Tag: astronomy

Milutin Milankovitch


Milutin Milankovitch (Milankovic) was a Serbian scientist, born in 1879 in the village of Dalj, in present-day Croatia. It was then part of the Austro-Hungarian Empire. At 17 he took up Civil Engineering at the Vienna University of Technology, going on to earn a Ph.D in engineering eight years later. His thesis was on pressure curves, useful in the planning and construction of load-bearing structures like bridges. He got work with an engineering firm, concentrating on reinforced and armored concrete, until he was offered the chair of applied mathematics at the University of Belgrade in 1909. He began to concentrate on fundamental research, though he kept his hand in concrete as well.

In his research he became interested in celestial mechanics and astronomical effects on planetary climate. He found that, although scientists were finding convincing evidence of ice ages in Earth’s past, including some indications that they might be cyclical, they were unable to come up with a plausible theory to explain it. He decided to use his interest in astronomy, and his facility with mathematics, to see if he could find any patterns that might explain the cycles in Earth’s climate. He began in 1912, following up on the work of his predecessors in the field, including James Croll, whose pioneering work on astronomical influences on ice ages was rejected by geologists and climatologists of the day. Milankovitch would face the same scepticism.

He began by publishing some papers on the effects of solar radiation, and its distribution on the planet’s surface, bringing some mathematical rigor to the science of meteorology. Then he began the more onerous task of calculating the cyclical variability of the Earth’s rotation on its axis as well as its orbit around the Sun. These eventually came to be called Milankovitch cycles, when everyone finally caught up and realized he was right. I’ll discuss those cycles independently in future posts.

His work was interrupted, though only briefly, by the beginning of World War One. He was imprisoned as a Serbian enemy of the Austro-Hungarian Empire, but was soon released upon the intervention of his friend and mentor, Emanual Czuber. He subsequently was allowed to work at the Hungarian Academy of Science for the duration of the war. After the war he returned to Belgrade where he continued to create the foundation for the mathematical treatment of climate science. He calculated the curve for variations in solar radiation impinging on the Earth going back 130,000 years, extending it to 650,000 years at the urging of climatologist Wladimir Koppen. He also impressed Alfred Wegener, of continental drift fame.

Milankovitch published many more papers, as well as popular science books, including a series on the history of science. The publication of his collected works on the problem of the Ice Ages was interrupted by the Second World War, and it ended up being published in German. It was almost lost in the bombing of Belgrade when the printing house entrusted with it was destroyed. Fortunately the warehouse where the printed sheets were stored was spared.

Milutin Milankovitch died in Belgrade in 1958. After his death his work was disputed and it languished for ten years. But it slowly gained support and is now accepted by most climatologists and geologists as an accurate theory. The Milankovitch cycles have been shown to bear a close relationship with the cycles of the Ice Ages. He shares the honor of being one of Serbia’s great scientists with the legendary Nikola Tesla.

Read the series on Milankovitch cycles, beginning with orbital eccentricity.

rjb

Evolution – Part One

Credit Steinhöfel-ESO - CC-BY

Credit Steinhöfel-ESO – CC-BY – Depicting the evolution of a main sequence star – tap for large image

Evolution: A gradual process in which something changes into a different and usually more complex or better form. The Free Dictionary, definition 1(a).

Some years ago I published a series of articles about evolution in my local newspaper. It generated some interest and a spate of letters to the editor, and my publisher liked it. There was even a creationist who challenged me to a debate over it. I decided to reproduce it here. This is part one, which I called Evolving in Spite of Us. See also Part Two and Part Three.

When we think of evolution we usually think of life. It seems natural to think of Darwin’s “origin of species” as being what evolution is all about. After all, that’s what people are usually talking about when they talk about evolution. It’s good to remember, though, that not only life evolves. Pretty well anything you can think of is changing over time. Everything is in the process of transforming from one state to another. Since that’s practically the definition of evolution, it’s safe to say that everything is evolving.

