by Paul Gilster | Feb 17, 2009 | Exoplanetary Science |
Alan Boss, whose new book The Crowded Universe will soon be on my shelves (and reviewed here), has driven the extrasolar planet story to the top of the news with a single statement. Speaking at the American Association for the Advancement of Science’s annual meeting in Chicago, Boss (Carnegie Institution, Washington) said that the number of Earth-like planets in the universe might be the same as the number of stars, a figure he pegged at one hundred billion trillion.
A universe teeming with life? Inevitably. The Telegraph quoted Boss on the matter in an early report on his presentation:
“If you have a habitable world and let it evolve for a few billion years then inevitably some sort of life will form on it,” said Dr Boss.
“It is sort of running an experiment in your refrigerator – turn it off and something will grow in there.
“It would be impossible to stop life growing on these habitable planets.”
Few Centauri Dreams readers would disagree with the notion that life may be common in the universe, but what about intelligent life leading to technology? That’s a far greater challenge, and Boss notes that our own civilization will be unlikely to exist in another 100,000 years. The odds on our running into another civilization at roughly the same stage of development are vanishingly small. Let’s see what Kepler finds. The planet-hunter lifts off in a scant three weeks on a mission Boss believes will find a habitable terrestrial planet within four years. How we would accomplish the unmanned mission to study this world that Boss refers to is something we continue to speculate about on Centauri Dreams.
Apropos of Boss’ comments, our man in the maritime antipodes, Paul Titze, sends along this memorable quotation from Christiaan Huygens, who wrote of these matters in 1695:
What a wonderful and amazing Scheme have we here of the magnificent Vastness of the Universe! So many Suns, so many Earths, and every one of them stock’d with so many Herbs, Trees and Animals, and adorn’d with so many Seas and Mountains! And how must our wonder and admiration be increased when we consider the prodigious distance and multitude of the Stars?
by Paul Gilster | Feb 16, 2009 | Exotic Physics |
Cosmic inflation, first proposed by Alan Guth (MIT) in 1979, seems about as intractable a subject as dark energy. How to study it? Inflation does something mind-bending to spacetime by making it expand far faster than the speed of light. Oddly, this doesn’t contradict anything Einstein said, because while nothing we know can travel faster than light through spacetime, there is no restriction implied in these equations on the expansion of spacetime itself. This is why Miguel Alcubierre’s ‘warp drive’ notions can fit within an Einsteinian universe.
After all, what Alcubierre proposed in his 1994 paper was that a spacecraft that could create the right kind of spacetime distortion would at no point in its journey go faster than the speed of light. Compressing spacetime in front while expanding spacetime behind, it would itself remain within a ‘bubble’ of normal spacetime. Of course, the amount of energy required to achieve this feat (and it’s negative energy, at that) may render the Alcubierre drive nothing more than a theoretical construct for we Kardashev Type 0 civilizations, as more than a few theorists have pointed out (more on this in the archives, if you’re interested).
But can we be sure that inflation happened in the early universe? Finding its traces would be a breakthrough of no mean proportion. One group trying to do just that is working with data from the South Pole Telescope (SPT), searching for evidence that comes in two forms, the first the result of fluctuations in the density of subatomic particles. Take the tiniest such fluctuation and write it large through the instantaneous power of inflation and you should see traces in the structure of the universe. Such fluctuations, says Scott Dodelson (University of Chicago) are common and, as presently understood, fit with inflation theory:
“Usually they’re just taking place on the atomic scale. We never even notice them. That picture [of a sudden stretching into cosmic proportions] actually works. We can calculate what those perturbations should look like, and it turns out they are exactly right to produce the galaxies we see in the universe.”
But such observations aren’t enough, for there are other ways to explain the early universe. To pin down a hot Big Bang emerging from a quantum fluctuation, something else is needed, and in the case of the SPT work, that something is gravity waves. Inflation would have stretched them to cosmic proportions as well, which is why the SPT team is building a highly sensitive polarimeter to attach to the telescope. Operating at submillimeter wavelengths, the instrument may be able to make the crucial gravity wave detection some time during the next decade.
Image: The South Pole Telescope under the aurora australis (southern lights). Credit: Keith Vanderlinde.
