Space Telescope Reawakened for an Asteroid Hunt
Friday, August 30, 2013
After the WISE telescope used up the coolant needed to operate its detectors, its primary mission as an infrared survey telescope ended. NASA's Amy Mainzer describes how the agency is repurposing the dormant craft for a new three-year mission looking for near-Earth asteroids. Astronomer Brett Gladman also discusses a newly spotted asteroid-like object trailing Uranus.
IRA FLATOW, HOST:
This is SCIENCE FRIDAY. I'm Ira Flatow. Now, a story of resurrection. In late 2009, NASA launched a space telescope called WISE to survey the sky in infrared wavelengths. And in the fall of 2010, the instrument used up the coolant needed to run its instruments - used them up. So, in February of 2011, NASA put the scope to sleep, turning off the radio transmitter. Well, now NASA is starting up the telescope again with a new mission looking for near-Earth asteroids, the kind that might cause some real damage if they hit us.
Amy Mainzer is principle investigator on the neo-WISE mission. She's based at NASA's jet propulsion laboratory in California. Welcome to SCIENCE FRIDAY.
AMY MAINZER: Thanks very much.
FLATOW: So this - how can you use this telescope to do something else?
MAINZER: Right. Well, it turns out this little telescope is particularly good at seeing these kinds of asteroids that get particularly close to our Earth. And when we put it into hibernation mode - this is after the coolant that we needed was gone, but it turns out we can still continue to operate with about half of the infrared channels that we once had.
And this is still very useful for looking at asteroids. So we're getting ready to wake it up.
FLATOW: What is there - what do you mean wake it up? What do you have to do to it?
MAINZER: Right. Well, right now, the spacecraft, it really is kind of in a sleep mode, sort of like your TV when you turn it off. It's not really off. There's still a little bit of power. In our case, the solar panels are still facing the sun, so we can still get power to the spacecraft, but most of the systems are off. So the first thing we're going to do here in a couple of weeks is send the commands to start gradually waking everything back up. Turning the main computer, you know, back to full functional state. And then we need to get the telescope cold again. And to do that, we need to stop looking at the Earth.
FLATOW: Oh. And when you say get cold, how cold do you need it to be, and why?
MAINZER: Right. Well, this is a telescope that senses infrared light, and most human beings, you know, we think of that as heat. So if you think about it, you need to get your infrared, heat-seeking telescope really cold so that it's not blinded by its own emission. So, you know, it would be sort of like to observe invisible light during the daytime.
MAINZER: If you don't get your telescope cold.
FLATOW: I gotcha.
MAINZER: That's that.
FLATOW: Yeah. And how much of the sky do you look at? How far away can you see with it?
MAINZER: Right. Well, this telescope is an all-sky survey telescope. It's really designed to have kind of a fish-eye lens, so to speak. It's got a very wide field of view, and, in fact, the name is actually Wide-Field Infrared Survey Explorer, or WISE. So it's designed to see pretty much everything. It can see the most distant galaxies and the closest asteroids.
FLATOW: Mm-hmm. And how...
MAINZER: It's kind of an all-purpose.
FLATOW: Yeah. So where - about what point in our solar system or our galaxy would you - what's the outer limit of what it would be looking at?
MAINZER: Well, some of the most distant things that we've observed are called quasars, and these are very energetic galaxies that are very, very far away. They're almost at the extreme edge of the universe. And we can see them because they're particularly bright in infrared light. But we can also see things that are really close to home.
And, in fact, some of the closest asteroids we detected were only just a few times the distance of the Earth to the Moon when we saw them.
FLATOW: Mm-hmm. And, of course, if we see something headed our way, there's not much we can do about it at this point, is there?
MAINZER: Well, it's actually not fair to say that. The news is a little better.
FLATOW: Oh, good.
MAINZER: NASA has funded a fair amount of, you know, systems in place to basically archive all the observations people send in of asteroids. And they do that at a place called the Minor Planet Center.
MAINZER: They keep track of all the - everything everybody's seen. Then here at JPL, we have a system that is charge of computing impact probabilities. So, in other words, it's taking all the observations of all the asteroids as they're being discovered, and it's looking actively to see if there are any near misses coming up.
FLATOW: Mm-hmm. And if it found one that's going to be closer than a near miss, what could we do about it?
MAINZER: Right. Well, I mean, ideally, we'd like to discover these things when they're decades away from impact.
MAINZER: That's the goal.
MAINZER: And, you know, the good news that we have so far is that we know now that about 90 percent of all the very large near-Earth asteroids have been discovered. These are things larger than about a kilometer in diameter. So, you know, mountain-sized things. And those have all been found, and they're being tracked. And that's good news.
For the smaller sizes, things down to, say, about 100 meters, what we found with the first primary mission with Neo-WISE is that about maybe 25 percent of those have been discovered to date.
MAINZER: So we still have a lot more work to do.
FLATOW: Mm-hmm. And how small an object can this WISE telescope pick up?
MAINZER: The smallest thing we've seen so far is about eight meters in diameter. So it's, you know, kind of the size of a large van. But it has to be pretty close in order for us to see something that small.
