Archive for the ‘Universe’ Category

Rocks and Stars with Amy: Sizing Up Near-Earth Asteroids

Wednesday, November 12th, 2008

By Amy Mainzer

Rocks and Stars with Amy

Asteroids. The word conjures images of pitted rocks zooming through space, the cratered surfaces of planets and moons, and for some, memories of a primitive video game. Just how hazardous are these nearest neighbors of ours? We think that one contributed to the extinction of the dinosaurs, giving rise to the age of mammals. How likely is this to happen again?

The Wide-field Infrared Explorer (WISE) mission, an infrared telescope launching in about a year, will observe hundreds of near-Earth asteroids, offering unique insights into this question. The risk posed by hazardous asteroids is critically dependent on how many there are of different sizes. We know that there are more small asteroids than large ones, but how many more, and what are they made of?

asteroidAsteroids reflect sunlight (about half of which is the visible light that humans see), but the sun also warms them up, making them glow brightly in infrared light. The problem with observing asteroids in visible light alone is that it is difficult to distinguish between asteroids that are small and highly reflective, or large and dark. Both types of objects, when seen as distant points of light, can appear equally bright in visible light. However, by using infrared light to observe asteroids, we obtain a much more accurate measurement of their size. This is because the infrared light given off by most asteroids doesn’t depend strongly on reflectivity.

WISE will give us a much more accurate understanding of how many near-Earth asteroids there are of different sizes, allowing astronomers to better assess the hazard posed by asteroids. The danger posed by a near-Earth asteroid depends not only on its size, but also on its composition. An asteroid made of dense metals is more dangerous than one of the same size made mostly of less dense silicates. By combining infrared and visible measurements, we can determine how reflective the asteroids are, which gives us some indication of their composition.


From the Edge

Tuesday, September 23rd, 2008
Ed Stone
by Ed Stone
Voyager Project Scientist

Winds of charged particles race outwards from the sun at 300,000 miles per hour. They are so faint that, here on the outer edge of the solar system, they would be undetectable if it were not for the very sensitive instruments carried by spacecraft.

From this distant, dark void, the sun is 100 times farther away than it is from Earth. Even so, our star is a million times brighter than Sirius, the brightest star seen from Earth. All around is a near-perfect vacuum, with only the most capable of instruments able to detect an ambient magnetic field that is 200,000 times weaker than the field back on Earth. To top off the loneliness factor, nothing from Earth has ever journeyed this far from home.

This remote zone is the domain now for Voyager 1 and 2.After 31 years of exploration, the twin spacecraft are the elder statesmen of space exploration, robotic envoys in the most distant reaches of our solar system. Voyager 1 is now 107 times farther from the sun than Earth is; Voyager 2 is 87 times farther. It takes about 15 hours for a signal leaving Earth to reach Voyager 1. (By contrast, it takes a little more than 20 minutes for a signal to go to Mars, even when the red planet is farthest from Earth.)

Voyager
This artist’s rendering depicts NASAs Voyager 2 spacecraft as it studies the outer limits of the heliosphere - a magnetic ‘bubble’ around the solar system that is created by the solar wind.

The twin spacecraft do not rest on the laurels of their discoveries at Jupiter, Saturn, Uranus and Neptune - the planets they flew by between 1977 and 1989. In fact, their findings at our solar system’s edge are changing scientists’ theories about what happens “way out there” and how interstellar space affects our solar system.

The Voyagers have shown that the heliosphere - the sun’s protective bubble surrounding our solar system — is not smooth and symmetric, as was originally thought. The robotic team discovered that this bubble is being pushed in and deformed by the pressure from the interstellar magnetic field outside our solar system. Another surprise came when the spacecraft passed an important milestone near the edge of the solar system, called the termination shock. The energy released from the sudden slowing of the sun’s supersonic wind had an unexpected outcome - it was absorbed not by the wind itself, but by ionized atoms that had come from outside our solar system. And inevitably, as theories are shattered in the wind, more questions arise. There are cosmic rays we know come from this distant region, for example, but their origin is yet to be found and explained.

After all this time, Voyager’s discoveries continue to do what they have always done - take us to new places we have never been, and shed light on the how our solar system interacts and interconnects with the surrounding regions of the Milky Way.

Both Voyagers have enough power to run until 2025. Voyager 1 will probably cross into interstellar space by about 2015. At that moment, Voyager 1 will become Earth’s first interstellar spacecraft, leaving the sun behind as it enters the interstellar wind produced by the supernova explosions of other stars.

Until their final transmissions — hopefully many years in the future — the Voyagers still have a long way to go and lots to tell us.


