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When worlds literally collide

It is theorized that our moon was formed when our planet was struck a glancing blow by an object roughly the size of Mars. The notion is known as the giant impact hypothesis. If such a large impact happened to our planet, what about the other planets. How common are giant impacts within our solar system? From the loss of the outer layers of Mercury, to the two-faced appearance of Mars, to the tipped over condition of Uranus, it seems that about half our planets were struck hard enough, by large enough objects, to have a major effect on how the planets appear today.

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Our big, beautiful moon

According to the rare Earth hypothesis, see episode 59, a large moon is needed for the development of complex life. Our moon isn’t the biggest moon in our solar system; but the moons that are bigger are orbiting much larger planets. Our moon is the largest as a percentage of the planet it orbits. Measured in that way, no other moon comes close. So how rare is such a large moon? Where did our big beautiful moon even come from?

Here are some articles about our moon and where it may have come from.

Where did the Moon come from?

Giant Moon-Forming Impact On Early Earth May Have Spawned Magma Ocean

New Moon-Formation Theory Also Raises Questions About Early Earth

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Why do big ones orbit so strangely?

Today, we consider all the large planets orbiting stars other than our sun, and their tendency to adopt eccentric orbits. The possible reasons include close encounters with other stars, interactions between the planets themselves, and different ways the large planets may have formed.

Here’s an article on the large size of Jupiter, and the core accretion model, versus disk instability as possible explanations.

How Jupiter Got Big

Here are several articles on computer simulations of planet to planet interaction, which could cause orbits to become eccentric, or planets to adopt a short-term nearly circular orbit, or even flip over.

Mystery Solved: How The Orbits Of Extrasolar Planets Became So Eccentric

The Architecture of Planetary Systems

Orbit Flips in Exoplanet Systems

Toward the end of the episode, I referenced a couple of earlier episodes. Here are links to said episodes.

Ep 55: The search for Planet 9

Ep 59: How to make a mind—part2

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Let’s keep it round

According to the “rare earth” hypothesis, see episode 59, one of the requirements for the development of complex life is a stable, and nearly circular orbit. If the orbit is too eccentric, the planet would be cooked during one part of its year, and frozen most of the rest of the time. That would mean the temperature extremes would be too much for complex life to arise. Since our solar system has planets with roughly circular orbits, it was assumed that such orbits were common. Once we started detecting planets around other stars, we found many planets whose orbits were anything but circular. As it happened, the methods first used to detect exoplanets, see episode 56, were much better at finding very large planets. More recent methods, see episode 57, have allowed us to look at planets that are closer in size to our own Earth. A recent study suggests that Earth sized planets are far more likely to adopt roughly circular orbits, a hopeful sign for the occurrence of complex life elsewhere in our Galaxy.

Here are a couple of articles about the study. Both of them say about the same thing, but each one includes slightly different details.

Circular orbits identified for small exoplanets

New discovery: small planets have circular orbits

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not quite a star, not quite a planet, not quite life

After a somewhat disjointed primer on organic chemistry, we talk about how the radiation of a protostar, bathing the protoplanetary disk, See the previous episode, can create the early chemical building blocks of life. This has happened in laboratory experiments, and the chemicals have been observed around young stars, in the material of comets, and in meteorites. This suggests that the very beginning of what would become life, happened during the very beginning of what would become our solar system, while we were not quite a star, not quite a planet and not quite life.

Here are a couple of articles about the laboratory experiments.

Amino Acids and Their Production during the Photolysis of Astrophysically relevant Ices

‘Building blocks for life’ may originate in space

Here are a couple of articles about sugar, detected in space!

Sugar Found In Space: A Sign of Life?

Space Sugar Discovered Around Sun-Like Star

Here’s an article on when a space craft examined material from a comet, discovering amino acids.

Building Blocks of Life Found in Comet’s Atmosphere

Burning through the atmosphere can get warm enough, but here’s an article that describes a meteorite that was heated much more, before it wiazed through the air and hit the surface of Earth. And yet, it still brought amino acids along for the ride.

Life’s Building Blocks Found on Surprising Meteorite

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The bumpy road to becoming a star

As a nebula collapses, there are forces which resist the collapse. Things like rotation, ionization and heat can overwhelm gravity and keep a given chunk of dust and gas from ever managing to start nuclear fusion and become a star. Those same forces, if the cloud manages to become a star, can help to form planets.

Here’s an article on how our solar system got the infusion of heavy elements needed to form rocky planets like our Earth.

A Step closer to understanding the birth of the sun

Here’s an article on an early stage collapsing cloud of dust and gas in the Eagle Nebula that has roughly the same amount of material as our solar system.

The Birth of the Sun

And here’s an article wherein a protostar was observed to increase in temperature, possibly from the in fall of material from its surrounding disk.

NASA Satellites Catch ‘Growth Spurt’ from Newborn Protostar

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Oh where o where did our sun come from?

In episode 59, we talked about the “rare Earth hypothesis.” According to that school of thought, when and where a star is born, and when and where it lives, matters. Our Sun apparently showed up after a very active epic of star formation. This may have protected our baby solar system from being bathed by too much radiation. In addition, we orbit our galaxy in an area that has enough heavy elements for making rocky planets, but not too close to the overly hot and violent center of the milky way. Only, that’s not where we started. In fact, nobody is quite certain where we started, or how we got where we are now.

Here’s a NASA press release about the evolution of spiral galaxies, and evidence that suggests that stars were being born, around 10,000,000,000 years ago, at roughly 30 times the rate they are being born now.

Our Sun Came Late to the Milky Way’s Star-Birth Party

Here’s an article wherein a candidate for the birth place of our sun was eliminated from consideration, leaving us all scratching our heads.

Mystery Deepens Over Where Sun Was Born

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How to make a mind—part2

What we need is our rare and wonderful Earth, and approximately 4.54 billion years. Of course, that begs the question. How did we end up with our Earth, and how important is it that a planet is like our Earth to create intelligent tool users? According to the “Rare Earth Hypothesis,” to get minds, many highly improbable things, things that happened to our planet, must take place. Otherwise you don’t even get to create anything as complicated as a flatworm, let alone intelligent tool users. Over the next several episodes, as we examine how our planet gave rise to our species, we’ll revisit this hypothesis and consider which of many factors are necessary, rare, or common in our cosmos.

Here are a couple of articles with further details on the “Rare Earth Hypothesis.”

The “Rare Earth” Hypothesis

How Rare Is the Earth?

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Can’t we just look at it?

In episode 56 and episode 57, we looked at a couple of methods of detecting planets that are orbiting around stars other than our own sun. These methods involve a good deal of analysis and inference. Today, we learn about how astronomers can look directly at a planet around another star, once the overwhelming glare of the star is blocked out.

Since this is the last episode on finding exoplanets, here are a couple of links to pages about finding them, should you desire to dig a bit deeper.

Exoplanet Exploration: Planets Beyond our Solar System

5 Ways to Find a Planet

Planet Hunters