Evidence for a nearby "solar system"

[Bob the Gunslinger]

Only 10.5 lightyears from Earth. Send the generation ships!

WASHINGTON — For the first time, astronomers think that they've found evidence of an alien solar system around a star close enough to Earth to be visible to the naked eye.

They say that at least one and probably three or more planets are orbiting the star Epsilon Eridani, 10.5 light-years — about 63 trillion miles — from Earth. Only eight stars are closer.

The host star, slightly smaller and cooler than our sun, is in the constellation Eridanus — the name of a mythological river — near Orion in the northern sky.

Epsilon Eridani is much younger than the sun, about 850 million years old compared with 4.5 billion years for our system.

"This really is a system like our solar system was when it was five times younger than it is now," said one of the discoverers, Massimo Marengo , an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "It's like a time machine for our solar system."

"This system probably looks a lot like ours did when life first took root on Earth," said Dana Backman , of the SETI Institute in Mountain View, Calif. , the lead author of a report to be published Jan. 10 in The Astrophysical Journal .

SETI chose Epsilon Eridani as one of the first targets in its long — but so far vain — search for signs of extraterrestrial intelligence in 1960.

The suspected planets are too far away to be detected directly, so their presence has to be inferred by indirect measurements. Their star is so near, however, that some astronomers think that they may be able to see its planets with better telescopes within the next decade.

One of the planets, a gas giant 1 { times heavier than Jupiter, was discovered in 2000 by Barbara McArthur , an astronomer at the University of Texas in Austin . She measured the slight wobble in the star's position as the planet swung around it. Further observations by the Hubble Space Telescope in 2006 confirmed its existence, McArthur said at the time.

Now Backman's team has deduced the presence of at least two more planets, after space- and ground-based telescopes separately revealed two belts of rocky asteroids and an outer icy ring circling Epsilon Eridani.

The inner asteroid belt is about 280 million miles from its host star, the same distance as our own ring of asteroids orbiting between Mars and Jupiter. The second belt is about the same distance as Uranus is in our system.

Finally, a wide, third ring of icy objects extends billions of miles beyond Epsilon Eridani, resembling the so-called Kuiper Belt of mini-planets outside Pluto.

In 2002, Alice Quillen , an astronomer at the University of Rochester in New York state , reported that unusual clumps of material in the outer ring probably indicated the presence of a Saturn -size planet in a Pluto-like orbit. Her finding hasn't been confirmed, but "I still think there is a planet out there of this size," Quillen said in an e-mail.

According to Marengo, the gaps between these belts were created when clouds of dust and rocks consolidated into planets, as happened in the early days of our solar system. He likened the process to the formation of Saturn's famous rings, which are separated by spaces cleared out by little moons.

"The easiest way to explain the gaps is to say there are planets there," Marengo said. "It's the same way as the rings of Saturn are kept stable by the moons of Saturn ."

"I think these rings are probably telling us about how systems clear out after planets have formed," Quillen said. "It's pretty exciting to catch such a nearby system in this critical stage."

Marengo raised the possibility that more Earthlike planets might exist in the space between Epsilon Eridani and the inner dust ring.

"The inside belt is cleared, like in our solar system," he said. "There could be terrestrial planets inside, but we can't detect them yet."

Score one for Babylon 5.

[Patrick Degan]

Just be sure, when we get there, not to fool with the Great Machine.

[Molyneux]

I wonder if we're ever going to figure out why our Solar System's wealth of (small, rocky) planets seems to be the exception rather than the norm...hopefully it'll be an artifact of our limited sensing capabilities, rather than an actual dearth of Earth-like planets.

[wautd]

I wonder if we're ever going to figure out why our Solar System's wealth of (small, rocky) planets seems to be the exception rather than the norm...

Is it? Isn't it the case that small & rocky planets are simply a lot harder to find than gas giants?

[General Zod]

I wonder if we're ever going to figure out why our Solar System's wealth of (small, rocky) planets seems to be the exception rather than the norm...hopefully it'll be an artifact of our limited sensing capabilities, rather than an actual dearth of Earth-like planets.

I don't think we can safely say that one way or the other until we have a more reliable means of detecting "small" bodies within a solar system. (By small I mean less than Jupiter-sized planets).

[Molyneux]

I wonder if we're ever going to figure out why our Solar System's wealth of (small, rocky) planets seems to be the exception rather than the norm...

