JPL BLOGS
Inside Views on Outer Space
Hear from scientists, engineers and other experts as they offer a fascinating look at JPL missions, science and history.
Alien Vs. Editor | March 30, 2012
A Pigment of Your Imagination?
Joel asked: If you were to find aliens next to the sun, why would they be blue?
The only blue aliens I'm aware of lived on a moon called Pandora in a popular movie released in 2009. The foundation of your question is the more general question of why we observe a wide variety of colors "used" by life on Earth. Those colors are "used" by their organisms in many different ways. And there are a variety of mechanisms that generate the colors.
The colors of plants and animals have a variety of goals. For plants, the green of their leaves comes from the chlorophyll that absorbs violet-blue and yellow-orange-red light for photosynthesis. Some plants (like Japanese plum) have additional pigments for protection from ultraviolet light and appear dark red. Flowers have colors specifically to attract pollinators, but the colors the pollinators see may not be the colors we see.
Animals have colors to camouflage themselves and attract mates. Some plant and animal coloring is designed to warn off predators. The red eye you see in flash pictures of your friends is a reflection of their eyes' retinas. Photographs of dogs show their retinas reflect greenish light. Is retinal color related to color vision? Most humans have color vision and dogs are color blind.
The colors we see around us are generated by different mechanisms, which can reflect (pun intended) on its use by an organism. The color of a pigment depends on the colors it absorbs and those it reflects. Chlorophyll is a green pigment, and hair and skin colors result from pigments as well.
Polar bear fur only looks white.
Polar bears' black skin pigmentation helps keep them warm. The bears' white fur only looks white in bulk. Individual hair follicles are actually transparent, so that they carry sunlight down from the "top" of the fur coat to the bear's skin, where all the colors of sunlight (you've seen them in a rainbow made by differential refraction, another mechanism!) are absorbed by the black skin, helping to keep the polar bear warm. The fiber optics we use to transfer data over the internet or between components in your home entertainment system carry light in the same way.
The iridescent color of bird feathers is produced by another mechanism, the same one that makes detergent bubbles and thin slicks of oil on water show colors. The structure of feathers and thickness of detergent and oil layers permits waves of light to "interfere" with each other. You've seen wave interference in a quiet pool or pond when you throw two small objects into the water and the circular waves move out from each impact point. When the waves cross over each other, their height is greater where the peaks combine and flat where a peak and a valley combine.
A similar thing happens with light waves in iridescent materials. In the feathers, waves of a particular color are reflected and combined before they are shunted out of the feather, while the other colors are absorbed by a black pigment. The colors come from the spacing of tiny reflectors, called lamellae, in the feathers: change the spacing and the color coming from the feather is different. In detergent bubbles and oil slicks, change the layer's thickness and you change the color seen.
So where might we expect blue-skinned aliens? My answer is on an exoplanet orbiting a cool, red star. Why? Because the alien probably wants to absorb as much stellar energy as it can from its star, and blue pigments absorb red light. It would be well-camouflaged in the blue vegetation trying to absorb as much energy from the red sun as it could.
TAGS: EXOPLANETS, ASTROPHYSICS, EXTRATERRESTRIAL LIFE, UNIVERSE
Rocks and Stars with Amy | November 15, 2010
This Asteroid Inspected by #32
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.
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!
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.
TAGS: UNIVERSE, SOLAR SYSTEM, ASTEROIDS, WISE
JPL | August 12, 2010
Planetary Trio Provides a Warm-Up Act for Perseids
Are you eager to see the annual Perseids meteor shower tonight? You'll have to wait until near midnight to see it, so why not pass the time by viewing Venus, Saturn and Mars right from your doorstep? Step outside for the planetary warm-up act just as soon as the sun sets. (Viewing times will be best over the next week. By August 20, the planets set lower on the horizon and are harder to see.)
All you have to do is look towards the west for bright Venus to appear. Now hold your clenched fist up to the sky, covering Venus. To the right of Venus, about half of a clenched fist away, is a second planet: That's Saturn! And to the upper left of Venus is another planet: Mars!
That's not all you'll be able to see. Look below Venus for the slender crescent moon. If you don't see the moon, look again on the night of Friday, August 13 -- it will be a larger crescent to the left of Venus.
Though the three planets appear together in our line of sight, they are really far apart from each other. Mars is about 300 million kilometers (about 185 million miles) from Earth, while Venus is 112 million kilometers (about 70 million miles) away. Saturn? It's 1,535 million kilometers (about 954 million miles) from Earth. And finally, the moon is only 363 thousand kilometers (about 225 thousand miles) away. It's fun to compare the size of the moon and Mars, especially if you received that annual email incorrectly stating that Mars will be as big as the moon this month.
