Goldilocks Zone

New Earth-sized Exoplanet is in Star’s Habitable Zone

29 Sep , 2010 by

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An enticing new extrasolar planet found using the Keck Observatory in Hawaii is just three times the mass of Earth and it orbits the parent star squarely in the middle of the star’s “Goldilocks zone,” a potential habitable region where liquid water could exist on the planet’s surface. If confirmed, this would be the most Earth-like exoplanet yet discovered and the first strong case for a potentially habitable one. The discoverers also say this finding could mean our galaxy may be teeming with prospective habitable planets.

“Our findings offer a very compelling case for a potentially habitable planet,” said Steven Vogt from UC Santa Cruz. “The fact that we were able to detect this planet so quickly and so nearby tells us that planets like this must be really common.”

Vogt and his team from the Lick-Carnegie Exoplanet Survey actually found two new planets around the heavily studied red dwarf star Gliese 581, where planets have been found previously. Now with six known planets, Gliese 581 hosts a planetary system most similar to our own. It is located 20 light years away from Earth in the constellation Libra.

The most interesting of the two new planets is Gliese 581g, with a mass three to four times that of the Earth and an orbital period of just under 37 days. Its mass indicates that it is probably a rocky planet with likely enough gravity to hold on to an atmosphere.

The planet is also tidally locked to the star, meaning that one side is always facing the star in sunlight, while the side facing away from the star is in perpetual darkness. One effect of this is to stabilize the planet’s surface climates, according to Vogt. The most habitable zone on the planet’s surface would be on the terminator, the line between shadow and light, with surface temperatures decreasing toward the dark side and increasing toward the light side.

“Any emerging life forms would have a wide range of stable climates to choose from and to evolve around, depending on their longitude,” Vogt said.

There has been debate about the other planets found previously around Gliese 581, whether they could be habitable or not. Two of them lie at the edges of the habitable zone, one on the hot side (planet c) and one on the cold side (planet d). While some astronomers still think planet d may be habitable if it has a thick atmosphere with a strong greenhouse effect to warm it up, others are skeptical. The newly discovered planet g, however, lies right in the middle of the habitable zone.

“We had planets on both sides of the habitable zone–one too hot and one too cold–and now we have one in the middle that’s just right,” Vogt said.

The researchers estimate that the average surface temperature of the planet is between -24 and 10 degrees Fahrenheit (-31 to -12 degrees Celsius). Actual temperatures would range from blazing hot on the side facing the star to freezing cold on the dark side.

If Gliese 581g has a rocky composition similar to the Earth’s, its diameter would be about 1.2 to 1.4 times that of the Earth. The surface gravity would be about the same or slightly higher than Earth’s, so that a person could easily walk upright on the planet, Vogt said.

The planet was found using the HIRES spectrometer (designed by Vogt) on the Keck I Telescope, measuring the star’s radial velocity. The gravitational tug of an orbiting planet causes periodic changes in the radial velocity of the host star. Multiple planets induce complex wobbles in the star’s motion, and astronomers use sophisticated analyses to detect planets and determine their orbits and masses.

“It’s really hard to detect a planet like this,” Vogt said. “Every time we measure the radial velocity, that’s an evening on the telescope, and it took more than 200 observations with a precision of about 1.6 meters per second to detect this planet.”

In addition to the radial velocity observations, coauthors Henry and Williamson made precise night-to-night brightness measurements of the star with one of Tennessee State University’s robotic telescopes. “Our brightness measurements verify that the radial velocity variations are caused by the new orbiting planet and not by any process within the star itself,” Henry said.

The researchers also explored the implications of this discovery with respect to the number of stars that are likely to have at least one potentially habitable planet. Given the relatively small number of stars that have been carefully monitored by planet hunters, this discovery has come surprisingly soon.

“If these are rare, we shouldn’t have found one so quickly and so nearby,” Vogt said. “The number of systems with potentially habitable planets is probably on the order of 10 or 20 percent, and when you multiply that by the hundreds of billions of stars in the Milky Way, that’s a large number. There could be tens of billions of these systems in our galaxy.”

Source: University of California – Santa Cruz

Here’s an article about abiogenesis, or the beginning of life on Earth.

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pink
Member
September 29, 2010 4:55 PM

Wowowow, it finally happened!

