Hi all,

I'm new here and this is my first post. The reason I'm posting is that ever since HD 28185 has been discovered, I've thought that it is our best chance for finding a compatible planet (so called 'Next Earth') to colonize. However, the 'experts' haven't focused on it, which I think is a huge mistake. Please read my article on this, and let me know your thoughts. If you'd like, you can e-mail me at astro_kct@hotmail.com

~ Thanks


The Case for HD 28185b:
An argument for why HD 28185b may be the most viable
Next-Earth of all known exoplanets
by kct

In the search for extraterrestrial life, there is an interesting subcategory investigating potential habitable planets. Astrophysicists agree that a planet must pass certain criteria in order to be considered a likely candidate for extraterrestrial intelligence. But if one was simply looking for a habitable planet (i.e. one that life could be sustained), as opposed to an inhabited planet (i.e. one that life, perhaps intelligent life, already exists), the criteria become a bit less stringent.

Habitable Zone

A key prerequisite for a planet to be deemed habitable is it must reside in the star system’s ‘habitable zone’ (HZ). In other words, it must orbit in the region of a solar system where temperature and pressure are such that liquid water can firmly exist on the planet surface, and where carbon-based life forms can live or evolve. This zone changes as the star ages, but for a star similar to our own sun, the HZ would roughly be between 0.95 astronomical units (AU) to 1.37 AU. HD 28185b not only meets this criteria, it hits the bulls-eye! ‘Big Blue,’ as I dubbed it for reasons that will become clear, orbits its star at a distance of 1.03 AU—almost precisely the same distance that Earth orbits around the sun.

The orbital distance alone is not the only criteria for a ‘habitable zone’: the orbit itself must be fairly circular, otherwise life-forms would alternately be burned or frozen as the planet moved towards and away from, its sun. Again, ‘Big Blue’ passes the test with flying colors: with an eccentricity of just 0.07 AU (± 0.04), HD 28185b’s orbit is nearly circular, once again much like the Earth’s. Finally, for the convenience of future human colonists, the planet’s period should be fairly similar to our Earth year—again, HD 28185b’s delivers, with a Big Blue-year consisting of 385 days, just 20 days longer than our own.

Main-sequence Star

Still, all this stuff about a habitable zone would be worthless if the star it orbited around was not of the right spectral class. In Search for Extra-Terrestrial Intelligence (SETI) terms, a planet’s corresponding star would have to be a G-class ‘main-sequence’ (V) yellow star (the temperature of the star is classified as O, B, A, F, G, K and M), which burns long and steady enough to support the evolution of life. Our sun is a G2V yellow star, and any star that would anchor a solar system capable of supporting life in its habitable zone would have to be a G-class ‘main-sequence’ (V) star (some theorize that some F-type or K-type stars could also provide enough stability for life, but for simplicity we’ll stick with G-class stars here). The star HD 28185 is a G5V yellow star, again superbly meeting this key criterion.

The Box

So wow, we’ve discovered a planet that is almost exactly as far away from its star as Earth is from its sun, smack in the middle of the ‘habitable zone,’ and its star is that rare, precious G-type main-sequence star?! This is major news—when is NASA sending a probe? Unfortunately, this is where every scientific article grinds to a halt. As a reader, examining article after article making an unnecessary (and I propose wrong) assumption, it’s as though each author has the inability to think outside the boundaries created by the commonalities of our own solar system.

A Massive Dilemma

HD 28185b is 5.6 times the mass of Jupiter, or about 1800 times the mass of the Earth. Such a massive, jovian planet would almost certainly be a gaseous planet, right? After all, every example of a massive planet in our own solar system is in fact gaseous: Jupiter, Saturn, Neptune, and Uranus are giant balls of gas, with intense atmospheric pressures and likely no solid rocky ‘ground’ for life-forms to live and/or develop.

Differentiation between Earth-sized and Earth-like planets

So for years we have been able to detect Jupiter-sized planets around extrasolar stars, only to dispose them as likely candidates for habitability due to their mass. Sustaining life, each scientist states, requires a small, rocky planet, not a large, gaseous planet. Perhaps the use of the term ‘jovian’ to describe both planets of similar mass as Jupiter as well as its gaseous nature is where this problem originated. But ask yourselves for just a minute, what if a planet’s large mass did not inevitably necessitate a gaseous planet? Well, make that leap outside the box, and it opens a vast new range of possibilities.
Doing so reveals that Santos, Mayor, Naef, Pepe, Queloz , Udry, and Burnet may have made a much bigger discovery than any of us have realized, perhaps finding the ‘Big Blue’ companion to Earth (that little blue marble in space) three years ago, and every scientist in the globe thoroughly dismissed this precious information as just another ‘jovian’ planet discovery.

