JPL Blogs

JPL Blogs

Hear from scientists, engineers and other experts as they offer a fascinating look at JPL missions, science and history.

Cassini imaging science team image of the geyser basin at the south pole of Enceladus.

After so many close flybys of Enceladus, we're starting to feel as if this little moon of Saturn is an old friend. But during the encounter planned for Nov. 2, 2009, we are going to get up-close and personal. Cassini is going to take its deepest dive yet into the plumes spewing out from the moon's south pole to try to learn more about their composition and density.

The spacecraft is going to approach within about 100 kilometers (62 miles) of the surface. We've been closer before (25 kilometers or 15 miles), but we've never plunged quite so deeply into the heart of the plume.

To get a better sense of our flyby, watch the animation created by my colleague Brent Buffington. This is the seventh targeted flyby of Enceladus, so we sometimes refer to it as "E7." The video starts out with our approach to Enceladus, rotating through the various instruments scanning Enceladus for data. Then at around 7:40 a.m. UTC (Coordinated Universal Time), we do our long-anticipated flyby through the plumes. The passage will be quick: traveling at about 8 kilometers per second (about 5 miles per second) - fast enough to go from Los Angeles to New York in less than 9 minutes - we'll spend only about a minute in the plume.

Then, we zoom away from the plumes and Cassini turns on an infrared instrument (red rays in the animation) to take the temperature of the south-pole fissures known as "tiger stripes" where the plumes originate. A few minutes later, Cassini uses an ultraviolet instrument (purple rays in the animation) to measure the plumes against the background of the peach-colored Saturn. The infrared instrument then gets another turn to examine Enceladus. For more details, see the mission description.

The focus of this flyby is to analyze the particles in the plume with instruments that can detect the size, mass, charge, speed and composition. Instead of using its eyes (the cameras), Cassini is going to use its senses of taste and smell. But we're going to get some pretty good pictures too, including some impressive shots of the plumes from far away.

So far, we have detected water vapor, sodium and organic chemicals such as carbon dioxide in the plumes that spew out from the tiger stripes, but we need more detail. Are there just simple organic molecules, or something more complex? This is the first time we've found activity on a moon this small (the width of Arizona, 500 kilometers or 310 miles in diameter). We really want to understand what's driving the plumes, especially whether there is liquid water underneath the surface. If we can put the pieces together - a liquid ocean under the surface, heat driving the geysers and the organic molecules that are the building blocks of life - Enceladus might turn out to have the conditions that led to the origin of life on an earlier version of Earth.

So if this is all so interesting, why did we wait so long to travel into the plumes? One reason is the plunge is tricky. We wanted to make sure we could do it. We worried that plume particles might damage the spacecraft. We did extensive studies to determine that it was safe at these distances. We also wanted to have the right trajectory so we didn't use an excessive amount of rocket fuel. We are going very fast through this sparse plume; so to play it safe, we're using Cassini's thrusters to keep it stable through this flyby.

We'll be monitoring the thrusters closely because we don't want to have to use them on another flyby through the plumes planned for April 28, 2010. In the future flyby, we plan on tracking the spacecraft very closely with the radio instruments on Cassini and on Earth so we can measure how the spacecraft wobbles as it passes near Enceladus. These measurements should tell us more about the interior of the moon, including whether it really does have a liquid subsurface ocean. With the thrusters on, we won't be able tell if the motion of the spacecraft comes from the gravity of Enceladus or the thrusters. We'd like to know whether we can rely on other kinds of attitude control equipment.

We're all eager to pore over the results of this flyby. Stay tuned. In the meantime, feast your eyes on this map of the surface of Enceladus that the Cassini imaging team has updated and released today. The tiger stripes are located in the lower middle left and lower middle right of the image.


  • Bonnie J. Buratti

Artist's concept of NASA's CloudSat spacecraft, which is providing the first global survey of cloud properties to better understand their effects on both weather and climate.

Su et al. (2008, Journal of Geophysical Research) suggested that cirrus clouds increase as sea surface temperature becomes warmer, further enhancing surface warming.

