Tag Archives: solar system

Rare Earth

4.76-4.51 billion years ago

A big day on Logarithmic History, the biggest since the beginning of the year: the origin of our Solar System including planet Earth. First a note on what’s odd about our planetary system.

Two preceding posts wrestled with the Fermi Paradox: If the universe is full of advanced civilizations, why haven’t we seen any sign of them so far? One answer to the paradox might be that our solar system is wildly unusual, so that abodes for the evolution of complex life are rare. We can finally start to address this matter with some real evidence. According to the NASA exoplanet archive, we’ve now discovered 4,108 exoplanets (planets outside our solar system; up from 3885 last year at this date), with many more unconfirmed candidates. This is enough to do some statistics, and indications are that our solar system might indeed be out of the ordinary.

grand-tack

Exoplanets smaller than Jupiter are overwhelmingly closer, mostly a lot closer, to their primary stars than Earth is to the Sun. And the same models of planet formation that have done a pretty good job predicting some of the wild variation we see in other systems – “Hot Jupiters” orbiting closer to their primaries than Mercury, “Super Earths” in between Earth and gas giants in size – don’t readily generate systems that look much like ours. One model that does seem to do a good job with our solar system, the Nice Model, involves something special, a Grand Tack, where Jupiter and Saturn are caught in an orbital resonance that carries them into the inner solar system and back out, shaking up inner-system planet formation in the process. Wild stuff, but another variation on the Nice model is even wilder: at the beginning of planet formation, there may have been a generation of Super Earths in the inner solar system. The Grand Tack of Jupiter and Saturn would have sent these planets colliding into one another. The Super-Earths and most of the debris of these collisions would have fallen into the sun, but what the debris left would then have condensed into the unusual inner planets we know, Mercury, Venus, Earth, Mars. And Theia. (Theia? you ask. See the next post). Remarkably, we may have recently found evidence here on Earth of minerals that formed deep inside a lost planet or protoplanet from the earliest days of the solar system.

If this model holds up, the formation of our solar system, like other major events in our history, takes on some of the flavor of mythology. This isn’t quite the old story about Chronos slaying Ouranos, and Zeus slaying Chronos. Instead, in the new story, two giants, Jupiter and Saturn, travel closer to the sun and set a generation of Titans – their like will not be there again – to fighting and destroying one another. Jupiter and Saturn depart, and a new generation is spawned from the wreckage. An unlikely sequence of events, but then our planet could be a very unlikely place. And all the more special for that.

Where is everybody? Maybe we’re (some of) the first

A followup to the previous post on the Fermi Paradox, some reasons the Universe could have been less suitable for the evolution of complex life until recently, making us one of the first intelligent species to evolve.

1) Metallicity. Chemical elements heavier than helium are formed inside stars, after the Big Bang. Elements heavier than iron are formed in exploding supernovas. These elements have been building up over time. Maybe they had to reach a threshold abundance to make complex life possible. Consider that in the “family tree” for the Sun, based on the concentrations of different elements, the Sun is the oldest member of its subfamily. Maybe it is only planetary systems associated with this subfamily that are well-suited for the evolution of intelligent life. And recent work suggests that phosphorus in particular may be a limiting and cosmically limited resource for the evolution of life.

2) Gamma Ray Bursts (GRBs). GRBs are bursts of gamma rays (high frequency radiation) lasting from milliseconds to minutes, like GRB 080319B. (Check out this tweet from January 11.) GRBs are probably supernovas or even larger explosions where one pole of the exploding star is pointed at the Earth. A major GRB could irradiate one side of the planet, and also affect the other side by destroying the ozone layer, causing mass extinctions. GRBs may have swept the Milky Way frequently in the past. The good news is they’re probably getting less frequent. This could be the first time in the history of the Milky Way that enough time has passed without a major GRB for intelligent life to evolve. If true, we should think about how to protect ourselves from the next one – lots of sunblock recommended.

If GRBs are such a threat, we might expect to find evidence that they have caused mass extinctions in the past (not wiping out all life obviously). For more on this, check out upcoming blog posts and tweets for the end-Ordovician, March 3.