Sample-size

Any pollster or mathematician will tell you that sample-size is essential to deriving an accurate determination for any calculation. A sample-size of nine (as in the planets of our solar system), when the overall field is one of billions (if not trillions) would be laughed at by any mathematician. It’s like asking nine people how they’ll vote in the upcoming election, and using that to predict the overall voting pattern for the entire country. Actually, it is significantly worse than that, since there are exponentially more planets in the galaxy than people in the United States. Yet that is exactly what we are doing when we eliminate any planet from consideration as a habitable planet simply due to its mass.

The Problem with Pressure

Now wait a second, some will still say. You forgot about gravity and atmospheric pressure. Well, in fact, gravity is actually not much of a problem: while Jupiter is 318 times the mass of the earth, its gravity is only 2.5 times the Earth’s—this is because gravity is also a function of the planet’s density and radius, so a massive planet could easily have gravity very similar to that of the Earth if it was less dense. I assert that any planet with gravity anywhere from 0.20 to 2.5 that of the Earth’s would be something that the human race could adapt to. There is no reason to believe HD 28185b would not have a favorable mass-gravity ratio.

Atmospheric pressure is a bit trickier. After all, Venus could have potentially been an interesting candidate if not for its bone-crushing atmospheric pressure. A planet more than five times the mass of Jupiter would almost certainly create crushing atmospheric pressure, would it not? Well, once again, not necessarily: Venus’ crushing pressure is a function of its heavy atmosphere, which is partly due to its gas composition (mainly CO2 and sulfuric acid). But imagine, if you will, an atmosphere primarily composed of nitrogen, with small parts of oxygen and H2O. In this scenario of, let’s say over 90% nitrogen, this gas, commonly acknowledged as vital to life, has the added benefit of reducing the partial pressure of oxygen and other gases.

That, of course, would be an almost ideal scenario. Even in a less hospitable atmosphere, a planet large enough to have the mass of 5.6 times that of Jupiter (and be rocky vice gaseous, as discussed previously) would almost certainly contain huge mountain ranges that dwarf those of Earth. As we hike up those mountains, the atmospheric pressure would eventually get to a level comfortable for life to exist. In a world the size of HD 28185, even the mountain ranges alone would cover a habitable area many times that of the entire Earth. Jupiter itself has a hospitable atmospheric pressure if you go up high enough in its methane clouds—the problem with Jupiter is primarily its gaseous state and gas composition, not it’s pressure. After all, if one goes deep enough in Earth’s oceans, the pressure is just as crushing and inhospitable as that of any exoplanet. But again, this jovian-by-association stigma has kept scientific thinking inside a box and has hampered scientific innovation and discovery.

A Great Risk-Reward Ratio

Critics may point out that there have been a couple of key assumptions made in this paper in order for HD 28185b to prove hospitable to life. Still, I maintain that those assertions are just as likely in our infinite universe as the common assumption that a jovian-size planet must also be a Jupiter-like planet and that the only Earth-like planets out there must also be Earth-sized. I challenge those assertions—and fortunately we have the means within our grasp to determine the viability of HD 28185b in the very near future.

The Terrestrial Planet Finder (TPF), a NASA mission scheduled for 2015, will have the means through the science of spectroscopy to determine whether exoplanets have atmospheres and establish whether they are habitable. Such a mission would expose the atmospheric composition of HD 28185b, and tell us whether Next-Earth lies within our grasp. However, with plans to focus on terrestrial planets, defined in the narrow sense I described above, the fear is that HD 28185b and other jovian-size planets in the habitable zone will be overlooked in favor of smaller planets. And that would be a shame, as a great opportunity for discovery may be missed.

So what will we do? Faced with such potentially great reward as the discovery of the Next Earth (‘Big Blue’), will we let our imagination guide us to greatness, or will we continue to remain confined within our narrow understanding of the cosmos? I submit that there is no choice at all: we must determine its atmosphere, and if the results yield favorable conditions, it would launch a new era in aeronautics similar to that of the great automobile and computer technology eras, one that could see us developing the right spacecraft to reach the HD 28185 star system within 50 years.

