How is planet age determined

[ErnieM]

Astronomers use the redshift of light from the observed galaxy in estimating the age of said galaxy. How do astronomers estimate the age of an observed planet? This is in reference to NASA's news release 03-0234 "Hubble Helps Confirm Oldest Know Planet. In part is says [quote]Long before our Sun and Earth ever existed, a Jupiter-sized planet formed around a sun-like star. Now, almost 13 billion years later, NASA's Hubble Space Telescope has precisely measured the mass of this farthest and oldest known planet.

The ancient planet has had a remarkable history, because it has wound up in an unlikely, rough neighborhood. It orbits a peculiar pair of burned-out stars in the crowded core of a globular star cluster. [/quote]
see http://www.nasa.gov/home/hqnews/2003/ju ... lanet.html for complete article.

[rstevenson]

I believe the simple answer is that planets form when the star they orbit forms. This planet and its star are in the M4 globular cluster. A GC forms all at once, so the age of the GC can be taken as the age of any individual star (and its planets) in the cluster. So the logic is, if the cluster is 13 billion years old, the star and its planet are too.

Rob

[Ann]

Like Rob said, if the planet is inside a globular cluster, then it almost certainly formed in there. What's more, it likely formed not much later than the stars inside the cluster, and the stars in most globulars are typically at least ten billion years old or more. To the best of our knowledge, all known Milky Way globulars stopped forming stars long before the Sun and the Earth were born. There is no reason to expect that planet formation continued long after star formation had ceased in the globulars.

So the planet in the globular cluster is assumed to be very old because the other denizens of the globular cluster, the stars, are very old.

Ann

[BMAONE23]

In most cases, likely > %99, the planets orbiting a star develop at the same time as their host star, the few exceptions being Rogue planets that form around other stars that were then subsequently expelled from their parent systems by gravitational interraction with larger siblings, sort of Kicked out of the nest. Then, at some point in the rogue planet's future, adopted by a later formed solar system family that it has wandered into. So unless the planet in question was an adopted former rogue, it should be as old as but not older than the parent star. Owing to the simple fact that at the initial ignition of solar fusion, the process of clearing out debris from the inner solar system regions that could be swept up into planets is initiated.

[ErnieM]

I believe the simple answer is that planets form when the star they orbit forms. This planet and its star are in the M4 globular cluster. A GC forms all at once, so the age of the GC can be taken as the age of any individual star (and its planets) in the cluster. So the logic is, if the cluster is 13 billion years old, the star and its planet are too.

Rob

Thank you Rob for this insight.

By the same logic, stars and planets in the same "local bubble" and nearby "Local Interstellar Clouds" are expected to be the same age and from the same supernovae (at least one per cloud) remnants and with very high probability of planets forming in similar processes and time frames. If Beta Canis Majoris and Antares are devoid of planets, then what caused our solar system to be so different? Would the answers using current data (in astronomical terms) closer to home give astronomers a better chance of locating earth-like planets in the habitable zones in less distant stars?

From Wikipedia, the free encyclopedia. Artist's conception of the Local Bubble (containing the Sun and Beta Canis Majoris) and the Loop I Bubble (containing Antares).

"The Local Bubble is a cavity in the interstellar medium (ISM) in the Orion Arm of the Milky Way which contains, among others, the Local Interstellar Cloud and G-cloud. It is at least 300 light years across and has a neutral-hydrogen density of about 0.05 atoms/cm3, or approximately one tenth of the average for the ISM in the Milky Way (0.5 atoms/cm3), and one sixth of the Local Interstellar Cloud (0.3 atoms/cm3). The hot diffuse gas in the Local Bubble emits X-rays.
The very sparse, hot gas of the Local Bubble is the result of supernovae that exploded within the past ten to twenty million years. It was once thought that the most likely candidate for the remains of this supernova was Geminga ("Gemini gamma-ray source"), a pulsar in the constellation Gemini. More recently, however, it has been suggested that multiple supernovae in subgroup B1 of the Pleiades moving group were more likely responsible. http://en.wikipedia.org/wiki/Local_Bubble

More about Local Interstellar Cloud: http://en.wikipedia.org/wiki/Local_interstellar_cloud"

[bystander]

The Solar System is not really thought to be a part of the Local Bubble, we're just passing through. There is less certainty about the Local Interstellar Cloud.