Today, JPL Earth scientist Hui Su joins thousands of other bloggers in more than 130 countries around the world for the Blog Action Day '09 Climate Change.

Blog Action Day is an annual event that unites the world's bloggers in posting about the same issue on the same day, with the aim of sparking discussion around an issue of global importance. The theme of this year's event, climate change, affects us all and will be the topic of international climate negotiations taking place in Copenhagen, Denmark, this December.

As a world leader in studying Earth's climate, NASA researchers play a vital role in shaping our understanding of global change. In today's post, Su discusses the critical role clouds play in climate, and why learning more about them is a key to predicting how our climate will change in the future. For more information on Blog Action Day, visit: .

Clouds are among the most fascinating natural phenomena and have inspired countless works of literature and art. Their ever-changing forms make them a great challenge to atmospheric scientists working to predict how our climate will change in the future in response to increasing greenhouse gases such as carbon dioxide.

Clouds occur at many different heights in our atmosphere and take many different forms. There are three main types of clouds: stratus, cumulus and cirrus. Stratus clouds are low clouds, usually within 2 kilometers (7,000 feet) above the surface. They look like a gray blanket, extending thousands of kilometers across the sky. Cumulus clouds look like puffy cotton balls and extend vertically for large distances. The third type is wispy and feathery-looking cirrus. Cirrus clouds are usually high in the sky, about 7 kilometers (23,000 feet) above the surface. These three types of clouds have different impacts on Earth's climate due to their unique abilities to reflect sunlight and trap heat radiated from Earth's surface.

Stratus clouds can effectively block sunlight from reaching the surface; therefore, they act as an umbrella that cools Earth. Cirrus clouds are relatively transparent to sunlight but can trap terrestrial radiation, JUST AS carbon dioxide does, so they have a net warming effect on Earth. Cumulus clouds can block sunlight and also trap terrestrial radiation. Their net effect varies greatly depending on their actual heights and thicknesses.

Climate scientists have long struggled to quantify how different types of clouds change when global warming occurs. For example, an increase in stratus clouds may cool Earth's surface, compensating for global warming; while an increase in cirrus clouds may further warm Earth's surface, exacerbating global warming. Up to now, scientists have not been able to come to a consensus as to whether stratus, cumulus or cirrus clouds will increase or decrease as global temperatures increase.

A key advancement in cloud studies in recent years has been the availability of global satellite observations of clouds, especially the measurements of clouds at different heights provided by NASA satellites like CloudSat, managed by NASA's Jet Propulsion Laboratory (JPL). These observations are allowing scientists to better simulate clouds in climate models, which are the primary tools climate scientists use to predict future climate change. Up till now, the dynamic nature of clouds has made them very difficult to simulate in current climate models. But by applying space data, we at JPL are working closely with modelers to improve cloud simulations and thereby improve predictions of future climate change.

To learn more about JPL's research in this field and the CloudSat mission, visit: .


  • JPL

Asteroid Eros - Mosaic of Northern Hemisphere

With the recent discovery of the amino acid glycine in the comet dust samples returned to Earth by the Stardust spacecraft, it is becoming a bit more clear how life may have originated on Earth. Water is a well-known ingredient in both comets and living organisms, and now it appears that amino acids are also common to comets and living organisms. Amino acids are used to make proteins, which are chains of amino acids, and proteins are vital in maintaining the cell structures of plants and animals.

Amino acids had previously been identified in meteorite samples, and these samples are thought to be the surviving fragments from asteroid collisions with the Earth. So now it appears that both comets and asteroids in the Earth's neighborhood, the so-called near-Earth objects, delivered some of the building blocks of life to the early Earth.

Impacts of comets and asteroids with the early Earth likely laid down the veneer of carbon-based molecules and water that allowed life to form. Once life did form, subsequent collisions of these near-Earth objects frustrated the evolution of all but the most adaptable species. The dinosaurs checked out some 65 million years ago because of an impact by a six mile-wide comet or asteroid off the coast of the Yucatan peninsula. Fortunately, the small, furry mammalian creatures at the time were far more adaptable and survived this impact event. Thus, present day mammals like us may owe our origin and current position atop Earth's food chain to these near-Earth objects, one of which took out our dinosaur competitors some 65 million years ago.

