Starship Asterisk*

heehaw wrote:A good picture: of a vast galaxy AND of human 'eyes' observing it. How many more civilizations are there out there, also eyeing that galaxy? A clue is our own solar system: yes, we have an Earth with our civilization. But perhaps more important we have Venus, which has lost ALL its hydrogen and hence NO water and hence NO chance of life. The fact that a Venus appears in our solar system almost guarantees that Venuses are common throughout the galaxy. But we can NOT conclude from our own presence that Earths are similarly common. That is the remaining huge unknown: how common are Earth/Venus-size planets in the habitable zone that do NOT lose their hydrogen? We do not know. It may be that an unusual event involving the origin of our big Moon was somehow crucial to our retaining our hydrogen and therefore having lots of water, leading to life and leading to this posting. If that is so, there may only be tiny numbers of 'Earths' in our galaxy. As it stands, we just don't know! But with future space telescopes, we are going to find out, through spectroscopy of the atmospheres of planets of other stars. (Of course I'd love to have it turn out that true Earths are common.)

MarkBour wrote:

BDanielMayfield wrote: I'd love for really earth-like exo-Earths to be common to, but alas, it don't appear to be so. Some think that having a gas giant or two out in orbits like Jupiter and Saturn also play roles in making our planet so inhabitable (and not just habitable ) One survey of 1,122 sunlike stars found only one gas giant out in a Jupiter like orbit.
Bruce

Bruce, can you elaborate on the notion of our needing gas giants? I certainly have seen things that made me realize that Jupiter is a godsend for us, but did not realize there would be other issues and cases that multiple large planets are helpful for. Thanks.

BDanielMayfield wrote: I'd love for really earth-like exo-Earths to be common to, but alas, it don't appear to be so. Some think that having a gas giant or two out in orbits like Jupiter and Saturn also play roles in making our planet so inhabitable (and not just habitable ) One survey of 1,122 sunlike stars found only one gas giant out in a Jupiter like orbit.
Bruce

heehaw wrote:A good picture: of a vast galaxy AND of human 'eyes' observing it. How many more civilizations are there out there, also eyeing that galaxy? A clue is our own solar system: yes, we have an Earth with our civilization. But perhaps more important we have Venus, which has lost ALL its hydrogen and hence NO water and hence NO chance of life. The fact that a Venus appears in our solar system almost guarantees that Venuses are common throughout the galaxy. But we can NOT conclude from our own presence that Earths are similarly common. That is the remaining huge unknown: how common are Earth/Venus-size planets in the habitable zone that do NOT lose their hydrogen? We do not know. It may be that an unusual event involving the origin of our big Moon was somehow crucial to our retaining our hydrogen and therefore having lots of water, leading to life and leading to this posting. If that is so, there may only be tiny numbers of 'Earths' in our galaxy. As it stands, we just don't know! But with future space telescopes, we are going to find out, through spectroscopy of the atmospheres of planets of other stars. (Of course I'd love to have it turn out that true Earths are common.)

geckzilla wrote: I agree, it's the SMC. LMC must be behind the telescope the whole time.

RJN wrote:An emailer claims that I have mis-identified the SMC as the LMC. After some preliminary checking that seems quite possible. Would someone be kind enough to double check this? - RJN

kenkahn wrote:All I see on my desktop is cat sleeping on a ledge next to a laptop. I understand that this is the 'alternate' picture when the APOD is a video. I'm just curious where do these pictures come from and who decides which one to d/l as the desktop?