For example, the interior of our planet Earth is gradually cooling over the eons. That means that there is less heat energy to drive the movement of the crustal plates, and therefore continental drift will gradually slow down. Eventually, if given enough time, Earth would cool enough to set and the continents would never move again. Fewer earthquakes. Fewer volcanoes. Less mixing of the various parts of the biosphere. The Earth is evolving.

Our Sun is also evolving. It’s much hotter now than it was when it was young. It’s been slowly heating up in the four-and-a-half billion years since it was born. If it follows the course of other stars of similar mass and composition, and there’s no reason why it shouldn’t, in another four or five billion years it will be a red giant. This will likely happen before the Earth can cool down enough to set. By that time it will have burned Earth to a crisp, possibly even growing large enough to engulf it. Life on Earth has been adapting to the Sun’s increasing output, even to the point of actively adjusting the atmosphere to keep it in the right temperature range. Nothing is likely to compensate for being engulfed, though.

Even the universe as a whole is evolving. We can tell that it’s expanding, which implies that it used to be smaller. We know that the universe was different in the past, to the point where there were no galaxies or stars at all. In the past it was very small and very hot. After about 14 billion years of expansion it exists in a state which supports life. Unfortunately, the rate of expansion is increasing. If nothing happens to change things, the universe is going to grow increasingly cold and dark. Eventually it will no longer support life.

We may continually come back to life when we think of evolution, but evolution goes on regardless of life.

rjb

20 Big Questions about the Future of Humanity

Scientific American has asked some scientists what they call “20 big questions about the future of humanity.” Not all of the questions are strictly about humans, but most of them are, and I think we can forgive them for those that are not. They’re still interesting questions.

We asked leading scientists to predict the future. Here’s what they had to say

Interestingly, they begin with the question, “Does humanity have a future beyond Earth?” Lifting the eyes, I guess. Setting the tone to think beyond the mundane. They asked Martin Rees, an established and well-respected British cosmologist and astrophysicist. To paraphrase his answer: yes, sort of, eventually.

I think it’s a dangerous delusion to envisage mass emigration from Earth. There’s nowhere else in the solar system that’s as comfortable as even the top of Everest or the South Pole. We must address the world’s problems here. Nevertheless, I’d guess that by the next century, there will be groups of privately funded adventurers living on Mars and thereafter perhaps elsewhere in the solar system. We should surely wish these pioneer settlers good luck in using all the cyborg techniques and biotech to adapt to alien environments. Within a few centuries they will have become a new species: the posthuman era will have begun. Travel beyond the solar system is an enterprise for posthumans—organic or inorganic.

Another question I found interesting has to do with consciousness, and whether we’ll ever understand it. The answer is not the usual one.

Some philosophers, mystics and other confabulatores nocturne (simply, people who make up stories in the night time – rjb) pontificate about the impossibility of ever understanding the true nature of consciousness, of subjectivity. Yet there is little rationale for buying into such defeatist talk and every reason to look forward to the day, not that far off, when science will come to a naturalized, quantitative and predictive understanding of consciousness and its place in the universe.

One of the questions that isn’t strictly about humans has to do with extraterrestrial life. I suppose it is about us in a way because the discovery of extraterrestrial life, or the prolonged lack of discovery, will affect us profoundly. I like this answer because it almost perfectly recapitulates what I said in my post, “Alien Life on Titan.”

If there is abundant microbial life on Mars, I suspect that we will find it within 20 years … Jupiter’s moon Europa and Saturn’s moon Titan are more compelling places. Europa is a water world where more complex forms of life may have evolved. And Titan is probably the most interesting place in the solar system to look for life. It is rich in organic molecules but very cold and has no liquid water; if life exists on Titan, it will be very different from life on Earth.

There are many more questions and many more interesting answers in the linked Scientific American article. They discuss the brain, which is getting a lot of interest from researchers right now. Will greater knowledge of the brain affect criminal law? Will we ever figure out afflictions like schizophrenia and autism? Then there’s the planet itself. Can we stop Earth’s sixth great extinction? Spoiler alert: scientists tend by their nature to be optimistic people. Follow the link and check out the article for yourself. You might find it stimulates some questions in yhour own mind.

