NASA designs new space telescope optics

Feb 15, 2013 by Ruth Dasso Marlaire
The PIAA system uses two specially designed non-spherical optics to reshape the light in the pupil of the telescope into a new "high-contrast" pupil pattern. Credit: Dominic Hart

Although hundreds of planets orbiting other stars have been discovered in the past 15 years, we cannot yet answer the age-old question of whether any of these planets are capable of sustaining life. However, new NASA technology may change that, by giving us our first look at distant planets that not only are the right size and traveling in the temperate habitable zone of their host star, but also show signs of potential life, such as atmospheric oxygen and liquid water.

Research scientists at NASA's Ames Research Center, Moffett Field, Calif., are developing new space that won't just detect similar to Earth, but actually take photos of them. To take photos, called "direct imaging," a new technology will be used called phase-induced amplitude apodization (PIAA). In development since 2003, it is a proof-of-concept and technology tested prototype that is a strong candidate for NASA's upcoming direct imaging exoplanet missions expected to launch in the 2020 decade and beyond.

"By blocking the glare and diffraction from the star, we can start seeing planets that would otherwise be obscured. With this technology, direct imaging confirmation of a exoplanet would happen for the first time," said Ruslan Belikov, a NASA astrophycist and technical lead of the coronagraph technical experiment at Ames.

Today, scientists use primarily indirect methods, such as the "transit method," to detect extra-solar planets. This method measures the dimming of a star as the planet passes between it and the telescope's line of sight. By observing the changes in starlight, scientists can determine a planet's size, its distance from the , and the . This method is currently used by NASA's , which was launched in 2009 to find Earth-size planets in the habitable zone.

In the future, however, a different approach in design and concept may be used to detect common biomarkers of life, such as oxygen and , on planets similar to Earth orbiting sun-like stars. PIAA is a "direct imaging" technique, which means it takes actual photos of exoplanets. The difficulty in taking such photographs is that the star's brilliance causes diffraction and glare to overwhelm dim planets in orbit around it. To solve this problem, a telescope needs to suppress the diffraction of the starlight.

The PIAA system uses two specially designed non-spherical mirrors to reshape the light in the pupil of the telescope into a new "high-contrast" pupil pattern. This new high-contrast pupil has the special property of confining all diffraction and glare from the star into a small spot, which virtually blocks all the starlight without appreciably affecting the light from the planet.

Instruments that block starlight are typically called "coronagraphs" (originally invented to block our sun's brilliance, so we can see its outer gaseous envelope or corona). PIAA is a particularly powerful type of a coronagraph, approaching fundamental physics limits.

Telescopic optics have tiny imperfections, called aberrations, that cause unclear images of the star. Optics completely free of aberrations presently cannot be made, but can be corrected by separate mirrors that can actively change shape. "These mirrors are called deformable mirrors. They counteract the existing distortions of the telescope optics," explained Belikov.

PIAA, or coronagraphs in general, block the brilliance of starlight, but only can work sufficiently to reveal Earth-size planets if telescope optics are perfect, which they never are. The deformable mirrors correct these imperfections with their wavefront control system. This system "fixes" the imperfect telescope optics to enable the coronagraph to work properly.

At the Ames coronagraph experiment facility, the deformable mirror, built by Boston Micromachines Corp., Mass., is a one-by-one centimeter square that employs a grid of 32-by-32, or 1024 actuators, which can generate any shape desired on the mirror. By controlling the shape of the surface of the error-compensating deformable mirror, the aberrations in the telescope can be reduced sufficiently to allow Earth-size planets to be directly imaged.

Telescopic optics have tiny imperfections, called aberrations, that cause unclear images or patterns.

"The surface of these deformable mirrors can be set to such high precision that we are incapable of measuring it," said Belikov.

Although PIAA is approved for further development, it still is awaiting a mission. It is designed for two classes of missions: one for small telescopes, the other for very large telescopes. A small telescope proposal, called Exoplanetary Circumstellar Environments and Disk Explorer (EXCEDE), was selected for technology development for a potential future science mission in September 2011 by NASA's Explorer program.

Above image shows a pattern (NASA meatball) made by manipulating the deformable mirrors. Pattern distortions can be corrected by such mirrors that can actively change shape.

