Interferometry is among the best ways (if not, the best way!) to have an image of a very distant object.

Recently a picture of the black hole at the center of M87 was released. It is the result of several data collected by the Event Horizon Telescope, a series of arrays all across our world, working as one like a giant Earth sized telescope. The picture is not really cutting edge and high definition however it is still very surprising and in a way detailed enough, considering the fact that M87 is 53.49 million light years away... and this is where I arrive to Pluto which is just around 6 to 7 billion kilometers from us.

If we used an interferometer, perhaps the same size as the EHT (or just a smaller one, the size of an entire continent), and point all the arrays at Pluto, then we should have a picture with a resolution that is at least higher as the Hubble Space Telescope, but likely not as high as the pictures from the New Horizons spacecraft which directly made a fly by of Pluto... right?

If so then why don't we use interferometry to take pictures of Pluto from Earth?


Radio interferometry can combine observations over very large baselines. But optical interferometry cannot. According to a list of interferometry instruments on wikipedia, the largest baseline for optical measurements is less than a kilometer. We can't take optical measurements with continent-sized instruments.

Then if you drop down to radio where the instruments do have that capability, I think you'll find Pluto is quite dim (it's not a radio source, and there's no strong radio emissions that it can reflect to us). There's no radio signal from Pluto that can be imaged.

From a page on optical interferometry:

Interferometers are seen by most astronomers as very specialized instruments, as they are capable of a very limited range of observations. It is often said that an interferometer achieves the effect of a telescope the size of the distance between the apertures; this is only true in the limited sense of angular resolution. The combined effects of limited aperture area and atmospheric turbulence generally limit interferometers to observations of comparatively bright stars and active galactic nuclei.

  • $\begingroup$ Might want to state Pluto is "dim" because it doesn't have many radio emissions (else one might infer you meant light). $\endgroup$ – Magic Octopus Urn Apr 10 at 20:19
  • $\begingroup$ "cannot" → "cannot yet" or "cannot currently" $\endgroup$ – uhoh Apr 11 at 7:06
  • $\begingroup$ Second to what @uhoh comment: can you clarify why it cannot? Is this a fundamental physical limitation, or is it an engineering limitation? $\endgroup$ – gerrit Apr 11 at 11:38
  • $\begingroup$ astronomy.stackexchange.com/questions/29082/… $\endgroup$ – BowlOfRed Apr 11 at 20:26

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