Source: 20 Big Questions about the Future of Humanity – Scientific American

rjb

Cassini’s Last Dance

NASA - Public Domain

NASA – Public Domain

The Cassini space probe is nearing the end of its life. Cassini is the spacecraft that NASA sent to explore Saturn. It arrived at the ringed planet in 2004, and here are a couple of pieces I wrote about it then:

NASA -Public Domain

NASA -Public Domain

Cassini Goes to Saturn

Saturn is the planet that’s always depicted with a big, wide ring around it. The ring is like the brim of Saturn’s hat or the skirt of its tutu. The ring looks big but an average moon of Saturn contains as much material as the whole ring system.

The ring around Saturn, when you get a closer look at it, is really made of many smaller rings, each in an orbit of its own. We got that closer look when the Voyager probes 1 and 2 went by Saturn in 1980 and 1981 on their way out of the Solar System.

Saturn’s rings played a role in the arrival of the space probe Cassini, which finished its seven year transit from Earth this summer with a perfect insertion into its pre-planned orbit. The Cassini probe is named after the 17th century Italian astronomer, Giovanni Cassini, who discovered the big gap in the rings, now called the Cassini division. The spacecraft approached Saturn’s rings from “below,” slipped through a gap between two rings, did a 95 minute engine burn to slow down enough to stay in orbit and popped back down through the rings. Now it’s going to settle in for a four year mission, collecting data on the Saturnian system.

One of Saturn’s 31 known moons, Titan, is of particular interest and will be approached 45 times on the 76 scheduled orbits of the planet. Titan is a big moon, even larger than the planet Mercury, and is known to have a thick atmosphere. On one of its close approaches, Cassini will be releasing its payload, the Huygens probe, which will drop into Titan’s atmosphere and, hopefully, safely land on the surface.

Cassini is the size and mass of a 30 passenger bus and is the largest interplanetary spacecraft ever made. It contains 12 scientific instruments in addition to the Huygens probe, and will be measuring everything from regular visible light images to radio waves to magnetic fields. By the time the four year mission is completed we will have learned more about Saturn than we have since Galileo puzzled over the planet with the “ears” in his telescope 400 years ago.

If all continues to go as well as it has so far, we can look forward to at least four years of new images and new knowledge about the beauty of the Solar System, Saturn.

NASA - Public Domain

NASA – Public Domain

Cassini-Huygens

After a flight of seven years and over three billion kilometers, the spacecraft Cassini successfully entered orbit around the planet Saturn. It then reconnoitered the ring system and the many moons there for six months. The data it’s sending home will keep planetologists busy for years.On Christmas eve Cassini released the Huygens probe. On January 14th the probe will plunge at 19,000 kilometers per hour into the thick atmosphere of Saturn’s moon, Titan. It will make a two hour descent to the surface, deploying parachutes three times to slow down.

After the ablative heat shield has slowed Huygens down most of the way, the first parachute opens. Huygens jettisons the heat shield at about 150 kilometers up, and starts collecting data. Then the other parachutes reduce the rate of descent as much as possible, both to prolong the data-collection phase and to try to ensure the probe’s survival on landing.

The scientists aren’t relying on a safe landing. Their mission will be a success if they get good data during descent. The probe will take more than a thousand pictures in addition to analyzing the atmosphere on the way down. Even if it dies on impact or gets glommed in a sea of goop, Huygens will be able to send back a very deep sample of Titan’s thick air first.

The three weeks between separation from Cassini and contact with the atmosphere have been tense. Huygens was turned off to save power and won’t be turned on until the last minute. Full power has to be available for the very busy descent and any surplus will be welcome if it survives to study the surface.

Scientists are interested in Titan because of the unusually thick, rich atmosphere it has. It’s about 50% thicker than Earth’s atmosphere and, like ours, is mostly nitrogen. The other notable constituents are methane and hydrocarbons. Titan’s smog problem makes ours pale by comparison.

