Starship Asterisk*

owlice wrote:
Kathleen (kat330) writes that she has now recorded her paean to Gliese 581g; it can be heard here.

http://en.wikipedia.org/wiki/Gliese_581_g wrote:

[img3=""Eyeball Earth" Gliese 581g model"]http://upload.wikimedia.org/wikipedia/c ... hSmall.gif[/img3]

<<Whether or not a tide-locked planet with the orbital characteristics of Gliese 581g is actually habitable depends on the composition of the atmosphere and the nature of the planetary surface. A comprehensive modeling study...identified two habitable states for a water-rich planet. If the planet has a very thin atmosphere, a thick ice crust forms over most of the surface, but the substellar point remains hot enough to yield a region of thin ice or even episodically open water. If the planet has an atmosphere with Earthlike pressures, containing approximately 20% carbon dioxide, then the greenhouse effect is sufficiently strong to maintain a pool of open water under the substellar point with temperatures comparable to the Earth's tropics. This state has been dubbed "Eyeball Earth" by the author. According to [Gliese 581 g discoverer & Zarmina hubby Steven S.] Vogt, the long lifetime of red dwarfs improves the chances of life being present. "It's pretty hard to stop life once you give it the right conditions", he said. "Life on other planets doesn't mean E.T. Even a simple single-cell bacteria or the equivalent of shower mold would shake perceptions about the uniqueness of life on Earth.">>

Daddyo wrote:Would a planet that is tidally locked be more apt to boil off it's atmosphere through the hot point facing it's sun? I wonder if that has been modeled for this or if that is not a significant factor. I also wonder about the likelyhood of having no wind to transport water/clouds to support life (except near shorelines).

Ann wrote:Design by Zarmina Khan. Maybe that's how they dress on Zarmina's world?

(Hey, I can see Captian Picard welcome these ladies on board the good ship Enterprise as ambassadors for Zarmina's world! How surprised the ambassadors will be when they realize that we had figured out the name of their planet even before we even knew if it was inhabited or not!)

APOD Robot wrote: Zarmina s World

... the planet is designated Gliese 581g, but Vogt's more personal name is Zarmina's world, after his wife ...

Steven Vogt (UC-Santa Cruz) is suddenly the buzz of the blogosphere, though not in ways he might have intended. The designer of the HIRES spectrometer that made the detection of Gliese 581g possible, Vogt can claim pride of place as the discoverer of the first near-Earth mass planet found in the habitable zone of its star. But he’s also taking his lumps for saying that he could all but guarantee life on that planet. An unwise call, as many commenters here have noted. Perhaps even more unwise is his hope to name the new planet after his wife, Zarmina.

Centauri Dreams has nothing against the notion of naming celestial objects for loved ones, but caution should always be the byword. Suppose, for example, that Mrs. Vogt, fed up with publicity and tired of the company of astronomers, should surprise her husband by leaving him. Vogt’s ex would be forever enshrined in the celestial sphere, a taunting presence whenever the poor man thought of the Gl 581 system.

Ann wrote:So how seriously should we take this Dave Goldberg? What are his credentials? How good is he seeing into the future and understanding what needs to be done for humans to achieve near-speead of light space travel?

bystander wrote:

durant1928 wrote:Using our fastest rocket-propelled space craft, approximately how long would a one-way trip to Zarmina take ? Let's be realistic about extraterrestrial colonization !

So, How Long Would It Take to Travel to That Exciting New Exoplanet?
Discover Blogs | Discoblog | 04 Oct 2010

... (David) McConville puts the trip at about 180,000 years. Bummer. But that’s assuming that humans only have access to current technology.

Dave Goldberg, coauthor of A User’s Guide to the Universe, took a more optimistic approach. In a blog post, he assumed an average travel speed of 92 percent of the speed of light, and figured that the trip could be accomplished in 22.4 years of Earth-time. Better yet, the time dilation effect described in Einstein’s theory of relativity would shorten the trip from the perspective of the bold travelers on their way to Gliese 581g. To them, the trip would only seem to take 6.1 years.

It is fairly generally acknowledged that technological knowledge roughly doubles every 7 years. Some experts insist that this rate will increase so that a few decades from now it may take only 5 years for a doubling of the technological knowledge. But even if we count only the current rate of doubling every 7 years, a time interval of half a century should result in a total amount of technological knowledge 250 times as large as it is today. Surely this will be enough to attack the problems posed by the desire to undertake an interstellar expedition.

durant1928 wrote:Using our fastest rocket-propelled space craft, approximately how long would a one-way trip to Zarmina take ? Let's be realistic about extraterrestrial colonization !

