‘The ultimate goal of astronomers who look for planets orbiting other stars is to find a planet like Earth—the same mass, orbiting at the same distance from a sun-like star.
We’re not there yet. But new observations are getting us closer and closer to that goal. Today, a team of scientists has reported the discovery of the lowest mass planet yet (view a news video of the discovery, or read about it here). The planet, called OGLE-2005-BGL-390Lb, is about 5 times the mass of the Earth, orbiting a star about 25,000 light years away. That’s halfway to the center of the Galaxy! So we won’t be visiting it any time soon. 
The planet is not exactly Earth-like; it’s still pretty hefty at five time Earth’s mass. Also, the parent star is only about 1/5 the Sun’s mass, making it red, dim, and cool. The planet orbits the star at three times the distance Earth orbits the Sun. So its distance, together with the cool temperature of its parent sun, means the planet is very cold, far too cold to sustain life as we know it.
The planet is way too far away to be seen directly. In fact, the way the astronomers found this planet is a little strange. They used a technique called "gravitational microlensing". Part of Einstein’s great contribution to science was the idea that gravity can bend space. Space is more than just a thing in which objects sit; Einstein’s math shows that space is itself a thing has properties, like shape. Gravity distorts the shape of space, similar to the way a heavy weight sitting on a bed warps the shape of the surface of the bed. If you take a ball and roll it on the bed, its path won’t be straight, but it will curve as it passes the depression caused by the weight.
Massive objects have gravity, and that gravity bends space. As light passes through that space, it can bend. If that’s not weird enough for you (and really, it should be), gravity can also act like a lens, amplifying light as well.
If a massive object is sitting between you and a distant light source, then the gravity of the object can make the light appear brighter. This is the method used to find the planet.
Astronomers look toward regions of the sky where there are lots of distant stars — like toward the center of our Milky Way Galaxy. In general, the stars give off a steady stream of light. But if a massive object happens to pass between us and one of those stars, we’ll see a jump in brightness. The amount of the brightening can tell astronomers how massive the object is.
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| Astronomers observe regions with lots of stars to look for microlensing events. Here is the view toward the center of our Milky Way galaxy… 10 million stars can be seen in the original image (click for higher-resolution and more info). |
Astronomers have dedicated projects looking for planets using this method. Two were involved in this case: OGLE, for Optical Gravitational Lensing Experiment, and PLANET, for Probing Lensing Anomalies Network, RoboNET, and MOA, for Microlensing Observations in Astrophysics (I love those first two names; I have a weakness for good puns).
In this case, the astronomers saw two peaks of brightness from the star. The first was big, and the second smaller. The first was from the parent star of the planet, and the second from the planet itself. From the way the distant star got brighter (how long it took, and how much brighter it got), the team was able to determine the mass of both the planet and its parent star.
This technique has been around a while, and astronomers have used it to look for planets, stars, black holes, even exotic dark matter out between the galaxies. It’s very different than the usual technique of planet hunters, which is to look for changes in a star’s spectrum as a planet orbits it. That technique works better for big, massive planets orbiting their star very close in. This lensing technique can work for any size planet, including a terrestrial one– a planet the size of the Earth. It’s very possible – even likely – that the first truly Earth-like planet will be found this way.
As a kid I always thought that the first Earth-like planet we find would be nearby, like around Alpha Centauri or some other well-known star. But in fact, it may be some distant world, orbiting an unnamed star tens of thousands of light years away.
Maybe as a kid I would have been disappointed knowing that. I’m not now! Just knowing there’s a planet like that out there is incredibly exciting. And if we know of one far away, then that makes the search for nearby ones all that much sweeter.’
January 25th, 2006 at 10:31 am
Great news, indeed! But am I correct in thinking that there is as yet no reason to believe that this planet is “rocky,” as was claimed here?
They write that “The planet has a solid, rocky surface similar to Earth and has its own star that it orbits, similar to our Sun.” I suspect that the journalist got a bit carried away there…
January 25th, 2006 at 10:31 am
SWEEEEET!
Sooner or Later we’re gonna get an Earth-Like Planet.
