365DaysDate:  January 20, 2009


Title:  Space Telescope of the Future:  SIM

Podcaster:  Nancy Atkinson

Organizations:  Universe Today, Space Lifestyle Magazine, Astronomy Cast, Solar System Ambassadors

Description:  Nancy talks with Stephen Edberg from the Jet Propulsion Laboratory, who is a System Scientist for the Space Interferometry Mission (also known as SIM Lite) discussing  how this future space telescope could help answer our questions about extrasolar planets and dark matter.  A longer, more detailed article about SIM on Universe Today.

Bio:   Nancy Atkinson writes daily for Universe Today, is a writer and editor-in-chief for Space Lifestyle Magazine, is on the production team for Astronomy Cast, and is part of the IYA New Media Working Group, helping to bring this podcast to you every day of 2009. She also is a NASA/JPL Solar System Ambassador.

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Nancy Atkinson:  Hi, this is Nancy Atkinson.  As a writer for Universe Today and Space Lifestyle Magazine, I have the opportunity to write about all the amazing things going on in space exploration and astronomy.  I’d have to say two of the hottest topics these days are extrasolar planets – planets orbiting other stars – and dark matter — that unknown stuff that seemingly makes up a considerable portion of our universe.  There’s a spacecraft that’s currently in development that could help answer our questions about whether there really are other Earth-like planets out there, and as well as provide clues as to the nature of dark matter.  The spacecraft is called SIM – the Space Interferometry Mission.  The concept for this mission has been around for awhile, and as technology has advanced, the proposed spacecraft has changed too.  Currently, the mission is being called SIM Lite, as the spacecraft itself has gotten smaller, however the mirrors for the interferometer have gotten bigger.

While interferometry at radio wavelengths has been done for over 50 years, optical interferometry has only matured recently.  Optical interferometry combines the light of multiple telescopes to perform as a single, much larger telescope. SIM Lite will have two visible-wavelength stellar interferometer sensors  – as well as other advanced detectors, that will work together to create an extremely sensitive telescope, orbiting outside of Earth’s atmosphere.

So what can this spacecraft do?  I had the opportunity to talk with Steve Edberg who is the System Scientist for SIM, and he offered an interesting analogy to demonstrate the spacecraft’s capabilities.

Steve Edberg:  These are instruments that can measure positions in the sky to an almost unbelievable accuracy.  When I say that, I ask you to envision Buzz Aldrin standing on the moon.  Pretend he’s holding a nickel between thumb and forefinger in his gloves.  SIM can measure the thickness the angle made by the thickness of that nickel as seen by someone standing on the surface of the earth.  That is one micro arc second, a very tiny fraction of the sky.  And by being able to make measurements like that, it’s possible to infer the presence of planets within about 30 light-years, and those planets can be as small and low mass as Earth. And so with SIM we anticipate studying between 65 and 100 stars over the five year mission, looking for Earth analogs, meaning planets that are roughly the same masses as Earth orbiting their stars in what we call the habitable zone, where liquid water could be existing.  The way we detect that is not detecting at the planet directly, but by detecting the motion that it causes in the parent star.

Nancy Atkinson: Now, that task is hard enough when there is just one planet orbiting a star, but if other solar systems are like ours, there are likely to be several planets in the system, and we do know from observations with current telescopes there are other multi-planet systems.  But SIM will be able to detect the different sized planets orbiting other stars.  SIM Lite recently passed a double blind study conducted by four separate teams who confirmed that SIM’s technology will allow the detection of Earth-sized planets among multiple-planet systems.

A second planet search program, called the “broad survey,” will probe roughly 2,000 stars in our galaxy to determine the prevalence planets the size of Neptune and larger.

SIM will also be used to measure the sizes of stars, as well as distances of stars, and be able to do so several hundred times more accurately than previously possible. SIM Lite will also measure the motion of nearby galaxies, in most cases, for the first time. These measurements will help provide the first total mass measurements of individual galaxies.  All of this will enable scientists to estimate the distribution of dark matter in our own galaxy and the universe.

Steve Edberg elaborated on how SIM Lite will endeavor to measure dark matter.

Steve Edberg:  Dark matter is known for its gravitational affects.  It doesn’t seem to interact with normal matter as we know it.  To get more clues on it, we want to know where it is.  SIM will measure on two different scales.  One is within the Milky Way Galaxy, making measurements of stars and globular clusters, making measurements of stars that have been torn out of smaller galaxies that orbit the Milky Way, we can do mass model of our galaxy and find out where that mass is including what has to be a lot of dark matter.  We make measurements of how our galaxy rotates, you find that it rotates like a solid.  Instead of being Keplerian, where you think of Mercury going around the sun faster than Pluto, from all the way inside the galaxy as close as we can measure to the center, out to beyond the sun’s distance, the milky way rotates like it’s a solid body.  It’s not a solid body, but that means it must have a density that is constant all the way through and that means there if far more matter than we can see.  So it must be dark.

The other things we’d like to know is the concentration of dark matter in cluster of galaxies. The Milky Way is part of the Local group of galaxies, and SIM has the capability to measure stars within the individual galaxies, which in turn can be modeled to tell us where the dark matter is within the local group.  This is cutting edge.  This is one of the big mysteries right now in astrophysics and cosmology.

Nancy  Atkinson:  This sounds like such an exciting mission that would answer so many of our current questions.  So what’s the status of this mission?

SIM Lite is currently in the design phase, and due to budgetary reasons, no launch date has been set by NASA headquarters.  However, Edberg said that if given the go-ahead, the spacecraft and team could likely be ready by 2015. Engineers are building prototypes to further test the capabilities of the instruments, but the project will need to pass another review to stay alive.

SIM Lite would provide an entirely new measurement capability in astronomy.  Its findings would likely stand firmly on their own, while complimenting the capabilities of our current, as well as other planned future space observatories.

I encourage you to find out more about this mission by checking out the website:

Let’s hope this mission is given the green light by NASA, as it is sure to provide new discoveries about the universe and re-write our textbooks.

Thanks for listening and be sure to tune in each day for more 365 Days of Astronomy podcasts

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