... (David) McConville puts the trip at about 180,000 years. Bummer. But that’s assuming that humans only have access to current technology.

Dave Goldberg, coauthor of A User’s Guide to the Universe, took a more optimistic approach. In a blog post, he assumed an average travel speed of 92 percent of the speed of light, and figured that the trip could be accomplished in 22.4 years of Earth-time. Better yet, the time dilation effect described in Einstein’s theory of relativity would shorten the trip from the perspective of the bold travelers on their way to Gliese 581g. To them, the trip would only seem to take 6.1 years.

Chris Peterson wrote:

neufer wrote:The sun is really only needed to keep water in a liquid state near the surface.
Many earth ecosystems don't rely on the sun for their energy source.

Certainly. My comments were directed towards the observation that the artist rendering
suggested the planet is heavily populated by something like chlorophyll-based life.

neufer wrote:The sun is really only needed to keep water in a liquid state near the surface.
Many earth ecosystems don't rely on the sun for their energy source.

Chris Peterson wrote:

dahowa wrote:I notice that the artist has included a healthy amount of green on the planet. Not only is it shown as livable, but alive!

I'd think, however, that the shifted spectral output of the star (compared with the Sun) might result in the evolution of entirely different pigments for photosynthesis. On the other hand, photosynthesis in most plants on Earth is adapted for absorbing red and near IR light, so perhaps you'd find a very similar process on a planet in the Gliese 581 system. You'd expect Earth plants to do very well there.

http://en.wikipedia.org/wiki/Photosynthesis wrote:
<<Not all wavelengths of light can support photosynthesis. The photosynthetic action spectrum depends on the type of accessory pigments present. For example, in green plants, the action spectrum resembles the absorption spectrum for chlorophylls and carotenoids with peaks for violet-blue and red light. In red algae, the action spectrum overlaps with the absorption spectrum of phycobilins for blue-green light, which allows these algae to grow in deeper waters that filter out the longer wavelengths used by green plants. The non-absorbed part of the light spectrum is what gives photosynthetic organisms their color (e.g., green plants, red algae, purple bacteria) and is the least effective for photosynthesis in the respective organisms.
Z scheme

dahowa wrote:I notice that the artist has included a healthy amount of green on the planet. Not only is it shown as livable, but alive!

Ann wrote:My software gives a GSC measurement for this star, but there is a Hipparcos measurement, too. Hipparcos says that the maximum V luminosity of Gliese 581 is 10.49, and its minimum V luminosity is 10.60. Could it be that the variability has anything to do with the many planets of Gliese 581?

My software also quotes "Johnson", whose measurement gives a V luminosity of 10.57 for this star.

Yes, but the given V magnitudes (10.49, 10.57, 10.60) are not absolute magnitudes. They are the V magnitudes measured for this star at its distance from us, which is, according to the Hipparcos measurements, 20.45 ± 0.29 light-years. But the absolute magnitude for a star describes how bright it would be if it was seen from a distance of ten parsecs. I can never remember exactly how much ten parsecs is, but I know that it is a little more than thirty light years.

Chris, I think I'm right here. I think that the absolute V luminosity of Gliese 581 is about 11.50.

Chris Peterson wrote:

Ann wrote:Interesting. According to my astronomy software, Gliese 581 has an absolute V magnitude of 11.584. That is a whole magnitude fainter than the paper you refer to. Someone must have made a significant mistake here.

What software? Most of it uses a mix of catalogs, and most catalogs do not contain very accurate photometric data. I do a lot of photometry, and generally cannot rely on standard catalogs to provide accurate photometric references.

The Hipparcos catalog, which is pretty good photometrically, gives V=10.5759±0.004. An error of a full magnitude might suggest your software is using GSC data, which has notoriously poor photometric values.

Craig Willford wrote:A Red Dwarf and a Red Giant are very different stars.

A Red Dwarf is a small star (smaller than our Sun) so that the nuclear furnace cooks more slowly because of decreased pressures at its core. As a consequence it is cooler and only red.

A Red Giant is a star in the final stages of life. It has used up much of its nuclear fuel and has switched to a different nuclear process, making even heavier elements than Helium. In the process, it bloats its surface far from its core and makes the star huge (and red).

Zarmina's world's star is reputed to be the former. It could be a young red dwarf or an old red dwarf. That info. hasn't been provided to us in this APOD entry.

Ann wrote:I didn't quite get that, Chris. Do you mean that there is a greater chance for life to develop on a tidally locked planet than on a planet that isn't tidally locked, like the Earth? Why would it be easier for life to develop on a tidally locked planet?