Posts Tagged ‘space’

Dawn’s Stellar Anniversary

Thursday, September 27th, 2012

By Marc Rayman
As NASA’s Dawn spacecraft makes its journey to its second target, the dwarf planet Ceres, Marc Rayman, Dawn’s chief engineer, shares a monthly update on the mission’s progress.

Artist's concept of the Dawn spacecraft
Artist’s concept of NASA’s Dawn spacecraft. Image credit: NASA/JPL-Caltech

Dear Dawnniversaries,

On the fifth anniversary of the beginning of its ambitious interplanetary adventure, Dawn can look back with great satisfaction on its spectacular exploration of the giant protoplanet Vesta and forward with great eagerness to reaching dwarf planet Ceres. Today Earth’s robotic ambassador to the main asteroid belt is in quiet cruise, gradually reshaping its orbit around the sun so it can keep its appointment in 2015 with the mysterious alien world that lies ahead.

This anniversary resembles the first three more than the fourth. Its first years in space were devoted to spiraling away from the sun, ascending the solar system hill so it could gracefully slip into orbit around Vesta in time for its fourth anniversary. One year ago, Dawn was in the behemoth’s gravitational grip and preparing to map its surface in stereo and make other measurements. The subsequent year yielded stunning treasures as Dawn unveiled the wondrous secrets of a world that had only been glimpsed from afar for over two centuries. While at Vesta, it spiraled around the massive orb to position itself for the best possible perspectives. Its final spiral culminated in its departure from Vesta earlier this month. Now for its fifth anniversary, it is spiraling around the sun again, climbing beyond Vesta so that it can reach Ceres.

For those who would like to track the probe’s progress in the same terms used on previous (and, we boldly predict, subsequent) anniversaries, we present here the fifth annual summary, reusing the text from last year with updates where appropriate. Readers who wish to cogitate about the extraordinary nature of this deep-space expedition may find it helpful to compare this material with the logs from its first, second, third, and fourth anniversaries.

In its five years of interplanetary travels, the spacecraft has thrust for a total of 1060 days, or 58 percent of the time (and about 0.000000021 percent of the time since the Big Bang). While for most spacecraft, firing a thruster to change course is a special event, it is Dawn’s wont. All this thrusting has cost the craft only 267 kilograms (587 pounds) of its supply of xenon propellant, which was 425 kilograms (937 pounds) on September 27, 2007.

The fraction of time the ship has spent in powered flight is lower than last year (when it was 68 percent), because Dawn devoted relatively little of the past year to thrusting. Although it did change orbits extensively at Vesta, most of the time it was focused on exactly what it was designed and built to do: scrutinize the ancient world for clues about the dawn of the solar system.

The thrusting so far in the mission has achieved the equivalent of accelerating the probe by 7.14 kilometers per second (16,000 miles per hour). As previous logs have described (see here for one of the more extensive discussions), because of the principles of motion for orbital flight, whether around the sun or any other gravitating body, Dawn is not actually traveling this much faster than when it launched. But the effective change in speed remains a useful measure of the effect of any spacecraft’s propulsive work. Having accomplished slightly more than half of the thrust time planned for its entire mission, Dawn has already far exceeded the velocity change achieved by any other spacecraft under its own power. (For a comparison with probes that enter orbit around Mars, refer to this earlier log.)

Since launch, our readers who have remained on or near Earth have completed five revolutions around the sun, covering about 31.4 AU (4.70 billion kilometers or 2.92 billion miles). Orbiting farther from the sun, and thus moving at a more leisurely pace, Dawn has traveled 23.4 AU (3.50 billion kilometers or 2.18 billion miles). As it climbed away from the sun to match its orbit to that of Vesta, it continued to slow down to Vesta’s speed. Since Dawn’s launch, Vesta has traveled only 20.4 AU (3.05 billion kilometers or 1.90 billion miles) and the even more sedate Ceres has gone 18.9 AU (2.82 billion kilometers or 1.75 billion miles).

› Continue reading Marc Rayman’s Dawn Journal


Asteroid Vesta, All in the Details

Thursday, November 3rd, 2011

By Marc Rayman

As NASA’s Dawn spacecraft investigates its first target, the giant asteroid Vesta, Marc Rayman, Dawn’s chief engineer, shares a monthly update on the mission’s progress.