Dare to Dream

Let your imagination release your imprisoned possibilities.
-- Robert H. Schuller

Man's mind, once stretched by a new idea, never regains its original dimensions.
-- Oliver Wendell Holmes

The true sign of intelligence is not knowledge but imagination.
-- Albert Einstein

Our imagination is the only limit to what we can hope to have in the future.
-- Charles F. Kettering

__________________
<span style='color:blue'>Let your imagination release your imprisoned possibilities. </span> -- Robert H. Schuller
<span style='color:green'><span style='color:green'>Man's mind, once stretched by a new idea, never regains its original dimensions.</span> </span> -- Oliver Wendell Holmes
<span style='color:blue'>The true sign of intelligence is not knowledge but imagination. </span> -- Albert Einstein
<span style='color:green'>Our imagination is the only limit to what we can hope to have in the future. </span> -- Charles F. Kettering

Congratulations!
A very bold paper. I am no physicist, but I like your train of though. The interactions at depth on a small gas giant at one AU, could we assume a large ocean under a thick atmosphere? If so, could we expect giant deep sea fish? Squid?

I have heard of atmospheric spectrum being taken as planets cross their stars, any chance of this with HD 28185b?

On a final note, I think it worth mentioning the pursuit of life as we know it, in any other situation we find, the possibility is that it will be life as we have never seen it or even imagined it, in the realm of science fiction, humanity has imagined a lot of possibilities.

I really like your paper though. Very well written, now brace yourself for the critics

Good luck.

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Hi astro_kct, welcome to the forum,

Generally, there are two things that I would suggest to you.

First is that it is very likely that HD 28185 is a gas giant with a surface gravity around ten times that of Earth, but it is also likely that it has some very large moons orbiting it. These moons would also be in the HZ. So even if the planet itself has some giant problems, it may have a moon with a sufficiently thick amosphere to protect the surface from the likely high levels of radiation [worse than what Europa gets].

Second, why the pressure to launch a probe within fifty years? The star is about 125 light years away. In fifty years we might be able to make a probe that could get up to 0.01 c, but we won't have a power source that will stay reliable for the 12,500 year voyage.

Certainly, the main point of your post makes sense. We should study this thing more with TPF and later even better instruments.

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Forming opinions as we speak

Well, with a mass 5 times that of Jupiter, and a gravity of 10 gee, this planet almost certainly has a hydrogen rich atmosphere. By combination with oxygen there may well be a lot of water in the atmosphere, and possibly a deep ocean layer overlaying the core; but there will almost certainly be no free oxygen...

oxygen combines too readily with hydrogen to remain in any great quantities.

This does not rule life out; but it does rule aerobic life out.

You may well get anaerobic life in the atmosphere of this gas giant; also other, closer gas giants like Gamma Cephei b are more or less in the habitable zone.

In fact, if we are considering such anaerobic lifeforms, which inhabit environments so different to our own, there is no real reason to limit our search to the habitable zone which would hold terrestrial planets like our own Earth;

At the end of the day, gas giant life will probably be limited in size and complexity
by the gaseous environment it in habits; too heavy, and it will sink in the light hydrogen rich atmosphere.

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Why'd you have to go and mention that Ant? B)

I was getting really excited - all that "within reach" - not in this atoms lifetime - sigh.

Hi astro_kct, I like the paper and your ideas. I agree all around we need to study this in greater depth.

By the way - how young/old is the planet?

I ask as a ref to another thread on proto-earths with Jovian atmospheres - I asked on that one could we see this process somewhere (the eventual shrinking of the atmosphere to reveal an earth-like planet underneath.)

Is this the answer?

Mild

Way to go!!

It's difficult to imagine a rocky planet large enough to contain most of the mass of HD28185b that would not accrete a thick, deep atmosphere (although less fromidable than that of Jupiter) that would be difficult for us. In the unlikely event the object turns out to be a cluster of planets (celestial dynamics permitting), some or each of them could be more pleasant habitats with little or no modification by us with appropriate deference to any aboriginals.

Has anyone done the arithmetic required to compute the radius of a rocky planet with average density 5 times that of Jupiter and the mass of HD28185b and a 5-bar atmosphere? Due to the plentifulness of water throughout the MW these days, this planet of hypothetical structure will probably have a several hundred mile deep ocean and no land (solid biostructures notwithstanding) anywhere above the water and a radius much smaller than that of the disk of Jupiter. Due to this smaller radius I would expect the gravitational force to be much larger than 5 times that of earth. What radius is commonly used to compute the "surface" gravity of Jupiter?

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For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

Yes; one other thing about a high gee planet- it would not have high mountains;
in fact the rocky core- if there is one, which is not guaranteed- woould be remarkably smooth; and the atmosphere would probably convert into liquid phase several hundred kilometers above the rocky surface.