Today, most of the attention directed toward near-Earth objects has to do with the potential future threat they can pose to life on Earth. However, the recent Stardust discovery of a cometary amino acid reminds us that, were it not for past impacts by these objects, the Earth may not have received the necessary building blocks of life, and humans may not have evolved to our current preeminent position on Earth. While giving thanks to these near-Earth objects, we still need to make sure we find the potentially hazardous comets and asteroids early enough so we don't go the way of the dinosaurs.

For more information on near-Earth objects, see:


  • Don Yeomans

August 2010 sky map

Updated Aug. 26, 2010

If you're like me, you may have received an e-mail this summer telling you to go outside on August 27 and look up in the sky. The e-mail, most likely forwarded to you by a friend or relative, promises that Mars will look as big as the moon on that date and that no one will ever see this view again. Hmmm, it looks like the same e-mail I received last summer and the summer before that, too. In fact this same e-mail has been circulating since 2003, but with a few important omissions from the original announcement.

I'm Jane Jones, an amateur astronomer and outreach specialist for the Cassini mission at Saturn, and I'm here to set the record straight on when and how you can actually see Mars this month.

1. How did the "Mars in August" e-mail get started in the first place?

In 2003, when Mars neared opposition -- its closest approach to Earth in its 22-month orbit around the sun -- it was less than 56 million kilometers (less than 35 million miles) away. This was the closest it had been in over 50,000 years. The e-mail that circulated back then said that Mars, when viewed through a telescope magnified 75 times, would look as large as the moon does with the unaided eye. Even back in 2003, to the unaided eye, Mars looked like a reddish star in the sky to our eyes, and through a backyard telescope it looked like a small disc with some dark markings and maybe a hint of its polar ice cap. Without magnification, it never looked as large as the moon, even back in 2003!

2. Can the moon and Mars ever look the same size?

No. The moon is one-quarter the size of Earth and is relatively close -- only about 384,000 kilometers (about 239, 000 miles) away. On the other hand, Mars is one-half the size of Earth and it orbits the sun 1-1/2 times farther out than Earth's orbit. The closest it ever gets to Earth is at opposition every 26 months. The last Mars opposition was in January and the next one is in March 2011.

At opposition, Mars will be 101 million kilometers (63 million miles) from Earth, almost twice as far as in 2003. So from that distance, Mars could never look the same as our moon.

3. Is Mars visible in August 2010?

Mars and Saturn made a dramatic trio with brighter Venus this month. Skywatchers enjoyed seeing the three planets closely gathered on the 12th and 13th with the slender crescent moon nearby. On the 27th, you'll see Venus shining brightly in the west. If you look above Venus, you may find faint Mars. Saturn is barely visible above the horizon, getting ready for its solar conjunction next month.

4. Can I see Mars and the moon at the same time this month?

Both the moon and Mars were next to one another on the 12th and 13th, but now you can see both planets a few hours apart. Look for Mars in the west at sunset, and watch the moon rise in the east a few hours later. On August 26th and 27th you can see the nearly full moon rising in the east at about 10 p.m. The bright planet below the moon on the 26th is Jupiter! On the 27th, the moon is to the left of the planet.

5. Will the "Mars in August" e-mail return next year?

Most certainly! But next year, you'll be armed with facts, and perhaps you will have looked at the red planet for yourself and will know what to expect. And you will know exactly where to put that email. In the trash!


  • Jane Houston Jones

This image shows a large impact shown on the bottom left on Jupiter's south polar region captured on July 20, 2009, by NASA's Infrared Telescope Facility in Mauna Kea, Hawaii.

We've had such great feedback and comments to our earlier post about the recent impact at Jupiter that we wanted to give you more details, plus answer some questions. My name is Glenn Orton, a senior research scientist at JPL. My colleague and fellow JPL blogger Leigh Fletcher is on a well-deserved vacation for a bit, and he filled in for me while I was at a conference talking about another aspect of our research and the Jupiter impact last week.

