The Solar System and Beyond
Solar System Debris
Trojan asteroids orbit along Jupiter’s orbit, sitting at the Lagrangian 4 and 5 points, 60 degrees in front of and behind Jupiter. Apollo asteroids cross Earth’s orbit. Amor asteroids only cross the orbit of Mars.
Astronomers measured Dactyl’s orbit around asteroid Ida, and used Newton’s law of gravity to estimate the mass.
The Jupiter probe Galileo provided us with the first close-up views of asteroids.
The Kirkwood gaps are gaps in the chart measuring the semimajor axis of the asteroids from the asteroid belt. They occur at points of resonance with Jupiter’s orbit. This is because Jupiter affects the asteroid’s orbits.
Some asteroids are not found in the asteroid belt. Some have such eccentric orbits, that they cross clear into Earth’s orbit. Some only cross into Mars’s orbit. There are some in the Lagrangian points of Jupiter.
Most comets in the solar system reside in the Oort cloud.
Experts now consider cometary nuclei to be largely made of dust particles trapped within a mixture of methane, ammonia, carbon dioxide, and ordinary water ice.
We know what comets are made of due to the Stardust and Deep Impact missions.
Possible fates of comets: stargrazer comets go boom in the Sun. Some breakup and become meteoroids. If a comet is caught in a strong enough gravitational pull, such as Jupiter’s, that gives it a strong push, it can be ejected from the solar system.
Comets may change their orbit either due to gravity from another body, such as a planet (Jupiter for example) perturbing the orbit, or possibly from the jets of material that come from the comets themselves. These can act as rocket jets, changing the rotation rate, and slightly changing the orbit of the comet.
The number of planets in the solar system decreased because a bunch of astronomers, who are prejudice against small planets, decided that Pluto isn’t massive enough to be a planet, and came up with a bogus rule stating a planet must “clear it’s orbit”, which Pluto doesn’t as it orbits on the inner edge of the Kuiper belt. EDITORIAL: The problem with this, however, is that Neptune also has Kupier belt objects in its orbit. It doesn’t clear it of all objects. In addition, the asteroids that stay in Jupiter’s Lagrangian points do not clear the orbit – they stay in the orbit. Therefore, Neptune and Jupiter aren’t planets either per this definition.
A meteor is the streak of light (also called a shooting star) in the Earth’s sky as a piece of debris (possibly a meteoroid) streaks across the Earth’s atmosphere. A meteoroid is a chunk of interplanetary debris prior to encountering Earth’s atmosphere. A meteorite is any part of a meteoroid that survives all the way to the Earth’s surface.
Radioactive dating shows that meteorites are very old – about 4.4 to 4.6 billion years old. Since these are left over material from the formation of the solar system, that means that the age of the solar system is about this old as well.
Most asteroids come from the asteroid belt. Because of this, they lie within the plane of the ecliptic. Long period comets, however, originally formed between Jupiter and Neptune, but Jupiter was a bully and kicked them out into space in all directions. This formed the Oort cloud, and is why they can come from all directions.
The explosion in 1908 in Siberia that had the same energy as a 10 megaton nuclear detonation was caused by only a 30 m object. If a 10 km diameter meteorite hit Earth, it would be game over.
Asteroids, meteoroids, and comets are remnants of the early solar system
Most asteroids move on eccentric orbits.
Kirkwood gaps are spacings of orbital semimajor axes of asteroids in the asteroid belt, produced by dynamical resonances with nearby planets, especially Jupiter.
Some comets travel in orbits that take them up to 50,000 AU from the Sun.
Cometary orbits from the Oort cloud can come in 90 degrees from the ecliptic – from all directions.
The Oort cloud is where all of the long period comets come from.
Eris is the largest known member of the class of Kuiper belt objects.
Some meteorites found on Earth originally came from the Moon or Mars.
Comets are the sources of many meteor showers.
Astronomers have succeeded in tracing the orbits of some meteorites back into the asteroid belt.
The asteroid groups with the smallest perihelion distances also tend to have orbits that are most eccentric.
Spectorscopic studies indicate that the majority of asteroids contain large fractions of carbon.
Trojan asteroids orbiting at Jupiter’s Lagrangian points are located behind and in front of Jupiter, sharing its orbit.
Kuiper belt objects are not regarded as planets because their masses are too low to clear other bodies from their orbital paths.
A meteorite is a piece of interplanetary debris that survives the trip to the surface.
The Formation of Planetary Systems
Things that may have happened after the initial state of the solar system was established, such as Mercury’s 3:2 spin, Venus’s runaway greenhouse effect, the Moon’s synchronous rotation. We don’t have to explain these because there are evolutionary explanations.
In the evolutionary theories, changes occur gradually. In the catastrophic theories, changes occur suddenly as the result of one-time events such as violent collisions.
