by Paul Gilster | Mar 14, 2006 | Exoplanetary Science |
9000 light years away, a planet thirteen times as massive as the Earth orbits a star half the size of the Sun. At -330 degrees Fahrenheit, the newly discovered planet is one of the coldest worlds ever discovered. And its placement within its solar system is interesting indeed, for the icy object occupies an area where, in our system, the asteroid belt holds sway. “We’ve never seen a system like this before,” said Andrew Gould (Ohio State University, and leader of the MicroFUN collaboration, “because we’ve never had the means to find them.”
MicroFUN (MicroLensing Follow-Up Network) is exoplanetary hunting via gravitational microlensing. A star crosses in front of a far more distant one as seen from Earth. The gravity of the intervening object bends light rays from the more distant star and magnifies the image, operating much like a lens. From our observational standpoint, the image of the star brightens as the ‘lensing’ star crosses in front of it, then fades as the lens moves further away. If there are any planets around the foreground star, they can create additional distortions to the light, thus making their presence known to astronomers.
It was the OGLE (Optical Gravitational Lensing Experiment) collaboration that first found the microlensed star last April while looking toward the galaxy’s center. After gathering extensive data, Gould and OGLE leader Andrzej Udalski (Warsaw University Observatory) worked through computer models that confirmed the existence of the planet. They believe it is a ‘super-Earth’, a mixture of rock and ice with a diameter several times that of Earth. Gould’s team argues that one-third of all main sequence stars are likely to have icy super-Earths like this one.
Image: The discovery of a “super-Earth” orbiting a red dwarf star 9,000 light-years away suggests that such worlds are three times more common than Jupiter-sized planets. The 13-Earth-mass planet (shown in this artist’s conception with a hypothetical moon) was detected by a search for microlensing events, in which the gravity of a foreground star distorts the light of a more distant background star. Microlensing is the only way to detect Earth-mass planets from the ground with current technology. Credit: David A. Aguilar (CfA).
This could mean super-Earths are more common than the Jupiter-class worlds we have grown used to finding through our exoplanet hunts. “Our discovery suggests that different types of solar systems form around different types of stars,” explains Scott Gaudi (Harvard-Smithsonian Center for Astrophysics). “Sun-like stars form Jupiters, while red dwarf stars only form super-Earths. Larger A-type stars may even form brown dwarfs in their disks.”
Microlensing is remarkably promising in terms of detecting small worlds. Listen to Gaudi again:
“Microlensing is the only way to detect Earth-mass planets from the ground with current technology. If there had been an Earth-mass planet in the same region as this super-Earth, and if the alignment had been just right, we could have detected it. By adding one more two-meter telescope to our arsenal, we may be able to find up to a dozen Earth-mass planets every year.”
The name of the new world? OGLE-2005-BLG-169Lb. The paper is Gould, Udalski, Bennett, et al., “Microlens OGLE-2005-BLG-169 Implies Cool Neptune-Like Planets are Common,” now available at the arXiv site, with abstract here.
by Paul Gilster | Mar 13, 2006 | Exoplanetary Science |
We have interesting exoplanetary news coming up in tomorrow’s post, but until then let’s talk about Pluto, and the latest Hubble findings about this intriguing system. The two recently found moons are now seen via Hubble imagery to have the same color as Charon, meaning that all three Plutonian satellites are roughly the same shade as Earth’s moon. That’s an interesting finding, because it suggests that all three moons were formed in the same event. It’s also interesting given the reddish hue of Pluto itself, about which we’ll learn more in the years leading to the New Horizons encounter in 2015.
Image: The new HST/ACS observations made on March 2nd reveal that all three of Pluto’s satellites are neutrally colored, unlike reddish Pluto itself. Pluto’s reddish color is believed to be due to reddening agents created by the effects of sunlight acting on its nitrogen and methane surface ices. Charon’s surface is known to consist primarily of water ice; the similar color of P1 and P2 may indicate they too have water ice surfaces. The color similarity of Pluto’s two small satellites to one another and to Charon is consistent with their all having been born as a result of a single giant impact, as previously indicated by their orbits and Charon’s large mass. Credit: NASA, ESA, A. Stern (SwRI) and Z. Levay (STScI).
