User Name:
print-friendly version

Mercury Magazine Autumn 2016

Autumn 2016 Mercury coverContents and Select Excerpts
Vol. 45 No. 4
Autumn 2016

In September 2017, the Cassini spacecraft will conclude its exploration of the Saturnian system with a swan dive into Saturn’s clouds. Emily Joseph (Lunar and Planetary Lab / Planetary Science Institute) describes Cassini’s Grand Finale — its last year at Saturn.

This page contains the table of contents and select excerpts only and is not a complete reproduction of this issue. Complete content for online Mercury is available to ASP members and institutional subscribers. Already a member? You can retrieve the latest issue of Mercury by logging into the ASP membership portal.

Table of Contents

[18] Cassini: The Grand Finale, Emily Joseph
One year from now it will be EoM — End of Mission — for Cassini at Saturn.

[25] Eclipse Bulletin: Total Solar Eclipse of 2017 August 21, Joe Rao
I regard this book as essential reading at any time prior to Eclipse 2017.

[30] For Better or Worse: Reflections of an Eclipse-Chasing Family, Richard H. Durisen, Annamaria Mecca, and Michael V. M. Durisen
Once you experience the rush of totality during a solar eclipse, you are forever trying to recapture it.

[36] Astronomy in the News
A lonely mountain inhabits Ceres, a supernova is ejected from the pages of history, and the observable universe contains 10 times more galaxies than previously thought. These are some of the discoveries that recently made news in the astronomical community.


[4] Perspectives, Paul Deans
The Magic of Saturn

[5] First Word, Linda Shore
Just Look Up

[7] Annals of Astronomy, Clifford J. Cunningham
Aristotle vs Pimentel

[8] Astronomer’s Notebook, Jennifer Birriel
Beyond Gravity Waves

[10] Planetary Perspectives, European Space Agency
Philae Lander Found

[11] Strange New Worlds, Peter Kelly
Could Proxima b Really Be Habitable?

[13] Armchair Astrophysics, Christopher Wanjek
A Neighboring Galaxy is Mostly Dark Matter

[15] Education Matters, Brian Kruse
Learning to See

[16] Reaching Out, Bethany Cobb
Missing Out

[44] The ASP’s AstroShop
Prepare for a Stellar 2017

[45] ASP Tidings
ASP’s Arthur B.C. Walker II Award

[48] Sky Sights, Paul Deans
Spot Neptune in January

[51] Reflections, NASA/SwRI/MSSS/Roman Tkachenko
Pinwheels on Jupiter

Cassini: The Grand Finale

by Emily Joseph

Artist's impression of Cassini around Saturn

Artist’s concept of Cassini diving between Saturn and its innermost rings in 2017. Cassini’s final orbits will bring the closest views of Saturn since the spacecraft’s arrival in 2004. (NASA/JPL-Caltech)

In 1997, Malala Yousafzai was born in Pakistan, Comet Hale-Bopp put on a spectacular show, and a book was published in the UK about an unusual boy named Harry Potter. And on October 15, the Cassini-Huygens mission launched from Cape Canaveral, Florida, aboard a Titan IV rocket.

After a seven-year cruise, the spacecraft reached Saturn and entered orbit on July 1, 2004. On Christmas Day 2004, the Huygens probe detached from the main spacecraft. Three weeks later it descended through the atmosphere of Saturn’s largest moon, Titan, and sent back the first images and data from the surface of a body in the outer solar system.

The last part of Cassini’s mission is known as the Grand Finale. In late November of 2016, the spacecraft will enter a high-inclination orbit that sweeps high above Saturn’s north pole and passes just outside the F ring, the thin border of the main ring system. After 20 of these orbits, the trajectory will change again, and Cassini’s final 22 circuits of Saturn will pass through the 2,000-mile gap between the inner rings and the planet’s atmosphere.