I understand what Lawrence B. Crowell is trying to say- we don’t know hardly anything yet, there are many ways in which this planet could be a hunk of rock- but I am nevertheless very excited. I think you would have to be very jaded for this not to ignite at least some excitement or awe. There is a distinct possibility- however slight- that we, human beings, could head on over and simply stroll around on this planet! (Maybe with an oxygen breather?)

And certainly this planet is not alone!

Uncle Fred
Member
Uncle Fred
September 29, 2010 2:31 PM

Very exciting – best candidate world so far. Still, the real magic for me will come when we start verifying the existence of rocky worlds around stars like our sun.

Lets get more sensitive instruments and more planet hunting teams online!

Kevin
Member
Kevin
September 29, 2010 3:29 PM

How do they know it’s tidally locked?

Lawrence B. Crowell
Member
Lawrence B. Crowell
September 29, 2010 3:32 PM

The tidal locking of this planet reduces the prospect for life. There might at best be an annular region where the star’s radiation is approximately tanget to the planet where life might exist. However, there are extreme differences of hot and cold. The atmosphere might also be in fact absent. The hot side might have the atmosphere blown away and the cold side the atmosphere might be frozen out, Over time this might leave litte atmosphere for the annular region where conditions are presumed to be right.

LC

Lawrence B. Crowell
Member
Lawrence B. Crowell
September 29, 2010 3:37 PM

How does we know it it tidally locked. Well Gliese 581 has other planets like this which have been in this news. The physics can be calculated. In my book “Can Star Systems be Explored? — The physics of starprobes” I run through these caluclations with respect to previous planets found around Gliese 581.

For life to exist on this planet there has to be mechanisms that distribute the heat around the planet. This could mean horrendous storms. Otherwise I fear this planet is dead as a doornail.

LC

Uncle Fred
Member
Uncle Fred
September 29, 2010 4:48 PM

Another question to be asked is what gravitational influences other planets have had on these core worlds? Could there be Neptune or Jupiter sized gas giant as yet undiscoved?

Specifically, has any large mass planet(s) influenced these planets enough to affect their standing within Gliese’s habitable zone?

Uncle Fred
Member
Uncle Fred
September 29, 2010 4:49 PM

One last thing. How stable is this red dwarf? How much radiation does it bletch?

CrazyEddieBlogger
Member
September 29, 2010 5:06 PM

I can see how the inhabitants of a tidally-locked planet would publish a book in which it categorically states that obviously you cannot have life on a rotating planets, since it it doesn’t have a stable annular ring (which is naturally the only way to support life).

Such planets will be subject to temperature changes on the order of even 40 degrees C between “Night” and “Day” (two words that scientists use to describe the periods of time of direct solar illumination and total darkness.

Seriously – given all we see on Earth regarding bio-diversity and extremophiles, I find it amazing that people still think something like a tidally locked planet is a serious barrier to life.

high_school_astronomer
Member
high_school_astronomer
September 29, 2010 5:20 PM
Wow, really exciting! I also have to agree that I don’t think it being tidally locked necessarily eliminates life. I read on New Scientist that the day side is something like 71C and the night side -40C. Couldn’t like evolve in the comfortable annular ring and then migrate outwards to the night and day regions. We certainly see extremophiles in harsher temperatures that here on Earth. However, the atmosphere being blown away/frozen out does seem concerning. But could it be regenerated? Doesn’t something like that happen on Titan? I don’t know…it’s not an area I have a lot of knowledge in. Nonetheless, very exciting. I bet the Kepler Scientists are kicking themselves that they couldn’t publish their findings… Read more »
Aqua4U
Member
September 29, 2010 6:00 PM

Very interesting news! It was on October 6, 1995 that the very first exoplanet was ID’d. Only 15 years later and we’ve got proof of a possible ‘Earthlike’ planet! Cool beans at a Bar-B-Que! Now, with data pouring in from the Keppler mission, we’ll no doubt have a BUNCH more candidates and proof that solar systems like ours are fairly common? ‘Drakes Equation’ may have to be revisited?