[Chris Peterson]

By the same logic, stars and planets in the same "local bubble" and nearby "Local Interstellar Clouds" are expected to be the same age and from the same supernovae (at least one per cloud) remnants and with very high probability of planets forming in similar processes and time frames. If Beta Canis Majoris and Antares are devoid of planets, then what caused our solar system to be so different?

Stars in the local bubble are not the same age, or even close. These bubbles are very transient affairs. The only place you find groupings of stars the same age is in clusters- globular clusters with very old stars, and open cluster or star forming nebulas, with very young stars. Any typical bit of our galaxy will likely contain a mix of stars that formed over a huge span of time, and in many widely distributed parts of the galaxy.

[Ann]

Bear in mind that all stars inside a globular cluster are more or less the same age, but the stars inside the Local Bubble are not the same age at all. Bear in mind that the Sun is more than four billion years old, whereas Beta Canis Majoris, a hot B-type star with a mass around 15 times that of the Sun, is certainly less than fifty million years old (and it could well be much younger). Antares, whose mass may be similar to that of Beta Canis Majoris, is also a stellar "toddler" (although a very big one).

But do Beta Canis Majoris and Antares lack planets? Perhaps they do, but it is equally probable that we have just failed to detect the planets. These two stars are very massive and extremely brilliant, and it isn't easy to detect any planet-mass bodies that may orbit them.

Ann

[rstevenson]

I see others have chimed in to answer your question Ernie, probably better than I could. I'd just like to add that some time ago, here on the forum, there was a post about scientists trying to find our companion stars - those stars that formed in the same cloud that our Solar System formed in - but having a hard time doing it. Ours was not a closely bound cluster, and those stars have all drifted away, following their own proper motions, over the past 4.6 billion years. We've gone around the Milky Way about 18 times since the Sun formed.

As for the clouds we're inside now - the Local Interstellar Cloud and the G-cloud - they are not remnants of the cloud we formed in. Rather they are remnants of stellar explosions of very massive (and therefore short-lived) stars, which weren't necessarily near us when they exploded; we're just passing through.

Rob

[ErnieM]

Bear in mind that all stars inside a globular cluster are more or less the same age, but the stars inside the Local Bubble are not the same age at all. Bear in mind that the Sun is more than four billion years old, whereas Beta Canis Majoris, a hot B-type star with a mass around 15 times that of the Sun, is certainly less than fifty million years old (and it could well be much younger). Antares, whose mass may be similar to that of Beta Canis Majoris, is also a stellar "toddler" (although a very big one).

But do Beta Canis Majoris and Antares lack planets? Perhaps they do, but it is equally probable that we have just failed to detect the planets. These two stars are very massive and extremely brilliant, and it isn't easy to detect any planet-mass bodies that may orbit them.

Ann

It is agreed that all stars and their planets form at roughly the same time. If any planets formed, they would be orbiting these two stars already. We have the technology. Mercury passing in front of the sun has been recorded using special filtering techniques blocking the sun's glare. I wonder if this technique has been tried at all. Watching these youngster planets (of any size) orbiting their stars is like sitting center front row seat in real time. How exciting and spectacular this would be! It would be like watching my great great grandson taking his first step. Doesn't anybodyelse think this is a worthwhile endeavor?

[rstevenson]

It is agreed that all stars and their planets form at roughly the same time. If any planets formed, they would be orbiting these two stars already. We have the technology. Mercury passing in front of the sun has been recorded using special filtering techniques blocking the sun's glare. I wonder if this technique has been tried at all. Watching these youngster planets (of any size) orbiting their stars is like sitting center front row seat in real time. How exciting and spectacular this would be! It would be like watching my great great grandson taking his first step. Doesn't anybodyelse think this is a worthwhile endeavor?

Scientists are expending a great deal of time, effort and money doing exactly that. What gave you the impression it's not happening?