Anyone want to start taking bets on when that will be?
January 25th, 2006 at 10:33 am
Rockin’ !
January 25th, 2006 at 10:58 am
Nifty. Are there any good hypotheses on the ultimate limitations of the lensing method with current instruments?
January 25th, 2006 at 11:02 am
Quite frankly, I can’t wait for the news of even a potentially Earth-like planet. It would be startling and quite literally vision-changing, although I’m convinced that numerous such planets must exist within our galaxy.
The trouble is, I’d then be champing at the bit to find out whether a planet with Earth-like conditions has developed life which we can recognise, and since an Earth-like planet is likely to be hundreds of light years away at least (unless we’re really really lucky), I have to face up to the very real probability that I’m never going to know the answer to that question.
Still hoping that when I die, I’ll get to find out all the secrets of this universe on another plane of existence or something.
January 25th, 2006 at 11:03 am
>> Anyone want to start taking bets on when that will be? >>
A class M find, will probably occur before the singularity I’m sure.
January 25th, 2006 at 11:33 am
[...] The BA Blog Space.com [...]
January 25th, 2006 at 11:36 am
Dare I admit I was hoping for an Earth-like planet all afternoon?
January 25th, 2006 at 11:41 am
Great news. I wonder how many exos we’ll confirm over the next decade.
January 25th, 2006 at 11:53 am
Great news. Nice experiment.
PK, my guess is the planet has to be either rocky or an iceball – a gas planet with only 5 earth masses does not sound very plausible. It may even have an atmosphere like Titan’s.
Does anyone know if anything else is reported about the parent star (other than its mass)?
January 25th, 2006 at 12:11 pm
Still hoping that when I die, I’ll get to find out all the secrets of this universe on another plane of existence or something.
You never know… maybe when we die we’ll be treated to a quick tour of the whole shebang. I mean, we’ve got all of eternity, what else are we gonna do?
Fantastic discovery! Getting closer to finding a little planet like Earth out there. It’ll happen someday. The disappointing part is that I think it will take a discovery of a planet just like Earth to really get the rest of the world excited. Something this “big” planet around such a little star still won’t have life (most likely, of course).
January 25th, 2006 at 12:14 pm
Nice. Techniques are really getting sharper and sharper.
January 25th, 2006 at 12:15 pm
You never know… maybe when we die we’ll be treated to a quick tour of the whole shebang. I mean, we’ve got all of eternity, what else are we gonna do?
Yeah, but all the atheists can’t come, because they spoiled the party…
January 25th, 2006 at 12:18 pm
Yawn. Wake me up when an “Earth-ish planet” (CNN’s headline) is *really* on par with the Earth. It’s obvious now that the galaxy has lots of planets — surely all sizes and orbiting around a variety of stellar types. It was exciting at first, but the asymptotic approach of each new “big news” that narrows exampes ever closer to 1 Earth mass is getting kind of boring. Enough with the popsicle planets and plasmatic gas giants!
January 25th, 2006 at 1:04 pm
Don’t worry about finding earth-like planets. The Terrestrial Planet Finder observatories
will be space-borne instruments to do just that.
Footnote: The center of the galaxy has been estimated to be between 25,000 and 28,000 light-years distant. Not 50,000 light-years as I believe the BA implied.
January 25th, 2006 at 1:52 pm
Yawn. Wake me up when an “Earth-ish planet†(CNN’s headline) is *really* on par with the Earth. It’s obvious now that the galaxy has lots of planets — surely all sizes and orbiting around a variety of stellar types.
Careful, Eighthman, or you’ll begin to sound like Richard Hoagland
The evidence so far points to the possibility that there are many similar solar systems in this galaxy, but this find is very important since it brings us closer to true confirmation. The “big whoop” attitude unfairly demeans the efforts of all the astronomers who put a lot of time and hard work into extending the reach of our knowledge of extra-solar planets.
January 25th, 2006 at 5:09 pm
If the planet is composed of vaguely similar stuff to earth, and has five times the mass, then it’s volume will be roughly 5 times earth’s volume as well. So if you set earth’s radius to 1, the diameter of the planet will be the cube root of 5, or 1.7. Am I right or am I screwing up the math?
