sunset from behind the wire

sunset from behind the wire

Monday, November 19, 2018

Big Long Rock from WAY Out There


In November 2017, scientists pointed NASA's Spitzer Space Telescope toward the object known as 'Oumuamua -- the first known interstellar object to visit our solar system. The infrared Spitzer was one of many telescopes pointed at 'Oumuamua in the weeks after its discovery that October.

The new size limit is consistent with the findings of a research paper published earlier this year, which suggested that outgassing was responsible for the slight changes in 'Oumuamua's speed and direction as it was tracked last year: The authors of that paper conclude the expelled gas acted like a small thruster gently pushing the object. That determination was dependent on 'Oumuamua being relatively smaller than typical solar system comets. (The conclusion that 'Oumuamua experienced outgassing suggested that it was composed of frozen gases, similar to a comet.)
"'Oumuamua has been full of surprises from day one, so we were eager to see what Spitzer might show," said David Trilling, lead author on the new study and a professor of astronomy at Northern Arizona University. "The fact that 'Oumuamua was too small for Spitzer to detect is actually a very valuable result."
'Oumuamua was first detected by the University of Hawaii's Pan-STARRS 1 telescope on Haleakala, Hawaii (the object's name is a Hawaiian word meaning "visitor from afar arriving first"), in October 2017 while the telescope was surveying for near-Earth asteroids. The fact that the name may remind you of a US Presidency with a different density is only circumstantial...

Subsequent detailed observations conducted by multiple ground-based telescopes and NASA's Hubble Space Telescope detected the sunlight reflected off 'Oumuamua's surface. Large variations in the object's brightness suggested that 'Oumuamua is highly elongated and probably less than half a mile (2,600 feet, or 800 meters) in its longest dimension.

But Spitzer tracks asteroids and comets using the infrared energy, or heat, that they radiate, which can provide more specific information about an object's size than optical observations of reflected sunlight alone would.

The new study suggests that 'Oumuamua may be up to 10 times more reflective than the comets that reside in our solar system -- a surprising result, according to the paper's authors. Because infrared light is largely heat radiation produced by "warm" objects, it can be used to determine the temperature of a comet or asteroid; in turn, this can be used to determine the reflectivity of the object's surface -- what scientists call albedo. Just as a dark T-shirt in sunlight heats up more quickly than a light one, an object with low reflectivity retains more heat than an object with high reflectivity. So a lower temperature means a higher albedo.

A comet's albedo can change throughout its lifetime. When it passes close to the Sun, a comet's ice warms and turns directly into a gas, sweeping dust and dirt off the comet's surface and revealing more reflective ice.

'Oumuamua had been traveling through interstellar space for millions of years, far from any star that could refresh its surface. But it may have had its surface refreshed through such "outgassing" when it made an extremely close approach to our Sun, a little more than five weeks before it was discovered. In addition to sweeping away dust and dirt, some of the released gas may have covered the surface of 'Oumuamua with a reflective coat of ice and snow -- a phenomenon that's also been observed in comets in our solar system.

'Oumuamua is on its way out of our solar system -- almost as far from the Sun as Saturn's orbit -- and is well beyond the reach of any existing telescopes.
"Usually, if we get a measurement from a comet that's kind of weird, we go back and measure it again until we understand what we're seeing," said Davide Farnocchia, of the Center for Near Earth Object Studies (CNEOS) at JPL and a coauthor on both papers. "But this one is gone forever; we probably know as much about it as we're ever going to know."

The Mortal Republic (book review)

Aspects of our modern politics reminded University of California San Diego historian Edward Watts of the last century of the Roman Republic, roughly 130 B.C. to 27 B.C. That’s why he took a fresh look at the period in his new book, Mortal Republic: How Rome Fell Into Tyranny. Watts chronicles the ways the republic, with a population once devoted to national service and personal honor, was torn to shreds by growing wealth inequality, partisan gridlock, political violence and pandering politicians, and argues that the people of Rome chose to let their democracy die by not protecting their political institutions, eventually turning to the perceived stability of an emperor instead of facing the continued violence of an unstable and degraded republic. Political messaging during the 2018 midterm elections hinged on many of these exact topics.

Tiberius and Gaius Gracchus. (Wikimedia Commons)

The U.S. Constitution owes a huge debt to ancient Rome. The Founding Fathers were well-versed in Greek and Roman History. Leaders like Thomas Jefferson and James Madison read the historian Polybius, who laid out one of the clearest descriptions of the Roman Republic’s constitution, where representatives of various factions and social classes checked the power of the elites and the power of the mob. It’s not surprising that in the United States’ nascent years, comparisons to ancient Rome were common. When President George Washington lay down his mantle and returned to his farm, it was reminiscent (to him and to us) of the noble Lucius Quintius Cincinnatus. To this day, Rome, whose 482-year-long Republic, bookended by several hundred years of monarchy and 1,500 years of imperial rule, is still the longest the world has seen.

Though he does not directly compare and contrast Rome with the United States, Watts says that what took place in Rome is a lesson for all modern republics. “Above all else, the Roman Republic teaches the citizens of its modern descendants the incredible dangers that come along with condoning political obstruction and courting political violence,” he writes. “Roman history could not more clearly show that, when citizens look away as their leaders engage in these corrosive behaviors, their republic is in mortal danger.”

Historians are cautious when trying to apply lessons from one unique culture to another, and the differences between the modern United States and Rome are immense. Rome was an Iron-Age city-state with a government-sponsored religion that at times made decisions by looking at the entrails of sheep. Romans had a rigid class system, relied on slave labor and had a tolerance for everyday violence that is genuinely horrifying. Then again, other aspects of the Roman Republic feel rather familiar.

Is the book worth reading? It depends on what you're looking for. It's not a comic book.