The Gloucester Area Astronomy Club

It Takes More Than Warm Porridge
to Make a Goldilocks Zone

By Diane K. Fisher

The “Goldilocks Zone” describes the region of a solar system that is just the right distance from the star to make a cozy, comfy home for a life-supporting planet. It is a region that keeps the planet warm enough to have a liquid ocean, but not so warm that the ocean boils off into space. Obviously, Earth orbits the Sun in our solar system’s “Goldilocks Zone.”

But there are other conditions besides temperature that make our part of the solar system comfortable for life. Using infrared data from the Spitzer Space Telescope, along with theoretical models and archival observations, Rebecca Martin, a NASA Sagan Fellow from the University of Colorado in Boulder, and astronomer Mario Livio of the Space Telescope Science Institute in Baltimore, Maryland, have published a new study suggesting that our solar system and our place in it is special in at least one other way.

This fortunate “just right” condition involves Jupiter and its effect on the asteroid belt.

Many other solar systems discovered in the past decade have giant gas planets in very tight orbits around their stars. Only 19 out of 520 solar systems studied have Jupiter-like planets in orbits beyond what is known as the “snow line”—the distance from the star at which it is cool enough for water (and ammonia and methane) to condense into ice. Scientists believe our Jupiter formed a bit farther away from the Sun than it is now. Although the giant planet has moved a little closer to the Sun, it is still beyond the snow line.

So why do we care where Jupiter hangs out? Well, the gravity of Jupiter, with its mass of 318 Earths, has a profound effect on everything in its region, including the asteroid belt. The asteroid belt is a region between Mars and Jupiter where millions of mostly rocky objects (some water-bearing) orbit. They range in size from dwarf planet Ceres at more than 600 miles in diameter to grains of dust. In the early solar system, asteroids (along with comets) could have been partly responsible for delivering water to fill the ocean of a young Earth. They could have also brought organic molecules to Earth, from which life eventually evolved.

Jupiter’s gravity keeps the asteroids pretty much in their place in the asteroid belt, and doesn’t let them accrete to form another planet.  If Jupiter had moved inward through the asteroid belt toward the Sun, it would have scattered the asteroids in all directions before Earth had time to form. And no asteroid belt means no impacts on Earth, no water delivery, and maybe no life-starting molecules either. Asteroids may have also delivered such useful metals as gold, platinum, and iron to Earth’s crust.

But, if Jupiter had not migrated inward at all since it formed father away from the Sun, the asteroid belt would be totally undisturbed and would be a lot more dense with asteroids than it is now. In that case, Earth would have been blasted with a lot more asteroid impacts, and life may have never had a chance to take root.

The infrared data from the Spitzer Space Telescope contributes in unexpected ways in revealing and supporting new ideas and theories about our universe. Read more about this study and other Spitzer contributions at spitzer.caltech.edu. Kids can learn about infrared light and enjoy solving Spitzer image puzzles at spaceplace.nasa.gov/spitzer-slyder.

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

After almost ten years at the St Paul Lutheran Church, we've started to outgrow the space, and have moved our meetings to the Lanesville Community Center, right up the street. Here's a map.

The Community Center has a lot of space to grow, all the amenities we'll ever need, and a nice dark area outside where we can set up scopes before and after meetings. This is a real plus. Maybe in the warmer months we can even do some guerrilla astronomy there for the folks in and around Lanesville.

Come and see us in our new digs on December 14, our Christmas party. We'll have door prizes, a new video from NASA on Saturn and the Cassini spacecraft, followed by a presentation by our own Steve K on what's up in the winter sky. And of course there'll be plenty of Christmas goodies to eat and lots of good conversation. See you there at 8:00!

Struve 2816 and 2819 – Triple and Double Stars in Cepheus
by Glenn Chaple

There’s something hypnotic about a double star – two gleaming points of light shining bravely through the surrounding darkness. A triple star is even more mesmerizing. Place a double star and triple star in the same eyepiece field, and the visual effect is stunning. This is what greets the eye when you view the triple/double star combo Struve 2816 and Struve 2819. 

Struve 2816 and Struve 2819 are among the 3000-plus double and multiple stars catalogued by the Russian astronomer F.G.W. Struve in the 1820s and 30s. They lie in Cepheus, about a degree south of mu (µ) Cephei (Herschel’s “Garnet Star”).