3) Panspermia (life from elsewhere). Pretty much as soon as Earth could support life, we see evidence of single-celled organisms. Then life evolves slowly for a long time. The usual story about this is that the origin of life is easy, and it happens as soon as possible. But there is another possibility (illustrated below). It may be that the transition from simple replicating chemical systems to bacteria with genomes of tens of thousands of DNA base pairs is a slow process that happened over many billions of years somewhere other than Earth. Then newly forming planets in the nebula that gave rise to Earth were “infected” by this source, by meteorites carrying early cells. (It would have been easier for meteorites to carry life from star system to star system when the Earth was first formed than it would be today.) Back when our hypothetical “Urth” was forming, a billion years before Earth, there might not have been any planets with cellular life on them as potential sources of life-bearing meteorites.

Untitled

Where is everybody?

5.04 – 4.77 billion years ago

Tomorrow is a big day on Logarithmic History, the origin of our solar system, of the Sun and planet Earth. But is this really such a big deal in a cosmic perspective? After all, stars and planetary systems have been forming a fast clip in the Milky Way and other spiral galaxies since long before this date. So let’s suppose … Suppose there was a star like the Sun, but older by a billion years. And suppose this star had a planet like Earth orbiting around it – call it Urth. And suppose life originated on Urth more or less as on Earth and followed more or less the same evolutionary path. With this head start, intelligent life could have evolved a billion years ago, and today there could be intelligent Urthians (or their self-replicating robot descendants) a billion years ahead of us.

There’s an urban legend that says that Einstein called compound interest the strongest force in the universe. Einstein didn’t actually quite say this, but it’s not a crazy thing to say. For example, consider how compound interest works, backward, on our Logarithmic History calendar. December 30 covers a period 5.46% longer than December 31, December 29 is 11.2% longer (because 1.0546 * 1.0546 = 1.112), and so on. At this rate of compounding (and allowing for 2020 being a leap year) we wind up with January 1 covering 751 million years. The same math implies that if we invested 1 dollar at 5.46% interest, compounded annually, then after 365 years we’d have 751 million dollars.

With even the slightest compound rate of increase, a billion year old Elder Race would have plenty of time to fill up a galaxy, and undertake huge projects like dismantling planets to capture more of their suns’ energy. Indeed, they could arguably colonize the whole reachable universe.

Traveling between galaxies – indeed launching a colonization project for the entire reachable universe – is a relatively simple task for a star-spanning civilization, requiring modest amounts of energy and resources. … There are millions of galaxies that could have reached us by now.

Which raises the question, posed by Enrico Fermi in 1950: “Where is everybody?” There are more than 100 billion stars in our galaxies, more than 100 billion galaxies in the visible universe (actually, according to recent estimates, the number is more than  1 trillion). If there are huge numbers of billion year old Elder Races around, why hasn’t at least one of them taken the exponential road and made themselves conspicuous? Yet a recent survey of more than 100,000 galaxies found no evidence of any really advanced civilizations harnessing the power of stars on a large scale.

A possible resolution of the paradox has been suggested recently. The argument goes like this: the easiest route to estimating the number of advanced civilizations in the universe is to multiply point estimates of the probabilities of events like the formation of an Earthlike planet around an appropriate star, the origin of life on such a planet, the origin of human-level intelligence, and so on. But there are enormous uncertainties in these estimates. Properly speaking, instead of just multiplying mean estimates, we should be doing a convolution of the range of estimates. The general point is that if you’re multiplying a whole lot of probabilities, and you’re not certain what those probabilities are, there a strong likelihood that at least one of those probabilities is close to 0, so their product is also close to 0. The authors therefore suggest that there is a strong possibility that there are few or no advanced civilizations, or even other human-level civilizations in the Milky Way or even the observable universe.

In short, if this is true, tomorrow on Logarithmic History may mark a truly momentous occasion, not just in the history of the Earth, but in the history of the universe.

Rare Earth

4.75-4.49 billion years ago

A big day on Logarithmic History, the biggest since the beginning of the year: the origin of our Solar System including planet Earth. First a note on what’s odd about our planetary system.

