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To celebrate the season, here is a special Christmastime Sunday space post! Discovered in 1948 Comet 46P/Wirtanen orbits the sun every 5.4 Earth years. The comet’s apoapsis (the point of its orbit farthest from the Sun) is out in the vicinity of Jupiter’s orbit, but the closest point in its orbit brings it to Earth’s orbit. Unfortunately, because of the dance of the planets it only in relative proximity to Earth every 11 years, and even then, it is generally barely visible except to hardened astronomers. The comet is also known as the Christmas comet because its periapsis (when it is closest to the sun—and thus, sometimes to Earth) is in December and because the comet has a distinct viridian tinge!
This year, 46P/Wirtanen’s periapsis is unusually close to Earth. Tonight, the comet will be a mere 11.4 million kilometers (7.1 million miles) from Earth. That sounds like a fairly large distance but it is quite close, astronomically speaking: only 10 comets have come in such near proximity to our home planet in the past 70 years! Filled with excitement, I glanced out my window only to see that it is raining in Brooklyn and the sky is filled with clouds. But don’t worry, the comet will nearly as visible for another week. If you have an internet connection (and if you don’t, how are you reading this?) you can go to this link and find the comet in the sky from your location (that link is an amazing resource, so maybe hold onto it).
So why is this comet such a delightful color? Comet 46P/Wirtanen is mostly melted—it consists of a solid kernel approximately a kilometer in diameter trailing a cloud of gases hundreds of thousands of kilometers long. The majority of these gases reflect light in green wavelengths. Additionally, the comet is hyperactive—which, in this case, does not mean that overpaid physicians will prescribe it unnecessary medications so it can learn rote facts. In an astronomical context, hyperactive bodies are emitting more water than expected.
Unless you are avidly examining the comet with a gas spectrograph, its color is likely to be a source of awe and reflection. Does the comet’s color reflect the seasonal green of Yuletide or is it an ironic reprimand for the envy and jealously which grip all of human society? Is it the eye of a great sky panther or a kindly celestial sea turtle (hint: actually more of a ball of gas with an icy nucleus). Whatever your conclusions, I hope you enjoy this close-up view of “the Christmas Comet” before it zips back towards Jupiter’s orbit. Season’s greetings to all of my readers. I will try to find some special posts for this solstice week, before we all take a much-needed Christmas break.
Seven hundred million miles away the Cassini spacecraft is preparing for death this coming September (2017). Launched in 1997 (when I moved to Brooklyn) the joint Italian/American space exploration mission to Saturn has seen and done things beyond comprehension. Lifted out of Earth’s gravity well by means of a Titan IVB/Centaur It flew through the nothingness and slingshotted around Venus (twice), the Earth, and Jupiter. It discovered new oceans on Enceladus and launched a lander onto the supermoon Titan (the first ever landing in the outer solar system). Cassini was used to tested general relativity: the craft broadcast radio past the sun to the Earth so that scientists could measure how the star’s gravity distorted the electromagnetic waves. Powered only by pluck (and, uh, 33 kilograms of plutonium-238) the little probe visited 20 moons.
But all good things come to an end, and this final phase may be the most dramatic. On April 26th the craft began weaving between Saturn’s rings and the top of the planet’s atmosphere. The image at the top is an artist’s conception of how this might look for Cassini. The second image is a picture of the enormous hexagonal storm at the north pole taken April 30th. The image below is an infrared picture of Saturn. Cassini is scheduled to make 20 more of these passes before its final fiery plunge into Saturn itself, so prepare for more mind-boggling images of the gas giant.
Robin Dunbar is an anthropologist/primatologist who discovered a correlation between the size of a primate’s brain (or really its neocortex) and the size of that animal’s social network. For example, clever chimpanzees tend to live in groups of 60 or so individuals, who maintain complex intimate social relations (yet chimpanzees don’t really care about outsiders without elaborate introductions). Howler monkeys tend to live in groups of 6 or 7. Dunbar studied primate brains until he believed he found the correlation index… then he applied it to human beings based on our own neocortices (is that the right word?). The number he arrived at was around 150. He posited that this is the average number of stable meaningful social relationships we can have at once. Here is a humorous (yet oddly serious) article which explains the concept elegantly (albeit with some fairly salty language and preachy talk).
When one starts looking for the number 150, it crops up all over the place. Hunter gatherer tribes were (and still are) limited to about that number. Military companies of all sorts of different armies throughout history have been that size. Business consultants say that this is an ideal size for companies (come to think of it there are 150 people at the company where I work) or for departments of companies.
But of course the 150 people I work with are not the entirety of my social interactions. I have 500 or so Facebook friends and not a one of them is from work….and the people I am closest to are not always on Facebook. And there are people I know about but have never (and will never) meet (like Susanna Hoffs, the emir of Qatar, and…Robin Dunbar). High functioning individuals like Presidents, CEOs, and world famous artists probably know many thousands of people—or at least know the one or two key pieces of information which makes each contact useful.
So there are lots of troubles and quibbles with Dunbar’s number…yet if you really write out everyone you have a true worthwhile meaningful relationship with you will probably come up with about 150 (if you are a gregarious adult with a full life in a big city—you can have many fewer close relations and there is nothing wrong with that…it doesn’t mean you are a capuchin monkey or something).
(Not that there is anything wrong with that either)
There is a line we draw around our tribe. Within this line are people we care about and need, outside it are… others—people we may care about in the abstract, or because they share a language, or a characteristic, or a nationality with us…but who are not dear to our heart in the same way as our intimate associates. The writer I linked to in the first paragraph up there asks us to imagine having a beloved pet…or two beloved pets…or six, or 23. How long would it be before our love and our attention were so diluted that we only cared about them in the most general abstract terms (or just outright despised them as a furry horde)? Whether you accept the premise of Dunbar’s number or not, it is a worthwhile question. If our brains are built by evolution in such a way as to make an “us” and a “them” what does it mean for all of us?
An artist’s’ conception of the planetary sytem of Wolf 1061C
Today Australian scientists announced the discovery of a very interesting exoplanet—a so-called “super-earth” which orbits around the red dwarf star Wolf 1061. The rocky planet (Wolf1061c) is actually only one of three worlds so far found in the solar system of Wolf 1061, but it is of particular note because it lies in an orbit which allows for liquid water to exist upon its surface.
Wolf 1061 is tidally locked to its star, so one side always faces the red ball in the heavens. It has a mass about 4.3 times that of Earth—so the surface gravity is nearly twice that of Earth. Its “years” are 18 Earth days long.
Perhaps most excitingly Wolf 1061c is “only” 14 light years away (about 84,000,000,000,000 miles). It is a neighbor! Perhaps we can use our best telescopes to assay the atmosphere and find out if anything resembling Earth life is there.
Stromatolites at dawn in Shark Bay, Western Australia
This place really exists! Spend a moment imaging what it is like on the surface. In my fantasy, one side of the world is a vast red desert while the other is a desolation of black glaciers…yet in a twilight ring between the sides there are sludgy water oceans filled with big green and violet pillows of fabulous squashed shapes—the analogs of stromatolites. Bubbles of gas pour up from these oddly shaped blobs of bacteria-like cells. Somewhere among the billions of little multiplying alien organisms, a few peptides have changed and the cells begin to exchange genetic material with one another. They are beginning to reproduce sexually instead of merely dividing. Life in the ring oceans of 1061c takes a leap forward. It is all imagination…and yet it may be so. The universe is vast. I wish we could find out more about this entire earthlike planet that we only just found.
ferrebeekeeper 