Super Earths Might Be Common

[Blob]

Astronomers on Monday announced the discovery of a newfound cold extrasolar planet, OGLE-2005-BLG-169lb, 13 times heavier than Earth , orbiting a small red dwarf star roughly 9,000 light-years away.

The finding alters astronomers' perceptions of solar system formation and the distribution of planets in the galaxy, suggesting that large rock-ice worlds might outnumber gas giants like Jupiter.
The planet has an icy and rocky but barren terrestrial surface, and is one of the coldest planets ever discovered outside of our solar system.
It orbits 400 million kilometres away from a red dwarf star, which is cooler than and about half the size of our sun. The planet is similar in rocky structure to Earth, and it is described a "super-Earth."

Source

[baric]

The finding alters astronomers' perceptions of solar system formation and the distribution of planets in the galaxy, suggesting that large rock-ice worlds might outnumber gas giants like Jupiter.

Was this ever in doubt? Think about it. Medium-mass stars like our Sun outnumber giants. Red dwarves outnumber those. Brown dwarves outnumber those.

As mass goes down, quantity goes up. This holds for stars & planets!

[baric]

Another interesting aspect to this story is that it shows that a cold planet can be Uranus-sized in mass (13-14 Earths) and still be a terrestrial planet rather than a gas planet.

[Blob]

Hum,
yeah.
The bit where it says "Further analysis of the system revealed the absence of Jupiter-like gas giants, and scientists suspect the system literally ran out of gas and failed to form any. This may have starved the newfound planet of the raw materials it needed to turn into a gas giant itself".

Is quite intresting.

Same Story, but faster on 56k modems, link

[Fraser]

SUMMARY: Nearly all the extrasolar planets discovered have been Jupiter-sized or larger. But astronomers from the Harvard-Smithsonian Center for Astrophysics think that super-earths - rocky planets several times larger that our planet - might actually be much more common. Based on the recent discovery of a super-earth around a red dwarf star 9,000 light-years away, the research team calculated that there are probably 3 times as many of these planets than the larger gas giants.

View full article
What do you think about this story? post your comments below.

[Kullat Nunu]

I wonder why they think so. It is hard to believe that it couldn't be a Uranus- or Neptune-type icy giant planet.

[antoniseb]

I recall reading a Scientific American article about ten years ago discussing the likelyhood of life forming in various places in our galaxy, at various times. One item that stuck with me from that article was the premise that the higher the metalicity of the star being formed, the higher the mass of the rocky planets would be from the resulting disks.

This article says nothing about the spectrum of the parent red dwarf in this system, but I'd be interested in knowing how it compares to the composition of the Sun.

Rocky planets 13 times the mass of the Earth might not be very handy for life as we know it. I'm guessing that it would also have too much gravity for a carbon nano-tube based space elevator to be possible to its surface. How would you get materials to and from such a place?

[mantiss]

I wonder why they think so. It is hard to believe that it couldn't be a Uranus- or Neptune-type icy giant planet.

Perhaps because Uranust and Neptune radiate significant amounts of heat whereas this one apparently does not? U suppose in a system such as this one, the star being so dim and cool, planets, even gas giants, would be just as cool after sometime, so I am not sure if my hypothesis holds at all

[jhwegener]

Soon scientists may find a lot of not only super-earths, but eartsised bodies an even smaller.
What is it about those bodies that fascinate us that much?
One thing is of course the possibillity of life other places in the universe. But could there be other reasons? To find out more about the "history" of our planet and our solar system by studies of other systems, to find out if we are "typical" or not. To find out more about their origin and development. Perhaps even soon to find out more about future scenarios for both, by research in older systems as well as younger ones. Perhaps we may observe some typical events from birth, lives and deaths of a lot of planetary systems. In some way get a glimpse of possible "futures". Could astrologers in that way get it "right" in some ironical way?

