October 2006 Newsletter

Stockton Astronomical Society

Valley Skies

Valley Skies - October 2006 Issue

Editor's Corner...

Dues Increase Approved

A formal recommendation was presented to members attending the September 14 general meeting to approve an increase in the "Basic" or General membership rate to $20 per year. The Committee recommended leaving the Student rate at $10 per year.

Without discussion, other than clarifying the "no change" recommendation for the Student rate, a motion to approve the committee's recommendation was approved unanimously by members at the September 14 meeting.

* * *

Oct. 12 Program Speaker: Dr. Richard Brand

I am currently an adjunct professor of Physics and Astronomy at San Joaquin Delta College and run an advanced materials consulting business. I was the Director of Engineering at Applied Aerospace Structures Corp. in Stockton. I also worked for a short time at Los Alamos National Laboratory. Most of my composite experience was obtained working at General Dynamics-Convair Division and Composite Optics, Inc. in San Diego. During these years we constructed graphite components including telescopes for various space programs including Hubble, the Spitzer IR telescope, Mars Observer Camera and others.

...Trevor Atkinson

The Science Directorate at NASA's Marshall Space Flight Center sponsors the Science@NASA web sites. The mission of Science@NASA is to help the public understand how exciting NASA research is and to help NASA scientists fulfill their outreach responsibilities.

Surprises from the Edge of the Solar System

Sept. 21, 2006: Almost every day, the great antennas of NASA's Deep Space Network turn to a blank patch of sky in the constellation Ophiuchus. Pointing at nothing, or so it seems, they invariably pick up a signal, faint but full of intelligence. The source is beyond Neptune, beyond Pluto, on the verge of the stars themselves.

It's Voyager 1. The spacecraft left Earth in 1977 on a mission to visit Jupiter and Saturn. Almost 30 years later, with the gas giants long ago seen and done, Voyager 1 is still going and encountering some strange things.

An artist's concept of Voyager 1.

"We've entered a totally new region of space," says Ed Stone, Voyager project scientist and the former director of JPL. "And the spacecraft is beaming back surprising new information."

Before we reveal the surprises, let us discuss exactly where Voyager 1 is:

Our entire solar system-planets and all-sits inside a gargantuan bubble of gas about four times wider than the orbit of Neptune. The sun is responsible. It blows the bubble by means of the solar wind. Astronomers call the bubble itself "the heliosphere" and its outer membrane "the heliosheath." [diagram] Voyager 1 is about 10 billion miles from Earth, inside the heliosheath.

A simulated heliosheath in your kitchen sink. Image credit: Tony Phillips.

"You can simulate the heliosheath in your kitchen sink," says Stone. "Turn on the faucet so that a thin stream of water pours into the sink. Look down into the basin. Where the stream hits bottom, that's the sun. From there, water flows outward in a thin, perfectly radial sheet. That's the solar wind. As the water (or solar wind) expands, it gets thinner and thinner, and it can't push as hard. Abruptly, a sluggish, turbulent ring forms. That ring is the heliosheath."

"The heliosheath is important to humans," continues Stone. "It helps protect us from galactic cosmic rays." Galactic cosmic rays are subatomic particles accelerated to nearly light speed by supernovas and black holes. Astronauts out in space are exposed to the particles-and that's not a good thing. Cosmic rays can penetrate flesh and damage DNA. Fortunately, the heliosheath deflects many cosmic rays before they ever reach the inner solar system. "Magnetic turbulence in the heliosheath scatters the particles harmlessly away."

Note: We have many shields against cosmic rays from the thin walls of spaceships to massive planetary atmospheres. But the heliosheath is our first line of defense, and that makes it special.

Because of its role as Solar System Protector, "we need to learn as much as we can about the heliosheath," says Stone. "Voyager 1 is giving us our first look inside."

And now for the surprises:

Magnetic Potholes: Every now and then, Voyager 1 sails through a "magnetic pothole" where the magnetic field of the heliosheath almost vanishes, dropping from a typical value of 0.1 nanoTesla (nT) to 0.01 nT or less. There are also "magnetic speed bumps" where the field strength jumps to twice normal, from 0.1 nT to 0.2 nT. These speed bumps and potholes are an unexpected form of turbulence. What role do they play in scattering cosmic rays? "This is under investigation," says Stone.

