Daily Archives: July 17, 2013

cassini, cassini mission, ring system, saturn

Smile for Cassini, Wave at Saturn

1 Comment

Get Ready for a LARGE Group Picture!

How we should look to Cassini on July 18. Courtesy NASA/JPL-Caltech.

On July 19 from 21:27 to 21:42 UTC, 5:27 to 5:42 EDT, 2:27 to 2:42 PDT—a period of about 15 minutes) the Cassini spacecraft circling Saturn is going to take an image of Saturn with Earth in the scene.  That means we’ll ALL be in the picture, as seen from a distance of 1.44 billion kilometers!  So, wherever you are, take a few minutes to get outside and wave in the direction of Saturn. Yes, it will be during the day for some of us, but you can still find out about where to look in the sky from this useful blog entry by Jane Houston Jones.

The Cassini Solstice mission’s main goal for this image is to study the very diffuse rings of ice and dust particles that surround Saturn. The best way to do this is to look at stars as their light twinkles through the rings. The mission team members will analyze visual and infrared light data collected by the spacecraft’s instruments and cameras. The spacecraft is at just the right distance and viewing angle to make a high-resolution mosaic of the planet and rings, and in that mosaic, Earth will appear as a small blue dot in the distance.

There’s been only one other chance to image Earth from the outer solar system in such a way. In fact, there have been only two images of Earth from the outer solar system. The first and most distant was one was taken 23 years ago by NASA’s Voyager 1 spacecraft from a distance of 6 billion kilometers. That image became known as the “Pale Blue Dot” view, memorialized by Carl Sagan in his book of the same name.  Cassini took the other image in 2006. So, if you’re out and about on July 19th, take a few moments to wave at Saturn and be part of the largest group picture of recent times. And, no photobombing!

astronomy

The End of the Road…for a Star

Leave a comment

Sun-like Stars Die Beautifully

A visible-light view of the Eskimo Nebula. Courtesy Hubble Space Telescope Science Institute.

I’ve talked about planetary nebulae many times on this blog. They fascinate me,  just as starbirth regions do. They both represent stars at opposite ends of their lives. Planetary nebulae are old stars in designer wardrobes made for their funerals. As a star like the Sun gets old and begins the long descent into old age and death, it loses much of its mass to space. That mass forms a cloud of gas and dust surrounding the remains of the star, which is slowing contracting to become a small, hot, massive object called a white dwarf.  The white dwarf heats up the material in its shroud, and that causes it to glow.

The design of a white dwarf’s burial shroud can be quite complex. Take the object called NGC 2392, or as it’s more commonly known, the Eskimo Nebula. As you can see in the image at the left, the  material surrounding the star was ejected long ago and forms what looks like the outer hood of an Eskimo’s hood. The central region is a set of concentric shells and criss-crossing clouds of gas that have led scientists to suspect there’s more than one star at the heart of this object. X-ray emissions coming from the center of the nebula and detected by the Chandra X-Ray Observatory also suggest there’s more than one star here, probably a pair of binary stars.

X-rays from the central region of the Eskimo Nebula, as detected by the Chandra X-Ray Observatory. They indicate superheated gas around the dying star at the center of the nebula. Courtesy Chandra X-Ray Observatory.

Our own Sun will die like this in about 5 billion years. It probably won’t look quite so intricate, but the process will be the same. First the Sun’s mass loss (through a speeded-up 50,000 kilometer-per-hour solar wind) will cause it to shed huge amounts of its outer atmosphere to space. It will swell up to become a red giant, possibly reaching out to about the orbit of Earth. Our planet, Venus, and Mercury probably won’t survive, but Mars or the moons of the outer solar system could have a short-lived renaissance where their atmospheres could swell and water might flow freely on their surfaces.

Eventually, the dying Sun will contract to become a dense white dwarf, which will light up the surrounding clouds. The rest of the solar system will cool and die as the Sun does. Tens of billions of years from now there will be no cloud left, just a slowly cooling white dwarf and its dead retinue of worlds. The cloud of gas and dust will have spread out to space, lending itself to the inventory of material available to create new generations of stars and planets.

Astronomers study planetary nebula such as the Eskimo, the Ring, and others, in different wavelengths of light. Each wavelength gives them a good idea of the processes occurring in the nebulae, the speeds of stellar winds, and the action at the cores of these ancient, dying stars. Their insights help us all understand what will eventually happen with the Sun.