What scientific instruments and man-made objects did the Apollo missions leave on the Moon? Are they still operational today?

Hey, that's a great question! The Apollo missions left quite a lot on the Moon. The lunar surface is now like an open-air museum of human space exploration. We can categorize these items into several groups.

What Did the Apollo Missions Leave Behind?

These "legacies" can be simply divided into four main categories: sophisticated scientific instruments, large hardware, commemorative items, and some "space junk" you might not expect.

1. Sophisticated Scientific Instruments (ALSEP)

This is the most valuable part. Starting with Apollo 11 (though its equipment was simpler, an early version), the subsequent Apollo 12, 14, 15, 16, and 17 missions each deployed a set of equipment called the Apollo Lunar Surface Experiments Package (ALSEP) at their landing sites. This was like an automated mini-science station, consisting of a central station and various experiments, powered by a small nuclear generator (a Radioisotope Thermoelectric Generator).

The main instruments included:

Seismometer: Used to "listen" to the Moon's interior, recording "moonquakes" and meteorite impacts. This helped us understand the Moon's internal structure, revealing it has a small core.
Laser Ranging Retroreflector: This is the coolest and most important one! It's essentially an array of small corner-cube mirrors. Powerful lasers fired from Earth hit it, and the light reflects precisely back along the same path. By measuring the laser's round-trip time, we can measure the Earth-Moon distance with millimeter precision.
Solar Wind Spectrometer: Used to "capture" and analyze the stream of charged particles blowing from the Sun (the solar wind).
Magnetometer: Measured the Moon's extremely weak magnetic field.

(ALSEP science station deployed by Apollo 14 astronauts)

2. "Transportation" and Large Hardware

Lunar Roving Vehicle (LRV): Apollo 15, 16, and 17 missions all brought this cool electric "lunar convertible." After the missions, the astronauts essentially turned off the ignition and left it on the Moon. All three rovers are still parked in their respective "parking spots."
Lunar Module Descent Stage: This is the largest single item left behind during each landing. After completing their surface missions, the Lunar Module's ascent stage would fire its engine to lift off and rendezvous with the Command Module in lunar orbit. The descent stage, with its four legs serving as the launch platform, was left permanently on the lunar surface. The large structure seen in the background of photos featuring the flags is this descent stage.

3. Commemorative Items

American Flags: One was planted at each landing site. However, with no atmosphere for protection, decades of intense solar ultraviolet radiation have likely bleached these nylon flags pure white. The Apollo 11 flag was knocked over by the exhaust when the ascent stage lifted off.
Commemorative Plaques: A metal plaque was attached to the ladder of each Lunar Module descent stage, depicting Earth and bearing a message of peace. For example, Apollo 11's plaque reads: "Here men from the planet Earth first set foot upon the Moon July 1969, A.D. We came in peace for all mankind."
Personal Items: Astronauts also left some personal mementos. The most famous is a laminated family photo left by Apollo 16 astronaut Charles Duke. The Apollo 15 crew left a small aluminum sculpture called "Fallen Astronaut," placed next to a plaque commemorating American and Soviet astronauts who died in the pursuit of space exploration.

4. "Space Junk"

To make precious weight allowance for the lunar rock samples being brought back, astronauts discarded many used items on the Moon. This includes:

Portable Life Support System (PLSS) backpacks
Cameras (Hasselblad camera bodies; only the film magazines were returned)
Tools (hammers, shovels, tongs, etc.)
Food wrappers, urine collection bags, and other waste

It's estimated that all Apollo missions combined left over 180 tons of human-made objects on the Moon.

Are They Still Working?

This is a crucial question. The answer is: Most have "retired," but there's one exception!

Most are inactive: The ALSEP scientific instruments that required power were designed to operate for about 10 years using their nuclear generators. They successfully sent back valuable data to Earth for many years, but on September 30, 1977, NASA officially shut down all remaining operational lunar surface experiments, ending their mission. So, the seismometers, magnetometers, etc., have all stopped working. The lunar rovers were also battery-powered and ran out of power long ago.
The only "miracle" still working – the Laser Ranging Retroreflectors! This is why they're the coolest. These reflectors are passive devices. They require no power source whatsoever. As long as they remain in place, the laws of physics ensure they continue to function. The principle is like the red reflector on your bicycle – shine a light at it, and it reflects the light back to your eye.

To this day, observatories around the world (like the Apache Point Observatory in the US) regularly fire powerful laser pulses at these reflectors on the Moon. By precisely measuring the laser's round-trip time, we can:
1. Measure the Earth-Moon distance with astonishing precision, with an error margin of less than a centimeter.
2. Verify predictions of Einstein's General Theory of Relativity.
3. Confirm that the Moon is moving away from Earth at a rate of about 3.8 centimeters per year.

So, next time you look up at the Moon, imagine not just the footprints, flags, and vehicles we left behind, but also these "mirrors" still silently working for scientists on Earth. They are among the most enduring and valuable scientific legacies of the Apollo era.