I've been on Anthony Wesley's email list (as I am for many in the amateur astronomy community) for some time, so it wasn't happenstance that I was aware of his Jupiter observation. Anthony is the Australian-based amateur astronomer who alerted the world to this big impact. When we received news of his discovery, we immediately wanted to verify it with some of the sophisticated telescopes NASA uses. Having actively observed in both the visible and infrared during the Shoemaker-Levy-9 impacts in 1994, I was aware that a quick verification was possible by looking at a wavelength with lots of gaseous absorption, which suppresses light reflected from Jupiter's deep clouds.

Luck was on our side. Several months before the impact, our JPL team had been awarded observing time on NASA's Infrared Telescope Facility (IRTF) atop Mauna Kea in Hawaii. We had the midnight to 6 a.m. shift (from our Pasadena office, which meant we started work at 3 a.m.) so much of our observing time would take place before Jupiter rose over Australian skies. Another piece of luck is that Anthony's "day job" involves software engineering so he was able to watch the same telescope instrument status and data screens as we were, while we did remote-style observing from the IRTF over the Internet. He would also be doing his own (now *very important*) post-impact observing. Weather was just as "iffy" over Mauna Kea as in Australia, so it was lucky for all of us that we could catch this event.

With Leigh, several JPL summer interns and me huddled at our side-by-side computers at JPL (one with instrument controls and one showing the data), and Anthony online from Australia, we got started. We knew the location of Anthony's dark spot would be coming over Jupiter's rising limb (edge) just as our allotted time was beginning. A near-infrared spectrometer was in the center of the telescope from the previous observer. Although it wasn't our instrument of choice (we wanted images!), it has a very nice guide camera sensitive to the near infrared, so we used it rather than waiting for the 20-40 minute hiatus needed by the telescope operator to move it out of the way and put our preferred instrument in its place. This turned out to be a good decision because the very first image showed us something brighter than anyplace else on the planet -- exactly where Anthony's dark feature was located. For me, this totally clinched the case that this was an impact. Even better was the fact that Anthony was looking on in real time. We e-mailed him what was obvious - he was *definitely* the father of a new impact!

Right after this we collected data that may help us sort out any exotic components of the impactor or of Jupiter's atmosphere and just how high the particulates have spread. Then we switched instruments to something at much longer wavelengths that told us the temperatures were higher, and that ammonia gas had probably been pushed up from Jupiter's troposphere (the lower part of the atmosphere) and ejected into its stratosphere (higher up in the atmosphere). We finished up with our preferred (more versatile) near-infrared camera and ended up, pretty tired, at 9 a.m. (this was a midnight to 6 a.m. run in Hawaii, and in California we were three hours ahead). Then we took some of the screen shots we'd been making and used them to submit a press release. Another person had already alerted a clearinghouse for important astronomical bulletins, so that was another thing that was important but that we didn't need to do.

Now some responses to posts:

Good post from Mike Salway who is another one of the cadre of the world's talented Jupiter observers. I should note that, in fact, there aren't all that many of us who track the time evolution of phenomena in the planets in the professional community, either.

Asim. Neither NASA nor JPL is capable of observing everything in the sky. There is a program to search for asteroids whose orbits will intersect the Earth's, but not at Jupiter. In fact, it's unlikely this object could have been seen, given that it may have been at most a half kilometer in size. For Shoemaker-Levy 9, we were both lucky and the disruption of the comets left a lot of very shiny material around it which made it easier to see.

Denise. It hit quite a bit further south than the Shoemaker-Levy 9 fragments, almost at 60 deg S latitude.

Patrick, Jim, BobK. I suspect that the only link between this and the SL9 fragments is the voracious appetite of Jupiter, the great gravitational vacuum cleaner in that part of the solar system! SL9 fragments impacted from the south; this was from the east.


  • Glenn Orton

This image shows a large impact shown on the bottom left on Jupiter's south polar region captured on July 20, 2009, by NASA's Infrared Telescope Facility in Mauna Kea, Hawaii.