I’ll be fascinated to learn what Alan Guth says about this ongoing investigation. Guth shares a platform today with Dodelson and University of Chicago astronomer John Carlstrom at a three-hour session at the American Association for the Advancement of Science’s annual meeting in Chicago. Inflation, dark matter, and dark energy offer potent reminders of how much we have to debate at such meetings. “We have these key components to our picture of the universe, but we really don’t know what physics produces any of them,” adds Dodelson. “The goal of the next decade is to identify the physics.” It’s shaping up to be quite a decade.
by Paul Gilster | Feb 14, 2009 | Outer Solar System |
Comet C/1919 Q2 Metcalf catches the attention. The intriguing object was discovered in August of 1919 and remained visible until early 1920, but no subsequent observations have been made. In 1973, Allan Cook discovered that the Omicron Draconids meteor stream seemed to be following the orbit of the earlier comet. Suspicion is strong that the comet broke up and that the Omicron Draconids are simply the result of that event, a manifestation of cometary debris.
All of which makes the fireball that streaked through European skies last July a bit more interesting than your average bolide. A new paper will suggest that the boulder that caused it — probably a meter across and massing 1.8 tons — was a chunk of the original comet, a boulder that broke apart from the original ice and rock nucleus as C/1919 Q2 Metcalf disintegrated. That would mean we have comet fragments out there waiting to be discovered. Josep M. Trigo-Rodríguez (Institute of Space Sciences, CSIC-IEEC, Spain) explains:
“If we are right, then by monitoring future encounters with other clouds of cometary debris, we have the chance to recover meteorites from specific comets and analyse them in a lab. Handling pieces of comet would fulfill the long-held ambitions of scientists – it would effectively give us a look inside some of the most enigmatic objects in the Solar System.”
Image: A close-up image of the Bejar bolide, photographed from Torrelodones, Madrid, Spain. Credit: J. Perez Vallejo/SPMN.
A fascinating prospect indeed. The fireball was seen on July 11, 2008 at 2117 UTC, reaching an intensity 150 times brighter than the full Moon. Tracked by three stations of the Spanish Fireball Network, it disappeared at an altitude of 21.5 kilometers above the town of Bejar, near Salamanca in Spain. Studying large pieces of a comet in a laboratory would reward the search for fragments, but tracking them down won’t be easy. The paper is Trigo-Rodríguez et al., “Observation of a very bright fireball and its likely link with comet C 1919 Q2 Metcalf,” scheduled for publication in Monthly Notices of the Royal Astronomical Society (abstract). An RAS news release is also available.
by Paul Gilster | Feb 13, 2009 | Exoplanetary Science |
Will the first ‘super-Earth’ in the habitable zone of its star be found around a red dwarf? An M5-dwarf with both mass and radius about a quarter that of the Sun would have 1/200th Sol’s luminosity. That’s interesting for transit purposes, for a planet in the habitable zone around this star would be close in indeed, some 0.074 AU out, with an orbital period of 14.8 days. Its transit probability would correspondingly be raised by a factor of three compared to the Earth-Sun system.
The result, as laid out by the transit survey called MEarth: Detecting such planets should be possible from the ground. Take a look at the live video of what MEarth is doing. Based at the Fred Lawrence Whipple Observatory on Mt. Hopkins in Arizona, the team works with 1976 nearby red dwarfs, visiting each repeatedly in hopes of snaring an ongoing transit, whose information would then be routed to larger instruments for confirmation. They’re looking at targets spread over the entire celestial northern hemisphere and varying the parameters of each observation to the individual target star. And for this survey, the smaller stars are best:
…the most favourable targets for such a transit survey are, in fact, the smallest stars: although these are intrinsically fainter, the reduced count rates are compensated by having deeper transits, and their faintness increases the number of suitable comparison stars available for a given field-of-view. It is important to recall that for small field-of-view observations of single targets, the noise in the comparison light curve can become an important, or even dominant, contributor to the total noise budget. We therefore further choose to concentrate on the smallest stars…
Small, low luminosity stars with possible planets in a habitable zone close enough to the parent to permit ground-based detection — these are exciting thoughts as we tune up our transit methods and await the launch of Kepler. The small radius of M-dwarfs means that any transiting super-Earth is going to block that much more starlight, throwing a clearer transit signature. We can add in the fact that the small stellar mass coupled with a close-in planet also offers a much clearer radial velocity signature for follow-ups.
