# Why haven't telescopes been sent to other planets?

Why haven't we sent telescopes to other planets? Wouldn't we be able to see further? Aren't we interested in seeing further without having to send a probe that will take years to get to where it's going.

I have a guess so tell me if I'm right. Is the reason because the lenses and apertures would break at the velocity and extremes?

• Well, in a sense, probes are telescopes sent to other planets. – Hohmannfan Jul 5 '16 at 15:56
• This question is a bit confused. We have wonderful pictures of all eight planets, Pluto, Ceres, and several other solar system bodies precisely because we have sent telescopes to those objects. – David Hammen Jul 5 '16 at 16:51
• @DavidHammen a lot of that body of imagery is from instruments that are not much different than really big "mirror lenses" you can buy at a camera shop - sometimes people think they are cameras, not telescopes, although really there is no firm line of distinction between them. I'm trying to see just how much bigger than camera lenses they really are. – uhoh Jul 5 '16 at 17:11
• The IAU currently lists no members who work on other planets so there isn't much demand. – A. I. Breveleri Jul 6 '16 at 1:06
• @DavidHammen I took the question to mean, why haven't we built permanent telescopes on other planets, like the ones we have on earth, so that we can view other locations from that planet and relay the information back. – JBentley Jul 6 '16 at 8:34

We have sent telescopes to other planets, almost all the optical sensors on probes are in fact telescopes so they can focus on a specific area in detail. These sensors are to explore the planets they orbit and their moons.

We don't send deep space telescopes to other planets because it's pointless, a few million miles closer to even our closest neighbor star system makes no difference, and it would be much harder to manage the telescope and receive the data from it.

• That's a good point, although many of them are more like small telescopes, or really big camera lenses. I've asked a follow-up question. – uhoh Jul 5 '16 at 17:07
• I don't know if you could accurately say that it's pointless to do this. With optical astronomy, it might not be very useful, but it could be very powerful for radio interferometry. Radio telescopes, after all, are still telescopes. And placing telescopes on the far side of the Moon is an idea that has been tossed around for a while, because they would be shielded from a great deal of the interference from Earth, while still being (relatively) close enough for servicing. – Phiteros Jul 5 '16 at 17:10
• @Phiteros by the time it's up and running, there will be plenty of interference from all the clandestine $^3He$ mining trucks with dirty distributor caps. (partial humor) – uhoh Jul 5 '16 at 17:21
• There seems to be at least one telescope that can be ~1AU from earth. Although in this case the point is to get away from Earth rather than towards the stars. – uhoh Jul 5 '16 at 17:27
• Actually, ~2 AU, @uhoh. Kepler and Earth will eventually be on opposite sides of the Sun, each at about 1 AU. Of course Kepler will be completely nonfunctional by then. Stereo A and B were similarly sent on heliocentric orbits to take them away from the Earth, A orbiting slightly faster than Earth, B slightly slower. This yielded a full view of the Sun. – David Hammen Jul 5 '16 at 19:17

You're right: on Earth we spend some significant amount of effort to combine large telescopes.

Advantages of a telescope on other planets could be

• less or even no atmospheric effects
• greater distance for enhanced resolution

On the other hand side, a telescope in space comes with several issues:

• how to carry a large telescope (>30m) into space? A small one would not help that much.
• how to maintain/repair it?
• how to power it?
• how to safely land it? Philae showed that this is not trivial.
• if safely landed, how to position it?
• if there's no atmosphere, how to protect it from meteors?
• communication and data transfer is slow

As you can see, putting it onto a planet is even worse than keeping it in space.

• There is little point sending a telescope that far. Most of these factors can be mitigated by sending the telescope into space, near Earth. There's little to no benefit to placing a telescope on a planet surface, vs having it orbit Earth. – SF. Jul 5 '16 at 20:44
• @SF. I totally agree, but that's what OP asked for. – Thomas Weller Jul 5 '16 at 20:46
• Going outside the atmosphere gives a big boost in resolution without the complexity and maintenance of adaptive optics. If more resolution is needed - say to verify planets around other starts by resolving them in images - you can use multiple mirrors "flying" in formation in space, rather than one large mirror (e.g. VLA or ALMA). They can be linked via interferometry, and either use micro-thrusters, or very low mass tethers or scaffolding, depending on curvature of their orbits. – uhoh Jul 6 '16 at 0:11
• @uhoh photonic laser thrusters are a great bet for this opportunity, and it might even provide enough stability by itself, or at least the interferometric data to feed the thruster logic with. – John Dvorak Jul 6 '16 at 18:52
• @JanDvorak for repulsive force to maintain tension between tethered objects using a cavity - mirrors on each end à la Fabry-Perot - it's OK because the power eventually dissipates within the 99.9% reflective mirrors. But if there are thousands of things up there all constantly shooting multi-Watt laser beams into space in random directions, gosh I don't know. 300 Watts per μN - sooner or later someone's going to loose an eye, or blind a spy satellite, and then, well, "Oh, sorry I blinded your spy satellite, honest, it was and accident!" might work the first time, but... – uhoh Jul 6 '16 at 23:43

There was a proposal to send a space telescope to Mars, known as MOST. It was turned down. Benefits were stated to include:

"MOST can provide a larger baseline for stereoscopic viewing of targets combined with Earth-based telescopes," they write in the SALSO presentation. "A greater range of viewing angles for targets in the outer solar system are possible from Mars than from Earth. The inner asteroid belt can be viewed from significantly closer range."

This proposal was eventually nixed for a higher priority idea, Wide Field Infrared Survey Telescope. That just goes to show that while there is some interest, there are a lot of limitations to putting a space telescope so far out there. The reasons why this is difficult have been mentioned before.

We have sent telescopes into deep space, often to the Earth-Sun L2 Lagrangian point. This is especially common for infra-red telescopes because water vapor in the atmosphere blocks IR. One example was the Herschel Space Observatory.

There is little reason to go through the trouble of landing on an other planet when the telescope can just as well stay in space.

Putting a telescope on any object with an atmosphere is a bad idea. Any atmosphere will screw up your pictures with clouds and dust. That's the reason all serious telescopes on Earth are on the highest points possible - to reduce that. You've still got problems though, just with the air being in the way. The best images of anything outside our planet all come from Hubble, which is up there precisely because atmospheric refraction is the limiting factor in getting decent pictures. Even if you're wanting to take pics of something in our solar system, Hubble in space is infinitely better than a telescope on Mars, even if Mars happens to be a bit closer to it (at certain points in its orbit anyway).

That's optical. If you're doing radio astronomy then refraction in air isn't an issue, but if you're looking for serious distance then you're using multiple dishes to give a larger baseline. Planets impose a natural limit to the baseline of your telescope, based on the size of the planet. Satellites OTOH can accurately fly in formation at huge distances, providing ludicrously large baselines which would never be possible any other way.