You might even get an ice mantle- like the one on my own imaginary planet Panthalassa
http://www.orionsarm.com/worlds/Panthalassa.html
which is based on this paper
http://arxiv.org/abs/astro-ph/0308324

Thank you and everyone else for the great replies!

Regarding your question, I believe that determining the atmosphere the way you discussed is being done through the Terrestrial Planet Finder (TPF) mission that I mentioned in my article. Professor Maggie Turnbull is putting together a list of planets to do this test on, and my point is that HD 28185b deserves to be on that list--I haven't seen the full list, so I don't know if it's on, but I don't believe it is because they are mainly concentrating on smaller "terrestrial" planets. But my assertion is that even if the probability is small that it has a breathable atmosphere, everything else about this planet is almost tailor-made for terrestrial life that we can't afford NOT to find out. So I'm spreading the word, hoping to add HD 28185b on the list of planets that this test will be conducted.

Thanks again!

__________________
<span style='color:blue'>Let your imagination release your imprisoned possibilities. </span> -- Robert H. Schuller
<span style='color:green'><span style='color:green'>Man's mind, once stretched by a new idea, never regains its original dimensions.</span> </span> -- Oliver Wendell Holmes
<span style='color:blue'>The true sign of intelligence is not knowledge but imagination. </span> -- Albert Einstein
<span style='color:green'>Our imagination is the only limit to what we can hope to have in the future. </span> -- Charles F. Kettering

Considering how much computer technology has advanced in just 25 years or so ( remember using 8086 processors and Commodore 64 in the 80s?), I have no doubt that if we had a target to shoot for, aeronautic engineering would "take off" (pun intended :P ). It's just a matter of having a reason to motivate us to shift/allocate resources in this area. Another analogy I mention in my article is that of the automobile industry: look at what we've done since the 1900s...

Here's the Catalog/Notes Page on HD28185 (both star and planet):
HD 28185 Notes

Keep the comments coming--I'm interested in hearing more!

Thanks!

__________________
<span style='color:blue'>Let your imagination release your imprisoned possibilities. </span> -- Robert H. Schuller
<span style='color:green'><span style='color:green'>Man's mind, once stretched by a new idea, never regains its original dimensions.</span> </span> -- Oliver Wendell Holmes
<span style='color:blue'>The true sign of intelligence is not knowledge but imagination. </span> -- Albert Einstein
<span style='color:green'>Our imagination is the only limit to what we can hope to have in the future. </span> -- Charles F. Kettering

It might be more fair to compare it to how much the airline industry, or space launch capability has improved in the last 25 years. Computers have been benefiting by our increased ability to handle fine details, but large-scale transportation is up against limits of the energy content of transportable matter [fuel]. I think getting a probe up to 0.01 c within fifty years was a fairly generous prediction of how much we will advance technically on that front.

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Forming opinions as we speak

It might be more fair to compare it to how much the airline industry, or space launch capability has improved in the last 25 years. Computers have been benefiting by our increased ability to handle fine details, but large-scale transportation is up against limits of the energy content of transportable matter [fuel]. I think getting a probe up to 0.01 c within fifty years was a fairly generous prediction of how much we will advance technically on that front. [/b][/quote]
Fair enough...

Another area of potential fast-paced growth that may help is nanotechnology -- depending on where that field takes us, we may make advances we can only dream about today.

__________________
<span style='color:blue'>Let your imagination release your imprisoned possibilities. </span> -- Robert H. Schuller
<span style='color:green'><span style='color:green'>Man's mind, once stretched by a new idea, never regains its original dimensions.</span> </span> -- Oliver Wendell Holmes
<span style='color:blue'>The true sign of intelligence is not knowledge but imagination. </span> -- Albert Einstein
<span style='color:green'>Our imagination is the only limit to what we can hope to have in the future. </span> -- Charles F. Kettering

There's no question that nanotechnology will have a big impact. It will enable us to make our probes much smaller, and our engines more efficient. However, it will not enable us to violate the laws of physics.

But all that is a tangent. The point is that there is a planet in a habitable zone around a relatively nearby star. If we are lucky, it will have habitable moons.

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Forming opinions as we speak

Please tell me more about your statement that the planet must be hydrogen-rich: I don't think that the facts strictly make that a necessity.
Also, I have seen that several have assumed that this planet's gravity will simply be 4-5 times that of Jupiter's gravity, an assumption I also think is not necessarily true. Please elaborate...
Having said that, I find the rest of your comments intriguing as well, especially the possibility of a deep ocean.

