You can sometimes tell quite a lot from remote sensing and looking at the reflection from an object. It can be illuminated by your own laser like in LiDAR or reflected light from the sun. However, you are not usually looking at a single element or compound unless it is in a laboratory with a prepared sample. In some cases you can use a technique called Raman spectroscopy and if you hit the sample with a laser a very small percentage of the photons that bounce back will have a signal that is related to the molecular bond vibrations of the sample and that fingerprint will tell you what the substance is.

On terms of unknown elements, science is pretty sure that we have found them all or can predict them. The undiscovered elements we think are there but have not been shown experimentally are very heavy, very radioactive and have very sort half lives. There is a theory of an “Island of stability” where if elements could be synthesized to have a larger number of neutrons they would have longer half-lives.

Like all the other elements if you wanted to excite their electrons and look at the optical emission you should see a set of atomic lines that should be unique to that element.

If they were an alloy or a compound looking at the reflections it might be hard to determine that it was a new element from far away, but as you got closer and if you zapped it with a laser or vaporized into a plasma by some other method, to the eye it might look like a normal plasma but with a spectrometer it would have a unique signature.

If it was a large object made of a pure material, you might be able tell it was unusual by reflection and maybe if you probed it across the whole EM spectrum tell that it was something new. But most things except metals are compounds so that would make it harder to tell.

You can sometimes tell quite a lot from remote sensing and looking at the reflection from an object. It can be illuminated by your own laser like in LiDAR or reflected light from the sun. However, you are not usually looking at a single element or compound unless it is in a laboratory with a prepared sample. In some cases you can use a technique called Raman spectroscopy and if you hit the sample with a laser a very small percentage of the photons that bounce back will have a signal that is related to the molecular bond vibrations of the sample and that fingerprint will tell you what the substance is.

On terms of unknown elements, science is pretty sure that we have found them all or can predict them. The undiscovered elements we think are there but have not been shown experimentally are very heavy, very radioactive and have very short half lives. There is a theory of an “Island of stability” where if elements could be synthesized to have a larger number of neutrons they would have longer half-lives.

Like all the other elements if you wanted to excite their electrons and look at the optical emission you should see a set of atomic lines that should be unique to that element.

If they were an alloy or a compound looking at the reflections it might be hard to determine that it was a new element from far away, but as you got closer and if you zapped it with a laser or vaporized into a plasma by some other method, to the eye it might look like a normal plasma but with a spectrometer it would have a unique signature.

If it was a large object made of a pure material, you might be able tell it was unusual by reflection and maybe if you probed it across the whole EM spectrum tell that it was something new. But most things except metals are compounds so that would make it harder to tell.