Image of the giant asteroid Vesta by Dawn
NASA’s Dawn spacecraft obtained this image with its framing camera on September 20, 2011. This image was taken through the camera’s clear filter. The distance to the surface of Vesta is 673 km and the image resolution is about 66 meters per pixel. Image credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA
› Full image and caption

Dear Dawnderfuls,

Dawn has completed another wonderfully successful phase of its exploration of Vesta, studying it in unprecedented detail during the past month. From the time of its discovery more than two centuries ago until just a few months ago, this protoplanet appeared as hardly more than a fuzzy blob, an indistinct fleck in the sky. Now Dawn has mapped it with exquisite clarity, revealing a fascinatingly complex alien world.

The high altitude mapping orbit (HAMO) includes the most intensive and thorough imaging of the entire year Dawn will reside at Vesta. Spectacular as the results from survey orbit were, the observations from HAMO are significantly better. From four times closer to the surface, Dawn’s sensors provided much better views of the extraordinary surface of craters large and small, tremendous mountains, valleys, towering cliffs, ridges, smooth and flat regions, gently rolling plains, systems of extensive troughs, many clusters of smaller grooves, immense landslides, enormous boulders, materials that are unusually bright and others that are unusually dark (sometimes adjacent to each other), and myriad other dramatic and intriguing features. There is no reason to try to capture in words what visual creatures like humans can best appreciate in pictures. To see the sites, which literally are out of this world, either go to Vesta or go here.

Circling the colossus 680 kilometers (420 miles) beneath it in HAMO, the probe has spent most of its time over the illuminated side taking pictures and other scientific measurements and most of the time over the dark side beaming its precious findings back to eager Earthlings.

Dawn revolves in a polar orbit around Vesta, passing above the north pole, then traveling over the day side to the south pole, and then soaring north over the night side. Each circuit takes 12.3 hours. Meanwhile, Vesta completes a rotation on its axis every 5.3 hours. Mission planners choreographed this beautiful cosmic pas de deux by choosing the orbital parameters so that in 10 orbits, nearly every part of the lit surface would come within the camera’s field of view. (Because it is northern hemisphere winter on that world, a region around the north pole is hidden in the deep dark of night. Its appearance in Dawn’s pictures will have to wait for HAMO2.) A set of 10 orbits is known to Dawn team members (and now to you) as a mapping cycle.

Although the HAMO phase was extremely complex, it was executed almost flawlessly, following remarkably well the intricate plan worked out in great detail last year. It consisted of six mapping cycles, and they were conducted in order of their overall importance. In the first cycle, Dawn aimed its camera straight down and took pictures with all of the instrument’s color filters. In addition to showing the startling diversity of exotic features, the color images provide scientists some information about the composition of the surface materials, which display an impressive variation on this mysterious protoplanet. Cycle 1 yielded more than 2500 photos of Vesta, nearly as many as were acquired in the entire survey orbit phase. These observations were deemed so important that not only were they first, but cycle 6 was designed to acquire nearly the same data. This strategy was formulated so that if problems precluded the successful mapping in cycle 1, there would be a second chance without requiring the small and busy operations team to make new plans. As it turned out, there were only minor glitches that interfered with some of the pictures in cycle 1, but the losses were not important. Nevertheless, cycle 6 did fill in most of the missing views.

Cycles 2 through 5 were devoted to acquiring images needed to develop a topographical map. Instead of flying over the sunlit side with its camera pointed straight down, the spacecraft looked at an angle. Each direction was chosen to provide scientists the best combination of perspective and illumination to build up a three dimensional picture of the surface. Knowing the elevations of different features and the angles of slopes is essential to understanding the geological processes that shaped them.

In cycle 2, the camera constantly was directed at the terrain ahead and a little to the left of the point directly below the spacecraft. Cycle 3, in contrast, looked back and slightly to the left. Cycle 4 pointed straight ahead but by a smaller angle than in cycle 2. Cycle 5 did not look forward or backwards; it only observed the surface to the right. With the extensive stereo coverage in each of these 10-orbit mapping cycles, most of the terrain now has been photographed from enough different directions that the detailed shape of the alien landscape can be determined.