FLATOW: Wow. And how close would that be?
MAINZER: A few times the distance of the Earth to the Moon. So these are things that get very, very close indeed. But this is why we like observing with infrared light.
MAINZER: Because we're sensing the heat coming off of these asteroids, not the reflected light. Not the sunlight bouncing off the surface. And that has a couple of advantages. First of all, we can see asteroids that are really dark, like pieces of coal because we're seeing the heat coming off of it.
MAINZER: It doesn't matter how light or dark they are.
FLATOW: It's like those night-vision binoculars.
FLATOW: Yeah. Yeah.
MAINZER: Exactly right.
FLATOW: Yeah. I think...
MAINZER: And then the other thing...
FLATOW: Yeah, go ahead.
FLATOW: I'm sorry. Go ahead.
MAINZER: Yeah. The other thing is we can measure sizes and that's a pretty important thing to be able to do if you're trying to figure out how hazardous something is.
FLATOW: Yeah. This is...
MAINZER: You want to know how big it is.
FLATOW: Yeah. Let me bring on someone else who's another expert in sort of talking about similar things. And these are other planets or small objects that are in orbits of other planets. Researchers reported this week that they've located an asteroid leading the planet Uranus, just going just ahead of the planet in its orbit. And they call that object - scientists call it a Trojan. Joining me now is Brett Gladman, professor of astronomy at the University of British Columbia in Vancouver and one of the researchers who spotted this Trojan.
Welcome to SCIENCE FRIDAY.
BRETT GLADMAN: Hi. Thanks, Ira.
FLATOW: Did I get that definition correct?
GLADMAN: Trojan asteroids are ones which share the planet's orbit and they either manage to stay a little bit ahead or a little bit behind the planet as it circulates around the sun.
FLATOW: And how many of them do we know of in our solar system?
GLADMAN: Oh, there's many, many hundreds of such objects known for a very long time that share the orbit of Jupiter. The other planets that have Trojans have a much smaller number but Neptune and Earth, for example, already had known Trojans.
FLATOW: We have another asteroid in our orbit that's going around like we are?
GLADMAN: Yes. Earth's first Trojan companion was just discovered a couple of years ago and so basically it snuck. It's one of the formerly Earth-crossing asteroids of the kind that Amy's so fond of studying that snuck into an orbit that was very similar to that of the Earth. That is, it goes around the sun at about the same distance from the sun as the Earth does, and it's a little bit ahead of the Earth.
And it manages in a complicated gravitational dance, to stay a little bit head, hovering around 60 degrees ahead of the Earth.
FLATOW: Can you see it for yourself?
GLADMAN: No. You need a pretty powerful telescope to spot it.
FLATOW: Mm-hmm. And how long will it stay there? Or is it - or will some other body come along and nudge it out of the way?
GLADMAN: Well, so this Trojan of the Earth and this new Trojan of Uranus that my doctoral student, Mike Alexanderson, found are both a new kind of Trojan that only did we recent understand exists in the solar system. And these are things that are temporarily trapped. So the Jovian Trojans have been there for billions of years and they're not going anywhere.
MAINZER: But this new object that was discovered sharing the orbit of Uranus and the Earth's Trojan and some of Neptune's Trojans, are clearly objects which have temporarily gotten stuck in this state. And will, on time scales that are tens of thousands or hundreds of thousands or millions of years - which, for an astronomer is short - will escape back into the planet crossing population from whence they came.
FLATOW: Oh. Amy, would the Neo-WISE mission be able to find Trojans?
MAINZER: Well, yeah. And as a matter of fact, the Earth Trojan that you mentioned was actually discovered by WISE.
MAINZER: In fact, just one day after the cryogen ran out. So we know that they're out there. And from our infrared observations of the object, we know that it's about 400 meters in diameter. So it's a pretty large asteroid. And as Brett says, it's not going to get particularly close to us now but eventually in a few thousand years it'll probably migrate out of its sort of stable spot and then will be able to start making close approaches again.
We think that there are others out there. And we found one.
MAINZER: So it's quite likely that there are others.
FLATOW: Brett, how did you find this? Do people look for these?
GLADMAN: Well, this was discovered in a search of the outer solar system using a ground-based telescope in this case, the Canada-France-Hawaii telescope that's up on top of Mauna Kea in Hawaii. And it was a hunt of the outer solar system for small moving objects. The primary targets were the distant trans-Neptunian objects beyond the orbit of Neptune in the so-called Kuiper Belt.
But this relatively fast-moving object in comparison was found in the foreground and it didn't take us very long to realize what it was.
FLATOW: Mm-hmm. Now, this involves something we've talked about many times before called the Lagrange Points.
GLADMAN: Lagrange, yes.
FLATOW: Lagrange. Lagrange Points, as they say in France. Could you explain that a little bit to us?
GLADMAN: Sure. So it's been known for a long time, a couple of hundred years, due to mathematicians and celestial machinations, that if you look at a problem of a planet going around the sun, there are five special points where if you put an object there relative to the planet in just the right spot at just the right speed, they will - it will actually sit there in a constant relation to the planet.