Two preceding posts wrestled with the Fermi Paradox: If the universe is full of advanced civilizations, why haven’t we seen any sign of them so far? One answer to the paradox might be that our solar system is wildly unusual, so that abodes for the evolution of complex life are rare. We can finally start to address this matter with some real evidence. According to the NASA exoplanet archive, we’ve now discovered 3885 exoplanets (planets outside our solar system; up from 3587 last year at this date), with many more unconfirmed candidates. This is enough to do some statistics, and indications are that our solar system might indeed be out of the ordinary.

grand-tack

Exoplanets smaller than Jupiter are overwhelmingly closer, mostly a lot closer, to their primary stars than Earth is to the Sun. And the same models of planet formation that have done a pretty good job predicting some of the wild variation we see in other systems – “Hot Jupiters” orbiting closer to their primaries than Mercury, “Super Earths” in between Earth and gas giants in size – don’t readily generate systems that look much like ours. One model that does seem to do a good job with our solar system involves something special, a Grand Tack, where Jupiter and Saturn are caught in an orbital resonance that carries them into the inner solar system and back out, shaking up inner-system planet formation in the process. Wild stuff, but another latest model is even wilder: at the beginning of planet formation, there may have been a generation of Super Earths in the inner solar system. The Grand Tack of Jupiter and Saturn would have sent these planets colliding into one another. The Super-Earths and most of the debris of these collisions would have fallen into the sun, but what the debris left would then have condensed into the unusual inner planets we know, Mercury, Venus, Earth, Mars. And Theia. (Theia? you ask. See the next post).

If this model holds up, the formation of our solar system, like other major events in our history, takes on some of the flavor of mythology. This isn’t quite the old story about Chronos slaying Ouranos, and Zeus slaying Chronos. Instead, in the new story, two giants, Jupiter and Saturn, travel closer to the sun and set a generation of Titans – their like will not be there again – to fighting and destroying one another. Jupiter and Saturn depart, and a new generation is spawned from the wreckage. An unlikely sequence of events, but then our planet could be a very unlikely place. And all the more special for that.

Where is everybody? Maybe we’re (some of) the first

5.31-5.03 billion years ago

A followup to yesterday’s post on the Fermi Paradox, some reasons the Universe could have been less suitable for the evolution of complex life until recently, making us one of the first intelligent species to evolve.

1) Metallicity. Chemical elements heavier than helium are formed inside stars, after the Big Bang. Elements heavier than iron are formed in exploding supernovas. These elements have been building up over time. Maybe they had to reach a threshold abundance to make complex life possible. Consider that in the “family tree” for the Sun, based on the concentrations of different elements, the Sun is the oldest member of its subfamily. Maybe it is only planetary systems associated with this subfamily that are well-suited for the evolution of intelligent life. And recent work suggests that phosphorus in particular may be a limiting and cosmically limited resource for the evolution of life.

2) Gamma Ray Bursts (GRBs). GRBs are bursts of gamma rays (high frequency radiation) lasting from milliseconds to minutes, like GRB 080319B. (Check out tweets for January 11.) GRBs are probably supernovas or even larger explosions where one pole of the exploding star is pointed at the Earth. A major GRB could irradiate one side of the planet, and also affect the other side by destroying the ozone layer, causing mass extinctions. GRBs may have swept the Milky Way frequently in the past. The good news is they’re probably getting less frequent. This could be the first time in the history of the Milky Way that enough time has passed without a major GRB for intelligent life to evolve. If true, we should think about how to protect ourselves from the next one – lots of sunblock recommended.

If GRBs are such a threat, we might expect to find evidence that they have caused mass extinctions in the past (not wiping out all life obviously). For more on this, check out upcoming blog posts and tweets for the end-Ordovician, March 3.

3) Panspermia (life from elsewhere). Pretty much as soon as Earth could support life, we see evidence of single-celled organisms. Then life evolves slowly for a long time. The usual story about this is that the origin of life is easy, and it happens as soon as possible. But there is another possibility (illustrated below). It may be that the transition from simple replicating chemical systems to bacteria with genomes of tens of thousands of DNA base pairs is a slow process that happened over many billions of years somewhere other than Earth. Then newly forming planets in the nebula that gave rise to Earth were “infected” by this source, by meteorites carrying early cells. (It would have been easier for meteorites to carry life from star system to star system when the Earth was first formed than it would be today.) Back when our hypothetical “Urth” was forming, a billion years before Earth, there might not have been any planets with cellular life on them as potential sources of life-bearing meteorites.

Untitled

Where is everybody?