The HAMO observations constitute the most comprehensive visible mapping of Vesta for the mission. The survey orbit images were obtained from a higher altitude and so do not show as much detail. When Dawn flies down to its low altitude mapping orbit (LAMO), its primary objectives will be to measure the atomic constituents with the gamma ray and neutron detector (GRaND) and to map the gravitational field. While some images will be acquired, they will be a secondary objective. The principal resources, both for the spacecraft and for the operations team, will be devoted to the higher priority science. In addition, the probe will be too close in LAMO for its camera to collect enough pictures for a global map. The subsequent observations in HAMO2 will be designed mostly to glimpse some of the northern latitudes that are currently too dark to see.

› Continue reading Marc Rayman’s Dawn Journal


Dawn Longs for Vesta’s Gravitational Pull

Friday, May 27th, 2011

By Marc Rayman

NASA’s Dawn spacecraft is less than two months away from getting into orbit around its first target, the giant asteroid Vesta. Each month, Marc Rayman, Dawn’s chief engineer, shares an update on the mission’s progress.

Artist's concept of the Dawn spacecraft
Artist’s concept of the Dawn spacecraft using its ion propulsion system during the approach to Vesta. Image credit: NASA/JPL-Caltech

Dear Dependawnble Readers,

Dawn remains healthy and on course as it continues to approach Vesta. Thrusting with its ion propulsion system, as it has for most of its interplanetary journey so far, the spacecraft is gradually matching its solar orbit to that of the protoplanet just ahead.

As these two residents of the asteroid belt, one very new and one quite ancient, travel around the sun, they draw ever closer. Vesta follows its own familiar path, repeating it over and over, just as Earth and many other solar system bodies do. Dawn has been taking a spiral route, climbing away from the sun atop a blue-green pillar of xenon ions. With an accumulated total in excess of two and a half years of ion thrusting, providing an effective change in velocity of more than 6.5 kilometers per second (14,500 mph), the probe is close to the end of the first leg of its interplanetary trek. On July 16, Vesta’s gravity will capture the ship as it smoothly transitions from spiraling around the sun to spiraling around Vesta, aiming for survey orbit in August. For several reasons, the date for the beginning of the intensive observations there has not yet been set exactly.

Astronomers have estimated Vesta’s mass, principally by measuring how it occasionally perturbs the orbits of some of its neighbors in the asteroid belt and even the orbit of Mars, but this method yields only an approximate value. Because the mass is not well known, there is some uncertainty in the precise time that Dawn will become gravitationally bound to the colossal asteroid. As we have seen before, entry into orbit is quite unlike the highly suspenseful and stressful event of missions that rely on conventional chemical propulsion. Dawn simply will be thrusting, just as it has for 70 percent of its time in space. Orbit entry will be much like a typical day of quiet cruise. That Vesta will take hold at some point will matter only to the many Dawnophiles throughout the cosmos following the mission. The ship will continue to sail along a gently curving arc to survey orbit.

› Continue reading Marc Rayman’s May 27, 2011 Dawn Journal


Alien Vs. Editor: Life As We May (or May Not) Know It

Monday, April 18th, 2011

By Steve Edberg

Alien vs. Editor is a forum for questions and answers about extrasolar planets and NASA’s search for life beyond our solar system. Leave your questions for author Steve Edberg and read more on the PlanetQuest website.

Tubeworms
Tubeworms that grow near the boundary where hot vent fluid mixes with cold seawater on the ocean floor are an example of extremophiles that broaden our perspective on where to look for life. Image credit: Nicolle Rager Fuller, National Science Foundation

A reader’s question (paraphrased): Why do astronomers assume there have to be conditions similar to Earth in order for life to exist? Who are we to define what life looks like and how would we know what we’re looking at if we really don’t know what we are looking for?

This has been a recurring question over the years, and I don’t think anyone interested in finding extraterrestrial life would dispute those thoughts. The problem is that we aren’t as clever as Mother Nature, so we don’t know what else to look for. More practically, we don’t know what other conditions to look for beyond those we are familiar with.

Science fiction writers have used their imaginations to propose other forms of life. Sir Fred Hoyle (an astronomer) wrote a novel titled “The Black Cloud,” (SPOILER/GIVEAWAY ALERT!! SKIP THE REST OF THIS SENTENCE IF YOU THINK YOU WILL READ THE BOOK) about a self-propelling interstellar cloud that came to orbit the sun to acquire energy (it stopped for lunch!) before moving on.

On the TV shows “Star Trek” and “Star Trek: The Next Generation,” the screenwriters came up with at least two forms of life that were completely novel. Naturally enough, the shows involving them were about recognizing that they were life and how to deal with it. The one on “Star Trek” was about rock-beings that tunneled through an asteroid or planet. The other, on “Star Trek TNG,” was about “nanites,” microscopic silicon crystals that were hive-like beings communicating among themselves electrically and with electromagnetic waves with the crew of Enterprise D.

These are three examples of potential life forms far different from what we are familiar with. But knowing what to look for and where is a long step from the presentation of these ideas in science fiction media.

Before the Viking landings on Mars in the 1970s, Carl Sagan gave talks about the life-detecting instruments aboard the landers, which were designed to detect life as we know it. He also mentioned that there was a camera aboard so that we could see any “silicon-based giraffes that might walk by,” so even then scientists were thinking about possible, unfamiliar forms of life.

The strategy being followed is to look for evidence of extraterrestrial life, as we recognize life, now, rather than wait until we figure out all the possibilities. Scientists study and search for new examples of “extremophiles” that live in extreme conditions compared to what most of life on Earth lives in, in order to broaden our perspective on where to look for life.

There are also radio and optical searches for evidence of extraterrestrial intelligence living (by whatever chemical process) on planets orbiting other stars that might be announcing their presence. And I recently heard that there is a meeting planned to consider what else we might look for in this arena, considering that the era of our radio transmissions out to the galaxy (TV and radio) could be coming to an end as we use more cable and fiber communications here on Earth.


Dawn Spacecraft Creeping Up on Vesta

Wednesday, March 9th, 2011

By Marc Rayman

NASA’s Dawn spacecraft is less than five months away from getting into orbit around its first target, the giant asteroid Vesta. Each month, Marc Rayman, Dawn’s chief engineer, shares an update on the mission’s progress.

Artist's concept of Dawn at Vesta
Artist’s concept of NASA’s Dawn spacecraft at the large asteroid Vesta. The mission is less than five months away from getting into orbit around the large asteroid, its first target.

Dear Pleasant Dawnversions,

Deep in the asteroid belt, Dawn continues thrusting with its ion propulsion system. The spacecraft is making excellent progress in reshaping its orbit around the sun to match that of its destination, the unexplored world Vesta, with arrival now less than five months away.

We have considered before the extraordinary differences between Dawn’s method of entering orbit and that of planetary missions employing conventional propulsion. This explorer will creep up on Vesta, gradually spiraling closer and closer. Because the probe and its target already are following such similar routes around the sun, Dawn is now approaching Vesta relatively slowly compared to most solar system velocities. The benefit of the more than two years of gentle ion thrusting the spacecraft has completed so far is that now it is closing in at only 0.7 kilometers per second (1600 mph). Each day of powered flight causes that speed to decrease by about 7 meters per second (16 mph) as their orbital paths become still more similar. Of course, both are hurtling around the sun much faster, traveling at more than 21 kilometers per second (47,000 mph), but for Dawn to achieve orbit around Vesta, what matters is their relative velocity.

It may be tempting to think of that difference from other missions as somehow being a result of the destination being different, but that is not the case. The spiral course Dawn will take is a direct consequence of its method of propelling itself. If this spacecraft were entering orbit around any other planetary body, it would follow the same type of flight plan. This unfamiliar kind of trajectory ensues from the long periods of thrusting (enabled by the uniquely high fuel efficiency of the ion propulsion system) with an extremely gentle force.

Designing the spiral trajectories is a complex and sophisticated process. It is not sufficient simply to turn the thrust on and expect to arrive at the desired destination, any more than it is sufficient to press the accelerator pedal on your car and expect to reach your goal. You have to steer carefully (and if you don’t, please don’t drive near me), and so does Dawn. As the ship revolves around Vesta in the giant asteroid’s gravitational grip, it has to change the pointing of the xenon beam constantly to stay on precisely the desired winding route to the intended science orbits.

Dawn will scrutinize Vesta from three different orbits, known somewhat inconveniently as survey orbit, high altitude mapping orbit (HAMO), and low altitude mapping orbit (LAMO). Upon concluding its measurements in each phase, it will resume operating its ion propulsion system, using the mission control team’s instructions for pointing its thruster to fly along the planned spiral to the next orbit.

› Continue reading Dawn Spacecraft Creeping Up on Vesta


Rocks and Stars with Amy: This Year I Saw the Universe

Tuesday, February 1st, 2011

By Amy Mainzer

Rocks and Stars with Amy

With WISE, I roamed the skies — seeing everything from the closest asteroids to the most distant galaxies. When I was a kid, maybe 6 or 7, I remember reading the encyclopedia about Andromeda, Mars and Jupiter. After that, I spent a lot of my free time (and a fair amount of gym class) wishing that I could be “out there” exploring the stars, imagining what it must be like to get close to a black hole or the lonely, cold surface of a moon. Fast-forwarding several decades, I’ve just spent a tremendously satisfying and delightful year using some of our most sophisticated technology to see “out there” for real. It’s pretty cool when your childhood dreams come true!

Today, the operations team sent the command to kill the survey sequence and put WISE into a deep sleep. While I’m sad to see the survey stop, the real voyage of discovery is just getting started as we unpack the treasures that our spacecraft beamed back to us. Although I’m going to miss waking up to see a new slew of pictures fresh from outer space, what I’ve looked at so far is only a tiny fraction of the millions of images we’ve garnered. My colleagues and I are working nonstop now to begin the decades-long process of interpreting the data. But I can already say for certain that we’re learning that the universe is a weirder, more wonderful place than any science fiction I’ve ever read. If I could go back in time to when I was kid, I’d tell myself not to worry and to hang in there through the tough parts — it was all worth it.

A cast of hundreds, maybe thousands, of people have worked on WISE and deserve far more credit than they get. The scientists will swoop in and write papers, but all those results are squarely due to the brilliance, stubborn persistence and imagination of the technicians, managers, engineers of all stripes (experts in everything from the optical properties of strange materials to the orbital perturbations of the planets), and administrative staff who make sure we get home safely from our travels. Although we may not be able to fly people around the galaxy yet, one thing Star Trek got right is the spirit of camaraderie and teamwork that makes projects like WISE go. For the opportunity to explore the universe with such fine friends and teammates, I am truly grateful.


Science Fact, Not Fiction: Isaac Asimov on the Greenhouse Effect

Monday, January 10th, 2011

By Amber Jenkins

I stumbled upon this video earlier today. It’s Isaac Asimov, famous science fiction writer and biochemist, talking about global warming — back in January 1989. If you change the coloring of the video, the facial hair style, and switch out Asimov for someone else, the video could pretty much have been made today.

Asimov was giving the keynote address at the first annual meeting of The Humanist Institute. “They wanted me to pick out the most important scientific event of 1988. And I really thought that the most important scientific event of 1988 will only be recognized sometime in the future when you get a little perspective.”

What he was talking about was the greenhouse effect, which, he goes on to explain, is “the story everyone started talking about [in 1988], just because there was a hot summer and a drought.” (Sound familiar, letting individual weather events drive talk of whether the Earth’s long-term climate is heating up or cooling down??)

The greenhouse effect explains how certain heat-trapping (a.k.a. “greenhouse”) gases in our atmosphere keep our planet warm, by trapping infrared rays that Earth would otherwise reflect back out into space. The natural greenhouse effect makes Earth habitable — without our atmosphere acting like an electric blanket, the surface of the earth would be about 30 degrees Celsius cooler than it is now.

The problem comes in when humans tinker with this natural state of affairs. Our burning of fossil fuels (coal, oil and gas) constantly pumps out carbon dioxide — a heat-trapping gas — into the atmosphere. Our cutting down of forests reduces the number of trees there are to soak up some of this extra carbon dioxide. All in all, our atmosphere and planet heats up, (by about 0.6 degrees Celsius since the Industrial Revolution) with the electric blanket getting gradually thicker around us.

“I have been talking about the greenhouse effect for 20 years at least,” says Asimov in the video. “And there are other people who have talked about it before I did. I didn’t invent it.” As we’ve stressed here recently, global warming, and the idea that humans can change the climate, is not new.

As one blogger notes, Asimov’s words are as relevant today as they were in 1989. “It’s almost like nothing has happened in all this time.” Except that Isaac Asimov has come and gone, and the climate change he spoke of is continuing.

