Sara: Hi, this is Sara Mitchell coming to you from NASA's Goddard Space Flight
Center, and I have a very special Skype call today with some
of the members of the SuperTIGER team who are calling me from
Antarctica. Hi guys, welcome! [Jason] Hello
[Sara] Tell me a bit about yourselves. [Jason] So, my name is Jason Link,
I am a scientist working at NASA Goddard,
I am down here for the SuperTIGER flight, this is my third
trip down. All of them have in fact been for the TIGER instrument.
Starting in 2001....
and, ah, Nathan? [Nathan] Hi my name is
Nathan Walsh, I am a graduate student at Washington University
and this is my first trip down to Antarctica.
to work on SuperTIGER, which I will be doing my thesis work
using the data that we get from it.
[Brian] Hello, I am Brian Rauch, I'm a research assistant professor at Washington University.
I have worked on TIGER since I was an
undergrad, I worked on it as a graduate student and I'm still on it, and this is my
second time to Antarctica. [Sarah] So where are you guys right now?
[Jason] So we right now are in Crary Lab which is the main
scientific laboratory at McMurdo Base in Antarctica.
We are in fact in the staging area for
where they take equipment out into the field.
[Sara] Terrific. So, what is SuperTIGER? [Brian] SuperTIGER is
a large-area ultra-heavy cosmic ray detector.
It's a balloon-born instrument meant to fly at stratospheric altitudes.
[Sara] Ok, why is it called SuperTIGER?
[Brian] Well, SuperTIGER is a
follow-on to the original TIGER experiment, which is a contrived acronym.
TIGER stands for Trans-Iron Galactic Element Recorder, so
what makes SuperTIGER super is that it is much larger than the
original TIGER, approximately four times the active area, and so
essentially it's a super-sized TIGER, so it's a SuperTIGER.
[Sara] Well, so what does your SuperTIGER observe?
[Jason] So as Brian mentioned, our SuperTIGER measures
galactic cosmic rays, specifically ultra-heavy, galactic
cosmic rays. [Sarah] What are cosmic rays and why are they interesting?
[Jason] So, cosmic rays are high-energy particles that originate
outside the solar system, propagate through the
galaxy and some of them come here to Earth where we detect them.
They're particularly interesting for a lot of reasons. One is
they are one of two kinds of matter from outside the solar system that we can
directly sample. The other being
stellar dust. Another reason they're interesting is that these particles
can be at incredibly high energies, much higher
than any accelerators here on Earth can produce, so
it's a way to study not only material from
outside the solar system, but to look at very high-energy particles
and understand the building blocks of nature.
[Sara] Wow. Well, so, in particular you're studying
ultra-heavy cosmic rays, what can they tell us about
cosmic rays in general and the universe?
[Nathan] So, ultra-heavy cosmic rays are
cosmic rays that are made up of elements with about 30 protons or more,
and these elements are ones that are
synthesized in extreme conditions like supernova, or
binary neutron star mergers, so if we
can measure the ultra-heavy cosmic rays, it can tell us
more about how cosmic rays are formed in these types of events,
and also how they're accelerated. [Sara] So you mentioned
binary neutron star mergers, and just this past month
there was a huge announcement of a neutron star merger that was observed
both in light and gravitational waves, and this was a big deal
because it was the first time that that was seen in both of those messengers.
How does this relate to the research you're doing with SuperTIGER?
[Nathan] So, well, as you said, LIGO measured the gravitational wave
signal from that event and that was first time that's happened.
And Fermi measured
the same, or they were able to look at it afterwards and see the gamma-ray
signal coming from that same event and so basically
we're in an age where multi-messenger astronomy
is possible and cosmic rays that could come from that event
offer a third, in addition to other
messengers, that we can use to look at these events.
[Brian] Well, cosmic rays wouldn't come directly to us
from that event because cosmic rays, being charged,
are deflected by magnetic fields and they take a lot longer to get here and don't travel
a direct path. But, cosmic rays from similar events
would be, would give a signature that would be indicative of this kind of
binary neutron star merger event. [Jason] And one of these
interesting things that we are able to do, is to
look at what elements we detect here at Earth,
and propagate it back to the source, which is believed
for many of the ultra-heavies, to be binary neutron star mergers.