So the Earth Trojan and these Uranus Trojan both circulate around but are not precisely at what's called the leading Lagrange Point, the L4 point. All science fiction and aficionados know about these because they're great places to put space stations or, in fact, space telescopes because the space station a telescope can, with a very minimal amount of fuel, stay parked in a constant configuration relative to the Earth.
Because it basically goes around the sun at the same rate.
FLATOW: Mm-hmm. And so these, are they locked in there at those Lagrange Points?
GLADMAN: Yeah. It depends on the Lagrange Points, but the triangular Lagrange Points where the Trojans are - so it's like a triangle between the sun and the Earth and the object - those points are dynamically stable if you ignore the other planets.
GLADMAN: So because the other planets are there and tugging weakly on, in this case Uranus, and the little object, there is actually a little escape hatch where you can go in and out of the Trojan state and go transfer between the planet crossing highly unstable state and this relatively calm Trojan state.
FLATOW: Mm-hmm. Let me just...
MAINZER: You know, I like to think of these as, you know, if you have a rushing river and there's a rock in the middle of the river, sometimes you'll see an eddy just behind the rock. And you can see leaves and things kind of get trapped in the eddy and swirl around for awhile. Eventually, they'll get knocked out of the eddy, but they can stay there for a long time.
FLATOW: Hmm. May I remind everybody that this is SCIENCE FRIDAY from NPR. I'm Ira Flatow talking with Amy Mainzer and Brett Gladman. Amy, what about future plans for other telescopes?
MAINZER: Well, one thing that the WISE mission has taught us is that we can actually use an infrared space telescope to discover a lot of asteroids and characterize them relatively quickly. And with WISE we were able to observe about 158,000 asteroids. Now, most of these are in the main asteroid belt, but because we have the infrared observations, combined with visible light observations, we can measure their sizes accurately as well as the reflectivity.
And that gives us a clue as to what they're made out of. So what we'd really like to do is design a more advanced telescope that just makes a few simple changes to really clean up on the near-Earth objects. Yeah. These are the ones that we're, you know, more worried about from a hazard perspective. Basically, we'd like to develop a system that has a longer lifetime, doesn't need these refrigerants that run out relatively quickly.
And to do that we need a slightly different electronic sensor. So the good news is we've actually invented that sensor and it's been shown to work. It works at a much higher temperature, which to an astronomer, is kind of a balmy temperature, about 40 degrees above absolute zero. Now, that sounds really cold to most people.
FLATOW: Yeah. But you don't need the - you don't need the refrigerants, then, right? That's what you're saying.
MAINZER: That's right.
MAINZER: Yeah, that's right.
FLATOW: Space is cold enough on its own right there.
MAINZER: Exactly. And with WISE, we had to get our detectors down to eight degrees above absolute zero and that's really cold.
FLATOW: Wow. Wow. That was - well, you said that was the good news. Now, the bad news is there's probably no money for this. Right?
MAINZER: Well, we actually have been given some seed money from NASA to go off and develop these detectors that we need to do a more advance survey. And the good news is they work great. The development's been a big success and we've made our first set of these things and we're really looking forward to using them now.
FLATOW: Mm-hmm. And so we'll keep in touch and see what's happening. Thank you both for taking time to be with us today.
MAINZER: Thank you.
GLADMAN: Thank you.
FLATOW: You're welcome. Amy Mainzer, she's the principle investigator on the Neo-WISE mission. She's based at NASA's Jet Propulsion Laboratory in California. And we also were talking to Brett Gladman. He's a professor of astronomy at the University of British Columbia in Vancouver.
Finally, you can't talk about exploration of our solar system without mentioning one of its pioneers, Bruce Murray. He joined the Jet Propulsion Laboratory in 1960. He was responsible for convincing NASA to send probe to the planets, probes that could take color photos and send them back to Earth for everyone to enjoy and marvel. It's hard to believe that they had to talk somebody into that.
Well, Murray died Thursday at his home in Oceanside, California and for those of us who knew him professionally, he was always willing and eager to put into perspective the role of humans in space, as he did 20 years ago on this program.
(SOUNDBITE OF ARCHIVED INTERVIEW)
BRUCE MURRAY: I think space is almost a mirror of us on Earth as it had been in so many other areas.
MURRAY: We have an opportunity to lead by example and by collaboration in an egalitarian manner with many different countries throughout the world, not just for exploration in the outer reaches of the solar system, but for monitoring the Earth, understanding the environmental and resource challenges that we have.
Or, we have the alternative of wishing that world hadn't changed and somehow hankering back for sort of an adolescence, like the Apollo program represented, and constantly pursuing that. If we can make the evolution away from the Cold War to an international era and focus on the long-time idea that humans going into space is a good thing, but it must be affordable in the current reality, then I think we're going to have a good program.
FLATOW: Dr. Bruce Murray, a pioneering space explorer, dead at the age of 81, complications from Alzheimer's Disease. That's all the time we have for today. Transcript provided by NPR, Copyright NPR.View this story on npr.org