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The Science of SIRTF Answer Board
Blake
from Hollywood, CA
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, Colora
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?
Guest: 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.
|
RichO
from Elk Grove, IL
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?
Guest: 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 Swiss
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 Augus, GA
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?
Guest: 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?
Guest: 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.
Guest: I certainly hope so. Yes I'm expecting it to.
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Curator:
NASA Official:
Web Development: JBOSC Web Development Team
Last Updated:
September 2, 2003
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