Free-floating planets may be born free

August 19, 2013, Chalmers University of Technology
Astronomers have found that tiny, round, dark clouds called globulettes have the right characteristics to form free-floating planets. The graph shows the spectrum of one of the globulettes taken at the 20-metre telescope at Onsala Space Observatory. Radio waves from molecules of carbon monoxide (13CO) give information on the mass and structure of these clouds. ESO/M. Mäkelä

Tiny, round, cold clouds in space have all the right characteristics to form planets with no parent star. New observations, made with Chalmers University of Technology telescopes, show that not all free-floating planets were thrown out of existing planetary systems. They can also be born free.

Previous research has shown that there may be as many as 200 billion free-floating planets in our galaxy, the Milky Way. Until now scientists have believed that such "rogue planets", which don't orbit around a star, must have been ejected from existing .

New observations of tiny dark clouds in space point out another possibility: that some free-floating planets formed on their own.

A team of astronomers from Sweden and Finland used several telescopes to observe the Rosette Nebula, a huge cloud of gas and dust 4600 light years from Earth in the constellation Monoceros (the Unicorn).

They collected observations in with the 20-metre telescope at Onsala Space Observatory in Sweden, in submillimetre waves with APEX in Chile, and in with the New Technology Telescope (NTT) at ESO's La Silla Observatory in Chile.

"The Rosette Nebula is home to more than a hundred of these tiny clouds – we call them globulettes", says Gösta Gahm, astronomer at Stockholm University, who led the project.

"They are very small, each with diameter less than 50 times the distance between the Sun and Neptune. Previously we were able to estimate that most of them are of , less than 13 times Jupiter's mass. Now we have much more reliable measures of mass and density for a large number of these objects, and we have also precisely measured how fast they are moving relative to their environment", he says.

"We found that the globulettes are very dense and compact, and many of them have very dense cores. That tells us that many of them will collapse under their own weight and form free-floating planets. The most massive of them can form so-called brown dwarfs", says team member Carina Persson, astronomer at Chalmers University of Technology.

Brown dwarfs, sometimes called failed stars, are bodies whose mass lies between that of planets and stars.

The study shows that the tiny clouds are moving outwards through the Rosette Nebula at high speed, about 80 000 kilometres per hour.

"We think that these small, round clouds have broken off from tall, dusty pillars of gas which were sculpted by the intense radiation from young stars. They have been accelerated out from the centre of the nebula thanks to pressure from radiation from the hot stars in its centre", explains Minja Mäkelä, astronomer at the University of Helsinki.

According to Gösta Gahm and his team, the tiny dark clouds are being thrown out of the Rosette Nebula. During the history of the Milky Way, countless millions of nebulae like the Rosette have bloomed and faded away. In all of these, many globulettes would have formed.

"There are so many of them that they could be a significant source of the free-floating planets that have been discovered in recent years", he says.

Astronomers know of almost 900 planets which orbit around other stars than the Sun, but free-floating planets have also been found. Some have been discovered using a technique called microlensing, in which the planet is found when it passes in front of a background star, temporarily making it look brighter. This is an effect predicted by Einstein's theory of general relativity, in which the light from the star is bent when the planet passes in front of it, a so-called gravitational lens. Scientists have estimated that the number of free-floating in our galaxy may exceed 200 billion.

The study has been published in the article "Mass and motion of globulettes in the Rosette Nebula" in the July issue of the journal Astronomy & Astrophysics. The team observed radio waves from molecules of carbon monoxide using the 20-metre radio telescope at Onsala Space Observatory, Sweden, and submillimetre light with the telescope APEX at 5100 metres altitude in the Atacama desert in northern Chile. APEX is a collaboration between the Max Planck Institute for Radio Astronomy in Bonn, Germany, Onsala Space Observatory and ESO, with operations of the telescope entrusted to ESO. Observations in infrared light were made using the 3.58 metre New Technology Telescope (NTT) at ESO's La Silla Observatory.

Explore further: Planets that have no stars: New class of planets discovered

More information: dx.doi.org/10.1051/0004-6361/201321547

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6 comments

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Going
5 / 5 (1) Aug 19, 2013
What temperature would a free floating planet achieve? Would fission at its core give it a high enough temperature for liquids to form and possibly life?
Birger
5 / 5 (3) Aug 19, 2013
"Planets" -as in Jupiter-size objects -will generate heat by gravitational separation of helium and hydrogen deep inside the interior, just like our Jupiter.
Fission requires a mass dozens of times bigger.
And since gas giants lack a solid surface and the atmosphere circulates between the compressed scaldingly hot depths and the icy cold upper atmosphere, there is zero hope of airborne bacteria surviving such a cycle.

Maybe a big moon would temporarily be heated by IR when the planet is young and hot, but such a transitional heat source would hardly support life on a moon.
antialias_physorg
4.2 / 5 (5) Aug 19, 2013
What temperature would a free floating planet achieve? Would fission at its core give it a high enough temperature for liquids to form and possibly life?

Depends on what kind of life we're talking about. The almost-stellar-object may have enough fission to be reasonably warm. But those are also pretty big and have high pressure environments (super-Jupiters)

As long as the shell of a rocky type planet hardens quickly (and it is of sufficient size) it'll stay molten inside - just like the Earth - for a considerable time. So depending on how far down you go you should find temperature ranges conductive to life as we know it (though the pressure, radiation and lack of water ...).

What I'm trying to say here is: Planets born that way can come in all shapes and sizes. And given that we know very little about where life can and cannot originate it's impossible to rule them out. Lack of a solar energy source is a definite drawback, though.
OdinsAcolyte
1 / 5 (2) Aug 20, 2013
How fun! Imagine fleeing the death of one's native star on a floating planet. Endless possibilities and that is just in this universe. Anything one can imagine exists and quite a bit that never enters our minds is also out there.
GSwift7
not rated yet Aug 20, 2013
Originally they thought that a gas/dust cloud small enough to make only a planet wouldn't be cold enough to collapse. The gas would be too turbulent, and would...


Interesting general point to be made from this:

If there's even a SMALL chance of something happening in the Universe, then it will be happening in large frequency on a human scale.

They should have known that there would be special cases where the gas was cool and calm enough to collapse into a planet, but it was just a matter of exactly how unlikey it is, not that it wasn't going to happen somewhere. At that point it just takes a little thought about the conditions needed, and then go to a telescope and look for it.

I think the same thing goes for smaller bodies as well. There's going to be someplace where the gas is cool enough, and it gets forced into a high enough density that it will form a small planet. I'm thinking of standing waves, bow shocks, boundary zones, lagrange points between massive objects, etc.
GSwift7
not rated yet Aug 21, 2013
There must be vast numbers of free-floating objects in the galaxy. Any such object, no matter how rare, is extremely dangerous. For example, if a rogue planet passed anywhere within our Oort cloud, it could kick off a storm of comets here in the inner solar system. The chance of a collision with a planet is astronomically low, but the debris from such a collision would probably sterilize every other planet in the system as well, with asteroid bombardments.

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