[contact_fusion]

That image is quite stunning. As the 2008 press release [1] states, this image was one of the first successes at direct imaging an exoplanet. It raised some interesting questions, such as why such a massive planet could be found so far out (330 AU!) The scientific paper for this observation can be found in [2] for those interested more astrophysical detail.

I feel compelled to offer an astronomer's clarification though. The planet in this image is not "resolved" in the technical sense. A resolved image usually means that fine details about the object are discernible spatially. For example, unresolved images of Betelgeuse provide a point source image, without details; a resolved image of Betelgeuse allows you to find spatial features such as that enormous bubble. Another example is, say, Jupiter: by eye or with a very modest telescope, Jupiter is a (bright) point of light. But with a moderate increase in resolving power, you can see all sorts of interesting features, such as the Great Red Spot, and the various cloud layers that vary with latitude.

Individual exoplanets are simply too small to resolve, even with JWST. Even being generous - assuming that the planet is bright enough to detect and that the host star doesn't overwhelm the signal - the angular sizes of exoplanets are miniscule. Lets assume some very generous numbers: a hypothetical exoplanet ten times the diameter of Jupiter (very large), and very, very close to Earth - let's say, 10 lightyears for simplicity and generosity. In arcseconds, the angular diameter of such an object on the sky is about 0.003". Smaller planets at more reasonable distances are even smaller. (The angular size of an object is just small angle trigonometry: in radians, about the width of the object divided by its distance.) Currently, science-class telescopes usually require about 1" resolution. JWST has about 0.1" resolution [3]; an interferometer like ALMA can, at its very best, achieve maybe 0.02" [4], though interferometers (as mentioned in other answers) sacrifice some things in exchange for spatial resolution.

This isn't to say you can't just detect exoplanets - you can, even with a ground based telescope like Gemini - but you probably won't resolve them, at least in this generation of telescopes, including JWST. But you can do a lot without spatial resolution - for example, you don't need to resolve the object to measure its spectrum, and spectral analysis can tell you a great deal.

[1] http://www.gemini.edu/sunstarplanet [2] https://arxiv.org/abs/0809.1424 [3] https://jwst.nasa.gov/faq.html#webbbetter (question 25) [4] https://almascience.eso.org/about-alma/alma-basics (section: spatial resolution)

[zucchini_head]

I think maybe your definition of "resolved" is a little skewed. It is not about the features of the object, but more by the Rayleigh Criterion [1][2]

So we can already (and have been able to for a long time) to "resolve" things as apparently-small as exoplanets, but for resolving _surface details_ we are one order of magnitude away for interferometers and two orders of magnitude away for standard single-mirror telescopes. Right?

[1] https://en.wikipedia.org/wiki/Angular_resolution#Explanation [2] Lord Rayleigh, F.R.S. (1879). "Investigations in optics, with special reference to the spectroscope".

[contact_fusion]

I gently disagree that this is a skewed definition. By convention, a "resolved" image of an object implies an extremely high quality measurement. On the other hand, we can resolve the separation of the star and planet in the Gemini image, but it would be misleading to claim that this is a resolved image of the planet. It may seem like a petty distinction, but I think it is better - for clarity's sake - to reserve the term "resolved" for its most natural contextual definition. Perhaps I am oversensitive to this as many non-astronomers are often led to believe that artistic renditions of exoplanets are actual images, not conceptions.

This type of direct detection was one of the first of its kind, so I wouldn't characterize this as an old capability - 2008 is relatively recent. Telescope turnover time is very long; Gemini remains a prominent telescope for science-class observations. Additionally, most new telescope generations don't achieve an order-of-magnitude improvement in resolution, or at least, not anymore. There are a lot of serious, decadal-scale barriers to improving resolution that must be overcome.

In terms of angular resolution, the order-of-magnitude estimates are the minimum improvements, assuming that such a close and large exoplanet exists. (AFAIK, there is no such system.) In practice it is likely that we need even better angular resolution, as there are not many systems within 10 ly away, and extremely large exoplanets are not very common (relatively speaking.)