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Launch Services: The Science of SIRTF
Question and Answer Board

Blake from Hollywood, California
What kind of things can scientists learn from the infrared that they can't learn from other telescopes like the Chandra or Compton observatories?
Right, that's a great question. Chandra and Compton both see in other wavelengths of lights besides infrared. Compton sees in gamma rays and Chandra sees in x-rays. Now those are both very high-energy kinds of light, and the only objects in space that omit those sorts of energies are things that are really hot and explosive, giant exploding stars, colliding stars, things like that. Now SIRTF will be seeing the universe in infrared light, and infrared light is normally what we colloquially think of as heat. When you think about your body heat being warm that's actually infrared radiation coming from you. So SIRTF can see things that don't give off any visible light, but are very cool. For example, planets that are around other stars. SIRTF doesn't have the resolution to see planets themselves, but it can see the warm dust around the star that would indicate that the planets are there. Anything that's warm SIRTF can see, so it sees a lot of objects that are lower energy, only the temperature of a human body.
Andy from Grangemouth, U.
They are saying that an earth trailing orbit has never been used before, why now are they deciding to use it?
SIRTF is in a very unusual orbit. We normally think of our space telescopes actually orbiting the Earth. But the Earth and the Moon's system are too warm for an infrared telescope. With an infrared telescope you're actually trying to sense the heat from the stars, and the example I always use is that if you close your eyes and look up at a warm summer sky, you can actually feel the sunlight on your face. But try to imagine feeling the heat from the stars at night, there's no way you can possibly do that. The telescope has to be cooled down to extremely low temperatures. In fact the operating temperature of the telescope is only about six degrees above absolute zero. That's well below 400 degrees Fahrenheit. So we need to keep the telescope very cold, we needed to get it away from the warm Earth, and so because of that we're actually just kicking it off into space and letting it drift away from the Earth over time. And it will get farther out into space, it will be much cooler than if it were orbiting the Earth.
Hal from Boulder, Colorado
At what temperature will the mirrors operate and why are they at that temperature?
Well I sort of the answered that in last thing that I spoke about. The entire CTA, the cryo telescope array, is going to be at 5.5 Kelvin. That means 5.5 degrees above absolute zero. So there's a part of the telescope that is kept very, very cold. There also is a heat shield that will always be facing the Sun, and that will shield the telescope from the warmth of the Sun. And that will allow the telescope to radiate its heat into space and stay very cold.

Host: How large are these mirrors, do you happen to know?

Yes, in the case of SIRTF it's an 85 cm mirror. So that's a little bit less than a meter. And even though that seems kind of small that's actually the largest telescope that has ever been flown on an infrared telescope.
Rich O. from Elk Grove, Illinois
The images that SIRTF will be taking, how will they compare to Hubble? Will there be a comparison photo made of and object from Hubble and SIRTF so we can see the difference?
Yes, one of the most exciting things we can do is compare infrared imagery, divisible imagery, because you are seeing an entirely different, new view of the universe. One of the most amazing things about infrared is that it can actually see through dust that exists between the stars. For example, stars and planets are formed inside giant dust clouds called nebulae, and visible light never gets through those. So with an infrared telescope you can actually look inside a star forming cloud and see where the stars and planets are forming inside there. So it's a very different view from Hubble, and we really want to make a lot of comparisons where in the case of Hubble you might see a dark cloud in space, but in the infrared with SIRTF you can actually see where the stars are being born. Now the one thing that Hubble has that's a little bit different from SIRTF as well is that when you look in visible light you get better resolution than when you use infrared light. That's just a matter of physics, the longer wavelength of light you have the less clarity you get as far as your image on the sky. I always think about in the case of a television you want your pixels to be as small as possible. Infrared gives you slightly larger pixels than visible light. So the Hubble has clarity to its images that SIRTF won't have, but our images will show you something entirely different. You will be able to look inside these dust clouds. We are going to be looking for warm areas around black holes that are hidden from visible light because there is so much dust around them. So it's a totally different view of the universe.

Host: So the resolution is not necessarily a major impact, it just provides different information?

