Notes & Queries 10/27/07

by Paul Gilster on October 27, 2007

More notes on the ‘wandering planet’ scenario advanced by John Debes (Carnegie Institution of Washington) and Steinn Sigurðsson (Penn State), which suggests that planets ejected from their stars as their solar systems formed could conceivably keep enough internal heat to maintain an atmosphere and sustain a liquid ocean under ice. Debes’ simulations show that a planet with a large moon could survive the ejection process.

Noting that between four and five percent of the simulations the duo ran on an Earth-mass planet with Luna-like companion resulted in the ‘Earth-Moon system surviving, Debes had this to say in an article in Sky & Telescope:

“Anytime something happens in astronomy a few percent of the time, it is interesting to us because on the grand scale of things, it means it’s happening a lot and people should probably know about it.”

Interesting indeed, because a large moon means tidal energies between moon and planet that could cause the interior of the planet to warm. Debes and Sigurðsson think the heating would be localized in hot spots of volcanism or other geothermal processes, making the case for extremophiles like those along Earth’s mid-ocean ridges as a perhaps common form of life in the cosmos. The paper is Debes and Sigurðsson, “The Survival Rate of Ejected Terrestrial Planets with Moons,” Astrophysical Journal 668 (October 20, 2007), L167-L170 (abstract).
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The unexpected outburst on Comet 17P/Holmes has made it brighter than any comet in the past decade. Now shining at 2nd or 3rd magnitude, it’s visible all night long at mid-northern latitudes, spanning an apparent diameter of 90 arc-seconds. You can find sky charts for viewing here. Nice to see cometary enthusiasm so intense that, when the Harvard-Smithsonian Center for Astrophysics asked their staff for viewing reports and images, responses poured in despite the competing attraction of the Red Sox in World Series game two. The comet, says one observer: “…looks like a big yellow globular cluster through binoculars. Truly a one of a kind object.” Even more one of a kind would be a Rockies comeback after their hard times at Fenway Park, but hope persists.
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Vinton Cerf, now a Google vice president but best known for the invention of the TCP/IP protocols that drive the Internet, told a gathering in Seoul that the InterPlanetary Internet project is on course. According to this AFP story, Cerf expects a key part of the IPN, which would establish broad standards for space communications, to be completed in three years: “This effort is now bearing fruit and is on track to be space qualified and standardized in the 2010 time frame.” Adapting Net protocols to the huge latency problems of deep space missions will result in a robust interplanetary communications infrastructure, one that will maximize the potential of the Deep Space Network as spacecraft collect and pool their data before phoning home.
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North Carolina State’s PULSTAR reactor is in the news with the production of the most intense low-energy positron beam operating anywhere. The idea, says NCSU’s Ayman Hawari, is simple: “…if we create this intense beam of antimatter electrons – the complete opposite of the electron, basically – we can then use them in investigating and understanding the new types of materials being used in many applications.” The focus now turns to new intstrumentation such as antimatter spectrometers and microscopes, but propulsion theorists will want to keep a long-term eye on the implications of such work for increasing our ability to produce and deploy antimatter.

Ron S October 28, 2007 at 21:59

If anyone hasn’t gone out to look at 17P/Holmes I highly recommend it. This evening it’s as bright as ever, and it is now grown to a visibly fuzzy ball to the naked eye.

Adam October 29, 2007 at 5:23

The comet’s photos are interesting – the long exposures are especially striking showing a luminous disk, a symmetrical gas cloud. Imagine if such a comet nucleus passed by the Earth at sufficiently close range to be seen as such a disk – might explain the reports of “second Suns” in the sky from ancient mythology.

Might also make sense of the battle of Aijalon in the book of “Joshua” in the Hebrew Scriptures, where Joshua is reported to have successfully kept the Sun in the sky for an extra day. There are several ways to interpret the passage, and the tale was written down some 500 years after the fact, but a passing comet might be seen as another Sun. Interestingly for the comet theory a sky-fall of rocks is also reported earlier in the battle, preceding the “Sun’s” long sojourn in the sky.

As I said there are a few more mundane ways of interpreting the original passage from the book of Jashar (c.950 BC), itself quoted and expanded upon by the later work we call “Joshua” (c.850-650 BC). The comet connection has a certain appeal in light of the other celestial events recorded through history – and evident in prehistory, such as the North American impact 13,000 years ago.

ljk November 20, 2007 at 15:38

Astronomers Say Moons Like Ours Are Uncommon

The next time you take a moonlit stroll, or admire a full, bright-white moon looming in the night sky, you might count yourself lucky. New observations from NASA’s Spitzer Space Telescope suggest that moons like Earth’s – that formed out of tremendous collisions – are uncommon in the universe, arising at most in only 5 to 10 percent of planetary systems.

“When a moon forms from a violent collision, dust should be blasted everywhere,” said Nadya Gorlova of the University of Florida, Gainesville, lead author of a new study appearing Nov. 20 in the Astrophysical Journal. “If there were lots of moons forming, we would have seen dust around lots of stars – but we didn’t.”

It’s hard to imagine Earth without a moon. Our familiar white orb has long been the subject of art, myth and poetry. Wolves howl at it, and humans have left footprints in its soil. Life itself might have evolved from the ocean to land thanks to tides induced by the moon’s gravity.

Scientists believe the moon arose about 30 to 50 million years after our sun was born, and after our rocky planets had begun to take shape. A body as big as Mars is thought to have smacked into our infant Earth, breaking off a piece of its mantle. Some of the resulting debris fell into orbit around Earth, eventually coalescing into the moon we see today. The other moons in our solar system either formed simultaneously with their planet or were captured by their planet’s gravity.

Gorlova and her colleagues looked for the dusty signs of similar smash-ups around 400 stars that are all about 30 million years old – roughly the age of our sun when Earth’s moon formed. They found that only 1 out of the 400 stars is immersed in the telltale dust. Taking into consideration the amount of time the dust should stick around, and the age range at which moon-forming collisions can occur, the scientists then calculated the probability of a solar system making a moon like Earth’s to be at most 5 to 10 percent.

“We don’t know that the collision we witnessed around the one star is definitely going to produce a moon, so moon-forming events could be much less frequent than our calculation suggests,” said George Rieke of the University of Arizona, Tucson, a co-author of the study.

In addition, the observations tell astronomers that the planet-building process itself winds down by 30 million years after a star is born. Like our moon, rocky planets are built up through messy collisions that spray dust all around. Current thinking holds that this process lasts from about 10 to 50 million years after a star forms. The fact that Gorlova and her team found only 1 star out of 400 with collision-generated dust indicates that the 30-million-year-old stars in the study have, for the most part, finished making their planets.

“Astronomers have observed young stars with dust swirling around them for more than 20 years now,” said Gorlova. “But those stars are usually so young that their dust could be left over from the planet-formation process. The star we have found is older, at the same age our sun was when it had finished making planets and the Earth-moon system had just formed in a collision.”

For moon lovers, the news isn’t all bad. For one thing, moons can form in different ways. And, even though the majority of rocky planets in the universe might not have moons like Earth’s, astronomers believe there are billions of rocky planets out there. Five to 10 percent of billions is still a lot of moons.

Other authors of the paper include: Zoltan Balog, James Muzerolle, Kate Y. L. Su and Erick T. Young of the University of Arizona, and Valentin D. Ivanov of the European Southern Observatory, Chile.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA.

For more information about Spitzer, visit

http://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer .

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