TAGS: UNIVERSE, SOLAR SYSTEM, METEORS, PERSIEDS
Rocks and Stars with Amy | July 20, 2010
Milestones
It's hard to believe that we've just crossed the six-month mark on WISE -- seems like just yesterday when we were all up at Vandenberg Air Force Base, near Santa Barbara, shivering in the cold at night while watching the countdown clock. But the time is flying (literally!) as WISE whips by over our heads. We're analyzing data ferociously now, trying to get the images and the data ready for the public release next May. Even though the mission's lifetime is short, we've gotten into a semblance of a routine. We receive and process images of stars, galaxies and other objects taken by the spacecraft every day, and we're running our asteroid-hunting routine on Mondays and Thursdays. We've got a small army (well, okay, three -- but they do the work of a small army!) of extremely talented students who are helping us verify and validate the asteroid detections, as well as hunt for new comets in the data. Plus, there is an unseen, yet powerful, cadre of observers out there all over the world following up our observations.
And so it's come to pass that we've achieved some milestones. We completed our first survey of the entire sky on July 17 -- and we just discovered our 100th new near-Earth object! That's out of the approximately 25,000 new asteroids we've discovered in total so far; most of these hang out in the main belt between Mars and Jupiter and never get anywhere near Earth's orbit. These new discoveries will allow us to conduct an accurate census of both the near-Earth and main belt asteroid populations. We're really busy chewing on the data right now and calculating what it all means.
Because it's so short, this mission reminds me a little bit of what the first days of college felt like -- a tidal wave of new ideas, new sights and new thoughts. The pace of learning has been incredibly quick, whether I'm trying to get up to speed on asteroid evolution theories or tinkering with the software we use to write papers.
Speaking of papers, we're in the process of preparing to submit several to science journals; in fact, I've already submitted one. The gold standard of science, of course, is the peer-review process. We submit our paper to a journal, and the scientific editor assigns another scientist who is an expert in the field but not involved in the project (and who usually remains anonymous) to read it and offer comments. The referee's job is to "kick the tires," so to speak, and ask tough questions about the work to make sure it's sound. We get a chance to respond, and the referee gets a chance to respond to our responses, and then when everybody's convinced the results are right, the paper is accepted and can be published. So stay tuned -- we should have some of the first papers done soon telling us what these milestones mean for asteroid science.
› Read more from "Rocks and Stars with Amy"
TAGS: UNIVERSE, SOLAR SYSTEM, ASTEROIDS, WISE
Rocks and Stars with Amy | January 29, 2010
The Golden Ticket
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 above.
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.
TAGS: WISE, ASTEROIDS & COMETS, SPACECRAFT, MISSION, UNIVERSE
JPL | January 6, 2010
400th Anniversary of Galileo's Discovery
The end of 1609 and the first months of 1610 mark the beginning of modern astronomy. 400 years ago today, January 7th, Galileo Galilei looked up towards the constellation Orion. He aimed his telescope at an object brighter than any of the surrounding stars - the planet Jupiter.
The view through his telescope startled him. He did not see only one object, but rather, one large world, with four smaller objects nearby.
These four objects are the moons we now call Io, Europa, Ganymede and Callisto.
Galileo wrote in his book Sidereus Nuncius, which was published in 1610 the following words:
"I should disclose and publish to the world the occasion of discovering and observing four Planets, never seen from the beginning of the world up to our own times, their positions, and the observations made during the last two months about their movements and their changes of magnitude; and I summon all astronomers to apply themselves to examine and determine their periodic times, which it has not been permitted me to achieve up to this day . . . On the 7th day of January in the present year, 1610, in the first hour of the following night, when I was viewing the constellations of the heavons through a telescope, the planet Jupiter presented itself to my view, and as I had prepared for myself a very excellent instrument, I noticed a circumstance which I had never been able to notice before, namely that three little stars, small but very bright, were near the planet; and although I believed them to belong to a number of the fixed stars, yet they made me somewhat wonder, because they seemed to be arranged exactly in a straight line, parallel to the ecliptic, and to be brighter than the rest of the stars, equal to them in magnitude . . .When on January 8th, led by some fatality, I turned again to look at the same part of the heavens, I found a very different state of things, for there were three little stars all west of Jupiter, and nearer together than on the previous night."
"I therefore concluded, and decided unhesitatingly, that there are three stars in the heavens moving about Jupiter, as Venus and Mercury around the Sun; which was at length established as clear as daylight by numerous other subsequent observations. These observations also established that there are not only three, but four, erratic sidereal bodies performing their revolutions around Jupiter."
