Posts Tagged ‘space telescope’

Rocks and Stars with Amy: The Golden Ticket

Friday, January 29th, 2010

By Amy Mainzer

Rocks and Stars with Amy

We have discovered our first new near-Earth asteroid with WISE. Our first “golden ticket” is now known as 2010 AB78. It’s an asteroid that is roughly 1 kilometer [about .6 miles] in diameter, so it’s fairly large. The most interesting thing about it so far is that we thought we knew of about 85 percent of all the asteroids 1 kilometer and larger, so finding a big one like this is a little unusual. Of course, unlike Charlie and his chocolate bars, finding the golden ticket wasn’t a matter of luck, but a meticulous search process more like a busy assembly line.

Near-Earth objects are asteroids and comets with orbits that get close to Earth’s orbit. That doesn’t mean they are going to hit the Earth, of course. It’s sort of like driving on a busy street; just because there are a lot of cars zipping by on either side of you, it doesn’t necessarily mean your car is going to hit one. The cars would have to be at the same place at the same time for that to happen. So even though the paths each car has traveled might get close, there is no collision.

WISE finds asteroids by using a sophisticated piece of software called the WISE Moving Object Processing System, or WMOPS. When we first get a set of images from WISE, we have software that automatically searches the images for all the sources in them, be they stars, galaxies or asteroids. The software records their positions and how bright they are. WMOPS goes into that source list and figures out which sources are moving compared to the fixed stars and galaxies in each frame. Then, it figures out which sources are actually the same object — just observed at different times. So it’s a pretty smart piece of code. The whole system has to be highly automated, since when the WISE survey is done, the source catalog will contain several hundred million sources! You can imagine that trying to sort through all of these to find individual objects would be very challenging without a nifty program like WMOPS.

Our newest addition to the approximately 6,600 near-Earth Asteroids that are currently known is shown in this new image:

artist's concept of the WISE space telescope
The red dot at the center of this image is the first near-Earth asteroid discovered by NASA’s Wide-Field Infrared Survey Explorer, or WISE — an all-sky mapping infrared mission designed to see all sorts of cosmic objects. Image credit: NASA/JPL-Caltech/UCLA
› Full image and caption

2010 AB78 shows up like a glowing red ember at the center of the image, because it’s glowing brightly in infrared light with a wavelength of 12 microns, which is about 20 times redder than your eye can see. The stars appear blue, because they’re much hotter, and they emit proportionally less of their energy at these long wavelengths. The color that the asteroids appear to WISE is an important feature we use to distinguish them from other stars and galaxies, in addition to their motion.

With this first asteroid discovery, we are flexing our muscles in preparation for the heavy lifting we’re about to start.


Rocks and Stars with Amy: It’s Time to Go

Friday, December 11th, 2009

By Amy Mainzer

Rocks and Stars with Amy

Now that we are just days from launch (wow!), the team is making final decisions and preparations. We’ve just held our Flight Readiness Review, at which the final commitment to launch was made by NASA, the United Launch Alliance (the rocket folks) and the WISE project. It turns out that fueling our Delta II rocket’s second stage engine is an irreversible process — once we fuel the second stage, we have 34 days to launch the rocket. If we don’t launch within 34 days of fueling it, we have to replace the second stage completely — and that would mean taking WISE off the rocket. So we needed to be really sure that we were “go for launch” before we decided to fuel up the second stage. That is now done, and we are in the process of putting the final finishing touches on cooling down our solid hydrogen tanks.

These last few weeks and days before launch require a lot of flexibility of the team, since the schedule can change on a dime. There are about a million things having nothing to do with the launch vehicle or the spacecraft that can delay a launch — winds, too much fog, too many clouds, lightning and even something as mundane as a fishing boat or aircraft straying into the “keepout” zone that’s established around the launch site. You would think that the prospect of running into a giant, 330,000-pound rocket loaded with fuel would be enough to make people move out of the way, but sometimes they don’t seem to get the message! Any of these items is enough to scrub a launch attempt.

But that’s why we’ve built in the ability to make two consecutive launch attempts with WISE, separated by 24 hours. We get two tries. After that, our tank full of frozen hydrogen starts to warm up too much, and it takes two days for us to cool it back down. To keep the tank of frozen hydrogen a frosty 7 degrees above absolute zero (minus 447 Fahrenheit), we circulate an even colder refrigerant, liquid helium, around the outside of the tank. But the process of re-cooling takes two days; we have to hook all the hoses back up, cool everything down, then disconnect the hoses again before the next launch attempt.

So we have to be flexible. We’ve all put our lives on hold for the duration, since we have to be ready for anything that happens. Meanwhile, I’ve frantically tried to take care of stuff like cleaning the house and laying in supplies, because once WISE launches, things will go into overdrive. Needless to say, our families have all been very patient with us!


Rocks and Stars with Amy: Hi Ho, Hi Ho, It’s Into Space We Go

Thursday, November 5th, 2009

By Amy Mainzer

Rocks and Stars with Amy

With WISE a mere month away from liftoff, it’s probably a little late to be asking why we need to send it into space. But it’s worth taking the time to explain why we go to all the trouble of sending something up on a rocket. While it’s really cool to go into space, we’re not just sending WISE up there for the fun of it. In this case, there’s no other reasonable way to accomplish the mission’s science goals: surveying the entire sky in infrared, finding the nearest star to our sun, and finding the most luminous galaxy in the universe. We can’t do this from the ground.

artist concept of WISEIt turns out that the main culprit that drives us into space and into an orbit more than 500 kilometers (about 360 miles) above the Earth’s surface is our atmosphere. As wonderful as our atmosphere is for life on Earth, it wreaks havoc on astronomical images in many ways. For one, shifting pockets of warm and cool air drifting above a telescope — or a human observer– cause stars to twinkle. While pretty, this twinkling makes it difficult to get a good measurement of a star’s true brightness (or, in astronomical terms, its “photometry”). The twinkling also reduces the telescope’s sensitivity and resolution by enlarging the images it produces, making them blurrier and less sharp. This is true for all kinds of telescopes not just infrared ones.