What an incredible few hours it's been for astronomers everywhere, as we witness a chance of a lifetime event: evidence of a space rock of some sort slamming into Jupiter. Images taken after the impact show the debris field and aftermath of a gigantic collision that occurred in the southern polar region of the enormous planet.

An extremely dedicated and meticulous team of amateur astronomers observe Jupiter's changing cloud patterns on a regular basis, and it came as an amazing surprise when Anthony Wesley, near Canberra, Australia, reported his Sunday-morning (July 19, 2009) observations ( of a dark scar that bore all the hallmarks of the Shoemaker Levy 9 impacts at Jupiter in 1994. By an amazing coincidence, I was part of a team that had already been allocated time to observe Jupiter from the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. Based on Anthony's discovery, we were crowded around our computers at 3 a.m. PDT (with Anthony observing with us remotely from Australia) as the first near- and mid-infrared images started to come in... it was such an exciting moment, seeing the high altitude particles that had been lofted by the impact (they appear bright in the infrared). Anthony celebrated with us, but then the real work began. We celebrated and then rolled up our sleeves and began an exciting night of observations.

With the assistance of William Golisch at the IRTF, Glenn Orton and I viewed the impacts in as many wavelengths and spectra as we possibly could, as Jupiter rotated and carried the impact scar out of Earth's view. We used these many views to show evidence for high temperatures at the impact location, and suggestions of ammonia and aerosols that had been carried high into the atmosphere. The observations were repeated again today, Tuesday morning, to track the shape and properties of the site. The scar is extremely large, almost as big as Earth and will continue to grow as Jupiter's atmospheric winds and jet streams redistribute the material, and then, like Shoemaker-Levy 9, it will begin to fade in the coming weeks and months. Based on comparisons to SL-9, the impactor was likely to be small despite the large aftermath, maybe a few hundreds of metres across. Not only will this tell us a lot about impacts in the outer solar system, and how they contribute to the nature of the planets and icy moons, but they'll also serve as a probe for the fundamental weather patterns in Jupiter's high atmosphere.

Amateur observers continue to flood the Internet with new images of the dark spot at approximately 60 degrees south on Jupiter, and so far it looks as though the impact took place sometime in the 24 hours preceding Anthony's discovery. The debris field now extends out to the west and northwest, with additional high-resolution images from the Keck telescope (Marchis, Wong, Kalas, Fitzgerald and Graham showing the detailed morphology of the impact region. The hard work continues today, as an international team of planetary astronomers scrambles for time on some of the world's largest astronomical facilities.

Finally, it's a shame but perhaps not surprising that we didn't see the collision, or the impactor itself, given the great distance to Jupiter. Like throwing a rock in a pond, we're seeing and analyzing the splash that it's made, and we can't yet infer many details about the rock itself - the detailed shape of the impact site could help determine the trajectory and energy of the collision. But it certainly made quite a splash, and we hope to learn a lot about Jupiter from this event!

Anthony's discovery is truly astounding, as it united astronomers in looking again at the gas giant Jupiter. It's overwhelming and spectacularly exciting to watch this event unfolding before our eyes!

You can follow Leigh on Twitter at


  • Leigh Fletcher

Hurricane Gustav moved along the southern side of Jamaica on Aug. 29, 2008.

JPL scientist Bjorn Lambrigtsen goes on hurricane watch every June. He is part of a large effort to track hurricanes and understand what powers them. Lambrigtsen specializes in the field of microwave instruments, which fly aboard research planes and spacecraft, penetrating through thick clouds to see the heart of a hurricane.

While scientists are adept at predicting where these powerful storms will hit land, there are crucial aspects they still need to wrench from these potentially killer storms.

Here are thoughts and factoids from Lambrigtsen in the field of hurricane research.

1. Pinpointing the moment of birth

Most Atlantic hurricanes start as a collection of thunderstorms off the coast of Africa. These storm clusters move across the Atlantic, ending up in the Caribbean, Gulf of Mexico or Central America. While only one in 10 of these clusters evolve into hurricanes, scientists do not yet know what triggers this powerful transformation.