Meanwhile, having dropped off its passenger, Cassini had to adjust course to not follow it into Titan. Once Huygens goes quiet and there are no more data to relay to Earth, Cassini will get back to the business of exploring. There are over sixty more orbits to do around Saturn. Sixty more chances to get a look at the moons, the rings and the storms of Saturn. So much to see and only four more years to see it.

Both parts of the Cassini-Huygens mission were successful, to put it mildly. Huygens, the probe released by Cassini, landed on Saturn’s moon, Titan, and sent up a lot of data, relayed to Earth by the mother ship. That happened in 2004-2005, but launch was in 1997. It took seven years and much fancy maneuvering to get there. Planning and design for the mission began in the 1980s, with a large team of people from seventeen countries. This has been a truly big international project.

After taking care of the Huygens-Titan phase, Cassini got on with the rest of its four year mission, then kept going for another seven or eight. It has far exceeded what was originally asked of it, but now it’s running down and the team is planning a spectacular finish for it. In this phase it’s going to trace some highly elliptical orbits of Saturn, ranging from a maximum distance many times the diameter of the planet to a minimum between the rings and the atmosphere. As a grand finale it will plunge into Saturn’s atmosphere, where it will be destroyed. But not before sending back even more data.

What a way to go.

rjb

Interstellar Seeds Could Create Oases of Life

In 2004 I wrote a short piece for my local newspaper in which I speculated about the possibility of comet impacts splashing chunks of Earth back into space, and some of the life in those chunks surviving long enough to fertilize other worlds. Here’s that story:

From The Book of Miracles - Public Domain

From The Book of Miracles – Public Domain

Tech Nickels
Fertile Comets

Comets are often compared to a dirty snowball, only not packed so hard. Their density is more like a snowbank. Comets aren’t big enough as a rule for gravity to pull them into a spherical shape, so they’re mostly irregular chunks of dirty snow. On highly elliptical orbits, the comets we see loop way out to the fringes of the Solar System and beyond, then back in close to the Sun. Near the warm center they heat up and blow off huge clouds of dust and water vapor which we are sometimes lucky enough to see. When closest to the Sun, they are venting vast plumes which leave holes on their surface.

We tend to worry about things like comets. All through history we’ve attached abnormal significance to their appearance. Of course, it had to be all about us. Whether portents of the fall of kingdoms or bearers of evil omens, we’ve shown a tendency to be a little self-centered about it. Not that there isn’t evidence of severe damage when Earth is struck by some of the bigger comets. Big ones can hit us so hard that the splash is blown right back into space. The dinosaurs probably went extinct after a big comet strike. We should definitely worry about them.

Something we don’t usually think about is what happens to the Earth material that gets blown into space. There must be tons of Earth ejecta in an expanding cloud throughout the galaxy, given how often and how long comets have been hitting us. The Milky Way has rotated about twenty times since Earth formed, spreading it further. There is evidence of life on Earth going back almost four billion years. It stands to reason that some of it was carried into space in cometary splashback. Most of it would die in such a harsh environment, but some microbes would survive. They would be capable of remaining as dormant spores preserved in Earth dust. Over the eons they would drift through cold space, and a few of them might end up settling onto a new planet capable of stimulating them back to life.

There is a debate whether life started on Earth or was seeded here from elsewhere. The Panspermia theory developed by Chandra Wickramasinghe and the late Sir Fred Hoyle favors the latter. Now Professor Wickramasinghe is one of a few researchers suggesting that life from Earth is also out there seeding other worlds. I like that.

That was then. Now some people at Harvard have suggested a way we can possibly test the Panspermia theory.

Cambridge, MA –
We only have one example of a planet with life: Earth. But within the next generation, it should become possible to detect signs of life on planets orbiting distant stars. If we find alien life, new questions will arise. For example, did that life arise spontaneously? Or could it have spread from elsewhere? If life crossed the vast gulf of interstellar space long ago, how would we tell?

Interstellar Seeds Could Create Oases of Life

In a nutshell, they think any life we discover would appear in a pattern resembling that formed in an epidemic, if it was spreading via panspermia. It’s fun watching ideas develop.

rjb

%d bloggers like this: