Archive for July, 2008

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

Tuesday, July 22nd, 2008

By Amy Mainzer

Rocks and Stars with Amy

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

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


An Infrared Glimpse of What’s to Come - by Amy Mainzer

Tuesday, July 22nd, 2008

The image on the left shows a picture of the constellation Orion taken in the visible light that humans see.
On the left, a picture of the constellation Orion taken in the visible light that humans see. On the right, an infrared view of Orion reveals a swirling mass of glowing gas and newly formed stars, which are invisible to the human eye.› Larger image

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

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


This animation shows the Sombrero galaxy, first in visible
light and then in infrared. The infrared view shows a bright,
smooth ring of dust circling the galaxy, and stars that are
hidden by dust in the visible-light view.
› Full caption

So how does one go about building an infrared space telescope? And why does it need to be in space in the first place? Since infrared is heat, you can imagine that trying to observe the faint heat signatures of distant astronomical sources from our nice warm Earth would be very difficult. A colleague of mine compares ground-based infrared astronomy to observing in visible light during the middle of the day, using a telescope made out of fluorescent light bulbs! Putting your infrared telescope in the deep freeze of space, well away from the warmth of Earth, improves its sensitivity by orders of magnitude over a much larger ground-based infrared telescope.

On the Wide-field Infrared Survey Explorer project, our team is in the middle of one of the most exciting phases of building a spacecraft — we’re assembling and testing the payload. Right now, the major pieces of the observatory have been designed and manufactured, and we’re in the process of integrating all these pieces together. The payload is elegantly simple. It has only one moving part — a small scan mirror designed to “freeze-frame” the sky for each approximately 10 second exposure as the spacecraft slowly scans. After six months, we will have imaged the entire sky. The telescope is flying the latest generation of megapixel infrared detector arrays, along with an off-axis telescope that gives us the wide field of view that we need to cover the whole sky so quickly. In the next few months, we’ll be setting the focus on our telescope, characterizing our detector arrays, and verifying the thermal performance of our cryostat. The observatory’s cryostat is essentially a giant thermos containing the cryogenic solid hydrogen that we use to keep our telescope and detectors at their operating temperatures near absolute zero.

telescope
Engineers install the telescope optics into the observatory’s
cryostat. The top dome of the cryostat can be seen in the
foreground. This cover will be ejected approximately two
weeks after launch, allowing the observatory an unfettered
view of the sky. Image courtesy of Space Dynamics
Lab/Utah State University. › Larger image

We are also in the midst of making detailed plans for verifying that the spacecraft is working properly once we launch. This is called the “in-orbit checkout” phase. For this mission, checkout is fast — only 30 days! The checkout commences right after our November 2009 launch, when we wake the spacecraft up and begin switching on its various subsystems: Power generation and distribution, communications, attitude control and momentum management, and the main computer system. We’ll also power on the payload electronics and detectors. Next, we will begin the calibration observations that we need to start the survey, such as verifying the telescope’s image quality and the way our detector arrays respond to light. Once these steps are completed, we’ll be ready to extend our gaze across the universe using the observatory’s infrared eyes.

The great thing about the mission’s all-sky dataset is that it will be accessible to everyone in the entire world via a Web interface. So you will literally be able to access some of the coldest, most distant and dustiest parts of the universe from the comfort of your couch. Stay tuned to explore the universe with us!


Water Ice and Soil Samples on Mars - by Deborah Bass

Thursday, July 17th, 2008

Phoenix landed on May 25, 2008 in the icy northern plains of Mars.
Phoenix landed on May 25, 2008 in the icy northern plains of Mars.› Full caption

We’ve been steadily learning about what it takes to run this thing called the Phoenix lander. As expected, not everything has gone exactly as planned. But that in its own way was planned — we work to maintain flexibility in our schedule and our design, so that we can absorb new things that happen without throwing the whole team into a tizzy!
So what have we been doing?

The Robotic Arm Camera on Phoenix  captured this image underneath the lander on the fifth Martian day of the  mission.
The Robotic Arm Camera on Phoenix captured this
image underneath the lander on the fifth Martian day
of the mission. The abundance of excavated smooth
and level surfaces adds evidence to a hypothesis
that the underlying material is an ice table covered
by a thin blanket of soil.
› Full caption

The really big thing so far is that the Phoenix team discovered what is believed to be water ice beneath the surface under the lander. Computer models suggested that the ice would be several inches beneath the surface and, in fact, that is where we found it! We watched some soil lumps fall apart over several days (in a set of images taken to “monitor change”) and concluded that what was holding the lumps together was ice. After a few days exposed to the Martian atmosphere the cementing agent sublimed — in other words, it changed from a solid to a gas without ever being a liquid. If it had been, say, salts that were holding the lumps together, exposure to the atmosphere over several days wouldn’t have made a difference.

This conclusion about the ice has been arrived at rather carefully. First we saw some bright patches under the lander that had been exposed by the thruster engines during landing. We couldn’t do much with those patches, so we just noted them as “light-toned, forward-reflecting material.” We tried to come up with different hypotheses to explain the bright patches that might be consistent with something other than water ice — like frozen hydrazine fuel that we brought with us, or salt patches, or just lighter-toned rock! We took pictures in different wavelengths and decided that the light-toned material had the right reflective properties of water. We also scraped down a few inches and found the same light-toned material as we were seeing just beneath the lander. Then the team looked at the cloddy soil.