Led by the University of Arizona, Tucson and in partnership with Ames and Lockheed Martin Space Science Company, Palo Alto, Calif., EXCEDE will directly image circumstellar dust and debris, and large planets in habitable zones, but not planets similar to Earth. "EXCEDE will do amazing science and may be a precursor to a larger mission, but won't quite capture exoEarths," said Belikov."

To see Earth-like planets, a much larger telescope is needed. While the current focus of the Ames Coronagraph Experiment (ACE) team is on the EXCEDE mission, they also are collaborating with NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif., to develop coronagraph technology for larger telescopes, capable of observing exo-Earths. Currently, there are two vacuum testbeds at JPL developing different kinds of coronagraph technologies.

NASA designs new space telescope optics
Each mirror is a one-by-one centimeter square that employs a grid of 32-by-32, or 1024 actuators, which can generate any shape desired on the mirror. Credit: NASA Ames/ Dominic Hart

Coronagraph technologies are initially developed in ambient conditions, rather than vacuum conditions. An ambient, stable, air-controlled, environment is a cheaper and faster development path than operating in a vacuum. Testing in vacuum conditions, however, is desirable because they are similar to conditions in space. Once these coronagraph technologies are tested in ambient conditions, they then are ready to be tested on vacuum testbeds.

"The ACE testbed is in air, not in a vacuum. Our team has advanced the technology for the EXCEDE mission to the point where it is ready for vacuum testing," said Belikov.

So what are its prospects?

Recently, the National Academy of Sciences produced a 2010 decadal survey that endorsed the Wide-Field Infrared Survey Telescope (WFIRST) mission as its large mission in the 2020 decade. NASA accepted this recommendation.

"Presently, it does not include a coronagraph to do direct imaging of exoplanets. But things can change," predicted Belikov.

It also seems promising that two 2.4 meter Astrophysics Focused Telescope Assets (AFTA) telescopes were given to NASA last year by another federal agency. If one of these telescopes becomes the WFIRST mission, its telescope size will be larger than originally planned. If this happens, and the mission has a powerful enough coronagraph, it may be able to survey the nearest stars for habitable exoEarths, according to Belikov.

"With sustained funding, NASA will be capable of launching a telescope large enough to find and characterize basically all the habitable planets around our galactic neighborhood, say the nearest hundreds of stars, within the 2030 decade," concluded Belikov.

Explore further: Eclipsing binary stars discovered by high school students

More information: proceedings.spiedigitallibrary… px?articleid=1362241

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User comments : 15

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Aliensarethere
5 / 5 (1) Feb 15, 2013
But finding oxygen and liquid water is not enough to conclude there is life on the planet.
nkalanaga
4.5 / 5 (6) Feb 15, 2013
No, but without oxygen and water, we can generally rule out advanced life as we know it, which is an advance in itself.

A large quantity of oxygen, which is unstable as an atmospheric gas, shows that something is producing it. Currently life is the most likely explanation for such an excess.
Tangent2
1.6 / 5 (7) Feb 15, 2013
No, but without oxygen and water, we can generally rule out advanced life as we know it, which is an advance in itself.

A large quantity of oxygen, which is unstable as an atmospheric gas, shows that something is producing it. Currently life is the most likely explanation for such an excess.


This would certainly be true, if we were looking for a preconceived notion of what life should look like. If we were looking for Carbon based organics that use oxygen/water, then the above statement would apply. If we were to open our minds and not make assumptions about what life can/can't do based on our limited experience with radically different life forms, then that statement would be false.
NikFromNYC
1 / 5 (4) Feb 15, 2013
What sort of optics can see the two edges of a man's iris which is covered by eyelids?
philw1776
1 / 5 (3) Feb 15, 2013
I find it depressing that the National Academy of Sciences produced a 2010 decadal survey did not recommend and exoplanet discovery missions, possibly because all proposals were either deemed too expensive or too technologically risky. I know that exoplanet pioneer Geoff Marcy and others were strongly critical of the survey's choices.
javjav
1 / 5 (1) Feb 15, 2013
If it can be ready for 2030, then this telescope should be the total priority, but only if it can be made big enough as to see habitable planets with enough resolution to detect live, from vegetation formations up to cities illuminated at night or big artificial infrastructures, as visible on earth from space. Then it would worth it to give it 80% of the Nasa budget for the next 15 years and even extra funds. But if all this at the end is just to see a point of light where you already know that there is a planet then forget about it.
grondilu
5 / 5 (4) Feb 15, 2013
This is awesome, and totally the kind of stuff NASA should focus on. Forget about manned mission. This is what matters for space exploration: telescopes and unmanned probes.
LED Guy
4 / 5 (4) Feb 15, 2013
@Tangent2:

Are you talking about false positives or false negatives? If we find free oxygen then it is safe to conclude that there is life (the kinds we know about).