Rob

[Chris Peterson]

It is agreed that all stars and their planets form at roughly the same time. If any planets formed, they would be orbiting these two stars already. We have the technology. Mercury passing in front of the sun has been recorded using special filtering techniques blocking the sun's glare. I wonder if this technique has been tried at all. Watching these youngster planets (of any size) orbiting their stars is like sitting center front row seat in real time. How exciting and spectacular this would be! It would be like watching my great great grandson taking his first step. Doesn't anybodyelse think this is a worthwhile endeavor?

We've looked at thousands of stars that way- it's how Kepler operates. But only a small fraction of stars with planets will be oriented nearly edge-on as is required to detect eclipses. For stars at other orientations, spectroscopic methods can be used, but they are generally less sensitive (especially to terrestrial planets far from their star) and more difficult to implement in a large scale survey.

[ErnieM]

It is agreed that all stars and their planets form at roughly the same time. If any planets formed, they would be orbiting these two stars already. We have the technology. Mercury passing in front of the sun has been recorded using special filtering techniques blocking the sun's glare. I wonder if this technique has been tried at all. Watching these youngster planets (of any size) orbiting their stars is like sitting center front row seat in real time. How exciting and spectacular this would be! It would be like watching my great great grandson taking his first step. Doesn't anybodyelse think this is a worthwhile endeavor?

Scientists are expending a great deal of time, effort and money doing exactly that. What gave you the impression it's not happening?

Rob

I did not see these two stars in the table of exoplanets. http://exoplanets.org/table
However on second look, I saw Alpha Centauri, same age and the closest star system to us, on the list.
Were these two young stars exempted from the survey (due to age) or were they surveyed and found not to have any planet?
Now I am wishing the approximate age and distance of the stars were included in the table of exoplanets. Life would have more time to evolve and develop on an older planet within the habitable zone.

[Chris Peterson]

I did not see these two stars in the table of exoplanets. http://exoplanets.org/table
However on second look, I saw Alpha Centauri, same age and the closest star system to us, on the list.
Were these two young stars exempted from the survey (due to age) or were they surveyed and found not to have any planet?
Now I am wishing the approximate age and distance of the stars were included in the table of exoplanets. Life would have more time to evolve and develop on an older planet within the habitable zone.

Statistically, it is unlikely that any planets around a particular star could be detected by the eclipse method.

If Earth is an example, it doesn't take life very long to form. Simple life has been here a very long time. Of course, it is likely that many planets have a fairly short period where life exists, such as may be the case with Mars.

[ErnieM]

I did not see these two stars in the table of exoplanets. http://exoplanets.org/table
However on second look, I saw Alpha Centauri, same age and the closest star system to us, on the list.
Were these two young stars exempted from the survey (due to age) or were they surveyed and found not to have any planet?
Now I am wishing the approximate age and distance of the stars were included in the table of exoplanets. Life would have more time to evolve and develop on an older planet within the habitable zone.

Statistically, it is unlikely that any planets around a particular star could be detected by the eclipse method.

If Earth is an example, it doesn't take life very long to form. Simple life has been here a very long time. Of course, it is likely that many planets have a fairly short period where life exists, such as may be the case with Mars.

Thank you all for your comments.

[ErnieM]

I see others have chimed in to answer your question Ernie, probably better than I could. I'd just like to add that some time ago, here on the forum, there was a post about scientists trying to find our companion stars - those stars that formed in the same cloud that our Solar System formed in - but having a hard time doing it. Ours was not a closely bound cluster, and those stars have all drifted away, following their own proper motions, over the past 4.6 billion years. We've gone around the Milky Way about 18 times since the Sun formed.

Rob

I wonder how much of the past "little ice ages" were direct results from the Earth's orbital location? Could these be some of the things recorded and visible in different layers of Australian rocks and sandstones? see Nova - Australia - First 4 Billion Years. http://www.pbs.org/wgbh/nova/earth/aust ... years.html

Of all the continents on Earth, none preserves a more spectacular story of our planet's origins than Australia. NOVA's four-part "Australia's First 4 Billion Years" takes viewers on a rollicking adventure from the birth of the Earth to the emergence of the world we know today. With help from host and scientist Richard Smith, we meet titanic dinosaurs and giant
Call this blending astronomy with geology a huge wishful thinking on my part.

