Looking Directly at Extrasolar Planets 92
D2Deek writes "Science Daily is reporting on a new device called an Optical Vortex Coronagraph that's been invented to directly image planets orbiting other stars by using a special lens that "spins out" the light from the star leaving only the reflected light from the planet." I just can't imagine trying to clean a lens shaped like a giant corkscrew.
Re:The light of a planet (Score:3, Informative)
I thought a planet must be illuminated by light from a star, and not emitting light itself?
What this is referring to is the light directly from the star outshining the planet's reflected light.
I would assume, at anyrate. I am still trying to load the article.
Re:The light of a planet (Score:4, Informative)
Actual Press Release text (Score:4, Informative)
A new optical device might allow astronomers to view extrasolar planets directly without the annoying glare of the parent star. It would do this by "nulling" out the light of the parent star by exploiting its wave nature, leaving the reflected light from the nearby planet to be observed in space-based detectors.
About ten years ago, the presence of planets around stars other than our sun was first deduced by the very tiny wobble in the star's spectrum of light imposed by the mutual tug between the star and its satellite. Since then, more than 100 extrasolar planets have been detected in this way. Also, in a few cases the slight diminution in the star's radiation caused by the transit of the planet across in front of the star has been observed. Many astronomers would, however, like to view the planet directly, a difficult thing to do.
Seeing the planet next to its bright star has been compared to trying to discern, from a hundred meters away, the light of a match held up next to the glare of an automobile's headlight. The approach taken by Grover Swartzlander and his colleagues at the University of Arizona is to eliminate the star's light by sending it through a special helical-shaped mask, a sort of lens whose geometry resembles that of a spiral staircase turned on its side.
The process works in the following way: light passing through the thicker and central part of the mask is slowed down. Because of the graduated shape of the glass, an "optical vortex" is created: the light coming along the axis of the mask is, in effect, spun out of the image. It is nulled, as if an opaque mask had been placed across the image of the star, but leaving the light from the nearby planet unaffected.
The idea of an optical vortex has been around for many years, but it has never been applied to astronomy before. In lab trials of the optical vortex mask, light from mock stars has been reduced by factors of 100 to 1000, while light from a nearby "planet" was unaffected (see figure).
Attaching their device to a telescope on Mt. Lemon outside Tucson, Arizona, the researchers took pictures of Saturn and its nearby rings to demonstrate the ease of integrating the mask into telescopic imaging system. This is, according to Swartzlander (520-626-3723, grovers@optics.arizona.edu), a more practical technique than merely attempting to cover the star's image, as is done in coronagraphs, devices for observing our sun's corona by masking out the disk of the sun. It could fully come into its own on a project like the Terrestrial Planet Finder, or TPF, a proposed orbiting telescope to be developed over the coming decade and designed to image exoplanets.
Foo et al., Optics Letters, 15 December 2005 Summary of articles related to optical vortex on Swartzlander's Web page
Someone more patient than I can put in the links to the figures. See http://aip.org/pnu/2005/755.html [aip.org] for everything.
corky screw reflection (Score:2, Informative)
Re:The light of a planet (Score:4, Informative)
(Actually, I don't know if the proportions are even remotely close, but meh.)
Here's additional linkage (Score:3, Informative)
Optical Vortex Coronagraph Figures
Optics Letters Preprint (4.8 Mb) [nyud.net][pdf] --- To Appear 15 December (ol.osa.org)
This work first appeared in the Master Degree Thesis of Greg Foo:
OSC QC350.O77 Vol. 353, 2005.
Re:Replacing coronography (Score:4, Informative)
"These calculations assume no aberrations or other scattering sources, and they assume the vortex mask can be made achromatic."
http://www.u.arizona.edu/~grovers/ovc.html [arizona.edu]
In other words, the lens material is made from unobtanium and the rest of the system has to be perfect. The author certainly knows this will never happen.
Mike
Re:The light of a planet (Score:2, Informative)
Re:The light of a planet (Score:3, Informative)
15years*300000km/s*86400s*364.25days = 14162040000000km, not 472068000km
Thus, the angle comes to 5.63e-7 degrees, or 0.002 arcseconds
Re:The light of a planet (Score:3, Informative)
I think you dropped a 300,000 km/s.
15 years * 300000 km/s * 86400s * 364.25days != 472068000km, it's 141620400000000km
(should probably use 365.25 days per year, not 364.25, but that's minor)
atan(139200km/141620400000000km) is ~ 0.00000005 degrees according to my calculator,
which seems a lot more astronomical.
Re:The light of a planet (Score:2, Informative)
On a side note, Eps Eri C (the smaller planet) seems to orbit about 28 au from its parent star - I would think this would be a perfect candidate for this technology! (I'm too lazy to work out the math right now, however, bonus points to anyone who does.)
Re:The light of a planet (Score:5, Informative)
Re:The light of a planet (Score:5, Informative)
Re:Extra-solar planets? (Score:2, Informative)
Re:The point (Score:3, Informative)
And you know this because you have witnessed the entirety of nature? Or this has been deduced and isn't actually a fact, but an assumption?
Actually, O2 does appear in places other than our planet (places assumed to be devoid of life), just not in abundance. But even an abundance is only a hint that life exists. There are inorganic processes that can create oxygen. These usually don't create abundant amounts, but we've only witnessed natural processes on a handful of planets and moons. There's always the possibility that some process we haven't witnessed in our own solar system could be creating abundant supplies of oxygen on a planet in another solar system.
Not that this is at all likely, but it's certainly possible.
Re:The point (Score:2, Informative)
Indeed. The real catch is, oxygen tends to get consumed by other common geological and chemical processes. If all life on Earth died today, oxygen would become a trace element in the Earth's atmosphere within a few thousand years (i.e. practically instantaneously on a geological timescale). Whatever process was generating atmospheric O2 would have to be doing it currently and continuously and on a massive scale. Although alternatives are not impossible, so far, there is only one process in nature known to do fit this bill: life. Occam's Razor would suggest if such an atmosphere were discovered, this would be the best assumption to make, rather than proposing new entites (in this case, new, unprecedented plant-wide processes -- of course, astronomy books are full of a history of unprecedented discoveries).
Of course, we'd have more to go on than just O2. Life turns the whole atmosphere topsy-turvy, probability wise. Earth's atmosphere has numerous chemicals in it at levels that are wildly improbable for a world dominated by inorganic processes. If there are other worlds rich in life, the improbable O2 level would just be the tip of the iceberg. A truly living world should be pretty easy to identify with a spectroscope...