The triple star Struve 2816 consists of a magnitude 5.7 primary flanked by two 7.5 magnitude stars at distances of 12 and 20 arc-seconds. Just 12 arc-minutes away is Struve 2916 - a magnitude 7.5 and 8.5 duo, separated by 13 arc-seconds.

Struve 2816 and Struve 2819 appear together even in the eyepiece field of large-aperture Dobs, but I find the most eye-pleasing views are through small-aperture scopes. Large instruments clutter up the field with a distracting number of faint background stars. Struve 2816 and Struve 2819 are part of the wide open cluster Trumpler 37 which, in turn, is immersed in the huge emission nebula IC 1396.

The accompanying finder chart/ photograph comes from the Starsplitters website (http://bestdoubles.wordpress.com), a wonderful collaboration by amateur astronomers John Nanson and Greg Stone. It’s a must-visit blog for the double star enthusiast!

A Cosmic Tease:
Trials of the Herschel Space Telescope Science Teams

By Dr. Marc J. Kuchner

Vast fields of marble-sized chunks of ice and rock spun slowly in the darkness this week, and I sat in the back of a grey conference room with white plastic tables spread with papers and laptops. I was sitting in on a meeting of an international team of astronomers gathered to analyze data from the Herschel Infrared Observatory. This telescope, sometimes just called Herschel, orbits the Sun about a million miles from the Earth.

The meeting began with dinner at Karl’s house. Karl charred chorizo on the backyard grill while the airplanes dribbled into Dulles airport. Our colleagues arrived, jetlagged and yawning, from Germany, Sweden, and Spain, and we sat on Karl’s couches catching up on the latest gossip. The unemployment level in Spain is about twenty percent, so research funding there is hard to come by these days. That’s not nice to hear. But it cheered us up to be with old friends.

The meeting commenced the next morning, as the vast fields of ice and rock continued to spin—shards glinting in the starlight. Or maybe they didn’t. Maybe they didn’t exist at all.

You see, this team is looking at a series of images of stars taken by a device called a bolometer that is blind to ordinary starlight. Instead, the bolometer inside Herschel senses infrared light, a kind of light that we would probably refer to as heat if we could feel it. But the idea of pointing the bolometer at the stars was not to collect ordinary starlight. It was to measure heat coming from the vicinity of these stars, like an infrared security camera, in case there was something else to be found lurking nearby.

And lo and behold, for a handful of stars, the bolometer measurements were off the charts! Maybe something was orbiting these stars. From the details of the bolometer readings—which channels lit up and so on—you would guess that this stuff took the form of majestic fields or rings of icy and rocky particles. It would be a new kind of disk, a discovery worth writing home to Madrid about.

There are several teams of astronomers analyzing data from the Herschel Space Telescope. They call themselves by oddly inappropriate sounding acronyms: GASPS, DUNES, DEBRIS. For the time being, the scientists on these teams are the only ones with access to the Herschel data. But in January, all the data these teams are working on will suddenly be released to the public. So they are all under pressure to finish their work by then. The team whose meeting I was sitting in on would like to publish a paper about the new disks by then.

But it’s not so simple. The stars that this team had measured were relatively nearby as stars go, less than a few hundred light years. But the universe is big, and full of galaxies of all kinds—a sea of galaxies starting from maybe a hundred thousand light years away, and stretching on and on. Maybe one of those background galaxies was lined up with each of the stars that had lit up the bolometer—fooling us into thinking they were seeing disks around these stars.

The team argued and paced, and then broke for lunch. We marched to the cafeteria through the rain. Meanwhile, vast fields of marble-sized chunks of ice and rock spun slowly in the darkness. Or maybe they didn’t.

What else did Herschel recently uncover? Find out at http://spaceplace.nasa.gov/comet-ocean.

Dr. Marc J. Kuchner is an astrophysicist at the Exoplanets and Stellar Astrophysics Laboratory at NASA’s Goddard Space Flight Center. NASA’s Astrophysics Division works on big questions about the origin and evolution of the universe, galaxies, and planetary systems. Explore more at http://www.science.nasa.gov/astrophysics/.

NGC 6934 - Globular Cluster in Delphinus
by Glenn Chaple

October sees the demise of the summer Milky Way and its swarm of globular clusters centered on the constellation Sagittarius. A few, notably M15 in Pegasus, lag behind to grace our autumn skies. Another of these stragglers is NGC 6934 in Delphinus. This small 9th magnitude globular was discovered by William Herschel in 1785. In early star atlases and in modern-day “Herschel 400” guides, it bears the designation H1031 - the 103rd entry in Category I (bright nebulae) of Herschel’s deep sky catalog.