[back to the top]

Eclipse Bulletin: Total Solar Eclipse of 2017 August 21

by Joe Rao

Book cover image

There can be no denying the value of this book. Fred Espenak — better known to eclipse chasers around the globe as “Mr. Eclipse” — is the established authority on eclipse calculations. Before he retired from NASA/Goddard, he published 13 similar eclipse bulletins (with coauthor Jay Anderson) between 1993 and 2008. This latest bulletin was published sans NASA funding and is by far the biggest and most extensive eclipse circular that he has ever produced. Amateur astronomers even vaguely interested in the subject of eclipses should have come across his work by now. If not, now is the time to start.

The title accurately describes the aims and objectives. Anybody who intends to witness firsthand the long-awaited 2017 “All American Eclipse” may have already given some thought as to where they intend to be on eclipse day, but I would regard this book as essential reading at any time. If, for example, on eclipse day I’m driving along an unfamiliar road within the path of totality, I would want this book within arm’s reach.

[back to the top]

For Better or Worse: Reflections of an Eclipse-Chasing Family

by Richard H. Durisen, Annamaria Mecca, and Michael V. M. Durisen

A post-totality family portrait in Hawai’i taken July 11, 1991, in the light of the partially eclipsed Sun.

A post-totality family portrait in Hawai’i taken July 11, 1991, in the light of the partially eclipsed Sun. (Courtesy the authors.)

Among the natural events that human beings can witness, the total phase of an eclipse of the Sun is one of the most spectacular and deeply moving. In any solar eclipse, there is only a narrow ribbon, if any, where the umbra of the Moon’s shadow touches Earth’s surface. There and only there, for a few precious minutes, does the Moon completely block the solar photosphere, the surface layer of gases from which most of the Sun’s light escapes.

Although this “path of totality” can be many thousands of kilometers long, it is never more than 270 kilometers wide. Outside the path, over a much larger area of Earth, the Moon only blocks the view of part of the photosphere. As a result, many people can see a partial solar eclipse without effort. There is a universe of difference, however, between the experiences of seeing a partial eclipse and seeing totality. At every eclipse for which totality occurs, there are people who will go out of their way to place themselves somewhere along the umbral path. As a family, we have become such “eclipse-chasers.” The following personal reflections may help you to understand some of the rewards and frustrations of this avocation.

[back to the top]

Pluto ‘Paints’ its Largest Moon Red

NASA/Johns Hopkins University Applied Physics Laboratory


NASA’s New Horizons spacecraft captured this enhanced color view of Charon just before closest approach on July 14, 2015. Charon is 753 miles (1,212 kilometers) across; this image resolves details as small as 1.8 miles (2.9 kilometers). (NASA/JHUAPL/SwRI.)

In June 2015, when the cameras on NASA’s approaching New Horizons spacecraft first spotted the large reddish polar region on Pluto’s largest moon, Charon, mission scientists knew two things: they’d never seen anything like it elsewhere in our solar system, and they couldn’t wait to get the story behind it.

Over the past year, after analyzing the images and other data that New Horizons has sent back from its historic July 2015 flight through the Pluto system, the scientists think they’ve solved the mystery. Charon’s polar coloring comes from Pluto itself — as methane gas escapes from Pluto’s atmosphere and becomes “trapped” by the moon’s gravity and freezes to the cold, icy surface at Charon’s pole. This is followed by chemical processing by ultraviolet light from the Sun that transforms the methane into heavier hydrocarbons and eventually into reddish organic materials called tholins.

The New Horizons team dug into the data to determine whether conditions on the Texas-sized moon (with a diameter of 753 miles or 1,212 kilometers) could allow the capture and processing of methane gas. The models using Pluto and Charon’s 248-year orbit around the Sun show some extreme weather at Charon’s poles, where 100 years of continuous sunlight alternate with another century of continuous darkness. Surface temperatures during these long winters dip to -430 Fahrenheit (-257 Celsius), cold enough to freeze methane gas into a solid.

[back to the top]