Is it? Isn't it the case that small & rocky planets are simply a lot harder to find than gas giants?

Uh...did you read the second half of my post, after the ellipsis?
Right now it looks like gas giants are far more common than small, rocky planets. I'm hopeful that that will turn out to not be the case.

[GrandMasterTerwynn]

I wonder if we're ever going to figure out why our Solar System's wealth of (small, rocky) planets seems to be the exception rather than the norm...

Is it? Isn't it the case that small & rocky planets are simply a lot harder to find than gas giants?

Uh...did you read the second half of my post, after the ellipsis?
Right now it looks like gas giants are far more common than small, rocky planets. I'm hopeful that that will turn out to not be the case.

Small rocky planets (less than 2 Earth-masses) are nigh-on-impossible for us to detect right now save for some very extreme circumstances. What you're seeing right now is observational bias. Our methods heavily favor the discovery of short-period, high-mass planets. There really is no need to wonder, because that's all there really is to it.

For that matter, as our sensitivity has increased, we've discovered Saturn-mass planets, Neptune-mass planets, and even planets merely four or five times more massive than Earth.

[Samuel]

Which is odd. There are no objects 4 or 5 times the mass of the Earth in our solar system. Or gas giants close to the Sun like in several of the systems we have found. Probably there are a variety of different ways solar systems can develop. This discovery is important because it shows another solar system that developed like ours. Given the closeness and the uniformity principle, this implies that such an arrangement isn't rare.

Any guess if there is a world with life in the system?

[Molyneux]

Which is odd. There are no objects 4 or 5 times the mass of the Earth in our solar system. Or gas giants close to the Sun like in several of the systems we have found. Probably there are a variety of different ways solar systems can develop. This discovery is important because it shows another solar system that developed like ours. Given the closeness and the uniformity principle, this implies that such an arrangement isn't rare.

Any guess if there is a world with life in the system?

My guess would be that it's unlikely, but worthy of celebration if it were found to be true.

[GrandMasterTerwynn]

Which is odd. There are no objects 4 or 5 times the mass of the Earth in our solar system. Or gas giants close to the Sun like in several of the systems we have found. Probably there are a variety of different ways solar systems can develop. This discovery is important because it shows another solar system that developed like ours. Given the closeness and the uniformity principle, this implies that such an arrangement isn't rare.

Any guess if there is a world with life in the system?

The quick answer is "Maybe." A habitable world would be orbiting Epsilon Eridani somewhere around where Venus orbits in our system (accounting for the fact that Epsilon Eridani has only 28% of Sol's radiative output.) Since the inner Epsilon Eridani system has been swept clean of dust and debris, it is very likely there are planets there, and it is extremely unlikely there's a hot Jupiter/Saturn/Neptune around to throw out any small rocky worlds (we'd have found a hot giant planet long before now.)

Would it be human-habitable? Not only no, but hell no. Any rocky planet would be at the same stage of development as Earth was 3.8 billion years ago. Which is to say, high impact flux, a volcanically-active (much, much moreso than Earth's) crust, and a dense 'primordial' atmosphere comprised mainly of carbon dioxide. Life would be about at the level of photosynthetic and geothermal bacteria, with the notion of multicellular life being literally billions of years off in the future. Which is to say, it would be distinctly boring and would have nothing of merit to talk to us about.

[Junghalli]

Uh...did you read the second half of my post, after the ellipsis?
Right now it looks like gas giants are far more common than small, rocky planets. I'm hopeful that that will turn out to not be the case.

I have a New York times article about a recent sky survey that suggests as much as 1/3 of stars may have superterrestrial planets (15-2 Earth masses). Here's a website that talks about it.

That's a lot more than seem to have big gas giants, so it's fairly encouraging news for terrestrial planets being common.

[Kitsune]

If I understand, it is eight "Known" stars closer than it. There could be Red Dwarfs closer that we still cannot detect........

[Samuel]

I'm pretty sure we can detect red dwarf that close- wouldn't they create a lensing effect or black the stars behind them?

[Kitsune]

Curious how close is the nearest type "G" star (besides Sol) which is believed to be around the same age as Sol?

Also, how do we tell that Epsilon Eridani is only around 850 my old?