That’s not that big of a difference in size; consider that Mars is only 0.1075 Earths in Mass, 0.533 Earths in radius, and volume is .151 Earths. Mars is also about half as dense as earth (mainly because its core is half the size) so if that effect scaled by a similar ratio as volume increases, then this new planet would actually be less than 1.7 times the radius of earth. In anycase by radius, the new planet is actually closer to the earth in radius than Mars is.
January 25th, 2006 at 5:13 pm
Scratch the word “diameter” above, I meant “radius”
January 25th, 2006 at 5:27 pm
This is interesting.
I was actually thinking something similar Corey. The surface gravity of this planet shouldn’t be too extreme. I mean, humans would probably have a hard time there, but I can see *something* developing there:) (assuming the planet has similar conditions to titan).
January 25th, 2006 at 6:02 pm
The astronomers decided that it is probably and icy or rocky planet because under the most-favored version of planetary core-accretion models, gas giants are not so easy to come by. Still, that does not mean that it is a rocky/icy body, it just means that it’s likely.
January 25th, 2006 at 8:57 pm
I can’t imagine current accretion models forming a 5 earth mass planet around a red dwarf and it being rocky. So feeble would be the solar wind from such a star, even when young, that gases wouldn’t be ‘blown out’ with quite so much reckless abandon.
Isn’t it somewhere around one to two earth masses where accretion models predict runaway gas accretion to at least ten earth masses? It’s so hard to form a gas giant because in most models, it’s very hard to get more than one Earth mass together in the first place. It happened less than ten times when forming our solar system, accounting for any planets which were either ejected or ended up inside Jupiter.
We can safely assume the nebula forming a red dwarf would be somewhat sparse in material, so the runaway of a large rocky core wouldn’t be as much as it would be in the solar nebula.
I don’t think it’s a rocky planet. A rocky planet at that mass would be, say 1.6 Earth radii? Gravity being pretty damn fierce? Local temperature being very cold? How could that have *not* become a gas giant? How possibly would it have escaped runaway accretion to be the giant rocky planet that’s being claimed?
January 25th, 2006 at 9:15 pm
At 3 AU from an M dwarf, it seems to me the atmosphere on such a planet would be pretty dense. It may very well be mostly ice and rock, but I bet it has a thick atmo.
January 25th, 2006 at 11:07 pm
Some of the many stories on various sites, lead me to judge that , as usual only the most basic,laymans terminology has been given out thus far. I still wait to see further info on make up and constiuent matter of this Exoplanet and more to the point how “Earthlike ” it really is. But I will keep further judgemeny open until much more has been deciminated to the general public.
January 25th, 2006 at 11:34 pm
Five divided by the square of the cube root of five is, um, er, the cube root of five — yes, invoking my trusty Python interpreter, that’s about 1.7. If it is a rock-and-ice world, a surface gravity of 1.7 g doesn’t sound so bad. Particularly since any, ahem, self-replicating patterns carrying genetic information and performing metabolism (coughs to cover up the L-word) will probably arise in the melted ice, where the surface gravity matters less.
January 26th, 2006 at 1:45 am
Down under in New Zealand this discovery has made the front pages of most of the countries major newspapers. This includes my local paper the Dominion Post, which has a huge picture of Astronomers Karen Pollard and Michael Albrow of Canturbury University (which is in the South Island of NZ) and a reasonable write up. According to the report, Pollard and Albrow are part of the team who published the paper in Nature. It’s great to see such scientific accomplishments being widely and publicly recognised (even it is only in a country of 4 million people!).
January 26th, 2006 at 3:00 am
The paper is now on astro-ph so you can read all the details even if if you don’t have access to Nature.
January 26th, 2006 at 5:49 am
A terrestrial planet (another great scientific discovery) orbiting a red dwarf star over 25,000 light years away but is just too, too far away to be practical for exploration! Even if a habitable planet was discovered at Vega, 25 light years away…
Anyways, these discoveries continue to add significantly to our scientific knowledge encyclopedia of Universe.