[BMAONE23]

Can't say much about Little Ice Ages (similar to the one ended a few hundres years ago and caused much famine in the population center of the time and deaths in the millions) but deep ice ages occur at almost regular 120,000 year intervals over the last 420,000 years per the Vostoc Ice Core data

Click to view full size image

Reconstructed global temperature over the past 420,000 years based on the Vostok ice core from the Antarctica (Petit et al. 2001). The record spans over four glacial periods and five interglacials, including the present. The horizontal line indicates the modern temperature. The red square to the right indicates the current holocene interglacial period.


The image above shows a reconstruction of global temperature derived from ice core analysis from the Vostoc Lake Core from Antarctica. The current interglacial period known as the Holocene, is depicetd as a red square on the right side of the graphic. The prior four interglacial periods are seen at approximately 120,000, 280,000, 320,000 and 410,000 years before presant, with much longer glacial periods in between. All four prior interglacial periods though seem to be 1 to 3^oC warmer than currnet temperatures.

Warm periods that follow the Deep Freezes over the last 1/2 million years typically last about 12,000 years while the following freezes last over 100,000 years and produce global average temperatures that are over 10c lower than today. In fact, according to the Vostoc Ice core
as reported by "Petit, J.R., et al., 2001. Vostok Ice Core Data for 420,000 Years. IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series #2001-076. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA."
Prior interglacial events have been much warmer than the current Holocene temperatures

[Ann]

That diagram of the temperature variations on the Earth over the last 420,000 years is really fascinating, BMAONE23. I note that each ice age seems to have been preceded by a sharp increase in the mean temperature of the Earth. At present, we appear to be at a stage where the Earth is getting warmer and warmer for each year. I have to wonder if we are going to reach a peak and then plunge into the next ice age.

Ann

[ErnieM]

Click to view full size image

Reconstructed global temperature over the past 420,000 years based on the Vostok ice core from the Antarctica (Petit et al. 2001). The record spans over four glacial periods and five interglacials, including the present. The horizontal line indicates the modern temperature. The red square to the right indicates the current holocene interglacial period.


The image above shows a reconstruction of global temperature derived from ice core analysis from the Vostoc Lake Core from Antarctica. The current interglacial period known as the Holocene, is depicetd as a red square on the right side of the graphic. The prior four interglacial periods are seen at approximately 120,000, 280,000, 320,000 and 410,000 years before presant, with much longer glacial periods in between. All four prior interglacial periods though seem to be 1 to 3^oC warmer than currnet temperatures.

Warm periods that follow the Deep Freezes over the last 1/2 million years typically last about 12,000 years while the following freezes last over 100,000 years and produce global average temperatures that are over 10c lower than today. In fact, according to the Vostoc Ice core
as reported by "Petit, J.R., et al., 2001. Vostok Ice Core Data for 420,000 Years. IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series #2001-076. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA."
Prior interglacial events have been much warmer than the current Holocene temperatures

From PhysicalGeography.net (chapter 10) on Glacieal Processes - Growth of Glaciers

Growth of Glaciers

Ice that makes up glaciers originally fell on its surface as snow. To become ice, this snow underwent modifications that caused it to become more compact and dense. Glacial ice has a density of about 850 kilograms per cubic meter. The density of snow ranges from about 50 to 300 kilograms per cubic meter (the density of fresh water is approximately 1000 kilograms per cubic meter). After the snow falls, the crystals can be reduced by the effects of melting and sublimation. Scientists call this process ablation. For most glaciers, ablation is a phenomena dominant in the summer months. The snow also undergoes physical compaction through melting and refreezing. At first, these processes cause the original snowflakes to be transformed into small round crystals. This partly melted, compressed snow is called névé. Névé has a density exceeding 500 kilograms per cubic meter. If the névé survives the ablation that occurs during the summer months it is called firn. When this process happens year after year, a number of layers of firn can accumulate. Accumulation then causes a further increase in density, modifying the firn into glacier ice, as the lower layers of firn are compressed by the weight of the layers above. On average, the transformation of névé into glacial ice may take 25 to 100 years.