[Surlethe]

Would it be human-habitable? Not only no, but hell no. Any rocky planet would be at the same stage of development as Earth was 3.8 billion years ago. Which is to say, high impact flux, a volcanically-active (much, much moreso than Earth's) crust, and a dense 'primordial' atmosphere comprised mainly of carbon dioxide. Life would be about at the level of photosynthetic and geothermal bacteria, with the notion of multicellular life being literally billions of years off in the future. Which is to say, it would be distinctly boring and would have nothing of merit to talk to us about.

Do you think it would be worth our while to seed it with photosynthesizers (after removing and studying lifeforms as appropriate) and so terraform it, as Earth was terraformed?

[GrandMasterTerwynn]

Would it be human-habitable? Not only no, but hell no. Any rocky planet would be at the same stage of development as Earth was 3.8 billion years ago. Which is to say, high impact flux, a volcanically-active (much, much moreso than Earth's) crust, and a dense 'primordial' atmosphere comprised mainly of carbon dioxide. Life would be about at the level of photosynthetic and geothermal bacteria, with the notion of multicellular life being literally billions of years off in the future. Which is to say, it would be distinctly boring and would have nothing of merit to talk to us about.

Do you think it would be worth our while to seed it with photosynthesizers (after removing and studying lifeforms as appropriate) and so terraform it, as Earth was terraformed?

Yes. In fact, for colonizing planets, you want the ones with these primitive microbial ecosystems that you can simply overlay an Earth ecology on top of, rather than the stereotypical sci-fi world with a pre-existing advanced ecology with macro-scale multicellular life that has had the advantage of however many billions of years of adaptation to the local conditions.

Epsilon Eridani has two giant asteroid belts, a monster Kuiper belt, and has at least another nine billion good years ahead of it. It's also got at least three gas giants. Even if we left any putative habitable worlds around it alone, it'd be the top system we'd want to colonize, if only because we could build quite the Dyson swarm around it.

But yes, if there were a planet in Epsilon Eridani's habitable zone, it actually would be a pretty good place for colonization; if you could live with all the volcanism, all the asteroids you'd have to deflect, and the natural nuclear reactors. Sure, it'd be preferable if the local blue-green algae had been around long enough to create an oxygen atmosphere before we declared war on them, and sure, Epsilon Eridani will be about twice as bright four billion years from now (Alpha Centauri B is a dead-ringer for Epsilon Eridani, except it is at least five or six times older and has roughly half of Sol's luminosity as a result) requiring that the planet eventually be moved, but you take what you can get. In fact, just landing on the planet will probably hopelessly contaminate it with Earthlife.

Curious how close is the nearest type "G" star (besides Sol) which is believed to be around the same age as Sol?

Also, how do we tell that Epsilon Eridani is only around 850 my old?

A) Alpha Centauri A is 4.3 light-years away. It is only slightly more massive than Sol, somewhat brighter, and only a billion years older.
B) It's an active, fast-rotating star with a luminosity lower than its mass would suggest. That implies youth. The quantity of dust and material orbiting the star also implies that it isn't very old. Looking around the night sky, astronomers have studied tens of thousands of stars in all sizes and all stages of life. The nuclear physics governing them are also well-understood. As a result, we understand how a given star should look and how it ought to behave, given its mass and age.

[Samuel]

Also, how do we tell that Epsilon Eridani is only around 850 my old?

Due to its composition and light spectrum. The first will tell us how long it has been burning, and the second can tell us where it is on the main sequence. Of course, it is ALOT more complicated than that and the details probably make sense only to astrophysicists (which I have a cursory understanding), but basically, as a star ages, it cools and expands and converts more and more of its original hydrogen and helium into heavier and heavier elements.

[GrandMasterTerwynn]

Also, how do we tell that Epsilon Eridani is only around 850 my old?

Due to its composition and light spectrum. The first will tell us how long it has been burning, and the second can tell us where it is on the main sequence. Of course, it is ALOT more complicated than that and the details probably make sense only to astrophysicists (which I have a cursory understanding), but basically, as a star ages, it cools and expands and converts more and more of its original hydrogen and helium into heavier and heavier elements.

Stars actually brighten as they age, as the accumulating helium ash is denser than the hydrogen, and has the effect of further biasing the star's mass distribution towards its core (causing the core to contract and the overall rate of fusion to increase.) A star's outer layers only cool and expand once the core becomes all helium ash and hydrogen fusion continues in the layer surrounding the core, which causes the star to expand into a red giant.