Asimov’s full speech can be seen here.

This post was written for “My Big Fat Planet,” a blog hosted by Amber Jenkins on NASA’s Global Climate Change site.


Red, Red Moon and Other Lunar Eclipse Phenomena

Monday, December 20th, 2010

By Dr. David Diner

Total Lunar EclipseTiny airborne particles, or aerosols, can affect the appearance of the moon during a total lunar eclipse, sometimes giving it a reddish hue. Copyright Ian Sharp

A lunar eclipse occurs when the Earth is positioned between the sun and the moon. Although the Moon passes through the Earth’s shadow, the lunar disk remains partially illuminated by sunlight that is refracted and scattered by the Earth’s atmosphere.

Refraction is the bending of light that occurs when the rays pass through media of different densities (our atmosphere is more dense near the surface and less dense higher up). Scattering of sunlight by molecules of air also deflects the light into different directions, and this occurs with much greater efficiency at shorter (bluer) wavelengths, which is why the daylight sky appears blue. As we view the sun near sunrise or sunset the light traverses a longer path through the atmosphere than at midday, and when the air is relatively clear, the absence of shorter wavelengths causes the solar disk to appear orange.

Tiny airborne particles, also known as aerosols, also scatter sunlight. The relative efficiency of the scattering at different wavelengths depends on the size and composition of the particles. Pollution and dust in the lower atmosphere tends to subdue the color of the rising or setting sun, whereas fine smoke particles or tiny aerosols lofted to high altitudes during a major volcanic eruption can deepen the color to an intense shade of red.

If you were standing on the Moon’s surface during a lunar eclipse, you would see the Sun setting and rising behind the Earth, and you’d observe the refracted and scattered solar rays as they pass through the atmosphere surrounding our planet. Viewed from the Earth, these rays “fill in” the Earth’s shadow cast upon the lunar surface, imparting the Moon’s disk with a faint orange or reddish glow. Just as we sometimes observe sunrises and sunsets with different shades of orange, pink or red due to the presence of different types of aerosols, the color of the eclipsed lunar disk is also affected by the types of particles that are present in the Earth’s atmosphere at the time the eclipse occurs.


Lunar Eclipse, the Moon’s Interior, and the Holy GRAIL

Wednesday, December 15th, 2010

By Sami Asmar

Earth's moon

In addition to the awesome views they offer, lunar eclipses have always provided scientific clues about the moon’s shape, location and even surface composition. Although there will continue to be opportunities for observers to examine and reflect on fundamental concepts about the moon, such as its origin and interior structure, more modern tools are aiding these observations.

When it comes to understanding what a moon or a planet is made of remotely — short of touching it or placing seismometers on its surface or probes below the surface — classical physics comes to the rescue. By measuring the magnetic and gravitational forces that are generated on the inside and manifested on the outside of a planet or moon, we can learn volumes about the structure of its interior.

A spacecraft in the proximity of the moon can detect these forces. In the case of gravity, the mass of the moon will pull on the spacecraft due to gravitational attraction. If the spacecraft is transmitting a stable radio signal at the time, its frequency will shift by an amount exactly proportional to the forces pulling on the spacecraft.

This is how we weigh the moon and go further by measuring the detailed distribution of the densities of mountains and valleys as well as features below the moon’s surface. This collection of information is called the gravity field.

In the past, this has lead to the discovery mascons on the moon, or hidden, sub-surface concentrations of mass not obvious in images or topography. If not accounted for, mascons can complicate the navigation of future landed missions. A mission, human or robotic, attempting to land on the moon would need to have a detailed knowledge of the gravity field in order to navigate the landing process safely. If a spacecraft sensed gravitational pull higher than planned, it could jeopardize the mission.

GRAIL spacecraft

The Gravity Recovery and Interior Laboratory (GRAIL) mission, scheduled to launch in September, is comprised of twin spacecraft flying in formation with radio links between them to measure the moon’s gravity field globally. This is because a single spacecraft with a link to Earth would be obstructed when the spacecraft goes behind the moon, leaving us with no measurement for nearly half of the moon, since the moon’s far side never faces the Earth. The GRAIL technique may also reveal if the Moon has a core with a fluid layer.