Pluto thus reinforces our view that the Solar System can be a very dangerous place. For the event we’re speaking of was doubtless a collision between Pluto itself and another object of about the same size. We had already begun to realize that the Moon that hangs in our own sky was the result of a similar collision in the inner system, and the evidence grows that the Kuiper Belt is likely littered with the debris of such impacts. It’s all good reason, even in our more sedate planetary era, to keep our eyes on near-Earth asteroids and to push for continuing research into the kind of technologies that could deflect large objects before they ever present a serious threat to Earth.
Centauri Dreams‘ note: This work, which was conducted by Hal Weaver (Johns Hopkins University Applied Physics Laboratory) and Alan Stern (Southwest Research Institute, and principal investigator for New Horizons), examined the images of Pluto and its moons by running them through blue and red/green filters. Ahead are more observations using filters at longer wavelengths to obtain new information on what the moons are made of — in these redder wavelengths, ice and mineral absorption lines should provide information about the surface.
As for New Horizons, the spacecraft performed a 76-second burn on March 9 to adjust its course for the Pluto ‘keyhole’ around Jupiter, that point that will provide the optimum gravity boost as the vehicle rounds the giant planet. New Horizons is currently moving along at a robust 37.5 kilometers (23.3 miles) per second.
by Paul Gilster | Mar 11, 2006 | Deep Sky Astronomy & Telescopes |
New Scientist is running an interesting piece by Zeeya Merali on the the theories of George Chapline (Lawrence Livermore National Laboratory) and Robert Laughlin (Stanford University), which attempt to explain both dark matter and dark energy in a way that would revise our view of black holes. The duo and their colleagues have examined the collapse of massive stars in relation to quantum critical phase transitions in superconducting crystals. During such transitions, electron fluctuations slow down, suggesting what might happen on the surface of a collapsing star.
From the article:
[Chapline] and Laughlin realised that if a quantum critical phase transition happened on the surface of a star, it would slow down time and the surface would behave just like a black hole’s event horizon. Quantum mechanics would not be violated because in this scenario time would never freeze entirely. “We start with effects actually seen in the lab, which I think gives it more credibility than black holes,” says Chapline.
With this idea in mind, they – along with Emil Mottola at the Los Alamos National Laboratory in New Mexico, Pawel Mazur of the University of South Carolina in Columbia and colleagues – analysed the collapse of massive stars in a way that did not allow any violation of quantum mechanics. Sure enough, in place of black holes their analysis predicts a phase transition that creates a thin quantum critical shell. The size of this shell is determined by the star’s mass and, crucially, does not contain a space-time singularity. Instead, the shell contains a vacuum, just like the energy-containing vacuum of free space. As the star’s mass collapses through the shell, it is converted to energy that contributes to the energy of the vacuum.
Now if this view is correct, the vacuum energy inside the shell would have anti-gravity properties like those of the dark energy that is presumed to be responsible for the acceleration of the universe’s expansion. Thus we move from black holes to ‘dark energy stars,’ with observational effects like the formation of accretion disks and the gravitational effects on nearby matter remaining the same. But there is this major difference: quantum critical shells would allow particles to move both into and back out of the shell.
And this is the part of the article I found the most fascinating: the strength of the vacuum energy inside a dark energy star is related to its size. If you calculate the amount of energy that would be in a star as large as the universe, the value matches the value of dark energy calculated in the universe today. Says Chapline, “”It’s like we are living inside a giant dark energy star.” The scientists also take a shot at explaining dark energy as the result of the formation of tiny dark energy stars created in the big bang.
All this is fascinating stuff, and the development of next generation telescopes may put it to the test, since the model predicts the infrared signature to be expected from matter falling into a dark energy star. It would be a humbling lesson indeed if we were forced to abandon the older model of black hole formation in favor of these new dark stars, and a reminder that we have a long way to go before living up to Stephen Hawking’s famous statement in A Brief History of Time (New York: Bantam, 1988). Remember it?