An aside and not to begin another religious frenzy but:
For those that opinionated:
“You never know… maybe when we die we’ll be treated to a quick tour of the whole shebang. I mean, we’ve got all of eternity, what else are we gonna do?”
“Yeah, but all the atheists can’t come, because they spoiled the party…”
Justin and PK may be jesting but if not, then:
Modern astronomy is providing us a tour back through 13.7 billion years of Universal evolution!
As an Atheist, factually, and as a Universally unique person, as all of us are, only through technology, science, good habits and living, genetics, will we live longer, and better. Death, unfortunately, is terminal for our own unique and nonreproducible brain-formed mind (personality) and body (even if cloned will not be a “you”). In-other-words, we only have this one life-time to be what we can be.
All of your wishful and make-believe thnking won’t change that.
Please, do not start a multi-blog nonsense debate on this. The only possible near “immortality” will only come through the continuing biological evolution of our species or through the advances in science, medical technologies, genetic engineering, etc.
You guys outta keep up with the sciences and read more science fiction.
January 26th, 2006 at 6:00 am
Another non-Earth-like “Earth-like” planet
Once again, headlines are proclaiming the discovery of an “Earth-like” planet orbiting another star. Once again, closer inspection of the reports indicates that this new-found planet, based on the very little we know about it, is very unlike Earth. D…
January 26th, 2006 at 6:00 am
It would be nice to find one of these objects “in our own backyard”, as it were. It would be nicer still to find one of them an M-class with a Gaia-type ecosphere (if that is the appropriate term for a self-regulating biosphere) and a whole lot of critters running around.
*Sigh* Maybe tomorrow…
January 26th, 2006 at 9:56 am
They could just call it a super-Plutonian planet.
January 26th, 2006 at 10:16 am
It would be neat if they found a rocky/icy body such as this, or somewhat smaller, out beyond the Kuiper belt. A mars-mass or larger body might be able to hold on to some helium in its atmosphere out there, which might make it the best place in the solar system to mine 3He.
January 26th, 2006 at 1:33 pm
To me, wouldn’t the ultimate discovery actually be an earth sized planet that actually has oxygen in it’s spectrum?
January 26th, 2006 at 4:23 pm
Any sized planet with oxygen detectable in its atmosphere would be a fantastic discovery!
The very nature of oxygen precludes it being present to any significant concentration without a constant supply of it.
January 26th, 2006 at 10:26 pm
Yeah that would be fantastic! But the Terrestrial Planet Finder missions intended to do just that are not flying yet. And since I’m not working on them all I can do is be a cheerleader. So here goes:
GO TPF! GO TPF!
CATCH THOSE PHOTONS! CATCH THOSE PHOTONS!
GIMME AN O!
GIMME AN X!
GIMME A Y!
GIMME A G!
GIMME AN E!
GIMME AN N!
OK, NOW GIVE ME A SPACE!
NOW GIMME AN S!
GIMME A P!
GIMME ANOTHER E!
GIMME A C!
GIMME A T!
GIMME AN R!
GIMME A U!
GIMME AN M!
WHAT’S THAT SPELL? UMMMM …. OXYGEN SPECTRUM!!!!
YAY! GOOOOOOOOOOOO – TPF!
January 28th, 2006 at 7:52 pm
What would really be interesting if they discovered a planet with both oxygen and traces of either NO(good) or He(better) in the atmosphere. The NO would indicate hydrocarbon combustion, meaning that they are industrialized, and He would indicate fusion
January 28th, 2006 at 9:22 pm
Why look tons of light years away when you can find a pretty good solar planet at the JPL/NASA site at
http://www.jpl.nasa.gov/missions/mer/images-print.cfm?id=1835
with a very impressive view from the Rover Opportunity posted then withdrawn on 5 Dec 2005.
January 30th, 2006 at 9:38 pm
A *quick* tour after death that spends a fair part of eternity …?
Sounds like a *long* tour to me!
& besides how fast does the ’soul’ travel – lightspeed, FTL, as fast as it wants?
But then again its all in context and all in fantasy (so far as any of us know)so what the heck … A nice daydream if nothing else.