Small clumps of Martian soil were delivered to the MECA wet chemistry experiment.
Small clumps of Martian soil were delivered to the MECA wet chemistry experiment. › Full caption

The wet chemistry experiment in one of the lander’s instruments called the Microscopy, Electrochemistry and Conductivity Analyzer, or MECA, also found salts in the soil samples. Salts are only formed when water has been present! So that is another indicator that there was abundant water in this region of Mars. What are these salts? They appear to be chemicals containing sodium, magnesium, potassium and chlorine. The soils were found to be alkaline, with a pH greater than 7 — similar to soils in the upper dry valleys of Antarctica.

Small clumps of Martian soil were delivered to the MECA wet chemistry  experiment.
This animation shows a sprinkle test,
where the scoop on the Robotic Arm
is vibrated so material gently falls to the target below.
› Full caption

But, like I said, everything hasn’t been totally smooth. The team discovered that the Martian soil is lumpy and sticks together. That made the first sample difficult to deliver! So the team thought about how to make the process easier, and we figured out various ways to break up the lumps. We tried three methods: de-lumping, sprinkling and agitation.

De-lumping refers to shaking the acquired material in the scoop by running a Dremel-like tool that vibrates the entire scoop, breaking up clumps. Then there is sprinkling: By running the rasp while slightly tipping the scoop, the team can command Phoenix to send a small shower and sift particles down into the TEGA (Thermal and Evolved-Gas Analyzer ) and MECA instruments rather than dumping a whole load of clumped-up dirt onto each instrument. As for agitation, the TEGA instrument has a method to shake itself — it has an agitator which shakes the sample loose if anything has stuck to its entry port. The sprinkle and agitation methods have been routinely adopted for sample delivery.

The neat consequence of this is that it solves what had always been our worry about how to deliver the same sample to each instrument for comparison of science results. The sprinkle delivery method enables us to put a large sample into the scoop and deliver part of it to MECA microscopy, part to MECA wet chemistry and part to the TEGA instrument. Same sample problem: solved!!

When life gives you lemons, make lemonade! Or in this case, Marsade!


Here We Are … at Saturn - by Bob Pappalardo

Monday, July 14th, 2008

Saturn
Cassini arrived at Saturn in 2004. › Full caption

Here we are, four years after the Cassini spacecraft entered orbit around Saturn. We’re about to begin the extended mission, termed the Cassini Equinox Mission. Cassini has been a scientifically remarkable mission and a fantastic return on the investment. If you are reading this blog, then you might already know about Cassini’s discoveries at Enceladus, Titan, the other icy moons, the rings, the magnetosphere and Saturn itself. But if you’re new to following this mission, you can catch up on those discoveries by reading about them here: http://saturn.jpl.nasa.gov/news/features/feature20080627.cfm. This great science is accomplished by an international team of scientists and engineers. I am thrilled to be able to carry the scientific reins for Cassini as its incoming project scientist. The project scientist is essentially the mission’s chief scientist, who watches out for the overall scientific integrity of the mission.

Enceladus
Unprocessed image
of Saturn’s moon Enceladus, taken during a
close flyby in March 2008. › Read more

My own background is in the geology of icy moons of the outer solar system. Though the planets have always enthralled me, I trace this specific icy interest back to a course I took as an undergraduate at Cornell University in about 1984, taught by Carl Sagan and his post-doctoral research associate Reid Thompson, entitled “Ices and Oceans in the Outer Solar System.” The course included discussion of Jupiter’s moon Europa, which it was thought might have a globe-girdling ocean beneath its icy surface — an idea that would be further tested by the Galileo spacecraft when it arrived at Jupiter a decade later. We also learned about Saturn’s haze-shrouded moon Titan, which might just have seas of organic rain and liquids on its surface — but we wouldn’t know for certain until the Cassini spacecraft arrived at Saturn two decades later. Who could possibly wait so long? And who would have thought that once we all did, both of these seemingly far-fetched ideas would turn out to be correct? (If only Carl and Reid could be here today to know it.)

Artist concept of Europa Orbiter concept mission.
Artist concept of Europa Orbiter concept mission.
› Larger image

Two years ago I came to JPL with the goal of getting the next flagship mission to the outer solar system off the ground. It takes a great deal of time and energy to make such a mission a reality. They are relatively expensive and take a long time from concept to completion. But just as others before me — such as Galileo Project Scientist Torrence Johnson and Cassini Project Scientist Dennis Matson — have worked to send those missions into space, I would help create the next mission, potentially to orbit Jupiter’s moon Europa. Currently I serve as JPL’s study scientist for the Europa Orbiter mission concept (described at http://opfm.jpl.nasa.gov). This mission concept is in friendly competition with a mission that would orbit Titan. I hope that somehow, in time, we can make both of these spectacular mission concepts come to fruition.

Entering into the wonderland that is Cassini, my eyes are wide open to the science and engineering behind the curtain, while wary of its history and complexity. My operating philosophy is to always be true to the science. With good planning and good fortune, Cassini will keep going down the road for many years to come, following up on its prime mission discoveries and in making new ones that we can’t dream of yet.

Stay tuned for more to come. It’ll be a great ride!