Working at infrared wavelengths just longer than visible light, MEarth’s eight robotic telescopes will need a total of two years to complete the survey of its target stars. And there’s this on potential findings:
The design study indicates that a yield of 2.6 habitable zone super-Earths would be predicted if the true occurrence of these planets was 10% around our targets, with larger and closer-in planets being easier to detect. A null result would limit the occurrence of > 2 R? super-Earth planets in the habitable zones of late-M dwarfs to be < 17% at the 99% confidence level, a result that again becomes a stronger limit for closer-in planets.
Remember the key advantages of transits. Measuring the planet’s size by examining the amount of light it subtracts from the star’s light can, when combined with radial velocity data, determine the planet’s true mass and help us work out its density. The James Webb Space Telescope, scheduled for a 2013 launch, might then be able to give us spectral information as starlight filters through a planetary atmosphere. Science News has a good story on MEarth, from which this quote by David Charbonneau (Harvard-Smithsonian Center for Astrophysics), whose team is behind the MEarth project:
“My goal is very much to learn about the robustness of life in different stellar environments. If we find planets in the habitable zones of low-mass stars, and determine that these planets have all the right building blocks for life—for example that they are rocky, are at room temperature and have liquid water—but find no life upon them, that would be a very interesting result indeed.”
There are all kinds of reasons why M-dwarfs might be hostile to life, including the consequences of flare activity on closely orbiting planets (not to mention the nature of super-Earths themselves). But one step at a time, as we first try to determine just how common such worlds are. The paper is Irwin et al., “The MEarth project: searching for transiting habitable super-Earths around nearby M-dwarfs,” appearing in Proceedings of the 253rd IAU Symposium: “Transiting Planets” (May 2008, Cambridge, MA) and available online.
by Paul Gilster | Feb 12, 2009 | Asteroid and Comet Deflection |
Things move around in the story queue here, but occasionally a particular item almost gets past me before I remember to cover it. Such is the recent work on the possible impact event some 12,900 years ago, which Richard Firestone (Lawrence Berkeley Laboratory) and colleagues have argued would have contributed to the extinction of such large mammals as woolly mammoths and mastodons, not to mention causing continent-wide wildfires that could have brought about the end of the Clovis culture in North America.
The period in question comes at the beginning of the Younger Dryas, a 1300-year cold spell whose termination saw the temperature of Greenland warm by over 5°C in just a few decades (see comments below). We’ve speculated about the possibility of an asteroid or comet impact on Centauri Dreams (the most recent story is here), but new analysis casts doubt on the theory. Sandy Harrison (University of Bristol) has gone to work on charcoal and pollen evidence to study how wildfires affected North America between 15,000 and 10,000 years ago. The team used charcoal and pollen accumulation in lake sediments to see whether fire regimes continent-wide showed a response to the rapid warming.
The result: There is no evidence for fires on a continent-wide scale. There are clear changes in fire frequency, however, whenever the climate changes abruptly. In fact, the authors find increases in biomass burning during periods of rapid climate change not only at 13,900 years ago, but again at 13,200 years ago and 11,700 years ago, with the timing of these changes not coincident with any changes in human populations or megafauna extinctions. The notion that a comet exploded over North America to trigger an extinction event thus appears less likely. If it did occur, it did not lead to a single, continent-wide fire event.
I dig into all this because those of us who argue that a space-based infrastructure is critical for planetary survival have an interest in publicizing the dangers of asteroid and comet impacts. But possible impacts have to be subject to the same critical methods as any other investigations, and the evidence for a Younger Dryas impact is now rendered less credible. Richard Firestone disagrees, commenting about Harrison’s work to the BBC:
“Their data is too low resolution to say much about what happened 12,900 years ago. The paper merely shows that fires increased near the onset of the Younger Dryas and continued for some time. These results are in complete agreement with what we observed.”
The more we learn about impact events, the better, and that includes finding out when extinctions are actually the result of climate change or other causes. Good science goes for the truth, wherever it may lead. The paper is Marlon et al., “Wildfire responses to abrupt climate change in North America,” Proceedings of the National Academy of Science (February 3, 2009 — published online before print). The abstract is here; the BBC story referenced above is also available online.