5.62 – 5.32 billion years ago

Today in Logarithmic History, January 17, covers a period beginning over a billion years before the origin of our solar system. Back then, stars were forming at a fast clip in the Milky Way and other spiral galaxies. So let’s suppose… Suppose one of those older stars resembled the Sun, and had a planet like Earth orbiting around it – call it Urth. And suppose life originated on Urth more or less as on Earth and followed more or less the same evolutionary path. With this head start, intelligent life could have evolved a billion years ago, and today there could be intelligent Urthians (or their robot descendants) a billion years ahead of us.

There’s an urban legend that says that Einstein called compound interest the strongest force in the universe. Einstein didn’t actually quite say this, but it’s not a crazy thing to say. For example, consider how compound interest works, backward, on our Logarithmic History calendar. December 30 covers a period 5.46% longer than December 31, December 29 is 11.2% longer (because 1.0546 * 1.0546 = 1.112), and so on. At this rate of compounding we wind up with January 1 covering 754 million years. The same math implies that if we invested 1 dollar at 5.46% interest, compounded annually, then after 364 years we’d have 754 million dollars.

With even the slightest compound rate of increase, a billion year old Elder Race would have plenty of time to fill up a galaxy, and undertake huge projects like dismantling planets to capture more of their suns’ energy. Which raises the question, posed by Enrico Fermi in 1950: “Where is everybody?” There are more than 100 billion stars in our galaxies, more than 100 billion galaxies in the visible universe (actually, according to recent estimates, the number may be more than  1 trillion). If there are huge numbers of billion year old Elder Races around, why hasn’t at least one of them taken the exponential road and made themselves conspicuous?

There’s a large literature on the Fermi paradox. One possible explanation is that we’re one of the first intelligent species to evolve because the universe was somehow less suitable for the evolution of complex life before now. I’ll take that one up tomorrow.

And here’s an interview, just out, from the New Yorker, with Harvard astronomer Abraham Loeb, about ‘Oumuamua, the mysterious interstellar object which passed through our solar system in 2017. ‘Oumuamua might – just might – be an alien light sail; it must be a pretty strange object in any case.

Rare Earth

4.75-4.50 billion years ago

A big day on Logarithmic History: the origin of our Solar System including planet Earth. First a note on what’s odd about our planetary system.

Two preceding posts wrestled with the Fermi Paradox: If the universe is full of advanced civilizations, why haven’t we seen any sign of them so far? One answer to the paradox might be that our solar system is wildly unusual, so that abodes for the evolution of complex life are rare. We can finally start to address this matter with some real evidence. According to the NASA exoplanet archive, we’ve now discovered 3587 exoplanets (planets outside our solar system; up from 3440 last year at this date), with many more unconfirmed candidates. This is enough to do some statistics, and indications are that our solar system might indeed be out of the ordinary.

grand-tack

Exoplanets smaller than Jupiter are overwhelmingly closer, mostly a lot closer, to their primary stars than Earth is to the Sun. And the same models of planet formation that have done a pretty good job predicting some of the wild variation we see in other systems – “Hot Jupiters” orbiting closer to their primaries than Mercury, “Super Earths” in between Earth and gas giants in size – don’t readily generate systems that look much like ours. One model that does seem to do a good job with our solar system involves something special, a Grand Tack, where Jupiter and Saturn are caught in an orbital resonance that carries them into the inner solar system and back out, shaking up inner-system planet formation in the process. Wild stuff, but the latest model is even wilder: at the beginning of planet formation, there may have been a generation of Super Earths in the inner solar system. The Grand Tack of Jupiter and Saturn would have sent these planets colliding into one another. The Super-Earths and most of the debris of these collisions would have fallen into the sun, but what the debris left would then have condensed into the unusual inner planets we know, Mercury, Venus, Earth, Mars. And Theia. (Theia? you ask. See the next post).

If this model holds up, the formation of our solar system takes on some of the flavor of mythology. This isn’t quite the old story about Chronos slaying Ouranos, and Zeus slaying Chronos. Instead, in the new story, two giants, Jupiter and Saturn, travel closer to the sun and set a generation of Titans – their like will not be there again – to fighting and destroying one another. Jupiter and Saturn depart, and a new generation is spawned from the wreckage. An unlikely sequence of events, but then our planet could be a very unlikely place. And all the more special for that.