Sluggish solar wind: The solar wind in the heliosheath is slower than anyone expected. "The solar wind is supposed to slow down out there, just as the water in your sink slowed down to make the 'sluggish ring,'" says Stone, "but not this slow." Before Voyager 1 arrived, computer models predicted a wind speed of 200,000 to 300,000 mph. Voyager 1 measured only about 34,000 mph. "This means our computer models need to be refined."

Anomalous Cosmic Rays: "This one takes a little explaining," he says. "While the heliosheath protects us from deep-space cosmic rays, at the same time it is busy producing some cosmic rays of its own. A shock wave at the inner boundary of the heliosheath imparts energy to subatomic particles which zip, cosmic-ray-like, into the inner solar system. "We call them 'anomalous cosmic rays.' They're not as dangerous as galactic cosmic rays because they are not so energetic."

A schematic diagram of the sun's heliosphere. Anomalous cosmic rays are supposed to come from the Termination Shock-but Voyager 1 found otherwise.

Researchers expected Voyager 1 to encounter the greatest number of anomalous cosmic rays at the inner boundary of the heliosheath "because that's where we thought anomalous cosmic rays were produced." Surprise: Voyager crossed the boundary in December 2004 and there was no spike in cosmic rays. Only now, 300+ million miles later, is the intensity beginning to grow.

"This is really puzzling," says Stone. "Where are these anomalous cosmic rays coming from?"

Voyager 1 may find the source-and who knows what else?-as it continues its journey. The heliosheath is 3 to 4 billion miles in thickness, and Voyager 1 will be inside it for another 10 years or so. That's a lot of new territory to explore and plenty of time for more surprises.

Author: Dr. Tony Phillips | Production Editor: Dr. Tony Phillips | Credit: Science@NASA

Staggering Distance

By Dr. Tony Phillips

Tonight, when the sun sets and the twilight fades to black, go outside and look southwest. There's mighty Jupiter, gleaming brightly. It looks so nearby, yet Jupiter is 830 million km away. Light from the sun takes 43 minutes to reach the giant planet, and for Earth's fastest spaceship, New Horizons, it's a trip of 13 months.

That's nothing.

Not far to the left of Jupiter is Pluto. Oh, you won't be able to see it. Tiny Pluto is almost 5 billion km away. Sunlight takes more than 4 hours to get there, and New Horizons 9 years. From Pluto, the sun is merely the brightest star in a cold, jet-black sky.

That's nothing.

A smidgen to the right of Pluto, among the stars of the constellation Ophiuchus, is Voyager 1. Launched from Florida 29 years ago, the spacecraft is a staggering 15 billion km away. It has traveled beyond all the known planets, beyond the warmth of the sun, almost beyond the edge of the solar system itself.

Now that's something.

"On August 15, 2006, Voyager 1 reached the 100 AU mark-in other words, it is 100 times farther from the Sun than Earth," says Ed Stone, Voyager project scientist and the former director of NASA's Jet Propulsion Laboratory. "This is an important milestone in our exploration of the Solar System. No other spacecraft has gone so far."

At 100 AU (astronomical units), Voyager 1 is in a strange realm called "the heliosheath."

In case it is ever found by intelligent beings elsewhere in the galaxy, Voyager carries a recording of images and sounds of Earth and its inhabitants. The diagrams on the cover of the recording symbolize Earth's location in the galaxy and how to play the record.

As Stone explains, our entire solar system-planets and all-sits inside a giant bubble of gas called the heliosphere. The sun is responsible; it blows the bubble by means of the solar wind. Voyager 1 has traveled all the way from the bubble's heart to its outer edge, a gassy membrane dividing the solar system from interstellar space. This "membrane" is the heliosheath.

Before Voyager 1 reached its present location, researchers had calculated what the heliosheath might be like. "Many of our predictions were wrong," says Stone. In situ, Voyager 1 has encountered unexpected magnetic anomalies and a surprising increase in low-energy cosmic rays, among other things. It's all very strange-"and we're not even out of the Solar System yet."

To report new developments, Voyager radios Earth almost every day. At the speed of light, the messages take 14 hours to arrive. Says Stone, "it's worth the wait."

Keep up with the Voyager mission at voyager.jpl.nasa.gov. To learn the language of Voyager's messages, kids (of all ages) can check out spaceplace.nasa.gov/en/kids/vgr_fact1.shtml.

This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.