[brokeAstronomer]

As someone in the field (I made an account just to comment on this), I agree that scientists will always be motivated to push the boundaries on questions that are relatively esoteric. People are right to be skeptical... However, even if they aren't immediate, there are enormous tangible benefits to society from conducting scientific research:

1. Basic research directly underpins the vast majority of the technology we have available. Or at the minimum provides the framework with which we understand how technology operates, making it easier to improve. I think the utility of this is greatly underappreciated.

2. It's impossible to know in advance how useful some basic piece of research will prove to be in the future. We can only guess at the $ value, and many of the most useful results are surprises from blue-sky research not applied goal-orientated work.

3. Academia produces an army of highly-trained disgruntled postdocs and PhD students (just look at the ratio of student to professor positions) who have beneficial transferable skills for industry. It's not that you can't learn to do research outside of the academic environment, but getting a PhD is good training for it.

Finally, just guessing here, but did you work on galaxies or the ISM? We're on the cusp (a couple of decades) from imaging potentially habitable Earth analogs with next-generation space missions. This is a huge step toward answering the 'are we alone' question. Personally, I'd happily spend a few billion on that though I know not everyone would agree...

[xhkkffbf]

Why is getting a PhD good training for being a disgruntled and unemployed post-doc? Why should society spend sooo much money training someone and filling their heads with knowledge only to just kick that person out of science? It is a horrible mystery why people like you feel this is a good way to run society.

[stef25]

> We're on the cusp (a couple of decades) from imaging potentially habitable Earth analogs with next-generation space missions

Would love to hear more!

[brokeAstronomer]

Sure! The summary is that we'll likely be able to detect Earth-sized exoplanets in the habitable zone of their host stars and conduct basic biosignature searches using direct-imaging missions like HabEx and Luvoir. Below I'll give a bit more context. (It's late here and this ended up being quite long so feel free to skip to the second last paragraph!)

There are currently three ways of studying exoplanets: the transit method, the radial velocity method and direct-imaging. (I'm excluding gravitational microlensing which is a fantastic technique for studying populations of planets, but each lensing event is a one off so the exoplanet is not amenable to follow-up observations.) The radial velocity method works by very carefully measuring the movement of a star (can reach sensitivities as low as a few meters per second!) in response to the planets orbiting around it. This gives us a good mass estimate, but no way to know about the atmosphere of the planets to search for biosignatures.

The transit methods works on chance alignment; occasionally a planet will cross ('transit') its host star blocking out a portion of the light that would otherwise reach us (~1% for Jupiter, ~0.1% Neptune, ~0.01% Earth). We're able to detect this dip/shadow and infer the presence of the planet indirectly. Some of the light from the star will filter through the planets atmosphere and we can use this signal to infer the composition. However, there are some limitations. Earth's radius is 6,400km and the atmosphere is about 100km in height, or about ~0.15% of the radius. If the signal from an Earth like planet in transit is about ~0.01% you can imagine how much smaller the signal from the atmosphere is. So in practice, when doing 'transmission spectroscopy' you want to observe multiple transits and combine them together to boost the signal. This works well for planets on short orbits, but if one orbit takes a year then we have to wait a long time search for our aliens...

Direct-imaging on the other hand aims to have a spatially separated image of the planet orbiting its host star. The planet itself isn't resolved - it's just a point of light - but it's separate from the star and so we can directly study its atmosphere. The technical challenges with imaging are extremely difficult, and primarily stem from the fact that the planet will be incredibly faint (~10^-10 times) compared to the host star. For comparison this is much smaller than aberrations induced by minuscule nanometer imperfections in your mirror, or by temperature induced changes in your optics. But, to make it feasible, we can use a coronagraph to block out most of the light of the star, observing from space affords a very stable temperature environment and use post-processing of the images to further boost sensitivity.

Finally this leads us to the next generation direct imaging missions. Three key examples are LIFE, HabEx and LUVOIR. All three are in the concept phase, but the key idea is to have a large mirror in space (4m for Habex and 8m or 15m for LUVOIR). One big enough to comfortably spot an object as faint as an Earth sized planet in reflected light from it's host star. The trick with HabEx is that they also want to use a starshade flying in formation with the telescope to physically block out light from the star being observed. A starshade would theoretically be much better at blocking out light than our current coronagraphs. LUVOIR is just plain big. Finally, LIFE is a little different. Instead of one large mirror it is a mission that relies on interferometry to search for biosignatures. By combining light from several different telescopes flying in tight formation you can simulate a much larger mirror and achieve a similar effect.

I'm leaving out a lot of details but I hope this gives you an idea of the direction astronomers are taking. Someone else mentioned the decadal survey (Astro2020), this is a great place to read some of the technical details. Feel free to PM any questions. It's not clear which one of these missions will be successful, and needless to say the required technology development is huge. However, I strongly suspect we'll be able to say something about habitability of a few dozen Earth like planets in the next couple of decades which is an incredible prospect. If we're lucky maybe we'll even see a biosignature!

[brokeAstronomer]

*1.5% of the radius, not 0.15%. Can't edit the comment for some reason...