How Can the Sun Become a Telescope?

How can we turn the sun into a telescope?

Imagine light coming from a distant target. Some of that light is aimed towards the sun and just barely grazes the surface.

The gravity of the sun is bending that light. It's already happening right now. That's the good news. We don't have to grind a lens. We don't have to polish a mirror. We don't have to unfold an instrument. The gravity of the sun is doing all the work. It's taking all these stray bits of light that skim its surface, and it's bending it towards the focal point.

So all we have to do is put a sensor at the focal point and collect that light.

That's the hard part. You can do the math and figure out where the focal point is, where all the light is concentrating towards with the solar gravitational lens, and its focal point is about 542 astronomical units away from the sun.

Let's put that in context. That's 542 times further than the distance from the sun to the earth. That's thirteen times the distance to Pluto, and that's over three times the distance to Voyager 1, the most distant current spacecraft, which was launched in 1977.

I guess it might be a small, tiny challenge to deploy an instrument to that extreme distance, get it to work, collect the data, build an image, and send the results back to Earth.

What’s more, the focal point here is more like the focal area because this image is so high resolution. Images of distant objects are spread out over tens of kilometers. So if you have a spacecraft just parked in one position, it will get that one little bit of light, and it will see that little patch of the target, and that'll be great. But if it wants to build a portrait, it has to scan over tens of kilometers. What this means is that if we want to get anything more than snapshots, we need a mobile spacecraft at that distance where we can't just fling it out and let it stay there. It has to move around so it can scan the image.

And we have to be really, really good at predicting the movements of the target so that by the time the spacecraft reaches this position, it’s not just looking at an empty patch of space.

But the craziest part about this is that it’s not that outlandish. Yes, this spacecraft, or fleet of spacecraft, would be sent three times further than Voyager. But it’s not like we have to send it to another star system altogether. It’s a (somewhat) reasonable extension of our current capabilities.

One method to make this work is to just to chuck a probe out there like a super-Voyager and hope for the best. Let it fly through this focal point and collect whatever data it can and then send it back to Earth, and then maybe we might get a small portion of a snapshot of one region of a target. There have been proposals going back decades to do just that. But that's not going to be super satisfying.

We want to have a spacecraft that can hang out there. We want a spacecraft that can spend some time there. We want a spacecraft that has enough fuel and energy to move around out there so it can scan this giant focal plane and build up an image of an entire target. The most recent proposals don't involve a single spacecraft, but many very, very small spacecraft, that dance around at the focal point to create a mosaic.

But this introduces other issues. Small spacecraft need instruments, power, and fuel, which makes them big…which defeats the purpose.

To solve this the latest proposals use solar sails. The idea here is to send a swarm of spacecraft, launch them from the earth, let them spiral in towards the sun, then unfurl their solar sails, let the radiation pressure from the sun push them out into the solar system, accelerate them very quickly, and get them to this point at 542 AU in the matter of a couple decades.

Still a long time, but not insane. Then we need them to start dancing around each other in a pattern where they can all individually start to collect data and then send that data back to Earth.

There's been a lot of work in this direction, but there are still a lot of unknowns. And you know what? It would still require a tremendous amount of technological advancement. We don't have super effective solar sales right now. We don't we don't have swarms of spacecraft that can work together super efficiently.

All of these proposals are on the edge of the possible. They’re right there just beyond our current technological capabilities, but not so far out that it's just science fiction and not worth thinking about in a serious way. It's entirely possible.

It’s crazy enough that it just might work.