[RedImperator]

Would it be human-habitable? Not only no, but hell no. Any rocky planet would be at the same stage of development as Earth was 3.8 billion years ago. Which is to say, high impact flux, a volcanically-active (much, much moreso than Earth's) crust, and a dense 'primordial' atmosphere comprised mainly of carbon dioxide. Life would be about at the level of photosynthetic and geothermal bacteria, with the notion of multicellular life being literally billions of years off in the future. Which is to say, it would be distinctly boring and would have nothing of merit to talk to us about.

Do you think it would be worth our while to seed it with photosynthesizers (after removing and studying lifeforms as appropriate) and so terraform it, as Earth was terraformed?

I don't really see the point. Epsilon Eridani is already a fantastic system for colonization thanks to the vast quantities of debris available for orbital habitats. The planet would amount to a tiny fraction of the system's overall population, the volcanism is going to be a serious problem, and I'm pretty sure a case can be made it's immoral to wipe out an entire planet's worth of alien life (even primitive life) for no good purpose.

[starslayer]

If I understand, it is eight "Known" stars closer than it. There could be Red Dwarfs closer that we still cannot detect........

Um, no. Small M class stars are easily visible at such distances; Proxima Centauri, for example, is a mere 4.25 ly from the Sun, and is 11th mag; my 8-inch telescope can see Pluto, which is 3 magnitudes fainter. Out to Epsilon Eridani's distance, and even farther, M class stars are not likely to appear fainter than 14th magnitude, if they're even that faint.

Even brown dwarfs are iffy; Epsilon Indi Ba and Bb are about 12 ly from us, farther out than Epsilon Eridani. Anything in our neighborhood that we don't know about is either a planet, or a Jupiter-mass body that has been ejected from a system, or somehow formed away from a protoplanetary disk.

[Kitsune]

I have heard that Sol, in a billion years, will be too bright to support life on earth, is this considered still true?

[Wyrm]

I wonder if we're ever going to figure out why our Solar System's wealth of (small, rocky) planets seems to be the exception rather than the norm...hopefully it'll be an artifact of our limited sensing capabilities, rather than an actual dearth of Earth-like planets.

Most (well, just about all) of the techniques we use to detect extrasolar planets do work better with increased mass of the planet, and gas giants tend to be the most massive: gravitational lensing, astrometric wobble, doppler effect, polarimetry, ect.

Believe me, astrophysicists are not at all surprised by the apparent dearth of earthlike exoplanets. It's just selection bias due to the fact that gas giants are easier to detect. When we get to the point where earthlike planets should be routinely detected and are not detected, that's when you should worry.

[GrandMasterTerwynn]

I have heard that Sol, in a billion years, will be too bright to support life on earth, is this considered still true?

That is correct, for reasons I detailed earlier in the thread:

Stars actually brighten as they age, as the accumulating helium ash is denser than the hydrogen, and has the effect of further biasing the star's mass distribution towards its core (causing the core to contract and the overall rate of fusion to increase.) A star's outer layers only cool and expand once the core becomes all helium ash and hydrogen fusion continues in the layer surrounding the core, which causes the star to expand into a red giant.

If there is a sapient species alive on Earth in that timeframe, they could move the planet via a 'gravity tractor,' which is just an asteroid directed on repeated flybys of Earth, boosting its orbital velocity a little each time. Or, alternately, they could simply disassemble the planet and move all the resulting orbital habitats directly. This assumes, of course, that humans didn't disassemble the planet for conversion into orbital habitats in a Dyson swarm.

[Kitsune]

I knew that stars brighten, the real question was if there was a feedback system which would allow life to survive.

The earth around 850 my was in a period of intense glaciation, almost an ice ball world if I understand.

[GrandMasterTerwynn]

I knew that stars brighten, the real question was if there was a feedback system which would allow life to survive.

No. Unless by "life" you mean "single-celled extremophile living in the rocks of Earth's crust."

In a billion years, the oceans will either be in the process of evaporating, or will have already evaporated. Changes in albedo resulting from increased cloud coverage can only reflect so much of the increased solar radiation back into space.

The earth around 850 my was in a period of intense glaciation, almost an ice ball world if I understand.

Sol was also nearly 10% dimmer back then. There is too much solar radiation falling on Earth now to make a 'Snowball Earth' possible, let alone in a billion years when the sun will be 10% brighter still.