Rocks and Stars with Amy: This Asteroid Inspected by #32

By Amy Mainzer

Rocks and Stars with Amy

Over the course of the nine months we’ve been operating WISE, we’ve observed over 150,000 asteroids and comets of all different types. We had to pick all of these moving objects out of the hundreds of millions of sources observed all over the sky — so you can imagine that sifting through all those stars and galaxies to find the asteroids is not easy!

We use a lot of techniques to figure out how to distinguish an asteroid from a star or galaxy. Even though just about everything in the universe moves, asteroids are a whole lot closer to us than your average star (and certainly your average galaxy), so they appear to move from place to place in the WISE images over a timescale of minutes, unlike the much more distant stars. It’s almost like watching a pack of cyclists go by in the Tour de France. Also, WISE takes infrared images, which means that cooler objects like asteroids look different than the hotter stars. If you look at the picture below, you can see that the stars appear bright blue, whereas the sole asteroid in the frame appears red. That’s because the asteroid is about room temperature and is therefore much colder than the stars, which are thousands of degrees. Cooler objects will give off more of their light at longer, infrared wavelengths that our WISE telescope sees. We can use both of these unique properties of asteroids — their motion and their bright infrared signatures — to tease them out of the bazillions of stars and galaxies in the WISE images.

Image of the first near-Earth asteroid discovered by WISE
The first near-Earth asteroid discovered by WISE (red dot) stands out from the stars (blue dots). The asteroid is much cooler than the stars, so it emits more of its light at the longer, infrared wavelengths WISE uses. This makes it appear redder than the stars. Image credit: NASA/JPL-Caltech/UCLA |   › Full image and caption

 
Thanks to the efforts of some smart scientists and software engineers, we have a very slick program that automatically searches the images for anything that moves at the longer, infrared wavelengths. With WISE, we take about a dozen or so images of each part of the sky over a couple of days. The system works by throwing out everything that appears again and again in each exposure. What’s left are just the so-called transient sources, the things that don’t stay the same between snapshots. Most of these are cosmic rays — charged particles zooming through space that are either spat out by our sun or burped up from other high-energy processes like supernovae or stars falling into black holes. These cosmic rays hit our detectors, leaving a blip that appears for just a single exposure. Also, really bright objects can leave an after-image on the detectors that can persist for many minutes, just like when you stare at a light bulb and then close your eyes. We have to weed the real asteroid detections out from the cosmic rays and after-images.

The data pipeline is smart enough to catch most of these artifacts and figure out what the real moving objects are. However, if it’s a new asteroid that no one has ever seen before, we have to have a human inspect the set of images and make sure that it’s not just a collection of artifacts that happened to show up at the right place and right time. About 20 percent of the asteroids that we observe appear to be new, and we examine those using a program that we call our quality assurance (QA) system, which lets us rapidly sift through hundreds of candidate asteroids to make sure they’re real. The QA system pops up a set of images of the candidate asteroid, along with a bunch of “before” and “after” images of the same part of the sky. This lets us eliminate any stars that might have been confused for the asteroids. Finally, since the WISE camera takes a picture every 11 seconds, we take a look at the exposures taken immediately before the ones with the candidate asteroid — if the source is really just an after-image persisting after we’ve looked at something bright, it will be there in the previous frame. We’ve had many students — three college students and two very talented high school students — work on asteroid QA. They’ve become real pros at inspecting asteroid candidates!

This is a screenshot from the WISE moving-object quality assurance system, which helps weed out false asteroid candidates.
This is a screenshot from the WISE moving-object quality assurance system, which helps weed out false asteroid candidates. The top two rows show an asteroid candidate detected in 16 different WISE snapshots, at two different infrared wavelengths. The lower rows show the same patch of sky at different times — they let the astronomers make sure that stars or galaxies haven’t been confused for the asteroid. Image credit: NASA/JPL-Caltech/UCLA

 
Meanwhile, the hunt continues — we’re still trekking along through the sky with the two shortest-wavelength infrared bands, now that we’ve run out of the super-cold hydrogen that was keeping two of the four detectors operating. Even though our sensitivity is lower, we’re still observing asteroids and looking for interesting things like nearby brown dwarfs (stars too cold to shine in visible light because they can’t sustain nuclear fusion). Our dedicated team of asteroid inspectors keeps plugging away, keeping the quality of the detections very high so that we leave the best possible legacy when our little telescope’s journey is finally done.