So as you go out to watch the lunar eclipse on the night of Dec. 20, think about how much we’ve learned about the moon so far and what more we can learn through missions like GRAIL. Even at a close distance from Earth, the moon remains a mystery waiting be uncovered.


Planetary Trio Provides a Warm-Up Act for Perseids

Thursday, August 12th, 2010

By Jane Houston Jones

Star chart showing visible planets in August, 2010

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.


Rocks and Stars with Amy: Milestones

Tuesday, July 20th, 2010
Rocks and Stars with Amy
By Amy Mainzer

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.

asteroids and comets detected by WISEThis plot shows asteroids and comets observed by NASA’s Wide-field Infrared Survey Explorer, or WISE. Image credit: NASA/JPL-Caltech/ULCA/JHU   |   ›See related video

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”


Super Swooper: Cassini wraps up its lowest pass through Titan atmosphere

Monday, June 21st, 2010
Julie Webster
Julie Webster

On Sunday evening, my eyes were glued to eight windows on my computer screen, watching data pop up every few seconds. NASA’s Cassini spacecraft was making its lowest swing through the atmosphere of Saturn’s moon Titan and I was on the edge of my seat. Trina Ray, a Titan orbiter science team co-chair, was keeping me company. Five other members of my team were also at JPL. Between us, we were keeping an eye on about 2,000 data channels.

One of the 34-meter antennas at the Deep Space Network’s Goldstone complex, DSS-24, was pointed at Saturn and listening for the signal that was expected to be here in just a few minutes. The data would be arriving at my computer as quickly as they could be sent back to Earth, though there was an agonizing hour-and-18-minute delay because of the distance the data had to travel. (We call this flyby T70, but it is actually Cassini’s 71st flyby of Titan.)

It was a nervous time for me — the previous night we had been at JPL to send some other real-time commands to the spacecraft when an alarm came in indicating that the magnetometer, the prime instrument taking data for the T70 flyby, needed a reset. Fortunately, the controller on duty immediately called the magnetometer instrument operations team lead in England. Within 90 minutes, the commands were on their way to do a computer reset and clear the alarm. At 2 a.m. Pacific time on Sunday, we got the email indicating all was well and the magnetometer was ready for the Titan closest approach.

So here we were, past one hurdle, hoping nothing else would come up. We had run hundreds of simulations over the past three-and-a-half years, so I knew we had done everything we could think to do. We did more training for this event than anything else we had done since we dropped off the Huygens probe in January 2005 for a descent through the moon’s hazy atmosphere.

Right on time, at 7:26 p.m., the Deep Space Network locked on the spacecraft downlink, a good start. I was focused on the data for spacecraft pointing. As long as we stayed within an eighth of a degree of the expected pointing, everything would be fine. At 7:45 p.m., we got the data from closest approach, a mere 880 kilometers (547 miles) in altitude. Over the vocabox, a cross between a telephone and walkie-talkie, the attitude control team reported that the thrusters were firing about twice as much as we expected. The Titan atmosphere appeared to be a little thicker than we expected, even though we had fed about 40 previous low Titan flybys by Cassini and the descent data from Huygens into our modeling.

But spacecraft control was right on the money, keeping the pointing within our predicted limits. Even with the extra thrusting, we stayed well within our safety margin.

At 7:53 p.m., the spacecraft turned away to go to the next observation. I let out a sigh of relief, happy that everything during closest approach had gone just as we planned. Five attitude control guys crowded into my office with smiles on their faces. Trina and I were marveling at what a wonderful spacecraft we have to work with. Another first for the Cassini mission!

Now, as Trina says, we have to finish the job by returning all the great science data. We have data playbacks today at two different Deep Space Network stations to make sure we have - as we say here - both belts and suspenders. Engineers will also go back to analyze the data with the scientists to see just how dense the Titan atmosphere turned out to be at our flyby altitude.

But last night, at least, my team and I went home happy!


Cassini to Swing Low Into Titan’s Atmosphere

Thursday, June 17th, 2010
César Bertucci
César Bertucci

This weekend, Cassini will embark on an exciting mission: trying to establish if Titan, Saturn’s largest moon, possesses a magnetic field of its own. This is important for understanding the moon’s interior and geochemical evolution.