My opinion: During consecutive cold years, one can presume that glaciers' growth were faster and more consistent and firns formed one on top of the other. Less so during prolonged warm periods.

Above a certain temperatures, even top layers of firn may have melted away.

How do scientists account for these "missing layers" when "reading" temperature and age of the contiguous layers of the ice cores? In other words, where does one get the "temperatures and duration of the warm years readings" of the missing firns.

Could the "red" spikes be representing only the "leading and trailing" data for the "missing years of warm periods" in the ice cores and that thus the core samples may be much "older" 1/2 million years?

[BMAONE23]

Here are some interesting Vostok Lake facts
From the WIKI Vostok Station article
Vostok is the World Pole of Cold. During the long winter, temperatures average about −65 °C (−85 °F); in the brief summer, about −30 °C (−22 °F).

The lowest reliably measured temperature on Earth of −89.2 °C (−128.6 °F) was in Vostok on 21 July 1983 (See List of weather records), beating the station's former record of -88.3°C (-126.9°F) on 24 August 1960. Lower temperatures occurred higher up towards the summit of the ice sheet as temperature decreases with height along the surface.

Though unconfirmed, it has been reported that Vostok reached the temperature of −91 °C (−132 °F) during the winter of 1997.

The warmest recorded temperature at Vostok is −12.2 °C (10.0 °F), which occurred on 11 January 2002.

The coldest month was August 1987 with a mean temperature of −75.4 °C (−103.7 °F) and the warmest month was December 1989 with mean of −28 °C (−18 °F).

In addition to the extremely cold temperatures, other factors make Vostok one of the most difficult places on Earth for human habitation:
An almost complete lack of moisture in the air.
An average windspeed of 5 m/s (18 km/h) (11 mph), sometimes rising to as high as 27 m/s (97 km/h)(60 mph).
A lack of oxygen because of its high elevation at 3,488 meters (11,444 ft).
A higher ionization of the air.
A polar night that lasts approximately 130 days, from mid April to late August,[14] including 80 continuous days of civil polar night (i.e. too dark to read, during which the Sun is more than 6 degrees below the horizon.)

There has never been a recorded temperature measurement above freezing at the Vostok Station since it was manned in 1959 so it is unlikely that the firns of any years snow deposit could have melted away. However, given the extremely low relative humidity and average wind speed, some sublimation might be possible

[Beyond]

VOSTOK = BRRRRR

Cold_Smiley.jpg (3.75 KiB) Viewed 2871 times

emo62.gif (4.15 KiB) Viewed 2871 times

Cold_Smiley.jpg (3.75 KiB) Viewed 2871 times

[ErnieM]

That diagram of the temperature variations on the Earth over the last 420,000 years is really fascinating, BMAONE23. I note that each ice age seems to have been preceded by a sharp increase in the mean temperature of the Earth. At present, we appear to be at a stage where the Earth is getting warmer and warmer for each year. I have to wonder if we are going to reach a peak and then plunge into the next ice age.

Ann

From Science Daily - Greenland Ice Cores Reveal Warmer Climate In The Past

The climate graph shows the temperature from the previous warm interglacial period, the Eemian (left) throughout the entire ice age to present time. The blue colours indicate ice from a cold period, the red colour is ice from a warm period and yellow and green is from the climate period in between. The new results show that during the Eemian period 130,000 to 115,000 thousand years ago the climate in Greenland was around 8 degrees C warmer than today. The top shows a graph of ice sheet surface temperature and altitude. In the beginning of the Eemian, 128,000 years ago, the ice sheet in northwest Greenland was 200 meters higher than today, but during the warm Eemian period the ice mass regressed, so 122,000 years before now the surface had sunk to a level of 130 meters below the current level. During the rest of the Eemian the ice sheet remained stable at the same level with an ice thickness of 2,400 meters. (Credit: Niels Bohr Institute)

