Starshade Prepares To Image New Earths

For countless generations, people have looked up at the stars and wondered if life exists somewhere out there, perhaps on planets much like ours. But it has only been in recent decades that we have been able to confirm the existence of extrasolar planets (aka. exoplanets) in other star systems. In fact, between 1988 and April 20th of 2016, astronomers have been able to account for the existence of 2108 planets in 1350 different star systems, including 511 multiple planetary systems.

Most of these discoveries have taken place within just the past three years, thanks to improvements in our detection methods, and the deployment of the Kepler space observatory in 2009. Looking ahead, astronomers hope to improve on these methods even further with the introduction of the Starshade, a giant space structure designed to block the glare of stars, thus making it easier to find planets – and perhaps another Earth!

While some planets have been observed directly with telescopes (a process known as “Direct Imaging”), the vast majority have been detected through indirect methods such as the Transit Method. This method attempts to spot planets as they cross in front of the parent star’s disk – during which time there will be a temporary drop in observed brightness – and can also reveal the radius of a planet and sometimes yield information on its atmosphere (with the help of spectrometers).

This method remains the most widely-used means of detection and is responsible for more exoplanet discoveries than all other methods combined. However, due to interference from other light sources, it also suffers from a substantial rate of false positives, and generally requires that part of the planet’s orbit intersect a line-of-sight between the host star and Earth.

To address this, NASA is developing some key technologies that will help block out light interference so that future astronomers can detect exoplanets more easily. For instruments here on Earth, they are developing coronographs, single instruments that fit inside telescopes to block light. But looking to space, NASA’s Jet Propulsion Laboratory is also developing the Starshade.

This concept calls for a giant, flower-shaped spacecraft that would be launched with one of NASA’s next-generation space telescopes. Once deployed, it would fly around in front of the telescope in order to obscure the light of distant stars. This way, the light being reflected off of planets in orbit around them will be detectable, thus making it that much easier to confirm the presence of exoplanets.

The project is led by Prof. Jeremy Kasdin of Princeton University, in conjunction with the JPL and support from Northrop Grumman (which leads the mission and system design for Starshade). As Kasdin explained to Universe Today via email:

“The starshade works just like your thumb when trying to block the Sun; it blocks the starlight from entering the telescope but allows light from he planet close by to pass unimpeded.  Since planets are so much dimmer than their host stars, this technology eliminates the problem of glare from the star swamping light from the planet.  And because the starlight never enters the telescope, any conventional telescope can be used; no special attention needs to be paid to stabilities and precision in the telescope.”

The shade, which is about the  size of a baseball diamond, would be deployed as part a single mission. As the video above shows, the large shade would be mounted at the end of a space telescope – in this case, NASA’s upcoming Wide Field Infrared Survey Telescope (WFIRST) – and then detaches and deploys to a distance of several thousands kilometers in front of it.

Such a large shade operating at such a long distance from of its paired telescope is essential when dealing with distant stars.”Because stars are so far away the angular distance between the planet and star is quite small,” said Kasdin, “requiring a very large starshade (20 to 50 meters in diameter) flying very far from the telescope (up to 50,000 km). Nevertheless, many astronomers believe this is the best technology to detect an Earthlike planet in the near future, a belief aided by the fact that few special requirements are placed on the telescope.”

Paired with other instruments, like spectrometers, devices like the Starshade will not only allow astronomers to be able to spot planets more easily, but also obtain information about their atmospheres. By studying their chemical compositions – i.e. looking for the presence of oxygen/nitrogen, water vapor, etc. – we would be able to tell with a fair degree of certainty whether or not life exists on them.

The Starshade technology is one of the top candidates for a flagship-level mission in the next decade and a top Astro2010 priority for technology development. In addition to working with WFIRST, it is possible it will be paired with missions like the Transiting Exoplanet Survey Satellite (TESS) and the James Webb Space Telescope.

“We are hoping that a starshade capable of Earth detection will be recommended to fly with the upcoming WFIRST mission,” Kasdin added, “allowing the first image of an Earth in the next decade.”


Further Reading: JPL News

9 Replies to “Starshade Prepares To Image New Earths”

  1. Does not sound like a very smart idea. Since the star shade telescope pair will have to arc around huge distances for a wide field survey of exo-solar systems. Multiple shades might increase the efficiency though.

    1. I like the idea of multiple shades, so different telescopes could share them.

  2. I suggest that “chronograph” should be “coronagraph” – no time keeping involved surely?

  3. be nice to know how the blocking disk is kept lined up with the far distant telescope – what part of orbital mechanics is required to line up for time exposures?

    1. @dlweld:
      Orbital mechanics will be THE biggest physical obstacle, so yeah, it’d be nice if the someone would address this aspect publically.

      Since there is no connection between them, the two objects will be in two independent (one presumes solar?) orbits. Inertial motion & star sensors combined with reaction wheels should allow the devices to stay lined up with each other (as long as the wheels keep turning! @_@), however imaging times will be relatively short and the parts of the sky observable will be limited to the ever-moving axis connecting them as they move through their respective orbits. If the theory behind the Starshade is correct though, the lack of stellar glare should enable the imaging of exoplanets with fairly short exposure times, times which can be obtained fairly easily with large enough orbits (= slow orbital velocities).

      Of course, observing the part of the sky you WANT to observe will either mean sending up STUPID amounts of fuel, or else waiting until the “stars” align, however long that may take. . .

  4. Other things being equal, the tiny spot would be better. So I assume there are tradeoffs between the 2 approaches, unfortunately the article never mentions them! I would like to know pros & cons for the point of view of the physics involved!

    1. @Gavin:
      This they HAVE addressed previously, among other places, in a previous Weekly Space Hangout (last Sept., I think?). The issue is that as small as these stars appear, a matching disc will be tiny enough that the physics of light propagation take over and end up “bending” the star’s light around the disc. To then be effective, your disc has to be made large enough to combat this effect; unfortunately, doing so means you’ve just blocked ALL the light coming from that system. The Starshade is specifically shaped in such a way as to counter this “bleed around,” and explains its general size & appearance in the article image, as well as the range needed between the telescope & the shade.

  5. Might seem off topic but is this technology might explain the Fermi paradox. Simply put, if X amount of resources exist for researching exoplanets then it is always a better science buy to put those resources into this kind of imaging rather than developing interstellar travel. The logic is this: this kind of exoplanet imaging allows continuous improvement. It provides near immediate research data that can raise new questions including biological signatures in atmospheres. It can research all exoplanets whatever their distance the limit being the number of craft built. In contrast, interstellar probes may take centuries, provide limited data feedback, can only investigate nearby exoplanets, and if they do a “Beagle 2”, and disappear, you will never know what went amiss–so you cannot know what to do so it does not happen again. Any intelligent form of life therefore would put resources into starshade type imaging and not interstellar travel. If so interstellar visiting never develops in spite of the rise across the Galaxy of forms of life with the intelligence to do so.

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