The Vehicle Assembly Building

I just got 3D glasses today through Alan Boyle of CosmicLog, and I couldn't resist using a 3D video I had seen of the inside of NASA's Vehicle Assembly Building for my glasses’ first light¹. The Vehicle Assembly Building is one of the largest buildings on the planet, fourth by volume. The 3D video gives a great idea of the immense scale of the structure, with great views from the inside.



The Vehicle Assembly Building was originally constructed in order to assemble the components of the Saturn V rockets vertically. The building was large enough to contain four of the gargantuan rockets at a time, and includes four massive doors (the largest in the world) that each allowed the Saturn V to pass under. Nowadays, the Vehicle Assembly Building is used for the stacking of the space shuttle, combining vertically the orbiter, the solid rocket boosters, and the external fuel tank.

Rollout of Apollo 11
Image: NASA

STS-36 Rollout
Image: NASA

The duties of the VAB are not so clear once the space shuttle program is retired in 2011. Any future program that utilizes Launch Complex 39² will have access to it, however, none have been upon yet. One possible route could be the Orion Asteroid Mission, a modification of the Constellation program that would allow human exploration of an asteroid.

Footnotes:

1: Yes, technically this isn’t first light, since that’s generally a term used for the first astronomical images taken by an instrument. I extended the definition to encompass the first 3D images viewed through my glasses. ↵
2: The set of two launchpads and the Vehicle Assembly Building that was originally designed for the Apollo program and now used by the space shuttle program. ↵

Fly Around the Solar System

Voyager 2 looking back at the planets in Eyes on the Solar System.

NASA’s new beta version of Eyes on the Solar System, developed by the Jet Propulsion Laboratory and Caltech, lets you do just that. The web application is essentially a 3D model of the solar system, containing many of its bodies and a great number of space probes sent out from Earth (including Epoxi 2, which recently performed a flyby of comet Hartley 2). With a number controls, you can zoom around the solar system exploring these objects, with beautiful 3D models for each of them. You can also manipulate the time to explore where the objects and the probes were in the past, or where they will be in the future.

Overall, this is a very glorious and well done project. It’s already a great tool for learning more about our planet's local neighborhood, and as it accumulates even more data and more components of the solar system, it can only get better. I can’t wait until this project leaves beta status, and includes further inclusions like nebulae and galaxies. You can head over to the project site right now to try it out. You will have to install the Unity Web Player plug-in in order to use it, and you will be prompted to install it on the site.

Cassini and Saturn in Eyes on the Solar System

Halley's Comet in Eyes on the Solar System

White Dwarfs as Pulsars

A little more than two years ago, in early 2008, there was a shocking discovery from the Suzaku team. Suzaku is an orbiting X-ray observatory, operated jointly by JAXA and NASA. It had detected a white dwarf star, AE Aquarii, emit high-energy X-ray pulses. What’s more was that these pulses lined up exactly with the white dwarf’s spin period of 33 seconds. The star was behaving nearly like a pulsar.

Before I go into further discussion about white dwarfs acting like pulsars, I want to explain what the two types of stars are.

White Dwarfs

White dwarfs are essentially remains of stars that initially had a mass of less than about 8 solar masses (like the Sun). As these stars finish undergoing their fusion reactions, they form a carbon-oxygen core that cannot undergo fusion reactions, which is enveloped by a layer of helium fusion and a layer of hydrogen fusion. Ultimately, the outer layers are expelled, and the carbon-oxygen core remains. Therefore, the composition of most white dwarfs is carbon and oxygen.

These stars have a mass similar to that of the Sun, but a volume which is near the size of the Earth. Subsequently, white dwarfs have a very high density. White dwarfs also can have strong magnetic fields.

Furthermore, since their radius is greatly reduced from their original states, white dwarfs also have a very high angular velocity. This is a result of the conservation of most of the angular momentum of the original star. Conservation of angular momentum is often demonstrated by a spinning ice skater. As a spinning ice skater brings his/her arms in (comparable to the radius of the star shrinking), he/she starts spinning much faster. Therefore, as the star shrinks dramatically, its rotation increases greatly.