That's right, yes.
Juan Rodriguez from Gijon, Spain
What is the resolution of SIRTF pictures? Will we see the same detail, in infrared, as in the Hubble pictures? Thanks.
Exactly, in the case of Hubble you might actually get a very, very small pixel and in case of SIRTF it'll be larger. To use scientific terms SIRTF will have the resolution of about an arc second. So if you divide the sky into 360 degrees all the way around, each degree into 60 minutes, and then into 60 seconds, it's still a very, very tiny part of the sky that SIRTF will be able to resolve. In fact it's so small that our resolution will still be able to get many, many pixels across some of these warm disks of dusts that surround stars. And by studying how that dust is distributed around the star we can actually see where planets are forming inside that. So there will be plenty of resolution to get a lot of science done.
Peter from Basel, Switzerland
Can SIRTF take photos of other planets like Mars, same as the Hubble Space Telescope?
Most of the major planets in our solar system are going to be too bright in the infrared for SIRTF to take pictures of. Our detectors are so sensitive; you know we're going to be able to sense the heat from galaxies that are 12 billion light years away. So unfortunately the closer planets are out of limits for us. They would actually burn out the detectors; so some of the maybe more distant planets at the very edge of our solar system, but none of the very near ones.
Marcus from Toronto, Canada
As SIRTF looks for extra-solar planets, will it find Hot Jupiters or Terrestrial Rocky planets?
Right, that's an excellent question. Like I was saying, SIRTF's resolution does not allow it to see small planets individually. So we will be able to detect these hot Jupiter's, which are sometimes called brown dwarfs. We won't really be able to resolve them, but we'll be able to see them as pixels in a SIRTF image. And brown dwarfs are fun; they're kind of like still born stars. They're stars that formed but never got enough mass to ignite nuclear reactions. And so instead they actually form an object very much like Jupiter. Jupiter in a way is one of these brown dwarfs that are actually in our solar system, and those we'll be able to detect directly. I'm hoping that we find hundreds and perhaps thousands of them with the SIRTF telescope.
Wes from Augusta, Georgia
Hello I'm here to ask a question about a future NASA program that I watched on a video! Supposedly in 2023 NASA is supposed to launch a group of satellites that once in orbit will fly in laser guided formation around a larger telescope! After all this is complete it is supposed to let NASA look directly at a planet in another system inside of looking for the shimmer of a star to know if its there? How is that project going and are there any new updates about it? thanks Wes Hopkins
Host: What project is this?

The project that they're talking about there is called the terrestrial planet finder. And just what I was talking about, SIRTF does not have the resolution to see individual planets. But we can detect entire solar systems, the warm dust left over from planets. So SIRTF is going to be a good mission that will be a precursor to the terrestrial planet finder. We'll be able to identify where entire solar systems exist, and then terrestrial planet finder can follow up and actually look for the small earthlike planets. That technique of actually linking many different spacecraft together with lasers is called interferometry. It's a technique that's being developed NASA. At JPL there's the Keck Interferometer right now. The two Keck telescopes in Hawaii are being linked that way. So this is an exciting new technique, it's the way of making a telescope. You trick two different telescopes into thinking they're really the same instrument. And so when you fly them apart in space you can build a telescope that's hundreds of miles across. It's an amazing idea. And we're hoping in the next 20 years or to be able to detect earthlike planets this way.

Host: And is this scheduled for 2023 or sooner?

Well it's still in development so I couldn't say exactly when it will launch. But yes it is scheduled for about 20 years from now.
Juan Rodriguez from Gijon, Spain
Are you going to use SIRTF to study Kuiper Belt objects? What kind of information will you obtain if so? Thanks!
The Kuiper Belt is a very cold region of our solar system outside the planets Neptune and Pluto. And in a way it's almost a bit of a leftover from when our planets formed. There are lots of rocky and icy bits out there floating around. And currently we've discovering larger and larger objects out there. One of the biggest ones, Quar is about half the mass of Pluto. So they're quite large, almost the little planets floating around in the Kuiper Belt. And traditionally they've been really hard to find because they are so far away from our sun they don't reflect much light and they're so cold, they're very difficult to see. But I mentioned that SIRTF's operating temperature is only four degrees above absolute zero, so anything warmer than that is actually going to glow as SIRTF looks at it. So we're going to be able to see these big chunks of ice out there actually glowing themselves. So we're going to be able to detect where these smaller planets in the Kuiper Belt are. And we're going to do something called a core sample of the solar system. When you think about drilling a core sample through the Earth, you can see all of the different layers that are in the Earth. We're going to do the same thing looking out into the solar system, seeing where all the asteroids are, where all these big chunks of ice are in the Kuiper Belt, and we'll probably find several more Kuiper Belt objects; I hope so.
Elaine from Tampa
What do you think the most important part of this mission will end up being? What new discoveries can we hope to gain from this mission?
Well, that's a hard thing to say. I think in a way the most important thing about SIRTF is that in some of the wavelengths of infrared that we're going to be studying we've actually never seen the universe in that kind of light before. They're going to be objects out there, things going on there, we don't know what to expect. We've never seen them. So SIRTF has the chance to give us lots of serendipity. We're going to try to answer one question, maybe what is this planet like or what is this black hole like and that will lead us to questions we can't even imagine now. We're going to look at an entirely new universe and in my imagination it's kind of a way of continuing the journey that Copernicus put us on. Copernicus said that Earth is not the middle of the universe, in fact we just go around the sun. And now we're extending that to the human senses. Everything that humans can see, touch and smell, well that's not all that's out there. We have to use our technology to show us these invisible parts of the universe. So we're going to be seeing something we've never seen before with this infrared telescope.

Host: And this telescope will probably be rewriting some science books.

I certainly hope so. Yes I'm expecting it to.