---

Jan. 23, 2013 — In the period between 130,000 and 115,000 years ago, Earth's climate was warmer than today. But how much warmer was it and what did the warming do to global sea levels? -- as we face global warming in the future, the answer to these questions is becoming very important. New research from the NEEM ice core drilling project in Greenland shows that the period was warmer than previously thought. The international research project is led by researchers from the Niels Bohr Institute and the very important results are published in the scientific journal, Nature.
In the last millions years Earth's climate has alternated between ice ages lasting about 100,000 years and interglacial periods of 10,000 to 15,000 years. The new results from the NEEM ice core drilling project in northwest Greenland, led by the Niels Bohr Institute at the University of Copenhagen show that the climate in Greenland was around 8 degrees C warmer than today during the last interglacial period, the Eemian period, 130,000 to 115,000 thousand years ago.
"Even though the warm Eemian period was a period when the oceans were four to eight meters higher than today, the ice sheet in northwest Greenland was only a few hundred meters lower than the current level, which indicates that the contribution from the Greenland ice sheet was less than half the total sea-level rise during that period," says Dorthe Dahl-Jensen, Professor at the Niels Bohr Institute, University of Copenhagen, and leader of the NEEM-project.
Past reveals knowledge about the climate
The North Greenland Eemian Ice Drilling project or NEEM, led by the Niels Bohr Institute, is an international project with participants from 14 countries. After four years of deep drilling, the team has drilled ice cores through the more than 2.5 kilometer thick ice sheet. The ice is a stack of layer upon layer of annual snow fall which never melts away, and as the layers gradually sink, the snow is compresses into ice. This gives thousands of annual ice layers that, like tree rings, can tell us about variations in past climate from year to year.
The ice cores are examined in laboratories with a series of analyses that reveal past climate. The content of the heavy oxygen isotope O18 in the ice cores tells us about the temperature in clouds when the snow fell, and thus of the climate of the past. The air bubbles in the ice are also examined. The air bubbles are samples of the ancient atmosphere encased in the ice and they provide knowledge about the air composition of the atmosphere during past climates.
Past global warming
The researchers have obtained the first complete ice core record from the entire previous interglacial period, the Eemian, and with the detailed studies have been able to recreate the annual temperatures -- almost 130,000 years back in time.
"It is a great achievement for science to collect and combine so many measurements on the ice core and reconstruct past climate history. The new findings show higher temperatures in northern Greenland during the Eemian than current climate models have estimated," says Professor Dorthe Dahl-Jensen, Niels Bohr Institute.
Intense melting on the surface
During the warm Eemian period, there was intense surface melting that can be seen in the ice core as layers of refrozen meltwater. Meltwater from the surface had penetrated down into the underlying snow, where it once again froze into ice. Such surface melting has occurred very rarely in the last 5,000 years, but the team observed such a melting during the summer of 2012 when they were in Greenland.
"We were completely shocked by the warm surface temperatures at the NEEM camp in July 2012," says Professor Dorthe Dahl-Jensen. "It was even raining and just like in the Eemian, the meltwater formed refrozen layers of ice under the surface. Although it was an extreme event the current warming over Greenland makes surface melting more likely and the warming that is predicted to occur over the next 50-100 years will potentially have Eemian-like climatic conditions," she believes.
Good news and bad news
During the warm Eemian period there was increased melting at the edge of the ice sheet and the dynamic flow of the entire ice mass caused the ice sheet to lose mass and it was reduced in height. The ice mass was shrinking at a very high rate of 6 cm per year. But despite the warm temperatures, the ice sheet did not disappear and the research team estimates that the volume of the ice sheet was not reduced by more than 25 percent during the warmest 6,000 years of the Eemian.
"The good news from this study is that the Greenland ice sheet is not as sensitive to temperature increases and to ice melting and running out to sea in warm climate periods like the Eemian,as we thought," explains Dorthe Dahl-Jensen and adds that the bad news is that if Greenland's ice did not disappear during the Eemian then Antarctica must be responsible for a significant portion of the 4-8 meter rise in sea levels that we know occurred during the Eemian.
This new knowledge about past warm climates may help to clarify what is in store for us now that we are facing a global warming.