For Titan scientists, this is one of the most anticipated flybys of the whole mission. We want to get as close to the surface with our magnetometer as possible for a one-of-a-kind scan of the moon. Magnetometer team scientists (including me) have a reputation for pushing the lower limits. In a world of infinite possibilities, we would have liked many flybys at 800 kilometers. But we went back and forth a lot with the engineers, who have to ensure the safety of the spacecraft and fuel reserves. We agreed on one flyby at 880 kilometers (547 miles) and both sides were happy.

Artist's concept of Cassini's Titan flyby
Cassini flies to within 880 kilometers (547 miles) of Titan’s surface during its 71st flyby of Titan, known as “T70,” the lowest in the entire mission. Image credit: NASA/JPL/Space Science Institute
› Full image and caption

Flying at this low altitude will mark the first time Cassini will be below the moon’s ionosphere, a shell of electrons and other charged particles that make up the upper part of the atmosphere. As a result, the spacecraft will find itself in a region almost entirely shielded from Saturn’s magnetic field and will be able to detect any magnetic signature originating from within Titan.

Titan orbits within the confines of the magnetic bubble around Saturn and is permanently exposed to the planet’s magnetic disturbances. Previous measurements by NASA’s Voyager spacecraft and Cassini at altitudes above 950 kilometers (590 miles) have shown that Titan does not possess an appreciable magnetic field capable of counterbalancing Saturn’s. However, this does not imply that Titan’s field is zero. We’d like to know what the internal field might be, no matter how small.

The internal structure of Titan can be probed remotely from its gravitational field or its magnetic properties. Planets with a magnetic field — like Titan’s parent Saturn or our Earth — are believed to generate their global-scale magnetic fields from a mechanism called a dynamo. Dynamo magnetic fields are generated from currents in a molten core where charge-conducting materials such as metals are flowing around each other and also undergoing other stresses because of the planet’s rotation.

We might not find a magnetic field at all. A positive detection of an internal magnetic field from Titan could imply one of the following:

a) Titan’s interior still bears enough energy to sustain a dynamo.
b) Titan’s interior is “cold” (and therefore has no dynamo), but its crust is magnetized in a similar way as Mars’ crust. If this is the case, we should find out how this magnetization took place.
c) Something under the surface of Titan got charged temporarily by Saturn’s magnetic field before this Cassini flyby. While I said earlier that the ionosphere shields the Titan atmosphere from Saturn’s magnetic bubble, the ionosphere is only an active shield when the moon is exposed to sunlight. During part of its orbit around the planet, Titan is in the dark and magnetic field lines from Saturn can reach the Titan surface. A temporary magnetic field can be created if there is a conducting layer, like an ocean, on or below the moon’s crust.

Once Cassini leaves Titan, the spacecraft will perform a series of rolls to fine-calibrate its magnetometer in order to assess T70 measurements with the highest precision. We’re looking forward to poring through the data coming down, especially after all the negotiations we had to make for them!


Comets and Life On Earth

Monday, August 17th, 2009
Donald Yeomans
Donald Yeomans

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.

Asteroid Eros - Mosaic of Northern Hemisphere
Asteroid Eros - Mosaic of Northern Hemisphere. Image Credit: NASA/JPL/JHUAPL
› Full image and caption

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: http://www.jpl.nasa.gov/asteroidwatch/index.cfm


The Lowdown on Jupiter’s Black Eye

Wednesday, July 29th, 2009
Glenn Orton
Glenn Orton

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.

Jupiter
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. Image credit: NASA/JPL/Infrared Telescope Facility

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 (see the web pages for the International Outer Planet Watch: http://dawn.ucla.edu/IJW/).

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.


All Eyes on Jupiter

Wednesday, July 22nd, 2009
Leigh Fletcher
Leigh Fletcher

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 (http://jupiter.samba.org/jupiter-impact.html) 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.

Jupiter
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. Image credit: NASA/JPL/Infrared Telescope Facility

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 http://keckobservatory.org/index.php/news/jupiters_adds_a_feature/) 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 http://twitter.com/LeighFletcher


Five ‘Holy Grails’ of Distant Solar Systems

Thursday, June 11th, 2009
Angelle Tanner
Angelle Tanner

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

Artist’s concept of an extraolar planet.
Artist’s concept of an extraolar planet.
Image credit: NASA/JPL-Caltech

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