Failure to find free oxygen doesn't mean that there isn't life, just that if there is life it is a kind we are not very familiar with. There was life on earth before there was free oxygen in the atmosphere. . .
philw1776
1.8 / 5 (5) Feb 15, 2013
Geoff Marcy, planet hunter, unloads on the NAS's lack of extrasolar planetary observatory missions for the next 10 years...

http://blogs.natu..._fo.html

Puzzling given Kepler's pioneering success and discovery that planets abound including around the most prevalent red M stars. Then again, getting Kepler itself to fly was a decade long battle against established science in itself.
xel3241
4.5 / 5 (4) Feb 15, 2013
What would be truly revolutionary would be to find an infrared detector that would not need liquid helium to operate. Such a discovery would allow infrared telescopes (which detect exoplanets directly) to operate for more than three years before being decommissioned.

If it can be ready for 2030, then this telescope should be the total priority, but only if it can be made big enough as to see habitable planets with enough resolution to detect live, from vegetation formations up to cities illuminated at night or big artificial infrastructures, as visible on earth from space. Then it would worth it to give it 80% of the Nasa budget for the next 15 years and even extra funds. But if all this at the end is just to see a point of light where you already know that there is a planet then forget about it.


Even a spectrum from such a star, without the lights of cities and the green/black of vegetation, would allow for biosignatures/technosignatures to be detected with some orecision.
baudrunner
1 / 5 (5) Feb 15, 2013
Just think, if those Vegans on 2012DA14 hadn't discovered how we are the hard way instead of having one of those telescopes to make them think twice about making this trip they wouldn't have wasted their time and have to turn back like they did to endure another lifetime and a half of being cooped up in that thing.
nkalanaga
4.7 / 5 (3) Feb 16, 2013
LED Guy: All true.

Tangent2: The problem with looking for life as we don't know it is that we probably wouldn't recognize it if we found it. Statistically, ET is likely to be a microbe, and if it doesn't act more or less familiar, we might not realize it was life, even if we were there.
Tangent2
1 / 5 (4) Feb 18, 2013
@Tangent2:

Are you talking about false positives or false negatives? If we find free oxygen then it is safe to conclude that there is life (the kinds we know about).

Failure to find free oxygen doesn't mean that there isn't life, just that if there is life it is a kind we are not very familiar with. There was life on earth before there was free oxygen in the atmosphere. . .


See my original post, it had the quote from the previous person that I was answering. That post contains the context of the statement and answers your question. You were basically reaffirming my assertion.
Torbjorn_Larsson_OM
5 / 5 (1) Feb 20, 2013
Good looking is looking good! =D An integrated coronagraph sounds much cheaper than having to launch a separate coronagraph.

@Tangent: It is impossible to untangle what you are asserting and then alluding to. Meanwhile nkalanaga's and LED's comments are certainly factual - seeing imbalances such as oxygen (or nitrogen oxides et cetera) on habitale planets (liquid water temperatures) is a test for life and life only.

@javkav: Direct imaging is a shortcut to uncover much more information on planets (size, habitability, et cetera) than earlier time consuming methods. It is therefore considered a priority in planet hunting circles.
antialias_physorg
1 / 5 (1) Feb 20, 2013
seeing imbalances such as oxygen (or nitrogen oxides et cetera) on habitale planets (liquid water temperatures) is a test for life and life only.

I'm not sure that's such a clean cut case. NOx can also be created using nothing but methane and oxygen (and an energy source) - none of which necessitate life.
And there are also plenty of non-biological processes that can release oxygen.

No, but without oxygen and water, we can generally rule out advanced life as we know it

Which is sort of a problem: looking only for life 'as we know it' introduces already a tremendous bias. Certainly when trying to deduce from the data how prevalent life is out there.
(Then again: how would we look for life "as we don't know it"?)