Basic features of the condensation theory: (starts with nebular theory, with a cloud contracting, and spinning). Dust rains help cool warm matter and act as condensation nuclei which act as glue for interstellar material to create planetesimals through accretion.
Two ways which the Jovian planets may have formed:
(1) Core-accretion theory: The Jovian planets formed when icy protoplanetary cores became massive enough to capture gas directly from the solar nebula.
(2) Gravitational instability theory: The Jovian planets formed directly from the solar nebula via instabilities in the gas leading to gravitational contraction.
The temperature structure of the solar nebula determined the planetary compositions because the temperature in the inner solar system was too high for light gases to freeze out and accumulate as part of the terrestrial planetesimals. Hence the terrestrial planets did not form with light compounds. In the outer solar system, the temperature was low enough to allow frozen gases to form and to become part of the Jovian planetesimals. These planetesimals grew large enough to accrete and hold hydrogen gas left over in the solar nebula, which gave them their high levels of hydrogen.
Asteroids and comets resulted from the process of fragmentation.
At any given location, the only materials to condense out were those able to survive the temperature there. In the innermost regions, around Mercury's present orbit, only metallic grains could form. It was simply too hot for anything else to exist. A little farther out, at about 1 A.U., it was possible for rocky, silicate grains to form, too. Beyond about 3 or 4 A.U., water ice could exist, and so on, with the condensation of more and more material possible at greater and greater distances from the Sun. The composition of the material that could condense out at any given radius would ultimately determine the types of planets that formed there.
The temperature in the inner part of the solar nebula was too high to allow frozen gases to form. The terrestrial planets therefore formed without water or other light compounds. However, water came to the Earth later in the form of icy comets deflected by Jupiter into the inner solar system.
Uranus and Neptune, in particular, probably moved outward as the icy planetesimals were cleared from the solar system due to gravitational interactions. Neptune captured Pluto and other plutinos and entered into a 3:2 resonance with Pluto and the plutinos. Jupiter is believed to have move inward and Saturn moved outward, but not by much. All of this migration occurred after all the outer giant planets moved inward due to friction with the solar nebula.
Plutions are Kuiper belt objects in a 3:2 resonance with Neptune (such as Pluto). The leading explanation is that as Neptune’s orbit slowly moved outward, the radius corresponding to a 3:2 resonance also swept outward. The process was slow enough that many of the planetesimals on near-resonant orbits were captured into resonance.
Over a period of hundreds of millions of years and after repeated "gravity assists" from the giant planets, many of the interplanetary fragments in the outer solar system were flung into orbits taking them far from the Sun. Astronomers believe that those fragments now make up the Oort Cloud, whose members occasionally visit the inner solar system as comets.
Extra-solar planets can be found in any of three ways. The first, and by far the most common, is the Doppler Shift method; this precisely measures the color of the star, and the minute periodic shifts towards red and blue caused by the tug of the unseen planet. A second method that is more preferable but is much less likely to work is the Transit Method. This only works if the star and planet line up directly along the line-of-sight to Earth. This will then cause the planet to periodically pass in front of the star and for the star to pass in front of the planet, which results in dimming of the total light output of the system. The third way that had never worked until 2004 is direct imaging, where telescopes are used to directly resolve the planet around its companion star.
The solar systems that we have observed thus far include hot Jupiters, which are very large (some larger than Jupiter by as much as 15 times), close to their star, with very eccentric orbits.
Observed extrasolar planets do not imply that Earth-like planets are rare. This is the selection effect: lightweight or distant planets don’t produce large enough velocity fluctuations for them to be easily detected.
Moons usually revolve in the same direction as their parent planet.
The asteroids were not recently formed from the collision and breakup of an object orbiting within the asteroid belt. They are leftover rocky material that never formed into planets.
The largest number of leftover planetesimals beyond about 5 AU were destined to become the jovian planets.
Giant collisions are the current explanation for the slow retrograde of Venus.
Random collisions can explain many of the odd properties found in the solar system.
he ejection of the comets from the outer solar system did not cause all four giant planets to move inward toward the Sun. It’s just the opposite: the inward migration ejected the comets to the Oort cloud.
Astronomers can detect extrasolar planets by observing the spectra of their parent stars.
Most of the planets observed so far have masses comparable to Jupiter, but their orbits are generally much smaller – less than a few AU across.
Astronomers have theoretical explanations for the hot Jupiters observed orbiting some other stars. Isolated or very massive Jupiters are expected to be in the hot orbits.
If interstellar dust did not exist, then the terrestrial planets would not have formed.
Water on Earth was transported there by comets.
Using the standard model of planetary system formation, scientists invoke catastrophic events to explain why Uranus has an extremely tilted rotation axis.
So far, most of the planets discovered orbiting other stars have orbits that approach within 1 AU of the parent star.