So we can actually quantify
the amount of heavy material that might be produced, which is something that
they can't quite yet do with the photon measurements.
that they're making. [Sara] Well, that's terrific, and it's wonderful
to see all the messengers coming together in astronomy.
So you mentioned that there have been other TIGER and SuperTIGER flights
How many flights have occurred before this one this year?
[Brian] Well, there've been essentially three
TIGER-like instruments. The first TIGER was more of a proof-of-concept,
It flew once after three campaigns, and it demonstrated
that the instrument configuration, the instrument design, was good to measure
cosmic rays past iron into the UH range. And then there was TIGER
LDB, that Jason worked on as a graduate student, and I did
analysis for and supported the flight, second flight, for as a graduate student.
And, you know, given the results, the preliminary results,
in the UH range. And then that flew twice, in 2001-2003.
And now SuperTIGER has flown once and we're going for its second flight.
[Sara] So, what results do you hope to get from this flight, and what do you hope to learn
that adds to what you got from the earlier TIGER flights?
[Jason] The ultra-heavy elements that we're measuring, have not been measured, or measured
well, by any other instrument. So we are truly making some of the
first measurements of the individual element abundances, and
these are very, very rare elements, so we need a large instrument with a
very long exposure time in order to get 10
15. 20 events. which is about the minimum we need to
be, to have good statistics to be able to do science.
[Brian] What distinguishes TIGER and SuperTIGER from previous
measurements is the ability to resolve individual elements, without
the confusion. [Sara] The elements you're measuring are the elements that we
have here on Earth, so you're making direct connections between the things that we're
made of, and that our world around us is made of, and these cosmic rays that
you're catching. [Jason] Yes. In fact,
people might be interested, but if you look at many of the
materials we use day-to-day: gold, platinum,
lead, that all came from these
high-energy astrophysical events, in the heart of stars, and
that is what we're in fact studying. [Sara] Awesome.
So, changing gears a little bit, how does the SuperTIGER instrument
work? In layman's terms.
[Nathan] So, the instrument is made
up of layers of detectors, and there's three different
types, and when a cosmic ray passes through the
detector it deposits energy in each layer and that energy
is in the form light, and that's how we collect it, using
photomultiplier tubes, which essentially give us a signal
telling us how bright the light was when it
passed through the detector.
[Sara] So, when people talk about measuring cosmic rays, you're really not "catching" them,
you're detecting them as they pass through your instrument.
[Nathan] Yes. Yes. [Brian] In fact, if we see
a sign that a cosmic ray has done more than just lose energy
passing through--if it were to collide with a nucleus within the detector--
and interact--that's an even we really can't analyze. We require the event to
pass through all the active parts of the detector without interacting for us to be able
analyze it. [Sara] So who built SuperTIGER? Where
was it built? [Brian] Well, SuperTIGER is a collaboration of four
institutions: Washington University in St. Louis, NASA Goddard
Space Flight Center, CalTech, with Jet Propulsion
Lab, so I guess that really makes us five institutions
and also the University of Minnesota.
Wash. U. and Goddard
do most of the construction. [Sarah] So it really takes a village. [Jason] Yes.
And it should also be mentioned that TIGER is an evolution from the very
first flight to where we are today and after each flight we
have improved on the instrument, and made
everything better. So when you say "who built it?", this starts
back with the folks who, in the 90's, built the first
TIGER instrument and it went through various iterations to where we are today.
[Sara] So, I think the big question would be
why does this have to go to Antarctica? Why can't you just fly this anywhere?
[Nathan] Well, there's
a few reasons I guess, but the main one
is that this is the place we can fly the longest.
safely. Above Antarctica,
during the summer here, a circumpolar vortex sets up,
so the wind basically circulates around the pole
and our balloon typically follows that path and
stays above Antarctica. So we can keep it up for as long
as possible. [Brian] Another particularly important reason
for flying in Antarctica, especially if you consider that we want to fly for a long time,
like 55 days, is that we need power. And back in the old
days when we started, we would fly with just batteries, but that works for maybe a day.