Pulsars

Larger stars, those with a mass greater than 8 solar masses, go a different route. In these stars, a growing iron core in the center of the star becomes so massive that it cannot support its own mass. The core collapses, creating neutrons and neutrinos as electrons are forced into the protons. This collapse results in an immense shockwave, which in turn causes the star itself to explode in what is called a supernova. The outer layers of the star are expelled in the supernova, leaving behind the remnants of the core of the star. This remaining star is very dense and very compressed, and is made up of mostly neutrons. These are called neutron stars.

The mass of a neutron star is typically not much greater than the mass of white dwarfs, usually between 1.35 and 2.1 solar masses. Their radius, on the other hand, is very small, just around 12 km. (In the case of very massive initial stars, the resulting neutron star is so massive that it further collapses into a black hole.) Therefore, their densities are extremely high. As Wikipedia states, it is comparable to the mass of the entire human population being squeezed into the size of a sugar cube.

In addition to their great density, neutron stars can also have a very large magnetic field. Plus, like white dwarfs, they conserve most of the angular momentum of their stars, so that when neutron stars form, they start spinning fast. They retains a very small fraction of the radius of the original star, so this results in an angular velocity which is much greater than that of a white dwarf. These two characteristics combine to create a pulsar.

The rotating magnetic field results in a powerful electric field forming on the star. This field accelerates protons and electrons on the surface of the star, and creates an electromagnetic beam which travels out from the magnetic poles of the star. The magnetic pole do not necessarily line up with the rotational axis of the star (just like the Earth’s magnetic poles do not correspond to the rotational axis of our planet), and as the star spins rapidly, the electromagnetic beam also spins around very rapidly. Sometimes, these beams can point in the direction of the Earth during their rotation, and when that happens, we can detect them as a pulsating source of emissions, resulting in the name pulsars (from pulsating stars). The period of the pulsation is the period of the rotation of the pulsar (ranging from 1.4 milliseconds to 8.5 seconds), and is very regular. In fact, the first pulsar discovered was temporarily dubbed LGM-1 for “Little Green Men,” since the discoverers considered extraterrestrial origins for the highly regular signal.

Eventually as energy is lost through the beam, the star slows down, and the pulsar mechanism turns off. This is expected to take place after around 10 to 100 million years.

White Dwarfs Acting Like Pulsars

White dwarfs and pulsars are often regarded as completely separate types of stars. That is why the discovery from the Suzaku team was so surprising. There were hard X-ray pulses which were being detected, and lining up exactly with the rotational period of the white dwarf star. The team had discovered a white dwarf star which was acting almost exactly like a pulsar.

This discovery has recently been brought back into focus because a recently published paper, led by Kazumi Kashiyama at Kyoto University, proposes a way for white dwarfs to act like pulsars.

This method could help explain the source of the high abundance of positrons in the range of 10 - 100 GeV, and of electrons and positrons in the range of 100 GeV - 1 TeV detected by the PAMELA spacecraft. Previously, a large number of objects were offered as the source of these particles, including pulsars. These, though, are expected not to result in the amount that has been detected by PAMELA. White dwarfs may however result in the amount of particles detected.

Typically, a white dwarf simply cannot reach a sufficient angular velocity to act like a pulsar. Their size during formation simply does not reduce as dramatically as it does for a neutron star. Kashiyama and others propose that in some cases, during a merger or accreting a large amount of mass from another star, can result in a greater angular velocity. Plus, about 10% of white dwarfs already are expected to have sufficiently powerful magnetic fields. Combining this magnetic field and sufficiently large angular velocity can result in a white dwarf behaving like a pulsar.

The proposition seems plausible since the idea of a white dwarf gaining mass is not very strange at all. This happens during the formation of a Type Ia supernova in binary star systems when a white dwarf gains mass from an accompanying star, or when two white dwarfs collide together. Furthermore, since white dwarfs have weaker magnetic fields, they would lose their energy slower, and keep spinning for a longer time. Subsequently, they can power the pulsar for a longer time, possibly accounting for the amount of particles detected by PAMELA. It also suggests that many of the pulsars that we observe in our own galaxy could in fact be white dwarf pulsars.

Next, it is necessary to provide conclusive evidence for the existence of such stars. AE Aquarii seems like a great candidate since it is a binary system, which could account for the white dwarf star accreting mass. In the meantime, this type of research, at least for me, is extremely exciting since it continues to show how the universe continues to surprise and amaze us.