Looking for Earths Far From Home - by Tracy Drain

Monday, August 4th, 2008
What is Kepler?
photometer lowered into spacecraft
The photometer is lowered into the spacecraft in this picture. › Larger image

Kepler is a mission that is designed to find Earth-sized planets outside our solar system. Specifically, it will look for these rocky planets in the “habitable zone” near their stars — meaning at a distance where liquid water could exist on the surface.

Kepler will accomplish this by monitoring a large set of stars (approximately 100,000) and looking for the signature dip in brightness that indicates that a planet has crossed between the spacecraft and the star. The instrument that detects this dip is called a photometer — literally, a “light meter.” It is basically a large telescope that funnels the light from the stars onto a CCD array (similar to the ones used in digital cameras).

By surveying such a large number of stars using this “transit” method, Kepler will be able to determine the frequency of Earth-sized (and larger) planets around a wide variety of stars.

What do I think is cool about this mission?

I love the fact that the Kepler approach - looking for the dips in stellar brightness that occur when a planet passes between the photometer and a star - is so straightforward. It is such a wonderfully simple way to look for planets! Of course in practice, there are plenty of complicating factors that make this a challenging mission to execute. The change in brightness that we are looking for is very small (on the order of 0.01 percent). To make sure we can detect that, we have to carefully control noise in the system - things like electronic noise from reading out the CCDs, smear from tiny motions of the spacecraft, etc. These and other aspects of the mission have provided plenty of challenges to keep things interesting for the design team.

One of my favorite things about the Kepler mission is that the patch of sky we will be surveying is near a particular group of highly recognizable constellations. The stars Kepler will look at are in the area of what is known as the Summer Triangle, a group of constellations - Aquila, Cygnus and Lyra - that are overhead at midnight when viewed from northern latitudes in the summer months. When the scientist team starts identifying planets in our field of view, anyone will be able to go outside, point towards the Summer Triangle and say “they’ve just discovered a planet over there.” To me, there is something about that which will make the discoveries that much more personal.

photometer lowered into spacecraft
This image shows the Milky Way region of the sky where the Kepler photometer will be pointing. Image credit: Carter Roberts, Eastbay Astronomical Society, Oakland, Calif. › Larger image

I am also a huge sci-fi fan and I have always been particularly fascinated by books and movies about how humans might some day colonize other worlds in the galaxy. I think it is fantastic to get to work on a mission that will be looking for planets outside our solar system that are Earth-sized and in a range around their stars that could be habitable; places where such colonization could one day take place… I can’t wait to see what we find!

What do I do?

I am a member of the Project System Engineering Team at JPL. This team is responsible for a wide variety of tasks on Kepler, aimed at ensuring the project meets the driving scientific and technological objectives. This often involves checking that the interfaces between the different elements of the project work smoothly. For example, one of our responsibilities is to conduct end-to-end tests of the mission’s information system. In this test, we check to make sure that the right commands are being generated to collect data, data is collected using spacecraft hardware, and then the data flows correctly through the ground data system. This lets us verify that the entire data flow chain functions as it should before we launch.

My particular focus has been ensuring that we work out all of the details associated with executing each of the mission phases (the launch phase, the on-orbit checkout period that we call the commissioning phase, and the main data-gathering portion of the mission, which is the science phase). I work closely with my colleagues at NASA Ames, Ball Aerospace and JPL to identify and resolve open issues associated with planning for, testing and eventually executing the activities associated with these phases.

What is happening on the project right now?

This animation shows how Kepler will work.

The project is in what is known as the Assembly, Test and Launch Operations phase. Right now, the assembled spacecraft and instrument (known collectively as the flight system) is in the middle of the environmental testing campaign at Ball. This involves many hours of running the flight system and monitoring its performance while exposing it to the types of temperatures, pressures and other conditions that it will see in space. The system that will collect and distribute the data is undergoing integrated testing as well, with teams of people working to push test data through all of the various ground interfaces. The operations team — the people who will be responsible for generating and testing commands, monitoring the health and safety of the spacecraft and ensuring that data is collected from it by the Deep Space Network — are undergoing training and getting ready for upcoming mission phase rehearsals that we call “operational readiness tests.” Even though we are still several months away from launch, it is a very busy time on the project!

Who is involved?

The principle investigator and the science office that will lead the scientific data analysis are at the NASA Ames Research Center in Mountain View, Calif. The spacecraft and photometer were built at Ball Aerospace & Technologies Corporation in Boulder, Colo. The mission operations center is located at the Laboratory for Atmospheric and Space Physics at the University of Colorado at Boulder. The mission is managed here at the Jet Propulsion Laboratory in Pasadena, Calif.


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!