So we rely on solar power and fortunately in the summer here the Sun's up all the
time. It might move and down in the sky some, but it's up and so we have power
continuously. [Jason] The other important thing about
flying when it is always daylight, is when you have day/night
cycling of the balloon you'll lose altitude in the balloon,
and so here without that day/night cycling, the gas
is always at roughly the same temperature, so it makes it possible
to be flying at the high altitudes for a long period of time.
[Nathan] And the reason why we don't want to change altitude is because
if you sink lower in the atmosphere, you have more atmosphere above you,
and when a cosmic ray is going through the atmosphere it has a higher
chance of interacting with a particle in the atmosphere
because it'll be passing through more of it. So the
higher-up we are, the less atmosphere we have to interfere with
the cosmic rays that we're measuring. [Brian] And we're above all but a half,
about a half a percent of the atmosphere, and even with just that little tiny fraction of
atmosphere, we lose a very significant fraction, around 50 percent or more,
of the particles will interact just passing through the atmosphere. [Sara] So
how high is that in the atmosphere? With just that tiny
bit above you? [Jason] About 130,000
feet is the goal that we try to reach, and it's
usually, and it will all depend on the balloon and the atmospheric
conditions, but usually it's between about 127 and 130,000
that we'll start off at. [Brian] SuperTIGER had a wonderful
balloon, that endured very well, Jason's TIGER flight
in 2001 had a leaky balloon [Jason] Yes! [Brian] That spanned
quite a greater, much greater range, but these are
things you have no control over. [Sara] So, you're
talking balloons; why a balloon? Why not, just send this up into space?
[Jason] So, a balloon has a lot of advantages,
the first is it's a lot less expensive
to build and fly on a balloon than to build
and fly on a rocket experiment. And so
that allows us to design and build our instrument
quicker, because we don't have the same expense
in design and we don't have to go through
all of the tests that you do for a space mission. For instance, a space mission
has issues of vibration, which we don't have on a balloon instrument.
It's also something
where you can have students
be far more involved in the building of the instrument.
A spacecraft is very technical and very complicated and very often you will need
a lot of specialized engineers and technicians and it is much harder for
students to be involved, as you know, Nathan, today, was
tightening cables and checking things out, and he
wouldn't have that opportunity on a spacecraft, so there's a lot of
good things about balloons that let us test
and move quickly. The other big advantage on SuperTIGER
is we have very large instrument, which would be very difficult
to launch into space given its mass and size.
And we need the instrument size in order to
measure the cosmic rays.
[Brian] One advantage to flying on a balloon is that
you can recover the instrument, right? So you get to fly it again,
and make improvements and work your way towards
a space instrument, for instance. I mean, we started...
TIGER wasn't the very first idea
along these lines. The group actually worked on previous experiments,
balloon-born experiments of different types, so one
can spend a lot of time on development for an experiment that you might hope to one day
put in space. You can do it iteratively with the balloon and try different things. See
what works, see what doesn't, and you can do that very cost effectively.
[Sara] So, what's your launch window, when does that open?
[Jason] So, the launch window depends on a couple of things
coming together. The first being that we have checked out our instrument
and it is ready to go, and our goal is to do that by the
first week of December. We also need to have the polar vortex
that Nathan mentioned set-up. That is in the process of doing so
and the weatherman down here thinks that
will hopefully have set up the first week of December
as well. The other thing that we need to have happen
is we need have a day where we have calm winds
and clear skies to have a good launch. When that happens
is anyone's guess with the weather down here in McMurdo, so
the first week of December we hope, but
a lot depends on the weather. [Sara] How big is the SuperTIGER team that's down in
Antarctica with you right now? [Brian] There will be nine people total deployed. Five from
Washington University and four from Goddard. [Sara] Well, so thank you for joining me,
Brian and Nathan and Jason, and best of luck getting ready for launch
and we'll keep following. Keep up updating us!
[Jason] We will! [Nathan] All right. [Brian] Thank you. [Jason] Thank you. [Nathan] Thank you.
[Beeping]