New Exoplanet Could Be First Hospitable to Life

An artist’s rendition of Gliese 581g.
Image: Copyright Lynette Cook

The first Earth-like exoplanet (a planet outside our Solar System has been discovered orbiting in a star’s habitable zone, a range of distances around a planet in which an Earth-like planet can keep and maintain liquid water. Essentially, this could mean that the planet may be hospitable to Earth-like life. The range is often referred to as the “Goldilocks zone” in that it is neither too hot nor too cold for life.

The existence of the planet, Gliese 581g, was recently announced by a team of astronomers from the University of California, Santa Cruz and the Carnegie Institute of Washington. The discovery used date from observations having been collected for over a decade at the Keck Observatory in Hawaii.

The Planet and Consequences for Life

Gliese 581g is one of two planets that was recently discovered orbiting Gliese 58, bringing the the total known planets orbiting the star to six. The star itself is located about 20 light years away from the Earth, and some of its other planets, lying on the edge of the habitable zone, have also been debated to be capable of harboring life. However, life on these planets would likely only be possible if these other planets had certain specific conditions, such as a very thick atmosphere in one case to result in a greenhouse effect that would sufficiently warm up the planet.

On the other hand, Gliese 581g lies very comfortably in the habitable zone. The planet itself is about three to four times the mass of the Earth. This mass likely means that the planet has a definite and rocky surface, and with enough gravity to hold on to an atmosphere. If its density is close to that of the Earth’s, the planet’s radius would be 1.2 to 1.4 times the size of the Earth’s. The gravity on the surface, therefore, would be similar to or slightly higher than on Earth.

Astronomers are estimating that the distance of Gliese 581g from its star is about 0.15 AU (1 AU is the distance from the Earth to the Sun), meaning that it can orbit around its star in a little less than 37 days. In our Solar System, this orbit would be even smaller than Mercury’s, and would make the planet severely hot. However, its star, Gliese 581, is classified as a red dwarf star, making it much cooler than our star, and at this radius, the average surface temperature on the planet is estimated to be between -31 to -12 °C.

This may be surprising in that this temperature is well below freezing, and likely not conducive to life as we know it. However, astronomers have been able to deduce that the planet is also tidally locked to the star. This means that there is one side continually facing the star while the opposing side is continually facing away from the star, just like how the Moon orbits the Earth (we only see one side of the Moon from the Earth). The consequence of this is that one side of Gliese 581g is in perpetual daylight and likely with a very high surface temperature. Meanwhile, the opposing side experiences the opposite treatment, receiving permanent nighttime and a low surface temperature. Life, could like likely only exist in a band between the light and the dark sides of the planet. This has some interesting consequences.

It is possible that lifeforms that prefer warmer temperatures could develop and exist on the brighter, warmer side of the planet, while those preferring a more colder and darker environment could live more towards the darker side. Plus differing longitudes on the planet could result in a wide range of hospitable temperatures. Therefore, despite the potential existence of just a narrow band of life, there could be very diverse ecosystems existing on the planet.

Method of Discovery

The discovery of Gliese 581g comes from 11 years of observations of the star Gliese 581. The team of astronomers working on this project used the HIRES spectrometer installed on the Keck I Telescope at the Keck Observatory in Hawaii. Using this tool, the astronomers were able to make very precise measurements of Gliese 581’s radial velocity. The radial velocity is the velocity of any object, including a star like Gliese 581, in the line of sight from Earth. As a planet orbits around its star, the star pulls on the planet gravitationally to keep it in orbit. The planet also pulls on the star, and this result in the star “wobbling” a little bit. The wobble can be detected from Earth by measuring the radial velocity of a star. Astronomers on Earth usually cannot actually see an exoplanet, but can detect changes in the radial velocity of the star. Studying this wobble allows astronomers to calculate the mass and distance from the star of the planet. Looking at the wobble over time allows astronomers to actually calculate the orbit of the planet.

If there are multiple planets, like in the case of Gliese 581, this technique gets a little more complicated. There is no longer just one pull from a planet, but multiple pulls. These gravitational pulls result in a combined complex wobble of the star. Performing analyses on this complex wobble, allows astronomers to detect the planets, and also calculate their orbits and masses.

This work however, requires many observations and measurements of radial velocity, spaced out over time. Detecting this particular planet took 238 observations, each of which lasted about an entire evening on the telescope.