Thanks

__________________
<span style='color:blue'>Let your imagination release your imprisoned possibilities. </span> -- Robert H. Schuller
<span style='color:green'><span style='color:green'>Man's mind, once stretched by a new idea, never regains its original dimensions.</span> </span> -- Oliver Wendell Holmes
<span style='color:blue'>The true sign of intelligence is not knowledge but imagination. </span> -- Albert Einstein
<span style='color:green'>Our imagination is the only limit to what we can hope to have in the future. </span> -- Charles F. Kettering

Although I didn't post the comment I can tell you that when we detect planets like this it is the planet's orbit and mass. As the gravity is determined by the mass you can guess pretty closely what the gravity will be.

I also agree that we can't rule out any world in the habitable zone of a star with a fairly circular orbit. Even if it is a massive gas giant, the comment has been made and I agree, the planet could have one or more habitable moons. Many people talk about Europa, but when the Sun expands and warms some of the prime real estate in this solar system will be Ganymede and Callisto. Both are outside of Jupiter's radiation belt and both are rocky worlds with suitable gravity and water rich. You will have two mini-Earths to move to, unless we terraform them both first. Add a nice thick greenhouse gas atmosphere and we could move there in short order.

Furthermore, just because we discover nothing in the habitable zone of a star doesn't mean there's nothing there. Are current methods of planet detection are mostly limited to high mass planets in either exceptionally tight or exceptionally eccentric orbits that cause a large radial velocity change to the star's wobble. Little worlds like the Earth are still completely invisible to our best detection method, and it may be a decade or more before we finally start seeing them. The problem is that we can't rely on the results of our current searches to rule out any star. Whether we've found no planets or ten, there could still be happy little Earths around any of them that we'll have to hunt patiently for to finally discover.

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...and we'll be saying a big hello to all intelligent life forms everywhere; and to everyone else out there, the secret is to bang the rocks together, guys...

Anton is absolutely right. The moons of this planet are what might be promising. The planet itself is almost certainly out of the question.

Let's talk about surface gravity - the formula is g/ge = (m/me)/((r/re)^2)
where g is surface gravity, m is mass and r is radius, and the ones followed by an e are the same values for earth. The planet is 1800 times the mass of the earth so that gives us m/me. If it is terrestrial, as you assume, then it's density is similar to the earth's, which means it's radius must be the cube root of 1800 = 12.2 times the earth's radius. Putting them in the formula, we get a surface gravity of 12 times the earth's.

I'd argue with your assertion that we could adapt to gravity of 2 g's on an ongoing basis, but no one could ever expect us to adapt to 12 g's. That would kill in minutes at best.

So even if it is a giant terrestrial planet, it is uninhabitable on that basis alone. Others have mentioned a variety of other reasons that would make it inhospitable. The energy required to get in and out of that immense gravity well is another practical issue.

But it's moons are much more promising. 3 of 4 gas giants in our solar system have relatively large moons. However, to hold an atmosphere this close to a star, an object has to be larger than Mars. We don't see any moons like that in our solar system, but we don't have any planets that arte 5.7 times as big as Jupiter either, so maybe it has a large enough moon.

With any luck, there might be a large moon far enough out to avoid the incredible radiation belts that undoubtedly surround this thing. Still, the immense tides that such a moon would suffer would likely be the big issue. Surface water is necessary for life, but close to a planet like this one, tides would wash right around the planet on a twice daily basis.

Maybe a trojan would be a better candidate?

Actually we can. Stars that have large planets in highly eccentric orbits that go through the habitable zone are out. Under those conditions there are no stable orbits in the habitable zone for a smaller planet to occupy.

The interesting thing is that many of the planets we are discovering are like that, which makes our solar system start to look special. But, as you point out, that's just a sampling bias. With our current methods, we could look at the sun from 10 light years away, and we'd be unable to detect any planets at all, even Jupiter (it's too far out). So maybe all those stars that look like they don't have planets have solar systems just like ours, and it's only the weird systems that we're currently seeing.

You quoted eburacum45, but I'll provide some answers.

It is not a necessity that the planet be Hydrogen rich, but it seems likely based on things we know:

-The planet has a mass about 5 times that of Jupiter
-The photosphere star has about 1/4 the concentration of heavy elements as our sun
-If the planet were made only of heavy elements, it would contain more mass of heavy elements than the star it orbits [pretty unlikely scenario]
-As John L points out, even if it didn't start with a heavy atmosphere, a ball of rocks and Iron that heavy would acquire one.

BTW, it is generally assumed that planets more massive than Jupiter have roughly the same radius as Jupiter, but are simply more dense in the center.

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