[Blob]

Title: Microlens OGLE-2005-BLG-169 Implies Cool Neptune-Like Planets are Common
Authors: A. Gould, A. Udalski, D. An, D.P. Bennett, A.-Y. Zhou, S. Dong, N.J. Rattenbury, B.S. Gaudi, P.C.M. Yock, I.A. Bond, G.W. Christie, K. Horne, J. Anderson, K.Z. Stanek, D.L. DePoy, C. Han, J. McCormick, B.-G. Park, R.W. Pogge, S.D. Poindexter, I. Soszynski, M.K. Szymanski, M. Kubiak, G. Pietrzynski, O. Szewczyk, L. Wyrzykowski, K. Ulaczyk, B. Paczynski, D.M. Bramich, C. Snodgrass, I.A. Steele, M.J. Burgdorf, M.F. Bode, C.S. Botzler, S. Mao, S.C. Swaving (The MicroFUN, OGLE, and PLANET/RoboNet collaborations)


We detect a Neptune mass-ratio (q = 8 x 10^-5) planetary companion to the lens star in the extremely high-magnification (A~800) microlensing event OGLE-2005-BLG-169.
If the parent is a main-sequence star, it has mass M~0.5 solar masses implying a planet mass of ~13 earth masses and projected separation of ~2.7 AU.
When intensely monitored over their peak, high-magnification events similar to OGLE-2005-BLG-169 have nearly complete sensitivity to Neptune mass-ratio planets with projected separations of 0.6 to 1.6 Einstein radii, corresponding to 1.6--4.3 AU in the present case. Only two other such events were monitored well enough to detect Neptunes, and so this detection by itself suggests that Neptune mass-ratio planets are common.
Moreover, another Neptune was recently discovered at a similar distance from its parent star in a low-magnification event, which are more common but are individually much less sensitive to planets. Combining the two detections yields 90% upper and lower frequency limits f=0.37^{+0.30}_{-0.21} over just 0.4 decades of planet-star separation. In particular, f>16% at 90% confidence. The parent star hosts no Jupiter-mass companions with projected separations within a factor 5 of that of the detected planet. The lens-source relative proper motion is µ ~ 7–10mas/yr, implying that if the lens is sufficiently bright, I<23.8, it will be detectable by HST by 3 years after peak. This would permit a more precise estimate of the lens mass and distance, and so the mass and projected separation of the planet. Analogues of OGLE-2005-BLG-169Lb orbiting nearby stars would be difficult to detect by other methods of planet detection, including radial velocities, transits, or astrometry.

Read more (PDF)

[Blob]

Was this ever in doubt? Think about it.
As mass goes down, quantity goes up. This holds for stars & planets!

Hum,
i would agree with you there...

But i suppose there was/is no `hard` evidence...

A bit like saying `we know life arose easily on the earth quickly after its formation, and the galaxy contains all the ingredients, like amino acids, to create life, therefore there is little doubt that the galaxy is teaming with life...`

[baric]

Hum,
i would agree with you there...

But i suppose there was/is no `hard` evidence...

A bit like saying `we know life arose easily on the earth quickly after its formation, and the galaxy contains all the ingredients, like amino acids, to create life, therefore there is little doubt that the galaxy is teaming with life...`

Well, except that the accretion of smaller bodies to larger bodies via gravity is a much simpler process.

At some point, you have to assume that local conditions extrapolate to other regions unless you have a specific reason to believe otherwise. You could probably invoke an "anthropic principle" exception for Earth-type planets, but that's about it.

[Eckelston]

Perhaps because Uranust and Neptune radiate significant amounts of heat whereas this one apparently does not? U suppose in a system such as this one, the star being so dim and cool, planets, even gas giants, would be just as cool after sometime, so I am not sure if my hypothesis holds at all

I find it highly unlikely that they could get that kind of information from 9000 light years. They'd need spectrographic data for that which would mean imaging the object and more. More likely the planets temperature was modelled using the stars luminousity and distance from the star.

I wonder why they think it has a rocky surface myself. Maybe that's what planetary models predict? Or maybe at that temperature Neptune would have a solid surface too?

[Blob]

Hum,
i think they don't mean that the planet definitely has a rocky surface - it just has a density of 13 earth masses.
i would predict at its orbit range that it would be composed of volatile elements as well.
A metallic core with a hydrogen atmosphere seems equally likely.
The magnitude of error in trying to resolve the diameter in such a microlensing event would be too great to say either way...

[Kullat Nunu]

You can't measure a planet's diameter from gravitational microlensing event. Only information the event yelds is the planet's mass relative to its star and projected distance from it.

[Blob]

Hum,
indeed,
there is a lot of assumptions that have to be made; the size of the parent size, the planets orbit position (its phase), and its a albedo.

In the future that may be a possibility. It may be possible to infer the albedo of such a planet, and work out from the size/intensity of the microlensed spike its size, (its orbital phase would be a guess - but there is a lot of data that can be derived from the falloff curve).

This link shows an image of the planetary spike of OGLE-2005-BLG-390Lb
IMAGE (333kb, 1053 x 800).