What is causing the 120-130 thousand years ice age cycles and the 10-14 thousand years interglacial periods?
Is the source or sources internal or external to our solar system? If "gravitational fluctuation" plays a major role, how and where is it coming from? Could it be the solar systems travel in and out of the cloud or the up and down travel thru the galactic plane, i.e., the closer we are to the plane, the warmer the temperature gets?

Whatever the mysterious force(s) is, it must be cyclic and strong enough to reduce the Sun's heat or block it from reaching Earth.

[Chris Peterson]

What is causing the 120-130 thousand years ice age cycles and the 10-14 thousand years interglacial periods?
Is the source or sources internal or external to our solar system? If "gravitational fluctuation" plays a major role, how and where is it coming from? Could it be the solar systems travel in and out of the cloud or the up and down travel thru the galactic plane, i.e., the closer we are to the plane, the warmer the temperature gets?

The primary mechanism is orbital forcing- cyclic changes in Earth's orbit around the Sun (e.g. axial tilt and eccentricity). There is absolutely nothing to suggest than our location with respect to the galactic plane plays any role.

[ErnieM]

The primary mechanism is orbital forcing- cyclic changes in Earth's orbit around the Sun (e.g. axial tilt and eccentricity). There is absolutely nothing to suggest than our location with respect to the galactic plane plays any role.

More about what Chris wrote:

From Wikipedia - Milankovitch Cycles

.... Currently the Earth is tilted at 23.44 degrees from its orbital plane, roughly halfway between its extreme values. The tilt is in the decreasing phase of its cycle, and will reach its minimum value around the year 11,800 CE ; the last maximum was reached in 8,700 BCE. This trend, by itself, tends to make winters warmer and summers colder with an overall cooling trend leading to an ice age, but the 20th century instrumental temperature record shows a sudden rise in global temperatures and a concurring glacial melt has led the scientific community to attribute recent changes to greenhouse gas emissions.
.....

In addition, the orbital ellipse itself precesses in space, primarily as a result of interactions with Jupiter and Saturn. Smaller contributions are also made by the sun's oblateness and by the effects of General Relativity that are well known for Mercury. The total orbital precession is in the same sense to the gyroscopic motion of the axis of rotation, shortening the period of the precession of the equinoxes with respect to the perihelion from 25,771.5 to ~21,636 years. Apsidal precession occurs in the plane of the Ecliptic and alters the orientation of the Earth's orbit relative to the Ecliptic. In combination with changes to the eccentricity it alters the length of the seasons.
.....
The amount of solar radiation (insolation) in the Northern Hemisphere at 65° N seems to be related to occurrence of an ice age. Astronomical calculations show that 65° N summer insolation should increase gradually over the next 25,000 years.[18] A regime of eccentricity lower than the current value will last for about the next 100,000 years. Changes in northern hemisphere summer insolation will be dominated by changes in obliquity ε. No declines in 65° N summer insolation, sufficient to cause a glacial period, are expected in the next 50,000 years.

An often-cited 1980 study by Imbrie and Imbrie determined that, "Ignoring anthropogenic and other possible sources of variation acting at frequencies higher than one cycle per 19,000 years, this model predicts that the long-term cooling trend that began some 6,000 years ago will continue for the next 23,000 years."[19]

More recent work by Berger and Loutre suggests that the current warm climate may last another 50,000 years.

see http://en.wikipedia.org/wiki/Milankovit ... ar_problem for complete article

From Universe Today - Past Climate Change Cannot Be Tied To Earth Passing Through The Galactic Plane

Although previous work found a correlation between the 140-Myr climate cycle on Earth and the intersection with spiral arms (Shaviv 2003, Shaviv & Veizer 2003, Svensmark 2006), with new data on the structure of the galaxy, this correlation disappears.
,,,,,,,,,,
We conclude that based on this new data there is no evidence to suggest any correlation between the transit
of our solar system through the spiral arms of our galaxy and the terrestrial climate.

see http://arxiv.org/ftp/arxiv/papers/0906/0906.2777.pdf for complete article.

Thank you Chris.

ErnieM