> If we presume there's nothing special about our little corner of the universe, then the distance to the nearest potentially habitable planets gives us an estimate of how many habitable planets are out there
I would put a slight caveat to this - I would argue we do know there's something "special" about our little corner of the galaxy, at least - we are in the continuously habitable zone - for example, there are billions of stars at higher densities closer to the core whose planets are likely uninhabitable due to toxic levels of radiation, GRBs, etc. So I actually might expect other planets near us to be more habitable on average than at least some other places in our galaxy.
But I also think it's too soon to know how potentially habitable these planets are, until we have a chance to check a bunch of other things on the checklist, like the long-term stability of the sun's output and the planet's orbits, the frequency of destructive solar flares, the frequency of asteroid bombardments (if there are no Jupiters to absorb them), etc.
Regardless the close distance should make it much easier to answer these sorts of questions than it would be far planets much farther away, and I'm excited to see what we can learn in the coming years.
Wouldn't each system's star do a decent job of pushing back extra-solar radiation? Up to a point, obviously, but it would seem that planetary background radiation levels aren't a direct function of solar density.
It's not the density of the star but the density of stars. Dense clusters like those found in the center of our galaxy create a lot of secondary effects like bigger stars pulling matter away from smaller stars (creating lots of background radiation and matter floating around) and then stars plow through those interstellar clouds, creating deadly bursts capable of cooking entire planets, stripping away their atmospheres, etc. In the center of the galaxy, these events happen so frequently that it's extremely unlikely life on any of the planets would survive long enough to evolve beyond simple single celled organisms.
Solar wind is a type of solar radiation. I thought perhaps a charged field of particles with an outward force could act at least partially as a shield in for some higher frequencies of electromagnetic waves.
It sounds like you're thinking of the heliosphere, which is the bubble in the interstellar medium created by the solar wind. The solar wind, in turn, is created by outflowing plasma from the Sun, and is also responsible for auroras and comet tails. The details of how far from the sun the heliosphere extends are complex, but it encompasses all the known planets.
The heliosphere does provide us with a significant amount of protect from cosmic rays, which aren't actually electromagnetic radiation. Cosmic rays are extremely energetic particles, typically protons, coming in from outside the solar system. The Earth's atmosphere also does a good job stopping cosmic rays, which means their primarily a hazard to spacecraft, both manned an unmanned. (I don't know what effect cosmic rays would ultimately have on Earth if we didn't have the protection of both the heliosphere and our own atmosphere, but I know they have been investigated for links to mass extinctions.) They're a threat to space travel because they cause soft errors in electronics, and DNA and other radiation damage to human beings.
The Sun's magnetic field - aka the interplanetary magnetic field or heliospheric magnetic field - travels with the solar wind and fills the solar system. It is magnetically coupled to solar system bodies like the Earth and Jupiter. As an amateur astronomer, the heliospheric magnetic field doesn't have any significant effects on photons coming into the solar system.
That is incorrect. Energetic particles are radiation. Radiation isn't just photons.
I don't think you understood my question very well because none of what you presented is new to me nor is it what I asked about. Still, thank you for the time and effort.
Electromagnetic radiation from one star does not repel electromagnetic radiation from other stars. If it did, we wouldn’t be able to see stars at night from the Earth.
I should have been more clear in my question. Solar wind is a form of solar radiation, and I was curious about the effect of solar wind + the magnetic field that carries it would have on some frequencies of electromagnetic waves.
I would expect mid-frequency radiation such as visible light to remain largely unaffected, I was thinking more about its effect on high-frequency extra-solar radiation. And it's likely not correct to visualize this as individual photons colliding but rather wave interference.
Here is an article explaining the effect [0]. An excerpt:
"The interplanetary magnetic field, which is embedded in the solar wind, deflects low-energy cosmic rays from us at the outer reaches of our solar system, decreasing the flux of these cosmic rays that reach us at Earth."
> If it did, we wouldn’t be able to see stars at night from the Earth.
Ha! I love straighforward sanity checks like this. My initial reaction was to ask myself about photon-photon collisions which are im fact possible, but your comment gives a nice Fermi bound on how rare such events actually are. Cool!
Photon-photon collisions are still technically possible... I remember a professor mentioning this as one question he got in grad school... draw out the Feynman diagram and you see a vanishingly small probability of photon-photon interaction.
But yeah. Ionized particles like Galactic Cosmic Rays can be repelled by the local stellar magnetic field, but mostly the lower energy rays are deflected. Higher energy -to-charge-ratio GCRs can punch right through the weak stellar magnetic field, just like do for our Sun’s interplanetary magnetic field.
Nope! Some stars are in a stable orbit in a region with some NASTY orbiting interlopers who are eating star systems every million years and have just not made their way to them yet.
We have made it at least a billion or so without getting too close to a nasty body so that says something about the region around us.
I'm guessing you've read Incandescence by Greg Egan?
It explores the possibility that general relativity could be discovered by a pre-industrial civilisation living inside an asteroid in a very tight orbit of one those nasty interlopers.
Egan is one of my all-time favorite SF authors. Was delighted and surprised to find his name popping up in some nitty-gritty, research-level algebra discussions recently. I haven't heard of Incadescence so it's definitely going on the list. Am also intrigued by Dichronauts too! Have you read it?
I often hear about the LY unit of distance. Why is it that we are still discovering things which are close to us in LY units? Wouldn’t we discover things at a distance of 5xLY before discovering things at a distance of 100xLY?
Things that are very luminous can be seen much further away than things that are very dim.
This particular star is a tiny red dwarf, which is so dim we only just found the star itself in 2003.
Our best planet-finding methods depend on finding signals in the light output of the host star. This is relatively insensitive to distance, but very sensitive to the properties of the star.
> If we presume there's nothing special about our little corner of the universe, then the distance to the nearest potentially habitable planets gives us an estimate of how many habitable planets are out there
I would put a slight caveat to this - I would argue we do know there's something "special" about our little corner of the galaxy, at least - we are in the continuously habitable zone - for example, there are billions of stars at higher densities closer to the core whose planets are likely uninhabitable due to toxic levels of radiation, GRBs, etc. So I actually might expect other planets near us to be more habitable on average than at least some other places in our galaxy.
But I also think it's too soon to know how potentially habitable these planets are, until we have a chance to check a bunch of other things on the checklist, like the long-term stability of the sun's output and the planet's orbits, the frequency of destructive solar flares, the frequency of asteroid bombardments (if there are no Jupiters to absorb them), etc.
Regardless the close distance should make it much easier to answer these sorts of questions than it would be far planets much farther away, and I'm excited to see what we can learn in the coming years.