Secondly, the atmosphere acts like a sponge at many wavelengths, soaking up light from the stars so that it never reaches the ground at all. Everybody’s seen a rainbow at one time or another, and that range of colors — from violet to red — spans the maximum range of wavelengths that our eyes can see. But that is only a small fraction of the entire spectrum of light that’s really out there in the universe. Our sun puts out most of its radiation in visible light, and most of that visible light makes it through our atmosphere to the ground. However, our atmosphere is only partially transparent to infrared wavelengths. Filled with water vapor, carbon dioxide, and methane, our atmosphere absorbs almost all infrared light, so most of the infrared light emitted by distant stars, asteroids, and planets doesn’t make it to observers on the ground. These molecules grab infrared light and trap it, preventing it from passing through the atmosphere (which is why they are called greenhouse gases). To see anything at all in most infrared colors, we have to get entirely above the Earth’s atmosphere.

The final problem posed by our atmosphere for infrared astronomers is that it — and the Earth itself — is warm. Infrared light is characteristically emitted by room-temperature objects. Objects like you and I glow brightly in infrared light, and so does the Earth and its atmosphere. If you could see in infrared light, the night sky would look as bright as daylight! So when we’re trying to detect the faint heat signatures of distant astronomical objects, a glowing, warm atmosphere is almost impossible to see through. This is why we must cool the WISE telescope to a mere 12 degrees above absolute zero (minus 438 Fahrenheit). Being in space with a cold telescope makes such a huge difference that the relatively modest-size WISE telescope, which is 40 centimeters (16 inches) in diameter, is equivalent in sensitivity to literally thousands of 8-meter (26-foot) telescopes on the ground. That small WISE telescope packs a punch.

So with that cleared up, we’re just about ready to put WISE into the nose cone and crane it up onto the Delta II rocket that’s waiting for us on the launch pad. Let’s go see some stars!


Rocks and Stars with Amy: Sizing Up Near-Earth Asteroids

Wednesday, November 12th, 2008

By Amy Mainzer

Rocks and Stars with Amy

Asteroids. The word conjures images of pitted rocks zooming through space, the cratered surfaces of planets and moons, and for some, memories of a primitive video game. Just how hazardous are these nearest neighbors of ours? We think that one contributed to the extinction of the dinosaurs, giving rise to the age of mammals. How likely is this to happen again?

The Wide-field Infrared Explorer (WISE) mission, an infrared telescope launching in about a year, will observe hundreds of near-Earth asteroids, offering unique insights into this question. The risk posed by hazardous asteroids is critically dependent on how many there are of different sizes. We know that there are more small asteroids than large ones, but how many more, and what are they made of?

asteroidAsteroids reflect sunlight (about half of which is the visible light that humans see), but the sun also warms them up, making them glow brightly in infrared light. The problem with observing asteroids in visible light alone is that it is difficult to distinguish between asteroids that are small and highly reflective, or large and dark. Both types of objects, when seen as distant points of light, can appear equally bright in visible light. However, by using infrared light to observe asteroids, we obtain a much more accurate measurement of their size. This is because the infrared light given off by most asteroids doesn’t depend strongly on reflectivity.

WISE will give us a much more accurate understanding of how many near-Earth asteroids there are of different sizes, allowing astronomers to better assess the hazard posed by asteroids. The danger posed by a near-Earth asteroid depends not only on its size, but also on its composition. An asteroid made of dense metals is more dangerous than one of the same size made mostly of less dense silicates. By combining infrared and visible measurements, we can determine how reflective the asteroids are, which gives us some indication of their composition.


Rocks and Stars with Amy: An Infrared Glimpse of What’s to Come

Tuesday, July 22nd, 2008

By Amy Mainzer

Rocks and Stars with Amy

Almost everyone has had the frustrating experience of getting lost. To avoid this problem, the savvy traveler carries a map. Similarly, astronomers need maps of the sky to know where to look, allowing us to make the best use of precious time on large telescopes. A map of the entire sky also helps scientists find the most rare and unusual types of objects, such as the nearest star to our sun and the most luminous galaxies in the universe. Our team (lead by our principal investigator, Dr. Ned Wright of UCLA) is building a new space telescope called the Wide-field Infrared Survey Explorer that will make a map of the entire sky at four infrared wavelengths. Infrared is a type of electromagnetic radiation with a wavelength about ten or more times longer than that of visible light; humans perceive it as heat.

Why do we want to map the sky in the infrared? Three reasons: First, since infrared is heat, we can use it to search for the faint heat generated by some of the coldest objects in the universe, such as dusty planetary debris discs around other stars, asteroids and ultra-cold brown dwarfs, which straddle the boundary between planets and stars. Second, we can use it to look for very distant (and therefore very old) objects, such as galaxies that formed only a billion years after the Big Bang. Since light is redshifted by the expansion of the universe, the most distant quasars and galaxies will have their visible light shifted into infrared wavelengths. And finally, infrared light has the remarkable property of passing through dust. Just as firefighters use infrared goggles to find people through the smoke in burning buildings, astronomers can use infrared to peer through dense, dusty clouds to see things like newborn stars, or the dust-enshrouded cores of galaxies.