Sounds to me more like a sub-Neptune than a super-Pluto type planet but hard to tell from what we know. Seems to me there’s a lot more guesswork thn solid knowledge here.
Is there a point when we can say definitely something is a gas-giant / ice-giant or aterrestrial rocky planet & if so what is it?
Is there a type of planet that’s intermediate between being a Neptunian style world and a super-earth type one?
I’m guessing a very thick & dense atmosphere of Hydrogen-Helium & trace elements. Then maybe an underlying oceanic mantle layer of ammonia /water – perhaps with icebergs /icesheets or perhaps not as that depends on the planets age (residual heat via gravitational collapse & radioactive element decay) & density (will ice float in whatever mix of fluid there might be?) among other factors. Only then perhaps a very large rock-ice core (if silicate-based) or a possible alternative carbon core – tar/ diamond -making up maybe a third or more of the total? Say 1/3 atmosphere, 1/3 fluid too? Not quite a Neptune, not quite a mega-earth but in-between both.
But that’s just my speculation based on what I’ve heard & imaginined from that.
As for downplaying these discoveries – hell no! These are entire strange new worlds and I think every extrasolarplanet found adds to the greater picture and deserves a fair bit of public recognition and interest. Kudos to theNZ media, wish our Aussie media hounds were better.
February 1st, 2006 at 1:27 pm
Back in a past life I was working with a group that was developing some of these core-accretion models for giant planets, and the work they and others did seemed to suggest that a planet had to be larger than around 10 Earth masses before a “runaway” gas accretion got started. However, that number was dependent on both the mass and temperature of the gas disk, and those would almost certainly be different for a red dwarf star. Also, worlds less than 10 Earth masses still could have a lot of hydrogen (up to half of their mass) even though they weren’t quite big enough to turn into Jupiters. So maybe this newly discovered work would be more like a “small Neptune” rather than a big Pluto.
Also, these models are not very dependent on clearing the gas disk out by solar winds. This is fortunate, because solar winds don’t look like a very good choice for doing the job (despite what most astronomy textbooks seem to claim). Observationally it appears that as soon as there is any significant gap between the disk and the surface of the star, those strong winds die down a lot.
February 1st, 2006 at 2:45 pm
Certainly, with the great magnitude of the universe, a planet similar to earth must exist. It is only a matter of time until such a planet is found, and new life forms are discovered. A discovery like this will be a huge scientific breakthrough. The thought of other galaxies and other forms of life is very interesting, but what is equally if not more interesting is how scientists are finding these planets. Gravitational lensing is a very complicated method, but thanks to Einstein’s theory of general relativity this method has been very useful. This method involves the bending of light by large masses in space. This occurance hints at a bend in the third dimension and the large scale effects of gravity.
February 5th, 2006 at 6:57 pm
It seems to me that we have an ‘Earth’ personality complex. Like, just because WE have been reasonably successful at Life, does not mean that there has to be a parallel existence, a clone as you will, out there. True, I reason that there has to be, statistically, Earth-like planets. Some of those may have similar conditions to enable Life to occur, prosper, develop to whatever stage is appropriate, and that may be nothing like we could imagine. Even on Earth there have been many setbacks and re-directions, our own existence was ensured by a certain comet or whatever, that caused a massive clear-out of the entrenched dominant lifeform- bye bye big dinos- and a certain small mammal developed to rule the roost. Some say we are on the verge of RUINing the roost!
This latest Earth-like candidate, with a huge slice of conjecture based on a telltale wiggle, seems to give us a sense of personal recognition- hey, we exist out here, 25000 light years out here. What we are contemplating is they existed then, and their mail has only just been delivered! Provided they did exist that is. Just what were OUR ancestors doing 25000 years ago? Learning to deface perfectly fine cave walls, burning dried tree branches and grasses, and wondering just what were those pinholes of light in the sky that won’t stay still, and besides who moves them?
So, just who are we trying to impress anyway? Those closer to the center of our galaxy, will also have asked that question long ago, being evolved that much earlier than we. What about the galaxies closer to the center of our universe, and those universes….. closer to the BIG BANG?