Pinpointing a hurricane's origin will be a major goal of a joint field campaign in 2010 between NASA and the National Oceanic and Atmospheric Administration (NOAA).

2. Predicting intensity

Another focus of next year's research campaign will be learning how to better predict a storm's intensity. It is difficult for emergency personnel and the public to gauge storm preparations when they don't know if the storm will be mild or one with tremendous force. NASA's uncrewed Global Hawk will be added to the 2010 research armada. This drone airplane, which can fly for 30 straight hours, will provide an unprecedented long-duration view of hurricanes in action, giving a window into what fuels storm intensity.

3. Deadly force raining down

Think about a hurricane. You imagine high, gusting winds and pounding waves. However, one of the deadliest hurricanes in recent history was one that parked itself over Central America in October 1998 and dumped torrential rain. Even with diminished winds, rain from Hurricane Mitch reached a rate of more than 4 inches per hour. This caused catastrophic floods and landslides throughout the region.

4. Replenishing "spring"

Even though hurricanes can wreak havoc, they also carry out the important task of replenishing the freshwater supply along the Florida and southeastern U.S. coast and Gulf of Mexico. The freshwater deposited is good for the fish and the ecological environment.

5. One size doesn't fit all

Hurricanes come in a huge a variety of sizes. Massive ones can cover the entire Gulf of Mexico (about 1,000 miles across), while others are just as deadly at only 100 miles across. This is a mystery scientists are still trying to unravel.

NASA and NOAA conduct joint field campaigns to study hurricanes. The agencies use research planes to fly through and above hurricanes, and scientists collect data from NASA spacecraft that fly overhead. NOAA, along with its National Hurricane Center, is the U.S. government agency tasked with hurricane forecasting.

For more information on how NASA and JPL study hurricanes, go to and



Artist’s concept of an extraolar planet.

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


  • Angelle Tanner

This image from NASA’s Mars Reconnaissance Orbiter shows gully channels in a crater in the southern highlands of Mars.The gullies emanating from the rocky cliffs near the crater's rim (upper left) show meandering and braided patterns typical of water-carv

A theme of Mars exploration is "Follow the Water," since understanding the history of water on our planetary neighbor will help us understand if there were environments favorable for life to occur and how climate has changed over time. This is because all life on Earth requires water and we assume the same applies elsewhere in the universe. The Mars Reconnaissance Orbiter has made numerous discoveries that have provided new insights into past wet environments on Mars, water vapor in the planet's current atmosphere and ice in the subsurface. However, so far, liquid water remains elusive.

The Shallow Radar, or "SHARAD" instrument is the only one on the Mars orbiter that was designed with a goal of discovering liquid water below Mars' surface. This ground-penetrating radar instrument, which was supplied by the Italian Space Agency, transmits a radar signal at approximately 20 megahertz, and receives any radar waves that bounce off the surface or subsurface layers. The radar instrument has sufficient strength to see layers to a depth of about one kilometer (a little more than one-half mile), and even deeper in the polar caps. Layers in the subsurface reflect the radar wave if there is sufficient contrast in their dielectric properties (their bulk electrical properties), as for example between dry sand and ice-filled sand. Water is a much better conductor than other geologic materials, and thus should be readily detected if present.

Of all the features believed to be formed by water on Mars, we have found only two gullies known to have recent flows – within the last 5-10 years. Gullies are narrow channels that emanate from cliff walls, starting well below the local ground surface. Dr. Michael Malin used the Mars Orbital Camera on Mars Global Surveyor to repeatedly image these features because of their fresh, unweathered appearance. These efforts led to the discovery of the two relatively new gullies.

To date, the Shallow Radar instrument's observations of dozens of regions containing gullies show no evidence of liquid water. Since slopes of the cliffs where the two new gullies occur are extremely steep, some scientists put forth an alternate hypothesis in which dry debris tumbling downhill could have formed the latest channels. Yet many of the features observed at these and other gullies strongly suggest that liquid water had at least some role in carving the channels. These channels may have formed when a past climate change caused subsurface ice to melt. Or perhaps liquid water was trapped in a past aquifer. But for now, liquid water, if it exists today on Mars, remains out of reach of the Mars Reconnaissance Orbiter.



