Cold, Lonely Planets More Common Than Sun-Like Stars
By Christopher Dombrowski for Wired News
May 19, 2011
Seems like every week astronomers find a new exoplanet, one
that’s the biggest or the smallest or the hottest or most habitable. However,
this week astronomers are announcing a truly unique and new class of
exoplanets: Jupiter sized planets that are in extremely large orbits or
completely unbound from a host star altogether. And there appear to be a lot of
them, as these planets seem to be more common than main sequence stars.
Finding a planet that
is not associated with a star is no easy task. In the new search, a team of
researchers used a technique called gravitational microlensing. As you look at
a background field of stars, if an object passes between you and one of the
stars, there will be a temporary brightening of that star. This occurs as the
gravity of the object bends light around itself, which acts as a lens for light
from the background star, hence “gravitational lensing.” Microlensing occurs
when the foreground object is too small to create measurable distortion of the
background star and only a brightening is observed. This makes it an ideal
detector for small, dim objects. The mass of the lensing object determines the
duration of the brightening event—the longer the duration, the more massive. A
Jupiter-sized object would produce lensing event with a duration of around one
day. The odds of a microlensing event occurring are exceedingly small, as the
lensing object has to line up exactly between you and the background star. To
compensate, astronomers looked at 50 millions of stars over several years,
which yielded 474 microlensing events. Out of those 474, 10 had durations of
less than two days, consistent with a Jupiter mass object.
No host stars were observed within 10 astronomical units of
the lensing object. Previous work from The Gemini Planet Imager had set limits
of the population of Jupiter-sized planets in extended orbits. From that data,
the astronomers were able to estimate that 75 percent of their observed planets
were most likely not bound to a host star at all, and are instead loose within
the Galaxy. By creating a galactic mass density model that takes into account
this new class of object, astronomers were able to predict how many of these
unbound planets there might be. They found that there are ~1.8 times as many
unbound Jupiter-sized object as there are main sequence stars in our Galaxy.
This raises a number of questions. Did these planets from near a star only to
be ejected from the system? And if they truly have never been bound to any
stars, do these planets represent a new planetary formation process? In any
case, these observations have discovered a whole new population of
Jupiter-sized planets in the Milky Way, and there are a lot of them.
I wonder if these new planets are like our Jupiter and, like
our Jupiter, have moons which are geologically active and warm. If so, these
new planets may have significantly increased the number of places that life may
exist.
[So the possible number of environments where life may exist
has just increased again. I’m confident that it’s just a matter of when we find
it rather than if…..]
6 comments:
I wonder how these planets formed. Are they possibly failed stars? And..can we even call a starless planet a planet? I thought our current definition of planet involve, at the very least, a body in orbit of a sun.
It's inevitable that there will be repeated circumstances like ours, many instances of the same materials in similar settings around similar stars; the numbers are just too overwhelming for this not to be the case.
The real question becomes: what happens when we diverge from this magical recipe? How much variance can still allow for the formation of life, and how will that life differ from what we know? Even when any particular outcome is almost impossibly rare, the sheer numbers of opportunities get around even that obstacle.
sc said: I wonder how these planets formed.
I'm guessing in the normal fashion in an accretion disk around a star. Maybe something later forced them out of its orbit? I suppose though that they could have formed in deep space between stars - if there was enough material around to form a planet..
sc said: I thought our current definition of planet involve, at the very least, a body in orbit of a sun.
Doesn't planet just mean 'wanderer'? I think a 'satellite' needs, by definition, to revolve around something.
wunelle said: It's inevitable that there will be repeated circumstances like ours, many instances of the same materials in similar settings around similar stars; the numbers are just too overwhelming for this not to be the case.
That's right. Given enough opportunities for life to emerge somewhere in our galaxy it'll inevitably do so. With the numbers presently being contemplated I doubt very much if only Earth hit the lucky jackpot of producing life.
wunelle said: Even when any particular outcome is almost impossibly rare, the sheer numbers of opportunities get around even that obstacle.
Totally agree. It's unfortunate that we only have one real example to work from ATM - but the study of extremophiles shows us just how far life on Earth can adapt to difficult environments. It certainly suggests that we shouldn't just be looking for ideal conditions to host life.
Sometimes, I think we live on cold, lonely planet. :-)
dbackdad said: Sometimes, I think we live on cold, lonely planet.
First, that *my* line [grin]
Second, I understand that it's not exactly *cold* over that side of the pond ATM....
[laughs]
Ain't that the truth! (as pertaining to the heat ... not my perception of your love life)
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