Additional steps are helpful to verify that the wobble is in fact caused by orbiting planets. In some cases, stars may wobble due to processes within the star itself. In this study, a separate group of astronomers working with a robotic telescope at Tennessee State University made careful and precise measurements of the brightness of the star. This step gives important evidence that the radial velocity changes are likely caused by this orbiting planet, and not something else.

What does it mean?

The planet’s position in the habitable zone itself is a great discovery. Although it does not confirm the existence of life, this planet is the most likely to harbor life out of all exoplanets that have yet been discovered. Plus, the circumstances surrounding its discovery also yield stunning realizations.

The discovery has been made relatively quickly. There are only a small number of stars that have been studied by astronomers for the existence of exoplanets. This particular exoplanet has been discovered at a time when only a few Earth-like exoplanets have been discovered. Plus this discovery is very nearby, only about 20 light years away. Both these suggest that the existence of habitable Earth-like planets is in no way rare, as some believe. In our galaxy alone, the astronomers working on the project hypothesize, there could be tens of billions of star systems containing habitable Earth-like exoplanets, which is definitely a mind-blowing realization.

Flying through the Carina Nebula

One of my favorite parts of the IMAX movie Hubble 3D was getting to fly through objects like the Orion Nebula in 3D. Often, when looking at objects in the night sky, I tend to forget that what I see is a complex three dimensional object of which I only get to see one side. Hubble 3D’s voyages through space provided a refreshing view in that it transformed those two dimensional pictures into three dimensional environments, a representation of what the actual objects may look like.




Using new and old images from the Hubble Telescope, the Hubble team has created a new three-dimensional virtual tour of the Carina Nebula, embedded above. Even though the tour is not completely based on solid scientific data and takes great artistic license, it is still breathtaking and inspiring. For me, it reminds me very powerfully of how dynamic, and in a way, tangible, the universe is.

In order to view the movie properly, you need red cyan anaglyphic glasses. If you don’t have the glasses (sadly I don’t either…) you can still enjoy the new image of the Carina Nebula recently released by the Hubble team below. It combines observations of radiation resulting from oxygen, captured this year, and that from hydrogen, captured in 2005.

The Carina Nebula, in Oxygen and Hydrogen Emissions
Image: NASA, ESA, Hubble Heritage Project

Equinox on Saturn

About every 15 Earth years, Saturn’s experiences an equinox, much like Earth’s equinox. On Earth it occurs twice in Earth’s orbit—two times every Earth year—when the Sun lies in the Earth’s equatorial plane. As a result, the duration of day and night are approximately equal, which is also the origin of the term equinox.

Saturn also experiences this twice in its orbit, but its orbit lasts about 30 Earth years, meaning that the equinox takes place every 15 Earth years. Plus, this event is even more special on Saturn. Saturn has a very famous and widely recognized set of rings. These rings lie in Saturn’s equatorial plane, and therefore, when Saturn undergoes an equinox, the Sun also lies in the plane of the rings. Since the rings are very thin (at least compared to the size of Saturn), during the equinox the shadow from the rings disappears. The rings themselves also are barely visible because only the edges catch the light of the Sun.

The Cassini Spacecraft was present to capture photos from the most recent equinox last August. The below photograph was just recently released by the Jet Propulsion Laboratory, captured on July 18, 2009, just a few weeks before the equinox. The barely visible rings cast a thin shadow on the body of Saturn, creating a stunning view. In fact, the rings captured in the original images from Cassini were so dim that it was necessary to brighten them by a factor of 9.5 relative to the planet in order to produce the result (I’d be very interested to see the picture where the rings are not brightened).

The picture below is from just after equinox, when the shadow from the rings on Saturn is barely visible. Again, the brightness of the rings relative to the planet had to be increased in order to generate the image.

This equinox was also important in allowing Cassini to gather important data about the structure of the rings. When the rings are at a large angle to the Sun, small bumps and features are very hard to detect. However, when the Sun’s rays are parallel to the plain of the rings, the bumps and features create large shadows which are much easier to detect. And the results from this work were surprising. Some areas of Saturn’s rings ripple up and down, forming vertical formations about 800 km high. This phenomenon has not been explained yet. Meanwhile in some other areas, the particles in the ring are affected by the gravity of moons of Saturn, towering above the plain as high as 4 km. So while the rings may appear simple and peaceful in the images above, they have some very complex and strange features.