The Spin on Planets
As the orbs whirl around Sol, human understanding of our space neighborhood rises and falls.
Mercury: The innermost planet has undergone a paradigm shift since the MESSENGER spacecraft arrived. Now, explosive volcanoes are prominent in explanations for its many flat-floored craters and volcanic plains, Robin Wylie discusses on The Conversation. Here’s his spin doctoring:
Before its explosive nature surfaced, experts assumed that, having formed so close to the sun, Mercury would have been stripped of its volatile gases early on in its life. So future theories of Mercury’s genesis must now take into account how the planet kept its fizz hidden. They will likely now invoke ideas of ancient collisions with volatile-rich “planetesimals” – balls of rock and dust that are thought to have formed the inner planets – which could have topped up Mercury’s levels.
All of this puts a new spin on the first rock from the sun, and its place among the others.
Venus: Water at 900 degrees? Live Science reported that a revisit of 30-year old data from the European Space Agency’s Venus Express orbiter and ground data from Russian Venera landers suggests (indirectly) that water molecules might have survived in the planet’s mantle. Since those early days of exploration, scientists have dreamed of proving that Venus was once host to Earth-like lakes and oceans of liquid water before the climate went terribly bad.
Earth and the Young Sun Paradox: How did the Earth stay warm when the early sun was 25% cooler than today? That old puzzle was revisted by Astrobiology Magazine. Astronomers are still working on the new spin. Maybe it was tiny bubbles in the wine of Earth’s early atmosphere: changes to the ratios of nitrogen, carbon dioxide and greenhouse gases. “We do have some choices for understanding the early atmosphere,” Bernard Marty said. It’s going to be tough to spin a solution out of the paradox, because as Earth was evolving, changes to the magnetic field, the atmosphere and the crust were evolving, too. Maybe noble gases helped: “We think that this implies that the xenon composition has been evolving through time and it was not fully in the atmosphere 3.5 billion years ago,” Marty said.
Mars: See the 2/13/14 entry for Mars news.
Asteroids: A paper in Nature found “unexpected diversity” of asteroid composition in the asteroid belt. This undermines the idea that a single body disrupted in that orbital region. “The asteroids in the main asteroid belt have been discovered to be more compositionally diverse with size and distance from the Sun than had previously been known,” the abstract says. “This implies substantial mixing through processes such as planetary migration and the subsequent dynamical processes.”
Jupiter’s Io: The volcanoes of Io have been popping off consistently for decades at least, a new paper on Icarus says. Based on comparative data from Galileo and New Horizons missions, the authors state this finding: “Most Ionian hot spots [are] very persistent on decade timescales.”
Jupiter’s Ganymede: The largest moon in the solar system, Jupiter’s 3rd Galilean satellite Ganymede, got a new map published. Combining data from the Voyager and Galileo spacecraft, the new map shows a splotchy surface that PhysOrg displayed. The article did not mention any new findings, but connected potential water to potential life, as is customary for NASA press releases: “With its varied terrain and possible underground ocean, Ganymede is considered a prime target in the search for habitable environments in the solar system, and the researchers hope this new map will aid in future exploration.” As John Grotzinger pointed out last week, habitable does not mean inhabited. A paper in Icarus comparing Ganymede and Europa shows the difficulty in inferring crustal depths from crater characteristics.
Saturn’s Titan: Three papers discussed Titan recently. One in Icarus tried to figure out how icy “sand” particles move around to form the equatorial dunes and infer something about the time involved. Another paper in Icarus tried to refine the distribution of methane in the atmosphere. A third paper in Icarus found that the equatorial dunes cover about 17% of the moon’s surface, and comprise the bulk of organics on Titan. One surprise involves dating: “Dunes are the largest visible surface reservoir of hydrocarbons and may be less than 730-Myr old.” That would be just 16% of Titan’s assumed age.
Saturn and rings: Another stunning photo of Saturn’s north polar vortex, shaped like a hexagon, was published by Space.com. Atmospheric scientist Andrew Ingersoll said that vortices like these are “notoriously turbulent and unstable,” yet this one has been spinning at least since Voyager’s flybys in 1981. A photo of little potato-shaped moon Prometheus is shown by PhysOrg pulling on the F-ring. “It’s a visual demonstration of gravity at work!” the article exclaimed. Icarus described a bit of “calm amidst the chaos” in this ephemeral ring of tiny ice particles, predicting a narrow, stable zone in the core of the ring. How can that be, with Prometheus and Pandora constantly tugging on it? “Essentially, we find that the F Ring core is not confined by a combination of Prometheus and Pandora, but a combination of Prometheus and precession.” How stable over time that arrangement could be is not clear; it seems like a tenuous balance. Astrobiology Magazine published an overview of “Cassini’s View of Weird & Wonderful Saturn,” ending with a prediction of the spacecraft’s daring attempt to “shoot the pier” in 2017 before it plunges into the gas giant.
Extrasolar planets: Now that planets around other stars are becoming commonplace, what’s new with them? On PhysOrg, Caltech astronomer Fraser Cain discussed “What are hot Jupiters?”. In text and video, she explains how new theories of migration were invented to account for the unexpected observation of gas giants orbiting their stars closer than Mercury to the sun every 2-3 days. Asked how they got there, she said, either the dust disk in which they formed created a torque pulling them in, or they got slingshotted in by interactions with other planets. Those are just some theories they’re working on.
Extrasolar moons: Space.com claims that extrasolar planets may not need a big moon to support life. Jack Lissauer at NASA-Ames found in computer simulations that changes to obliquity without a large moon were not as dramatic as previously calculated. “For timescales that are relevant to advanced life, it changes by maybe plus or minus 10 degrees — a lot bigger than we have with our moon, but a lot smaller and a lot fewer climate effects [than predicted by previous models],” he said. Still, this is only a simulation. “We’re not talking about, really, the Earth without the moon as a realistic model for the Earth, unless somebody goes out there and destroys the moon,” he said. “We’re using this as the first case of studying a plausible exoplanet, and we’re going to use some future calculations — we’re going to do the same thing with other systems.”
Good time to recall Finagle’s Second Law: “No matter what the experiment’s result, there will always be someone eager to: (a) misinterpret it, (b) fake it, or (c) believe it supports his own pet theory.” Planets spin, and so do their spin doctors. Ask them, “What do you know?” and you get a much smaller subset of verbiage. This is confirmed by the number of times previously held beliefs have been overturned.
This is also a good time to remember Ken Ham’s debate argument contrasting observational science and historical science. Despite Bill Nye’s denials, there is a difference (see also Todd Friel’s explanation on Wretched TV). We can observe hot Jupiters, but we cannot retrace how they got there. We can see Saturn’s F-ring, and dunes on Titan, but nobody was there to see how they got that way. All one can do is model it, or create a plausible story that doesn’t violate known physics. That being the case, alternative models should be welcomed, and any consensus view must be humbly considered tentative.