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    3 Responses to “Rocks and Stars with Amy: This Asteroid Inspected by #32”

  1. Daniel Veira Canle Says:
    November 19th, 2010 at 4:36 am

    I am a spanish 18 years old student of physics. I have begun to study this degree since I would like to understand better the motion and structure of the universe. So that when I have finished my studies I will make the MS in astrophysics.

    I have read that have been found materials in comets,like olivine even clay that could only have been formed with high temperature.

    Nevertheless, if the comets have been formed so close to the Sun and later they have emigrated towards the Oort cloud ¿how can it be that they are covered of such pristine ice?

    Also I am interested astronautics and the exploration of the solar system ¿What kind of studies should I do to be employed as a scientist in a reaserch center like JPL?

    Thanks for your patience and comprehension. And sorry about my bad english.

    Daniel Veira Canle

    JPL astronomer Joe Masiero responds:

    You’ve hit on one of the most interesting and perplexing questions facing us today in the study of the formation of the solar system, Daniel. New results, particularly from the Stardust mission, have indeed shown that there are minerals in comets that formed in high temperature environments like the inner solar system. However, to still contain the ices we observe on them, the whole comet could not have been that temperature, and must have formed far from the sun. Our current understanding of these observations is that these minerals formed very quickly near the sun and were transported across the solar system to colder areas, possibly by turbulence in our sun’s protoplanetary disk (although many mechanisms are being explored right now). They then became incorporated into the icy bodies that were growing there, which after about 4.5 billion years of collisions and orbit changes (mostly by Jupiter) became the comets we see today. All of these areas are hot topics in current studies of the solar system.

    A research career in astronomy and astrophysics is built on a strong foundation of math and physics. Calculus, differential equations, mechanics, electricity & magnetism, quantum, and relativity all are critical to this kind of science. Statistics is also a very important subject, as you need to be able to say how accurate your measurements and predictions are. For studies of the solar system, geology, mineralogy, and atmospheric chemistry also play important roles depending on the type of object you are investigating (e.g., the Moon, planets, asteroids, or comets). But above all, a love of the topic is critical: it’s a lot of work, with many long nights doing problem sets, but if you enjoy what you are learning, it will all be worth it.

    Best of luck on your degree!

    Joe Masiero works with Amy Mainzer on the asteroid portion of NASA’s WISE mission.

  2. David Ruben Says:
    January 27th, 2011 at 11:13 pm

    I am curious about the origin of near-Earth asteroids. I wonder if some are remnants of the giant impact collision that created the Earth’s Moon?

    From what I know about the asteroids in the belt between Mars and Jupiter, they all orbit basically in the plane of the Solar System. Is the same true for near-Earth asteroids? I am wondering if any near-Earthers might travel through space in a polar orbit around the Sun, i.e, perpendicular, or inclined, to the plane of the Solar System? If this is possible, would such asteroids be more difficult to spot?

    Thanks for your hard work in finding nearby asteroids. I like to think that with enough advanced warning, a dangerous potential impactor might be redirected to a safer orbit.

    Amy Mainzer responds:

    Current evidence shows that the NEOs most likely originated in either the main asteroid belt or from more distant regions in the solar system. They are likely to have been scattered inward by gravitational resonances with the planets or by thermal forces. You correctly note that their orbits tend to have a wider variety of inclinations than the main belt asteroids; this is probably due to the many interactions they’ve had by the time they are near Earth. The distribution of NEO orbital inclinations is something we are studying right now with the NEOWISE data, and we hope to have a result soon. It is certainly true that these high-inclination NEOs tend to be harder for conventional ground-based asteroid surveys to spot, but NEOWISE was particularly good at finding them because we spent a lot of time looking away from the plane of the solar system.

  3. Erik Neelsen Says:
    February 9th, 2011 at 6:55 am

    What are the possibilities of developing our moon into an intergalatic spaceship? Are the propulsion requirements too great? We do know that the moon has an element used in fusion reactors. I suppose this could be a primary source of energy. Is it possible to escavate the moon to create living quarters, greenhouses, and other essential facilities underground? We do know that moon dust heated to 800 degrees C yielded water as a byproduct. Our Earth will be getting strained in resources and over the next thousand years or so. It seems we have to get the moon developed somehow and find another planet to populate. Of course, if we use the moon to travel away from Earth, the Earth will lose it’s current axis of rotation and begin to “wobble” thus severly interfering with weather patterns and living conditions, so conditions would have to deteriorate badly on Earth first before leaving.

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