On the 400th anniversary of their first sighting, use a pair of binoculars to spot Galileo's four tiny moons directly next to the planet. On the evening of January 7 look to the southwest after sunset. Europa and Ganymede will appear to the upper left and Io and Callisto on the lower right of Jupiter.
Letters with translations http://www2.jpl.nasa.gov/galileo/ganymede/discovery.html
TAGS: UNIVERSE, SOLAR SYSTEM, JUPITER, GALILEO, TELESCOPE
Rocks and Stars with Amy | November 11, 2009
It's Time to Go
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!
TAGS: WISE, ASTEROIDS & COMETS, SPACECRAFT, MISSION, UNIVERSE
Rocks and Stars with Amy | November 5, 2009
Hi Ho, Hi Ho, It's Into Space We Go
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.
It 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!
TAGS: WISE, ASTEROIDS & COMETS, SPACECRAFT, MISSION, UNIVERSE
JPL | June 11, 2009
Five 'Holy Grails' of Distant Solar Systems
Angelle Tanner, a post-doctoral scholar at JPL and Caltech, studies planets in distant solar systems, called extrasolar planets. The golden prize in this field is to find a planet similar to Earth - the only planet we know that harbors life. While more than 350 extrasolar planets have been detected, most are gas planets, with no solid surface. Many are located in orbits closer to their parent star than Mercury is to the sun. In other words, not very similar to Earth.
Here's Tanner's short list of what she and her colleagues would love to find in another planet - the elements that might enable life on another world. With the powerful tools scientists have now and with new technology and missions coming soon, the odds are going up for finding an Earth-like planet, if one is out there.
Tanner's top five "holy grails" of extrasolar planet research are hoped-for findings that she predicts will happen within the next 15 years.
1. First planet that weighs the same as Earth
Although most planets discovered have been giant gas planets with no surface, a handful of rocky planets, called super-earths, have also been detected. Super-earths are akin to Earth in their rocky make-up, but with a mass up to 10 times that of Earth.
There is no reason these planets could not host an atmosphere or even life as we know it. The discovery of a true Earth clone – Earth-like in size and make-up -- could happen within a year or two. NASA's recently launched Kepler mission has the ability to find planets as small as Earth.
2. First Earth-sized planet in the 'habitable zone'
The so-called habitable zone is the area around a star where a rocky planet could have the right temperature to have liquid water on its surface. In our solar system, Earth sits in the habitable zone. Venus sits just inside the habitable zone and is too hot while Mars is just outside and too cold. Finding an Earth-sized planet is this geographically desirable location is the next big step in extrasolar research. One super-earth has already been detected near to its parent star's habitable zone and it is only a matter of time -- using existing technologies –- before a planet is found in this friendly environment. Ground-based telescopes and NASA's Kepler mission are searching stars within a few hundred light years of Earth right now.
3. First atmosphere on a rocky planet
A planet's atmosphere, along with other factors, helps determine whether a planet could sustain life. For the past few years, astronomers have studied the atmospheres of Jupiter-like, extrasolar planets. These gas giant planets have hydrogen-rich atmospheres inhospitable to life as we know it. However, many of the techniques developed for studying gas giants could be used to study the atmospheres of super-earths. This would mark an important step in beginning to understand the environment of rocky planets.
4. First hint of habitability and life
Once astronomers have enough Earth-sized planet atmospheres to study, they will be looking for biosignatures – indicators in a planet's atmosphere that the planet might be hospitable to or even support life. Some of the molecules they will be looking for include water vapor, methane, ozone and carbon dioxide. NASA's James Webb Space Telescope, scheduled to launch in 2014, will provide scientists with the sophisticated instruments needed for these potential observations on super-earths orbiting small stars. Assuredly, astrobiologists will be studying such data for years to come since potential life may, or may not be, in a form we expect. Keeping an open mind is critical.
5. The unexpected
The final grail -- the unexpected. The history of science is marked with findings that were never predicted. As in all fields of science and exploration, it's what we don't know that will be the most exciting.
For more information about extrasolar planets, visit planetquest.jpl.nasa.gov
TAGS: UNIVERSE, SOLAR SYSTEM, EXTRASOLAR PLANET, HABITABLE ZONE, PLANETQUEST
Rocks and Stars with Amy | November 12, 2008
Sizing Up Near-Earth Asteroids
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?
Asteroids 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.
TAGS: WISE, ASTEROIDS & COMETS, SPACECRAFT, MISSION, UNIVERSE