Life in the Universe
The hypothesis that simple chemical compounds in the ancient atmosphere and ocean combined by natural and spontaneous chemical reactions to form larger, more complex substances that eventually lead to the origin of life and the start of biological evolution
The Urey-Miller experiment was the first experimental verification that complex molecules could have evolved naturally from simpler ingredients found on the primitive Earth. It created amino acids by taking a “primordial soup” of water, methane, carbon dioxide and ammonia and passing an electrical discharge (lightning) through the gas.
Other than the Urey-Miller, scientists have also taken amino acids and fused them with heat to form protein like blobs.
The basic ingredients from which biological molecules formed on Earth is water, methane, carbon dioxide, and ammonia which make more complex materials called amino acids and nucleotide bases.
Some scientists think life originated in space because interstellar molecular clouds are known to contain complex molecules, and a small fraction of meteorites contain organic compounds.
Fossil records chronicle how life on Earth became widespread and diversified over the course of time.
Language played an important part in evolution. It allowed for individuals to signal one another while hunting for food or seeking protection. Experience could be passed down from generation to generation.
There is no conclusive evidence if Mars did or did not have life at one time. Viking could not find any evidence. However, meteorites found in Antarctica from Mars have found fossilized bacteria, indicating that life of some sort, possibly bacterial, did exist on Mars.
"Life as we know it" is generally taken to mean carbon-based life that originated in a liquid water environment—in other words, life on Earth. Some scientists have pointed out that the abundant element silicon has chemical properties somewhat similar to those of carbon and have suggested it as a possible alternative to carbon as the basis for living organisms. Ammonia (made of the common elements hydrogen and nitrogen) is sometimes put forward as a possible liquid medium in which life might develop, at least on a planet cold enough for ammonia to exist in the liquid state. Together or separately, these alternatives would surely give rise to organisms with radically different biochemistries from those we know on Earth. Conceivably, we might have difficulty even recognizing these organisms as alive.
Of the factors of the Drake equation, none are really known with any degree of certainty. Rate of Star Formation is probably the only one we have any idea of. The average lifetime of a technological civilization is the least known, as we can only guess since ours has been around for a whopping 100 years.
From the viewpoint of a distant observer, the spinning Earth emits a bright flash of radio radiation every few hours. In fact, Earth is now a more intense radio emitter than the Sun. The flashes result from the periodic rising and setting of hundreds of FM radio stations and television transmitters). Each station broadcasts mostly parallel to Earth's surface, sending a great "sheet" of electromagnetic radiation into interstellar space. Because the great majority of these transmitters are clustered in the eastern United States and western Europe, a distant observer would detect blasts of radiation from Earth as our planet rotates each day.
Do you think that advanced civilizations would continue to emit large amounts of radio energy as they evolved? Radio energy is currently the most well known and fastest form of communication. However, at one time, this was thought of with smoke signals. Therefore, it is only logical to believe that a more advanced civilization would find an even better way to communicate. Imagine being able to communicate at the speed of thought!
Electromagnetic radiation is the fastest known means of transferring information from one place to another.
The water hole is the area between 18 and 21 cm where there are the fewest naturally occurring wavelengths, and astronomers believe this is the best area to search for alien radio signals.
Due to the fact that we need to be able to communicate with alien civilizations as quickly as possible, we need to focus on those closest. The closest star is over 4 light years away. That means if we sent a signal to them, it would take four years for them to get it, and another four years for us to get the reply. With 8 to 9 years to send a message and get a reply, a conversation will take a long time. Therefore, I’d concentrate on close stars, that were of the type most likely to harbor life(such as F, G or K types. Those above F would not have large enough habitable zones, and those under K wouldn’t be around long enough for civilizations to evolve.
The definition of life requires something to be able to react to their environment, grow by taking in nourishment, reproduce, and have the capacity to evolve.
Organic molecules do not exist only on Earth, they are all through the universe.
Laboratory experiments have not created living cells from non-biological material.
Dinosaurs lived on Earth for a thousand times longer than human civilization has existed to date.
The Viking landers did not find any evidence of life on Mars.
We have no direct evidence for Earth-like planets orbiting other stars.
Our civilization has already launched probes into interstellar space and broadcast our presence to our neighbors.
The Drake equation estimates the probability of intelligent life in the Galaxy.
Planets in binary-star systems are not considered habitable, because the planetary orbits are usually unstable.
The development of life and intelligence on Earth are extremely unlikely if chance is the only evolutionary factor involved.
The “assumptions of mediocrity” Suggest that life should be common throughout the cosmos.
The chemical elements that form the basic molecules needed for life are found commonly throughout the cosmos.
The discovery of bacteria on another planet would be an important discovery because bacteria are the lowest form of life known to exist.
The strongest radio-wavelength emitter in the solar system is human-made signals from Earth.