They will be the ones further from us, on the outskirts. They obviously will never hear from us, even if sent priorty paid, but those closer may. Our near neighbour would have to be in the right place at the right time in a suitable mindset and nothing better to do that night. And we will be another 25000 years into the future to boot. Isn’t it frustrating?
February 5th, 2006 at 7:41 pm
Oh, I forgot to mention a little something that may interest those astros coming on line. Check the photo of the Sky in Phil’s piece- a beautiful shot of the center of our Milky Way. Download the enlarged version. Wonder at that for a wlile. Then at least in Macintosh, the others may also have the facility, try switching to a White-on- Black Presentation, as found in Mac OS 10.4.4 in the System Preferences and found under the Blue Apple. Proceed to Universal Access, open it and click the appropriate radio button. Though it toggles between black and white, it actually is a positive/negative effect, so colors are complementary. Of course you could also use the greyscale button too. There is a wealth of detail not seen in the ‘normal’ shot. You won’t forget to switch back, will you?!!
February 6th, 2006 at 5:57 pm
The punability of MOA is enhanced if you know about the now extinct 2m + high flightless birds of that name once native to New Zealand (where the MOA observations are made). Mind you, one of the MOA team was responsible for HERCULES as the acronym title of a high resolution spectrograph.
In a follow up to the comments about the NZ coverage of the report, it has been interesting seeing the different angles/author focusses taken by reporters on different continents. Hence the focus on Albrow and Pollard in NZ (and a lesser extent MOA) in NZ, Sackett (Mount Stromlo), the Tasmanians and Perth observatory people in Australia, the British team members in Britain etc. Knowing about 8 of the authors, it has been fun to follow:)
February 7th, 2006 at 6:51 pm
[...] Published Research Synopsis: 5.5 Earth Mass Exoplanet Found Astronomy» ESA» Exoplanet» Gravitational Lensing» Microlensing» OGLE 2005 BLG 390Lb» Research Synopsis» Science» In a press conference this morning, astronomers announced the discovery of a planet with a likely mass of 5.5 times that of the Earth orbiting a red dwarf star some 21,500 light years away. This is not the lowest mass exoplanet discovered thus far, but it is the first one that is both near Earth mass and near Earth orbital distance. I’m sure you’ve all heard the news, but now read on and hear the science (I’ll note that the Bad Astronomer did a science explanation too, but mine has pictures and graphs in it, so it must be better! Okay, also Centauri Dreams has done a summary as well, but again, mine has more pictures and graphs, plus an original analysis in the Context section below.). Also, I made a cool graph of all of the exoplanets we’ve found so far, that’s below too. So, here’s a second bonus published research synopsis in as many weeks: [...]
February 8th, 2006 at 3:19 pm
[...] Published Research Synopsis: 5.5 Earth Mass Exoplanet Found Tags:Astronomy» ESA» Exoplanet» Gravitational Lensing» Microlensing» OGLE 2005 BLG 390Lb» Research Synopsis» Science» In a press conference this morning, astronomers announced the discovery of a planet with a likely mass of 5.5 times that of the Earth orbiting a red dwarf star some 21,500 light years away. This is not the lowest mass exoplanet discovered thus far, but it is the first one that is both near Earth mass and near Earth orbital distance. I’m sure you’ve all heard the news, but now read on and hear the science (I’ll note that the Bad Astronomer did a science explanation too, but mine has pictures and graphs in it, so it must be better! Okay, also Centauri Dreams has done a summary as well, but again, mine has more pictures and graphs, plus an original analysis in the Context section below.). Also, I made a cool graph of all of the exoplanets we’ve found so far, that’s below too. So, here’s a second bonus published research synopsis in as many weeks: [...]
August 12th, 2006 at 2:06 am
Great! We found a planet that is almost earth-like – But how are we gonna get there, its too far away even if we travel at 0.99c (travelling at c is just impossible) it would take us 3562.31 years to get there and even if we can come across that theres still the issue of the long-term affects of a non gravitational environment (calcium depletion is an example). Maybe it might have been an extraordinary discovery but i think we should just stick to planets within our own galaxy for the time being