However, if we discover a complete theory, it should in time be understandable by everyone, not just by a few scientists. Then we shall all, philosophers, scientists and just ordinary people, be able to take part in the discussion of the question of why it is that we and the universe exist. If we find the answer to that, it would be the ultimate triumph of human reason — for then we should know the mind of God. (p. 193)
The ‘if’ in Hawking’s first sentence above may be the biggest ‘if’ in the history of science.
by Paul Gilster | Mar 10, 2006 | Outer Solar System |
A few years ago, the idea of life on Enceladus would have seemed preposterous, but the Cassini orbiter has sent back images suggesting that the Saturnian moon houses reservoirs of liquid water near the surface. And liquid water is intriguing indeed in any discussion of life.
“We realize that this is a radical conclusion – that we may have evidence for liquid water within a body so small and so cold,” said Dr. Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, Colo., and the lead author of the report in the journal Science. “However, if we are right, we have significantly broadened the diversity of solar system environments where we might possibly have conditions suitable for living organisms. It doesn’t get any more exciting than this.”
Take a look at the high-resolution Cassini image above (and be sure to click to enlarge it), where a spray of material is clearly visible above the moon’s southern polar region. Then compare to the image below, where the colors have been enhanced to make the contours (and extent) of the plume more apparent. What catches the eye is the sheer extent of the ejected material, which seems to rule out simple frozen mist condensing out of a plume of water vapor. The most plausible solution here is liquid water near the surface erupting like the geysers of Yellowstone.
Image credits: NASA/JPL/Space Science Institute.
What happens to the vapor and ice that is ejected? The evidence points to much of it falling back to the surface, which would account for the south pole’s bright surface, although some of this material evidently feeds Saturn’s E-ring and spreads oxygen into the Saturnian system as the water molecules break down. What we now have to figure out is why the south pole region is as warm as it is, an issue being studied in terms of a combination of tidal flexing and heating of the interior by radioactive materials that may power the geysers.
Enceladus now emerges as the fourth place in the Solar System — after Earth, Io and (perhaps) Triton — to show active volcanism. The March 10 issue of Science includes a set of papers on Enceladus including the one discussed above, which is Porco, Helfenstein, Thomas, et al., “Cassini Observes the Active South Pole of Enceladus,” pp. 1393-1401, with abstract available here.
by Paul Gilster | Mar 9, 2006 | Deep Sky Astronomy & Telescopes
A new seven-pixel radio ‘camera’ installed on the 300-meter Arecibo radio dish two years ago this April has brought extraordinary new sensitivity to the huge radio telescope. Called the Arecibo L-Band Feed Array (ALFA), the system of detectors is being used to image large areas of sky at a much faster rate than before, while searching for tricky time-variable phenomena like pulsars. The latter are rapidly spinning neutron stars that are the result of supernovae.
Where the Arecibo upgrade impacts interstellar flight studies is in what it may tell us about some of the most crucial subjects in cosmology. Stephen Torchinsky, who is the former ALFA project manager, has this to say:
“ALFA is going to discover probably 1,000 new pulsars that we haven’t seen yet,” said former ALFA project manager Stephen Torchinsky. “The expectation is that we’re going to find some exotic objects. We could use these systems to test the limits of the theory of relativity — and at the most extreme cases, to find gravitational waves.”
ALFA is a a cluster of seven cooled dual-polarization feeds, a fiber-optical transmission system, and digital back-end signal processors that will significantly broaden Arecibo’s capabilities. One key study that it will enable is a survey of extragalactic objects. This includes a search for radio targets in distant hydrogen clouds, with the expectation that Arecibo will detect some 20,000 galaxies at distances up to 750 million light years.
And out of that work we are likely to learn a great deal about dark matter. High on astronomers’ lists is the discovery of dark galaxies, those widely hypothesized objects believed to consist largely of dark matter and hydrogen gas but few — if any — stars. Scientists at Cornell University are creating a computer system to manage the data that may help us understand these elusive structures, which would be invisible to optical telescopes.
The word at Arecibo is that the ALFA changes aren’t entirely for the good, in that ALFA science has become such a hot ticket that individual proposals may have a harder time finding acceptance. But the creation of huge archival databases that will sharpen our knowledge of exotic matter and help us probe fundamental theories of the universe seems a tradeoff worth making.
