How Many Loose Planets in the Milky Way?

Sky & Telescope ^ | February 29, 2012 | Monica Young

[SunkenCiv]

Researchers at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at Stanford University estimate that "nomad" planets, ejected from their home stellar system and now free-floating through the Milky Way, could outnumber stars by as many as 100,000 to 1. Earlier estimates were more like a handful to 1, though previous studies have only counted unbound planets more massive than Jupiter.

To estimate the number of unbound planets as small as Pluto that could be roaming the galaxy, Louis Strigari (KIPAC), lead author of the study, began with a basic rule of nature: where a few big objects are found, there are many more small, just like a few boulders may be surrounded by thousands of pebbles. Strigari and colleagues calculated the number of unbound planets by extrapolating from the small number detected so far by direct imaging and by gravitational microlensing.

Direct imaging has severe limits because planets are so faint. Microlensing offers more promise. It looks for the characteristic brightening and fading of a background star when an object, even one as wimpy as Pluto, passes nearly in front of it and bends its light slightly by gravity. So far, 24 planet-mass objects have been detected by microlensing -- 14 bound to their parent stars, 10 apparently not. Microlensing offers hope for detection of loose objects large and small even if they are completely dark, and even at great distances across the galaxy.

[Windflier]

To get a feeling for current events and your seemingly correct thoughts on asteroids, bing “asteroid 2011”. They are here now!

I fell asleep the other night with the TV on, and woke up in the wee hours. There was a show on about that very subject. It was so riveting, I watched the whole thing.

[Windflier]

Jupiter keeps disturbing the process.

I can picture that.

[Windflier]

Thanks for the chart.....I think - LOL.

At least the projections are in “miss” distances.

[bigheadfred]

Well, the one next February is SUPPOSED to miss us by a mere 13,000 miles. But it is only a baby. Something like 60 meters. My guess is if it does hit it will be D.C. The way they suck...

[SunkenCiv]

Planets formerly in orbit around stars that exploded, and planets ejected from their original systems by larger planets which are still there, and planets which formed from a diffuse mass insufficient to form an entire system are all good reasons rogue planets could exist.

[dfwgator]

Well I’ve heard Pluto puts out on the first date.

[SunkenCiv]

In the rush to bash America by demoting Pluto, the politicians calling themselves scientists created a very stupid problem:

Planet Definition Doesn’t Apply Beyond Solar System
By Ray Villard | Tue Jan 26, 2010 03:03 AM ET
http://www.freerepublic.com/focus/chat/2438897/posts
http://news.discovery.com/space/planet-definition-doesnt-apply-beyond-the-solar-system.html

[SunkenCiv]

And not just because of this. :’)

[SunkenCiv]

:’D

[SunkenCiv]

That about sums it up.

[SunkenCiv]

Thanks all.

http://en.wikipedia.org/wiki/Geothermal_gradient

[snip] Mean heat flow is 65 mW/m2 over continental crust and 101 mW/m2 over oceanic crust.[12] This is approximately 1/10 watt/square meter on average, (about 1/10,000 of solar irradiation,)... [/snip]

(1 percent of 1 percent)

[SunkenCiv]

The number is really only 100K times the number of planets in orbit around stars, a number currently less than 1000. Not for long of course, and our ability to detect extrasolar planets has ever-expanding limits, but...

[SunkenCiv]

Good idea, imho.

[SunkenCiv]

http://www.metaresearch.org/solar%20system/solar.asp

[yefragetuwrabrumuy]

I agree that there are many ways that rogue planets could be created during the 13.7 billion year life of the Milky Way. But there are many ways also that such rogue planets would be destroyed.

Unlike stars that are massive enough to maintain equilibrium as they rotate around the galaxy, with their planets subordinate to them, rogue planets are too small to maintain this equilibrium, so there are all sorts of outside forces that can act on them in destructive ways.

Since our own Sun circles the galaxy about every 250m years, imagine what would happen to it if it was out of balance even a tiny amount. Over such vast distances its orbit might change by many light years in a single rotation.

But compare that with a moving rogue planet that is not following that same rotational path and speed around the galaxy, but is off in its own direction. In the time it takes for a single rotation, it will end up nowhere near its previous location.

Instead the odds are that it will be hurling either towards the galactic center and destruction, or towards the tidal edges of the galaxy, which may likely deflect it back inside the galaxy.

In either case, the life span of a rogue planet would likely be a billion years or less.

[cripplecreek]

I know that at least a couple of the extra solar planets we’ve discovered are in retrograde orbits around their stars like WASP-17.

http://www.planetary.org/news/2009/0812_Scientists_Detect_WrongWay_Planet.html

[cripplecreek]

[bigheadfred]

The number is really only

This is one of those "As our circle of knowledge expands, so does the circumference of darkness surrounding it" moments.

[SunkenCiv]

The entire galaxy rotates, it’s analogous to leaves swirling around atop a whirlpool; this has no bearing on the maximum age of anything.

[pjd]

The definition doesn’t even work for planets in our own solar system. If Pluto is not a planet because it hasn’t cleared its orbit, then neither is Jupiter.

Jupiter’s orbit happens to contain two clusters of asteroids called Trojans. They lie 60 degrees ahead and 60 degrees behind Jupiter, right smack in Jupiter’s orbit. So this criteria also disqualifies Jupiter as a planet.

They clearly did not think this through!