[enlightenment]

It is interesting that the more we know the more we don't know. Presumably one will catch the other. If we observe that physics is universally the same, and if there is basic uniformity to what we see then it might not be a stretch to predict some eventualities. Matter is the same, galaxies seem to be dynamic and structured basically the same, stars vary within a few parameters, stars have companions of stars and now observable planets ...... planets are like earth??? why not .... planets formed life ??? why not. We cannot be a unique intelligence. As with above what we think we do not know will hopefully some day be known, and I hope to live to see that.

[Spherical]

Do the tell us anything about the spectrum of the system primary? I thought the majority of red dwarfs were very low in metals.

[Kullat Nunu]

In a few years the separation between the primary star and the background lensed star will be large enough for Hubble to resolve it. Then we'll know lot more about it.

Lack of metals may be one reason why there are so few jovian planets around red dwarfs. But terrestrial planets don't need as much heavy elements to form.

[antoniseb]

I thought the majority of red dwarfs were very low in metals.

I don't know why you thought this, but it is the case that stars forming a long time ago were more likely to be low metalicity than stars forming today. Giant stars formed a long time ago are long gone, but the red dwarfs are still around. There are, however, new high-metal red dwarfs being formed right now, and they will probably have large planets.

[Kullat Nunu]

Planet's mass may be dependent on the mass of the protoplanetary disc from it formed. Red dwarfs have much smaller protoplanetary discs than sunlike stars, and massive stars much more massive. It may be that red dwarfs have super-Earths or ice giants instead of gas giants, and massive stars may have brown dwarf mass planets.

[Spherical]

I don't know why you thought this, but it is the case that stars forming a long time ago were more likely to be low metalicity than stars forming today. Giant stars formed a long time ago are long gone, but the red dwarfs are still around. There are, however, new high-metal red dwarfs being formed right now, and they will probably have large planets.

Okay, is this particular red dwarf high in metallicity? I would expect it to be if it has a large rocky planet in its orbit.

[filrabat]

Rocky planets 13 times the mass of the Earth might not be very handy for life as we know it. I'm guessing that it would also have too much gravity for a carbon nano-tube based space elevator to be possible to its surface. How would you get materials to and from such a place?

I read somewhere that rocky-metallic worlds with 13 X Earth mass were liable to accumulate a hydrogen-helium atmosphere (and hence become a gas giant). Is that true?

[antoniseb]

I read somewhere that rocky-metallic worlds with 13 X Earth mass were liable to accumulate a hydrogen-helium atmosphere (and hence become a gas giant). Is that true?

Is that true? I'd guess that there are situations where it would happen, and situations where it wouldn't. A situation where it wouldn't would be when the planet formed close to the star, after the planetary disk had had most of its lighter gasses blown outward... but is that true? we can't know whether it is true or not till we see some examples.

[Duane]

I have merged two threads regarding this subject.

[Halcyon Dayz]

I'm guessing that it would also have too much gravity...

What would be the surface gravity on a planet 13 times the mass
of Earth, assuming the same av. density as earth?

[antoniseb]

What would be the surface gravity on a planet 13 times the mass of Earth, assuming the same av. density as earth?

Please keep in mind that I think the density would go up for a more massive planet, as the core would be under enough pressure to cause additional compression, but for the sake of you calculation, lets look at a planet that is eight times the mass of Earth, and has the same density.

It would have exactly double the radius, and eight times the mass. Gravity is inversely proportional to the square of the distance, so the gravity would be twice as strong at the surface (8 divided by 4).

The math is pretty easy.

[Halcyon Dayz]

That's to heavy for me.

[cress]

It's all very exciting when we see headlines about something-Earths, but let point out that much of the the more excitable reports are just speculation. The number of planets in this mass range we have found is still in single digits. I get quite surprised when I read reports claiming how common they are. They might be, sure, but we really know hardly anything just yet.

Individual cases need to be treated with caurion - for example, the one a couple of weeks ago - 5.5 Earth masses - if you looked at the error bars, you'd see they were +/- almost that much again. It's probably around 5.5 ME, but...

In a few years the separation between the primary star and the background lensed star will be large enough for Hubble to resolve it. Then we'll know lot more about it.

No. Microlensing events are unrepeatable; the planet is gone forever. Even if we find accidentally it again in 20 years, we'll likely not recognise it for the same body. That's the biggest problem with these stories. Individual events are interesting in their own way, but they don't really tell us anything. Once we have a hundred microlensing events, and we can get some statistics from the data, then I'll be interested.