looking for the dimming of a star caused by repeated transits of a planet across its face.
The size of a planet can be calculated from changes in the star’s brightness, and the size of its orbit can be measured.
The parameters of the mission are the most challenging ever attempted for extrasolar detection. Kepler is designed to survey nearby stars to determine how often terrestrial and larger planets occur in the habitable zone of different types of star. This, in turn, will allow the follow-on Space Interferometer Mission (2010) to target systems already known to have terrestrial planets.
By ‘habitable zone,’ the Kepler scientists mean the distances from a given star where liquid water can exist on the planet’s surface.
The changes in brightness to be measured are vanishingly small. According to NASA, “Transits by terrestrial planets produce a fractional change in stellar brightness of 5 x 10-5 to 40 x 10-5 lasting for 2 to 16 hours. The orbit and size of the planets can be calculated from the period and depth of the transit.”
Kepler will test two hypotheses: that most main sequence stars have terrestrial planets in or near the habitable zone, and an average of two Earth-sized planets form in the region between 0.5 and 1.5 AU (based on our own Solar System, and what we now believe about planetary formation).
We now know about approximately 130 planets around other stars, a number which should increase enormously by 2007. But Kepler will likely be the first chance at detecting terrestrial worlds, paving the way for the Terrestrial Planet Finder mission that will study such planets in detail. For more on the mission, see NASA’s Kepler page.
by Paul Gilster | Jan 8, 2005 | Culture and Society
“The existence of plausible fastship concepts suggest[s] that once the available technology base has grown sufficiently large, small bands of explorers and pioneers will make the leap between stellar oases. How large the movement of people might be depends, of course, on the cost. If fastship voyages require a significant fraction of the total human wealth, they will be few and far between. We can estimate the relative cost. The sun outputs enough energy to permit 50,000 emigrants to leave the Solar System each second (if that were the only use of the gathered sunlight). If, by the time humanity is ready for the interstellar adventure, our descendants have managed to tap even a modest fraction of the solar output, they could easily afford emigration at a rate sufficient to sustain the human expansion. If we take the figure of 500 men, women, and children, a number suggested by studies of breeding populations among surviving hunter and gatherer peoples, as the minimum size of a genetically and socially healthy population, and if we stretch the launch period over a year, a collector 3700 km across will suffice to launch one such party each year. The need to carry a deceleration mechanism would increase the cost, which could be partially alleviated by building the collector closer to the Sun. The reader may make a private assessment as to the feasibility of such a system; but keep Clarke’s laws in mind and remember that human capabilities have a way of growing with time. We are not invoking dramatic scientific breakthroughs, just engineering on a very large scale by a people, our descendants, already used to living and working in space.”
From Finney, Ben R. and Eric M. Jones, “Fastships and Nomads: Two Roads to the Stars,” an essay in a collection the authors edited, Interstellar Migration and the Human Experience (Berkeley: University of California Press, 1985), pp. 94-95.
Centauri Dreams‘ take: Interstellar Migration and the Human Experience deserves a place in the library of anyone interested in our future in space. Long out of print, it can still be tracked down in used book stores or on the Internet. The book consists of the proceedings of the Conference on Interstellar Migration held at Los Alamos in May of 1983, and the range of its authors — biologists, physicists, historians, anthropologists — gives a sense of its multidisciplinary approach. There is simply no other book like it.
by Paul Gilster | Jan 7, 2005 | Exoplanetary Science
The ‘concordance’ model of the universe suggests that it is mostly composed of dark matter. In fact, a cluster of hundreds of galaxies would, in the concordance scenario, house fully 90 percent of its mass in dark matter. Never mind that we know almost nothing about dark matter — theorists have still been able to simulate how it would clump together, forming an intricate substructure that should be capable of observation.
Now a Yale astronomer and her colleagues have used gravitational lensing to study galactic clusters, finding a tight fit between the concordance model’s predictions and their observations. A gravitational lens might be a galaxy that intervenes between us and a more distant object, focusing the light from that object so that we see things we would not otherwise be able to observe.
Says assistant professor of astronomy and physics Priyamvada Natarajan:
“We used an innovative technique to pick up the effect of precisely the clumps which might otherwise be obscured by the presence of more massive structures. When we compared our results with theoretical expectations of the concordance model, we found extremely good agreement, suggesting that the model passes the substructure test for the mass range we are sensitive to with this technique.”
Do these clumps provide the insights we’ll need to understand what dark matter is? If so, expect to hear a great deal more about them, and soon. Natarajan’s work appeared as “Substructure in Clusters of Galaxies,” Astrophysical Journal Letters 617: L13-L16 (December 10, 2004). Also see “Quantifying substructure using galaxy-galaxy lensing in distant clusters,” available here (PDF warning). Other articles on substructure in galactic clusters and gravitation lensing can be found at her Yale Web page.
Centauri Dreams‘ take: gravitational lensing is rapidly becoming a key tool for distant observations, and we’ve seen a variant of it called ‘microlensing’ suggested as a possible way to detect planets around stars in the galactic core. A mission to the gravitational lensing point some 550 AU from the Sun will one day allow us to use our own star as a gravitational lens. Gregory Matloff reviews gravity lens mission concepts — including a 60-year mission of his own design — in his book Deep Space Probes (Chichester, UK: Springer-Praxis, 2000), pp. 27-29.