Klatu! Barada, CHEETO’s! ~@; )

Lawrence B. Crowell
Member
Lawrence B. Crowell
September 29, 2010 6:10 PM
There is a bit of a critical issue here. I don’t know how atmospheres form on planets particularly, but let me conjecture two extreme cases. The first case is this planet started with a rather modest or tenuous atmosphere. If that happens there is not much heat capacity to distribute heat. So the atmosphere on the dark side freezes out and the atmosphere on the hot side evaporates off. In that case you have a dead planet. The other case is this planet has a pretty dense atmosphere. When the planet formed it was likely N_2 and CO_2, so this atmosphere trapped heat as well. So if this is two thick we might not want to compare this… Read more »
CrazyEddieBlogger
Member
September 29, 2010 6:48 PM
In a tidally locked planet, you could have a fast-evaporating ocean on the hot side, and constant rain on the night side, and all the rivers flowing from cold side into the hot side. Since the temperature gradient is persistent, this would be a hugely efficient (self regulating) heat transfer mechanism, since it relies on phase-change rather than simple convection. And of course now you have the people living in the temperate zone being a a thermodynamic heaven… An infinite heat source to the North, an infinite heat sink to the South – what else can a civilization ask for? You can have lifeforms that travel the water from South to North, then send spores via the atmospheric… Read more »
Uncle Fred
Member
Uncle Fred
September 29, 2010 7:10 PM

“The more I think about this type of planet, the more I like it!”

It’s my understanding that atmosphere’s are very temperature sensitive. Seems like we might have a very windy/cloudy planet with a thick atmosphere, or a dead world with much of the atmosphere frozen on the dark size and vaporized away on the hot one.

Either or, it doesn’t sound very appealing. Hopefully observations can show us that alternatives to these two scenarios are possible.

Lawrence B. Crowell
Member
Lawrence B. Crowell
September 29, 2010 7:35 PM

That is a possible problem. Huge thermal gradients between the two sides could cause huge winds that permanently blow. So to make the temperature distribution more even you need a thicker atmosphere with a larger heat capacity. Then the detailed trick is to avoid creating a Venusian situation.

LC

Uncle Fred
Member
Uncle Fred
September 29, 2010 8:17 PM

LC: Interesting.

Do you suppose a Venusian style runaway greenhouse effect would be less likely if the planet had a sizable quantity of liquid surface water?

Uncle Fred
Member
Uncle Fred
September 29, 2010 8:29 PM

I imagine multiple large bodies of water would help equalize temperatures. Also, wouldn’t substantial bodies of water lubricate the crust and facilitate the development of plate tectonics?

A Venusian style periodical meltdown or semi-meltdown would be pretty rough on any developing life. Furthermore, I’m uncertain how being tidally locked would effect the formation or function of tectonics, if at all.

CrazyEddieBlogger
Member
September 29, 2010 8:38 PM
A greenhouse effect becomes “runaway” if an increase in temperature creates an increase in the amount of greenhouse gas. Once it does, it keeps running away until it hits the next equilibrium condition. Where the equilibrium points are is a function of many parameters, and nothing says it’s outside the habitable condition. Earth’s atmosphere has “run away” and reached where it is today. (or rather was 100 years ago, but that’s a separate story) With a phase-change system like I described, there will be a steady state solution (globally), and the “fast winds” will be totally normal to the inhabitants. What’s a little wind? We have creatures that live in much harsher conditions than just a little wind,… Read more »
Paul Eaton-Jones
Member
September 30, 2010 12:12 AM

I think we ought to reign in our enthusiasm a bit here I mean we haven’t actually seen the bloody thing yet have we? All of a sudden we go from a barely detectable twitch on a screen to constructing a habitat which may or may not support life. What next, a long-lost civilisation that struggled vainly against a leaking atmosphere? Pah!

Olaf
Member
Olaf
September 30, 2010 12:14 AM

What about sea life in a sea just right at the border of dark and light isolated from the rest of the planet? Under water volcano’s can warm up the water too.

hydrazine
Member
hydrazine
September 30, 2010 12:38 AM
Hmm…. a “period of just under 37 days” probably means not too much of a magnetic field. That would mean that the planet has problems holding on at least to the lighter elements like the hydrogen. Consequently we have a water problem. In the worst case almost all of its atmosphere might be gone like on Mars. In the bad news department, on the hot side the atmosphere might be a bit puffed up making the loss of constituent gases even more of an issue. With its size the planet likely has some form of plate tectonics going on with volcanoes spewing out stuff on regular basis so I would be guessing that there’s at least A mechanism… Read more »
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