Artist concept of NASA's Aura spacecraft.

Oxygen, or O2 on the table of chemical elements, is a vital component for life on Earth. It is the second most abundant gas in Earth's atmosphere, making up about 21 percent of its volume. On the other hand, its cousin ozone (O3) makes up less than 0.00001 percent. In fact, if all the ozone in Earth's atmosphere were brought down to the surface, air pressure and temperature conditions would compress ozone into a layer just three millimeters thick, equivalent to two pennies stacked one on top of the other. ! Despite its tiny amount, ozone is also a vital ingredient for life on Earth.

Ozone in fact is vital for life on Earth, but it also has a "bad" side as well - that is, there is both good and bad ozone out there. Good ozone, which accounts for about 91 percent of the ozone in Earth's atmosphere, is present in the stratosphere, the middle layer in Earth's atmosphere. This portion of ozone is commonly referred to as the "ozone layer." The ozone layer absorbs more than 90 percent of the sun's high-frequency ultraviolet light, which is potentially damaging to life on Earth. Without the ozone layer, this radiation would not be filtered as it reaches the surface of Earth, resulting in detrimental health effects for life on Earth. Among the health effects humans could experience as a result of overexposure to ultraviolet radiation are skin cancers, premature aging of the skin and other skin problems, cataracts and other forms of eye damage, and suppression of our bodies' immune systems and our skin's natural defenses.

The troposphere, the part of the atmosphere closest to Earth, contains both good and bad ozone. In the lower troposphere, ozone may serve as an air pollutant since it is a major component of photochemical smog. In the middle troposphere, ozone acts as an atmospheric cleanser, and in the upper troposphere, ozone is a greenhouse gas, which could be bad if concentrations get too high.

The Tropospheric Emission Spectrometer, a science instrument onboard NASA's Aura satellite, is improving our understanding of the good and bad ozone in the troposphere. The spectrometer, which was launched in 2004, provides the first global view of tropospheric ozone and vertical concentrations of ozone, as well as temperature and other important tropospheric features, including carbon monoxide (CO), methane (CH4), water vapor and ammonia (NH3). The instrument has studied the origin and distribution of tropospheric ozone. It has also shed light on how the increasing ozone abundance in the troposphere is affecting air quality on a global scale, as well as ozone's role in chemical reactions that "clean" the atmosphere, and climate change.

These data are used by scientists to determine the degree to which natural sources, like lightning and plant growth, and human-produced sources, like automobiles, industrial pollution, and biomass burning, contribute to ozone production and chemistry. For example, during summertime in the upper troposphere, where ozone acts as a greenhouse gas, lightning generates much greater amounts of ozone than do human activities, thereby having a big impact on regional pollution. Over the last few years, the spectrometer has obtained global data on ozone and chemicals that participate in ozone formation. The fact that the instrument is able to quantify vertical profiles of ozone improves our understanding of how various reactions taking place at specified heights contribute to ozone chemistry. Similar to ozone, chemicals that participate in its production also exist in tiny amounts. Still, this enables scientists to better understand long-term variations in the quantity, distribution and mixing of many tropospheric gases that have a large impact on climate and air quality.

My role with the instrument is to validate the quality of the most recent ozone measurements, which are taken in a special observation mode, called "stare." This mode is used to monitor biomass burning events and volcanic activity. I compare measurements taken by an ozonesdone (a lightweight, balloon-borne instrument that measures ozone, air pressure, temperature and humidity as it ascends through the atmosphere) with measurements from the tropospheric spectrometer. We do this so we can demonstrate the accuracy and precision of the instrument's readings. I am also participating in projects that use the instrument data to better understand the chemistry and transport of pollutants coming from wildfires, such as those that occurred in Australia in December 2006. For the future, I am interested in using the tropospheric spectrometer satellite data for ozone and methane to better quantify the degree to which they contribute to global warming and climate change.


  • Chris Boxe