NGC 6934 may be glimpsed in small scopes. In fact, my only encounter with this globular was with a 3-inch f/10 reflector through which it appeared as a “faint patch of light, but definitely identified.” The circular smudge was only a few arc-minutes across and lay just east of a 9th magnitude star. My observing guides, including Kepple and Sanner’s The Night Sky Observer’s Guide, indicate that resolution will require more substantial instruments – 8 to 12 inches for partial resolution of the outer halo, 14 inches or more combined with high magnification for a more definitive view. To that end, my October “to-do” list includes a study of NGC 6934 with medium and large-aperture telescopes. Anybody have an 18-inch Dob handy?

The finder chart, from the Touring the Universe with Binoculars Atlas (TUBA) by Phil Harrington shows the location of NGC 6934. Owners of GoTo scopes or traditional equatorially-mounted instruments can lock it in using the coordinates 20h 34.2m, +07o24.2’. Star hoppers will want to try the 4 degree trek southward from epsilon () Delphini. Harrington 9 (Hrr 9) is an asterism he found that surrounds and includes the star theta () Delphini.

At our October 12 meeting we'll be taking a look at where the Voyager spacecraft are now (right at the edge of the solar system), where they're going (interstellar space!), and where they've been (Jupiter, Saturn, Uranus, Neptune, and a whole bunch of moons). We'll look again at the amazing path they had to take to get where they are, and what's up next for these hardy spacecraft, about to become our first starships. GAAC meets on the second Friday of every month at St. Paul Lutheran church in Lanesville. See our Contact page for more info.

Friday night September 21 we'll have our final star party of the season at Halibut Point, from dusk to 10:00 pm at the visitor's center. There will be telescopes and goodies, double stars, the moon and star clusters and galaxies and more, to see and wonder at. This activity, like everything GAAC does, is free and open to the public. Come and enjoy our dark Cape Ann sky. If it's cloudy we'll try again the next evening, Saturday the 22nd. Park in the main lot and walk on up. Here's a map: http://goo.gl/maps/KbrQ

Doing Science with a Spacecraft’s Signal

By David Doody

Mariner 2 to Venus, the first interplanetary flight, was launched August 27 fifty years ago.  This was a time when scientists were first learning that Venus might not harbor jungles under its thick atmosphere after all. A Russian scientist had discovered that atmosphere during the rare Venus transit of 1761, because of the effects of sunlight from behind.

Mariner 2 proved interplanetary flight was possible, and our ability to take close-up images of other planets would be richly rewarding in scientific return. But it also meant we could use the spacecraft itself as a “light” source, planting it behind an object of our choosing and making direct measurements.

Mariner 4 did the first occultation experiment of this sort when it passed behind Mars as seen from Earth in July 1965. But, instead of visible light from the Sun, this occultation experiment used the spacecraft’s approximately 2-GHz radio signal.

The Mariner 4 experiment revealed Mars’ thin atmosphere. Since then, successful radio science occultation experiments have been conducted at every planet and many large moons. And another one is onschedule to investigate Pluto and its companion Charon, when the New Horizons spacecraft flies by in July 2015.  Also, during that flyby, a different kind of radio science occultation experiment will investigate the gravitational field.

The most recent radio science occultation experiment took place September 2, 2012, when the Cassini spacecraft carried its three transmitters  behind Saturn. These three different frequencies are all kept precisely “in tune” with one another, based on a reference frequency sent from Earth. Compared to observations of the free space for calibration just before ingress to occultation, the experiment makes it possible to tease out a wide variety of components in Saturn's ionosphere and atmosphere.

Occultation experiments comprise only one of many categories of radio science experiments. Others include tests of General Relativity, studying the solar corona, mapping gravity fields, determining mass, and more.  They all rely on NASA’s Deep Space Network to capture the signals, which are then archived and studied.

Find out more about spacecraft science experiments in “Basics of Space Flight,” a website and book by this author, http://jpl.nasa.gov/basics. Kids can learn all about NASA’s Deep Space Network by playing the “Uplink-Downlink” game at http://spaceplace.nasa.gov/dsn-game